Hydroxyapatite porous coating and the osteointegration of the total hip replacement.

Introduction: The main purpose of this study is to evaluate the efficacy of the plasma sprayed, combined porous titanium alloy/HA coating in promoting bony ingrowth and mechanical stabilization of total hip implants. The performance of the titanium alloy/HA type coated hip prostheses and the one of the same shape but without any coating, is compared in this paper.

Material And Methods: The implants were manufactured from titanium alloy VT-6 (ASTM F-136). The hip stems utilized in the control group were identical to those subsequently coated. The coating consists of a plasma deposited first layer of porous titanium alloy (TiAl(6)V(4)), similar in composition to the forged substrate and a plasma deposited second layer of over-sprayed hydroxyapatite, Ca(10)(PO(4))6(OH)2. Coating is located in the critical area of the hip stems, where high fixation interface strength is desired, i.e. in the proximal area of the stem where the highest stresses occur. The porous titanium alloy/hydroxyapatite (HA) coated femoral stems were implanted in 50 patients. The results were compared with a control group of 50 patients with the same type of endoprosthesis, but without the porous titanium alloy/HA coating. Both groups of patients were operated on and evaluated by the same orthopedic surgeons with a mean follow up of 11.4 years in the HA group and 10.6 years in the control group.

Results: HHS in the control group was preoperatively 35.5 points (range 26-49) and 85.1 points (range 54-100) in the time of the last control. HHS in the HA group was preoperatively 34.1 points (range 27-56) and 94.4 points (range 89-100) in the time of the last control. In 28 cases (56%) of the control group a range of translucencies were obvious. These translucent lines, however, did not appear with any of the patients in the coated implant group except one infection stem migration.

Conclusion: Experience with the HA-type coated hip implants demonstrates substantially higher degree and quality of osteointegration in the porous titanium alloy/HA type implants.