Bone loss from the proximal femur after arthroplasty with an isoelastic femoral stem. BMD measurements in 25 patients after 9 years.

To quantify the bone loss from the proximal femur after total hip arthroplasty with an isoelastic femoral stem, the bone mineral densities (BMD) around 25 such stems were measured after an 8.5 (7.5-9.5)-year follow-up. The contralateral, healthy side was used as a control. The BMD on the prosthesis side was lower by a mean of 14 percent than on the control side. The difference was greatest in the calcar area and smallest in the cortex medially of the prosthesis stem. The decreases in BMD around the metaphyseal and diaphyseal areas of the stem were smaller than those reported for stiff stems. The marked bone loss in the calcar region is possibly due to stress bypass-i.e., the axial load is transmitted directly into the metaphyseal area of the femoral shaft, causing an increase in its stiffness and in the jamming of the prosthesis stem.