34th Annual Scientific Meeting proceedings

Objectives:

To determine whether microscopic changes observed in synthetic bone prototypes occur in ex vivo equine third metacarpal/metatarsal models of lateral condylar fractures repaired using 4.5 mm cortical screws inserted in positional and lag fashion using a torque of 6 Nm. 

Methods:

Lateral condylar fractures were simulated creating parasagittal osteotomies of the lateral condyle of 9 metacarpal and 9 metatarsal bones. The specimens were randomly assigned to the positional group (PG) and lag group (LG), so that half of the osteotomies underwent drilling using a positional technique and the other half using a lag technique. Following tapping, 3 bones from each group were randomly assigned to the control group (CG), which did not undergo screw insertion and was stored for histopathologic examination. All drilling and screw insertions were performed by the same ECVS experienced surgeon using an aiming device under radiographic guidance. Following screw removal, the bones were processed for histopathologic examination to assess the microscopic appearance of the threads.

Results:

In the PG, the degree of bone damage in the cis segment was significantly higher than in the trans segment (p=0.03).Furthermore, the percentage of thread damage in the trans segment was significantly different when comparing the three groups. The control group presented significantly lower damage of the trans segment compared to the LG (p=0.03) and the PG (p=0.003).

Conclusions:

The microscopic damage observed in the cis segment of cortical screws inserted in positional fashion may allow positional screws to function similarly to lag screws.