Characterisation of size and direction of osteophyte in knee osteoarthritis: a radiographic study

Objectives: To examine the size and direction of osteophyte in knee osteoarthritis (OA) and to determine associations between osteophyte size and other radiographic features. Methods: Knee radiographs (standing extended anteroposterior and 30 degrees flexion skyline views) were examined from 204 patients referred to hospital with symptomatic knee OA (155 women, 49 men; mean age 70, range 34-91 years). A single observer assessed films for osteophyte size and direction at eight sites; narrowing in each compartment; varus/valgus angulation; patellofemoral subluxation; attrition; and chondrocalcinosis using a standard atlas, direct measurement, or visual assessment. For analysis, one OA knee was selected at random from each subject. Results: Osteophyte direction at the eight sites was divisible into five categories. At all sites, except for the lateral tibial plateau and the medial patella, osteophyte direction varied according to (a) the size of osteophyte and (b) the degree of local narrowing. At the medial femur, medial tibia, and lateral femur osteophyte direction changed from being predominantly horizontal to predominantly vertical with increasing size. The size of osteophyte correlated positively with the severity of local narrowing, except for the medial patellofemoral compartment where osteophyte size correlated positively with the severity of narrowing in the medial tibiofemoral compartment. Logistic regression analysis showed that osteophyte size was associated not only with local narrowing but also with local malalignment and bone attrition, and that chondrocalcinosis was positively associated with osteophyte size at multiple sites. Conclusion: In patients referred to hospital with knee OA different patterns of osteophyte direction are discernible. Osteophyte size is associated with local compartmental narrowing but also local alignment and attrition. Chondrocalcinosis is associated with osteophytosis throughout the joint. These data suggest that both local biomechanical and constitutional factors influence the size and direction of osteophyte formation in knee OA.