LIMITED INTERNAL-FIXATION OF THE TIBIA WITH EXTERNAL FIXATION - AN IN-VIVO CANINE STUDY

This study reports the results of the healing of canine tibial osteoto mies with external fixation alone or in combination with a single lag screw. Twelve dogs had a midshaft tibial osteotomy performed at a 45-d egrees obliquity. Half of the dogs had a six-pin, unilateral, medial, external half-frame applied after the osteotomy. The remaining six had an identical frame plus a lag screw placed perpendicular to the osteo tomy site. When compared with their contralateral controls, the fixato r-alone group had a 16.3% (p < 0.05) decrease in bone density, whereas no significant density change was seen in the group with the addition al lag screw. Torsional stiffness was 29% higher in the osteotomies tr eated, and tested, with the lag screw, but this did not achieve statis tical significance. Computed tomography scanning revealed that the sur face area was increased by an average of 30-40% in both groups, relati ve to contralateral controls, but there was no difference between the two treatment groups. Three tibias in the group with external fixation alone, and two tibias in the screw group showed primary bone healing without evidence of callus formation. The combination of a semirigid e xternal fixation construct with a lag screw resulted in increased tors ional stiffness but healing equal to that seen with external fixation alone.