The effect of powered ankle prostheses on muscle activity during walking.

Individuals with transtibial amputation (TTA) walk with greater muscle activity and metabolic costs than non-amputees. Powered prostheses aim to address these deficits by replicating the active function of the biological ankle. The purpose of this study was to determine if people with TTA alter muscle activity when walking with a powered prosthesis, and if this change relates to changes in metabolic costs. Ten individuals with TTA and 10 non-amputees walked on a treadmill while we measured metabolic cost and muscle activity from 16 lower limb muscles. Participants with TTA walked with their prescribed unpowered prosthesis and a commercial powered prosthesis (BiOM T2, Bedford, MA, USA), in random order. The integrated EMG across the gait cycle was greater with the powered prosthesis for the intact limb gluteus medius (p = 0.002) and residual limb vastus medialis (p = 0.013). There were several non-significant, moderate-to-strong correlations between changes in muscle activity and changes in metabolic cost between prostheses (p > 0.0504). Decreased muscle activity in the residual limb gluteus medius correlated with lower metabolic cost (r = 0.543). In contrast, lower metabolic cost was correlated with increased residual limb rectus femoris activity (r = -0.627) and increased co-contractions in the residual limb thigh muscles in terminal stance (r = -0.585) and late swing (r = -0.754). Overall, there were no consistent changes in muscle activity in response to the powered prosthesis. The correlations suggest that individuals who can effectively stabilize their residual limb during stance are more likely to benefit metabolically.

Choosing appropriate prosthetic ankle work to reduce the metabolic cost of individuals with transtibial amputation.

Powered ankle prostheses have been designed to reduce the energetic burden that individuals with transtibial amputation experience during ambulation. There is an open question regarding how much power the prosthesis should provide, and whether approximating biological ankle kinetics is optimal to reduce the metabolic cost of users. We tested 10 individuals with transtibial amputation walking on a treadmill wearing the BiOM powered ankle prosthesis programmed with 6 different power settings (0-100%), including a prosthetist-chosen setting, chosen to approximate biological ankle kinetics. We measured subjects' metabolic cost of transport (COT) and the BiOM's net ankle work during each condition. Across participants, power settings greater than 50% resulted in lower COT than 0% or 25%. The relationship between power setting, COT, and net ankle work varied considerably between subjects, possibly due to individual adaptation and exploitation of the BiOM's reflexive controller. For all subjects, the best tested power setting was higher than the prosthetist-chosen setting, resulting in a statistically significant and meaningful difference in COT between the best tested and prosthetist-chosen power settings. The results of this study demonstrate that individuals with transtibial amputation may benefit from prescribed prosthetic ankle push-off work that exceeds biological norms.

A controlled clinical trial of a clinically-tuned powered ankle prosthesis in people with transtibial amputation.

OBJECTIVE: To determine whether there are changes in level walking performance for people using a powered ankle prosthesis that was tuned by an independent, manufacturer-certified prosthetist in accordance with device recommendations. DESIGN: Intervention study with cross-over design. SETTING: Laboratory. PARTICIPANTS: Convenience sample of 10 individuals with unilateral, transtibial amputation, and 10 age- and gender-matched control participants. INTERVENTIONS: Powered ankle prosthesis (BiOM T2 Ankle System). Main outcome metrics: Metabolic costs of walking, preferred walking speed. RESULTS: There were no significant differences in oxygen consumption (2.9% difference; P = 0.606, d = 0.26), cost of transport (~1% difference; P = 0.652, d = 0.23), or preferred walking speed (~1% difference; P = 0.147, d = 0.76) when using the powered ankle compared to unpowered prostheses. Secondary analyses of user characteristics revealed that participants who were classified as having the highest function (K4 on Medicare's 5-point scale from K0 to K4) were significantly more likely to exhibit energy cost savings than those classified as having lower function (K3; P = 0.014, d = 2.36). CONCLUSIONS: Participants did not demonstrate significant improvements in energetics or preferred speed when wearing a clinically tuned powered ankle prosthesis compared to their non-powered prostheses. Prescribers of powered devices should understand that not all users will show an immediate reduction in energy expenditure.

Decreased Knee Joint Loading Associated With Early Knee Osteoarthritis After Anterior Cruciate Ligament Injury.

BACKGROUND: Anterior cruciate ligament (ACL) injury predisposes individuals to early-onset knee joint osteoarthritis (OA). Abnormal joint loading is apparent after ACL injury and reconstruction. The relationship between altered joint biomechanics and the development of knee OA is unknown. HYPOTHESIS: Altered knee joint kinetics and medial compartment contact forces initially after injury and reconstruction are associated with radiographic knee OA 5 years after reconstruction. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: Individuals with acute, unilateral ACL injury completed gait analysis before (baseline) and after (posttraining) preoperative rehabilitation and at 6 months, 1 year, and 2 years after reconstruction. Surface electromyographic and knee biomechanical data served as inputs to an electromyographically driven musculoskeletal model to estimate knee joint contact forces. Patients completed radiographic testing 5 years after reconstruction. Differences in knee joint kinetics and contact forces were compared between patients with and those without radiographic knee OA. RESULTS: Patients with OA walked with greater frontal plane interlimb differences than those without OA (nonOA) at baseline (peak knee adduction moment difference: 0.00 ± 0.08 N·m/kg·m [nonOA] vs -0.15 ± 0.09 N·m/kg·m [OA], P = .014; peak knee adduction moment impulse difference: -0.001 ± 0.032 N·m·s/kg·m [nonOA] vs -0.048 ± 0.031 N·m·s/kg·m [OA], P = .042). The involved limb knee adduction moment impulse of the group with osteoarthritis was also lower than that of the group without osteoarthritis at baseline (0.087 ± 0.023 N·m·s/kg·m [nonOA] vs 0.049 ± 0.018 N·m·s/kg·m [OA], P = .023). Significant group differences were absent at posttraining but reemerged 6 months after reconstruction (peak knee adduction moment difference: 0.02 ± 0.04 N·m/kg·m [nonOA] vs -0.06 ± 0.11 N·m/kg·m [OA], P = .043). In addition, the OA group walked with lower peak medial compartment contact forces of the involved limb than did the group without OA at 6 months (2.89 ± 0.52 body weight [nonOA] vs 2.10 ± 0.69 body weight [OA], P = .036). CONCLUSION: Patients who had radiographic knee OA 5 years after ACL reconstruction walked with lower knee adduction moments and medial compartment joint contact forces than did those patients without OA early after injury and reconstruction.

Knee contact force asymmetries in patients who failed return-to-sport readiness criteria 6 months after anterior cruciate ligament reconstruction.

BACKGROUND: After anterior cruciate ligament (ACL) injury, contact forces are decreased in the injured knee when compared with the uninjured knee. The persistence of contact force asymmetries after ACL reconstruction may increase the risk of reinjury and may play an important role in the development of knee osteoarthritis in these patients. Functional performance may also be useful in identifying patients who demonstrate potentially harmful joint contact force asymmetries after ACL reconstruction. HYPOTHESIS: Knee joint contact force asymmetries would be present during gait after ACL reconstruction, and performance on a specific set of validated return-to-sport (RTS) readiness criteria would discriminate between those who demonstrated contact force asymmetries and those who did not. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 29 patients with ACL ruptures participated in gait analysis and RTS readiness testing 6 months after reconstruction. Muscle and joint contact forces were estimated using an electromyography (EMG)-driven musculoskeletal model of the knee. The magnitude of typical limb asymmetry in uninjured controls was used to define limits of meaningful limb asymmetry in patients after ACL reconstruction. The RTS testing included isometric quadriceps strength testing, 4 unilateral hop tests, and 2 self-report questionnaires. Paired t tests were used to assess limb symmetry for peak medial and tibiofemoral contact forces in all patients, and a mixed-design analysis of variance was used to analyze the effect of passing or failing RTS testing on contact force asymmetry. RESULTS: Among all patients, neither statistically significant nor meaningful contact force asymmetries were identified. However, patients who failed RTS testing exhibited meaningful contact force asymmetries, with tibiofemoral contact force being significantly lower for the involved knee. Conversely, patients who passed RTS testing exhibited neither significant nor meaningful contact force asymmetries. CONCLUSION: Joint contact force asymmetries during gait are present in some patients 6 months after ACL reconstruction. Patients who demonstrated poor functional performance on RTS readiness testing exhibited significant and meaningful contact force asymmetries. CLINICAL RELEVANCE: When assessing all patients together, variability in the functional status obscured significant and meaningful differences in contact force asymmetry in patients 6 months after ACL reconstruction. These specific RTS readiness criteria appear to differentiate between those who demonstrate joint contact force symmetry after ACL reconstruction and those who do not.

Clinically-relevant measures associated with altered contact forces in patients with anterior cruciate ligament deficiency.

BACKGROUND: Knee joint contact forces are altered after anterior cruciate ligament injury during walking and may be related to clinically-relevant measures of impairments or self-reported function. The purpose of this study was to investigate the association of several clinically-relevant measures with altered knee contact forces in patients with anterior cruciate ligament injury. METHODS: Data for this study represent a cross-sectional observational analysis of thirty-seven (23 M, 14 F) patients with complete unilateral anterior cruciate ligament injury. Gait analysis with electromyography was used to obtain estimates of tibiofemoral joint contact force using an electromyography-driven musculoskeletal model. Multivariable linear regression was used to identify measures associated with tibiofemoral joint contact force. FINDINGS: Involved knee extensor muscle strength and patient-reported knee function on the Global Rating Scale of perceived function were significantly associated with peak tibiofemoral contact force for the involved limb. Patients who were stronger and who perceived higher knee function walked with greater contact forces on their involved knees. After controlling for walking speed, involved extensor strength explained 8.9% of the variance in involved peak tibiofemoral contact force and score on the Global Rating Scale explained an additional 9.4% of the variance. INTERPRETATION: Improvements in involved quadriceps strength and overall function as measured by patient self-report may be important for increasing involved limb contact forces, thereby restoring loading symmetry in these patients who demonstrate decreased involved limb loading after injury. These results highlight the potential value of studying the recovery of strength, self-reported function and joint loading symmetry in patients with anterior cruciate ligament injury.

Minimum detectable change for knee joint contact force estimates using an EMG-driven model.

UNLABELLED: Adequate test-retest reliability of model estimates is a necessary precursor to examining treatment effects or longitudinal changes in individuals. PURPOSE: The purpose of this study was to establish thresholds for minimal detectable change (MDC) for joint contact forces obtained using a patient specific EMG-driven musculoskeletal model of the knee. DESIGN: A sample of young, active individuals was selected for this study, and subjects were tested on 2 separate days. Three-dimensional motion analysis with electromyography (EMG) was used to obtain data from each subject during gait for model input. An EMG-driven modeling approach was used to estimate joint contact forces at each session. RESULTS: MDC's for contact force variables ranged from 0.30 to 0.66 BW. The lowest MDC was for peak medial compartment force (0.30 BW) and the highest was for peak tibiofemoral contact force (0.66 BW). Test-retest reliability coefficients were also reported for comparison with previous work. CONCLUSIONS: Using the present model, changes in joint contact forces between baseline and subsequent measurements that are greater than these MDCs are greater than typical day-to-day variation and can be identified as real change.

Gait patterns differ between ACL-reconstructed athletes who pass return-to-sport criteria and those who fail.

BACKGROUND: The current standard of practice for an athlete to return to sport after anterior cruciate ligament (ACL) reconstruction is varied. Attempt to return to activity is typically advised 6 months after surgery, but functional performance deficits and gait abnormalities are often still evident and may have important implications on future function. HYPOTHESIS: When comparing the involved and uninvolved limbs, patients who failed return-to-sport (RTS) criteria would demonstrate (1) smaller peak knee angles, extensor moments, and peak power absorption at the knee of the involved limb and (2) larger peak hip angles, extensor moments, and peak power generation of the involved limb. STUDY DESIGN: Controlled laboratory study. METHODS: A total of 42 patients completed functional and biomechanical gait assessment 6 months after ACL reconstruction. Functional testing involved an isometric quadriceps strength test, 4 single-legged hop tests, and 2 self-report questionnaires. Three-dimensional motion analysis was used to measure sagittal plane kinematics and kinetics of the hip and knee. A mixed-model analysis of variance and post hoc t tests were used to compare the limb symmetry of those who passed and those who did not pass RTS criteria. Minimal clinically important differences were calculated from healthy gait data and used to further define meaningful limb asymmetries. RESULTS: Twenty of the 42 (48%) patients passed RTS criteria 6 months after ACL reconstruction. Patients who did not pass the criteria demonstrated statistically significant differences between limbs on all kinematic and kinetic variables at the knee (P ≤ .027). Clinically meaningful asymmetries at the hip were also identified in this group. Only kinetic asymmetries at the knee were identified in the patients who passed RTS criteria. CONCLUSION: Athletes who demonstrate superior functional performance 6 months after ACL reconstruction may have fewer abnormal and asymmetrical gait behaviors than their poorer performing counterparts. Patients who did not pass RTS criteria not only demonstrated larger kinematic and kinetic asymmetries between limbs but also appeared to use a gait strategy more closely aligned with athletes early after ACL rupture. CLINICAL RELEVANCE: Poor performance on a battery of functional performance measures may be related to the presence of movement asymmetries in athletes after ACL reconstruction. Objective RTS criteria have the potential to provide information to clinicians who determine when these athletes return to activity, and may aid in the prescription of targeted rehabilitation to address underlying movement asymmetry.

Altered loading in the injured knee after ACL rupture.

Articular loading is an important factor in the joint degenerative process for individuals with anterior cruciate ligament (ACL) rupture. Evaluation of loading for a population that exhibits neuromuscular compensation for injury requires an approach which can incorporate individual muscle activation strategies in its estimation of muscle forces. The purpose of this study was to evaluate knee joint contact forces for patients with ACL deficiency using an EMG-driven modeling approach to estimate muscle forces. Thirty athletes with acute, unilateral ACL rupture underwent gait analysis after resolving range of motion, effusion, pain, and obvious gait impairments. Electromyography was recorded bilaterally from 14 lower extremity muscles and input to a musculoskeletal model for estimation of muscle forces and joint contact forces. Gait mechanics were consistent with previous reports for individuals with ACL-deficiency. Our major finding was that joint loading was altered in the injured limb after acute ACL injury; patients walked with decreased contact force on their injured knee compared to their uninjured knee. Both medial and lateral compartment forces were reduced without a significant change in the distribution of tibiofemoral load between compartments. This is the first study to estimate medial and lateral compartment contact forces in patients with acute ACL rupture using an approach which is sensitive to individual muscle activation patterns. Further work is needed to determine whether this early decreased loading of the injured limb is involved in the development of osteoarthritis in these patients.

Gait and neuromuscular asymmetries after acute anterior cruciate ligament rupture.

UNLABELLED: The decreased internal knee extensor moment is a significant gait asymmetry among patients with anterior cruciate ligament (ACL) deficiency, yet the muscular strategy driving this altered moment for the injured limb is unclear. PURPOSE: This study aimed to determine whether patients with ACL deficiency and characteristic knee instability would demonstrate normal extensor and increased flexor muscle force to generate a decreased internal extensor moment (i.e., use a hamstring facilitation strategy). METHODS: Gait analysis was performed on 31 athletes with acute ACL rupture who exhibited characteristic knee instability after injury. Peak internal knee extensor moment was calculated using inverse dynamics, and muscle forces were estimated using an electromyography-driven modeling approach. Comparisons were made between the injured and contralateral limbs. RESULTS: As expected, patients demonstrated decreased peak knee flexion (P = 0.028) and internal knee extensor moment (P = 0.0004) for their injured limb but exhibited neither an isolated decrease in extensor force (quadriceps avoidance) nor an isolated increase in flexor force (hamstring facilitation) at peak knee moment. Instead, they exhibited decreased muscle force from both flexor (P = 0.0001) and extensor (P = 0.0103) groups. This strategy of decreased muscle force may be explained in part by muscle weakness that frequently accompanies ACL injury or by apprehension, low confidence, and fear of further injury. CONCLUSIONS: This is the first study to estimate muscle forces in the ACL-deficient knee using an electromyography-driven approach. These results affirm the existence of neuromuscular asymmetries in the individuals with ACL deficiency and characteristic knee instability.