A new model to assess tibial fixation in knee arthroplasty. I. Histologic and roentgenographic results.

A model to assess tibial fixation in knee arthroplasty is described. Eighteen mongrel dogs were implanted with a right tibial hemiarthroplasty. Implantation was of a press-fit, smooth implant (eight dogs) or a titanium alloy beaded device (ten dogs). Animals were studied at six, 12, 18, and 24 weeks. Roentgenographic and histologic analysis was performed for all implants. All animals were ambulatory. Roentgenographically, smooth implants showed progressive radiolucencies with increasing trabecular sclerosis under the implants. These changes were less prominent under the porous implants. Histologically, fibrous interfaces were identified focally under all implants but were thicker under smooth devices. Eighteen- and 24-week specimens showed substantial ingrowth into the porous pegs but minimal ingrowth into the porous plateau. Concurrent histologic and biochemical evaluation in dogs demonstrates the possible fate of implants in knee arthroplasty in human beings. As has been observed, histologic analyses suggest that clinically satisfactory results do not constitute evidence of stabilization by bone ingrowth.