Effect of proximal abducting ulnar osteotomy (PAUL) on frontal plane thoracic limb alignment: An ex vivo canine study.

Objective To determine the effect of proximal abducting ulnar osteotomy (PAUL) on frontal plane thoracic limb alignment in standing and recumbent positions. Study design Ex vivo cadaveric study. Sample population Canine thoracic limbs (n = 15 limb pairs). Methods Limbs were acquired from healthy Labrador retrievers that had been euthanized for reasons unrelated to this study. A limb press was used to obtain standing and recumbent caudocranial radiographs before and after PAUL. Foot lateralization and rotation were directly measured in standing position. Mechanical joint angles were determined using full limb radiographic montages and the center of rotation of angulation (CORA) method for pre-PAUL (Pre), 2-mm PAUL (PAUL2), and 3-mm PAUL (PAUL3). Data are reported as mean +/- SD and 95% CI. Mixed linear modeling was used to identify differences in limb alignment values and foot position, with significance established at P <= .004. Results There were differences in five of 12 limb alignment values pre-PAUL and post-PAUL in standing and recumbent positions. In the standing position, there was an increase in mechanical medial proximal radioulnar angle (Pre, 80.6 degrees +/- 2.5 degrees; PAUL2, 82.6 degrees +/- 2.4 degrees; PAUL3, 84 degrees +/- 2.4 degrees) and a decrease in elbow compression angle (Pre, 1.4 degrees +/- 1.3 degrees; PAUL2, 1 degrees +/- 0.9 degrees; PAUL3, 0.8 degrees +/- 1 degrees). There was a movement of mechanical humeral radioulnar angle (Pre, -8.9 degrees +/- 2.8 degrees; PAUL2, -6.1 degrees +/- 2.7 degrees; PAUL3, -5.2 +/- 2.7 degrees), mechanical thoracic humeral angle (Pre, 3.9 degrees +/- 1.7 degrees; PAUL2, 2.4 degrees +/- 1.4 degrees; PAUL3, 2.6 degrees +/- 1.5 degrees), and elbow mechanical axis deviation (Pre, 1.9% +/- 1.1%; PAUL2, 0.9% +/- 1.1%; PAUL3, 0.4% +/- 1.4%) toward a value of "0" representing coaxial alignment of the limb. The foot underwent lateralization (Pre, 1.4 +/- 0.6 cm; PAUL2, 1.8 +/- 0.7 cm; PAUL3, 2.3 +/- 0.7 cm) and external rotation (Pre, 10.5 degrees +/- 4.7 degrees; PAUL2, 13.7 degrees +/- 5.1 degrees; PAUL3, 16 degrees +/- 6.6 degrees). Conclusion In the ex vivo setting, PAUL resulted in translation of the mechanical axis of the thoracic limb from a medial to lateral direction through alterations in limb alignment values associated with the elbow, humerus, and proximal radius/ulna. Clinical significance Additional studies are required to determine whether PAUL alters thoracic limb alignment in client-owned dogs.