Arthrodesis of the equine proximal interphalangeal joint: a mechanical comparison of 2 parallel 5.5 mm cortical screws and 3 parallel 5.5 mm cortical screws.

This study examined the strength and failure mode of two different techniques for pastern joint arthrodesis in horses, using either two or three parallel 5.5mm screws for fixation. The results suggest both techniques provide equal strength and stiffness, with no significant differences detected. Therefore, using two parallel 5.5mm screws may be a simpler yet equally effective option for performing this surgical procedure.

Research Methodology

• The research used a randomized block design with the variables being: the horse (1-5), the method of fixation (two or three 5.5 mm screws), the side of the limb (right or left), and the end of the limb (front or hind).
• Twenty limbs from five cadavers were used for testing.
• A specialized tool was used to ensure accurate screw placement. In one limb, two parallel 5.5mm screws were inserted in a specific manner referred to as ‘lag fashion’, while the other limb had three 5.5mm screws inserted.
• The strength of the constructs was tested using a three-point bending method in a dorsal-to-palmar (plantar) direction, using a materials testing machine at a loading rate of 19mm/s.
• The maximal bending moment at failure, and stiffness, were recorded and analyzed.

Research Findings

• Results revealed no statistically significant difference in bending moment and stiffness between the constructs using two screws and those using three screws.
• All constructs ultimately failed either due to bone fracture or screw bending.
• No significant effects were found on maximal bending moment or stiffness from the variables of treatment, side, or end when loaded in a three-point bending method.

Conclusions

• The conclusion of this study was that a simpler surgical procedure of inserting two 5.5 mm cortical screws in parallel should provide an equally sturdy joint arthrodesis as compared to a procedure using three 5.5mm screws.
• The researchers state that two screws should perform similarly to three when used in this specific procedure, under the conditions tested in this experiment.