A quantitative assessment of cross‐sectional cortical bone remodeling in the femoral diaphysis following hip arthroplasty in elderly females

A quantitative assessment of cross‐sectional cortical bone remodeling in the femoral diaphysis following hip arthroplasty was made by direct in vitro measurements of cross‐sectional geometric properties. We obtained eight femora from four female cadavers ranging in age from 77 to 96 years. In three cases unilateral uncemented Austin Moore implants were used, and in one case a unilateral cemented Thompson prosthesis had been implanted. The time of implantation in the two specimens where this information could be obtained was greater than 40 months. Sections were made at 12 diaphyseal locations from the superior aspect of the lesser trochanter through the distal diaphysis. Section properties (areas and second moments of area, or area moments of inertia) were determined by tracing photographs of the cross‐sections with a digitizer. In this sample of prosthetic femora, we found reductions in both total subperiosteal area (TA) and endosteal area (ENDA) relative to the contralateral unoperated side in most sections distal to the lesser trochanter. The average pairwise reduction in ENDA for this region was 21.1 mm², reaching statistical significance in one distal diaphyseal section. The average decline in TA in this region was 10.2 mm². Because the reduction in endosteal dimensions was generally greater than the reduction in subperiosteal dimensions, cortical area (CA) was maintained or increased throughout the distal 80% of this region in prosthetic femora with an average increase in CA of 9.3 mm², reaching statistical significance in one mid‐diaphyseal section. A completely different pattern of remodeling occurred in the two most proximal sections through the lesser trochanter and base of the femoral neck. Here, both endosteal and subperiosteal dimensions increased in the prosthetic femora, but ENDA increased more than TA, resulting in cortical thinning. The average pairwise increase in ENDA and TA, and loss in CA for these two sections was 59.8 mm², 15.7 mm², and 44.1 mm², respectively, with a near‐significant increase in ENDA in one section and a significant loss of CA in the other. In comparisons between the methods of fixation, the three uncemented specimens demonstrated an increase in mediolateral bending rigidity (relative to the contralateral unoperated side) in the sections surrounding the stem tip, wherease the cemented specimen lost mediolateral bending rigidity in this region. Changes in cross‐sectional cortical bone geometry following prosthetic implantation throughout the entire femoral diaphysis, even well below the stem tip, have not been reported previously in the literature.