Abstract
Introduction
Tibial patho-morphology has been described as a factor that predisposes to medial compartment osteoarthritis of the knee in 2D analysis. The aim of this study was to investigate whether the morphology of normal and pre-OA medial compartments are really different in 3 dimensions.
Method
A total of 20 normal (group A) and 20 pre-OA knees (group B) were included. Group A consisted of contra-lateral knees of young patients awaiting hip surgery and group B of asymptomatic contra-lateral knees of patients awaiting unicompartmental knee arthroplasty (UKA).
Using 3D reconstructions from CT scans, femurs were aligned to the transcondylar and anatomical axes. The medial femoral extension facet was modelled as a sphere. Its radius and the offsets between its centre and the medial flexion facet centre were measured. The tibias were aligned to a flat portion of the flexion facet (flexion facet plane. A model of analysis was developed by rotating several increments towards and away from the midline to obtain several sagittal section images. For each sagittal section the extension facet angle (EFA), its length, and the submeniscal plane angle and length were analysed.
Results
The medial femoral extension facet was larger and more offset in pre-OA knees (radius 43 vs 40 mm). The tibial extension facets appeared similar. The EFA varied considerably across the anterior face of the medial plateau (10.3o–18.8o). The submeniscal plane was on average horizontally inclined (median 0o, range -15–14o) and formed a crescent shape anteriorly. There was no significant difference in tibial measured parameters between normal and pre-OA tibias (p>0.05). The method showed good reproducibility (ICC value>0.9).
Discussion
We have found evidence of a predisposing pathomorphology to medial OA, but in the femoral condyle, not the tibia. There is an enlarged extension facet on the medial femoral condyle in the pre-OA knees. There was no significant difference in the geometry of the medial tibial plateau.
