Summary
This study examined inertial measurement unit-derived knee kinematics and kinetics (tibial acceleration) during a hop-land task in 52 males and 62 females at late phase ACLR. Compared to their non-surgical limb, females showed lower knee flexion and tibial acceleration during landing in their surgical limb, which could be used clinically to improve female-specific outcomes post ACLR.
Abstract
Introduction
Females have higher risk and worse outcomes than males following ACL injury and subsequent reconstruction (ACLR) [1]. However, female-specific ACLR rehabilitation protocols and return to sport (RTS) testing do not exist to mitigate these risks. Targeted rehabilitation is challenging, as it relies on objective biomechanical data, which has been traditionally precluded from clinical settings. Thus, this study aimed to use clinically viable wearable sensors (inertial measurement unit; IMU) to examine knee kinematics and kinetics during a hop-land task in females and males during the late phase of their ACLR rehabilitation.
Methods
A cross-sectional study was conducted on 114 participants (62 females, 52 males) following unilateral ACLR during the late phase (9-12 months) of their rehabilitation. Eight IMUs (Xsens, Netherlands) were placed upon participants bilateral foot, tibial region, thigh, pelvis, and trunk and calibrated as per manufacturer recommendations. Participants then performed three trials for each limb of a triple forward hop task. The trial with the longest distance was selected for data analysis. Total hop distance was measured, and a limb symmetry index (LSI) calculated. Kinematic and kinetic outcomes were examined during the final land of the hop task. Knee flexion angle (°) was calculated as the difference between the thigh and tibial sensors rotation about the sensor’s longitudinal axis. Knee kinetics were quantified via resultant acceleration (g) of the IMU sensor located on the tibial region (i.e., tibial acceleration), given its established association with in vivo ACL force [2]. Knee flexion angles and tibial acceleration waveforms for each sex were compared between surgical and non-surgical limbs using statistical parametric mapping [3]. Peak knee flexion and tibial acceleration values at foot contact for each sex were compared between limbs using paired samples t-tests.
Results
Limb symmetry indexes for hop distance were 99% and 96% for males and females, respectively. Knee flexion was found to be lower in the operated limb compared to the non-surgical limb during 0-30% (p=0.027) and 65-100% (p=0.021) of stance for females; and 0-8% (p=0.047) for males. Compared to the non-surgical limb, tibial acceleration was lower in the surgical limb during 5.1-9.1% (p=0.044) of stance for females, with no statistical difference in males (p>0.05). Limb differences in kinematic and kinetic waveform features (mean [95% confidence intervals]) indicated lower peak knee flexion (-4.8° [-7.9, -1.7], p=0.003) and lower tibial acceleration at ground contact (-0.98g [-1.8, -0.17], p=0.019) during landing for females but not males (-2.2° [-5.9, 1.5], p=0.24) and (-0.93g [-1.96, 0.11], p=0.08).
Conclusion
These findings highlight an “underloading” landing pattern in the surgical limb for the female cohort, as quantified by reduced knee flexion during landing and lower tibial acceleration shortly after foot contact. [2]). Such a phenomenon was largely absent in the male cohort. Such parameters could be used clinically (via sensor biofeedback and/or rehabilitation protocol refinement) to improve female-specific outcomes post ACLR.
[1] Bruder et al., 2023. Br J Sports Med.10.1136/bjsports-2022-106099
[2] McLean et al., 2011. J Bone Joint Surg Am.10.2106/JBJS.J.00259
[3] Pataky et al. 2012. Comput Methods Biomed Engin. 10.1080/10255842.2010.527837