Shorter Femoral Stems in Total Hip Replacement
Total hip design has come a long way since Sir John Charnley’s original cemented hip in the late 1960’s. Cement has largely been replaced with cementless (bony ingrowth) technology, plastic sockets are being replaced with highly crosslinked polyethylene, ceramics, and metal, and femoral stem shapes continue to evolve.
Some long stem femoral components cause problems including “stem tip thigh pain,” difficulty if removal is ever required, and stress-shielding (osteoporosis) of the upper femur which does not see the normal weight-bearing forces when part of the body weight is carried by the lower tip of the femoral component. Sometimes, the upper part of the femur literally melts away when a long stem femoral component is used.
One of the advantages of a resurfacing arthroplasty (where the ball is resurfaced with a metal cap rather than replacing it with an artificial ball anchored by a stem down the center of the femur) is that it loads the femur more effectively, reducing the risk of stress-shielding bone loss.
Another total hip design which is gaining popularity is the short femoral stem. With improvements in bony ingrowth technologies, much shorter femoral components can now achieve stable fixation to bone. Shorter stems will result in loading of the femur from top down reducing the rate of stress shielding and bone loss. It is likely that the next new step in design technology is the use of shorter and shorter femoral components.