Arthrodesis of the proximal interphalangeal joint in the horse: a cyclic biomechanical comparison of two and three parallel cortical screws inserted in lag fashion.

This study investigates the cyclic fatigue properties of two compared to three screws used in a surgical procedure that fuses the proximal interphalangeal joint in horses. The research found that the number of screws used does not significantly impact the performance under cyclic fatigue conditions.

Objective

The research aimed to compare the biomechanical properties of using two versus three transarticular 5.5 mm cortical screws in the procedure of fusing (arthrodesis) the proximal interphalangeal (PIP) joint in horses. The screws were inserted in a cadaveric equine limbs model, and the cyclic fatigue conditions were simulated to evaluate the performance.

Methodology

• The researchers used a randomized block design, taking into account factors such as the fixation method (two or three screws), side (right or left), and end (front or hind).
• The subjects used for the study were cadaveric adult equine fore- and hindlimbs (a total of five pairs).
• In one limb of a pair, two parallel 5.5 mm cortical screws were inserted transarticularly through the PIP joint. In the contralateral limb, three 5.5 mm cortical screws were similarly inserted.
• These constructs were tested in a materials testing machine using a 3-point bending approach in a dorsal-to-palmar direction. The tests were conducted under a cyclic load of -500 to -3500 N at a rate of 6 Hz.

Results

• There was no significant difference in displacement at failure, force at failure, or number of cycles between limbs, irrespective of the number of screws used.
• Forelimb constructs were observed to fail at a greater mean displacement than hindlimb constructs, but this difference was not statistically significant.
• No significant difference was observed in any tested biomechanical variable between left- and right-sided limbs.

Conclusions

• The study concluded that the number of cycles to failure was not significantly different between the two methods tested.
• Using two 5.5 mm cortical screws for PIP joint arthrodesis was found to be surgically simpler and yielded comparable biomechanical performance in the model used for this study. Therefore, it should perform as well as three 5.5 mm screws under cyclic fatigue conditions.