Effects of simulated radioulnar synostosis on supination and pronation in cats. A cadaveric study.

OBJECTIVE: To evaluate the effect of an induced synostosis with a screw on pronation and supination in cats. STUDY DESIGN: Ex vivo biomechanical study. SAMPLE POPULATION: A total of 58 feline forelimbs. METHODS: A total of 58 cadaveric feline thoracic limbs were mounted on a custom-built jig with the elbow and carpus flexed at a 90° angle. To exclude any orthopedic disease, radiographs of the forelimbs were performed prior to the mechanical tests. Radioulnar synostosis was imitated with a 2 mm cortical screw through the radius into the ulna in the proximal (Group P; n = 54), middle (Group M; n = 52), and distal (Group D; n = 53) radial diaphysis. The angles of pronation and supination were recorded after manually applying a two-finger tight rotational force to the metacarpus. Rotational tests were performed without a screw (Group N) and with a screw in each of the aforementioned positions. Pairwise comparisons between the groups were performed based on their angles of rotation with a paired t-test with the Benjamini-Hochberg procedure and a mixed model ANOVA. RESULTS: Mean angles of rotation decreased between Group N (129.5 ± 15.9°) and all groups with imitated radioulnar synostosis to a mean angle of 37.5 ± 14.5° (p < .0001). Mean angles of rotation did not differ between the groups with imitated radioulnar synostosis. CONCLUSION: Induced radioulnar synostosis decreases antebrachial rotation by more than two-thirds, regardless of location. CLINICAL SIGNIFICANCE: Implants fixating the radius to the ulna should be avoided in cats, regardless where they are located along the radial diaphysis.

Ex vivo comparison of lateral plate repairs of experimental oblique ilial fractures in cats.

OBJECTIVE: To determine the biomechanical behavior of different plate systems used for oblique ilial fracture fixation in cats. STUDY DESIGN: Ex vivo biomechanical study. SAMPLE POPULATION: Fifty fresh-frozen feline hemipelvises. METHODS: Standardized simple oblique ilial fractures were created and fixed via lateral plating, using different implant systems (10 fractures in each group) The systems were: (1) the Advanced Locking Plate System (ALPS-5); (2) the Advanced Locking Plate System (ALPS-6.5); (3) the Locking Compression Plate 2.0 (LCP); (4) the FIXIN 1.9-2.5 Series (FIXIN), and (5) the Dynamic Compression Plate 2.0 (DCP). Stepwise sinusoidal cyclic loading was applied until failure (10-mm displacement). The groups were compared with regard to construct stiffness and the number of cycles withstood before 1-, 2-, 5-, and 10-mm displacement. RESULTS: Bending stiffness was lower in ALPS-5 than in other specimens (P < .05). The ALPS-6.5 specimens withstood more cycles (P < .05) before 2-, 5-, and 10-mm displacement than the ALPS-5 and DCP specimens . The LCP and FIXIN specimens endured more cycles than DCP specimens before displaying 5- and 10-mm displacement (P < .05). The ALPS-6.5, FIXIN, and LCP specimens endured higher loads before failure than the DCP specimens (P < .05). Screw loosening occurred in all nonlocking specimens, and bone slicing occurred in all locking specimens. CONCLUSION: The DCP and ALPS-5 constructs are less resistant to cyclic loading. Failure in nonlocking specimens involved screw loosening. It involved bone slicing in locking specimens. CLINICAL SIGNIFICANCE: Both the plate size and the plate-screw interface are key to lateral plating success in cases of feline ilial fractures. The use of locking plates reduces the risk of the screw loosening in such cases.