Differential effect of a bone morphogenetic protein-7 (OP-1) on primary and revision loaded, stable implants with allograft

Morselized impacted bone allograft is often used to reconstruct the bone bed in the revision of failed total joint arthroplasties. We hypothesized that addition of the bone morphogenetic protein OP-1 (BMP-7) to bone allograft would improve early implant fixation. We inserted one loaded 6-mm-diameter titanium implant (surrounded by 0.75-mm gap) in each medial condyle of 24 canines. On one side, the implant was inserted in a controlled experimental revision setting resembling the clinical revision situation. A primary implant was inserted on the contralateral side in a previously unoperated site. Three groups were studied: 1) allograft alone, 2) allograft + 0.4 mg OP-1, and 3) allograft + 0.8 mg OP-1. Implant fixation was evaluated at 4 weeks. Grafted implants inserted in the primary setting without OP-1 had better fixation than the grafted revision setting with or without OP-1 (significantly more bone coverage, more mineralized tissue in the gap, and better mechanical interface strength). However, grafted primary implants with OP-1 had impaired fixation compared with grafted primary implants without OP-1 (less bone coverage of the implant and less bone formation in the gap). In contrast, grafted revision implants with OP-1 significantly increased implant fixation compared with grafted revision implants without OP-1 (increased mechanical interface strength and fraction of mineralized tissue in the gap). We found no differences between the two doses in any of the settings. Addition of OP-1 to bone allografted implants may show benefit at sites with impaired bone healing capacities, such as the revision setting.