NICOLE S. AMATO, DVM 1,2 , ANDREW RICHARDS, MD 1,2 , TREVOR A. KNIGHT, BS 1,2 , DANIEL SPECTOR, DVM 1,2 , RANDY J. BOUDRIEAU, DVM, Diplomate ACVS and ECVS 1,2 , and STEPHEN BELKOFF, PhD 1,2 1 Department of Clinical Sciences, Cummings School of Veterinary Medicine at Tufts University, North Grafton, MA; and 2 Department of Orthopaedic Surgery, International Center for Orthopaedic Advancement, the Johns Hopkins University/Johns Hopkins Bayvi Vet Surg 2008 Dec 37 8 741-48 ABSTRACT Objective—To compare the accuracy of reduction and the biomechanical characteristics of canine acetabular osteotomies stabilized with locking versus standard screws in a locking plate. Study Design—Ex vivo biomechanical study. Sample Population—Cadaveric canine hemipelves and corresponding femurs (n=10 paired). Methods—Transverse acetabular osteotomies stabilized with 5-hole 2.4 mm uniLOCK® reconstruction plates using either 2.4 mm locking monocortical or standard bicortical screw fixation (Synthes® Maxillofacial). Fracture reduction was assessed directly (craniocaudal acetabular width measurements and gross observation) and indirectly (impression casts). All constructs were fatigue-tested, followed by acute destructive testing. All outcome measures (mean±SD) were evaluated for significance (P<.05) using paired t-tests. Results—Craniocaudal acetabular diameters before and after fixation were not significantly different (21.9±1.2 and 21.5±1.2 mm; P=.45). No significant differences were observed in acetabular width differences between pre- and postoperative fixation between groups (locking −0.4±0.4 mm; standard −0.4±0.3 mm; P=.76). Grossly, there was no significant difference in the repairs and impression casts did not reveal a significant (P=.75) difference in congruency between the groups. No significant differences were found in fracture gap between groups either dorsally (locking 0.38±0.23 mm versus standard 0.22±0.05 mm; P=.30) or ventrally (locking 0.80±0.79 mm versus standard 0.35±0.13 mm; P=.23), and maximum change in amplitude dorsally (locking 0.96±2.15 mm versus standard 0.92±0.89 mm; P=.96) or ventrally (locking 2.02±2.93 mm versus standard 0.15±0.81 mm; P=.25). There were no significant differences in stiffness (locking 241±46 N/mm versus standard 283±209 N/mm; P=.64) or load to failure (locking 1077±950 N versus standard 811±248 N; P=.49). Conclusion—No significant differences were found between pelves stabilized with locking monocortical screw fixation or standard bicortical screw fixation with respect to joint congruity, displacement of fracture gap after cyclic loading, construct stiffness, or ultimate load to failure. Clinical Relevance—There is no apparent advantage of locking plate fixation over standard plate fixation of 2-piece ex vivo acetabular fractures using the 2.4 mm uniLOCK® reconstruction plate.