Microscopic analysis of autograft bone applied at the interface of porous-coated devices in human cancellous bone

This study describes the response of human cancellous bone when autologous bone chips are added at operation to the interface between host bone and porous-coated implants. During the first operation of a staged bilateral total knee arthroplasty, seven patients consented to have paired porous-coated devices implanted into their opposite medial femoral condyle. One device of each pair had autologous bone chips applied to the porous-coating, and the other was not grafted and was a control. The devices were removed en bloc at the second total knee arthroplasty 6 to 49 weeks later. Backscattered electron imaging showed significantly more bone (p < or = 0.05) in the porous-coating of the implant treated with autologous bone chips which significantly increased (p < or = 0.05) the amount of bone available at the interface. The grafted devices had a mineral apposition rate of 1.04 +/- 0.20 microns/day for the interface and 0.81 +/- 0.09 microns/day for the peripheral bone. This compared with corresponding figures of 1.03 +/- 0.38 microns/day and 0.79 +/- 0.19 microns/day at the ungrafted devices. The mineral apposition rate at the interface of the porous-coated implants was significantly increased (p < or = 0.05) relative to the host bone in the periphery. Our results support the view that autologous bone chips are effective in attaching cementless porous-coated total knee replacements to the human skeleton by bone ingrowth.