Bone scintigraphic appearance of asymptomatic hydroxyapatite-coated hip arthroplasties.

To obtain information about the bone scintigraphic appearance of a hydroxyapatite (HA)-coated proximal femoral implant, this examination was performed on 24 patients with a clinically and radiologically successful femoral implant in hip arthroplasty. The prosthesis had a proximal HA coating for supplementary fixation. The patients' mean age was 50.3 years (range, 28-65 years) at operation. The interval from the operation to the scintigraphy ranged from 6 months to 5.5 years (mean, 2.2 years). Scintigraphy was performed using 99mTc-medronic acid. Quantitative counts were recorded in 4 zones: 3 along the length of the implant (trochanteric region with HA coating, midprosthesis, and distal tip) and 1 below the prosthesis. The results were expressed as ratios using the nonoperated femur as a control value. The results demonstrated that the mean activities in all 4 zones were increased relative to the untreated side. The highest activity was observed in the region around the prosthetic tip, with an elevation of 46% above the control value. This activity showed a significant decline over time. The counts recorded in the trochanteric region, where the implant was coated with HA, were 20% above the control value and similar to those seen in its adjacent noncoated midprosthetic region. In the trochanteric region, however, the activity did not show a decline over the follow-up period.