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 osteotomies with external fixation alone or in combination with a single lag screw. Twelve dogs had a midshaft tibial osteotomy performed at a 45-degrees 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 osteotomy site. When compared with their contralateral controls, the fixator-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 additional lag screw. Torsional stiffness was 29% higher in the osteotomies treated, and tested, with the lag screw, but this did not achieve statistical significance. Computed tomography scanning revealed that the surface area was increased by an average of 30-40% in both groups, relative 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 external fixation construct with a lag screw resulted in increased torsional stiffness but healing equal to that seen with external fixation alone.