Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of two 7-hole 3.5-mm broad and two 5-hole 4.5-mm narrow dynamic compression plates.

Abstract

To compare the biomechanical characteristics and mode of failure of two different dynamic compression plate (DCP) techniques for proximal interphalangeal joint (PIPJ) arthrodesis in horses.
Randomized block-design blocking on horse (1-5), method of fixation (two 7-hole, 3.5-mm broad DCP vs two 5-hole, 4.5-mm narrow DCP), side (left, right), and end (front, hind). Constructs were loaded to failure in 3-point bending in a dorsal-to-palmar (plantar) direction.
Ten paired limbs from 5 equine cadavers.
Two 7-hole, 3.5-mm broad dynamic compression plates (bDCP) were used in 1 limb of a pair, and two 5-hole 4.5-mm narrow dynamic compression plates (nDCP) were used on the contralateral limb. Plates were positioned abaxially across the dorsomedial and dorsolateral aspect of the PIPJ. Arthrodesis constructs were loaded (19 mm/s) in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials-testing machine. Composite stiffness, yield point, and maximal bending moment at failure were obtained from bending moment-angular deformation curves. Data were analyzed using ANOVA, X(2) analysis, and Fisher's exact tests; the power of the test was calculated when differences were not significant.
There were no significant differences in composite stiffness (P >.05; power = 0.8 @ delta = 21.9%), yield point (P >.05; power = 0.8 @ delta = 34.4%), or maximal bending moment (P >.05; power = 0.8 @ delta = 17.8%) between the two fixation techniques. For bDCP constructs, 11% (15 of 140) of the 3.5-mm screws were damaged; 7 of the screw heads pulled through plates where the plates bent, 1 screw head broke off, and 7 screws were bent or pulled out of the phalanx. For nDCP constructs, 8% (8 of 100) of the 4.5-mm screws were damaged; 1 screw head pulled through a plate, 1 screw head broke off, and 6 screws were bent or pulled out of the phalanx.
There were no biomechanical or failure differences between bDCP and nDCP fixation of the PIPJ in horses when evaluated in single-cycle 3-point bending to failure.
There is no biomechanical advantage to the use of two 7-hole, 3.5-mm bDCP in equine proximal interphalangeal arthrodesis compared with two 5-hole, 4.5-mm nDCP. Two 5-hole, 4.5-mm nDCP may be easier to place, whereas two 7-hole, 3.5-mm bDCP may provide more versatility in fracture repair.