Knee Kinematics Are Related to Patient-Reported Outcomes 6 Months After Anatomic ACL Reconstruction

OBJECTIVES: Anterior cruciate ligament (ACL) reconstruction is among the most common procedures performed in orthopaedics. Patient reported outcomes (PRO) are widely utilized to evaluate symptoms, activity, and participation in sport after ACL reconstruction. Although altered in vivo knee kinematics after ACL reconstruction have been reported, the association with PRO has not been established. The purpose of this study was to determine the relationship between PRO and dynamic knee kinematics as tracked by a Dynamic Stereo X-ray system (DSX system). METHODS: Fifty subjects (33 males, age: 24.2 years ± 7.6, BMI: 24.7 ± 2.97) participating in a randomized clinical trial to compare anatomic single- and double-bundle ACL reconstruction underwent surgery using quadriceps tendon bone block autograft. Six months post-operatively, patients performed downhill treadmill running (3.0 meters/second, 10° slope) within a DSX system (150 hertz). Knee kinematics, determined using a validated process of matching DSX images and subject-specific tibiofemoral bone models derived from computed tomography scans, were expressed as a function of the gait cycle. Involved limb and differences in side-to-side kinematics were analyzed from foot-strike to mid-stance phase (0-15% gait cycle corresponding to the loading phase). Subjects also completed the International Knee Documentation Committee Subjective Knee Form (IKDC-SKF) and Knee Injury and Osteoarthritis Outcome Score (KOOS). Correlation coefficients were calculated to determine the associations between PRO and knee kinematics. RESULTS: Greater post-operative knee flexion and more symmetric restoration of knee flexion and axial rotation in comparison to the contralateral knee had the highest correlations with the IKDC-SKF and KOOS Sports and Recreation and Knee-Related Quality of Life subscales (p < 0.05). Symmetry of anterior tibial translation and varus-valgus rotation of the surgical knee were less strongly associated with PRO. CONCLUSION: Knee kinematics when running 6 months after ACL reconstruction were associated with patient-reported symptoms, activity, and participation levels. Therefore, clinicians should strive for anatomic precision during ACL reconstruction to optimally restore knee kinematics so as to achieve optimal PRO.