In Vitro Biomechanical Comparison of a 4.5mm Narrow Locking Compression Plate Construct Versus a 4.5mm Limited Contact Dynamic Compression Plate Construct for Arthrodesis of the Equine Proximal Interphalangeal Joint

Objectives To compare the in vitro biomechanical properties of a 4.5mm narrow locking compression plate (PIP-LCP) with 2 abaxially located transarticular screws and a 4.5mm 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 5.5mm 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 1kN over 3600 cycles at 1Hz 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 +/- 0.10mm) than for the PIP-LCP (0.17 +/- 0.11mm) constructs (P=.016). During single cycle testing there was no significant difference in the bending moment between the LC-DCP (148.7 +/- 19.4Nm) and the PIP-LCP (164.6 +/- 17.6Nm) constructs (P=.553) and the stiffness of the LC-DCP (183.9 +/- 26.9Nmm) was significantly lower than for the PIP-LCP (279.8 +/- 15.9N/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.