Are the ligaments contracted on the concave side of a deformed arthritic knee? – An MRI study

INTRODUCTION: The role of ligament contractures in arthritic knees with fixed flexion (FFD) or fixed varus deformities (FVD) remains controversial. This study aims to determine if the posterior cruciate ligament (PCL) or the superficial medial collateral ligament (sMCL) is contracted in arthritic knees with FFD and/or FVD. MATERIALS AND METHODS: Using Magnetic Resonance Imaging (MRI), the length of the PCL and sMCL were measured in four groups of patients; Group 1: Patients without knee Osteoarthritis (OA) or deformity, Group 2: Patients with OA but no deformity, Group 3: Patients with OA and an FFD and Group 4: Patients with OA and an FVD. One hundred knee MRIs were included in this study and each group consisted of 25 Knee MRIs. RESULTS: The PCL was significantly shorter in those patients with arthritis (Groups 2-4) regardless of whether they had a deformity or not (mean difference 5.0 mm, p < 0.0001). The sMCL was also shorter in patients with OA with an FFD and/or FVD (Groups 3 and 4) when compared to the groups with no deformity (Group 1 and 2), (difference 8.6 mm, p < 0.0001). CONCLUSION: This study shows that ligament contractures do exist in arthritic knees. The PCL is shortened in arthritic knees but seems to play little role in FFD. The sMCL is shortened in arthritic knees with an FFD and /or a varus deformity but is normal in length in arthritic knees with no deformity. These findings may influence the soft tissue balancing technique or implant choice during total knee arthroplasty.