Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of three 4.5-mm and two 5.5-mm cortical screws.
OBJECTIVE
To compare the biomechanical characteristics and mode of failure of 2 parallel-screw techniques for proximal interphalangeal joint arthrodesis in horses.


METHODS
Randomized block design, blocking for horse (1-5), method of screw fixation (three 4.5-mm vs two 5.5-mm), side (left limb vs right limb), and end (front limb vs hind limb). Constructs were loaded to failure in 3-point bending in a dorsal-to-palmar (plantar) direction.


METHODS
Twenty limbs (10 limb pairs) from 5 equine cadavers.


METHODS
A combined aiming device was used to facilitate consistent screw placement. Three parallel 4.5-mm cortical screws were placed in lag fashion in 1 limb of a pair, and 2 parallel 5.5-mm cortical screws were placed in lag fashion in the contralateral limb. Arthrodesis constructs were tested in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials-testing machine. Loading rate was 19 mm/s. Maximal bending moment at failure and composite stiffness were obtained from bending moment-angular deformation curves. Data were analyzed using ANOVA and chi(2) analysis.


RESULTS
There were no significant differences in bending moment (P >.05, power = 0.8 @ delta = 19%) or composite stiffness (P >.05, power = 0.8 @ delta = 19%) between the 2 fixation techniques. Higher maximal bending moment was found in front limbs than hind limbs, and front limbs with two 5.5-mm screws than hind limbs with two 5.5-mm screws. In all cases, constructs completely failed. A greater number of 4.5-mm cortical screws failed than 5.5-mm cortical screws. CONCLUSIONS-In pastern arthrodesis constructs loaded in 3-point bending, end (front limb vs hind limb) affected maximal bending moment at failure of constructs. There was no significant effect of horse, treatment, or side on maximal bending moment or stiffness. Two 5.5-mm cortical screws should provide a surgically simpler pastern arthrodesis than three 4.5-mm cortical screws while maintaining similar biomechanical characteristics.


CONCLUSIONS
Three 4.5-mm screws or two 5.5-mm screws will provide similar biomechanical characteristics in bending when performing equine pastern arthrodesis.
Watt
B C
BC
Comparative Orthopaedic Research Laboratory, Department of Surgical and Medical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, Madison, WI, USA.
Edwards
R B
RB
Markel
M D
MD
McCabe
R
R
Wilson
D G
DG
D000818:Animals; D001174:Arthrodesis / Q000295:instrumentation / Q000662:veterinary*; D001696:Biomechanical Phenomena; D001863:Bone Screws / Q000662:veterinary*; D005552:Forelimb; D006614:Hindlimb; D006724:Hoof and Claw / Q000601:surgery*; D006736:Horses / Q000293:injuries / Q000601:surgery*; D008422:Materials Testing; D011897:Random Allocation