Ex vivo contact mechanics and three-dimensional alignment of normal dog elbows after proximal ulnar rotational osteotomy.

OBJECTIVE: To evaluate the effect of proximal ulnar rotational osteotomy (PURO) on the contact mechanics and 3-dimensional (3D) alignment of cadaveric normal dog elbows. STUDY DESIGN: Ex vivo biomechanical study. ANIMALS: Unpaired thoracic limbs from 12 dogs (mean ± SD weight, 26 ± 4 kg). METHODS: PURO consisted of a transverse osteotomy with 30° external rotation of the proximal segment. With the limb under 200 N axial load, contact area (CA), mean contact pressure (CP) and peak contact pressure (PCP) were measured using digital pressure sensors in the medial and lateral compartments and 3D static elbow poses were obtained, before and after PURO. Each specimen was tested at 115°, 135°, and 155° elbow flexion, with the antebrachium in neutral rotation, in 28° supination, and in 16° pronation. Repeated measures ANOVAs with post-hoc Bonferroni (P ≤ .05) were performed. RESULTS: PURO caused significant changes, mostly at 135° elbow flexion and neutral antebrachial rotation, characterized by decreased CP (10%) and PCP (10%) in the medial compartment, and increased CP (27%) and PCP (23%) in the lateral compartment. The apex of the medial coronoid process translated 3.4 mm caudally, 1.7 mm abaxially, and rotated 1.8° externally relative to the radial head. Humeroradial varus angulation reduced by 6.7°. CONCLUSIONS: In limited poses, PURO displaces the medial coronoid process caudally and abaxially and shifts contact pressures towards the lateral elbow compartment by decreasing varus angulation.