Minimally Invasive Arthrodesis of the Equine Proximal Interphalangeal Joint: A Biomechanical Comparison of Three 5.5-mm Cortical Screws Inserted in Lag Fashion and Two 7.0-mm Headless Cannulated Dual-Pitch Compression Screws

Objective The aim of this study was to compare the biomechanical properties of two minimally invasive arthrodesis techniques of the equine proximal interphalangeal (PIP) joint (three transarticular 5.5-mm cortical screws [AO-3TLS] vs. two transarticular 7.0-mm headless cannulated multi-use compression screws [MUC-2TS]) in dynamic non-destructive testing and compression testing to failure.Study Design The experimental study included six pairs of cadaveric adult equine forelimbs; one limb from each horse was randomly assigned to one of the treatments, and the contralateral limb was submitted to the remaining treatment. The dynamic test was performed alternating non-destructive compression tests at a displacement rate of 5 mm/min up to 5,000 N and sinusoidal compressive cyclic tests at 6 Hz, using a 3,600-N amplitude for 8,550 cycles. Construct stiffness and maximum sagittal plane rotation about the PIP joint markers were determined during the dynamic test. After the dynamic test reached 136,800 cycles, the monotonic compressive test until failure was performed on each construct: load, displacement and sagittal plane rotation about the PIP joint marker at failure were analysed.Results The evaluated biomechanical properties showed no statistical difference between the AO-3TLS and MUC-2TS treatment groups in any of the ramps of the dynamic non-destructive test and in the compression loading until failure test.Conclusion The MUC-2TS treatment produced biomechanical properties equivalent to the AO-3TLS treatment for PIP joint arthrodesis.