Journal of Sport Rehabilitation, 2014, 23, 259-269 http://dx.doi.org/10.1123/JS R .2013-0088 © 2014 Hum an Kinetics, Inc.
Quadriceps Femoris Strength and Sagittal-Plane Knee Biomechanics During Stair Ascent in Individuals With Articular Cartilage Defects in the Knee Louise M.Thoma, David C. Flanigan, Ajit M. Chaudhari, Robert A. Siston, Thomas M. Best, and Laura C. Schmitt Context: Few objective data are available regarding strength and m ovem ent patterns in individuals with articu lar cartilage defects (ACDs) o f the knee. Objectives: To test the follow ing hypotheses: (1) The involved lim b o f individuals w ith ACDs would dem onstrate low er peak knee-flexion angle, peak internal knee-extension m om ent, and peak vertical ground-reaction force (vG R F) than the contralateral lim b and healthy controls. (2) On the involved lim b o f individuals w ith ACDs, quadriceps fem oris strength would positively correlate with peak knee-flexion angle, peak internal knee-extension m om ent, and peak vGRF. Design: Cross-sectional. Setting: Biom echanics research laboratory. Participants: 11 individuals with ACDs in the knee who were eligible for surgical cartilage restoration and 10 healthy controls. Methods: Q uadriceps fem oris strength was quantified as peak isom etric knee-extension torque via an isokinetic dynam om eter. Sagittal-plane knee kinem atics and kinetics were m easured during the stance phase o f stair ascent with 3-dim ensional motion analysis. Main Outcome Measures: Q uadriceps strength and knee biom echanics during stair ascent were com pared betw een the involved and contralateral lim bs o f participants with ACD (paired t tests) and with a control group (independent-sam ples t tests). Pearson correlations evaluated relationships betw een strength and stair-ascent biom echanics. Results: L ow er quadriceps strength and peak internal knee-extension m om ents w ere observed in the involved limb than in the contralateral lim b ( P < .01) and the control group (P < .01). F or the involved lim b o f the ACD group, quadriceps fem oris strength was strongly correlated ( r = .847) with involved-lim b peak internal knee-extension m om ent and inversely correlated ( r = -.6 3 5 ) w ith contralateral peak vGRF. Conclusions: Individuals with ACDs dem onstrated deficits in quadriceps fem oris strength with associated alterations in m ovem ent patterns during stair ascent. The results o f this study are not com prehensive; further research is needed to understand the physiological characteristics, activity perform ance, and m ovem ent quality in this population.
Keywords: m uscle strength, stair clim bing, focal chondral defects A rticular cartilage defects (ACDs) in the knee are focal lesions o f the articular cartilage o f traum atic or insidious onset surrounded by healthy articular cartilage and subchondral bone. R etrospective and prospective studies report a 19% to 40% l~3 prevalence o f focal ACDs found during knee arthroscopy. In contrast to m ore dif fu se cartilage pathology such as o steoarthritis, knee A CD s m ost com m only affect young (40 kg/m 12, history o f back, hip or ankle pathology or surgery, history o f neurologic injury or pathology, or history o f inflam m atory arthritis. Ten indi viduals w ithout history o f knee or lower-extrem ity injury and o f sim ilar age and activity level were recruited from the com m unity and participated in the study for com parison with the ACD group. This study was approved by the institutional review board, and inform ed consent was obtained from all participants. In addition to age, height, weight, and BM I, M arx35 and Tegner36 scores were collected to quantify level o f activity. The M arx A ctivity Rating Scale was developed to characterize subject level o f activity in running, cut ting, decelerating, and pivoting.35 The original version of the M arx Activity Rating Scale (M arx) evaluates activity
Subject Characteristics G ro u p W ith A rtic u la r C a rtila g e D efec ts M ea n ± SD
Sex (male:female) Age (y) Height (m) Weight (kg) Body-mass index (kg/m2) Marx score before injury3 Marx score at time of testing6,3 Tegner score before injury3 Tegner score at time of testing3
6:5 30.9 ± 5.4 1.76 ± .1 0 80.9 ± 15.7 26.0 ± 3.6 8.6 ± 5.5 3.1 ± 4 .4 7.4 ± 1.6 3.8 ± 2.3
R ang e —
21—41 1.57-1.91 57.6-118.9 21.6-35.5 0-16 0-12 5-10 1-9
C o n tro l G ro u p M ea n ± SD
Range
5:5 28.5 ± 6.9 1.75 ± .0 7 77.4 ± 6.9 25.4 ± 1.9
21-44 1.63-1.84 62.4-85.9 22.2-28.0
—
—
—
8.7 ± 5.0 — 6.0 ± 2.3
0-1 2 — 2-9
a Not different from the control group’s scores at time of testing (P > .05). h Data not collected for first 2 ACD subjects.c Significantly different between groups (P < .05).
Strength and Biomechanics in Individuals with ACDs
Table 2
261
Defect Information T im e s in c e In vo lved
s y m p to m
L es io n
P revio u s
P revio u s
L es io n lo c a tio n
lo c a tio n
ip s ila tera l
c o n tra la te ral
(M R I s ize )
(P D B s ize )
in ju rv /s u rq e rv
in ju ry /s u rq e ry
Tro (0.6 cm), Pat (NM) Tro (NM)
Tro (2.0 x 1.4 cm). Pat (NM) No surgical debridement Tro (2.0 x 2.0 cm). LFC (NM). MFC (NM), Pat (1.0 X 1.0 cm) Tro (3.2 X 1.2 cm)
MFC grade II chondromalacia
Not available
Meniscus tear
Osteochondral allograft Microfracture
Meniscectomy
None ACI
S u b je c t
s id e
o n s e t (m o )3
l
Left
24
2
Right
2.5
3
Left
168
Tro (0.5 cm), LFC (0.9 cm), MFC (NM), Pat (0.3 cm)
4
Right
13
Tro (0.5 cm)
5
Right
9
6 7
Right Right
13 6
8
Left
3
Tro (1.5 X 1.4 cm), Tro (0.9 x 0.6 cm) MFC (2.5 X 1.6 cm) Tro (1.6 x 1.3 cm). Pat (NM) Tro (0.4 cm), MFC (NM), LFC (NM)
9 10
Right Left
3 9
II
Left
8
MFC (2.4 x 1.3 cm) Tro (3 X 3 cm), Pat (NM) Tro (2.4 X 2.2 cm). MFC (1.6 X 1.2 cm), LFC (1.0 X 1.0 cm) LFC (1.5 x 0.6 cm) LFC (2.0 X 2.5 cm) MFC (2.9 X 0.8 cm) No surgical debridement MFC (0.3 X 0.5 MFC (0.6 X 0.8 cm), cm), MFC (NM) MFC (0.6 X 0.8 cm)
S u rq ic a l p lan
ACI None
ACLR, chondroplasty
Meniscectomy
Microfracture, deep-vein thrombosis
Tibial fracture
ACI
ACLR. deepvein thrombosis
None
Meniscectomy
None None Planning for ACI, scheduling at time of publication
Abbreviations: ACI, autologous chondrocyte implantation; ACLR, anterior cruciate ligament reconstruction; LFC, lateral femoral condyle; MFC, medial femoral condyle; NM, no measurement; Pat, patella; PDB, postdebridement; Tro, trochlea. a Patient-reported.
level during “healthiest and most active state in the past year,” which was not reflective of the current activity levels of our subjects. After the first 2 subjects, we added a second Marx scale, replacing in the past year with cur rently. For this reason, we only have data for the Marx scale at the time of data collection for 9 subjects with ACD. The Tegner Activity Scale (Tegner) describes the highest level of activity the subject performed before and after knee injury. The score ranges from 0 (sick leave or disability because of knee problems) to 10 (competitive sports—soccer, football, rugby—national elite).36
Procedures After informed consent was obtained, data collection consisted of quadriceps femoris strength testing and 3-dimensional motion analysis.
Q uadriceps Fem oris Strength Testing Quadriceps femoris strength was quantified and opera tionally defined as the peak knee-extension torque during a maximal volitional isometric contraction on an iso kinetic dynamometer (Biodex System 3, Biodex Medical Systems, Shirley, NY) normalized by body mass (Nm/ kg).32-37 The same strength-testing protocol was followed for all participants for comparison of results. Participants
were seated in approximately 90° of hip flexion and 60° of knee flexion and the knee-joint line aligned with the axis of rotation of the dynamometer. The thigh of the tested limb and trunk were secured to minimize extraneous motion. After submaximal practice to ensure that the task was understood, the individuals completed 3 maximal volitional isometric contractions for 5 seconds with 15 seconds rest between trials. Maximal practice was not completed to minimize muscle fatigue before testing. For subjects with ACD, the contralateral limb was tested first to ensure that they were fully aware of the testing demands before the introduction of potential pain on the involved limb. Furthermore, in the clinic it is customary to test the uninvolved limb before the involved limb. For healthy controls, limb test order was randomized. After strength testing, there was a 10- to 15-minute time frame to prepare the subject and the system for motion capture, during which the subject had time to recover. Isometric strength testing was chosen instead of isokinetic testing to minimize potential friction across the defect and pain with test. The angle of testing 60° of flexion was chosen to maximize quadriceps torque capac ity (muscle length) while considering patellofemoral contact stress and patellofemoral-joint reaction force.38 In addition, Ploutz-Snyder et al32 found that 60° isometric testing was most correlated to functional performance on
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activities of daily living, including stair ascent, compared with 4 other knee-flexion angles ranging from 24° to 96°.
Three-Dimensional Motion Analysis Knee biomechanics during stair ascent were quantified by tracking retroreflective markers secured to the pelvis, thigh, shank, and foot39 (Figure 1) using a 10-camera 3-dimensional motion-analysis system (Vicon Nexus, Oxford, UK; sampled at 150 Hz). Markers at anatomical landmarks were used to determine the joint centers, and markers on the anterior surface of the thigh and shank were used for tracking. Ground-reactionforce data were simultaneously sampled (1500 Hz) on a custom-built instrumented staircase. To instrument the staircase (Figure 2), 2 wooden steps were individually secured to 2 independent force plates (Bertec Corp, Columbus, OH). An uninstrumented platform constituted a third step to create a 3-step staircase with a slope of 39° (18.5-cm rise, 26-cm tread). E q u ip m e n t.
Subjects were positioned 60 cm in front of the first step, allowing for 1 forward step on level ground before initiating stair ascent. Participants ascended the stairs at a self-selected pace. Within a trial, 3 distinct stance phases were collected on independent force plates: the step before ascent, the first step of ascent, and the second step of ascent. The second step of ascent was used for this study, as it is the only instrumented step in which the limb enters stance from a full stair-ascent swing phase (from floor to step 2). For step 1, the limb enters stance with a swing phase from the floor, which is
only half of a full stair-ascent swing phase. To collect 5 stance phases on step 2 for each leg, 10 total stair-ascent trials were collected, 5 initiated by each leg. Visual3D software (C-Motion, Inc, Germantown, MD) was used to calculate the joint centers from the anatomical markers and kinematic (peak knee-flexion angle), kinetic (peak internal knee-extension moment), and vGRF (peak) variables of interest during test-limb stance phase on the second instrumented step. Marker trajectories and force-plate data were filtered with a low-pass Butterworth filter at 6 Hz. The force-structure mechanism through Visual3D was used to translate the forces measured by the force plate to the surface of action on the step. Joint moments were calculated using inverse dynamics and normalized by the product of body mass (kg) and body height (m). Peak vGRFs were normalized by body weight (N) to give a percentage of body weight (%BW).40-41 For each variable of interest, the mean peak value of the collected trials for the involved and contra lateral limbs was calculated and used for further analysis. D a ta M a n a g e m e n t .
T esting P r o c e d u re .
Figure 1
Statistical Analyses Statistical analyses were conducted with IBM SPSS Sta tistics 19 (SPSS, Chicago, IL). Group means and standard deviations were calculated for participant characteristics and each variable of interest. Independent 2-sample t tests were used to compare group characteristics. Paired t tests were used to evaluate differences between the involved and contralateral limbs for individuals with ACDs. Independent 2-sample t tests evaluated the dif-
— Marker set: From data collection to postprocessing model.
Strength and Biomechanics in Individuals with ACDs
263
Figure 2 — Instrumented stair case. The floor in front of the stair case, step 1, and step 2 are instrumented with independent force plates. Step 2 was analyzed for this study.
ferences between individuals with ACD and healthy controls. For the control group, a limb was randomly chosen to calculate group means. A modified Bonferroni correction (Holm method) was used to correct for multiple comparisons of biomechanical variables during stair ascent. In individuals with ACDs, the relationships between nvolved quadriceps strength and biomechanics were evaluated with Pearson product-moment correla tions. The a level was set at .05. The Shapiro-Wilk test for normality was performed for all variables and revealed that the normalized quad riceps strength was not normally distributed. A natural log transformation established normality in peak torque values, and the transformed data were used for the parametric statistical tests. The Levene test for normal ity of variance was performed for the independent t tests. Between groups, equal variance was assumed for group characteristics but not assumed for biomechanical variables.
Results The ACD and control groups were similar for all par ticipant characteristics except activity score at time of testing (Table 1). Individuals with ACD had lower levels of activity and participation in sports at the time of testing compared with controls; however, it should be noted that subject-reported activity levels before injury were not different from the control group. In the ACD group, 5 individuals had single lesions and 6 had multiple lesions (Table 2). The most common lesion site was the trochlea, followed by the patella, lateral femoral condyle, and medial femoral condyle. No participants had ACDs on the lateral or medial tibial plateaus. Two individuals had no surgical debridement; 9 participants received an arthroscopic debridement with postdebridement defect measurement. Patient-reported onset of symptoms ranged from 3 to 168 months (median = 9 mo) before data collection.
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Thoma et al
Quadriceps femoris strength deficits were evident in the involved limbs of individuals with ACDs (Table 3, Figure 3). During stair ascent, peak knee-flexion angle and peak knee-extension moment were significantly lower in the involved limb compared with the contralat eral limb; however, only the peak knee-extension moment was significantly lower compared with controls (Table 3). Within the ACD group, 2 significant relationships emerged between the involved limb quadriceps strength and knee biomechanics of either limb (Figure 4, Table 4).
addition, we observed a significant association between involved-limb quadriceps femoris strength and contra lateral vGRF. Quadriceps Femoris Strength i
*
D iscussion The purpose of this study was to evaluate quadriceps femoris strength and sagittal-plane knee biomechan ics during stair ascent in individuals with ACDs of the knee and to evaluate for possible relationships between strength and biomechanics. Our hypotheses were partially confirmed. The involved limb demonstrated quadriceps femoris strength deficits and lower knee-flexion angle and internal-extension moment compared with the contralat eral limb; however, the knee-flexion angle was similar to that of healthy controls. vGRFs on the involved limb were not different than the contralateral limb or healthy controls. Regarding associations between variables of interest in individuals with ACD, our hypothesis was partially supported as involved-limb quadriceps femo ris strength and involved-limb internal knee-extension moment during stair ascent were positively associated. In
0
Involved
Uninvolved
F ig u re 3 — Comparison of quadriceps strength between the involved and uninvolved limbs. *P = .002
Table 3 Comparison of Strength and Biomechanics Between the Involved and Contralateral Limbs, Mean ± SD Variable
Involved
Contralateral
Control
Peak quadriceps strength (Nm/kg)
1.65 ±.70
Peak knee-flexion angle (°) Peak knee-extension moment (N/kg) Peak vertical ground-reaction force (%BW)
62.4 ± 4.2 0.37 ± .26 109.9 ±5.2
2.29 ± ,54t 64.6 ± 2.3*
2.62 ±.5 I t 65.2 ± 6.7 0.65 ± ,12f 115.2 ± 12.9
0.68 ± . 17f 116.9 ± 9.1
*P < .05 compared with the involved limb. fP < .01 compared with the involved limb. Significant according to P from modified (Holm) Bonferroni correction for multiple comparisons.
Table 4
Correlations of Biomechanics Variables With Quadriceps Femoris (QF) Strength Involved QF Strength
Contralateral QF strength
Pearson correlation
P
Pearson correlation
P
Variable
Side
Peak knee-flexion angle
Involved
-.187
.581
.106
.755
Uninvolved
-.185
.586
.276
.411
.847
.001*
.458
.156
-.069
.840
.313
.349
.374
.257
.152
.656
-.635
.036*
-.284
.397
Peak knee-extension moment
Involved Uninvolved
Peak vertical ground-reaction force
Involved Uninvolved
*P
< .05.
Strength and Biomechanics in Individuals with ACDs
265
Figure 4 — (a) Correlation between quadriceps strength and peak internal knee-extension moment on the involved side, cases labeled by subject number, P = .001. (b) Correlation between involved-limb quadriceps strength and uninvolved-limb peak vertical ground-reaction force (vGRF), P = .036.
Quadriceps femoris weakness is commonly associ ated with acute and chronic knee pathologies,20’27“2942_45 and as hypothesized the involved limb demonstrated significant quadriceps femoris strength deficits compared with the contralateral side and healthy controls in the current study. To our knowledge, this is only the second
report of quadriceps femoris strength in individuals with ACDs. In a population similar to our sample, Van Assche et al8 reported quadriceps femoris strength deficits with isokinetic testing at 607s in individuals with ACD before microfracture or characterized chondrocyte implantation. Over 50% of their sample demonstrated >20% quadriceps
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T h o m a et al
femoris deficit compared with the contralateral limb. Although the current study quantified strength with isometric assessment instead of isokinetic assessment for reasons outlined in the Methods section, the strength deficits in our study were consistent with findings from Van Assche et al.8 Over 70% of the participants in our sample also dem onstrated >20% quadriceps femoris strength deficit, with a high variability of quadriceps femoris strength on the involved limb. The weakest third of our participants demonstrated 45% to 56% quadriceps femoris strength deficits compared with the contralateral limb, whereas the strongest third demonstrated less than a 10% deficit on the involved limb. Given the large vari ability in quadriceps femoris deficits in individuals with ACDs, future work should consider evaluating the extent to which preoperative quadriceps femoris strength can predict postoperative function after cartilage restoration, as this has been shown in individuals receiving an anterior cruciate ligament reconstruction.46 Quadriceps femoris weakness may be attributable to various factors including fear, pain, arthrogenic muscle inhibition, and atrophy.45’47-49 Most (9 of 11) participants reported pain during data collection, which may have inhibited their quadriceps femoris strength during testing and confounded the results. Due to variable defect loca tion, the fixed angle of strength testing we used potentially influenced pain response differently among participants. Though the quadriceps femoris strength values reported in this study may not reflect the maximal capacity of the muscle, we believe this voluntary measure of quadriceps femoris strength remains relevant for several reasons: This measure is clinically applicable, as pain may also be present in the clinic during strength testing; pain may be present during stair climbing, thus inhibiting functional quadriceps femoris strength; and recent work demonstrated that pain does not affect the relationship between isom etric quadriceps strength and function (performance-based or self-reported) in individuals with knee osteoarthritis.37 Due to small sample size, it was beyond the scope of this study to elucidate the contribu tors to decreased quadriceps femoris strength; however, this remains a goal of our ongoing work. Nonetheless, the substantial quadriceps femoris strength deficits observed in this population are concern ing, as adequate lower extremity strength is necessary for normal limb function, especially during dynamic weight bearing activities. Quadriceps femoris weakness is associ ated with impaired ability to dissipate loads and absorb shock, with resultant alterations in loading rates, contact forces, and load distribution on the articular surfaces.20 Thus, quadriceps femoris weakness in a population with compromised cartilage and altered cartilage loading may promote lesion progression and have devastating effects on future joint health. This is the first study to report knee biomechanics during stair ascent in individuals with ACD. O f particular interest, high variability existed in peak knee internalextension m om ents despite consistent knee-flexion angles. Peak internal knee-extension moment during
stair ascent was lower on the involved side compared with the uninvolved side and compared with the control group. Lower internal knee-extension moments on the involved limb have been reported in other studies evaluat ing stair-ascent biomechanics in populations with knee pathology.41'50"52 The internal knee-extension moment can be con ceptualized as the demand on the quadriceps femoris muscle to maintain knee extension against gravity and, when ascending stairs, reflects the muscular demand used to advance up the stairs. The decreased moments we observed in the involved limb may reflect a strategy to decrease the demand placed on the quadriceps femoris in light of the concurrent quadriceps femoris strength deficits. This notion is strengthened by the strong and significant direct relationship between quadriceps femo ris strength and peak internal knee-extension moment during stair ascent on the involved side. In our sample of individuals with ACDs, 72% of the variance in peak knee internal knee-extension moment could be explained by the peak quadriceps femoris strength on the involved side. Electromyography data on quadriceps femoris activ ity would be useful in further interpreting these findings but were not evaluated as part of this study. In addition, evaluation of hip, ankle, and trunk kinematics and kinetics during stair ascent may reveal the compensatory strate gies employed to ascend the stairs with such divergent knee moments in light of small differences in knee angle. Despite the lack of side-to-side differences in peak vGRF during stance in this study, there was a significant inverse relationship between involved quadriceps femoris strength and contralateral vGRF. For all subjects, the peak vGRF on the contralateral side occurred during the second half of stance, which corresponds with the beginning of stance on the involved limb on the following step. We speculate that the significant inverse correlation between contralateral vGRF and involved quadriceps femoris strength reflects an increased compensatory effort by the contralateral limb in individuals with weak knee extensors. Our results indicate that previously suggested quad riceps femoris strength thresholds to predict ability to successfully complete functional tasks such as rising from a chair, walking, and stair climbing through performancebased assessments32 may be inappropriate for younger subjects with ACDs. Ploutz-Snyder et al32 evaluated the quadriceps femoris strength necessary to “successfully” climb stairs, defined as the ability to reciprocally ascend and descend 1 flight of stairs without a handrail. In our study, all subjects reciprocally ascended the instrumented staircase without handrails and without concern for safety. Although the task would have been considered function ally “successful” by Ploutz-Snyder et al,32 based on their proposed quadriceps femoris strength threshold, only 2 participants in our study would have been categorized as having sufficient quadriceps femoris strength to ascend stairs without difficulty. The population of interest in their study (community-dwelling adults over 50 y old) was not representative of our sample, which may account
Strength and Biomechanics in Individuals with ACDs
for the differences. Furthermore, despite the ability of our participants to ascend without a handrail, we observed profound alterations in movement strategies (ie, reduced peak internal knee-extension moments). This highlights a need to consider clinically evaluating stair-climbing movement quality beyond stepping-pattern strategies and upper-extremity assistance to identify compensatory movement patterns in individuals with ACDs. In addition, elucidating the role of compensatory patterns in promot ing or limiting long-term function will be essential in guiding rehabilitation interventions in this population. The findings of this study indicate the potential for rehabilitation interventions to focus on quadriceps femoris strength and activation during dynamic activi ties. However, this should be considered on an individual basis. While decreased quadriceps femoris strength may alter load distribution within the joint in a manner that could propagate further joint damage,20 the long-term consequences of normal joint loading and normal quad riceps femoris strength on progression of symptoms and defects of various sizes53 54 and locations55 is unknown. Local joint mechanical factors may mediate the potential benefits of quadriceps femoris strengthening.56 For exam ple, for individuals with knee osteoarthritis, quadriceps femoris strengthening resulted in decreased symptoms for individuals with normal knee alignment but not for those with m alalignm ent.56 It is also possible that persistent function with weak quadriceps alters movement patterns in the contralateral limb, with potentially detrimental impact on future joint health. Further understanding of the riskrbenefit ratio for quadriceps femoris strengthen ing in this population is needed, before interventions to maximize function and minimize defect progression can be designed and tested. There were several limitations to this study. (1) Limb testing was not randomized, which is a potential source of bias. For strength testing, the rationale underlying testing the contralateral limb first is detailed in the Methods sec tion. The starting limb for stair climbing was not defined or randomized, as stair climbing is a bipedal task. Despite the rationale that supports the task order that was used, the lack of randomization remains a potential source of bias. (2) The population was heterogeneous, with variable defect location, number of defects per person, mechanism of injury (traumatic vs gradual), time since symptom onset, symptom severity, and previous injury. We anticipate that these factors uniquely contribute to pain, movement patterns, function, and possibly quad riceps femoris strength. Although it would be ideal to have homogeneous samples with respect to these factors, ACDs do not commonly occur in isolation. Widuchowski et al3 found that 70% of cartilage lesions found on knee arthroscopy were focal and concomitant with another injury, most commonly meniscus or ligamentous tears.3 For similar reasons, it is challenging to define the time since injury/symptom onset for individuals with a prior history of injury (ie, anterior cruciate ligament recon struction 10 y prior) or individuals who report insidious or gradual symptom onset. (3) The homogeneity of the
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sample demographics may also be considered a limita tion, as all subjects were young (3,0.CO;2-9 Slemenda C, Brandt KD, Heilman DK. et al. Quadriceps weakness and osteoarthritis of the knee. Ann Intern Med. 1997; 127(2):97—104. PubMed doi: 10.7326/0003-4819-1272-199707150-00001 Oiestad BE, Holm I, Gunderson R. Myklebust G, Risberg MA. Quadriceps muscle weakness after anterior cruciate ligament reconstruction: a risk factor for knee osteoarthri tis? Arthritis Care Res. 2010;62(12):1706-1714. PubMed doi: 10.1002/acr.20299 Palmieri-Smith RM. Thomas AC. Karvonen-Gutierrez C, Sowers MF. Isometric quadriceps strength in women with mild, moderate, and severe knee osteoarthritis. Am J Phys Med Rehabil. 2010;89(7):541-548. PubMed doi: 10.1097/ PH M ,0b013e3181 ddd5c.3 Lewek MD. Rudolph KS, Snyder-M ackler L. Q uadri ceps femoris muscle weakness and activation failure in patients with symptomatic knee osteoarthritis. J Orthop Res. 2004:22(0:110-115. PubMed doi: 10.1016/S07360266(03)00154-2 Engelhart L, Nelson L, Lewis S, et al. Validation of the Knee Injury and Osteoarthritis Outcome Score subscales for patients with articular cartilage lesions of the knee. Am J Sports Med. 2012;40(10):2264-2272. PubM ed doi: 10.1177/0363546512457646 Andriacchi TP, Andersson GB, Fermier RW. Stem D, Galante JO. A study of lower-limb mechanics during stair-climbing. J Bone Joint Surg Am. 1980;62(5):749-757. PubMed Ploutz-Snyder LL, Manini T, Ploutz-Snyder RJ, Wolf DA. Functionally relevant thresholds of quadriceps femoris
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45. Hart JM, Pietrosimone B, Hertel J, Ingersoll CD. Quadriceps activation following knee injuries: a systematic review. JAthl Train. 2010:45(1 ):87-97. PubMed doi: 10.4085/1062-605045.1.87 46. Eitzen I, Holm I, Risberg MA. Preoperative quadriceps strength is a significant predictor of knee function two years after anterior cruciate ligament reconstruction. Br J Sports Med. 2009;43(5):371-376. PubMed doi:10.1136/ bjsm.2008.057059 47. Pietrosimone BG, Hertel J, Ingersoll CD, Hart JM, Saliba S A. Voluntary quadriceps activation deficits in patients with tibio femoral osteoarthritis: a meta-analysis. PMR. 2011 ;3(2): 153162, quiz 162. PubMed doi:10.1016/j.pmrj.2010.07.485 48. van W ilgen CP, A kkerm an L. W ieringa J, D ijk stra PU. M uscle strength in patients with chronic pain. C lin R e h a b il. 2 0 0 3 ; 1 7 ( 8 ) :8 8 5 - 8 8 9 . P u b M e d doi: 10.1191/0269215503cr693oa 49. Brasileiro JS, Pinto OM, Avila MA, Salvini TF. Functional and morphological changes in the quadriceps muscle induced by eccentric training after ACL reconstruction. Rev Bras Fisioter. 2011; 15(4):284-290. PubMed doi:10.1590/ S1413-35552011005000012 50. Salsich GB, Brechter JH, Powers CM. Lower extrem ity kinetics during stair ambulation in patients with and without patellofemoral pain. Clin Biomech (Bristol, Avon). 2 0 0 1 ;1 6 (1 0 ):9 0 6 -9 1 2 . PubM ed d oi:10.1016/S 02680033(01)00085-7 51. Crossley KM, Cowan SM, Bennell KL, McConnell J. Knee flexion during stair ambulation is altered in individuals with patellofemoral pain. J Orthop Res. 2004;22(2):267-274. PubMed doi: I0.1016/j.orthres.2003.08.014 52. Mandeville D, Ostemig LR, Chou LS. The effect of total knee replacement on dynamic support of the body during walking and stair ascent. Clin Biomech (Bristol, Avon). 2 0 0 7 ;2 2(7):787-794. PubM ed doi: 10.1016/j.clinbiomech.2007.04.002 53. DongY-F, Hu G-H, Zhang, L-L, Hu,Y, Dong,Y-H, Xu, Q-R. Accurate 3D reconstruction of subject-specific knee finite element model to simulate the articular cartilage defects. J Shanghai Jiaotong. 2011; 16(5):620—627. doi: 10.1007/ s 12204-011-1199-z 54. Flanigan DC, Harris JD, Brockmeier PM, Lathrop RL, Siston RA. The effects of defect size, orientation, and location on subchondral bone contact in oval-shaped experi mental articular cartilage defects in a bovine knee model. Knee Surg Sports TraumatolArthrosc. 2014;22(1): 174-180. PubMed doi: 10.1007/s00167-012-2342-6 55. de Windt TS, Bekkers JE, Creemers LB, Dhert WJ, Saris DB, Patient profiling in cartilage regeneration: prognostic factors determ ining success o f treatm ent for cartilage defects. Am J Sports Med. 2009;37(Suppl 1):58S-62S. PubMed doi: 10.1177/0363546509349765 56. Lim BW, Hinman RS, Wrigley TV, Sharma L, Bennell KL. Does knee malalignment mediate the effects of quadriceps strengthening on knee adduction moment, pain, and func tion in medial knee osteoarthritis?: a randomized controlled trial. Arthritis Rheum. 2008;59(7):943—951. PubM ed doi: 10.1002/art.23823
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Quadriceps Femoris Strength and Sagittal-Plane Knee Biomechanics During Stair Ascent in Individuals With Articular Cartilage Defects in the Knee Louise M.Thoma, David C. Flanigan, Ajit M. Chaudhari, Robert A. Siston, Thomas M. Best, and Laura C. Schmitt Context: Few objective data are available regarding strength and m ovem ent patterns in individuals with articu lar cartilage defects (ACDs) o f the knee. Objectives: To test the follow ing hypotheses: (1) The involved lim b o f individuals w ith ACDs would dem onstrate low er peak knee-flexion angle, peak internal knee-extension m om ent, and peak vertical ground-reaction force (vG R F) than the contralateral lim b and healthy controls. (2) On the involved lim b o f individuals w ith ACDs, quadriceps fem oris strength would positively correlate with peak knee-flexion angle, peak internal knee-extension m om ent, and peak vGRF. Design: Cross-sectional. Setting: Biom echanics research laboratory. Participants: 11 individuals with ACDs in the knee who were eligible for surgical cartilage restoration and 10 healthy controls. Methods: Q uadriceps fem oris strength was quantified as peak isom etric knee-extension torque via an isokinetic dynam om eter. Sagittal-plane knee kinem atics and kinetics were m easured during the stance phase o f stair ascent with 3-dim ensional motion analysis. Main Outcome Measures: Q uadriceps strength and knee biom echanics during stair ascent were com pared betw een the involved and contralateral lim bs o f participants with ACD (paired t tests) and with a control group (independent-sam ples t tests). Pearson correlations evaluated relationships betw een strength and stair-ascent biom echanics. Results: L ow er quadriceps strength and peak internal knee-extension m om ents w ere observed in the involved limb than in the contralateral lim b ( P < .01) and the control group (P < .01). F or the involved lim b o f the ACD group, quadriceps fem oris strength was strongly correlated ( r = .847) with involved-lim b peak internal knee-extension m om ent and inversely correlated ( r = -.6 3 5 ) w ith contralateral peak vGRF. Conclusions: Individuals with ACDs dem onstrated deficits in quadriceps fem oris strength with associated alterations in m ovem ent patterns during stair ascent. The results o f this study are not com prehensive; further research is needed to understand the physiological characteristics, activity perform ance, and m ovem ent quality in this population.
Keywords: m uscle strength, stair clim bing, focal chondral defects A rticular cartilage defects (ACDs) in the knee are focal lesions o f the articular cartilage o f traum atic or insidious onset surrounded by healthy articular cartilage and subchondral bone. R etrospective and prospective studies report a 19% to 40% l~3 prevalence o f focal ACDs found during knee arthroscopy. In contrast to m ore dif fu se cartilage pathology such as o steoarthritis, knee A CD s m ost com m only affect young (40 kg/m 12, history o f back, hip or ankle pathology or surgery, history o f neurologic injury or pathology, or history o f inflam m atory arthritis. Ten indi viduals w ithout history o f knee or lower-extrem ity injury and o f sim ilar age and activity level were recruited from the com m unity and participated in the study for com parison with the ACD group. This study was approved by the institutional review board, and inform ed consent was obtained from all participants. In addition to age, height, weight, and BM I, M arx35 and Tegner36 scores were collected to quantify level o f activity. The M arx A ctivity Rating Scale was developed to characterize subject level o f activity in running, cut ting, decelerating, and pivoting.35 The original version of the M arx Activity Rating Scale (M arx) evaluates activity
Subject Characteristics G ro u p W ith A rtic u la r C a rtila g e D efec ts M ea n ± SD
Sex (male:female) Age (y) Height (m) Weight (kg) Body-mass index (kg/m2) Marx score before injury3 Marx score at time of testing6,3 Tegner score before injury3 Tegner score at time of testing3
6:5 30.9 ± 5.4 1.76 ± .1 0 80.9 ± 15.7 26.0 ± 3.6 8.6 ± 5.5 3.1 ± 4 .4 7.4 ± 1.6 3.8 ± 2.3
R ang e —
21—41 1.57-1.91 57.6-118.9 21.6-35.5 0-16 0-12 5-10 1-9
C o n tro l G ro u p M ea n ± SD
Range
5:5 28.5 ± 6.9 1.75 ± .0 7 77.4 ± 6.9 25.4 ± 1.9
21-44 1.63-1.84 62.4-85.9 22.2-28.0
—
—
—
8.7 ± 5.0 — 6.0 ± 2.3
0-1 2 — 2-9
a Not different from the control group’s scores at time of testing (P > .05). h Data not collected for first 2 ACD subjects.c Significantly different between groups (P < .05).
Strength and Biomechanics in Individuals with ACDs
Table 2
261
Defect Information T im e s in c e In vo lved
s y m p to m
L es io n
P revio u s
P revio u s
L es io n lo c a tio n
lo c a tio n
ip s ila tera l
c o n tra la te ral
(M R I s ize )
(P D B s ize )
in ju rv /s u rq e rv
in ju ry /s u rq e ry
Tro (0.6 cm), Pat (NM) Tro (NM)
Tro (2.0 x 1.4 cm). Pat (NM) No surgical debridement Tro (2.0 x 2.0 cm). LFC (NM). MFC (NM), Pat (1.0 X 1.0 cm) Tro (3.2 X 1.2 cm)
MFC grade II chondromalacia
Not available
Meniscus tear
Osteochondral allograft Microfracture
Meniscectomy
None ACI
S u b je c t
s id e
o n s e t (m o )3
l
Left
24
2
Right
2.5
3
Left
168
Tro (0.5 cm), LFC (0.9 cm), MFC (NM), Pat (0.3 cm)
4
Right
13
Tro (0.5 cm)
5
Right
9
6 7
Right Right
13 6
8
Left
3
Tro (1.5 X 1.4 cm), Tro (0.9 x 0.6 cm) MFC (2.5 X 1.6 cm) Tro (1.6 x 1.3 cm). Pat (NM) Tro (0.4 cm), MFC (NM), LFC (NM)
9 10
Right Left
3 9
II
Left
8
MFC (2.4 x 1.3 cm) Tro (3 X 3 cm), Pat (NM) Tro (2.4 X 2.2 cm). MFC (1.6 X 1.2 cm), LFC (1.0 X 1.0 cm) LFC (1.5 x 0.6 cm) LFC (2.0 X 2.5 cm) MFC (2.9 X 0.8 cm) No surgical debridement MFC (0.3 X 0.5 MFC (0.6 X 0.8 cm), cm), MFC (NM) MFC (0.6 X 0.8 cm)
S u rq ic a l p lan
ACI None
ACLR, chondroplasty
Meniscectomy
Microfracture, deep-vein thrombosis
Tibial fracture
ACI
ACLR. deepvein thrombosis
None
Meniscectomy
None None Planning for ACI, scheduling at time of publication
Abbreviations: ACI, autologous chondrocyte implantation; ACLR, anterior cruciate ligament reconstruction; LFC, lateral femoral condyle; MFC, medial femoral condyle; NM, no measurement; Pat, patella; PDB, postdebridement; Tro, trochlea. a Patient-reported.
level during “healthiest and most active state in the past year,” which was not reflective of the current activity levels of our subjects. After the first 2 subjects, we added a second Marx scale, replacing in the past year with cur rently. For this reason, we only have data for the Marx scale at the time of data collection for 9 subjects with ACD. The Tegner Activity Scale (Tegner) describes the highest level of activity the subject performed before and after knee injury. The score ranges from 0 (sick leave or disability because of knee problems) to 10 (competitive sports—soccer, football, rugby—national elite).36
Procedures After informed consent was obtained, data collection consisted of quadriceps femoris strength testing and 3-dimensional motion analysis.
Q uadriceps Fem oris Strength Testing Quadriceps femoris strength was quantified and opera tionally defined as the peak knee-extension torque during a maximal volitional isometric contraction on an iso kinetic dynamometer (Biodex System 3, Biodex Medical Systems, Shirley, NY) normalized by body mass (Nm/ kg).32-37 The same strength-testing protocol was followed for all participants for comparison of results. Participants
were seated in approximately 90° of hip flexion and 60° of knee flexion and the knee-joint line aligned with the axis of rotation of the dynamometer. The thigh of the tested limb and trunk were secured to minimize extraneous motion. After submaximal practice to ensure that the task was understood, the individuals completed 3 maximal volitional isometric contractions for 5 seconds with 15 seconds rest between trials. Maximal practice was not completed to minimize muscle fatigue before testing. For subjects with ACD, the contralateral limb was tested first to ensure that they were fully aware of the testing demands before the introduction of potential pain on the involved limb. Furthermore, in the clinic it is customary to test the uninvolved limb before the involved limb. For healthy controls, limb test order was randomized. After strength testing, there was a 10- to 15-minute time frame to prepare the subject and the system for motion capture, during which the subject had time to recover. Isometric strength testing was chosen instead of isokinetic testing to minimize potential friction across the defect and pain with test. The angle of testing 60° of flexion was chosen to maximize quadriceps torque capac ity (muscle length) while considering patellofemoral contact stress and patellofemoral-joint reaction force.38 In addition, Ploutz-Snyder et al32 found that 60° isometric testing was most correlated to functional performance on
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activities of daily living, including stair ascent, compared with 4 other knee-flexion angles ranging from 24° to 96°.
Three-Dimensional Motion Analysis Knee biomechanics during stair ascent were quantified by tracking retroreflective markers secured to the pelvis, thigh, shank, and foot39 (Figure 1) using a 10-camera 3-dimensional motion-analysis system (Vicon Nexus, Oxford, UK; sampled at 150 Hz). Markers at anatomical landmarks were used to determine the joint centers, and markers on the anterior surface of the thigh and shank were used for tracking. Ground-reactionforce data were simultaneously sampled (1500 Hz) on a custom-built instrumented staircase. To instrument the staircase (Figure 2), 2 wooden steps were individually secured to 2 independent force plates (Bertec Corp, Columbus, OH). An uninstrumented platform constituted a third step to create a 3-step staircase with a slope of 39° (18.5-cm rise, 26-cm tread). E q u ip m e n t.
Subjects were positioned 60 cm in front of the first step, allowing for 1 forward step on level ground before initiating stair ascent. Participants ascended the stairs at a self-selected pace. Within a trial, 3 distinct stance phases were collected on independent force plates: the step before ascent, the first step of ascent, and the second step of ascent. The second step of ascent was used for this study, as it is the only instrumented step in which the limb enters stance from a full stair-ascent swing phase (from floor to step 2). For step 1, the limb enters stance with a swing phase from the floor, which is
only half of a full stair-ascent swing phase. To collect 5 stance phases on step 2 for each leg, 10 total stair-ascent trials were collected, 5 initiated by each leg. Visual3D software (C-Motion, Inc, Germantown, MD) was used to calculate the joint centers from the anatomical markers and kinematic (peak knee-flexion angle), kinetic (peak internal knee-extension moment), and vGRF (peak) variables of interest during test-limb stance phase on the second instrumented step. Marker trajectories and force-plate data were filtered with a low-pass Butterworth filter at 6 Hz. The force-structure mechanism through Visual3D was used to translate the forces measured by the force plate to the surface of action on the step. Joint moments were calculated using inverse dynamics and normalized by the product of body mass (kg) and body height (m). Peak vGRFs were normalized by body weight (N) to give a percentage of body weight (%BW).40-41 For each variable of interest, the mean peak value of the collected trials for the involved and contra lateral limbs was calculated and used for further analysis. D a ta M a n a g e m e n t .
T esting P r o c e d u re .
Figure 1
Statistical Analyses Statistical analyses were conducted with IBM SPSS Sta tistics 19 (SPSS, Chicago, IL). Group means and standard deviations were calculated for participant characteristics and each variable of interest. Independent 2-sample t tests were used to compare group characteristics. Paired t tests were used to evaluate differences between the involved and contralateral limbs for individuals with ACDs. Independent 2-sample t tests evaluated the dif-
— Marker set: From data collection to postprocessing model.
Strength and Biomechanics in Individuals with ACDs
263
Figure 2 — Instrumented stair case. The floor in front of the stair case, step 1, and step 2 are instrumented with independent force plates. Step 2 was analyzed for this study.
ferences between individuals with ACD and healthy controls. For the control group, a limb was randomly chosen to calculate group means. A modified Bonferroni correction (Holm method) was used to correct for multiple comparisons of biomechanical variables during stair ascent. In individuals with ACDs, the relationships between nvolved quadriceps strength and biomechanics were evaluated with Pearson product-moment correla tions. The a level was set at .05. The Shapiro-Wilk test for normality was performed for all variables and revealed that the normalized quad riceps strength was not normally distributed. A natural log transformation established normality in peak torque values, and the transformed data were used for the parametric statistical tests. The Levene test for normal ity of variance was performed for the independent t tests. Between groups, equal variance was assumed for group characteristics but not assumed for biomechanical variables.
Results The ACD and control groups were similar for all par ticipant characteristics except activity score at time of testing (Table 1). Individuals with ACD had lower levels of activity and participation in sports at the time of testing compared with controls; however, it should be noted that subject-reported activity levels before injury were not different from the control group. In the ACD group, 5 individuals had single lesions and 6 had multiple lesions (Table 2). The most common lesion site was the trochlea, followed by the patella, lateral femoral condyle, and medial femoral condyle. No participants had ACDs on the lateral or medial tibial plateaus. Two individuals had no surgical debridement; 9 participants received an arthroscopic debridement with postdebridement defect measurement. Patient-reported onset of symptoms ranged from 3 to 168 months (median = 9 mo) before data collection.
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Thoma et al
Quadriceps femoris strength deficits were evident in the involved limbs of individuals with ACDs (Table 3, Figure 3). During stair ascent, peak knee-flexion angle and peak knee-extension moment were significantly lower in the involved limb compared with the contralat eral limb; however, only the peak knee-extension moment was significantly lower compared with controls (Table 3). Within the ACD group, 2 significant relationships emerged between the involved limb quadriceps strength and knee biomechanics of either limb (Figure 4, Table 4).
addition, we observed a significant association between involved-limb quadriceps femoris strength and contra lateral vGRF. Quadriceps Femoris Strength i
*
D iscussion The purpose of this study was to evaluate quadriceps femoris strength and sagittal-plane knee biomechan ics during stair ascent in individuals with ACDs of the knee and to evaluate for possible relationships between strength and biomechanics. Our hypotheses were partially confirmed. The involved limb demonstrated quadriceps femoris strength deficits and lower knee-flexion angle and internal-extension moment compared with the contralat eral limb; however, the knee-flexion angle was similar to that of healthy controls. vGRFs on the involved limb were not different than the contralateral limb or healthy controls. Regarding associations between variables of interest in individuals with ACD, our hypothesis was partially supported as involved-limb quadriceps femo ris strength and involved-limb internal knee-extension moment during stair ascent were positively associated. In
0
Involved
Uninvolved
F ig u re 3 — Comparison of quadriceps strength between the involved and uninvolved limbs. *P = .002
Table 3 Comparison of Strength and Biomechanics Between the Involved and Contralateral Limbs, Mean ± SD Variable
Involved
Contralateral
Control
Peak quadriceps strength (Nm/kg)
1.65 ±.70
Peak knee-flexion angle (°) Peak knee-extension moment (N/kg) Peak vertical ground-reaction force (%BW)
62.4 ± 4.2 0.37 ± .26 109.9 ±5.2
2.29 ± ,54t 64.6 ± 2.3*
2.62 ±.5 I t 65.2 ± 6.7 0.65 ± ,12f 115.2 ± 12.9
0.68 ± . 17f 116.9 ± 9.1
*P < .05 compared with the involved limb. fP < .01 compared with the involved limb. Significant according to P from modified (Holm) Bonferroni correction for multiple comparisons.
Table 4
Correlations of Biomechanics Variables With Quadriceps Femoris (QF) Strength Involved QF Strength
Contralateral QF strength
Pearson correlation
P
Pearson correlation
P
Variable
Side
Peak knee-flexion angle
Involved
-.187
.581
.106
.755
Uninvolved
-.185
.586
.276
.411
.847
.001*
.458
.156
-.069
.840
.313
.349
.374
.257
.152
.656
-.635
.036*
-.284
.397
Peak knee-extension moment
Involved Uninvolved
Peak vertical ground-reaction force
Involved Uninvolved
*P
< .05.
Strength and Biomechanics in Individuals with ACDs
265
Figure 4 — (a) Correlation between quadriceps strength and peak internal knee-extension moment on the involved side, cases labeled by subject number, P = .001. (b) Correlation between involved-limb quadriceps strength and uninvolved-limb peak vertical ground-reaction force (vGRF), P = .036.
Quadriceps femoris weakness is commonly associ ated with acute and chronic knee pathologies,20’27“2942_45 and as hypothesized the involved limb demonstrated significant quadriceps femoris strength deficits compared with the contralateral side and healthy controls in the current study. To our knowledge, this is only the second
report of quadriceps femoris strength in individuals with ACDs. In a population similar to our sample, Van Assche et al8 reported quadriceps femoris strength deficits with isokinetic testing at 607s in individuals with ACD before microfracture or characterized chondrocyte implantation. Over 50% of their sample demonstrated >20% quadriceps
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femoris deficit compared with the contralateral limb. Although the current study quantified strength with isometric assessment instead of isokinetic assessment for reasons outlined in the Methods section, the strength deficits in our study were consistent with findings from Van Assche et al.8 Over 70% of the participants in our sample also dem onstrated >20% quadriceps femoris strength deficit, with a high variability of quadriceps femoris strength on the involved limb. The weakest third of our participants demonstrated 45% to 56% quadriceps femoris strength deficits compared with the contralateral limb, whereas the strongest third demonstrated less than a 10% deficit on the involved limb. Given the large vari ability in quadriceps femoris deficits in individuals with ACDs, future work should consider evaluating the extent to which preoperative quadriceps femoris strength can predict postoperative function after cartilage restoration, as this has been shown in individuals receiving an anterior cruciate ligament reconstruction.46 Quadriceps femoris weakness may be attributable to various factors including fear, pain, arthrogenic muscle inhibition, and atrophy.45’47-49 Most (9 of 11) participants reported pain during data collection, which may have inhibited their quadriceps femoris strength during testing and confounded the results. Due to variable defect loca tion, the fixed angle of strength testing we used potentially influenced pain response differently among participants. Though the quadriceps femoris strength values reported in this study may not reflect the maximal capacity of the muscle, we believe this voluntary measure of quadriceps femoris strength remains relevant for several reasons: This measure is clinically applicable, as pain may also be present in the clinic during strength testing; pain may be present during stair climbing, thus inhibiting functional quadriceps femoris strength; and recent work demonstrated that pain does not affect the relationship between isom etric quadriceps strength and function (performance-based or self-reported) in individuals with knee osteoarthritis.37 Due to small sample size, it was beyond the scope of this study to elucidate the contribu tors to decreased quadriceps femoris strength; however, this remains a goal of our ongoing work. Nonetheless, the substantial quadriceps femoris strength deficits observed in this population are concern ing, as adequate lower extremity strength is necessary for normal limb function, especially during dynamic weight bearing activities. Quadriceps femoris weakness is associ ated with impaired ability to dissipate loads and absorb shock, with resultant alterations in loading rates, contact forces, and load distribution on the articular surfaces.20 Thus, quadriceps femoris weakness in a population with compromised cartilage and altered cartilage loading may promote lesion progression and have devastating effects on future joint health. This is the first study to report knee biomechanics during stair ascent in individuals with ACD. O f particular interest, high variability existed in peak knee internalextension m om ents despite consistent knee-flexion angles. Peak internal knee-extension moment during
stair ascent was lower on the involved side compared with the uninvolved side and compared with the control group. Lower internal knee-extension moments on the involved limb have been reported in other studies evaluat ing stair-ascent biomechanics in populations with knee pathology.41'50"52 The internal knee-extension moment can be con ceptualized as the demand on the quadriceps femoris muscle to maintain knee extension against gravity and, when ascending stairs, reflects the muscular demand used to advance up the stairs. The decreased moments we observed in the involved limb may reflect a strategy to decrease the demand placed on the quadriceps femoris in light of the concurrent quadriceps femoris strength deficits. This notion is strengthened by the strong and significant direct relationship between quadriceps femo ris strength and peak internal knee-extension moment during stair ascent on the involved side. In our sample of individuals with ACDs, 72% of the variance in peak knee internal knee-extension moment could be explained by the peak quadriceps femoris strength on the involved side. Electromyography data on quadriceps femoris activ ity would be useful in further interpreting these findings but were not evaluated as part of this study. In addition, evaluation of hip, ankle, and trunk kinematics and kinetics during stair ascent may reveal the compensatory strate gies employed to ascend the stairs with such divergent knee moments in light of small differences in knee angle. Despite the lack of side-to-side differences in peak vGRF during stance in this study, there was a significant inverse relationship between involved quadriceps femoris strength and contralateral vGRF. For all subjects, the peak vGRF on the contralateral side occurred during the second half of stance, which corresponds with the beginning of stance on the involved limb on the following step. We speculate that the significant inverse correlation between contralateral vGRF and involved quadriceps femoris strength reflects an increased compensatory effort by the contralateral limb in individuals with weak knee extensors. Our results indicate that previously suggested quad riceps femoris strength thresholds to predict ability to successfully complete functional tasks such as rising from a chair, walking, and stair climbing through performancebased assessments32 may be inappropriate for younger subjects with ACDs. Ploutz-Snyder et al32 evaluated the quadriceps femoris strength necessary to “successfully” climb stairs, defined as the ability to reciprocally ascend and descend 1 flight of stairs without a handrail. In our study, all subjects reciprocally ascended the instrumented staircase without handrails and without concern for safety. Although the task would have been considered function ally “successful” by Ploutz-Snyder et al,32 based on their proposed quadriceps femoris strength threshold, only 2 participants in our study would have been categorized as having sufficient quadriceps femoris strength to ascend stairs without difficulty. The population of interest in their study (community-dwelling adults over 50 y old) was not representative of our sample, which may account
Strength and Biomechanics in Individuals with ACDs
for the differences. Furthermore, despite the ability of our participants to ascend without a handrail, we observed profound alterations in movement strategies (ie, reduced peak internal knee-extension moments). This highlights a need to consider clinically evaluating stair-climbing movement quality beyond stepping-pattern strategies and upper-extremity assistance to identify compensatory movement patterns in individuals with ACDs. In addition, elucidating the role of compensatory patterns in promot ing or limiting long-term function will be essential in guiding rehabilitation interventions in this population. The findings of this study indicate the potential for rehabilitation interventions to focus on quadriceps femoris strength and activation during dynamic activi ties. However, this should be considered on an individual basis. While decreased quadriceps femoris strength may alter load distribution within the joint in a manner that could propagate further joint damage,20 the long-term consequences of normal joint loading and normal quad riceps femoris strength on progression of symptoms and defects of various sizes53 54 and locations55 is unknown. Local joint mechanical factors may mediate the potential benefits of quadriceps femoris strengthening.56 For exam ple, for individuals with knee osteoarthritis, quadriceps femoris strengthening resulted in decreased symptoms for individuals with normal knee alignment but not for those with m alalignm ent.56 It is also possible that persistent function with weak quadriceps alters movement patterns in the contralateral limb, with potentially detrimental impact on future joint health. Further understanding of the riskrbenefit ratio for quadriceps femoris strengthen ing in this population is needed, before interventions to maximize function and minimize defect progression can be designed and tested. There were several limitations to this study. (1) Limb testing was not randomized, which is a potential source of bias. For strength testing, the rationale underlying testing the contralateral limb first is detailed in the Methods sec tion. The starting limb for stair climbing was not defined or randomized, as stair climbing is a bipedal task. Despite the rationale that supports the task order that was used, the lack of randomization remains a potential source of bias. (2) The population was heterogeneous, with variable defect location, number of defects per person, mechanism of injury (traumatic vs gradual), time since symptom onset, symptom severity, and previous injury. We anticipate that these factors uniquely contribute to pain, movement patterns, function, and possibly quad riceps femoris strength. Although it would be ideal to have homogeneous samples with respect to these factors, ACDs do not commonly occur in isolation. Widuchowski et al3 found that 70% of cartilage lesions found on knee arthroscopy were focal and concomitant with another injury, most commonly meniscus or ligamentous tears.3 For similar reasons, it is challenging to define the time since injury/symptom onset for individuals with a prior history of injury (ie, anterior cruciate ligament recon struction 10 y prior) or individuals who report insidious or gradual symptom onset. (3) The homogeneity of the
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sample demographics may also be considered a limita tion, as all subjects were young (3,0.CO;2-9 Slemenda C, Brandt KD, Heilman DK. et al. Quadriceps weakness and osteoarthritis of the knee. Ann Intern Med. 1997; 127(2):97—104. PubMed doi: 10.7326/0003-4819-1272-199707150-00001 Oiestad BE, Holm I, Gunderson R. Myklebust G, Risberg MA. Quadriceps muscle weakness after anterior cruciate ligament reconstruction: a risk factor for knee osteoarthri tis? Arthritis Care Res. 2010;62(12):1706-1714. PubMed doi: 10.1002/acr.20299 Palmieri-Smith RM. Thomas AC. Karvonen-Gutierrez C, Sowers MF. Isometric quadriceps strength in women with mild, moderate, and severe knee osteoarthritis. Am J Phys Med Rehabil. 2010;89(7):541-548. PubMed doi: 10.1097/ PH M ,0b013e3181 ddd5c.3 Lewek MD. Rudolph KS, Snyder-M ackler L. Q uadri ceps femoris muscle weakness and activation failure in patients with symptomatic knee osteoarthritis. J Orthop Res. 2004:22(0:110-115. PubMed doi: 10.1016/S07360266(03)00154-2 Engelhart L, Nelson L, Lewis S, et al. Validation of the Knee Injury and Osteoarthritis Outcome Score subscales for patients with articular cartilage lesions of the knee. Am J Sports Med. 2012;40(10):2264-2272. PubM ed doi: 10.1177/0363546512457646 Andriacchi TP, Andersson GB, Fermier RW. Stem D, Galante JO. A study of lower-limb mechanics during stair-climbing. J Bone Joint Surg Am. 1980;62(5):749-757. PubMed Ploutz-Snyder LL, Manini T, Ploutz-Snyder RJ, Wolf DA. Functionally relevant thresholds of quadriceps femoris
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