The effects of cementless femoral stem shape and proximal surface texture on 'fit-and-fill' characteristics and on bone remodeling

We measured the post-operative radiological "fit and fill" of two different femoral stem designs, one with a straight proximally porous-coated (Bi-Met ric, n=50) and the other with a proximally anatomic, hydroxyapatite-coated and distally over-reamed stem (ABG, n=26). A comparison was then made betwe en the clinical and radiological 5-year follow-up data of these two series and also of the bone remodeling changes around the stems. The observed diff erences in "fit and fill" parameters in the metaphyseal region were minute. However, in the diaphyseal bone the straight stem had substantially mon co rtical contact. The clinical results were excellent for both groups. Subsid ence (>2 mm) was mon frequent with the anatomical ABG stems, although the A BG stems had better bone ingrowth in the lower metaphyseal area. The presen t results indicate that the anatomical design may improve the fit and fill of a femoral stem in the metaphysis. On the other hand, a looser fill of th e diaphyseal bone made the stems of this type more susceptible to subsidenc e. The straight stem with tight diaphyseal fit showed excellent stability, but the good bone ingrowth and remodeling around the distal part of the ste m indicates stress transfer through this region and increased stress shield ing of the proximal metaphyseal femur.