An in vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: two parallel transarticular headless tapered variable pitch screws versus two parallel transarticular AO cortical bone screws inserted in lag fashion.

The research compares two methods for equine proximal interphalangeal joint arthrodesis, a surgical fixation procedure. The study found that the technique involving two parallel transarticular screws inserted in a lag fashion displayed more resistance to cyclic fatigue under axial compression than that involving two parallel headless screws.

Objective and Method

• The primary aim of the study was to compare two techniques for equine proximal interphalangeal joint (PIP) arthrodesis, a procedure that aims to stabilize joints. The two methods in question involve the use of 2 parallel transarticular screws: one uses Acutrak Plus screws (AP-TS) and the other uses 5.5mm cortical screws inserted in a ‘lag’ fashion (AO-TLS).
• In order to make this comparison, the research team used paired in vitro (lab-based) biomechanical testing on adult equine forelimbs. Each forelimb pair had one PIP joint stabilized with the AP-TS method and one with the AO-TLS. The constructs were then tested for cyclic fatigue under axial compression, effectively simulating the strains experienced by a joint over time.

Results

• The study focused on the mean number of cycles each construct could withstand before failure – in other words, where the stabilization of the joint gave way under pressure. The Mean number of cycles to failure under axial compression for AO-TLS fixation and AP-TS fixation were 57,723±8488 and 35,322±4698, respectively. The measurements were statistically significant (P<.05) and therefore notable.
• The AO-TLS method demonstrated a superior resistance to cyclic fatigue under axial compression when compared to the AP-TS method. This suggests that constructs stabilized with the AO-TLS technique would last longer under the same amount of strain. The paper did not discuss why this might be the case or the implications for surgical procedure choice.

Conclusions

• Given the study’s findings, the authors suggest that the AO-TLS method of equine PIP joint arthrodesis is more resilient to strain and cyclic fatigue than the AP-TS method. This information could influence veterinary surgeons’ choice of surgical techniques when stabilizing equine PIP joints. However, further research may be needed to fully understand why the AO-TLS method outperforms the AP-TS method and whether there are other factors at play that could influence the choice of procedure.