Effects of sample site and size, skin tension lines, surgeon, and formalin fixation on shrinkage of skin samples excised from canine cadavers.

OBJECTIVE: To assess the effects of sample size and location, skin tension lines, surgeon, and formalin fixation on the extent of shrinkage that occurs in excised canine skin samples. ANIMALS: Cadavers of 4 adult purpose-bred mixed-breed hound dogs with grossly normal skin. PROCEDURES: 54 circular areas of skin (2-, 4-, and 6-cm-diameter samples from each of 9 body regions on each side) were excised by 1 of 2 surgeons from each cadaver. The diameter of each sample was measured in 4 orientations (parallel to previously reported tension lines, perpendicular to tension lines, in a dorsoventral orientation, and in a craniocaudal [or rostrocaudal] orientation) at 3 time points (before and immediately after excision and after 24 hours of formalin fixation). RESULTS: 216 samples were measured in all 4 orientations at all 3 time points. For all samples, mean ± SE decrease in diameter after fixation, compared with pre-excision findings, was 6.2 ± 0.7 mm. No significant correlations were found between percentage of skin shrinkage and surgeon, body side or region, or measurement orientation in relation to skin tension lines. The mean sample diameter immediately after excision differed significantly from that before excision (mean diameter decrease, 5.5 ± 0.7 mm). Overall, sample diameter immediately after excision and after formalin fixation did not differ. CONCLUSIONS AND CLINICAL RELEVANCE: The extent of shrinkage of skin samples from hound cadavers that occurred immediately after excision was notable. A better understanding of the effectors of excised skin sample shrinkage is needed, especially when histopathologic findings provide guidelines for surgical margins.

In vitro biomechanical comparison of 3.5 string of pearl plate fixation to 3.5 locking compression plate fixation in a canine fracture gap model.

OBJECTIVE: To compare the 3.5 string of pearls (SOP) plate with a 3.5 mm locking compression plate (LCP) using a fracture model in static loading and cyclic fatigue testing. STUDY DESIGN: In vitro biomechanical testing of paired tibias with a mid-diaphyseal ostectomy, stabilized by 1 of 2 locking systems. SAMPLE POPULATION: Cadaveric canine tibiae (n = 24 pairs). METHODS: Tibias were randomly divided into 4 equal groups: (1) 4-point bending single cycle to failure, (2) 4-point bending cyclic fatigue, (3) torsion single cycle to failure, and (4) torsion cyclic fatigue. Randomly assigned SOP and LCP bridged a 20 mm mid-diaphyseal ostectomy. Mean test variables values for each method were compared using a paired t-test within each group with significance set at P < .05. RESULTS: The SOP construct had significantly greater mean yield load, mean yield displacement, mean yield bending moment, mean composite rigidity and mean failure bending moment under static 4-point bending to failure than the LCP construct. Mean number of cycles to failure under 4-point bending was significantly greater for the SOP constructs but the mean number of cycles to failure in torsion was significantly greater for the LCP constructs. The LCP construct had significantly greater mean composite stiffness and significantly lesser mean displacement to yield and to failure in static torsion testing. CONCLUSION: The SOP construct was superior under bending static and cycling testing but the LCP construct was superior in static and cycling torsion testing.