Osteogenic protein 1 device increases bone formation and bone graft resorption around cementless implants

In each femoral condyle of 8 Labrador dogs, a non weight-bearing hydroxyapatite-coated implant was inserted surrounded by a 3 mm gap. Each gap was filled with bone allograft or ProOsteon with or without OP-1 delivered in a bovine collagen type I carrier (OP-1 device). 300 mug OP-1 was used in the 0.75 cc gap surrounding the implant. After 3 weeks, the OP-1 device enhanced implant fixation by 800% (p<0.05) in the ProOsteon group, but OP-1 had no significant effect on implant fixation in the allograft group. By adding the OP-1 device, the volume fraction of woven bone close to the implant increased from 12% to 20% (p<0.05) in the bone allograft group and from 6% to 25% (p<0.05) in the ProOsteon group. The volume fraction of bone allograft decreased from 29% to 9% (p<0.05) in the OP-1 treated group versus 33% to 30% in the allograft group not treated with OP-1. No resorption of ProOsteon was found. In conclusion, OP-1 accelerates resorption of bone allograft and enhances new bone formation around cementless implants grafted with bone allograft or semisynthetic hydroxyapatite bone substitute. Our findings do not support the use of ProOsteon alone around cementless implants.