Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of three 4.5-mm and two 5.5-mm cortical screws.

The research compared the biomechanical characteristics and the mode of failure between two parallel-screw techniques used for the fusion of the proximal interphalangeal joint (pastern arthrodesis) in horses. It concluded that using two 5.5-mm screws or three 4.5-mm screws yielded similar characteristics and robustness, though two 5.5-mm cortical screws offered a simpler surgical procedure without compromising biomechanical integrity.

Research Methodology

• The study made use of 20 limbs (10 pairs) extracted from 5 equine cadavers.
• It employed a randomized block design method, where the researchers divided the study’s variables into specific blocks: horse number, method of screw fixation, side (left vs right limb), and end (front vs hind limb).
• During the experiment, the researchers utilized a combined aiming device to facilitate consistent screw placement.
• They placed three parallel 4.5-mm cortical screws in the lag fashion in one limb of a pair, while two parallel 5.5-mm cortical screws were placed similarly in the opposite limb.

Testing Procedure

• Testing of the arthrodesis constructs involved a 3-point bending process in a dorsal-to-palmar (plantar) direction, utilizing a materials-testing machine. The loading rate applied was 19 mm per second.
• Through this process, they collected data on the maximal bending moment (the peak force exerted on the construct before failure) and composite stiffness from bending moment-angular deformation curves.

Results Analysis

• When it came to the bending moment and composite stiffness, there were no significant differences between the two fixation techniques.
• However, the study found that front limbs exhibited a higher maximal bending moment than hind limbs.
• Front limbs that utilized two 5.5-mm screws had a higher maximal bending moment than hind limbs with the same screws.
• In all cases, constructs completely failed, which indicates the force applied in the experiment was greater than their ability to withstand.
• Between the two screw sizes, more 4.5-mm cortical screws failed than the larger 5.5-mm cortical screws.

Conclusions

• Results showed that in pastern arthrodesis constructs subjected to 3-point bending, the use of either front or hind limb affected the maximal bending moment at failure of constructs.
• The horse number, treatment method, and side of the limb used had no significant effect on the maximal bending moment or stiffness.
• It was found that using two 5.5-mm cortical screws offered a simpler surgical procedure than using three 4.5-mm cortical screws, while preserving comparable biomechanical characteristics.
• Whether three 4.5-mm screws or two 5.5-mm screws were used, similar biomechanical characteristics in bending were found when performing equine pastern arthrodesis.