Tricalcium phosphate (TCP) is an osteoconductive bioceramic which, when applied to a porous-coated prosthesis, may enhance osseous ingrowth and mechanical stability. TCP plasma-sprayed and unsprayed porous-coated tibial intramedullary r o d s were bilaterally implanted in seven adult rabbits. All rabbits were killed at 12 weeks. Pull-out tests w e r e p e r f o r m e d o n 4 r a b b i t s while all were evaluated histologically for osseous response and adverse tissue reaction. TCP-sprayed implants showed significantly greater osseous ingrowth i n comparison to unsprayed implants. N e i t h e r i m p l a n t t y p e e x h i b i t e d adverse tissue reactions. Average pull-out strengths were 69 lb for treated rods and 72 lb for controls (p > 0.05); quality of fit for all pull-out specimens except one was deemed poor. We conclude that plasmasprayed TCP enhances osseous ingrowth into porous-coated devices. However, our data further suggest that enhanced ingrowth may not always lead to enhanced fixation.
1 N T RODUC T ION
Porous-coated devices provide biologic fixation via osseous ingrowth. As long-term complications of bone cement become evident,'-3 the porous-coated system is becoming an effective alternative. Although a promising system, the porous-coated device has several limitations. First, time is needed for bone ingrowth and patients must limit weight bearing for the first 6 to 8 weeks after implantati~n.~ Second, a good tight fit during surgery is necessary to ensure bone-implant apposition and minimize micr~motion.~-~ Third, certain devices, namely tibial components of total knee protheses, exhibit poor bone ingrowth, independent of surgical technique and implant design.'" Calcium phosphate ceramics, in particular tricalcium phosphate (TCP) and hydroxyapatite (HA), are bioactive ceramics which are osteoc~nductive~ and may form a strong bond with bone;" these ceramics when plasma-sprayed onto a porous-coated device may enhance ingrowth and fixation. Various animal studies have shown enhanced OSS~OUS response and fixation of smooth implants plasma-sprayed with TCP or HA."," A clinical trial of smooth HAsprayed hip prostheses has yielded encouraging 2-year re~u1ts.l~ However,