Biomechanical stability and biological effect of titanium intramedullary implant in rabbit femur with the filler of fast-setting calcium phosphate cement

This in vivo study evaluated the biomechanical stability and biological effects of titanium implant with the filler of fast-setting calcium phosphate cement (CPC) and polymethyl methacrylate (PMMA) as a retarder. Histological and biomechanical studies were conducted in New Zealand white rabbits to evaluate the effects of CPC on bone formation around a titanium rod in femoral bone marrow. The animals received injections of CPC into the femoral bone marrow from the distal end of the right femur, where a titanium rod was inserted bilaterally. The titanium rod being inserted without cement in the left femur was the control group. Four rabbits were sacrificed for pullout test and two for obtained histological samples at 1st, 4th, 12th, 26th and 70th postoperative week (total n=30). On mechanical evaluation, titanium rod implanted with CPC showed significant differences in maximum pullout force at week 4 and week 12 comparing with the control groups. On the examination of decalcified specimens, at week 1, new bone formation around titanium implant was clearly identified in CPC group, on the contrary, fibrous stroma in the control group and necrosis in PMMA sections were found around titanium implants. Residual CPC separates into pieces and was found in peripheral bone at week 12, and chronic inflammation was found around PMMA at week 4 and 12. These results suggest that the fast-setting CPC filled bone defects around the rod and promoted bone formation at a relatively early stage.