An in vitro biomechanical comparison of a 5.5 mm limited-contact dynamic compression plate fixation with a 4.5 mm limited-contact dynamic compression plate fixation of osteotomized equine third metacarpal bones.
OBJECTIVE
To compare monotonic biomechanical properties and fatigue life of a 5.5 mm broad limited-contact dynamic compression plate (5.5-LC-DCP) fixation with a 4.5 mm broad LC-DCP (4.5-LC-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones.


METHODS
In vitro biomechanical testing of paired cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation.


METHODS
Adult equine cadaveric MC3 bones (n=18 pair).


METHODS
MC3 were divided into 3 test groups (6 pairs each) for: (1) 4-point bending single cycle to failure testing; (2) 4-point bending cyclic fatigue testing; and (3) torsional single cycle to failure testing. The 8-hole, 5.5 mm broad LC-DCP (5.5-LC-DCP) was applied to the dorsal surface of 1 randomly selected bone from each pair. One 8-hole, 4.5 mm broad LC-DCP (4.5-LC-DCP) was applied dorsally to the contralateral bone from each pair. Plates and screws were applied using standard ASIF techniques. All MC3 bones had mid-diaphyseal osteotomies. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P<.05.


RESULTS
Mean yield load, yield bending moment, composite rigidity, failure load and failure bending moment under 4-point bending, single cycle to failure, of the 5.5-LC-DCP fixation were significantly greater (P<.024) than those of the 4.5-LC-DCP fixation. Mean cycles to failure for 4-point bending was significantly (P<.05) greater for the 4.5-LC-DCP fixation compared with the 5.5-LC-DCP fixation. Mean yield load, mean composite rigidity, and mean failure load in torsion for the 5.5-LC-DCP fixation was not significantly different (P>.05) than those with the 4.5-LC-DCP fixation.


CONCLUSIONS
5.5-LC-DCP fixation was superior to 4.5-LC-DCP fixation in resisting the static overload forces under palmarodorsal 4-point bending. There was no significant difference between 5.5-LC-DCP fixation and 4.5-LC-DCP fixation in resisting static overload forces under torsion; however, the 5.5-LC-DCP offers significantly less stability (80% of that of the 4.5-LC-DCP) in cyclic fatigue testing.


CONCLUSIONS
The results of this in vitro study may provide information to aid in the selection of a biological plate for long bone fracture repair in horses.
Sod
Gary A
GA
Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA. gsod@vetmed.lsu.edu
Mitchell
Colin F
CF
Hubert
Jeremy D
JD
Martin
George S
GS
Gill
Marjorie S
MS
D000818:Animals; D001696:Biomechanical Phenomena; D001860:Bone Plates / Q000592:standards / Q000662:veterinary*; D002102:Cadaver; D019245:Compressive Strength; D004868:Equipment Failure / Q000662:veterinary; D005593:Fracture Fixation, Internal / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D006736:Horses; D016268:Internal Fixators / Q000662:veterinary*; D050279:Metacarpal Bones / Q000293:injuries* / Q000601:surgery*; D010027:Osteotomy / Q000379:methods / Q000662:veterinary; D011897:Random Allocation