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 arth roplasty 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 fo llow-up. The contralateral, healthy side was used as a control. The BM D 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 smal lest in the cortex medially of the prosthesis stem. The decreases in B MD around the metaphyseal and diaphyseal areas of the stem were smalle r than those reported for stiff stems. The marked bone loss in the cal car region is possibly due to stress bypass-i.e., the axial load is tr ansmitted directly into the metaphyseal area of the femoral shaft, cau sing an increase in its stiffness and in the jamming of the prosthesis stem.