Progressive femoral cortical and cancellous bone density loss after uncemented tapered-design stem fixation.

BACKGROUND: Aseptic implant loosening and periprosthetic bone loss are major problems after total hip arthroplasty (THA). We present an in vivo method of computed tomography (CT) assisted osteodensitometry after THA that differentiates between cortical and cancellous bone density (BD) and area around the femoral component. METHOD: Cortical and cancellous periprosthetic femoral BD (mg CaHA/mL), area (mm(2)) and contact area between the prothesis and cortical bone were determined prospectively in 31 patients 10 days, 1 year, and 6 years after uncemented THA (mean age at implantation: 55 years) using CT-osteodensitometry. RESULTS: 6 years postoperatively, cancellous BD had decreased by as much as 41% and cortical BD by up to 27% at the metaphyseal portion of the femur; this decrease was progressive between the 1-year and 6-year examinations. Mild cortical hypertrophy was observed along the entire length of the diaphysis. No statistically significant changes in cortical BD were observed along the diaphysis of the stem. INTERPRETATION: Periprosthetic CT-assisted osteodensitometry has the technical ability to discriminate between cortical and cancellous bone structures with respect to strain-adapted remodeling. Continuous loss of cortical and cancellous BD at the femoral metaphysis, a homeostatic cortical strain configuration, and mild cortical hypertrophy along the diaphysis suggest a diaphyseal fixation of the implanted stem. CT-assisted osteodensitometry has the potential to become an effective instrument for quality control in THA by means of in vivo determination of periprosthetic BD, which may be a causal factor in implant loosening after THA.

An ABJS Best Paper: Progressive cancellous and cortical bone remodeling after press-fit cup fixation: a 3-year followup.

Periprosthetic bone loss after total hip arthroplasty is common. It can be progressive and, in the extreme, may compromise survival of the prosthesis. With quantitative computed tomography, we determined the pattern of periacetabular cortical and cancellous bone density changes after press-fit cup implantation with alumina liners. We recruited 24 patients (24 hips; 15 men and nine women) with degenerative joint disease and used a press-fit cup with an alumina/alumina pairing. The average patient age was 57 years. Computed tomography examinations were performed 10 days, 1 year, and 3 years after the index operation. Cancellous bone density decreased in all periacetabular regions by as much as -66%; the decrease was progressive between the 1- and 3-year examinations. In contrast, cortical bone density above the dome of the cup remained constant but progressively decreased by as much as -22% at the level of the cup 3 years postoperatively. Within the first 3 postoperative years, progressive periacetabular remodeling of cancellous and cortical bone structures was observed after press-fit cup fixation. The bone density changes suggest high stress shielding of retroacetabular cancellous bone while load is transmitted solely to the cortical bone above the dome of the cup.