Introduction: There are many studies on the short and medium term results of hydroxyapatite (HA) coated acetabular components, but information on survival in the longer run is sparse. In this paper, we report 11 to 16 years follow up results of HA coated threaded versus HA coated hemispherical press fit cups.
Patients and methods: During the years 1988-1993, we performed 323 primary total hip replacements in 276 patients with an HA coated acetabular component. In 128 cases we used a HA coated threaded cup, and in 195 cases a HA coated hemispherical press fit cup was inserted. There were 189 women and 87 men aged 15-79 (mean 48) years. During follow-up, 14 patients died and 21 patients would not come for the follow-up examination as they were doing quite well with their prostheses. These patients were censored at their last control examination. This left 241 patients (287 hips) followed for 11 to 16 (mean 13) years after the operation.
Results: During the follow-up period 48 press fit cups and 9 threaded cups were revised, none because of infection. Survival analyses indicated a cumulative survival of the threaded HA coated cup of 0.91 (95% CI: 0.86-0.97) at 16 years with one patient at risk. The cumulative survival of the HA coated press fit cup was 0.74 (0.69-0.80) at 15 years with no patient at risk. The difference is significant (P = 0.0002). Wear and age was significantly associated with revision (P < 0.0001 and 0.0002, respectively), and wear was significantly (P < 0.0001) associated with osteolysis.
Conclusion: These results indicate that HA coated threaded cups provide satisfactory bony interlock to resist force loads in the long run whereas the HA coated hemispherical press fit cups do not.