Effect of Cortical Screw Diameter on Reduction and Stabilization of Type III Distal Phalanx Fractures: An Equine Cadaveric Study.

OBJECTIVE: To compare reduction of type III distal phalangeal fractures using 4.5 and 5.5 mm cortical screws placed in lag fashion and an intact hoof capsule model.

STUDY DESIGN: Cadaveric experimental study.

SAMPLE POPULATION: Hooves from 12 adult horses (n=24).

METHODS: Sagittal fractures were created in pairs of distal phalanges after distal interphalangeal joint disarticulation and were reduced with either 4.5 or 5.5 mm cortical screws placed in lag fashion. Contralateral phalanges served as non-reduced controls. Fracture reduction following screw placement was assessed by comparing pre-reduction and post-reduction fracture gap measurements from radiographs using paired t-tests. Effects of incremental loading (0, 135, 270, 540, 800, 1070, and 1335 kg) on fracture gaps in 6 phalanges reduced with 4.5 mm screws and 5 phalanges reduced with 5.5 mm screws were measured from fluoroscopic images and assessed by 2-way ANOVA. Significance was set at P<.05.

RESULTS: Type III distal phalanx fractures were reliably created. Only 5.5 mm cortical screws, not 4.5 mm screws, significantly reduced fracture gaps and constrained fracture gap expansion 3 cm distal to the articular surface. Compressive loading closed the fracture gaps at the articular surface in both non-reduced control groups and those reduced with either 5.5 or 4.5 mm screws.

CONCLUSION: The 5.5 mm cortical screws were more effective than 4.5 mm screws in reducing type III distal phalanx fractures and restricting distal fracture gap expansion under load.