Does the proximal screw type affect stress and strain in pastern arthrodesis with locking plate in horses?

This research paper studies the effect of different types of proximal screws on the stress and strain in pastern arthrodesis with a locking plate in horses. The findings suggest that bicortically placed cortex screws are the most suitable for the procedure.

Research Context

• In the field of veterinary orthopedics, proximal interphalangeal (PIP) arthrodesis, a procedure to fuse the joint, is often performed in horses.
• The use of locking compression plates (LCP) with unicortical cortex screws in the proximal hole has been recommended to prevent fractures resulting from stress risers in the proximal phalanx (P1).

Research Problem

• While the above technique is effective in minimizing fractures, it may restrict efficient dorsal compression of the PIP joint by the plate. This circumstance could potentially affect the stability of the construct.

Aims of the Research

• The aim of the study was to measure and analyze the stress and strain in P1 and the plate during ex vivo PIP arthrodesis in horses using different proximal screw types and implantation methods.

Methods

• Two types of screws were tested: cortex screws and locking screws. In each case, screws were placed either unicortically or bicortically.
• These variations were applied to ten pairs of equine forelimbs, which were divided into four groups based on the screw placement method used.
• Following the implantation process, the forelimbs were subjected to axial compression mechanical testing, during which the magnitude and direction of strain, strain ratio, and stress were calculated.

Results and Conclusions

• The results showed that the palmar surface of P1 experienced higher stress and strain compared to the dorsal surface, and the plate part located at the articular level carried more stress than the proximal part.
• The proximal screw type and the implantation method both played significant roles in influencing the stress and strain parameters.
• The research concluded that using a bicortically placed cortex screw to fill the proximal hole of the LCP was the most optimal method. It provided effective dynamic compression via the plate and prevented abrupt shifts in the direction of the forces acting on the proximal part of P1 during loading.