Fracture healing after reamed and unreamed intramedullary nailing in sheep tibia.

Intramedullary nailing is a well-established method for stabilisation of long-bone shaft fractures. It is still a controversy as to whether the procedure should be done by an unreamed or reamed technique. In the present animal study, 24 sheep were treated with intramedullary nailing. Midshaft fractures (Arbeitsgemeinschaft für Osteosynthese (AO) type 42-A2/3) were created. Eight sheep were treated with an unreamed nailing technique (UN), a further eight sheep underwent tibia nailing by the reamed technique using the conventional AO reaming system (RC) and in a further eight sheep, reamed nailing was performed using an experimental reaming system (RE). Intra-operatively, the intramedullary pressure was measured and, during a healing time of 10 weeks, the growth of callus formation was labelled with fluorescence markers after 4 and 6 weeks. After 10 weeks, the animals were euthanised and the quality of fracture healing was determined by recording stiffness in torsion, antero-posterior and mediolateral bending and the load at yield. In addition, the callus formation at the fracture zone was evaluated by fluorescence microscopy and macroradiographs. The results showed a decrease of intramedullary pressure when reamed nailing was performed with the RE (72.5 mmHg) system compared with the conventional AO reaming system (227 mmHg). Mechanical testing did not reveal any significant differences either for torsional or bending stiffness or for load at yield for any of the three procedures. Histological evaluation showed a similar callus formation for the UN group and the RE group. Callus formation in the UN (65 mm(2)) and RE (63 mm(2)) groups showed a higher increase during the first 6 weeks than those treated with the conventional AO reaming system (27 mm(2)). This means that, especially during the first weeks of fracture healing, damage to the bone by the reaming process can be reduced by reaming with a reaming device with lowered cutting flutes and smaller drive-shaft diameter. Intramedullary pressure can be significantly reduced by using reaming systems with reduced drive-shaft diameters and deepened cutting flutes. In the early phase of fracture healing, callus formation can be influenced positively when using the RE system.