George Dehn, David Kieser, Rod Maxwell, Gary Hooper, Chris Frampton and Mark Coates
Aim: Cam impingement in the hip is well recognised with the relative incongruity between the femoral head and acetabulum implicated in the development of osteoarthritis (OA). We propose that a similar situation may occur in the knee joint and explain the commonly observed anteromedial OA in medial compartment disease. This study asked whether a relatively larger femoral condyle could cause impingement on the smaller tibial articular surface and result in early osteoarthritis (OA).
Methods: A retrospective randomised study of 400 age and sex matched knee x-ray and MRI scans of patients aged between 40 and 60 years was performed. Patients with any conditions that could affect their knee joint congruence or predispose them to degenerative changes were excluded. Measurements of the femoral and tibial articular surfaces were performed in the coronal and sagittal planes. The degree of OA was assessed with the modified ICRS grading system. Inter- and intra-observer bias was measured.
Results: There were 234 knees with OA,171 (42.7%) with medial compartment OA, 35 (8.8%) lateral compartment OA and 28 (7%) with bicompartment OA. A significant difference was found between the ratio of the coronal width of the medial femoral condyle and the medial tibial plateau in the presence of early OA (0.85, 95% CI 0.842-0.858) compared those without OA (0.91, 95% CI 0.902-0.919) (p=0.001), and for the same comparison on the lateral side (0.866, (95% CI 0.853-0.879) for knees with OA and 0.917 (95% CI 0.911-0.924) without OA) (p=0.001). Additionally, knees with medial compartment OA had a relative ratio (comparison between medial and lateral ratios) of 0.905 (95% CI 0.896-0.913) compared to 0.993 in knees without OA (95% CI 0.984-1.002) (p=0.001).
Conclusion: Knees with OA had a significantly smaller femur to tibia coronal articular surface ratio. These findings did not support impingement of the femur on the tibial articular surface as a cause for OA. Given this previously unrecognised association, further research is needed to confirm and determine its clinical effect.