| Summary: | Objective -To compare the compression produced in reduction of experimentally created medial condylar fractures using lag screw fixation with medial vs. lateral approach, and to determine the maximum torque at screw failure.
Materials and Methods- Twelve (12) pairs (left and right) 3rd metacarpal bones (MC3) were collected from adult (2-7 years) Thoroughbreds euthanized for reasons unrelated to orthopedic disease. Complete parasagittal medial condylar osteotomies were created at a measurement of 9, 13, and 21 mm axial to the epicondylar fossa on four pairs each of cadaveric MC3 bones resulting in fracture fragments measuring 8, 12, and 20 mm in thickness. For each pair of cadaveric MC3, a lateral or medial approach was randomly selected to repair the condylar fracture using a single 4.5 mm AO cortical screw. Each repair was tested for fracture plane compression and screw torque to failure.
Results-There was no significant difference in compression between the medial and lateral approaches for the 8 or 12-mm fragment groups. There was significantly more compression generated in the lateral approach when compared to the medial approach for the 20-mm fragment group. Failure occurred at significantly lower torque in the 8-mm group. There was no significant difference between medial and lateral approach in torque to failure for the 12 and 20-mm groups.
Conclusion-Based on this data we have concluded that there was no significant difference in torque to failure between a medial vs. lateral approach for the 12 mm fragments but there was a significant difference for the 8 mm fragments and that a lateral approach may be acceptable for the repair of medial condylar fractures in 12-mm or thicker fragments. The compression achieved by a medial approach was not significantly greater for the 8, 12 or 20-mm groups.
Clinical Relevance- Based on our results the 20 mm size fragments reaches a higher compression at a faster rate when compared to the 8 and 12 mm size fragments. We recommend using caution when repairing medial condylar fractures with a lateral approach for fragment sizes measuring 8-mm thick. The smaller fragment torque to failure was low and not much higher than the insertional torque. Failure resulted from the screws stripping in the bone fragment. The screws in the thicker fragments (12 and 20 mm) engage more bone and have a higher torque to failure as a result.
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