Patterns of femorotibial cartilage loss in knees with neutral, varus, and valgus alignment.

OBJECTIVE: Malalignment is known to alter medial-to-lateral femorotibial load distribution and to affect osteoarthritis (OA) progression in the mechanically stressed compartment. We investigated the pattern of cartilage loss in neutral, varus, and valgus knees.
METHODS: Alignment was measured from full-limb radiographs in 174 participants with symptomatic knee OA. Coronal magnetic resonance images were acquired at baseline and a mean +/- SD of 26.6 +/- 5.4 months later. The weight-bearing femorotibial cartilages were segmented from paired images. Cartilage volume, surface area, and thickness were determined in total cartilage plates and defined subregions using proprietary software.
RESULTS: The medial-to-lateral ratio of femorotibial cartilage loss was 1.4:1 in neutral knees (n = 74), 3.7:1 in varus knees (n = 57), and 1:6.0 in valgus knees (n = 43). The relative contribution of cartilage thickness change tended to be greater in knees with mild cartilage loss, whereas the increase of denuded area was greater in knees with accelerated cartilage loss. In both varus and neutral knees, the greatest changes were observed in the same subregions of the medial femorotibial compartment (central and external medial tibia, and central medial femur). In valgus and neutral knees, the subregions with the greatest changes in the lateral femorotibial compartment were also similar (internal and central lateral tibia, external lateral femur).
CONCLUSION: The medial-to-lateral rate of femorotibial cartilage loss strongly depended on alignment. Subregions of greater-than-average cartilage loss within the stressed compartment were, however, similar in neutral, varus, and valgus knees. This indicates that the medial-to-lateral loading pattern is different, but that the (sub)regional loading pattern may not differ substantially between neutral and malaligned knees.