Graded exchange reaming and nailing of non-unions. Strength and mineralisation in rat femoral bone.

The effect of graded exchange reaming and intramedullary nailing on a non-union model in the rat femur was studied by clinical, radiological, bone mineralisation and biomechanical methods. A standardised procedure was first developed to create a non-union that did not heal and in which non-union developed consistently. In 30 male Wistar rats a standardised osteotomy was produced in the left femur diaphysis. The fractures were reamed to 1.5 mm and nailed with a soft polyethylene nail for 12 weeks. After 1 week the fractures were manipulated in bending and rotation every 2nd day for 5 weeks. At 12 weeks radiographs demonstrated a hypertrophic non-union in all fractures, and the rats were randomly divided into three groups. In the control group no reoperation was performed (group C). In group 1.6 exchange reaming to 1.6 mm and medullary nailing were performed, and reaming and nailing to 2.0 mm in group 2.0. The effect of extensive versus modest reaming and nailing on bone repair was then assessed 12 weeks later. Physical examination, radiographs, bone mineralisation measurements by dual energy X-ray absorptiometry (DEXA) and biomechanical femurs evaluated by a three-point bending test in a Mini Bionix (MTS) testing system were employed. In the control group radiographs revealed a state of non-union in all fractures, and the mechanical strength was significantly reduced compared with both intervention groups. Bone mineral content (BMC) and bone mineral density (BMD) were reduced in the callus region compared with group 2.0. In the intervention groups radiographs showed various degrees of union. Mechanical testing showed that the fracture energy was significantly higher in group 2.0 than in group 1.6. The finding that extensive exchange reaming and nailing seems favourable in non-unions of diaphyseal fractures compared with modest reaming may have clinical implications.