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Immediate effect of valgus bracing on knee joint moments in meniscectomized patients: An exploratory study
Abstracts / Osteoarthritis and Cartilage 24 (2016) S63eS534
patients with established OA. Thus, the purpose of this study was to test the hypothesis that KFA and KERA at the instant when the vector sum of KFM and KAM is a maximum (KCM) correlate with changes in cartilage thickness in regions of the medial and lateral tibial plateau (MTP, LTP) between 2 and 4 years after ACLR. Methods: Twenty-three participants (28.3 ± 6.1 years old, 1.71 ± 0.07 m, 72.0 ± 9.7 kg, 2.6 ± 2.0 months between injury and surgery, 11 females) with unilateral ACLR and no other history of serious lower limb injury participated in this study after providing IRB approved informed consent. Subjects were tested at a baseline 2 years (2.19 ± 0.29) and a follow-up 4 years (4.34 ± 0.29) after ACLR. At both time points, all participants received MRIs (1.5T, 3D SPGR) of both knees, and 3D tibial cartilage thickness maps of both knees were generated and divided into 5 sub-regions for analysis in both the medial and lateral compartments: central, anterior, external, posterior, and internal. At 2 years after ACLR, gait was evaluated using motion capture and a force plate. The KCM was used to identify the key kinematic measures (KFA and KERA) at peak loading in early stance. Correlations between baseline kinematics and changes in regional cartilage thicknesses were tested using Pearson correlation coefficients with p ¼ 0.05 considered significant. Results: While both thicker and thinner cartilage was found after ACLR, patients with higher KFA at the instant of peak KCM showed more cartilage thinning from 2 to 4 years in both the entire MTP (P ¼ 0.019, R ¼ 0.486) and LTP (P ¼ 0.004, R ¼ 0.578). These correlations were
S99
driven by sub-regional changes in the posterior (Figure 1A) and internal MTP (P ¼ 0.05, R ¼ 0.414), and the posterior (Figure 1B) and external (P ¼ 0.022, R ¼ 0.474) LTP. Additionally, patients with higher KERA at peak KCM showed more cartilage thickening from 2 to 4 years in the LTP (Figure 1C). In the contralateral knee, KFA at peak KCM was correlated with thinning cartilage in the LTP (P ¼ 0.016, R ¼ 0.496), driven by changes to the central (P ¼ 0.005, R ¼ 0.569), anterior (P ¼ 0.021, R ¼ 0.480), and external (P ¼ 0.013, R ¼ 0.508) sub-regions. No significant correlations were found between KERA at peak KCM and cartilage change in the contralateral knee. Conclusions: This study suggests there is an interaction between knee kinematics and loading during walking that may influence morphological changes in cartilage between 2 and 4 years after ACLR, and supports the conclusion that the kinematic changes during peak loading can provide a better understanding of the mechanical factors associated with OA development. We observed that the peak KCM occurs at approximately the same instant during early stance as peak KAM and peak KFM, both of which have been associated with cartilage thinning in OA. Thus a change in kinematics that changes the location of cartilage contact in the tibiofemoral joint during high loading can play an important role in OA initiation following ACLR. Future use of compositional MRI may provide additional insight into the earliest changes to cartilage after ACLR. Longer term follow-up is necessary to determine if these kinematic risk factors lead to radiographic OA in this population.
154 IMMEDIATE EFFECT OF VALGUS BRACING ON KNEE JOINT MOMENTS IN MENISCECTOMIZED PATIENTS: AN EXPLORATORY STUDY M. Thorning y, J.B. Thorlund y, E.M. Roos y, T.V. Wrigley z, M. Hall z. y Dept. of Sports Sci. and Clinical Biomechanics, Univ. of Southern Denmark, Odense, Denmark; z Ctr. for Hlth., Exercise and Sports Med., Dept. of Physiotherapy, Sch. of Hlth.Sci., The Univ. of Melbourne, Melbourne, VIC, Australia Purpose: Individuals undergoing arthroscopic partial meniscectomy (APM) are typically middle-aged adults, who are at high risk of developing or progressing knee osteoarthritis (OA). Higher knee joint loading, assessed as the external knee adduction moment (KAM) during gait is thought to be a potential contributor to OA in these individuals. In addition to the KAM, increasing evidence implicates the role of the external knee flexion moment (KFM) in OA development and progression. The purpose of this study was to test the hypothesis that wearing a valgus unloader knee brace would reduce peak KAM during gait in people following medial APM. The secondary exploratory aims of this study was to assess the immediate effect of the valgus unloader brace on KAM impulse and the peak KFM during gait, and all three parameters of moment (peak KAM, KAM impulse and peak KFM) during a forward lunge and single-leg sit-to-stand. Methods: Twenty-two patients who had undergone a medial APM within the previous 8e15 months (age 35e55 years) were recruited from the existing cohort study “Knee Arthroscopy Cohort Southern Denmark” (KACS). The participants completed three-dimensional analysis of gait, forward lunge and single-leg sit-to-stand during two conditions: with and without a valgus unloader knee brace while barefoot. The sequence of tasks and conditions were randomized for each participant. Outcome measures included: 1) peak KAM during the first half of stance, 2) positive KAM impulse (positive area under the KAM-time curve) during the stance phase, 3) peak KFM throughout stance. The valgus knee brace tested was the Rebound® Cartilage knee brace. The brace was individually fitted to the APM leg according to instructions provided by the manufacturing consultant. Ethical approval was granted from the Regional Scientific Ethics Committee of Southern Denmark. All included participants provided written informed consent. Results: Seventeen of the 22 participants had data available for gait trials. Twenty-one participants completed the forward lunge and 16 completed the single-leg sit-to-stand. There were no significant differences between the conditions for our primary outcome, the peak KAM during gait (mean difference 0.07 [95% CI -0.24 to 0.11] (Nm/ (BWHT)%), p ¼ 0.442). There were no significant differences in KAM impulse or peak KFM between conditions during gait. Notably, there was large variation of the individual percentage changes in all the included variables between the conditions. For the more challenging tasks assessed, there were no significant differences in peak KAM or
S100
Abstracts / Osteoarthritis and Cartilage 24 (2016) S63eS534
KAM impulse between brace conditions during forward lunge or singleleg sit-to-stand. However, wearing the brace resulted in a 10% higher peak KFM during forward lunge (mean difference 0.54 [95% CI 0.27 to 0.82] (Nm/(BWHT)%), p<0.001) and an 8% higher peak KFM during a single-leg sit-to-stand (mean difference 0.45 [95% CI 0.08 to 0.82] (Nm/ (BWHT)%), p ¼ 0.022) compared to not wearing a brace. Conclusions: This study is, to our knowledge, the first to investigate the immediate effect of a valgus unloader knee brace on knee joint moments in people following APM. Contrary to our hypothesis, we found no immediate effect of the valgus unloader knee brace in peak KAM (or impulse). Conversely, an increase in peak KFM was detected during forward lunge and single-leg sit-to-stand when wearing the brace. These results may reflect enhanced stability of the knee provided by the brace, which may induce increased knee function and kneerelated confidence. In conclusion, our preliminary findings suggest that the immediate effect of valgus bracing in people following a medial APM increases the peak KFM during challenging tasks including forward lunge and single-leg sit-to-stand. Alterations in the peak KFM provide the impetus for conducting larger scale studies investigating the implication on physical function and structural change. 155 ASSOCIATIONS BETWEEN QUADRICEPS SPINAL REFLEX EXCITABILITY, CORTICOMOTOR EXCITABILITY AND JUMP-LANDING MECHANICS IN INDIVIDUALS WITH ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTIONS S. Ward y, z, J.T. Blackburn y, D.A. Padua y, L.E. Stanley y, M.S. Harkey y, B.A. Luc y, B. Pietrosimone y. y Univ. of North Carolina at Chapel Hill, Chapel Hill, NC, USA; z Univ. of Melbourne, Victoria, Australia Purpose: Altered quadriceps function and aberrant biomechanics are evident in individuals who have undergone anterior cruciate ligament reconstruction (ACLR), potentially contributing to the heightened risk of developing knee osteoarthritis (OA). The inability to generate adequate eccentric quadriceps action to control knee joint motion and attenuate energy through the joint may increase the risk of OA development. It has been hypothesized that changes in quadriceps spinal reflexive and corticomotor excitability observed in individuals with ACLR are a mechanistic cause of altered neuromuscular activation and the development of biomechanics that lead to the development of knee OA. ACLR patients demonstrate significant asymmetries in knee joint kinematics and force attenuation during landing, particularly in both the peak vertical ground reaction force (vGRF) and sagittal plane knee moments during vertical drop jumps. Furthermore, ACLR patients demonstrate reduced knee flexion angle and knee extension moment, which may be maladaptations that are related to quadriceps dysfunction. Prior to developing therapeutic strategies that target corticomotor or spinal reflex excitability for the purpose of improving biomechanics, we must determine the association between quadriceps corticomotor excitability and biomechanics during dynamic activity in people with an ACLR. The aim of the study was to determine if there is an association between quadriceps spinal reflex and corticomotor excitability, and knee sagittal plane kinetics and kinematics during jump landing in individuals with ACLR. Methods: Thirty-four individuals with a history of a unilateral ACLR participated in this cross-sectional study (68% female, 22.1 ± 3.3 years; 73.4 ± 17.8 Kg; 1.69 ± 0.1 m; 45 ± 39 months post-ACLR). Quadriceps spinal reflex excitability was assessed bilaterally using the H-reflex normalized to the maximal muscle response (H:M ratio). To elicit the quadriceps H-reflex, an electrical stimulus was delivered to the femoral nerve where it passes through the femoral triangle. An MP150 data acquisition system (BIOPAC Systems, Inc.) and Acqknowledge BIOPAC Software was used to visualize the EMG signals and manipulate the electrical stimulus. Corticomotor excitability was assessed as active motor threshold (AMT). A double-cone transcranial magnetic stimulation coil (Magstim Company, UK) was used to establish AMT in the vastus medialis. AMT was defined as the minimum stimulus intensity required to elicit a motor evoked potential >100 mV while the participant maintained a quadriceps contraction at 5% of MVIC. Participants performed five successful jump landings, in a 3-dementional motion analysis laboratory, from a 30cm box positioned 50% of the participant’s height from the front edge of two force plates (Bertec Corporation, Columbus, OH). Participants were instructed to jump forward off the box to a double-leg landing with one foot on each force plate, and immediately jump vertically as high as possible. Lower extremity
biomechanics for each limb were evaluated during the loading phase, which was defined as the interval from initial contact (IC) to peak knee flexion angle. IC was defined as the time point when the vGRF exceeded 10N. Knee flexion angle excursion was calculated by subtracting the IC joint angle from the peak knee flexion joint angle during the loading phase. Peak vGRF (N) was identified during the loading phase. Peak vGRF and knee moments were normalized to body weight. Pearson product-moment correlations were used to assess associations between kinetic, kinematic, and neuromuscular variables in the ACLR limb (a ¼ 0.05) Results: Greater quadriceps spinal reflex excitability was associated with greater peak vGRF (r ¼ 0.453 P ¼ 0.023). There were no significant associations between AMT and landing kinetics (Peak vGRF r ¼ -0.140 P ¼ 0.495; peak knee extension moment r ¼ 0.296 P ¼ 0.144) or kinematics (knee angle at IC r ¼ e0.291 P ¼ 0.150; peak knee flexion angle r ¼ 0.320 P ¼ 0.111; knee flexion excursion r ¼ 0.251 P ¼ 0.216) Conclusions: High quadriceps spinal reflex excitability was associated with higher loading during landing, suggesting that individuals with ACLR may rely more heavily on spinal reflexes during a dynamic movement exerting high loads on lower extremity joints. Individuals that rely on spinal reflexive excitability to manage movement strategies during dynamic activity, rather than cortical excitability, may not be able to best anticipate the attenuation of high joint loads. Training individuals with ACLR to develop movement strategies that attenuate high loads during activity may improve long-term joint health. 156 SQUATTING BIOMECHANICS IN INDIVIDUALS WITH SYMPTOMATIC FEMOROACETABULAR IMPINGEMENT: UNCONSTRAINED AND CONSTRAINED TASKS L. Diamond y, K. Bennell y, T. Wrigley y, R. Hinman y, J. O'Donnell z, P. Hodges x. y The Univ. of Melbourne, Melbourne, Australia; z St Vincent's Hosp., Melbourne, Australia; x The Univ. of Queensland, Brisbane, Australia Purpose: Femoroacetabular impingement (FAI) is becoming increasingly recognised as a frequent cause of hip pain and reduced function in younger active adults. Importantly, FAI has been identified as a risk factor for the onset and development of hip osteoarthritis. Surgical treatment for FAI is recommended within the literature, despite unknown effects. Conservative treatments in individuals with symptomatic FAI, in lieu of or in conjunction with surgical treatments might be beneficial. However, the physical impairments of these patients must first be identified in order to design and inform these non-surgical treatments. To date, abnormal hip function in individuals with symptomatic FAI has not been well defined. Squatting is a demanding task that necessitates a large hip flexion range, where impingement typically occurs. This study aimed to determine whether hip and pelvis biomechanics differ between individuals with and without symptomatic FAI during an unconstrained deep squat and a constrained squat designed to limit contribution from the pelvis. Methods: Fifteen participants diagnosed with symptomatic cam-type or combined (cam plus pincer) FAI who were scheduled for arthroscopic surgery and 14 age-, and sex-matched disease-free controls underwent three-dimensional motion analysis for two squatting tasks. The triphase squats were performed at a self-selected pace and included: (i) descent to the end of available range; (ii) a 3-second hold; and (iii) ascent to an upright standing position. The constrained squat was designed to minimize trunk flexion, while promoting isolated hip flexion and limiting pelvic tilt. Trunk, pelvis, and hip kinematics, and hip kinetics were compared between the groups. Spatiotemporal and demographic variables were examined for between-group differences using independent t-tests and Pearson’s chi-square as appropriate. Between-group kinematic and kinetic comparisons were made using independent t-tests and Mann-Whitney U tests as required. When significant differences (P < 0.05) in squat speed or depth were identified between the groups, an analysis of covariance was also performed using the appropriate variable as a covariate. Results: The FAI and control groups were comparable for age, height, sex and BMI. FAI participants reported an average pain score of 2/10 during both the unconstrained and constrained squats. There were no between-group differences in squat depth for either task. Descent speed was slower for the FAI group during the unconstrained squat (P<0.05). There were no other between-group differences for this task. Participants with FAI demonstrated increased ipsilateral pelvic rise (P ¼ 0.04) and increased hip adduction (P ¼ 0.04) compared to controls during the
patients with established OA. Thus, the purpose of this study was to test the hypothesis that KFA and KERA at the instant when the vector sum of KFM and KAM is a maximum (KCM) correlate with changes in cartilage thickness in regions of the medial and lateral tibial plateau (MTP, LTP) between 2 and 4 years after ACLR. Methods: Twenty-three participants (28.3 ± 6.1 years old, 1.71 ± 0.07 m, 72.0 ± 9.7 kg, 2.6 ± 2.0 months between injury and surgery, 11 females) with unilateral ACLR and no other history of serious lower limb injury participated in this study after providing IRB approved informed consent. Subjects were tested at a baseline 2 years (2.19 ± 0.29) and a follow-up 4 years (4.34 ± 0.29) after ACLR. At both time points, all participants received MRIs (1.5T, 3D SPGR) of both knees, and 3D tibial cartilage thickness maps of both knees were generated and divided into 5 sub-regions for analysis in both the medial and lateral compartments: central, anterior, external, posterior, and internal. At 2 years after ACLR, gait was evaluated using motion capture and a force plate. The KCM was used to identify the key kinematic measures (KFA and KERA) at peak loading in early stance. Correlations between baseline kinematics and changes in regional cartilage thicknesses were tested using Pearson correlation coefficients with p ¼ 0.05 considered significant. Results: While both thicker and thinner cartilage was found after ACLR, patients with higher KFA at the instant of peak KCM showed more cartilage thinning from 2 to 4 years in both the entire MTP (P ¼ 0.019, R ¼ 0.486) and LTP (P ¼ 0.004, R ¼ 0.578). These correlations were
S99
driven by sub-regional changes in the posterior (Figure 1A) and internal MTP (P ¼ 0.05, R ¼ 0.414), and the posterior (Figure 1B) and external (P ¼ 0.022, R ¼ 0.474) LTP. Additionally, patients with higher KERA at peak KCM showed more cartilage thickening from 2 to 4 years in the LTP (Figure 1C). In the contralateral knee, KFA at peak KCM was correlated with thinning cartilage in the LTP (P ¼ 0.016, R ¼ 0.496), driven by changes to the central (P ¼ 0.005, R ¼ 0.569), anterior (P ¼ 0.021, R ¼ 0.480), and external (P ¼ 0.013, R ¼ 0.508) sub-regions. No significant correlations were found between KERA at peak KCM and cartilage change in the contralateral knee. Conclusions: This study suggests there is an interaction between knee kinematics and loading during walking that may influence morphological changes in cartilage between 2 and 4 years after ACLR, and supports the conclusion that the kinematic changes during peak loading can provide a better understanding of the mechanical factors associated with OA development. We observed that the peak KCM occurs at approximately the same instant during early stance as peak KAM and peak KFM, both of which have been associated with cartilage thinning in OA. Thus a change in kinematics that changes the location of cartilage contact in the tibiofemoral joint during high loading can play an important role in OA initiation following ACLR. Future use of compositional MRI may provide additional insight into the earliest changes to cartilage after ACLR. Longer term follow-up is necessary to determine if these kinematic risk factors lead to radiographic OA in this population.
154 IMMEDIATE EFFECT OF VALGUS BRACING ON KNEE JOINT MOMENTS IN MENISCECTOMIZED PATIENTS: AN EXPLORATORY STUDY M. Thorning y, J.B. Thorlund y, E.M. Roos y, T.V. Wrigley z, M. Hall z. y Dept. of Sports Sci. and Clinical Biomechanics, Univ. of Southern Denmark, Odense, Denmark; z Ctr. for Hlth., Exercise and Sports Med., Dept. of Physiotherapy, Sch. of Hlth.Sci., The Univ. of Melbourne, Melbourne, VIC, Australia Purpose: Individuals undergoing arthroscopic partial meniscectomy (APM) are typically middle-aged adults, who are at high risk of developing or progressing knee osteoarthritis (OA). Higher knee joint loading, assessed as the external knee adduction moment (KAM) during gait is thought to be a potential contributor to OA in these individuals. In addition to the KAM, increasing evidence implicates the role of the external knee flexion moment (KFM) in OA development and progression. The purpose of this study was to test the hypothesis that wearing a valgus unloader knee brace would reduce peak KAM during gait in people following medial APM. The secondary exploratory aims of this study was to assess the immediate effect of the valgus unloader brace on KAM impulse and the peak KFM during gait, and all three parameters of moment (peak KAM, KAM impulse and peak KFM) during a forward lunge and single-leg sit-to-stand. Methods: Twenty-two patients who had undergone a medial APM within the previous 8e15 months (age 35e55 years) were recruited from the existing cohort study “Knee Arthroscopy Cohort Southern Denmark” (KACS). The participants completed three-dimensional analysis of gait, forward lunge and single-leg sit-to-stand during two conditions: with and without a valgus unloader knee brace while barefoot. The sequence of tasks and conditions were randomized for each participant. Outcome measures included: 1) peak KAM during the first half of stance, 2) positive KAM impulse (positive area under the KAM-time curve) during the stance phase, 3) peak KFM throughout stance. The valgus knee brace tested was the Rebound® Cartilage knee brace. The brace was individually fitted to the APM leg according to instructions provided by the manufacturing consultant. Ethical approval was granted from the Regional Scientific Ethics Committee of Southern Denmark. All included participants provided written informed consent. Results: Seventeen of the 22 participants had data available for gait trials. Twenty-one participants completed the forward lunge and 16 completed the single-leg sit-to-stand. There were no significant differences between the conditions for our primary outcome, the peak KAM during gait (mean difference 0.07 [95% CI -0.24 to 0.11] (Nm/ (BWHT)%), p ¼ 0.442). There were no significant differences in KAM impulse or peak KFM between conditions during gait. Notably, there was large variation of the individual percentage changes in all the included variables between the conditions. For the more challenging tasks assessed, there were no significant differences in peak KAM or
S100
Abstracts / Osteoarthritis and Cartilage 24 (2016) S63eS534
KAM impulse between brace conditions during forward lunge or singleleg sit-to-stand. However, wearing the brace resulted in a 10% higher peak KFM during forward lunge (mean difference 0.54 [95% CI 0.27 to 0.82] (Nm/(BWHT)%), p<0.001) and an 8% higher peak KFM during a single-leg sit-to-stand (mean difference 0.45 [95% CI 0.08 to 0.82] (Nm/ (BWHT)%), p ¼ 0.022) compared to not wearing a brace. Conclusions: This study is, to our knowledge, the first to investigate the immediate effect of a valgus unloader knee brace on knee joint moments in people following APM. Contrary to our hypothesis, we found no immediate effect of the valgus unloader knee brace in peak KAM (or impulse). Conversely, an increase in peak KFM was detected during forward lunge and single-leg sit-to-stand when wearing the brace. These results may reflect enhanced stability of the knee provided by the brace, which may induce increased knee function and kneerelated confidence. In conclusion, our preliminary findings suggest that the immediate effect of valgus bracing in people following a medial APM increases the peak KFM during challenging tasks including forward lunge and single-leg sit-to-stand. Alterations in the peak KFM provide the impetus for conducting larger scale studies investigating the implication on physical function and structural change. 155 ASSOCIATIONS BETWEEN QUADRICEPS SPINAL REFLEX EXCITABILITY, CORTICOMOTOR EXCITABILITY AND JUMP-LANDING MECHANICS IN INDIVIDUALS WITH ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTIONS S. Ward y, z, J.T. Blackburn y, D.A. Padua y, L.E. Stanley y, M.S. Harkey y, B.A. Luc y, B. Pietrosimone y. y Univ. of North Carolina at Chapel Hill, Chapel Hill, NC, USA; z Univ. of Melbourne, Victoria, Australia Purpose: Altered quadriceps function and aberrant biomechanics are evident in individuals who have undergone anterior cruciate ligament reconstruction (ACLR), potentially contributing to the heightened risk of developing knee osteoarthritis (OA). The inability to generate adequate eccentric quadriceps action to control knee joint motion and attenuate energy through the joint may increase the risk of OA development. It has been hypothesized that changes in quadriceps spinal reflexive and corticomotor excitability observed in individuals with ACLR are a mechanistic cause of altered neuromuscular activation and the development of biomechanics that lead to the development of knee OA. ACLR patients demonstrate significant asymmetries in knee joint kinematics and force attenuation during landing, particularly in both the peak vertical ground reaction force (vGRF) and sagittal plane knee moments during vertical drop jumps. Furthermore, ACLR patients demonstrate reduced knee flexion angle and knee extension moment, which may be maladaptations that are related to quadriceps dysfunction. Prior to developing therapeutic strategies that target corticomotor or spinal reflex excitability for the purpose of improving biomechanics, we must determine the association between quadriceps corticomotor excitability and biomechanics during dynamic activity in people with an ACLR. The aim of the study was to determine if there is an association between quadriceps spinal reflex and corticomotor excitability, and knee sagittal plane kinetics and kinematics during jump landing in individuals with ACLR. Methods: Thirty-four individuals with a history of a unilateral ACLR participated in this cross-sectional study (68% female, 22.1 ± 3.3 years; 73.4 ± 17.8 Kg; 1.69 ± 0.1 m; 45 ± 39 months post-ACLR). Quadriceps spinal reflex excitability was assessed bilaterally using the H-reflex normalized to the maximal muscle response (H:M ratio). To elicit the quadriceps H-reflex, an electrical stimulus was delivered to the femoral nerve where it passes through the femoral triangle. An MP150 data acquisition system (BIOPAC Systems, Inc.) and Acqknowledge BIOPAC Software was used to visualize the EMG signals and manipulate the electrical stimulus. Corticomotor excitability was assessed as active motor threshold (AMT). A double-cone transcranial magnetic stimulation coil (Magstim Company, UK) was used to establish AMT in the vastus medialis. AMT was defined as the minimum stimulus intensity required to elicit a motor evoked potential >100 mV while the participant maintained a quadriceps contraction at 5% of MVIC. Participants performed five successful jump landings, in a 3-dementional motion analysis laboratory, from a 30cm box positioned 50% of the participant’s height from the front edge of two force plates (Bertec Corporation, Columbus, OH). Participants were instructed to jump forward off the box to a double-leg landing with one foot on each force plate, and immediately jump vertically as high as possible. Lower extremity
biomechanics for each limb were evaluated during the loading phase, which was defined as the interval from initial contact (IC) to peak knee flexion angle. IC was defined as the time point when the vGRF exceeded 10N. Knee flexion angle excursion was calculated by subtracting the IC joint angle from the peak knee flexion joint angle during the loading phase. Peak vGRF (N) was identified during the loading phase. Peak vGRF and knee moments were normalized to body weight. Pearson product-moment correlations were used to assess associations between kinetic, kinematic, and neuromuscular variables in the ACLR limb (a ¼ 0.05) Results: Greater quadriceps spinal reflex excitability was associated with greater peak vGRF (r ¼ 0.453 P ¼ 0.023). There were no significant associations between AMT and landing kinetics (Peak vGRF r ¼ -0.140 P ¼ 0.495; peak knee extension moment r ¼ 0.296 P ¼ 0.144) or kinematics (knee angle at IC r ¼ e0.291 P ¼ 0.150; peak knee flexion angle r ¼ 0.320 P ¼ 0.111; knee flexion excursion r ¼ 0.251 P ¼ 0.216) Conclusions: High quadriceps spinal reflex excitability was associated with higher loading during landing, suggesting that individuals with ACLR may rely more heavily on spinal reflexes during a dynamic movement exerting high loads on lower extremity joints. Individuals that rely on spinal reflexive excitability to manage movement strategies during dynamic activity, rather than cortical excitability, may not be able to best anticipate the attenuation of high joint loads. Training individuals with ACLR to develop movement strategies that attenuate high loads during activity may improve long-term joint health. 156 SQUATTING BIOMECHANICS IN INDIVIDUALS WITH SYMPTOMATIC FEMOROACETABULAR IMPINGEMENT: UNCONSTRAINED AND CONSTRAINED TASKS L. Diamond y, K. Bennell y, T. Wrigley y, R. Hinman y, J. O'Donnell z, P. Hodges x. y The Univ. of Melbourne, Melbourne, Australia; z St Vincent's Hosp., Melbourne, Australia; x The Univ. of Queensland, Brisbane, Australia Purpose: Femoroacetabular impingement (FAI) is becoming increasingly recognised as a frequent cause of hip pain and reduced function in younger active adults. Importantly, FAI has been identified as a risk factor for the onset and development of hip osteoarthritis. Surgical treatment for FAI is recommended within the literature, despite unknown effects. Conservative treatments in individuals with symptomatic FAI, in lieu of or in conjunction with surgical treatments might be beneficial. However, the physical impairments of these patients must first be identified in order to design and inform these non-surgical treatments. To date, abnormal hip function in individuals with symptomatic FAI has not been well defined. Squatting is a demanding task that necessitates a large hip flexion range, where impingement typically occurs. This study aimed to determine whether hip and pelvis biomechanics differ between individuals with and without symptomatic FAI during an unconstrained deep squat and a constrained squat designed to limit contribution from the pelvis. Methods: Fifteen participants diagnosed with symptomatic cam-type or combined (cam plus pincer) FAI who were scheduled for arthroscopic surgery and 14 age-, and sex-matched disease-free controls underwent three-dimensional motion analysis for two squatting tasks. The triphase squats were performed at a self-selected pace and included: (i) descent to the end of available range; (ii) a 3-second hold; and (iii) ascent to an upright standing position. The constrained squat was designed to minimize trunk flexion, while promoting isolated hip flexion and limiting pelvic tilt. Trunk, pelvis, and hip kinematics, and hip kinetics were compared between the groups. Spatiotemporal and demographic variables were examined for between-group differences using independent t-tests and Pearson’s chi-square as appropriate. Between-group kinematic and kinetic comparisons were made using independent t-tests and Mann-Whitney U tests as required. When significant differences (P < 0.05) in squat speed or depth were identified between the groups, an analysis of covariance was also performed using the appropriate variable as a covariate. Results: The FAI and control groups were comparable for age, height, sex and BMI. FAI participants reported an average pain score of 2/10 during both the unconstrained and constrained squats. There were no between-group differences in squat depth for either task. Descent speed was slower for the FAI group during the unconstrained squat (P<0.05). There were no other between-group differences for this task. Participants with FAI demonstrated increased ipsilateral pelvic rise (P ¼ 0.04) and increased hip adduction (P ¼ 0.04) compared to controls during the