The resultant force on the femoral head in rheumatoid arthritis.

The resultant force on the femoral head was measured by suing a roentgenographic method in 100 rheumatoid patients (152 hips) who had Charnley arthroplasties. Postoperative avulsion of the greater trochanter has been frequently observed in the rheumatoid hip. After operation the resultant force and the abductor pull were increased in 18 of 31 with the detached trochanter, whereas decreased in the non-detached group in 81 of 121. In the hips with acetabular protrusion, preoperative values of the force were less than in that the trochanter united and postoperative increase in the abductor force was noted. This seems to be related to the great tendency for trochanteric avulsion in this group.