Specific mechanism of the knee joint preventing tumor invasion

Abstract

Tumor extension from the anterior aspect of the distal femur into the knee joint was examined histologically and with MRI in 10 patients with primary malignancy of bone. Histologically, 1 tumor had invaded the joint with destruction of the transitional area between the articular cartilage and bone. In another case, the transitional area had been destroyed by mechanical traction of the periosteum by the tumor without invasion. The fatty connective tissue and superficial synovial layer were detached from the femoral cortex and elevated upwards by tumor growth without destruction in 7 tumors but were unchanged in 3 tumors. Tl-weighted MRI clearly revealed high signal intensity of the connective tissue and synovium in the 7 tumors with elevation. The average elevation of this detachment of the fatty connective tissue and synovium from the femoral cortex calculated from MR images was 12 mm. Destruction of the transitional area between the articular cartilage and bone was detected in 2 tumors on Tl-weighted MR images. Our results indicate that fatty connective tissue and the superficial synovial layer are easily detached and elevated by tumors. This mechanism probably prevents tumor extension into the joint space.