In vitroand In vivostudy on the effect of autogenous cancellous bone and intramedullary polymethylmethacrylate on allograft construct strength

An in vitrostudy was performed to compare the effects of augmenting interlocking nails of one of two diameter (5 or 6 mm) with intramedullary polymethylmethacrylate. Subsequently, an in vivostudy was performed to compare the effects of augmenting the interlocking nail with five combinations of intramedullary polymethylmethacrylate and autogenous cancellous bone applied to the periosteal surface or within the medullary canal. Dogs were killed 6 months after the procedure for biomechanical evaluation of the femora in axial compression, mediolateral and craniocaudal bending, and torsion. Results from the in vitrostudy at the proximal osteotomy indicated the 6‐mm inteilocking nail with intramedullary polymethylmethacrylate had greater stiffness than the 5‐mm interlocking nail without it (p < 0.05). At the distal osteotomy, regardless of the diameter of the interlocking nail, the addition of intramedullary polymethylmethacrylate increased stiffness (p < 0.05). Results from the in vivostudy indicated greater global construct stiffness with an interlocking nail alone, an interlocking nail augmented with intramedullary polymethylmethacrylate and cancellous bone at the periosteal surface, and an interlocking nail augmented with cancellous bone within the medullary canal and at the periosteal surface (p < 0.05). At the osteotomy level, the interlocking nail augmented with intramedullary polymethylmethacrylate and cancellous bone at the periosteal surface had greater stiffness than did an interlocking nail alone or an interlocking nail augmented with either intramedullary polymethylmethacrylate. 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 medullary canal and at the periosteal surface. The results suggest that augmenting interlocking nail fixation with intramedullary polymethylmethacrylate by itself offers no advantage but that acombination of intramedullary polymethylmethacrylate and cancellous bone at the periosteal surface improves structural properties at 6 months.