Knee Joint Morphology and Biomechanics in Athletes and People Following ACL Reconstruction

Abstract

Comprehensive understanding of knee biomechanics and bone morphology remains crucial for advancing treatment strategies for knee pathologies. Despite this importance, current research provides insufficient data on knee bone morphology and biomechanical function during activities of daily living, particularly regarding athletic populations and individuals following anterior cruciate ligament reconstruction (ACLR) surgery. This thesis addresses these knowledge gaps through measuring and describing: (a) the structural profile (i.e. geometrical shapes) of knee bones (i.e. femur, tibia, and patella), and (b) the knee biomechanical profiles at the tibiofemoral (TF) and patellofemoral (PF) joints in athletic populations and individuals following ACLR surgery. The methodology employed precise measurement of patellofemoral and tibiofemoral joint kinematics (i.e. 6-degree-of-freedom motion) and arthrokinematics (i.e. condylar motion, location of TFJ center of rotation, and the location of the contact centers) parameters, during activities of daily living (i.e. level walking, downhill walking, and stair ascent). Advanced statistical-shape-modeling approaches were utilized, alongside linear measurements, to detect morphological differences. Four knee groups were analyzed: intact knees of athletes (HKA), intact knees of non-athletes (HKS), ACL reconstructed knees of athletes (ACLR), and their contralateral knees (Contra), through six comprehensive comparisons. The methodology includes a) one comparison between athlete and non-athlete knees [i.e. HKA vs control group (HKS)] to explore the structural & biomechanical profiles of the athletic knees, along with b) five comparisons to explore the structural & biomechanical profiles of the reconstructed knees [i.e. ACLR vs its control groups (Contra, HKA, and HKS)] and their contralateral knees [i.e. Contra vs its control groups (HKA and HKS)].

The morphological findings revealed distinct patterns of bone remodeling (i.e. bone shape changes) across knee bones, characterized by coordinated changes. ACLR knees exhibited ovoid femoral condyles, narrower intercondylar notches, increased distal sulcus angle, along with posteromedial tibial enlargement and greater patellar convexity. Contralateral knees displaying intermediate morphological changes that challenge the conventional use of the uninjured limb as a control reference. Healthy athletic knees demonstrated distinct morphological adaptations, including wider intercondylar notches and modified plateau slopes. Our comprehensive morphological assessment reveals remarkable plasticity of the knee joint complex, highlighting crucial implications for surgical planning, rehabilitation protocols, and long-term joint health management.

The biomechanical findings, utilizing mobile biplane X-ray imaging system, revealed deviations from normal knee joints’ kinematics and arthrokinematics. Specifically, both ACLR and contralateral knees exhibited enhanced anterior patellar translation, greater patellar extension, persistent medial tibial shift, and increased anterior tibial translation. ACLR knees showed reduced tibial internal rotation along with "quadriceps avoidance" gait patterns, characterized by minimal flexion range changes. Condylar motion analysis reveals posterior displacement of the medial femoral condyle and a deficit in the natural femoral rollback mechanism in ACLR knees, while both ACLR and contralateral knees display reduced medial-lateral range of motion. Healthy athletic knees exhibit elevated lateral tibial shifts, superior patellar translation, and posterior condylar shifts. The center of rotation of the TFJ shifts posteriorly in ACLR, contralateral and athletic knees. Contact kinematics analysis shows that athletic populations demonstrate more lateral and superior femoral contact (in the medial compartment) while both ACLR and contralateral knees show greater medially-directed shift of femoral contact location (in the lateral compartment).

Task-specific strategies during ramp descent and stair ascent revealed different kinematic patterns than level walking, emphasizing limitations of relying solely on level walking assessments in post-ACLR evaluations. These findings underscore the complex association between surgical intervention, athletic training, and joint mechanical adaptation, necessitating comprehensive rehabilitation accounting for TFJ and PFJ mechanics, bilateral adaptations, and task-specific demands. This PhD research provides insights into detection, diagnosis, and management of prevalent knee problems while serving as a foundation for future investigations into knee joint function and adaptation mechanisms.