Effect of the Proximal Abducting Ulnar Osteotomy on Intra-Articular Pressure Distribution and Contact Mechanics of Congruent and Incongruent Canine Elbows Ex Vivo.

OBJECTIVE: To determine the effects of the Proximal Abducting Ulnar Osteotomy (PAUL) on contact pressures of congruent and incongruent (short radius) canine elbows. STUDY DESIGN: Ex vivo biomechanical study. SAMPLE POPULATION: Unpaired normal cadaveric canine forelimbs (n=16). METHODS: A servohydraulic testing frame and thin-film sensors were utilized to measure intra-articular contact area (CA), mean contact pressure (mCP), and peak contact pressure (pCP) for medial and lateral elbow compartments. Percent contribution of the medial compartment relative to the whole (%Med) was also examined. Baseline data were collected in 9 congruent elbows and 7 incongruent elbows where the radius was shortened. Both sets of elbows were tested following ulnar osteotomy and sequential placement of 2 and 3 mm PAUL plates and paw repositioning (to account for any medial to lateral shift of transarticular forces). Paired t-tests compared sequential procedural steps. P<.05 was significant. RESULTS: For congruent elbows, the 2 mm PAUL plate decreased CA in both compartments compared to baseline; lateral pCP increased with subsequent paw repositioning. Induction of radio-ulnar incongruity decreased CA and increased mCP medially, decreased pCP laterally, and increased %MedCA and %MedmCP compared to baseline. Both PAUL plates decreased mCP and pCP medially, with no effect laterally. Paw repositioning had no effect. CONCLUSION: The PAUL procedure had no effect on medial compartment pressure in the congruent elbow. It may ameliorate increased medial compartment pressure in the incongruent elbow. This change does not result from a medial to lateral compartmental shift and deserves further investigation.