Journal of Applied Biomechanics, 2015, 31, 205 -210 http://dx.doi.org/10.1123/jab.2013-0233 © 2015 Human Kinetics, Inc.
ORIGINAL RESEARCH
Ankle Dorsiflexion Displacement During Landing is Associated With Initial Contact Kinematics but not Joint Displacement Rebecca L. Begalle,1 Meghan C. Walsh,2 Melanie L. McGrath,3 Michelle C. Boling,4 J. Troy Blackburn,2 and Darin A. Padua2 1Illinois
State University; 2University of North Carolina at Chapel Hill; of Nebraska Omaha; 4University of North Florida
3University
The ankle, knee, and hip joints work together in the sagittal plane to absorb landing forces. Reduced sagittal plane motion at the ankle may alter landing strategies at the knee and hip, potentially increasing injury risk; however, no studies have examined the kinematic relationships between the joints during jump landings. Healthy adults (N = 30; 15 male, 15 female) performed jump landings onto a force plate while three-dimensional kinematic data were collected. Joint displacement values were calculated during the loading phase as the difference between peak and initial contact angles. No relationship existed between ankle dorsiflexion displacement during landing and three-dimensional knee and hip displacements. However, less ankle dorsiflexion displacement was associated with landing at initial ground contact with larger hip flexion, hip internal rotation, knee flexion, knee varus, and smaller plantar flexion angles. Findings of the current study suggest that restrictions in ankle motion during landing may contribute to contacting the ground in a more flexed position but continuing through little additional motion to absorb the landing. Transverse plane hip and frontal plane knee positioning may also occur, which are known to increase the risk of lower extremity injury. Keywords: ankle, jump landing, lower extremity, biomechanics Landing tasks place a very high demand on ankle joint structures, as they play a substantial role in absorbing and dissipating ground reaction forces.1,2 The hip, knee, and ankle joints work in synchrony to absorb these forces. Landing strategies, whether soft or stiff, lead to varied contributions from the hip, knee, and ankle.1 Reduced ankle dorsiflexion motion during landing may potentially alter landing strategies at the hip and knee. Less ankle dorsiflexion range of motion, assessed passively as a measure of flexibility, has been associated with movement patterns known to increase tibiofemoral and patellofemoral joint loading,3–5 thereby elevating knee injury risk. The mechanism by which ankle dorsiflexion range of motion may increase the risk for knee injury, such as osteoarthritis, anterior cruciate ligament (ACL) injury, and patellofemoral pain syndrome, is currently unknown. Theoretically, limited ankle dorsiflexion range of motion may contribute to compensatory movements in the frontal and transverse planes, thereby increasing knee injury risk. Limited ankle dorsiflexion range of motion has been associated with greater frontal plane knee motion during controlled squatting tasks.3,4 Knee valgus motion, or the visual appearance of medial Rebecca L. Begalle is with the School of Kinesiology and Recreation, Illinois State University, Normal, IL. Meghan C. Walsh, J. Troy Blackburn, and Darin A. Padua are with the Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, NC. Melanie L. McGrath is with the Department of Health, Physical Activity, and Recreation, University of Nebraska Omaha, Omaha, NE. Michelle C. Boling is with the Department of Clinical and Applied Movement Science, University of North Florida, Jacksonville, FL. Address author correspondence to Rebecca L. Begalle at [email protected].
knee displacement, is considered a risk factor for noncontact knee injuries. Bell et al3 eliminated medial knee displacement during a double-leg squat by placing a 2 in (5.08 cm) wedge under the heel of participants. The wedge also decreased activation of the gastrocnemius and tibialis anterior muscles, which had been greater in the medial knee displacement group when performing the double-leg squat on a flat surface.6 Theoretically, decreasing coactivation of the lower leg musculature may have contributed to decreased ankle joint stiffness, thereby improving ankle dorsiflexion and eliminating medial knee displacement. Limited passive ankle dorsiflexion range of motion has also been found in participants demonstrating medial knee displacement during a single-leg squat in comparison with those without medial knee displacement.4 Therefore, ankle dorsiflexion range of motion does seem to influence knee motion during squatting tasks. However, the double-leg and single-leg squats do not involve the impact loading and sudden deceleration that many sport-specific movements do. The rapid deceleration during loading may begin at the ankle; therefore, studying the relationship between ankle dorsiflexion range of motion and lower extremity biomechanics during higher impact movements is important. Limited ankle dorsiflexion range of motion5 and less ankle dorsiflexion displacement during landing1,7 have both been associated with larger vertical ground reaction forces, known to increase knee joint loading. Limited ankle dorsiflexion range of motion has also been associated with greater frontal plane knee motion during double-leg8 and single-leg9 landings. Hagins et al9 intentionally restricted ankle dorsiflexion displacement by having participants jump from a 40-cm platform onto an anteriorly inclined surface. The result was greater knee valgus (1.4°), greater ankle plantar flexion at initial contact (4°), and smaller peak ankle dorsiflexion (3°) angles in comparison with landing on a flat surface.9 The anteriorly 205
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inclined landing surface theoretically restricted ankle dorsiflexion displacement, contributing to knee valgus; however, displacement values were not reported. While research has started to investigate the impact of ankle motion on lower extremity biomechanics, the majority of these relationships were identified between passive assessments of dorsiflexion range of motion (flexibility) and subsequent biomechanical performance. Previous research has not investigated ankle dorsiflexion displacement during a jump landing in relation to three-dimensional (3D) biomechanics at the hip, knee, and ankle. Thus, it is unknown if ankle dorsiflexion displacement during landing influences frontal and transverse plane knee and hip motion. The advantage of understanding these relationships further is that restricted ankle dorsiflexion is modifiable10,11 and may serve as a means to decrease knee injury rates. Therefore, our purpose was to determine the relationship between ankle dorsiflexion displacement and 3D knee and hip displacements during the loading phase of the jump landing. A second purpose was to determine the relationship between ankle dorsiflexion displacement and 3D knee and hip joint angles at the time point of initial contact (IC). We hypothesized that individuals with less ankle dorsiflexion displacement during the jump landing would demonstrate smaller sagittal plane and greater frontal and transverse plane displacements as well as IC angles at the knee and hip.
Methods Subjects Thirty physically active young adults participated in this research project. Fifteen males (mean [SD] age: 22.20 [1.78] years, height: 183.36 [6.92] cm, mass: 82.21 [11.91] kg) and 15 females (age: 21.07 [2.12] years, height: 164.53 [7.38] cm, mass: 62.93 [8.91] kg) were recruited for this study. All subjects were physically active, defined as 30 minutes of moderate activity at least 3 days per week.12 Participants had prior experience or were currently participating in organized soccer, volleyball, basketball, or lacrosse, so the jump landing task would be familiar. Subjects were excluded if they had a history of lower extremity surgery or had experienced a lower extremity musculoskeletal injury within the 6 months leading up to data collection that resulted in 2 or more days of restricted physical activity. Participants reported to the research laboratory for a single testing session wearing their own athletic shoes and were provided with dark colored spandex shorts and a shirt for motion analysis. Participants were informed of the study protocol and any risks or potential harm as described by the consent form approved by the institutional review board. Height, body mass, and dominant leg were recorded for each participant and a health history questionnaire confirmed inclusion/exclusion criteria. Participants performed a 5-minute stationary bicycle warm-up at a self-selected pace. The dominant leg was defined as the leg chosen to kick a soccer ball for maximum distance and was used for all data analyses.
Jump Landing Task The starting position for the jump landing task was atop a 30-cm high box placed at a distance of 50% of each participant’s height from the force plate. We instructed participants to jump forward from the box to a double-leg landing, with the dominant foot on the force plate and nondominant foot on the floor, and immediately
jump vertically for maximum height. A maximum of 3 practice trials were allowed, followed by 1 minute of rest. A total of 5 jump landing trials were captured and the middle 3 trials were averaged for data analysis to standardize trial selection. If one of the middle 3 trials was not deemed successful, a separate trial was selected. Successful trials included both feet leaving the box at the same time, the dominant foot landing on the force plate, and the participant immediately jumping vertically for maximum height.
Three-Dimensional Motion Analysis Lower extremity, 3D kinematics were collected using a 7-camera motion capture system sampled at 120 Hz (Vicon Motion Systems, Centennial, CO) and calibrated for a 2.5-m long × 1.5-m wide × 2.5-m high capture volume. Twenty-five reflective markers were applied to each participant on the following anatomical landmarks: bilaterally on acromion process, anterior superior iliac spine (ASIS), greater trochanter, anterior thigh, medial and lateral femoral condyles, anterior shank, medial and lateral malleoli, calcanei, first and fifth metatarsals, and L4–L5 spinous process. A static standing trial was captured in the anatomical position to estimate the locations of critical landmarks needed to calculate joint centers. Following the static trial, the medial malleoli and medial femoral condyle markers were removed for data collection. Kinetic data were captured at 1200 Hz using a floor embedded force plate (Bertec Corporation, Columbus, OH). Vertical ground reaction forces (VGRF) were used to identify jump landing phases for kinematic analysis. All data were recorded by Vicon Nexus Software (version 1.1, Vicon Motion Systems, Centennial, CO) and time synchronized to 1200 Hz using linear interpolation. Kinematic data were filtered using a fourth-order low-pass Butterworth filter with a 12 Hz cutoff frequency. The 3D local coordinates of the medial and lateral femoral condyles and medial malleoli were estimated from the coordinates of markers on the shank in the standing trial. The knee and ankle joint centers were defined as the midpoint between the medial and lateral femoral condyle and medial and lateral malleoli, respectively. The 3D coordinates of the hip joint centers were estimated from the 3D coordinates of the reflective markers on the right and left ASIS and L4–L5 joint using the Bell method.13 The tibia reference frame was defined by the 3D coordinates of the knee and ankle joint centers, medial and lateral malleoli, and the anterior shank, whereas the femur reference frame was defined by the coordinates of the knee and hip joint centers, medial and lateral femoral condyles, and the anterior thigh. The 3D coordinates of the first and fifth metatarsal heads, ankle joint center, and the calcaneus defined the foot reference frame. Joint angles were calculated as motion of the distal segment relative to the proximal segment via Euler angles in a sagittal (y-axis), frontal (x-axis), transverse (z-axis) plane rotation sequence.14 Ankle joint angles were calculated with Euler angle conventions of plantar flexion-dorsiflexion about the y-axis.
Data Processing Lower extremity biomechanics for the dominant leg were evaluated over the loading phase, defined as the interval from initial ground contact to peak knee flexion. IC was the time point when the VGRF exceeded 10 N.15 Peak knee flexion was the time point when the dominant knee reached its maximal knee flexion angle after IC from the box. IC joint angles and peak joint angles were identified during the loading phase for hip, knee, and ankle kinematics. Joint displacements were calculated for each trial by subtracting the IC
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Ankle Dorsiflexion Displacement During Landing 207
joint angle from the peak angle during the loading phase. Displacement values were averaged over the 3 trials of the jump landing for each subject and used for statistical analysis.
Statistical Analysis Simple Pearson product–moment correlation analyses were performed to determine the relationships between ankle dorsiflexion displacement during the jump landing with hip and knee sagittal, frontal, and transverse plane displacement, as well as joint angles at the time point of IC. A priori alpha level was set at P < .05. SPSS software v. 19.0 (IBM Inc., Chicago, IL) was used to perform all statistical analyses.
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Results Ankle dorsiflexion displacement during the jump landing was not associated with 3D displacement variables at the knee or hip (Table 1). Overall, ankle motion was not related to hip and knee
motion during the loading phase of the jump landing. However, ankle motion (during the loading phase) was related to hip and knee joint position when subjects first made contact with the ground. Less ankle dorsiflexion displacement during the jump landing was associated with larger knee flexion (P = .003), knee varus (P = .041), hip flexion (P < .001), hip internal rotation (P = .003), and smaller plantar flexion angles (P < .001) at the time point of IC (Table 2).
Discussion Previous research has linked restricted passive ankle dorsiflexion range of motion with undesirable knee motion during squatting3,4,6 and landing tasks.8,9 These findings identified ankle dorsiflexion range of motion as a contributor to potentially injurious lower extremity movement patterns, which is very valuable for clinicians, as ankle restrictions are modifiable. These research studies assessed passive ankle dorsiflexion range of motion before movement analysis and explored relationships with dynamic movement patterns during a functional task. However, few studies have
Table 1 Correlations between ankle dorsiflexion displacement (–40.26 [18.08]) and hip and knee displacement values, 95% confidence interval (CI), correlation coefficient (r value), and level of significance (P value) Displacement Variable
Value, mean (SD)
CI
r value
P value
Knee flexion
68.24 (17.78)
(61.60, 74.88)
–.043
.820
Knee valgus
–5.97 (3.05)
(–7.11, –4.84)
–.082
.665
Knee varus
6.99 (6.37)
(4.61, 9.37)
.243
.195
Knee internal rotation
9.86 (5.48)
(7.82, 11.91)
–.067
.725
–2.67 (2.61)
(–3.64, –1.70)
–.154
.418
–24.96 (10.21)
(–28.78, –21.15)
.071
.711
Knee external rotation Hip flexion Hip adduction
4.23 (2.83)
(3.17, 5.29)
–.095
.618
Hip abduction
–1.22 (1.50)
(–1.77, –0.66)
–.288
.123
Hip internal rotation
9.35 (6.12)
(7.06, 11.63)
.158
.403
Hip external rotation
–2.46 (2.64)
(–3.45, –1.48)
–.080
.676
Note. Hip (external, adduction, internal rotation), knee (flexion, varus, internal rotation), ankle (plantar flexion) are positive (+).
Table 2 Correlations between ankle dorsiflexion displacement (–40.26 [18.08]) and hip, knee, and ankle joint angles at initial contact, 95% confidence intervals (CI), correlation coefficient (r value), and level of significance (P value) Initial Contact Variable
Mean Angle, mean (SD)
CI
r value
P value
Ankle plantar flexion
38.62 (19.11)
(31.48, 45.75)
–.951
.000*
Knee flexion
20.56 (9.46)
(17.03, 24.09)
.531
.003*
Knee varus
0.36 (3.61)
(–0.99, 1.71)
.376
.041*
Knee external rotation
–2.28 (5.91)
(–4.49, –0.07)
.191
.382
Hip flexion
–25.89 (8.11)
(–28.92, –22.86)
–.657
.000*
Hip abduction
–5.08 (4.26)
(–6.67, –3.49)
.042
.849
Hip internal rotation
0.77 (6.00)
(–1.47, 3.01)
.530
.003*
Note. Hip (external, adduction, internal rotation), knee (flexion, varus, internal rotation), ankle (plantar flexion) are positive (+). *Indicates significant correlation with ankle dorsiflexion displacement (P < .05). JAB Vol. 31, No. 4, 2015
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analyzed ankle kinematics (eg, ankle dorsiflexion displacement) during functional tasks in relation to total lower extremity function.16 It has been suggested that investigating dynamic movement patterns, as opposed to passive flexibility measurements, offers better comprehension of the most important factors contributing to knee injury.17 Therefore we set out to explore the relationships between dynamic ankle dorsiflexion displacement during the loading phase of a landing task and how this was related to proximal joint movement. We originally hypothesized that decreased ankle dorsiflexion displacement during landing would be accompanied by limited sagittal plane movement at the knee and hip, thereby leading to alterations in frontal and transverse plane displacement to absorb the landing forces. However, our findings did not support these relationships; rather, our results indicate ankle dorsiflexion displacement during landing was associated with the way in which an individual made IC with the ground. The majority of acute noncontact knee injuries occur during landing or cutting tasks at or around the time point of IC.18,19 Therefore, we felt these relationships were clinically relevant. Less ankle dorsiflexion displacement during landing was associated with contacting the ground with greater knee frontal plane and hip transverse plane angles. However, this was also accompanied by greater knee and hip flexion as well as less plantar flexion (more dorsiflexion) at IC. This finding was unexpected given previous research has demonstrated a coupling effect of joint motions, such that less sagittal plane motion at one joint was accompanied by less sagittal plane motion at adjacent joints.1,20 Our results suggest individuals that used less ankle dorsiflexion displacement after ground contact may have compensated earlier by landing in a more flexed hip and knee position. This finding has also been supported by recent research.16 These landing patterns may be both beneficial and potentially injurious. The greatest known risk factors for knee injury include frontal and transverse plane positioning at the knee and hip during landing tasks.21,22 Therefore, our observed relationship between less ankle dorsiflexion displacement during the jump landing and greater knee varus and hip internal rotation at IC may provide insight into the treatment and prevention of knee injuries such as osteoarthritis, ACL injury, and patellofemoral pain syndrome. There are deleterious consequences to frontal plane knee stress. Knee varus alignment causes the ground reaction force vector to pass more medially to the knee joint center during movement, resulting in increased loads across the medial compartment of the knee.23 This alignment increases the risk of medial osteoarthritis progression,24 which is one of the major causes of pain and physical disability in aging adults. Research has also demonstrated that frontal plane knee movement, both valgus and varus, increases ACL loading25 and may contribute to the risk of ACL rupture.18,21,26 Consequently, much of the emphasis in developing preventative strategies for osteoarthritis and ACL injury has focused on minimizing frontal plane knee movement and loading. Our findings suggest that strategies to increase ankle dorsiflexion displacement during dynamic landing tasks may contribute to minimizing knee varus alignment and allow for a more neutral frontal plane knee position when landing. Greater hip internal rotation has been shown to decrease the contact area between the lateral patellar border and femoral condyle, thus resulting in greater contact pressures.27,28 In the current study, individuals with less ankle dorsiflexion displacement during landing demonstrated a larger degree of hip internal rotation at initial ground contact. Previous research has focused on the role of gluteal muscle strength, hip internal rotator muscle flexibility, and foot
pronation as factors that contribute to hip internal rotation and thus patellofemoral pain development.22,29,30 Our findings suggest that ankle dorsiflexion displacement is another important factor that may contribute to the development of patellofemoral pain syndrome, but requires further study. Future research should investigate training strategies to improve ankle dorsiflexion displacement during landing and its subsequent impact on injury. Our study also revealed that individuals who use less ankle dorsiflexion displacement during landing displayed greater knee and hip flexion, as well as less plantar flexion (more dorsiflexion), at IC. Thus, these individuals contact the ground in a generally more flexed position. Theoretically, landing in greater hip flexion, knee flexion, and ankle dorsiflexion may be a compensatory strategy to prevent larger ground reaction forces, typically associated with stiff landings. This finding is in agreement with previous research demonstrating lower extremity joints work in synchrony in the sagittal plane to absorb landing forces. For example, Blackburn and Padua20,31 revealed that individuals experienced less VGRF when landing with greater trunk, hip, and knee flexion compared with a more upright (less flexed) body posture. Similarly, Fong et al5 found that individuals with greater passive ankle dorsiflexion range of motion displayed greater knee flexion displacement and smaller VGRF during landing. In all of these studies, ankle kinematics were not reported so we cannot directly compare our findings. However, these studies support our theory that participants land in a more flexed position as a strategy to control and minimize VGRF. Devita and Skelly1 found that ankle musculature absorbed more energy during a stiff landing (less flexed), whereas the knee and hip joint contributed more during a soft landing (more flexed). We theorize that individuals undergoing less ankle dorsiflexion displacement during landing may have adapted more of a hip and knee energy absorption strategy so that they made impact with the ground in a more flexed position. While this may be an effective strategy to manage and maintain VGRF, it also contributes to larger knee varus and hip internal rotation alignment at IC. As previously discussed, these movement patterns can be associated with the development of osteoarthritis, ACL injury, and patellofemoral pain syndrome. Perhaps assuring individuals can land and move effectively through a greater amount of sagittal plane motion after IC at all 3 joints (ankle, knee, hip) is a safer mechanism, and potentially avoids deleterious frontal and transverse plane loading. Researchers have begun to use a potentially more functional weight-bearing assessment of ankle dorsiflexion range of motion to categorize participants and investigate lower extremity biomechanics during landing. A recent study by Whitting et al16 assessed ankle dorsiflexion range of motion via a weight-bearing lunge and placed individuals into low (37.7° ± 2.5°) and high (48.4° ± 2.5°) dorsiflexion range of motion groups. The maximum angle was averaged over 4 trials of the weight-bearing lunge to define the dorsiflexion range of motion capacity of each participant. The authors then compared ankle kinematics during a single-leg landing from 2 different heights (32 cm, 72cm). Sagittal plane ankle kinematics, including IC and peak angles, did not differ between groups. However, the percentage of each participant’s ankle dorsiflexion range of motion capacity used during the landing was different at critical time points, such as peak plantar flexor moment (close to IC) and peak dorsiflexion. The low dorsiflexion range of motion group used a greater percentage of their capacity at both time points, suggesting they placed their ankle plantar flexor muscle tendon unit in a more lengthened position (greater dorsiflexion) relative to their maximum.16 This result may help clarify our findings, such
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Ankle Dorsiflexion Displacement During Landing 209
that those that used less ankle dorsiflexion displacement during the loading phase contacted the ground in an already lengthened position compared with those with greater ankle dorsiflexion displacement. Unfortunately, we did not assess ankle dorsiflexion range of motion aside from during the dynamic task and these authors did not evaluate knee and hip biomechanics in relation to ankle motion, so a direct comparison cannot be made. A potential limitation of the current study is due to the correlational nature; no cause and effect relationship has been established. We also did not quantify passive ankle dorsiflexion range of motion (flexibility), therefore we do not know if passive restrictions were present. We chose not to assess passive ankle dorsiflexion range of motion before testing, as we were most interested in dynamic ankle movement during a jump landing. However, future research will aim to better understand the cause of restriction and the influence on lower extremity kinematics. Finally, unilateral data on the dominant kicking limb was collected and analyzed for this research study. Research has demonstrated asymmetrical absorption of landing forces during a similar jump landing task,32–34 which may influence lower extremity kinematics. However, these profiles were largely observed in previously injured participants such that less force was absorbed on the previously injured limb. Regardless of the healthy population used for this research study, the relationships discussed in this paper are generalizable only to the dominant kicking limb as we cannot assume symmetry in landing kinematics within the sample. A potential defense against devastating knee injuries and the onset of knee osteoarthritis is identifying mechanisms that contribute to potentially injurious movement patterns and modifying them through clinical interventions. Our results suggest that available ankle motion (displacement) during a jump landing may contribute to IC landing biomechanics. The clinical significance of this study is that if ankle joint restrictions during movement are associated with known knee injury risk factors, steps can be taken to modify these injury risks. Rehabilitation and neuromuscular training can improve ankle dorsiflexion range of motion deficits and improve movement patterns, regardless of soft tissue or bony tissue origin.
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29. Ireland ML, Willson JD, Ballantyne BT, Davis IM. Hip strength in females with and without patellofemoral pain. J Orthop Sports Phys Ther. 2003;33(11):671–676. PubMed doi:10.2519/ jospt.2003.33.11.671 30. Powers CM. The influence of altered lower-extremity kinematics on patellofemoral joint dysfunction: a theoretical perspective. J Orthop Sports Phys Ther. 2003;33(11):639–646. PubMed doi:10.2519/ jospt.2003.33.11.639 31. Blackburn JT, Padua DA. Sagittal-plane trunk position, landing forces, and quadriceps electromyographic activity. J Athl Train. 2009;44(2):174–179. PubMed doi:10.4085/1062-6050-44.2.174 32. Paterno MV, Ford KR, Myer GD, Heyl R, Hewett TE. Limb asymmetries in landing and jumping 2 years following anterior cruciate ligament reconstruction. Clin J Sport Med. 2007;17(4):258–262. PubMed 33. Paterno MV, Schmitt LC, Ford KR, et al. Biomechanical measures during landing and postural stability predict second anterior cruciate ligament injury after anterior cruciate ligament reconstruction and return to sport. Am J Sports Med. 2010;38(10):1968–1978. PubMed doi:10.1177/0363546510376053 34. Nyland J, Klein S, Caborn DN. Lower extremity compensatory neuromuscular and biomechanical adaptations 2 to 11 years after anterior cruciate ligament reconstruction. Arthroscopy. 2010;26(9):1212–1225. PubMed
JAB Vol. 31, No. 4, 2015
ORIGINAL RESEARCH
Ankle Dorsiflexion Displacement During Landing is Associated With Initial Contact Kinematics but not Joint Displacement Rebecca L. Begalle,1 Meghan C. Walsh,2 Melanie L. McGrath,3 Michelle C. Boling,4 J. Troy Blackburn,2 and Darin A. Padua2 1Illinois
State University; 2University of North Carolina at Chapel Hill; of Nebraska Omaha; 4University of North Florida
3University
The ankle, knee, and hip joints work together in the sagittal plane to absorb landing forces. Reduced sagittal plane motion at the ankle may alter landing strategies at the knee and hip, potentially increasing injury risk; however, no studies have examined the kinematic relationships between the joints during jump landings. Healthy adults (N = 30; 15 male, 15 female) performed jump landings onto a force plate while three-dimensional kinematic data were collected. Joint displacement values were calculated during the loading phase as the difference between peak and initial contact angles. No relationship existed between ankle dorsiflexion displacement during landing and three-dimensional knee and hip displacements. However, less ankle dorsiflexion displacement was associated with landing at initial ground contact with larger hip flexion, hip internal rotation, knee flexion, knee varus, and smaller plantar flexion angles. Findings of the current study suggest that restrictions in ankle motion during landing may contribute to contacting the ground in a more flexed position but continuing through little additional motion to absorb the landing. Transverse plane hip and frontal plane knee positioning may also occur, which are known to increase the risk of lower extremity injury. Keywords: ankle, jump landing, lower extremity, biomechanics Landing tasks place a very high demand on ankle joint structures, as they play a substantial role in absorbing and dissipating ground reaction forces.1,2 The hip, knee, and ankle joints work in synchrony to absorb these forces. Landing strategies, whether soft or stiff, lead to varied contributions from the hip, knee, and ankle.1 Reduced ankle dorsiflexion motion during landing may potentially alter landing strategies at the hip and knee. Less ankle dorsiflexion range of motion, assessed passively as a measure of flexibility, has been associated with movement patterns known to increase tibiofemoral and patellofemoral joint loading,3–5 thereby elevating knee injury risk. The mechanism by which ankle dorsiflexion range of motion may increase the risk for knee injury, such as osteoarthritis, anterior cruciate ligament (ACL) injury, and patellofemoral pain syndrome, is currently unknown. Theoretically, limited ankle dorsiflexion range of motion may contribute to compensatory movements in the frontal and transverse planes, thereby increasing knee injury risk. Limited ankle dorsiflexion range of motion has been associated with greater frontal plane knee motion during controlled squatting tasks.3,4 Knee valgus motion, or the visual appearance of medial Rebecca L. Begalle is with the School of Kinesiology and Recreation, Illinois State University, Normal, IL. Meghan C. Walsh, J. Troy Blackburn, and Darin A. Padua are with the Department of Exercise and Sports Science, University of North Carolina at Chapel Hill, Chapel Hill, NC. Melanie L. McGrath is with the Department of Health, Physical Activity, and Recreation, University of Nebraska Omaha, Omaha, NE. Michelle C. Boling is with the Department of Clinical and Applied Movement Science, University of North Florida, Jacksonville, FL. Address author correspondence to Rebecca L. Begalle at [email protected].
knee displacement, is considered a risk factor for noncontact knee injuries. Bell et al3 eliminated medial knee displacement during a double-leg squat by placing a 2 in (5.08 cm) wedge under the heel of participants. The wedge also decreased activation of the gastrocnemius and tibialis anterior muscles, which had been greater in the medial knee displacement group when performing the double-leg squat on a flat surface.6 Theoretically, decreasing coactivation of the lower leg musculature may have contributed to decreased ankle joint stiffness, thereby improving ankle dorsiflexion and eliminating medial knee displacement. Limited passive ankle dorsiflexion range of motion has also been found in participants demonstrating medial knee displacement during a single-leg squat in comparison with those without medial knee displacement.4 Therefore, ankle dorsiflexion range of motion does seem to influence knee motion during squatting tasks. However, the double-leg and single-leg squats do not involve the impact loading and sudden deceleration that many sport-specific movements do. The rapid deceleration during loading may begin at the ankle; therefore, studying the relationship between ankle dorsiflexion range of motion and lower extremity biomechanics during higher impact movements is important. Limited ankle dorsiflexion range of motion5 and less ankle dorsiflexion displacement during landing1,7 have both been associated with larger vertical ground reaction forces, known to increase knee joint loading. Limited ankle dorsiflexion range of motion has also been associated with greater frontal plane knee motion during double-leg8 and single-leg9 landings. Hagins et al9 intentionally restricted ankle dorsiflexion displacement by having participants jump from a 40-cm platform onto an anteriorly inclined surface. The result was greater knee valgus (1.4°), greater ankle plantar flexion at initial contact (4°), and smaller peak ankle dorsiflexion (3°) angles in comparison with landing on a flat surface.9 The anteriorly 205
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inclined landing surface theoretically restricted ankle dorsiflexion displacement, contributing to knee valgus; however, displacement values were not reported. While research has started to investigate the impact of ankle motion on lower extremity biomechanics, the majority of these relationships were identified between passive assessments of dorsiflexion range of motion (flexibility) and subsequent biomechanical performance. Previous research has not investigated ankle dorsiflexion displacement during a jump landing in relation to three-dimensional (3D) biomechanics at the hip, knee, and ankle. Thus, it is unknown if ankle dorsiflexion displacement during landing influences frontal and transverse plane knee and hip motion. The advantage of understanding these relationships further is that restricted ankle dorsiflexion is modifiable10,11 and may serve as a means to decrease knee injury rates. Therefore, our purpose was to determine the relationship between ankle dorsiflexion displacement and 3D knee and hip displacements during the loading phase of the jump landing. A second purpose was to determine the relationship between ankle dorsiflexion displacement and 3D knee and hip joint angles at the time point of initial contact (IC). We hypothesized that individuals with less ankle dorsiflexion displacement during the jump landing would demonstrate smaller sagittal plane and greater frontal and transverse plane displacements as well as IC angles at the knee and hip.
Methods Subjects Thirty physically active young adults participated in this research project. Fifteen males (mean [SD] age: 22.20 [1.78] years, height: 183.36 [6.92] cm, mass: 82.21 [11.91] kg) and 15 females (age: 21.07 [2.12] years, height: 164.53 [7.38] cm, mass: 62.93 [8.91] kg) were recruited for this study. All subjects were physically active, defined as 30 minutes of moderate activity at least 3 days per week.12 Participants had prior experience or were currently participating in organized soccer, volleyball, basketball, or lacrosse, so the jump landing task would be familiar. Subjects were excluded if they had a history of lower extremity surgery or had experienced a lower extremity musculoskeletal injury within the 6 months leading up to data collection that resulted in 2 or more days of restricted physical activity. Participants reported to the research laboratory for a single testing session wearing their own athletic shoes and were provided with dark colored spandex shorts and a shirt for motion analysis. Participants were informed of the study protocol and any risks or potential harm as described by the consent form approved by the institutional review board. Height, body mass, and dominant leg were recorded for each participant and a health history questionnaire confirmed inclusion/exclusion criteria. Participants performed a 5-minute stationary bicycle warm-up at a self-selected pace. The dominant leg was defined as the leg chosen to kick a soccer ball for maximum distance and was used for all data analyses.
Jump Landing Task The starting position for the jump landing task was atop a 30-cm high box placed at a distance of 50% of each participant’s height from the force plate. We instructed participants to jump forward from the box to a double-leg landing, with the dominant foot on the force plate and nondominant foot on the floor, and immediately
jump vertically for maximum height. A maximum of 3 practice trials were allowed, followed by 1 minute of rest. A total of 5 jump landing trials were captured and the middle 3 trials were averaged for data analysis to standardize trial selection. If one of the middle 3 trials was not deemed successful, a separate trial was selected. Successful trials included both feet leaving the box at the same time, the dominant foot landing on the force plate, and the participant immediately jumping vertically for maximum height.
Three-Dimensional Motion Analysis Lower extremity, 3D kinematics were collected using a 7-camera motion capture system sampled at 120 Hz (Vicon Motion Systems, Centennial, CO) and calibrated for a 2.5-m long × 1.5-m wide × 2.5-m high capture volume. Twenty-five reflective markers were applied to each participant on the following anatomical landmarks: bilaterally on acromion process, anterior superior iliac spine (ASIS), greater trochanter, anterior thigh, medial and lateral femoral condyles, anterior shank, medial and lateral malleoli, calcanei, first and fifth metatarsals, and L4–L5 spinous process. A static standing trial was captured in the anatomical position to estimate the locations of critical landmarks needed to calculate joint centers. Following the static trial, the medial malleoli and medial femoral condyle markers were removed for data collection. Kinetic data were captured at 1200 Hz using a floor embedded force plate (Bertec Corporation, Columbus, OH). Vertical ground reaction forces (VGRF) were used to identify jump landing phases for kinematic analysis. All data were recorded by Vicon Nexus Software (version 1.1, Vicon Motion Systems, Centennial, CO) and time synchronized to 1200 Hz using linear interpolation. Kinematic data were filtered using a fourth-order low-pass Butterworth filter with a 12 Hz cutoff frequency. The 3D local coordinates of the medial and lateral femoral condyles and medial malleoli were estimated from the coordinates of markers on the shank in the standing trial. The knee and ankle joint centers were defined as the midpoint between the medial and lateral femoral condyle and medial and lateral malleoli, respectively. The 3D coordinates of the hip joint centers were estimated from the 3D coordinates of the reflective markers on the right and left ASIS and L4–L5 joint using the Bell method.13 The tibia reference frame was defined by the 3D coordinates of the knee and ankle joint centers, medial and lateral malleoli, and the anterior shank, whereas the femur reference frame was defined by the coordinates of the knee and hip joint centers, medial and lateral femoral condyles, and the anterior thigh. The 3D coordinates of the first and fifth metatarsal heads, ankle joint center, and the calcaneus defined the foot reference frame. Joint angles were calculated as motion of the distal segment relative to the proximal segment via Euler angles in a sagittal (y-axis), frontal (x-axis), transverse (z-axis) plane rotation sequence.14 Ankle joint angles were calculated with Euler angle conventions of plantar flexion-dorsiflexion about the y-axis.
Data Processing Lower extremity biomechanics for the dominant leg were evaluated over the loading phase, defined as the interval from initial ground contact to peak knee flexion. IC was the time point when the VGRF exceeded 10 N.15 Peak knee flexion was the time point when the dominant knee reached its maximal knee flexion angle after IC from the box. IC joint angles and peak joint angles were identified during the loading phase for hip, knee, and ankle kinematics. Joint displacements were calculated for each trial by subtracting the IC
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Ankle Dorsiflexion Displacement During Landing 207
joint angle from the peak angle during the loading phase. Displacement values were averaged over the 3 trials of the jump landing for each subject and used for statistical analysis.
Statistical Analysis Simple Pearson product–moment correlation analyses were performed to determine the relationships between ankle dorsiflexion displacement during the jump landing with hip and knee sagittal, frontal, and transverse plane displacement, as well as joint angles at the time point of IC. A priori alpha level was set at P < .05. SPSS software v. 19.0 (IBM Inc., Chicago, IL) was used to perform all statistical analyses.
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Results Ankle dorsiflexion displacement during the jump landing was not associated with 3D displacement variables at the knee or hip (Table 1). Overall, ankle motion was not related to hip and knee
motion during the loading phase of the jump landing. However, ankle motion (during the loading phase) was related to hip and knee joint position when subjects first made contact with the ground. Less ankle dorsiflexion displacement during the jump landing was associated with larger knee flexion (P = .003), knee varus (P = .041), hip flexion (P < .001), hip internal rotation (P = .003), and smaller plantar flexion angles (P < .001) at the time point of IC (Table 2).
Discussion Previous research has linked restricted passive ankle dorsiflexion range of motion with undesirable knee motion during squatting3,4,6 and landing tasks.8,9 These findings identified ankle dorsiflexion range of motion as a contributor to potentially injurious lower extremity movement patterns, which is very valuable for clinicians, as ankle restrictions are modifiable. These research studies assessed passive ankle dorsiflexion range of motion before movement analysis and explored relationships with dynamic movement patterns during a functional task. However, few studies have
Table 1 Correlations between ankle dorsiflexion displacement (–40.26 [18.08]) and hip and knee displacement values, 95% confidence interval (CI), correlation coefficient (r value), and level of significance (P value) Displacement Variable
Value, mean (SD)
CI
r value
P value
Knee flexion
68.24 (17.78)
(61.60, 74.88)
–.043
.820
Knee valgus
–5.97 (3.05)
(–7.11, –4.84)
–.082
.665
Knee varus
6.99 (6.37)
(4.61, 9.37)
.243
.195
Knee internal rotation
9.86 (5.48)
(7.82, 11.91)
–.067
.725
–2.67 (2.61)
(–3.64, –1.70)
–.154
.418
–24.96 (10.21)
(–28.78, –21.15)
.071
.711
Knee external rotation Hip flexion Hip adduction
4.23 (2.83)
(3.17, 5.29)
–.095
.618
Hip abduction
–1.22 (1.50)
(–1.77, –0.66)
–.288
.123
Hip internal rotation
9.35 (6.12)
(7.06, 11.63)
.158
.403
Hip external rotation
–2.46 (2.64)
(–3.45, –1.48)
–.080
.676
Note. Hip (external, adduction, internal rotation), knee (flexion, varus, internal rotation), ankle (plantar flexion) are positive (+).
Table 2 Correlations between ankle dorsiflexion displacement (–40.26 [18.08]) and hip, knee, and ankle joint angles at initial contact, 95% confidence intervals (CI), correlation coefficient (r value), and level of significance (P value) Initial Contact Variable
Mean Angle, mean (SD)
CI
r value
P value
Ankle plantar flexion
38.62 (19.11)
(31.48, 45.75)
–.951
.000*
Knee flexion
20.56 (9.46)
(17.03, 24.09)
.531
.003*
Knee varus
0.36 (3.61)
(–0.99, 1.71)
.376
.041*
Knee external rotation
–2.28 (5.91)
(–4.49, –0.07)
.191
.382
Hip flexion
–25.89 (8.11)
(–28.92, –22.86)
–.657
.000*
Hip abduction
–5.08 (4.26)
(–6.67, –3.49)
.042
.849
Hip internal rotation
0.77 (6.00)
(–1.47, 3.01)
.530
.003*
Note. Hip (external, adduction, internal rotation), knee (flexion, varus, internal rotation), ankle (plantar flexion) are positive (+). *Indicates significant correlation with ankle dorsiflexion displacement (P < .05). JAB Vol. 31, No. 4, 2015
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analyzed ankle kinematics (eg, ankle dorsiflexion displacement) during functional tasks in relation to total lower extremity function.16 It has been suggested that investigating dynamic movement patterns, as opposed to passive flexibility measurements, offers better comprehension of the most important factors contributing to knee injury.17 Therefore we set out to explore the relationships between dynamic ankle dorsiflexion displacement during the loading phase of a landing task and how this was related to proximal joint movement. We originally hypothesized that decreased ankle dorsiflexion displacement during landing would be accompanied by limited sagittal plane movement at the knee and hip, thereby leading to alterations in frontal and transverse plane displacement to absorb the landing forces. However, our findings did not support these relationships; rather, our results indicate ankle dorsiflexion displacement during landing was associated with the way in which an individual made IC with the ground. The majority of acute noncontact knee injuries occur during landing or cutting tasks at or around the time point of IC.18,19 Therefore, we felt these relationships were clinically relevant. Less ankle dorsiflexion displacement during landing was associated with contacting the ground with greater knee frontal plane and hip transverse plane angles. However, this was also accompanied by greater knee and hip flexion as well as less plantar flexion (more dorsiflexion) at IC. This finding was unexpected given previous research has demonstrated a coupling effect of joint motions, such that less sagittal plane motion at one joint was accompanied by less sagittal plane motion at adjacent joints.1,20 Our results suggest individuals that used less ankle dorsiflexion displacement after ground contact may have compensated earlier by landing in a more flexed hip and knee position. This finding has also been supported by recent research.16 These landing patterns may be both beneficial and potentially injurious. The greatest known risk factors for knee injury include frontal and transverse plane positioning at the knee and hip during landing tasks.21,22 Therefore, our observed relationship between less ankle dorsiflexion displacement during the jump landing and greater knee varus and hip internal rotation at IC may provide insight into the treatment and prevention of knee injuries such as osteoarthritis, ACL injury, and patellofemoral pain syndrome. There are deleterious consequences to frontal plane knee stress. Knee varus alignment causes the ground reaction force vector to pass more medially to the knee joint center during movement, resulting in increased loads across the medial compartment of the knee.23 This alignment increases the risk of medial osteoarthritis progression,24 which is one of the major causes of pain and physical disability in aging adults. Research has also demonstrated that frontal plane knee movement, both valgus and varus, increases ACL loading25 and may contribute to the risk of ACL rupture.18,21,26 Consequently, much of the emphasis in developing preventative strategies for osteoarthritis and ACL injury has focused on minimizing frontal plane knee movement and loading. Our findings suggest that strategies to increase ankle dorsiflexion displacement during dynamic landing tasks may contribute to minimizing knee varus alignment and allow for a more neutral frontal plane knee position when landing. Greater hip internal rotation has been shown to decrease the contact area between the lateral patellar border and femoral condyle, thus resulting in greater contact pressures.27,28 In the current study, individuals with less ankle dorsiflexion displacement during landing demonstrated a larger degree of hip internal rotation at initial ground contact. Previous research has focused on the role of gluteal muscle strength, hip internal rotator muscle flexibility, and foot
pronation as factors that contribute to hip internal rotation and thus patellofemoral pain development.22,29,30 Our findings suggest that ankle dorsiflexion displacement is another important factor that may contribute to the development of patellofemoral pain syndrome, but requires further study. Future research should investigate training strategies to improve ankle dorsiflexion displacement during landing and its subsequent impact on injury. Our study also revealed that individuals who use less ankle dorsiflexion displacement during landing displayed greater knee and hip flexion, as well as less plantar flexion (more dorsiflexion), at IC. Thus, these individuals contact the ground in a generally more flexed position. Theoretically, landing in greater hip flexion, knee flexion, and ankle dorsiflexion may be a compensatory strategy to prevent larger ground reaction forces, typically associated with stiff landings. This finding is in agreement with previous research demonstrating lower extremity joints work in synchrony in the sagittal plane to absorb landing forces. For example, Blackburn and Padua20,31 revealed that individuals experienced less VGRF when landing with greater trunk, hip, and knee flexion compared with a more upright (less flexed) body posture. Similarly, Fong et al5 found that individuals with greater passive ankle dorsiflexion range of motion displayed greater knee flexion displacement and smaller VGRF during landing. In all of these studies, ankle kinematics were not reported so we cannot directly compare our findings. However, these studies support our theory that participants land in a more flexed position as a strategy to control and minimize VGRF. Devita and Skelly1 found that ankle musculature absorbed more energy during a stiff landing (less flexed), whereas the knee and hip joint contributed more during a soft landing (more flexed). We theorize that individuals undergoing less ankle dorsiflexion displacement during landing may have adapted more of a hip and knee energy absorption strategy so that they made impact with the ground in a more flexed position. While this may be an effective strategy to manage and maintain VGRF, it also contributes to larger knee varus and hip internal rotation alignment at IC. As previously discussed, these movement patterns can be associated with the development of osteoarthritis, ACL injury, and patellofemoral pain syndrome. Perhaps assuring individuals can land and move effectively through a greater amount of sagittal plane motion after IC at all 3 joints (ankle, knee, hip) is a safer mechanism, and potentially avoids deleterious frontal and transverse plane loading. Researchers have begun to use a potentially more functional weight-bearing assessment of ankle dorsiflexion range of motion to categorize participants and investigate lower extremity biomechanics during landing. A recent study by Whitting et al16 assessed ankle dorsiflexion range of motion via a weight-bearing lunge and placed individuals into low (37.7° ± 2.5°) and high (48.4° ± 2.5°) dorsiflexion range of motion groups. The maximum angle was averaged over 4 trials of the weight-bearing lunge to define the dorsiflexion range of motion capacity of each participant. The authors then compared ankle kinematics during a single-leg landing from 2 different heights (32 cm, 72cm). Sagittal plane ankle kinematics, including IC and peak angles, did not differ between groups. However, the percentage of each participant’s ankle dorsiflexion range of motion capacity used during the landing was different at critical time points, such as peak plantar flexor moment (close to IC) and peak dorsiflexion. The low dorsiflexion range of motion group used a greater percentage of their capacity at both time points, suggesting they placed their ankle plantar flexor muscle tendon unit in a more lengthened position (greater dorsiflexion) relative to their maximum.16 This result may help clarify our findings, such
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that those that used less ankle dorsiflexion displacement during the loading phase contacted the ground in an already lengthened position compared with those with greater ankle dorsiflexion displacement. Unfortunately, we did not assess ankle dorsiflexion range of motion aside from during the dynamic task and these authors did not evaluate knee and hip biomechanics in relation to ankle motion, so a direct comparison cannot be made. A potential limitation of the current study is due to the correlational nature; no cause and effect relationship has been established. We also did not quantify passive ankle dorsiflexion range of motion (flexibility), therefore we do not know if passive restrictions were present. We chose not to assess passive ankle dorsiflexion range of motion before testing, as we were most interested in dynamic ankle movement during a jump landing. However, future research will aim to better understand the cause of restriction and the influence on lower extremity kinematics. Finally, unilateral data on the dominant kicking limb was collected and analyzed for this research study. Research has demonstrated asymmetrical absorption of landing forces during a similar jump landing task,32–34 which may influence lower extremity kinematics. However, these profiles were largely observed in previously injured participants such that less force was absorbed on the previously injured limb. Regardless of the healthy population used for this research study, the relationships discussed in this paper are generalizable only to the dominant kicking limb as we cannot assume symmetry in landing kinematics within the sample. A potential defense against devastating knee injuries and the onset of knee osteoarthritis is identifying mechanisms that contribute to potentially injurious movement patterns and modifying them through clinical interventions. Our results suggest that available ankle motion (displacement) during a jump landing may contribute to IC landing biomechanics. The clinical significance of this study is that if ankle joint restrictions during movement are associated with known knee injury risk factors, steps can be taken to modify these injury risks. Rehabilitation and neuromuscular training can improve ankle dorsiflexion range of motion deficits and improve movement patterns, regardless of soft tissue or bony tissue origin.
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