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Abstract
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.