IN-VITRO AND IN-VIVO STUDY ON THE EFFECT OF AUTOGENOUS CANCELLOUS BONE AND INTRAMEDULLARY POLYMETHYLMETHACRYLATE ON ALLOGRAFT CONSTRUCT STRENGTH

An in vitro study was performed to compare the effects of augmenting i nterlocking nails of one of two diameters (5 or 6 mm) with intramedull ary polymethylmethacrylate. Subsequently, an in vivo study was perform ed to compare the effects of augmenting the interlocking nail with fiv e combinations of intramedullary polymethylmethacrylate and autogenous cancellous bone applied to the periosteal surface or within the medul lary canal. Dogs were killed 6 months after the procedure for biomecha nical evaluation of the femora in axial compression, mediolateral and craniocaudal bending, and torsion. Results from the in vitro study at the proximal osteotomy indicated the 6-mm interlocking nail with intra medullary polymethylmethacrylate had greater stiffness than the 5-mm i nterlocking nail without it (p < 0.05). At the distal osteotomy, regar dless of the diameter of the interlocking nail, the addition of intram edullary polymethylmethacrylate increased stiffness (p < 0.05). Result s from the in vivo study indicated greater global construct stiffness with an interlocking nail alone, an interlocking nail augmented with i ntramedullary polymethylmethacrylate and cancellous bone at the perios teal surface, and an interlocking nail augmented with cancellous bone within the medullary canal and at the periosteal surface (p < 0.05). A t the osteotomy level, the interlocking nail augmented with intramedul lary polymethylmethacrylate and cancellous bone at the periosteal surf ace had greater stiffness than did an interlocking nail alone or an in terlocking nail augmented with either intramedullary polymethylmethacr ylate, cancellous bone within the medullary canal, or cancellous bone at the periosteal surface (p < 0.05) but produced the same results as an interlocking nail augmented with cancellous bone within the medulla ry canal and at the periosteal surface. The results suggest that augme nting interlocking nail fixation with intramedullary polymethylmethacr ylate by itself offers no advantage but that a combination of intramed ullary polymethylmethacrylate and cancellous bone at the periosteal su rface improves structural properties at 6 months.