Kristamarie A. Pratt

Knee loading asymmetries during gait and running in early rehabilitation following anterior cruciate ligament reconstruction: A longitudinal study☆

BACKGROUND Normalization of gait is expected 8-12 weeks after anterior cruciate ligament reconstruction and is a criterion for progression to running. Long-term persistence of sagittal knee loading deficits suggests that early goals are not met. Magnitude and progression of deficits in gait during this time and their relationship to deficits in running are not known. METHODS 12 individuals status-post reconstruction (5 males) underwent 3-dimensional motion analysis of gait after surgery: one (T1) and three (T2) months and at initiation of running (T3); and running T3. Repeated measures ANOVAs (limb × time) assessed differences in knee flexion, extensor moment impulse and negative work in gait; paired t-tests compared limbs during running; and Pearsons correlations determined associations between limb ratios (moment and work) in gait and running. FINDINGS Less flexion (-4.4 (0.63) degrees; mean (SE)), 35% smaller extensor moment (-0.15 (0.006) Nm∗s/kg) and 47% less work (-0.03 (0.008) J/kg) were observed in the surgical knee during gait across time. Moment and work were 1.7 (-0.1 (0.03) Nm∗s/kg) and 1.6 times greater (-0.23 (0.047) J/kg) in non-surgical knee during running. Moment and work limb asymmetries correlated across time during gait (r=0.778-0.929, P<0.001) and to asymmetries during running. INTERPRETATION Limb asymmetries in knee loading present one month after reconstruction persist 4 months post-reconstruction. Correlations between limb asymmetries during gait across time and to running suggest that early gait behaviors relate to longer-term loading. Greater attention should be placed on early gait training.

Knee Loading Deficits During Dynamic Tasks in Individuals Following Anterior Cruciate Ligament Reconstruction

•STUDY DESIGN: Controlled laboratory study, cross‐sectional. •BACKGROUND: Well‐documented deficits in sagittal plane knee loading during dynamic tasks indicate that individuals limit the magnitude of knee loading following anterior cruciate ligament reconstruction (ACLR). It is unknown how these individuals modulate the speed of knee flexion during loading, which is particularly important as they progress to running during rehabilitation. •OBJECTIVE: To investigate how individuals following ACLR perform dynamic knee loading tasks compared to healthy controls. •METHODS: Two groups of recreationally active individuals participated: 15 healthy controls and 15 individuals post‐ACLR (ACLR group). Participants performed 3 trials of overground running and a single‐limb loading (SLL) task. Sagittal plane range of motion, peak knee extensor moment, peak knee flexion angular velocity, peak knee power absorption, and rate of knee extensor moment were calculated during deceleration. A mixed‐factor multivariate analysis of variance was performed to compare differences in variables between groups (ACLR and control), limbs (within ACLR), and tasks (within control). •RESULTS: Knee power absorption, knee flexion angular velocity, and rate of knee extensor moment were lower in reconstructed limbs (for the SLL task: 5.6 W/kg, 325.8°/s, and 10.5 Nm/kg/s, respectively; for running: 11.8 W/kg, 421.4°/s, and 38.2 Nm/kg/s, respectively) compared to nonsurgical limbs (for the SLL task: 9.7 W/kg, 432.0°/s, and 19.1 Nm/kg/s, respectively; for running: 18.8 W/kg, 494.1°/s, and 72.8 Nm/kg/s, respectively) during both tasks (P<.001). The magnitudes of between‐limb differences in knee flexion angular velocity were similar in both tasks. •CONCLUSION: Despite lower loading demands during SLL, individuals post‐ACLR exhibit deficits in knee dynamics during SLL and running, suggesting an inability or reluctance to dynamically accommodate forces at the knee when progressing to running in rehabilitation. •KEY WORDS: anterior cruciate ligament reconstruction, kinetics, knee, rehabilitation, running

Detection of Knee Power Deficits Following ACL Reconstruction Using Wearable Sensors

BACKGROUND Following anterior cruciate ligament reconstruction (ACLR), individuals present with significant knee power absorption deficits during deceleration of dynamic tasks. An inability to quantify these deficits clinically may underlie their persistence. Recent studies suggest that segment angular velocities measured with wearable inertial sensors have the potential to provide valuable information about knee power during a single-limb loading (SLL) task. However, the diagnostic accuracy of these measures and procedures needs to be established before translating this information to clinical practice. OBJECTIVE To determine the diagnostic accuracy of using inertial-sensor thigh angular velocities to detect asymmetrical knee loading during a dynamic SLL task in individuals following ACLR. METHODS In this controlled laboratory study, 21 individuals following ACLR performed 3 trials of SLL on each limb. Sagittal plane peak knee power absorption was calculated for each limb (reconstructed and nonsurgical) during deceleration. Between-limb ratios (reconstructed/nonsurgical limb) were calculated for knee power using marker-based motion analysis, and thigh angular velocity was extracted from inertial sensors. Sensitivity and specificity of thigh angular velocity ratios in diagnosing asymmetrical knee loading (knee power deficits greater than 15%) were determined using receiver operating characteristic curve analysis. RESULTS Thigh angular velocity ratios detected asymmetrical knee loading when performing SLL with high sensitivity (81%) and specificity (100%). CONCLUSION These findings support the use of cost-effective wearable sensors to objectively quantify movement clinically in this population of individuals following ACLR. This study establishes procedures for the clinical quantification of dynamic knee loading deficits. J Orthop Sports Phys Ther 2018;48(11):895-902. Epub 11 Jul 2018. doi:10.2519/jospt.2018.7995.

Inertial Sensor Angular Velocities Reflect Dynamic Knee Loading during Single Limb Loading in Individuals Following Anterior Cruciate Ligament Reconstruction

Difficulty quantifying knee loading deficits clinically in individuals following anterior cruciate ligament reconstruction (ACLr) may underlie their persistence. Expense associated with quantifying knee moments (KMom) and power (KPow) with gold standard techniques precludes their use in the clinic. As segment and joint kinematics are used to calculate moments and power, it is possible that more accessible inertial sensor technology can be used to identify knee loading deficits. However, it is unknown if angular velocities measured with inertial sensors provide meaningful information regarding KMom/KPow during dynamic tasks post-ACLr. Twenty-one individuals 5.1 ± 1.5 months post-ACLr performed a single limb loading task, bilaterally. Data collected concurrently using a marker-based motion system and gyroscopes positioned lateral thighs/shanks. Intraclass correlation coefficients (ICC)(2,k) determined concurrent validity. To determine predictive ability of angular velocities for KMom/KPow, separate stepwise linear regressions performed using peak thigh, shank, and knee angular velocities extracted from gyroscopes. ICCs were greater than 0.947 (p < 0.001) for all variables. Thigh (r = 0.812 and r = 0.585; p < 0.001) and knee (r = 0.806 and r = 0.536; p < 0.001) angular velocities were strongly and moderately correlated to KPow and KMom, respectively. High ICCs indicated strong agreement between measurement systems. Thigh angular velocity (R2 = 0.66; p < 0.001) explained 66% of variance in KPow suggesting gyroscopes provide meaningful information regarding KPow. Less expensive inertial sensors may be helpful in identifying deficits clinically.

Compensatory Strategies That Reduce Knee Extensor Demand During a Bilateral Squat Change From 3 to 5 Months Following Anterior Cruciate Ligament Reconstruction

• BACKGROUND: Decreased extensor moments in the surgical knee during bilateral squats can persist beyond 1 year following anterior cruciate ligament reconstruction (ACLR). This is accomplished using interlimb and intralimb compensations. • OBJECTIVES: This study sought to assess loading during squatting longitudinally, 3 and 5 months post ACLR, and to determine the extent to which interlimb and intralimb compensations contribute to reduced knee extensor moments. • METHODS: In this controlled, longitudinal laboratory study, 11 individuals (4 male) underwent 3‐D motion analysis of a squat at 3 and 5 months post ACLR. A repeated‐measures multivariate analysis of variance (limb by time) assessed differences in peak knee and hip flexion angles, knee extensor moment, vertical ground reaction force, and hip‐to‐knee extensor moment ratio. Stepwise linear regression analysis was used to determine the contribution of interlimb (between‐limb vertical ground reaction force ratio) and intralimb (within‐surgical‐limb hip‐to‐knee moment ratio) compensations to the between‐limb knee extensor moment ratio. • RESULTS: A significant effect of limb was observed for knee flexion angle, knee extensor moment, vertical ground reaction force, and hip‐to‐knee extensor moment ratio, while a significant effect of time was observed for knee extensor moment and hip‐to‐knee extensor moment ratio. At 3 months, the vertical ground reaction force ratio and hip‐to‐knee extensor moment ratio predicted the knee extensor moment ratio (R2 = 0.854, P<.001). At 5 months, the hip‐to‐knee extensor moment ratio predicted the knee extensor moment ratio (R2 = 0.584, P = .006). • CONCLUSION: Individuals used interlimb and intralimb compensations to reduce the knee extensor moment of the surgical limb at 3 months post ACLR. Similar reductions in the knee extensor moment at 5 months were accomplished with only intralimb compensations. • KEY WORDS: anterior cruciate ligament reconstruction, interlimb compensation, intralimb compensation, knee extensor moment deficit, rehabilitation