Healing patterns of transverse and oblique osteotomies in the canine tibia under external fixation

Healing patterns were compared between transverse and 60 degrees oblique osteotomies in canine tibiae stabilized under external fixation. Under similar in vitro testing conditions (osteotomy ends in contact), the axial stiffness of the oblique osteotomy under external fixation was 45% of the paired transverse osteotomy. Under torsion and bending, the two sides exhibited similar fixation rigidity. The animals put significantly less weight on the oblique side than on the transverse side in the early phases of bone healing (p less than 0.05 for static and p = 0.024 for dynamic weight bearing). The osteotomy bending stiffness at 60 days (in vivo) and the torsional stiffness of osteotomy union measured after sacrifice at 90 days were significantly higher on the transverse side (p = 0.013 and p = 0.016, respectively). Intracortical new bone formation was significantly higher on the transverse side (p less than 0.01), indicating a difference in the rate of cortical healing and remodeling. The average pin removal torque was significantly lower on the oblique side (p less than 0.05), a sign of increased pin loosening. In the clinical situation, unstable oblique or spiral fractures should be protected from weight bearing even under stable external fixation due to the delayed recovery of bone union stiffness property as well as increased pin tract problems.