[Long-term experience with the combined ARBOND hydroxyapatite coating in implant osteointegration].

PURPOSE OF THE STUDY: The hydroxyapatite coating of an implant surface provides osteoactive conditions that can support osteointegration of cementless joint arthroplasties. However, the possibilities of hydroxyapatite degradation, resorption and delamination that may become responsible for failure of total hip arthroplasty (THA) have been reported. The aim of the study was to assess the properties of Arbond hydroxyapatite coating by comparing the long-term survival of implants identical in construction but different in surface coating.

MATERIAL: One group (HA) comprised 86 patients (100 THAs) with an average age of 45.14 years (range, 22.3 to 77.4 years) at the time of surgery who received a femoral stem (Walter) with a coating of Arbond sprayed over the proximal half. The other group (control) included 92 patients (100 THAs) with an average age of 49.7 years (range, 33 to 68.7) who had an identical femoral component without coating. In both groups the conical-shaped acetabular cup (Walter) and femoral head made of sintered ceramics were used. The patients in whom one or both components were replaced or extracted were not included in the final clinical evaluation (Harris Hip Score). For the statistical analysis of survival, a stable component still in place at the date of the revision procedure was regarded as surviving; a lose component at the same date was considered a failure. Finally, 71 hips of the HA group followed up for an average of 15.51 (range, 5.6 to 18.56) years and 39 control hips at an average follow-up of 14.19 (range, 6.24 to 18.48) years were clinically evaluated. The data of patients who died in the course of study (HA group, 11; control group, 14) were included in the clinical evaluation with the date of their last follow-up.

METHODS: For both groups, the Kaplan-Meier survival curves were constructed for overall survival and for the survival of acetabular and femoral components separately. Differences in survival curves were evaluated with the use of Gehan's Wilcoxon test. Component survival was also calculated using 15-year life-table survivorship analysis. Differences in variables under study were assessed with the use of the two-tailed Student's t-test. A p value of less than 0.05 was considered significant.

RESULTS: A total of 29% hips were revised in the HA group, 27% for aseptic loosening of the acetabular cup, in 2% both components were removed because of deep infection. In the control group revision procedures were performed in 61% of the hips. Except for one case of deep infection (1%), the reason was cup loosening in 30%, stem loosening in 12% and both components loosening in 18% of the hips. The HA group showed a significantly longer survival of both total hip prostheses and individual components. The final HHS was significantly better than the initial score in both groups. There was no difference in the degree of improvement between the two groups. The radiographic data showed full osteointegration of stems in the HA group. The control group, on the other hand, had 87% of the stems with translucent lines in zone I and zone VII according to Gruen's classification.

DISCUSSION: The significantly longer survival of hips in the HA group gives support to the use of hydroxyapatite coating in total hip arthroplasty. The poorer results in grit-blasted implants, as compared with the literature data, can be explained by allow degree of roughness of the Walter implant surfaces.

CONCLUSIONS: The combined Arbond hydroxyapatite coating improves conditions for implant osteointegration in the bone.