Changes in bone mineral density of the distal femur following uncemented total knee arthroplasty

The aim of the study was to quantitate changes in bone mineral density (BMD) in the distal femur following uncemented porous-coated total knee arthroplasty. Eight patients with total knee arthroplasties (PCA Primary, Howmedica, Rutherford, NJ) (female:male ratio, 6:2; mean age, 70 years; range, 51-77 years) were scanned by dual-photon absorptiometry within 3 months after surgery and at 2 years. An average decrease of 36% (P = .01) was found in BMD behind the anterior flange of the femoral prosthesis. Proximal to the fixation pegs, BMD increased by 22% (P = .12), but behind the posterior flange of the femoral component, BMD remained unchanged (P = .53). Stress shielding anteriorly in the distal femur occurred in all patients examined 2 years after surgery, and the increase in BMD proximal to the fixation pegs was probably a result of increased and altered mechanical loading.