THE EFFECT OF ACL RECONSTRUCTION ON TOTAL JOINT WORK AND JOINT WORK CONTRIBUTIONS

Abstract

Context: Increased long-term risk of developing knee osteoarthritis (OA) following anteriorcruciate ligament reconstruction (ACLR) is widely established. Mechanical loading plays a significant role in keeping articular cartilage healthy. Examining the mechanical joint work in joints or legs offers the potential to provide a fuller understanding of overall knee loading because it encompasses exposure to both positive and negative power throughout the entire stance phase. Persistent compensatory underloading of the knee during running may play a critical role in driving cellular and metabolic changes associated with the progression of knee OA. Therefore, the purpose of this study was to examine differences in sagittal plane joint work during running between ACLR (ACL) and healthy control (MATCHED) subjects at least two years after unilateral ACLR. Methods: Running biomechanics of 37 ACLR (27.0 ± 6.6yr, 1.7 ± 0.1m, 75.6 ± 21.1kg; 23 females; 8.3 ± 5.3 years post-ACLR) and 37 healthy control subjects (24.6 ± 4.7yr, 1.7 ± 0.1m, 73.0 ± 20.1kg; 23 females) were evaluated. Current activity levels were evaluated with the Tegner Activity Scale (5.84 ± 1.4 ACLR, 5.73 ± 1.6 CON). Subjects performed trials running at a velocity of 4.0 m/s-1 ± 10%. The ACLR limb was individually matched to CON via limb dominance. Kinematics were collected at 240Hz via 3D motion capture system (Vicon, Colorado, USA); kinetics were collected at 960Hz using a force plate (AMTI, Massachusetts, USA). Kinematic and kinetic data were smoothed using a Butterworth filter with a 10Hz cut-off frequency, except for ground reaction force which was filtered at 50 Hz, and processed using Visual 3D (C-Motion, Inc., Germantown, MD). T-tests were used to determine differences in gait-related variables during stance between ACLR vs their contralateral limb (CONTRA) and vs CON matched limbs. Sagittal plane work was calculated by taking the integral of the pow\]er curve during stance via the trapezoidal rule. Total joint work was 1 calculated as the absolute value of positive and negative work. Total leg work was calculated as the sum of hip, knee, and ankle work while the percentage of total joint work to total leg work represented the joint work contribution. Results: Total negative knee work and total knee work were significantly (P<0.05) lower in the ACLR limb than in the matched CON limb. The largest differences were demonstrated between ACLR and CONTRA limbs which included total negative knee work, total positive knee work, total knee work, total leg work, knee work contribution, and ankle work contribution (Table 1). Conclusions: ACLR limbs with an average of 8 years post-surgery demonstrated lower knee joint work loading during running than their CONTRA limb and matched CON limbs. Consequently, ACLR limbs demonstrated a compensatory pattern of increasing the percentage of ankle work contribution in response to the reduced knee joint work contribution. Similar reports of long-term abnormal underloading of discrete gait variables following ACLR have been associated with cartilage thinning and degeneration. Joint work may provide a more comprehensive representation of loading exposure and volume over stance. These chronic underloading patterns of the knee during gait may influence long-term cartilage degeneration and increased risks of developing OA within 10-20 years after ACLR.