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Abstract

Objectives

To compare the in vitro biomechanical properties of a 4.5 mm narrow locking compression plate (PIP-LCP) with 2 abaxially located transarticular screws and a 4.5 mm limited contact dynamic compression plate (LC-DCP) with 2 abaxially located transarticular screws using equine pasterns.

Study Design

Experimental. Paired in vitro biomechanical testing of 2 methods for stabilizing adult equine forelimb PIP joints.

Animal

Adult equine forelimbs (n = 8 pairs).

Methods

Each pair of PIP joints were randomly instrumented with either a PIP-LCP or LC-DCP plate axially and 2 parasagitally positioned 5.5 mm transarticular screws. The proximal aspect of the proximal phalanx (P1) and the distal aspect of the middle phalanx (P2) were embedded to allow for mounting on a mechanical testing machine. Each construct was tested in both cyclic and subsequently single cycle to failure in 4-point bending. The displacement required to maintain a target load of 1 kN over 3600 cycles at 1 Hz was recorded. Maximum bending moment at failure and construct stiffness was calculated from the single cycle to failure testing.

Results

In cyclic testing, significantly more displacement occurred in the LC-DCP (0.46 ± 0.10 mm) than for the PIP-LCP (0.17 ± 0.11 mm) constructs (P = .016). During single cycle testing there was no significant difference in the bending moment between the LC-DCP (148.7 ± 19.4 N m) and the PIP-LCP (164.6 ± 17.6 N m) constructs (P = .553) and the stiffness of the LC-DCP (183.9 ± 26.9 N mm) was significantly lower than for the PIP-LCP (279.8 ± 15.9 N/mm) constructs (P = .011). All constructs failed by fracture of the bone associated with the transarticular screws and subsequently bending of the plates at the middle hole.

Conclusions

Use of the PIP-LCP resulted in a stiffer construct of the same strength as the LC-DCP in vitro using this 4-point bending model.