Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-014-3110-6
KNEE
The effect of knee extensor open kinetic chain resistance training in the ACL-injured knee Massimo G. Barcellona • Matthew C. Morrissey • Peter Milligan • Melissa Clinton • Andrew A. Amis
Received: 15 November 2013 / Accepted: 29 May 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose To investigate the effect of different loads of knee extensor open kinetic chain resistance training on anterior knee laxity and function in the ACL-injured (ACLI) knee. Methods Fifty-eight ACLI subjects were randomised to one of three (12-week duration) training groups. The STAND group trained according to a standardised rehabilitation protocol. Subjects in the LOW and HIGH group trained as did the STAND group but with the addition of seated knee extensor open kinetic chain resistance training at loads of 2 sets of 20 repetition maximum (RM) and 20 sets of 2RM, respectively. Anterior knee laxity and measurements of physical and subjective function were performed at baseline, 6 and 12 weeks. Thirty-six subjects were tested at both baseline and 12 weeks (STAND n = 13, LOW n = 11, HIGH n = 12). Results The LOW group demonstrated a reduction in 133 N anterior knee laxity between baseline and 12 weeks
testing when compared to the HIGH and the STAND groups (p = 0.009). Specifically, the trained-untrained knee laxity decreased an average of approximately 5 mm in the LOW group while remaining the same in the other two groups. Conclusion Twelve weeks of knee extensor open kinetic chain resistance training at loads of 2 sets of 20RM led to a reduction in anterior knee laxity in the ACLI knee. This reduction in laxity does not appear to offer any significant short-term functional advantages when compared to a standard rehabilitation protocol. These results indicate that knee laxity can be decreased with resistance training of the thigh muscles. Level of evidence Randomised controlled trial, Level II. Keywords Therapeutic exercise Quadriceps Joint stability Hypermobility Resistance training
Introduction M. G. Barcellona Academic Department of Physiotherapy, School of Medicine, King’s College London, London, UK M. C. Morrissey (&) Faculty of Health Sciences, University of Ljubljana, Ljubljana, Slovenia e-mail: [email protected] P. Milligan King’s College London, London, UK M. Clinton Guy’s and St. Thomas’ Hospital, London, UK A. A. Amis Department of Mechanical Engineering, Imperial College London, London, UK
The anterior cruciate ligament (ACL) and in particular the anterior medial bundle of the ACLis the primary restraint to anterior translation of the tibia at the knee [1]. Fleming et al. [12] reported that the magnitude of anterior cruciate ligament (ACL) strain during knee extensor open kinetic chain exercise is related to absolute load. This finding has received support in more recent, clinical work where the change in anterior knee laxity in rehabilitation after ACL injury and surgery was found to be related to the load used during knee extensor open kinetic chain resistance training with greater loads being associated with decreases in laxity [25]. These findings raise the possibility that anterior knee laxity can be decreased with knee extensor open kinetic chain training and this requires a randomised, controlled clinical trial.
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If anterior knee laxity can be decreased with knee extensor open kinetic chain training, there are at least three groups that might benefit from such training effects. The first group is uninjured individuals with higher than usual anterior knee laxity who are concerned about injuring their knee in sports; as it has been found that increased anterior knee laxity is a significant predisposer to traumatic knee injury [37], generally, and ACL injury, in particular [31, 36]. Another group that might benefit consists of individuals recovering from ACL reconstruction surgery following full or partial rupture [6]; the main mechanical purpose of which is to decrease anterior knee laxity. In this group, there are seemingly conflicting reports regarding the safety of knee extensor open kinetic chain resistance exercise in terms of knee laxity change in the early stages post ACL reconstruction [13, 14, 29]. The discrepancy in findings may relate to differences in exercise dosage [25], exercise range of movement [13] and timing of initiation following surgery [14]. The third group that might benefit from resistance training-induced decreases in anterior knee laxity consists of individuals who have injured their ACL and are being treated conservatively. The amount of anterior tibial translation provided by knee extensor open kinetic chain resistance exercise has been shown to be greater in individuals with ACL-injured knees when compared to uninjured individuals [27] and if performed at knee flexion angles including 30° to 0° [27], may provide the load stimulus for change in anterior knee laxity over time. The main purpose of this study was to evaluate whether anterior knee laxity can be decreased with knee extensor open kinetic chain training in this latter group. This purpose was served with a randomised, controlled clinical trial consisting of three groups in rehabilitation after ACL injury—two groups receiving either relatively high or low load knee extensor open kinetic chain training along with their standard programme and a third group that only received the standard programme (which did not consist of knee extensor open kinetic chain resistance training). This design allowed an additional purpose to be served—to evaluate whether relatively high and low knee extensor open kinetic chain training loads might differ in their effects on anterior knee laxity. A final, general purpose was to compare the different groups for changes in knee physical and self-assessed function. The main hypothesis to be tested in this study was that the supplementation of a standard rehabilitation programme with high load knee extensor open kinetic chain resistance training would lead to a greater reduction in anterior knee laxity compared to lower loads of this exercise in ACL-injured (ACLI) individuals. The findings of this study will aid clinical decision making concerning the use of knee extensor open kinetic chain resistance training and optimal dosage parameters in
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individuals following ACL injury. In the wider context, if laxity is found to decrease with resistance training, the focus of rehabilitation for joint laxity problems is likely to switch to using exercises focussed on loading joints to enhance their passive stability.
Materials and methods This study was a prospective, single-blind (examiner), randomised controlled clinical trial with repeat measures at baseline, 6 weeks and 12 weeks (Fig. 1). The chief investigator (MB), a senior physical therapist and clinical researcher, performed all measurements. Ethics, subjects and recruitment Subjects were recruited from five sites, from which local ethics approval was granted (National Research Ethics Service reference number 08/H0804/28). At each site, individuals diagnosed with an ACLI who were at least 6 weeks post-injury or post-arthroscopic surgery for the knee were approached for recruitment if they: (1) had been diagnosed with an ACLI via magnetic resonance imaging or arthroscopy, or if they had a greater than 3 mm side-toside difference in anterior knee laxity as measured by the KT2000 ligament arthrometer (manual maximal force); (2) were aged between 18 and 60 years; (3) had not sustained any trauma or injury that required medical attention to the contralateral lower limb within the last 6 months; and (4) had improved to a level such that no undue aggravation was expected as a result of the testing and training required for participation in the study. Subjects were excluded from participating in the study if they did not have a competent command of the English language, if they had a posterior cruciate ligament injury and/or if they had neurological, systemic, rheumatological or muscular diseases. Clinical measurement After signing a consent form, subjects completed a general questionnaire. Each test procedure lasted for approximately 1.5 to 2 h and for all measurements the uninjured leg was tested prior to the injured leg. Each subject completed the Lysholm and Tegner questionnaires [34], the IKDC 2000 Subjective Knee Evaluation Form [17], the Hughston Clinic subjective knee questionnaire [15] and the MOS 36-item Short Form Health Survey Version 2 [38]. Body mass, height and the limit of passive knee joint flexion and extension motion were recorded according to standardised procedures. Knee girth measures were also obtained at the level of the joint line and 5 cm above this using a cloth tape measure.
Knee Surg Sports Traumatol Arthrosc Fig. 1 Flowchart of participants in the study
79 subjects recorded as approached / screened
21 unable to participate: 15 for personal reasons 6 did not meet criteria
Randomised (n=58)
Group 1 Standard (STAND) (n=21)
Group 2 2 x 20 RM (LOW) (n=18)
5 subjects withdrew:
7 subjects withdrew:
3 for personal reasons 1 injured the other knee 1 moved away from area
5 for personal reasons 1 had ACLR 1 moved away from area
16 subjects tested to 6 weeks
Group 3 20 x 2 RM (n=19)
7 subjects withdrew 6 for personal reasons 1 consultant decision
11 subjects tested to 6 weeks
12 subjects tested to 6 weeks
3 subjects withdrew: 2 for personal reasons 1 had ACLR
0 subjects withdrew
13 subjects tested to 12 weeks
Anterior knee laxity measurement was performed according to the manufacturer’s instructions [10] using the KT2000 knee joint arthrometer (Medmetric Corporation, San Diego, USA) with concurrent measurement of lateral hamstrings muscle activity as described in detail previously [2]. Surface electromyography (EMG) data for the lateral hamstrings was recorded during each laxity test using the Delsys Bagnoli-4 System with DE-2.1 single differential electrodes (Delsys Inc., Boston, MA). Electrode placement was performed as described by Cram and Kasman [8]. Prior to laxity testing, three maximal voluntary isometric contractions (MVIC) of the knee flexors was carried out against the resistance applied by the principal examiner in a seated position on the edge of a plinth with the hip and knee at 90°. Standardised verbal instructions were given.
0 subjects withdrew
11 subjects tested to 12 weeks
12 subjects tested to 12 weeks
Two separate anterior knee laxity tests were conducted for each leg; a 133 N and a manual maximal test. For each test, three anterior and posterior repetitions at the 88 N force were performed [10]. This was followed by 5 repetitions of the particular test. Both EMG and KT2000 laxity data signals were sampled at a frequency of 2000 Hz using a National Instruments USB-6210 portable analogue to digital converter (National Instruments Corporation, Texas, USA) and Labview Signal Express 2.5.0 software (National Instruments Corporation, Texas, USA). Subjects were asked to perform two functional hop tests at baseline and 12 weeks in order to assess lower limb functional performance. The second of these two tests was the widely used single horizontal hop for distance (SHH)
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Knee Surg Sports Traumatol Arthrosc
with a single-leg land [7, 9, 32]. Prior to this test, a two-leg land single horizontal hop test was performed. This test was performed prior to the single-leg land test in order to: (1) familiarise subjects with the nature of such a test, (2) allow subjects to decide whether they felt able to perform a single-leg land, and (3) minimise the risk of the knee giving way during testing. For both tests, the uninjured leg was tested first. Following a practice trial for each test 5 separate successful trials were recorded [28]. Where a subject did not feel confident to perform one or both of the hop testing procedures, this was recorded. Randomisation and intervention Following baseline testing, subjects were allocated to one of three groups using block randomisation, in blocks of 6 assignments. A separate random number list, controlled by the relevant principal investigator, was used for each of the five training sites in order to ensure balanced groupings at each site and in order to ensure that the chief investigator remained blind to treatment allocation. Subjects from each of the three groups were invited to participate in a 12-week supervised training programme with a target of three sessions per week. Each session lasted approximately 45 min to 1 h depending on group allocation and the level of intensity for each exercise. All subjects in each of the three groups received a standardised rehabilitation protocol for those with ACL injury that was similar to the current programmes delivered at each of the training sites, and that was based on previous research [29]. The training procedures were standardised across each site by providing the physical therapists involved with the training of subjects with a detailed study treatment protocol and through specific training by the chief investigator prior to the start of the study. Exercise equipment for the study was equal across sites and included a cycle ergometer (Tunturi F300, Tunturi Oy Ltd., Turku, Finland), a standard 30-cm wooden wobble board, a standard 92-cm mini-trampette, an 11.5-inch step or bench, 1-kg leg weights and a seated knee extensor training device (Body-Solid CAM series leg extension and curl GCEC340, Body-Solid Inc., IL, USA). Subjects allocated to group 1, also known as the standard (STAND) group, performed the standardised rehabilitation protocol without the inclusion of seated knee extensor open kinetic chain resistance training. Subjects in group 2, also known as the LOW group, performed the same standard protocol with the addition of injured leg knee extensor open kinetic chain resistance training, of two sets of 20 repetition maximum (RM), on the seated knee extensor training device. Subjects in group 3, also known as the HIGH group, performed the standard rehabilitation protocol with the addition of the knee extensor open kinetic
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chain resistance training at loads of 20 sets of 2RM. The knee extensor open kinetic chain resistance training for subjects in the LOW and HIGH groups was performed from 0° to 90° of knee flexion and at an average speed of 60°/s (metronome guided). Ethical approval for the study was granted by the Guy’s and St. Thomas’ Research Ethics Committee (REC Reference: 08–HO804/28). Statistical analysis For each individual subject, the training load used for each exercise at each training session was recorded on specific treatment record sheets. The specifics for each exercise was calculated as follows: (1) total time for cycling, wobble board and mini-trampette; (2) total number of repetitions 9 load used in each repetition for hamstring curls and OKC knee extensor exercise; and (3) total repetitions for calf raises, ballistic hamstrings, step ups, mini squats, hip abductors, bridging and deep lunges. Anterior knee laxity and surface electromyography (EMG) data were analysed as described previously [2] with anterior knee laxity corrected for lateral hamstrings EMG activity [2] as the main outcome. Matlab Software (The MathWorks Inc., Natik, MA, USA) was used to determine the laxity value for each test (133 N or manual maximal) by calculating an average of the 5 trials. This allowed for greater precision of measurement (reported to the nearest 0.1 mm) and reduces the potential for bias on the part of the examiner. Intra-rater test–retest reliability, as determined by calculation of the intraclass correlation coefficient ICC(3,1)—for absolute scores of the manual maximal and 133 N anterior knee laxity tests, in the hands of the principal examiner, was ICC 0.84 and ICC 0.83, respectively, when tested in 12 uninjured subjects on two separate days. For hop test performance, the maximal distance for each leg from the 5 trials of each test was used for analysis. Where subjects did not perform a particular hop test due to fear of instability, this was recorded. Statistical analyses were performed using SPSS version 16.0. Non-nominal baseline and outcome data were tested for normality using the Kolmogorov–Smirnov test and through observation of the P–P plots. In order to identify potential confounding variables, baseline differences between groups were analysed using a one-way independent ANOVA for normally distributed baseline measures, or the Kruskal–Wallis test for non-parametric baseline measures. Testing for between group differences for nominal baseline data was analysed using chi-square testing. Differences between groups for the change in knee girth and range of motion measures were analysed using a two-way (group x time) ANOVA.
Knee Surg Sports Traumatol Arthrosc
A two-way mixed (group 9 test session) univariate ANOVA was performed to compare side-to-side differences between groups over time for both manual maximal and 133 N anterior knee laxity. In order that the hop test data for all subjects, even those who did not perform the tests due to fear of instability or lack of confidence, was considered, changes between baseline and 12-week data were categorised as follows. Those subjects where the trained leg improved more than the untrained leg were given a score of 1. Where the untrained leg improved more than the trained leg, a score of 2 was given. Where subjects did not jump at both baseline and 12 weeks or where the trained and the untrained leg changed equally, they were given a score of 3. If the subjects jumped at 12 weeks on the trained leg when they did not jump at baseline, they were also given a score of 1. Cross-tabulation according to group allocation was then performed and chi-square testing was used to analyse for differences between groups. Outcome data for the subjective questionnaires was analysed using the Kruskal–Wallis test to compare differences between groups at baseline, 12 weeks and on the 12-week minus baseline score. In addition, the Wilcoxon test was used to analyse each group separately for the
change in the questionnaire scores from baseline to 12 weeks.
Results Of 58 subjects, 36 were tested at both baseline and 12 weeks (see Fig. 1). Baseline subject characteristics are presented in Table 1. Subjects in the STAND group had a significantly lower passive range of knee flexion than the LOW group (U = 27.0, p = 0.009) and did not differ for any of the questionnaire total or sub-domain scores apart for the Tegner score (see Table 1). Knee joint girth and range of motion There was a significant improvement in knee joint flexion range of motion (p \ 0.001), but not for the change in knee joint extension range of motion (n.s.). The groups did not differ for knee flexion (n.s.) or extension (n.s.) changes. There was no significant change in knee joint girth at either the level of the joint line (n.s.) or 5 cm above the joint line (n.s.) nor were group differences found in girth changes at these two levels (both n.s.).
Table 1 Baseline subject characteristics for participants who participated up to the 12-week testing Group 1 (STAND)
Range
N
13
–
Age (yrs)
35 ± 9
24 to 53
Body mass (kg) Height (cm)
83 ± 12 174 ± 11
64 to 109 159 to 190
Body mass index (kg/m2)
27 ± 4
Gender (M/F)
10/3
Dominant limb (R/L)
Group 2 (LOW)
Range
Group 3 (HIGH)
Range
p value for between group differences
11
–
12
–
32 ± 5
25 to 40
29 ± 7
19 to 45
n.s.
73 ± 14 173 ± 12
53 to 93 150 to 191
86 ± 19 180 ± 10
61 to 130 160 to 197
n.s. n.s.
22 to 36
24 ± 3
20 to 29
27 ± 7
20 to 44
n.s.
–
8/3
–
11/1
–
n.s.b
11/2
–
11/0
–
12/0
–
n.s.b
Inj. limb (R/L)*
2/11
–
7/4
–
6/6
–
0.05b
Knee extension inj. PROM (°)
1±5
-7 to 9
-1 ± 3
-7 to 4
1±6
-9 to 9
n.s.
Knee extension uninj. PROM (°)
2±3
-3 to 8
1±4
-6 to 9
3±3
-2 to 8
n.s.
Knee flexion inj. PROM (°)*
137 ± 12
117 to 152
150 ± 8
141 to 164
147 ± 9
128 to 160
0.02a
Knee flexion uninj. PROM (°)
150 ± 10
126 to 162
157 ± 4
151 to 163
153 ± 8
139 to 162
n.s.
Joint line knee girth inj. (cm)
37 ± 2
33 to 40
36 ± 2
33 to 39
37 ± 3
31 to 43
n.s.
Joint line knee girth uninj. (cm)
37 ± 3
33 to 42
35 ± 2
31 to 39
37 ± 3
31 to 43
n.s.
Knee girth 5 cm above joint line inj. (cm)
40 ± 3
37 to 45
38 ± 2
35 to 41
40 ± 4
33 to 48
n.s.
Knee girth 5 cm above joint line uninj. (cm)
40 ± 4
33 to 47
38 ± 2
34 to 42
39 ± 4
33 to 48
n.s.
Tegner score at baseline (/10)*
3 (3)
1 to 4
3 (2)
2 to 4
4 (5)
1 to 6
0.02a
n.s. not statistically significant, Inj. injured/trained limb, Uninj. uninjured/untrained limb, PROM passive range of motion * Statistically significant at the p \ 0.05 level a
Kruskal–Wallis test as data was found to be non-parametric
b
chi-square analysis
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Knee Surg Sports Traumatol Arthrosc Table 2 Descriptive injury statistics for participants who participated up to 12-week testing
Time from injury to baseline test (wks)a Time from baseline to 6-week test (wks)
a
Time from baseline to 12-week test (wks)
a
At work at time of baseline test (Y/N)
GROUP 1 (STAND)
GROUP 2 (LOW)
GROUP 3 (HIGH)
p value for between group differences
10 (6–1251)
18 (6–1279)
127 (7–1262)
n.s.b
6 (5–8)
6 (6–6)
6 (5–8)
n.s.b
12 (11–14)
13 (11–15)
12 (12–16)
n.s.b
13/0
10/1
12/0
n.s.c
At work at time of 12-week test (Y/N)
13/0
11/0
12/0
–
Mechanism of injury (Non-contact/Contact)
10/3
9/2
12/0
n.s.c
Surgery for meniscal injury (Y/N) Method of diagnosis (MRI/Arthroscopy/KT2000)
2/11 12/1/0
3/8 7/3/1
1/11 9/1/2
n.s.c n.s.c
Lateral meniscus
6
3
3
–
Medial meniscus
5
2
5
–
Injuries associated with ACL injuryd
MCL grade 1 or 2
3
3
1
–
LCL grade 1 or 2
0
1
0
–
Osteochondral
1
3
1
–
Football
8
6
5
–
Skiing/Snowboarding
3
2
3
–
Other
2
3
4
–
Activity of injury
n.s. not statistically significant, MCL medial collateral ligament, LCL lateral collateral ligament, Y yes, N no, NC non-contact, C contact, MRI magnetic resonance imaging, KT2000 KT2000 knee joint arthrometer, Full complete ACL tear, Partial partial ACL tear, Injury KT2000 arthrometer clinical diagnosis of ACL injury ([3 mm side-to-side difference) a
Data presented as median(range)
b
Kruskal–Wallis test
c
Chi-square analysis
d
One patient can have several associated injuries
For descriptive injury statistics for participants who participated up to 12 weeks of the study see Table 2. Laxity data To correct for a positively skewed difference in laxity for both the manual maximal and 133 N tests, natural logarithmic (log) transformation of the data was performed. Trained minus untrained laxity data at baseline, 6 weeks and 12 weeks are presented in Table 3. Pre-planned contrast analysis revealed that there was a significant difference between groups (Fig. 2) for the change in 133 N LHcorrected knee laxity between the baseline and 12-week test session [F(2,29) = 4.8, p = 0.02]. There were no significant differences between any other time point comparisons for both the 133 N and manual maximal tests. Due to an increased injured—uninjured baseline laxity in the LOW group, a univariate analysis of covariance was used to assess for differences in 12-week laxity scores between groups, whilst including baseline knee laxity scores as a covariate. Even when accounting for baseline differences in knee laxity, there were statistically
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significant differences between groups for the 133 N anterior knee laxity scores at 12 weeks [F(2,28) = 3.8, p = 0.04]. Contrast analysis revealed that the LOW group 12-week laxity scores were significantly reduced compared to both the STAND (p = 0.02) and the HIGH (p = 0.04) groups, when baseline laxity was considered as a covariate. There was no significant difference between the STAND and the HIGH groups (n.s.). Questionnaire data There were no significant differences between groups with regard to the baseline to 12-week change in the IKDC total score (n.s.), the Lysholm score (n.s.), the Tegner score (n.s.), the Hughston score (n.s.), the SF36 mental component summary score (n.s.) and the SF36 physical component summary score (n.s.). Functional hop tests There were no statistically significant differences between groups over time when the change in single horizontal hop
Knee Surg Sports Traumatol Arthrosc Table 3 Injured minus uninjured knee laxity as corrected for lateral hamstrings muscle activity over time and between groups
GROUP All subjects (N = 32)
a
a
Presented as mean (SD). P p value for the main effect of time. Pb p value for the interaction effect between time and group n.s. not statistically significant, MM manual maximal, STAND standard, I injured leg, UI uninjured leg * Significant at the p \ 0.05 level. ** Significant at the p \ 0.01 level
Test session
I-UI 133 N laxity
Log I-UI 133 N laxity
I-UI MM laxity
Log I-UI MM laxity
Baseline
7.7 (6.3)
0.73 (0.56)
12.1 (7.3)
0.88 (0.49)
6 weeks
6.6 (5.2)
0.64 (0.50)
10.0 (7.1)
0.78 (0.51)
12 weeks
6.0 (5.2)
0.61 (0.57)
8.8 (6.6)
0.66 (0.50)
P (session)
–
n.s.
–
0.001**
Group 1 STAND (n = 12)
Baseline
6.0 (6.0)
0.71 (0.69)
11.5 (6.4)
0.96 (0.52)
6 weeks
7.0 (3.8)
0.77 (0.43)
11.0 (5.5)
0.89 (0.45)
12 weeks
5.7 (4.5)
0.71 (0.64)
9.1 (5.4)
0.76 (0.45)
Baseline
11.3 (6.3)
0.95 (0.44)
15.3 (9.9)
0.97 (0.51)
6 weeks
8.5 (7.0)
0.76 (0.62)
11.7 (8.3)
0.92 (0.49)
12 weeks
6.3 (5.5)
0.57 (0.62)
9.5 (7.8)
0.64 (0.63)
Baseline 6 weeks
6.2 (5.7) 4.2 (3.9)
0.53 (0.46) 0.37 (0.36)
9.5 (6.4) 6.9 (7.2)
0.70 (0.41) 0.52 (0.55)
12 weeks
5. 9 (6.0)
0.52 (0.48)
7.8 (7.1)
0.53 (0.47)
–
–
0.05*
–
n.s.
Group 2 LOW (n = 10)
Group 3 HIGH (n = 10)
b
P (session*group)
–
group than in the LOW group (p = 0.02). Compliance with the rehabilitation protocol of this study (number of sessions attended) was not significantly different between groups (n.s.) with the mean (SD) of attendances being 15 (5), 14 (7) and 15 (7) for the STAND, LOW and HIGH groups, respectively.
Discussion
Fig. 2 Trained/injured (T) minus untrained/uninjured (UT) 133 N laxity change from baseline to 12 weeks, with laxity values corrected for lateral hamstrings activity, as split by training group
(SHH) was measured with two-leg (n.s.) or single-leg landing (n.s.). Training data Training data was available for 31 of the 36 subjects that reached the 12-week testing point in the study. There were no statistically significant differences between groups for the number of sessions performed, or the amount performed for any of the exercises. As expected, the exception to this was the total OKC knee extensor exercise load which was significantly greater in the HIGH
The main and novel finding from this study is that the supplementation of a 12-week rehabilitation programme for ACLI individuals with knee extensor open kinetic chain resistance training using 2 sets of 20 RM on an exercise machine leads to a reduction in anterior knee laxity when compared to a programme without specific knee extensor open kinetic chain resistance training (STAND group) or to a programme with 2 sets of 20RM of knee extensor open kinetic chain resistance training (HIGH group). A 12-week rehabilitation programme also leads to a reduction in manual maximal anterior knee laxity corrected for LH activity, independent of the inclusion or exclusion of knee extensor open kinetic chain resistance training. Despite no statistically significant difference between groups for manual maximal laxity change, the LOW group demonstrated a 1.9 mm greater mean reduction from baseline to 12 weeks (Table 3), when compared to the HIGH and the STAND group scores. The low subject numbers and the poor compliance with the rehabilitation programme are significant limitations of the present study. However, although baseline to 12-week knee laxity change was studied in a total of only 36 subjects (13 in the STAND group, 11 in the LOW group and 12 in the HIGH group), large differences between groups
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and over time were found when knee laxity data was corrected for lateral hamstrings muscle activity. To date, no other study has shown that knee joint laxity in the ACLI knee can be reduced by using specific loads of knee extensor open kinetic chain resistance training. Morrissey et al. [25] found that, in a pooled sample of 25 ACLI and 24 ACL-reconstructed individuals, knee laxity change over a 6-week period was significantly negatively correlated with knee extensor open kinetic chain resistance training load. However, this was a secondary finding from the combined data sets of two separate studies [29, 30] and one must also be careful when using correlation to imply causation [11]. An increase in passive stability of the ACLI knee (i.e. a ‘‘tightening’’ of the joint) in response to a general rehabilitation programme has been reported [18] in a group of 12 ACLI subjects who partook in a pre-surgical 6-week (home-based) rehabilitation programme. Due to the use of different test forces, these results cannot be directly compared to the results of the present study. However, since the rehabilitation protocol in that study did not include knee extensor open kinetic chain resistance training, it may be that reductions in knee laxity can occur independently of the inclusion or exclusion of knee extensor open kinetic chain resistance training. This is supported by the results of the current study where manual maximal knee laxity was significantly reduced from baseline to 12 weeks for the study cohort, seemingly independent of group allocation. Others have reported that knee laxity in ACLI individuals does not change in response to rehabilitation programmes that include knee extensor open kinetic chain resistance training [3, 33]. One study [33] reported that there were no changes in either static knee laxity (at 90 N and 134 N anterior forces) or in dynamic knee laxity (measured as the maximal tibial anterior translation during a single-leg squat) following either open versus closed chain knee extensor muscle resistance training, in addition to a comprehensive rehabilitation programme, in ACLI individuals. In that study [33], OKC-seated knee extensor exercises were introduced at anywhere between weeks 5 and 13 of the 16-week programme, and the loads used were between 50 and 80 % of the 1 repetition maximum of the uninjured side. The differences in exercise dosage used in previous studies and the dosage used in the current study may explain the seemingly conflicting findings in terms of knee laxity response. The main finding in this study, the greater reduction in 133 N anterior knee laxity in the LOW group compared to the STAND and HIGH groups, may have been due to a number of possible reasons. Firstly, these results may be a result of a type I error (false positive), especially considering the small number of training sessions. A false positive finding would be more likely to occur if the groups
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differed significantly for characteristics that govern their knee laxity response to resistance training. Analysis of group differences here is difficult because so little is known about factors that affect knee laxity change in the ACL injured (or in any other group, for that matter), generally, and response to loading, specifically. We do know that after ACL reconstruction laxity change is related to how stiff the knee is to begin with [24]. This suggests that it is important to evaluate the study groups for baseline laxity and to include this variable as a confounder. In the present study, the LOW group had significantly greater laxity at baseline but the results of univariate analysis of covariance showed that the 12-week injured–uninjured 133 N anterior knee laxity scores were significantly different between groups, with the LOW group laxity being least, even when baseline score was considered as a covariate in the analysis. A false positive finding might have also occurred if the loads placed on the knee differed in ways other than as designed by the study. Although subjects were encouraged to complete an activity diary for those physical activities that they performed in addition to the study intervention, due to poor compliance with completion of this diary it was not possible to reach any meaningful conclusions regarding whether the activities performed outside of the study were similar between groups. Finally, the main result of this study could be real, which indicates that the loads placed on the soft tissue restraints to anterior translation of the tibia at the knee were sufficient to induce stiffening of those structures for those subjects in the LOW group. It is well known that mechanical loading plays a significant role in the maintenance and adaptation of the mechanical, ultrastructural, histological and functional properties of ligaments and connective tissues [5, 16, 19–22, 39, 40]. A possible explanation for why the LOW group (2 9 20RM) demonstrated a greater reduction in knee laxity when compared to the HIGH group (20 9 2RM) is that the soft tissues demonstrate a non-linear relationship to loading over time [39, 41]. Both immobilisation and/or supraphysiological loading have been shown to cause detrimental changes to soft tissues, whereby the mechanical and ultrastructural properties of those tissues such as tissue size and strength will be reduced [4, 35, 41]. The clinical significance of the findings of this study must also be considered alongside the literature regarding the association between knee joint laxity and ACLI risk. In the uninjured knee, it has been shown that knee laxity is a significant risk factor for ACL injury [26, 36, 37]. Females with a 1.3 mm [26] to 1.9 mm [36] increase in laxity above group means have been shown to be three to four times more likely to sustain an ACL injury; with the risk of ACLI injury rising 38-fold in the presence of both knee joint
Knee Surg Sports Traumatol Arthrosc
laxity and an increased body mass index of greater than one standard deviation above the mean [26]. The effect of changes or differences in knee laxity of the same order of magnitude as those reported in these studies [26, 36, 37], on clinical outcome (i.e. the risk of instability) in the ACLI knee is largely unknown. Additionally, it may be important to recall that the present study consisted of individuals who had pathological levels of anterior knee laxity and that the changes in laxity found may not be possible, or indeed desired, in individuals with normal anterior knee laxity. One study [23] has demonstrated that those individuals who were found to be copers (i.e. they had not had episodes of instability) one year after ACLI had significantly lower (p = 0.02) KT1000 manual maximal side-to-side knee laxity differences (median = 5 mm, 95 % CI 4–7 mm), than did those who were non-copers (median = 8 mm, 95 % CI 6–11 mm). These results do not necessarily imply that the functional differences between copers and non-copers were due to differences in knee laxity. However, of the physical measurements in the study (Four hop tests and knee laxity testing) knee laxity was the only significantly different physical measure between the two groups. This finding should be investigated further.
Conclusion These results suggest that knee extensor open kinetic chain resistance training at the correct dose may lead to a reduction in anterior knee laxity in the ACLI knee. Consequently, this study may indicate the possible beginning of a paradigm shift in rehabilitation for joint laxity. Traditionally, it has been believed that the only way to decrease joint laxity is surgical reconstruction of the joint. The findings in this study indicate that resistance training designed to load a joint’s passive restraints may result in these restraints responding by becoming stronger and, thus, more resistant to tension. Clinicians have long known that resistance training is effective for increasing muscle strength. More recently, this form of exercise has been used to increase bone strength. Might we soon accept that resistance training increases the strength of ligament and other non-contractile soft tissue? When using knee extensor open kinetic chain resistance training, clinicians should not only consider the effect that this exercise has on muscle strength, but also how it may be used to affect knee joint laxity. Finally, knee extensor open kinetic chain resistance training may be useful as an exercise for reducing the secondary complications associated with ACL injury and future studies should examine this possibility.
References 1. Amis AA (2012) The functions of the fibre bundles of the anterior cruciate ligament in anterior drawer, rotational laxity and the pivot shift. Knee Surg Sports Traumatol Arthrosc 20:613–620 2. Barcellona MG, Morrissey MC, Milligan P, Amis AA (2013) The effect of hamstrings muscle activity on anterior knee laxity testing in the uninjured and anterior cruciate ligament-injured knee: a cross-sectional study. Knee Surg Sports Traumatol Arthrosc. doi:10.1007/s00167-013-2695-5 3. Beard DJ, Dodd CAF, Trundle HR, Simpson AHRW (1994) Proprioception enhancement for anterior cruciate ligament deficiency—a prospective randomized trial of 2 physiotherapy regimes. J Bone Joint Surg Br 76B:654–659 4. Binkley JM, Peat M (1986) The effects of immobilization on the ultrastructure and mechanical-properties of the medial collateral ligament of rats. Clin Orthop Relat Res 203:301–308 5. Burroughs P, Dahners LE (1990) The effect of enforced exercise on the healing of ligament injuries. Am J Sports Med 18:376–378 6. Chouteau J, Testa R, Viste A, Moyen B (2012) Knee rotational laxity and proprioceptive function 2 years after partial ACL reconstruction. Knee Surg Sports Traumatol Arthrosc 20:762–766 7. Clark NC (2001) Functional performance testing following knee ligament injury. Phys Ther Sport 2:91–105 8. Cram JR, Kasman GS, Holtz J (1998) Introduction to surface electromyography, 1st edn. Aspen Publishers, Gaithersburg 9. Daniel DM, Stone ML, Riehl BMMR (1982) A measurement of lower limb function: the one leg hop for distance. Am J Knee Surg 1:212–214 10. Daniel DM, Stone ML, Sachs R, Malcom L (1985) Instrumented measurement of anterior knee laxity in patients with acute anterior cruciate ligament disruption. Am J Sports Med 13:401–407 11. Field A (2005) Correlation. In: Wright DB (ed) Discovering statistics using SPSS. SAGE publications, London, pp 107–142 12. Fleming BC, Ohlen G, Renstrom PA, Peura GD, Beynnon BD, Badger GJ (2003) The effects of compressive load and knee joint torque on peak anterior cruciate ligament strains. Am J Sports Med 31:701–707 13. Fukuda TY, Fingerhut D, Moreira VC, Camarini PMF, Scodeller NF, Duarte A, Martinelli M, Bryk FF (2013) Open kinetic chain exercises in a restricted range of motion after anterior cruciate ligament reconstruction: a randomized controlled clinical trial. Am J Sports Med 41:788–794 14. Heijne A, Werner S (2007) Early versus late start of open kinetic chain quadriceps exercises after ACL reconstruction with patellar tendon or hamstring grafts: a prospective randomized outcome study. Knee Surg Sports Traumatol Arthrosc 15:402–414 15. Hooper DM, Morrissey MC, Drechsler WI, McDermott M, McAuliffe TB (2001) Validation of the hughston clinic subjective knee questionnaire using gait analysis. Med Sci Sports Exerc 33:1456–1462 16. Hsieh AH, Sah RL, Sung KLP (2002) Biomechanical regulation of type I collagen gene expression in ACLs in organ culture. J Orthop Res 20:325–331 17. Irrgang JJ, Anderson AF, Boland AL, Harner CD, Kurosaka M, Neyret P, Richmond JC, Shelborne KD (2001) Development and validation of the international knee documentation committee subjective knee form. Am J Sports Med 29:600–613 18. Keays SL, Bullock-Saxton JE, Newcombe P, Bullock MI (2006) The effectiveness of a pre-operative home-based physiotherapy programme for chronic anterior cruciate ligament deficiency.[erratum appears in Physiother Res Int. 2007 12(3):195]. Physiother Res Int 11:204–218
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Knee Surg Sports Traumatol Arthrosc 19. Kjaer M (2004) Role of extracellular matrix in adaptation of tendon and skeletal muscle to mechanical loading. Physiol Rev 84:649–698 20. Langberg H, Skovgaard D, Petersen LJ, Bulow J, Kjaer M (1999) Type I collagen synthesis and degradation in peritendinous tissue after exercise determined by microdialysis in humans. J Physiol London 521:299–306 21. Langberg H, Skovgaard D, Asp S, Kjaer M (2000) Time pattern of exercise-induced changes in type I collagen turnover after prolonged endurance exercise in humans. Calcif Tissue Int 67:41–44 22. Laros GS, Tipton CM, Cooper RR (1971) Influence of physical activity on ligament insertions in knees of dogs. J Bone Joint Surg Am Vol A 53:275–286 23. Moksnes H, Snyder-Mackler L, Riseberg MA (2008) Individuals with an anterior cruciate ligament-deficient knee classified as noncopers may be candidates for nonsurgical rehabilitation. J Orthop Sports Phys Ther 38:586–595 24. Morrissey MC, Hudson ZL, Drechsler WI, Coutts FJ, Knight PR, King JB (2000) Effects of open versus closed kinetic chain training on knee laxity in the early period after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 8:343–348 25. Morrissey MC, Perry MC, King JB (2009) Is knee laxity change after ACL injury and surgery related to open kinetic chain knee extensor training load? Am J Phys Med Rehabil 88(369):375 26. Myer GD, Ford KR, Paterno MV, Nick TG, Hewett TE (2008) The effects of generalized joint laxity on risk of anterior cruciate ligament injury in young female athletes. Am J Sports Med 36:1073–1080 27. Norouzi S, Esfandiarpour F, Shakourirad A, Salehi R, Akbar M, Farahmand F (2013) Rehabilitation after ACL Injury: a fluoroscopic study on the effects of type of exercise on the knee sagittal plane arthrokinematics. Biomed Res Int 2013:7 28. Perry MC, Morrissey MC, Morrissey D, Knight PR, McAuliffe TB, King JB (2005) Knee extensors kinetic chain training in anterior cruciate ligament deficiency. Knee Surg Sports Traumatol Arthrosc 13:638–648 29. Perry MC, Morrissey MC, King JB, Morrissey D, Earnshaw P (2005) Effects of closed versus open kinetic chain knee extensor resistance training on knee laxity and leg function in patients during the 8-to 14-week post-operative period after anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 13:357–369 30. Perry MC, Morrissey MC, Jones JS, Paton B, McAuliffe TB, King JB, Thomas P (2005) Number of repetitions to maximum in
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hop tests in patients with anterior cruciate ligament injury. Int J Sports Med 26:688–692 Ramesh R, Von Arx O, Azzopardi T, Schranz PJ (2005) The risk of anterior cruciate ligament rupture with generalised joint laxity. J Bone Joint Surg Br 87-B:800–803 Reid A, Birmingham TB, Stratford PW, Alcock GK, Giffin JR (2007) Hop testing provides a reliable and valid outcome measure during rehabilitation after anterior cruciate ligament reconstruction. Phys Ther 87:337–349 Tagesson S, Oberg B, Good L, Kvist J (2008) A comprehensive rehabilitation program with quadriceps strengthening in closed versus open kinetic chain exercise in patients with anterior cruciate ligament deficiency: a randomized clinical trial evaluating dynamic tibial translation and muscle function. Am J Sports Med 36:298–307 Tegner Y, Lysholm J (1985) Rating systems in the evaluation of knee ligament injuries. [Report]. Clin Orthop Relat Res 198:42–49 Tipton CM, Vailas AC, Matthes RD (1986) Experimental studies on the influences of physical-activity on ligaments, tendons and joints—a brief review. Acta Med Scand 711:157–168 Uhorchak JM, Scoville CR, Williams GN, Arciero RA, St PP, Taylor DC (2003) Risk factors associated with noncontact injury of the anterior cruciate ligament: a prospective four-year evaluation of 859 West Point cadets. Am J Sports Med 31:831–842 Vauhnik R, Morrissey M, Rutherford O, Turk Z, Pilih I, Pohar M (2008) Knee anterior laxity: a risk factor for traumatic knee injury among sportswomen? Knee Surg Sports Traumatol Arthrosc 16:823–833 Ware JE, Kosinski M, Bjorner JB, Turner-Bowker DM, Gandek B, Maruish ME (2010) User’s manual for the SF-36v2 health survey, 2nd edn. QualityMetric Inc, Lincoln Woo SLY, Abramowitch SD, Kilger R, Liang R (2006) Biomechanics of knee ligaments: injury, healing, and repair (Review). J Biomech 39:1–20 Woo SLY, Amiel D, Akeson WH, Kuei SC, Tipton CM (1979) Effect of long-term exercise on ligaments, tendons and bones of swine. Med Sci Sports Exerc 11:105 Woo SLY, Gomez MA, Woo YK, Akeson WH (1982) Mechanical-properties of tendons and ligaments. 2. the relationships of immobilization and exercise on tissue remodeling. Biorheology 19:397–408
KNEE
The effect of knee extensor open kinetic chain resistance training in the ACL-injured knee Massimo G. Barcellona • Matthew C. Morrissey • Peter Milligan • Melissa Clinton • Andrew A. Amis
Received: 15 November 2013 / Accepted: 29 May 2014 Ó Springer-Verlag Berlin Heidelberg 2014
Abstract Purpose To investigate the effect of different loads of knee extensor open kinetic chain resistance training on anterior knee laxity and function in the ACL-injured (ACLI) knee. Methods Fifty-eight ACLI subjects were randomised to one of three (12-week duration) training groups. The STAND group trained according to a standardised rehabilitation protocol. Subjects in the LOW and HIGH group trained as did the STAND group but with the addition of seated knee extensor open kinetic chain resistance training at loads of 2 sets of 20 repetition maximum (RM) and 20 sets of 2RM, respectively. Anterior knee laxity and measurements of physical and subjective function were performed at baseline, 6 and 12 weeks. Thirty-six subjects were tested at both baseline and 12 weeks (STAND n = 13, LOW n = 11, HIGH n = 12). Results The LOW group demonstrated a reduction in 133 N anterior knee laxity between baseline and 12 weeks
testing when compared to the HIGH and the STAND groups (p = 0.009). Specifically, the trained-untrained knee laxity decreased an average of approximately 5 mm in the LOW group while remaining the same in the other two groups. Conclusion Twelve weeks of knee extensor open kinetic chain resistance training at loads of 2 sets of 20RM led to a reduction in anterior knee laxity in the ACLI knee. This reduction in laxity does not appear to offer any significant short-term functional advantages when compared to a standard rehabilitation protocol. These results indicate that knee laxity can be decreased with resistance training of the thigh muscles. Level of evidence Randomised controlled trial, Level II. Keywords Therapeutic exercise Quadriceps Joint stability Hypermobility Resistance training
Introduction M. G. Barcellona Academic Department of Physiotherapy, School of Medicine, King’s College London, London, UK M. C. Morrissey (&) Faculty of Health Sciences, University of Ljubljana, Ljubljana, Slovenia e-mail: [email protected] P. Milligan King’s College London, London, UK M. Clinton Guy’s and St. Thomas’ Hospital, London, UK A. A. Amis Department of Mechanical Engineering, Imperial College London, London, UK
The anterior cruciate ligament (ACL) and in particular the anterior medial bundle of the ACLis the primary restraint to anterior translation of the tibia at the knee [1]. Fleming et al. [12] reported that the magnitude of anterior cruciate ligament (ACL) strain during knee extensor open kinetic chain exercise is related to absolute load. This finding has received support in more recent, clinical work where the change in anterior knee laxity in rehabilitation after ACL injury and surgery was found to be related to the load used during knee extensor open kinetic chain resistance training with greater loads being associated with decreases in laxity [25]. These findings raise the possibility that anterior knee laxity can be decreased with knee extensor open kinetic chain training and this requires a randomised, controlled clinical trial.
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If anterior knee laxity can be decreased with knee extensor open kinetic chain training, there are at least three groups that might benefit from such training effects. The first group is uninjured individuals with higher than usual anterior knee laxity who are concerned about injuring their knee in sports; as it has been found that increased anterior knee laxity is a significant predisposer to traumatic knee injury [37], generally, and ACL injury, in particular [31, 36]. Another group that might benefit consists of individuals recovering from ACL reconstruction surgery following full or partial rupture [6]; the main mechanical purpose of which is to decrease anterior knee laxity. In this group, there are seemingly conflicting reports regarding the safety of knee extensor open kinetic chain resistance exercise in terms of knee laxity change in the early stages post ACL reconstruction [13, 14, 29]. The discrepancy in findings may relate to differences in exercise dosage [25], exercise range of movement [13] and timing of initiation following surgery [14]. The third group that might benefit from resistance training-induced decreases in anterior knee laxity consists of individuals who have injured their ACL and are being treated conservatively. The amount of anterior tibial translation provided by knee extensor open kinetic chain resistance exercise has been shown to be greater in individuals with ACL-injured knees when compared to uninjured individuals [27] and if performed at knee flexion angles including 30° to 0° [27], may provide the load stimulus for change in anterior knee laxity over time. The main purpose of this study was to evaluate whether anterior knee laxity can be decreased with knee extensor open kinetic chain training in this latter group. This purpose was served with a randomised, controlled clinical trial consisting of three groups in rehabilitation after ACL injury—two groups receiving either relatively high or low load knee extensor open kinetic chain training along with their standard programme and a third group that only received the standard programme (which did not consist of knee extensor open kinetic chain resistance training). This design allowed an additional purpose to be served—to evaluate whether relatively high and low knee extensor open kinetic chain training loads might differ in their effects on anterior knee laxity. A final, general purpose was to compare the different groups for changes in knee physical and self-assessed function. The main hypothesis to be tested in this study was that the supplementation of a standard rehabilitation programme with high load knee extensor open kinetic chain resistance training would lead to a greater reduction in anterior knee laxity compared to lower loads of this exercise in ACL-injured (ACLI) individuals. The findings of this study will aid clinical decision making concerning the use of knee extensor open kinetic chain resistance training and optimal dosage parameters in
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individuals following ACL injury. In the wider context, if laxity is found to decrease with resistance training, the focus of rehabilitation for joint laxity problems is likely to switch to using exercises focussed on loading joints to enhance their passive stability.
Materials and methods This study was a prospective, single-blind (examiner), randomised controlled clinical trial with repeat measures at baseline, 6 weeks and 12 weeks (Fig. 1). The chief investigator (MB), a senior physical therapist and clinical researcher, performed all measurements. Ethics, subjects and recruitment Subjects were recruited from five sites, from which local ethics approval was granted (National Research Ethics Service reference number 08/H0804/28). At each site, individuals diagnosed with an ACLI who were at least 6 weeks post-injury or post-arthroscopic surgery for the knee were approached for recruitment if they: (1) had been diagnosed with an ACLI via magnetic resonance imaging or arthroscopy, or if they had a greater than 3 mm side-toside difference in anterior knee laxity as measured by the KT2000 ligament arthrometer (manual maximal force); (2) were aged between 18 and 60 years; (3) had not sustained any trauma or injury that required medical attention to the contralateral lower limb within the last 6 months; and (4) had improved to a level such that no undue aggravation was expected as a result of the testing and training required for participation in the study. Subjects were excluded from participating in the study if they did not have a competent command of the English language, if they had a posterior cruciate ligament injury and/or if they had neurological, systemic, rheumatological or muscular diseases. Clinical measurement After signing a consent form, subjects completed a general questionnaire. Each test procedure lasted for approximately 1.5 to 2 h and for all measurements the uninjured leg was tested prior to the injured leg. Each subject completed the Lysholm and Tegner questionnaires [34], the IKDC 2000 Subjective Knee Evaluation Form [17], the Hughston Clinic subjective knee questionnaire [15] and the MOS 36-item Short Form Health Survey Version 2 [38]. Body mass, height and the limit of passive knee joint flexion and extension motion were recorded according to standardised procedures. Knee girth measures were also obtained at the level of the joint line and 5 cm above this using a cloth tape measure.
Knee Surg Sports Traumatol Arthrosc Fig. 1 Flowchart of participants in the study
79 subjects recorded as approached / screened
21 unable to participate: 15 for personal reasons 6 did not meet criteria
Randomised (n=58)
Group 1 Standard (STAND) (n=21)
Group 2 2 x 20 RM (LOW) (n=18)
5 subjects withdrew:
7 subjects withdrew:
3 for personal reasons 1 injured the other knee 1 moved away from area
5 for personal reasons 1 had ACLR 1 moved away from area
16 subjects tested to 6 weeks
Group 3 20 x 2 RM (n=19)
7 subjects withdrew 6 for personal reasons 1 consultant decision
11 subjects tested to 6 weeks
12 subjects tested to 6 weeks
3 subjects withdrew: 2 for personal reasons 1 had ACLR
0 subjects withdrew
13 subjects tested to 12 weeks
Anterior knee laxity measurement was performed according to the manufacturer’s instructions [10] using the KT2000 knee joint arthrometer (Medmetric Corporation, San Diego, USA) with concurrent measurement of lateral hamstrings muscle activity as described in detail previously [2]. Surface electromyography (EMG) data for the lateral hamstrings was recorded during each laxity test using the Delsys Bagnoli-4 System with DE-2.1 single differential electrodes (Delsys Inc., Boston, MA). Electrode placement was performed as described by Cram and Kasman [8]. Prior to laxity testing, three maximal voluntary isometric contractions (MVIC) of the knee flexors was carried out against the resistance applied by the principal examiner in a seated position on the edge of a plinth with the hip and knee at 90°. Standardised verbal instructions were given.
0 subjects withdrew
11 subjects tested to 12 weeks
12 subjects tested to 12 weeks
Two separate anterior knee laxity tests were conducted for each leg; a 133 N and a manual maximal test. For each test, three anterior and posterior repetitions at the 88 N force were performed [10]. This was followed by 5 repetitions of the particular test. Both EMG and KT2000 laxity data signals were sampled at a frequency of 2000 Hz using a National Instruments USB-6210 portable analogue to digital converter (National Instruments Corporation, Texas, USA) and Labview Signal Express 2.5.0 software (National Instruments Corporation, Texas, USA). Subjects were asked to perform two functional hop tests at baseline and 12 weeks in order to assess lower limb functional performance. The second of these two tests was the widely used single horizontal hop for distance (SHH)
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with a single-leg land [7, 9, 32]. Prior to this test, a two-leg land single horizontal hop test was performed. This test was performed prior to the single-leg land test in order to: (1) familiarise subjects with the nature of such a test, (2) allow subjects to decide whether they felt able to perform a single-leg land, and (3) minimise the risk of the knee giving way during testing. For both tests, the uninjured leg was tested first. Following a practice trial for each test 5 separate successful trials were recorded [28]. Where a subject did not feel confident to perform one or both of the hop testing procedures, this was recorded. Randomisation and intervention Following baseline testing, subjects were allocated to one of three groups using block randomisation, in blocks of 6 assignments. A separate random number list, controlled by the relevant principal investigator, was used for each of the five training sites in order to ensure balanced groupings at each site and in order to ensure that the chief investigator remained blind to treatment allocation. Subjects from each of the three groups were invited to participate in a 12-week supervised training programme with a target of three sessions per week. Each session lasted approximately 45 min to 1 h depending on group allocation and the level of intensity for each exercise. All subjects in each of the three groups received a standardised rehabilitation protocol for those with ACL injury that was similar to the current programmes delivered at each of the training sites, and that was based on previous research [29]. The training procedures were standardised across each site by providing the physical therapists involved with the training of subjects with a detailed study treatment protocol and through specific training by the chief investigator prior to the start of the study. Exercise equipment for the study was equal across sites and included a cycle ergometer (Tunturi F300, Tunturi Oy Ltd., Turku, Finland), a standard 30-cm wooden wobble board, a standard 92-cm mini-trampette, an 11.5-inch step or bench, 1-kg leg weights and a seated knee extensor training device (Body-Solid CAM series leg extension and curl GCEC340, Body-Solid Inc., IL, USA). Subjects allocated to group 1, also known as the standard (STAND) group, performed the standardised rehabilitation protocol without the inclusion of seated knee extensor open kinetic chain resistance training. Subjects in group 2, also known as the LOW group, performed the same standard protocol with the addition of injured leg knee extensor open kinetic chain resistance training, of two sets of 20 repetition maximum (RM), on the seated knee extensor training device. Subjects in group 3, also known as the HIGH group, performed the standard rehabilitation protocol with the addition of the knee extensor open kinetic
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chain resistance training at loads of 20 sets of 2RM. The knee extensor open kinetic chain resistance training for subjects in the LOW and HIGH groups was performed from 0° to 90° of knee flexion and at an average speed of 60°/s (metronome guided). Ethical approval for the study was granted by the Guy’s and St. Thomas’ Research Ethics Committee (REC Reference: 08–HO804/28). Statistical analysis For each individual subject, the training load used for each exercise at each training session was recorded on specific treatment record sheets. The specifics for each exercise was calculated as follows: (1) total time for cycling, wobble board and mini-trampette; (2) total number of repetitions 9 load used in each repetition for hamstring curls and OKC knee extensor exercise; and (3) total repetitions for calf raises, ballistic hamstrings, step ups, mini squats, hip abductors, bridging and deep lunges. Anterior knee laxity and surface electromyography (EMG) data were analysed as described previously [2] with anterior knee laxity corrected for lateral hamstrings EMG activity [2] as the main outcome. Matlab Software (The MathWorks Inc., Natik, MA, USA) was used to determine the laxity value for each test (133 N or manual maximal) by calculating an average of the 5 trials. This allowed for greater precision of measurement (reported to the nearest 0.1 mm) and reduces the potential for bias on the part of the examiner. Intra-rater test–retest reliability, as determined by calculation of the intraclass correlation coefficient ICC(3,1)—for absolute scores of the manual maximal and 133 N anterior knee laxity tests, in the hands of the principal examiner, was ICC 0.84 and ICC 0.83, respectively, when tested in 12 uninjured subjects on two separate days. For hop test performance, the maximal distance for each leg from the 5 trials of each test was used for analysis. Where subjects did not perform a particular hop test due to fear of instability, this was recorded. Statistical analyses were performed using SPSS version 16.0. Non-nominal baseline and outcome data were tested for normality using the Kolmogorov–Smirnov test and through observation of the P–P plots. In order to identify potential confounding variables, baseline differences between groups were analysed using a one-way independent ANOVA for normally distributed baseline measures, or the Kruskal–Wallis test for non-parametric baseline measures. Testing for between group differences for nominal baseline data was analysed using chi-square testing. Differences between groups for the change in knee girth and range of motion measures were analysed using a two-way (group x time) ANOVA.
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A two-way mixed (group 9 test session) univariate ANOVA was performed to compare side-to-side differences between groups over time for both manual maximal and 133 N anterior knee laxity. In order that the hop test data for all subjects, even those who did not perform the tests due to fear of instability or lack of confidence, was considered, changes between baseline and 12-week data were categorised as follows. Those subjects where the trained leg improved more than the untrained leg were given a score of 1. Where the untrained leg improved more than the trained leg, a score of 2 was given. Where subjects did not jump at both baseline and 12 weeks or where the trained and the untrained leg changed equally, they were given a score of 3. If the subjects jumped at 12 weeks on the trained leg when they did not jump at baseline, they were also given a score of 1. Cross-tabulation according to group allocation was then performed and chi-square testing was used to analyse for differences between groups. Outcome data for the subjective questionnaires was analysed using the Kruskal–Wallis test to compare differences between groups at baseline, 12 weeks and on the 12-week minus baseline score. In addition, the Wilcoxon test was used to analyse each group separately for the
change in the questionnaire scores from baseline to 12 weeks.
Results Of 58 subjects, 36 were tested at both baseline and 12 weeks (see Fig. 1). Baseline subject characteristics are presented in Table 1. Subjects in the STAND group had a significantly lower passive range of knee flexion than the LOW group (U = 27.0, p = 0.009) and did not differ for any of the questionnaire total or sub-domain scores apart for the Tegner score (see Table 1). Knee joint girth and range of motion There was a significant improvement in knee joint flexion range of motion (p \ 0.001), but not for the change in knee joint extension range of motion (n.s.). The groups did not differ for knee flexion (n.s.) or extension (n.s.) changes. There was no significant change in knee joint girth at either the level of the joint line (n.s.) or 5 cm above the joint line (n.s.) nor were group differences found in girth changes at these two levels (both n.s.).
Table 1 Baseline subject characteristics for participants who participated up to the 12-week testing Group 1 (STAND)
Range
N
13
–
Age (yrs)
35 ± 9
24 to 53
Body mass (kg) Height (cm)
83 ± 12 174 ± 11
64 to 109 159 to 190
Body mass index (kg/m2)
27 ± 4
Gender (M/F)
10/3
Dominant limb (R/L)
Group 2 (LOW)
Range
Group 3 (HIGH)
Range
p value for between group differences
11
–
12
–
32 ± 5
25 to 40
29 ± 7
19 to 45
n.s.
73 ± 14 173 ± 12
53 to 93 150 to 191
86 ± 19 180 ± 10
61 to 130 160 to 197
n.s. n.s.
22 to 36
24 ± 3
20 to 29
27 ± 7
20 to 44
n.s.
–
8/3
–
11/1
–
n.s.b
11/2
–
11/0
–
12/0
–
n.s.b
Inj. limb (R/L)*
2/11
–
7/4
–
6/6
–
0.05b
Knee extension inj. PROM (°)
1±5
-7 to 9
-1 ± 3
-7 to 4
1±6
-9 to 9
n.s.
Knee extension uninj. PROM (°)
2±3
-3 to 8
1±4
-6 to 9
3±3
-2 to 8
n.s.
Knee flexion inj. PROM (°)*
137 ± 12
117 to 152
150 ± 8
141 to 164
147 ± 9
128 to 160
0.02a
Knee flexion uninj. PROM (°)
150 ± 10
126 to 162
157 ± 4
151 to 163
153 ± 8
139 to 162
n.s.
Joint line knee girth inj. (cm)
37 ± 2
33 to 40
36 ± 2
33 to 39
37 ± 3
31 to 43
n.s.
Joint line knee girth uninj. (cm)
37 ± 3
33 to 42
35 ± 2
31 to 39
37 ± 3
31 to 43
n.s.
Knee girth 5 cm above joint line inj. (cm)
40 ± 3
37 to 45
38 ± 2
35 to 41
40 ± 4
33 to 48
n.s.
Knee girth 5 cm above joint line uninj. (cm)
40 ± 4
33 to 47
38 ± 2
34 to 42
39 ± 4
33 to 48
n.s.
Tegner score at baseline (/10)*
3 (3)
1 to 4
3 (2)
2 to 4
4 (5)
1 to 6
0.02a
n.s. not statistically significant, Inj. injured/trained limb, Uninj. uninjured/untrained limb, PROM passive range of motion * Statistically significant at the p \ 0.05 level a
Kruskal–Wallis test as data was found to be non-parametric
b
chi-square analysis
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Knee Surg Sports Traumatol Arthrosc Table 2 Descriptive injury statistics for participants who participated up to 12-week testing
Time from injury to baseline test (wks)a Time from baseline to 6-week test (wks)
a
Time from baseline to 12-week test (wks)
a
At work at time of baseline test (Y/N)
GROUP 1 (STAND)
GROUP 2 (LOW)
GROUP 3 (HIGH)
p value for between group differences
10 (6–1251)
18 (6–1279)
127 (7–1262)
n.s.b
6 (5–8)
6 (6–6)
6 (5–8)
n.s.b
12 (11–14)
13 (11–15)
12 (12–16)
n.s.b
13/0
10/1
12/0
n.s.c
At work at time of 12-week test (Y/N)
13/0
11/0
12/0
–
Mechanism of injury (Non-contact/Contact)
10/3
9/2
12/0
n.s.c
Surgery for meniscal injury (Y/N) Method of diagnosis (MRI/Arthroscopy/KT2000)
2/11 12/1/0
3/8 7/3/1
1/11 9/1/2
n.s.c n.s.c
Lateral meniscus
6
3
3
–
Medial meniscus
5
2
5
–
Injuries associated with ACL injuryd
MCL grade 1 or 2
3
3
1
–
LCL grade 1 or 2
0
1
0
–
Osteochondral
1
3
1
–
Football
8
6
5
–
Skiing/Snowboarding
3
2
3
–
Other
2
3
4
–
Activity of injury
n.s. not statistically significant, MCL medial collateral ligament, LCL lateral collateral ligament, Y yes, N no, NC non-contact, C contact, MRI magnetic resonance imaging, KT2000 KT2000 knee joint arthrometer, Full complete ACL tear, Partial partial ACL tear, Injury KT2000 arthrometer clinical diagnosis of ACL injury ([3 mm side-to-side difference) a
Data presented as median(range)
b
Kruskal–Wallis test
c
Chi-square analysis
d
One patient can have several associated injuries
For descriptive injury statistics for participants who participated up to 12 weeks of the study see Table 2. Laxity data To correct for a positively skewed difference in laxity for both the manual maximal and 133 N tests, natural logarithmic (log) transformation of the data was performed. Trained minus untrained laxity data at baseline, 6 weeks and 12 weeks are presented in Table 3. Pre-planned contrast analysis revealed that there was a significant difference between groups (Fig. 2) for the change in 133 N LHcorrected knee laxity between the baseline and 12-week test session [F(2,29) = 4.8, p = 0.02]. There were no significant differences between any other time point comparisons for both the 133 N and manual maximal tests. Due to an increased injured—uninjured baseline laxity in the LOW group, a univariate analysis of covariance was used to assess for differences in 12-week laxity scores between groups, whilst including baseline knee laxity scores as a covariate. Even when accounting for baseline differences in knee laxity, there were statistically
123
significant differences between groups for the 133 N anterior knee laxity scores at 12 weeks [F(2,28) = 3.8, p = 0.04]. Contrast analysis revealed that the LOW group 12-week laxity scores were significantly reduced compared to both the STAND (p = 0.02) and the HIGH (p = 0.04) groups, when baseline laxity was considered as a covariate. There was no significant difference between the STAND and the HIGH groups (n.s.). Questionnaire data There were no significant differences between groups with regard to the baseline to 12-week change in the IKDC total score (n.s.), the Lysholm score (n.s.), the Tegner score (n.s.), the Hughston score (n.s.), the SF36 mental component summary score (n.s.) and the SF36 physical component summary score (n.s.). Functional hop tests There were no statistically significant differences between groups over time when the change in single horizontal hop
Knee Surg Sports Traumatol Arthrosc Table 3 Injured minus uninjured knee laxity as corrected for lateral hamstrings muscle activity over time and between groups
GROUP All subjects (N = 32)
a
a
Presented as mean (SD). P p value for the main effect of time. Pb p value for the interaction effect between time and group n.s. not statistically significant, MM manual maximal, STAND standard, I injured leg, UI uninjured leg * Significant at the p \ 0.05 level. ** Significant at the p \ 0.01 level
Test session
I-UI 133 N laxity
Log I-UI 133 N laxity
I-UI MM laxity
Log I-UI MM laxity
Baseline
7.7 (6.3)
0.73 (0.56)
12.1 (7.3)
0.88 (0.49)
6 weeks
6.6 (5.2)
0.64 (0.50)
10.0 (7.1)
0.78 (0.51)
12 weeks
6.0 (5.2)
0.61 (0.57)
8.8 (6.6)
0.66 (0.50)
P (session)
–
n.s.
–
0.001**
Group 1 STAND (n = 12)
Baseline
6.0 (6.0)
0.71 (0.69)
11.5 (6.4)
0.96 (0.52)
6 weeks
7.0 (3.8)
0.77 (0.43)
11.0 (5.5)
0.89 (0.45)
12 weeks
5.7 (4.5)
0.71 (0.64)
9.1 (5.4)
0.76 (0.45)
Baseline
11.3 (6.3)
0.95 (0.44)
15.3 (9.9)
0.97 (0.51)
6 weeks
8.5 (7.0)
0.76 (0.62)
11.7 (8.3)
0.92 (0.49)
12 weeks
6.3 (5.5)
0.57 (0.62)
9.5 (7.8)
0.64 (0.63)
Baseline 6 weeks
6.2 (5.7) 4.2 (3.9)
0.53 (0.46) 0.37 (0.36)
9.5 (6.4) 6.9 (7.2)
0.70 (0.41) 0.52 (0.55)
12 weeks
5. 9 (6.0)
0.52 (0.48)
7.8 (7.1)
0.53 (0.47)
–
–
0.05*
–
n.s.
Group 2 LOW (n = 10)
Group 3 HIGH (n = 10)
b
P (session*group)
–
group than in the LOW group (p = 0.02). Compliance with the rehabilitation protocol of this study (number of sessions attended) was not significantly different between groups (n.s.) with the mean (SD) of attendances being 15 (5), 14 (7) and 15 (7) for the STAND, LOW and HIGH groups, respectively.
Discussion
Fig. 2 Trained/injured (T) minus untrained/uninjured (UT) 133 N laxity change from baseline to 12 weeks, with laxity values corrected for lateral hamstrings activity, as split by training group
(SHH) was measured with two-leg (n.s.) or single-leg landing (n.s.). Training data Training data was available for 31 of the 36 subjects that reached the 12-week testing point in the study. There were no statistically significant differences between groups for the number of sessions performed, or the amount performed for any of the exercises. As expected, the exception to this was the total OKC knee extensor exercise load which was significantly greater in the HIGH
The main and novel finding from this study is that the supplementation of a 12-week rehabilitation programme for ACLI individuals with knee extensor open kinetic chain resistance training using 2 sets of 20 RM on an exercise machine leads to a reduction in anterior knee laxity when compared to a programme without specific knee extensor open kinetic chain resistance training (STAND group) or to a programme with 2 sets of 20RM of knee extensor open kinetic chain resistance training (HIGH group). A 12-week rehabilitation programme also leads to a reduction in manual maximal anterior knee laxity corrected for LH activity, independent of the inclusion or exclusion of knee extensor open kinetic chain resistance training. Despite no statistically significant difference between groups for manual maximal laxity change, the LOW group demonstrated a 1.9 mm greater mean reduction from baseline to 12 weeks (Table 3), when compared to the HIGH and the STAND group scores. The low subject numbers and the poor compliance with the rehabilitation programme are significant limitations of the present study. However, although baseline to 12-week knee laxity change was studied in a total of only 36 subjects (13 in the STAND group, 11 in the LOW group and 12 in the HIGH group), large differences between groups
123
Knee Surg Sports Traumatol Arthrosc
and over time were found when knee laxity data was corrected for lateral hamstrings muscle activity. To date, no other study has shown that knee joint laxity in the ACLI knee can be reduced by using specific loads of knee extensor open kinetic chain resistance training. Morrissey et al. [25] found that, in a pooled sample of 25 ACLI and 24 ACL-reconstructed individuals, knee laxity change over a 6-week period was significantly negatively correlated with knee extensor open kinetic chain resistance training load. However, this was a secondary finding from the combined data sets of two separate studies [29, 30] and one must also be careful when using correlation to imply causation [11]. An increase in passive stability of the ACLI knee (i.e. a ‘‘tightening’’ of the joint) in response to a general rehabilitation programme has been reported [18] in a group of 12 ACLI subjects who partook in a pre-surgical 6-week (home-based) rehabilitation programme. Due to the use of different test forces, these results cannot be directly compared to the results of the present study. However, since the rehabilitation protocol in that study did not include knee extensor open kinetic chain resistance training, it may be that reductions in knee laxity can occur independently of the inclusion or exclusion of knee extensor open kinetic chain resistance training. This is supported by the results of the current study where manual maximal knee laxity was significantly reduced from baseline to 12 weeks for the study cohort, seemingly independent of group allocation. Others have reported that knee laxity in ACLI individuals does not change in response to rehabilitation programmes that include knee extensor open kinetic chain resistance training [3, 33]. One study [33] reported that there were no changes in either static knee laxity (at 90 N and 134 N anterior forces) or in dynamic knee laxity (measured as the maximal tibial anterior translation during a single-leg squat) following either open versus closed chain knee extensor muscle resistance training, in addition to a comprehensive rehabilitation programme, in ACLI individuals. In that study [33], OKC-seated knee extensor exercises were introduced at anywhere between weeks 5 and 13 of the 16-week programme, and the loads used were between 50 and 80 % of the 1 repetition maximum of the uninjured side. The differences in exercise dosage used in previous studies and the dosage used in the current study may explain the seemingly conflicting findings in terms of knee laxity response. The main finding in this study, the greater reduction in 133 N anterior knee laxity in the LOW group compared to the STAND and HIGH groups, may have been due to a number of possible reasons. Firstly, these results may be a result of a type I error (false positive), especially considering the small number of training sessions. A false positive finding would be more likely to occur if the groups
123
differed significantly for characteristics that govern their knee laxity response to resistance training. Analysis of group differences here is difficult because so little is known about factors that affect knee laxity change in the ACL injured (or in any other group, for that matter), generally, and response to loading, specifically. We do know that after ACL reconstruction laxity change is related to how stiff the knee is to begin with [24]. This suggests that it is important to evaluate the study groups for baseline laxity and to include this variable as a confounder. In the present study, the LOW group had significantly greater laxity at baseline but the results of univariate analysis of covariance showed that the 12-week injured–uninjured 133 N anterior knee laxity scores were significantly different between groups, with the LOW group laxity being least, even when baseline score was considered as a covariate in the analysis. A false positive finding might have also occurred if the loads placed on the knee differed in ways other than as designed by the study. Although subjects were encouraged to complete an activity diary for those physical activities that they performed in addition to the study intervention, due to poor compliance with completion of this diary it was not possible to reach any meaningful conclusions regarding whether the activities performed outside of the study were similar between groups. Finally, the main result of this study could be real, which indicates that the loads placed on the soft tissue restraints to anterior translation of the tibia at the knee were sufficient to induce stiffening of those structures for those subjects in the LOW group. It is well known that mechanical loading plays a significant role in the maintenance and adaptation of the mechanical, ultrastructural, histological and functional properties of ligaments and connective tissues [5, 16, 19–22, 39, 40]. A possible explanation for why the LOW group (2 9 20RM) demonstrated a greater reduction in knee laxity when compared to the HIGH group (20 9 2RM) is that the soft tissues demonstrate a non-linear relationship to loading over time [39, 41]. Both immobilisation and/or supraphysiological loading have been shown to cause detrimental changes to soft tissues, whereby the mechanical and ultrastructural properties of those tissues such as tissue size and strength will be reduced [4, 35, 41]. The clinical significance of the findings of this study must also be considered alongside the literature regarding the association between knee joint laxity and ACLI risk. In the uninjured knee, it has been shown that knee laxity is a significant risk factor for ACL injury [26, 36, 37]. Females with a 1.3 mm [26] to 1.9 mm [36] increase in laxity above group means have been shown to be three to four times more likely to sustain an ACL injury; with the risk of ACLI injury rising 38-fold in the presence of both knee joint
Knee Surg Sports Traumatol Arthrosc
laxity and an increased body mass index of greater than one standard deviation above the mean [26]. The effect of changes or differences in knee laxity of the same order of magnitude as those reported in these studies [26, 36, 37], on clinical outcome (i.e. the risk of instability) in the ACLI knee is largely unknown. Additionally, it may be important to recall that the present study consisted of individuals who had pathological levels of anterior knee laxity and that the changes in laxity found may not be possible, or indeed desired, in individuals with normal anterior knee laxity. One study [23] has demonstrated that those individuals who were found to be copers (i.e. they had not had episodes of instability) one year after ACLI had significantly lower (p = 0.02) KT1000 manual maximal side-to-side knee laxity differences (median = 5 mm, 95 % CI 4–7 mm), than did those who were non-copers (median = 8 mm, 95 % CI 6–11 mm). These results do not necessarily imply that the functional differences between copers and non-copers were due to differences in knee laxity. However, of the physical measurements in the study (Four hop tests and knee laxity testing) knee laxity was the only significantly different physical measure between the two groups. This finding should be investigated further.
Conclusion These results suggest that knee extensor open kinetic chain resistance training at the correct dose may lead to a reduction in anterior knee laxity in the ACLI knee. Consequently, this study may indicate the possible beginning of a paradigm shift in rehabilitation for joint laxity. Traditionally, it has been believed that the only way to decrease joint laxity is surgical reconstruction of the joint. The findings in this study indicate that resistance training designed to load a joint’s passive restraints may result in these restraints responding by becoming stronger and, thus, more resistant to tension. Clinicians have long known that resistance training is effective for increasing muscle strength. More recently, this form of exercise has been used to increase bone strength. Might we soon accept that resistance training increases the strength of ligament and other non-contractile soft tissue? When using knee extensor open kinetic chain resistance training, clinicians should not only consider the effect that this exercise has on muscle strength, but also how it may be used to affect knee joint laxity. Finally, knee extensor open kinetic chain resistance training may be useful as an exercise for reducing the secondary complications associated with ACL injury and future studies should examine this possibility.
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