In vitro biomechanical comparison of a 4.5 mm narrow locking compression plate construct versus a 4.5 mm limited contact dynamic compression plate construct for arthrodesis of the equine proximal interphalangeal joint.

This research presents an in vitro examination comparing two methods, 4.5 mm narrow locking compression plate (PIP-LCP) and 4.5 mm limited contact dynamic compression plate (LC-DCP), for stabilizing the equine proximal interphalangeal (PIP) joint in horses. The evaluation, using adult equine forelimbs, found that the PIP-LCP method resulted in a stiffer construct with similar strength to the LC-DCP, providing an alternative tool for equine surgery.

Introduction and Methodology

• The research sought to compare the efficacy of two stabilization techniques for equine PIP joints: the 4.5 mm narrow locking compression plate (PIP-LCP) and the 4.5 mm limited contact dynamic compression plate (LC-DCP). These techniques are used to stabilize the joints to facilitate healing or to manage joint diseases.
• The study ran mechanical tests on the forelimbs of 8 pairs of adult horses, using both the PIP-LCP and LC-DCP techniques. The joints were randomly assigned a plate type and then outfitted with two parasagitally positioned 5.5 mm transarticular screws. The proximal (P1) and distal (P2) aspects of these joints were embedded to fit onto a mechanical testing machine.

Testing and Results

• The authors applied two types of testing to the constructs: cyclic testing and single-cycle-to-failure testing in a 4-point bending model. The target load for the cyclic testing was set at 1 kN across 3600 cycles at a frequency of 1 Hz. The team then recorded the amount of displacement required to maintain this load.
• In the cyclic tests, LC-DCP-constructs exhibited significantly more displacement (0.46 ± 0.10 mm) than PIP-LCP constructs (0.17 ± 0.11 mm). However, in the single cycle tests, there was no significant difference in the bending moment, a measure of torque, between the LC-DCP (148.7 ± 19.4 N m) and the PIP-LCP (164.6 ± 17.6 N m).
• The stiffness of the LC-DCP (183.9 ± 26.9 N mm) was significantly lower than that of the PIP-LCP (279.8 ± 15.9 N/mm), indicating that the PIP-LCP produced a significantly stiffer construct. All constructs failed due to fracture of the bone related to the transarticular screws and bending of the plates at the middle hole.

Conclusions

• The results highlight the PIP-LCP as a viable alternative to the LC-DCP. It yielded a stiffer construct without sacrificing strength, potentially improving stability and recovery when used in an in-vivo clinical setting on equine pasterns, especially when dealing with joint diseases. However, actual in vivo application would require additional study.