The torn acetabular labrum; a block to reduction of a dislocated hip.

Case 1-An agricultural worker, a man of thirty-eight, fell under a tractor, which ran over the inner side of his right thigh causing a backward dislocation of the head of the femur. Radiographs showed what appeared to be a simple posterior dislocation of the hip with a tiny linear fracture of the postero-superior bony rim of the acetabulum (Fig. I ). Reduction was attempted by a closed manipulation. Clinically the head of the femur appeared to go back into the acetabulum, but a radiograph showed that the reduction was not complete (Fig. 2). It will be seen from the radiograph that the head is low in the acetabulum, there is a wide gap between the upper surface of the head and the lower surface of the acetabulum, and Shenton’s line is broken. It was considered that there was some soft-tissue obstruction preventing complete reduction and so, forty-eight hours after the accident, the hip was opened through a posterior incision. Lying across the floor of the acetabulum, blocking reduction, was the detached cotyloid ligament-the fibrocartilaginous rim of the acetabulum. It was firmly attached at both ends and lay tightly across the articular surface (Fig. 3). It had to be pulled out forcibly by a hook. It was excised and the femoral head could then be reduced completely. The rent in the capsule and a tear ofthe short lateral rotator muscles, made by the original dislocation, were repaired and the hip was immobilised. The post-operative radiograph showed normal relationship of head and acetabulum (Fig. 4).