Comparison of the Mechanical Behaviors of Locked and Nonlocked Plate/Screw Fixation Applied to Experimentally Induced Rotational Osteotomies in Canine Ilia.

OBJECTIVE:
To compare the mechanical behaviors of 2 locked (parallel and diverging screws) and 1 nonlocked (NL) version of triple pelvic osteotomy (TPO) plate/screw fixation.
STUDY DESIGN:
In vitro biomechanical evaluation.
ANIMALS:
Cadaveric canine hemipelves.
METHODS:
Comparison 1-NL screws 20° TPO (NL-20) construct versus locked parallel (LP) screws 20° TPO (LP-20) construct (n = 7). Comparison 2-LP-20 construct versus locked diverging (LD) screws 20° TPO (LD-20) construct (n = 6). Condition 1-Nondestructive loading to determine stiffness. Condition 2-Cyclic loading to determine stiffness, screw loosening, and osteotomy gap displacement. Condition 3-Load to failure (yield load, yield displacement, maximum load, load to failure, failure mode).
RESULTS:
Stiffness was not significantly different for NL-20 versus LP-20 constructs (P = .48) or for LP-20 versus LD-20 constructs (P = .83). Screw loosening was significantly more frequent for NL-20 versus LP-20 (P = .01) and for LD-20 versus LP-20 constructs (P = .02). The relative risk for screw loosening with NL-20 constructs versus LP-20 constructs was 1.4 (95% CI: 1.1-1.8). The relative risk for screw loosening with LD-20 versus LP-20 was 1.6 (95% CI: 1.1-2.2). Yield load was significantly greater for LP-20 versus NL-20 and LD-20 constructs (P = .04, P = .03), respectively.
CONCLUSIONS:
No TPO constructs tested maintained complete integrity after cyclic loading; however, screw loosening was significantly reduced and yield loads were significantly larger for LP-20 plate/screw constructs.