Objective. To investigate the role of joint shape in knee osteoarthritis (OA) by determining which aspects of bone shape are different in OA knees compared with control knees. Methods. Using a statistical shape model, we compared radiographs showing the shape of OA knees with radiographs showing the shape of control knees in a population of 609 women (1,218 knees) extracted from the Rotterdam Study. Furthermore, we used magnetic resonance imaging to compare the shape of knees with cartilage defects with the shape of knees without cartilage defects. Results. Three statistical shape modes, referring to 3 distinct aspects of the shape of the knee, were significantly associated with the presence of radiographic OA (modes 2, 4, and 15). Mode 2 reflected the width of the femoral and tibial bones, which was increased in patients with OA. Knees with cartilage defects also had wider femoral and tibial bones compared with knees without cartilage defects. Mode 4 reflected the variation in flexion of the knee during radiography. OA knees were more extended compared with control knees. Mode 15 showed that patients with OA had an elevated lateral tibial plateau, which was associated with pain. Conclusion. In women, knees with OA were wider, more extended during radiography, and had an elevated lateral tibial plateau. These results show that the shape of the knee is involved in OA, which might lead to novel imaging biomarkers to monitor or predict knee OA.