Fixation technique influences the monotonic properties of equine mandibular fracture constructs.

This study seeks to identify the best method for fixing interdental space fractures in horse mandibles. It compares the biomechanical properties of four different fixation techniques and finds that dynamic compression plates (DCP) have the highest stiffness, but the relatively low yield value might lead to premature failure in fatigue testing without additional fixation.

Research Design and Methodology

• The research adopted an in vitro randomized block design using twenty-seven adult horse mandibles.
• The mandibles, featuring interdental osteotomies, were randomly split into four groups, each representing a different fixation technique: dynamic compression plates (DCP), external fixator (EF), external fixator with interdental wires (EFW), and intraoral splint with interdental wires (ISW).
• These mandibles were then subjected to monotonic cantilever bending until failure. Extensometers, placed across the osteotomy site, continuously recorded gap width measurements to derive angular displacement data.
• The researchers selected osteotomy gap width data at 50 and 100 Nm for a standard comparison of gap width before the yield point and failure point of all constructs tested.
• Characteristics such as stiffness, yield strength, and failure strength were determined from bending moment-angular displacement curves and compared using ANOVA, with post hoc testing applied as required. Radiographs were taken before fixation, after fixation, and after testing.

Results of the Study

• The study revealed that bending stiffness, yield, and ultimate failure loads were greatest for intact mandibles.
• Among osteotomized mandibles, DCP constructs had the highest stiffness, and there was no significant difference between
  EF, EFW, and ISW constructs.
• The yield load was greatest for ISW constructs, and not much difference was found between DCP and EFW constructs.
• The EF constructs showed the lowest yield and ultimate failure loads with the greatest osteotomy gap width at both 50 and 100 Nm.
• The failure modes of the constructs varied, occurring through the screw-bone interface in DCP, the acrylic splint in ISW, the acrylic connecting bar or pin-bone interface in EF and EFW, and wire loosening in EFW. All intact mandibles fractured through the vertical ramus at its attachment to the testing apparatus.

Conclusion

• The research determined that among osteotomized mandibles, DCP fixation demonstrated the highest stiffness under monotonic bending to failure. However, its relatively low yield value may predispose it to earlier failure during fatigue testing without supplemental fixation.
• The techniques using tension-band wiring (EFW and ISW) were similar to DCP constructs in yield, failure, and osteotomy displacement. The EF constructs, however, were biomechanically weaker than the other constructs.
• Therefore, the research suggested that DCP fixation is probably the most stable form of fixing comminuted interdental space fractures. For simple interdental space fractures, though, ISW fixation might present a less invasive and more cost-efficient alternative with adequate stability.
• Given the notable enhancement of strength in type II external skeletal fixators, the research recommended the use of tension-band wiring to supplement mandibular fracture repairs.