Little is known about risk factors for patellofemoral (PF) osteoarthritis (OA). The lateral vector at the PF joint increases the likelihood of lateral PF versus medial PF pathology. Both valgus and varus malalignments affect forces at the PF joint and may predispose to PF OA. We examined whether lateral PF OA is more common than medial PF OA, whether valgus malalignment is more frequent in lateral PF OA than in medial PF OA, and whether knees with PF OA are more often valgus than knees with isolated tibiofemoral (TF) OA.
In 292 knee OA patients, we obtained semiflexed, fluoroscopy-confirmed radiographs of the TF joint and weight-bearing, 30° flexion, axial views of the PF joint. Varus–valgus alignment (the angle formed by the intersection of the mechanical axes of the femur and tibia) was measured on a full-limb radiograph.
Lateral PF OA was more common than medial PF OA (P < 0.0001). Forty-three of 75 knees with lateral PF OA had valgus malalignment compared with only 5 of 21 patients with medial PF OA (P = 0.0066). Conversely, varus malalignment was more likely in the medial PF OA group. Knees with isolated PF OA were more likely to have valgus malalignment than those with isolated TF OA (P = 0.0002), as were knees with mixed PF–TF OA (P = 0.0006).
Varus–valgus alignment may influence the risk of PF OA and, in particular, which compartment is affected.