BONE SCINTIGRAPHIC APPEARANCE OF ASYMPTOMATIC HYDROXYAPATITE-COATED HIP ARTHROPLASTIES

To obtain information about the bone scintigraphic appearance of a hyd roxyapatite (HA)-coated proximal femoral implant, this examination was per formed on 24 patients with a clinically and radiologically succes sful femoral implant in hip arthroplasty. The prosthesis had a proxima l HA coating for supplementary fixation. The patients' mean age was 50 .3 years (range, 28-65 years) at operation. The interval from the oper ation to the scintigraphy ranged from 6 months to 5.5 years (mean, 2.2 years). Scintigraphy was performed using Tc-99m-medronic acid. Quanti tative counts were recorded in 4 zones: 3 along the length of the impl ant (trochanteric region with HA coating, midprosthesis, and distal ti p) and 1 below the prosthesis. The results were expressed as ratios us ing the nonoperated femur as a control value. The results demonstrated that the mean activities in all 4 zones were increased relative to th e untreated side. The highest activity was observed in the region arou nd the prosthetic tip, with an elevation of 46% above the control valu e. This activity showed a significant decline over time. The counts re corded in the trochanteric region, where the implant was coated with H A, were 20% above the control value and similar to those seen in its a djacent noncoated midprosthetic region. Zn the trochanteric region, ho wever, the activity did not show a decline over the follow-up period.