Infiltration of sarcomas into the hip joint: comparison of CT, MRI and histologic findings in 67 cases.

We analyzed the incidence, route, and characteristics of hip joint infiltration in pelvic or proximal femoral sarcomas. 67 patients with a sarcoma that originated around the hip joint (50 pelvic and 17 femoral) were included in this study. Preoperative CT and MRI were matched with the histological findings in tumor specimens. Tumor infiltration into the hip joint was suspected on the basis of preoperative imaging in 29 patients due to articular cartilage disruption, diffuse signal changes in the acetabulum or femoral neck, signs of a tumor in the joint, or markedjoint effusion. Of these 29 patients, 15 showed tumor invasion on histological examination. 12 of 31 chondrosarcomas, none of 12 Ewing's sarcomas, and 3 of 24 osteosarcomas infiltrated into the hip joint (p = 0.008). 10 of 26 low-grade sarcomas and 5 of 41 high-grade sarcomas infiltrated into the hip joint (p = 0.02). The joint infiltration rate of the chondrosarcomas was related to their size. Of 10 tumors originating in the acetabulum, 9 penetrated through or around the osseous-ligamentous junction and one through the acetabular cartilage. In 5 proximal femur lesions, all infiltrated the joint through the femoral neck, 3 of them also through the ligamentum teres.