Biologic response to uncemented Madreporic canine hip arthroplasty

The Madreporic hip arthroplasty has provided encouraging clinical results. The surface of the prosthesis is unlike other uncemented prostheses since the rough surface is formed by multiple 1-mm diameter beads that are cast as an integral part of the prosthesis and increase its surface area four times. Seven Madreporic hip arthroplasties were implanted in adult male mongrel dogs. Specimens were harvested 5, 6, 9, 12, 20 and 52 weeks after insertion. One specimen became septic and loosened. The prosthesis was stabilized initially by friction fit between the prosthesis and the endosteal cortex of the proximal femur. Dense, uniformly organized, fibrous tissue surrounded the prosthesis at 5 weeks. The fibrous tissue appeared similar to Sharpey's fibres. Circumferential bone contact increased from 26% at 5 weeks to 60% at 52 weeks. Fluorescent labelling revealed active new bone formation within the interstices of the prosthesis without evidence of an intervening soft-tissue membrane. Firm mechanical anchorage of the Madreporic femoral prosthesis was demonstrated in this study.