BIOMECHANICAL AND HISTOLOGICAL ANALYSIS OF AN HA COATED, ARC DEPOSITED CPTI CANINE HIP-PROSTHESIS

The interfacial shear strength and bone tissue response was investigat ed for an are deposited (AD) commercially pure titanium implant surfac e, with (AD/HA) and without (AD) plasma-sprayed hydroxyapatite (HA) co ating. Ten purpose bred coonhounds received bilateral femoral stem imp lantation (AD and AD/HA) in the proximal femurs (hemiarthroplasty). Th e femoral prosthesis consisted of a modular CoCr alloy head, modular T i-6Al-4V neck, and a 10-mm diameter cylindrical Ti-6Al-4V femoral stem . The AD surface had 30-35% greater surface roughness than the AD/HA s urface. The HA coating had a purity greater than 90% and a crystallini ty greater than 65%. After 6, 12, and 24 weeks, the implants were retr ieved and analyzed with mechanical testing, qualitative and quantitati ve histology, and electron microscopy. The AD/HA implants had equivale nt interfacial shear strengths to the AD implants at all time periods. The AD/HA implants had significantly greater linear bone contact than the AD implants. The 6-week implants had significantly thicker cortic al bone than the 12- and 24-week implants. The HA coating was very sta ble in vivo, evidenced by no thickness reduction at any time period. Q ualitatively, the AD/HA implants primarily had bone contacting the imp lant surface with little fibrous tissue present, and the AD implants h ad bone and fibrous tissue contacting the implant surface. The electro n microscopy analysis showed that the mechanically tested implants exh ibited a mixed failure mode at the bone, HA coating, and titanium inte rfaces. (C) 1996 John Wiley & Sons, Inc.