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.

The research essentially compares two plate sizes (5.5 mm and 4.5 mm) used to repair equine third metacarpal bones. The study finds that the 5.5 mm plate offers better resistance against static overload forces under bending, while there’s no significant difference in resistance under torsion. However, the smaller 4.5 mm plate offers more stability in cyclic fatigue testing.

Objective of the Study

• The study aimed to compare the efficiency of two different sizes of limited-contact dynamic compression plates (LC-DCPs) used for the fixation of osteotomized (cut for surgical purposes) third metacarpal bones in horses.
• These two plate sizes were the 5.5 mm broad LC-DCPs and the 4.5 mm broad LC-DCPs. The comparison was made based on their biomechanical properties and their fatigue life.

Methodology

• The researchers used 18 pairs of cadaveric (obtained from corpses) equine third metacarpal (MC3) bones for in vitro testing.
• The study categorized these MC3 bones into three groups, each with six pairs, for three different types of testing: single cycle to failure testing using 4-point bending, cyclic fatigue testing with 4-point bending, and single cycle to failure testing using torsion.
• One bone from each pair in each group was randomly selected and attached to a 5.5-LC-DCP while the contralateral bone was attached to a 4.5-LC-DCP. These plates and screws were applied using standard AO/ASIF techniques (Association for the Study of Internal Fixation).

Results

• Under 4-point bending single cycle to failure testing, the results revealed significantly greater yield load, yield bending moment, composite rigidity, failure load, and failure bending moment for the 5.5-LC-DCP compared to the 4.5-LC-DCP.
• In terms of 4-point bending cyclic fatigue testing, the rotations to failure were significantly more for the 4.5-LC-DCP when compared to the 5.5-LC-DCP.
• For torsional single cycle to failure testing, there was no significant difference between the yield load, composite rigidity, and failure load of the two plates.

Conclusions

• The study concludes that, under static overload forces, the 5.5-LC-DCP fixation was superior in resisting palmarodorsal 4-point bending compared to the 4.5-LC-DCP fixation.
• The smaller-sized 4.5-LC-DCP showed significantly more stability during cyclic fatigue testing.
• These findings are critical in guiding the selection of plates for long bone fracture repair in horses.