PRELIMINARY EXPERIENCE WITH A NOVEL MODEL ASSESSING IN-VIVO MECHANICAL STRENGTH OF BONE-GRAFTS AND SUBSTITUTE MATERIALS

A novel canine tibia model was used to evaluate four bone graft materi als: autologous cortical bone, allograft cortical bone, hydroxyapatite /tricalcium phosphate (HA/TCP) ceramic granules, and a HA/TCP and coll agen composite. Mechanical material properties were assessed using cus tom-designed stainless steel plugs for control of graft volume and int erface surface area. These plugs held the bone graft materials in the cortex of the tibia shaft and allowed in vivo mechanical testing. Afte r 6 months of ad Iib weight bearing, the grafts were harvested and tes ted in torsion. The samples in each animal were compared with the test plugs into which new bone had grown without the addition of graft. Co ntrol bone peak shear strength averaged 47 (+/-8.3) MPa (6.78 +/- 1.2 kpsi). Compared on the basis of peak torque, stiffness, and energy to peak torque, no significant differences were found among any of the gr aft materials or control bone. Histologic examination revealed the mat erials to be osteoconductive with the extensive formation of dense, co mpact cancellous bone. The new bone in the autograft and allograft sam ples completely filled the available space, whereas gaps persisted in the synthetic ceramics.