The enhancement of fixation of a porous-coated femoral component by autograft and allograft in the dog

Revision total arthroplasty of the hip, without cement, was done in dogs to compare the abilities of autologous grafts and allografts of bone to enhance histological ingrowth of bone and biomechanical strength. Six weeks after primary total hip arthroplasty with cement, the femoral component was revised to a titanium fiber-metal prosthesis. On the basis of the type of graft that was impacted into the voids around the ingrowth surface at revision, three study groups were created: no graft (control), four dogs; fresh autograft, six dogs; and frozen allograft, six dogs. Twelve weeks after revision, histological analysis revealed the greatest amount of ingrowth proximally in the grafted specimens. A mean of 22.3 per cent ingrowth was observed in the dogs that had an autograft; this was not significantly different from the mean of 17.5 per cent in those that had an allograft. The non-grafted specimens showed little ingrowth, the values being significantly less than those for the grafted specimens. Push-out testing showed greater ultimate shear strength proximally than distally in the grafted specimens, and at the proximal level there was a significant difference between the group that had an autograft and the control group (mean, 4.03 and 1.22 megapascals, respectively). Ultimate strength correlated positively with ingrowth of bone (r = 0.82). Radiographically, subsidence of the components and lucent lines were observed more frequently in the nongrafted specimens, and if both were present, significantly less ingrowth of bone and strength were observed. Clinical relevance: The degree of stability of the implant and the apposition to bone that are required for effective growth of bone into a porous surface are often difficult to achieve during revision total hip arthroplasty without cement. Fresh autologous bone graft is the biological material of choice to recreate lost bone stock. However, when this material is not available or is in limited supply, and the implant is stable, a frozen allogeneic graft is an acceptable alternative.