Effects of Humeral Rotational Osteotomy on Contact Mechanism of the Canine Elbow Joint. An Ex Vivo Study

Introduction
Elbow joint disease is a common cause of front limb lameness in the dog, with usually the medial part of this joint being affected. Although this syndrome is well known, the outcome, especially long term, is unsatisfactory since patients develop osteoarthritis regardless of treatment. In an attempt to improve outcome, new options of treatment aiming to relieve pressure in the medial part of this joint have recently been published. It has been suggested that, an external rotational osteotomy of the distal humerus would result in lateral translation of the paw, and this translation would cause a lateral shift of the weight- bearing axis and a lateral shift of the transarticular forces in the elbow joint. The purpose of this ex-vivo study was to investigate the effects of the humeral rotational osteotomy on the forces acting in the canine elbow joint. Our hypothesis was that external humeral rotation of 15 ° would shift the peak pressure location and the center of pressure towards lateral.

Materials and Methods
Eight forelimbs of 5 adult dogs were harvested by forequarter amputation. Computer tomography was performed to ensure that the elbows were free of orthopedic disease and to plan for the rotation. An approach by osteotomy of the lateral humeral epicondyle was performed. The epicondyle was reflected distally, and a second osteotomy (used later on to position a pressure sensor into it) was performed parallel to the articular surface of the radius and ulna, proximal to the insertion of the lateral collateral ligament in the radius, including the ventral part of the articular surface of the ulnar notch, and the entire radial head. The semilunar notch and the anconeal process were mobilized by a third subchondral osteotomy perpendicular to the second osteotomy. This osteotomy allowed the articular part of the separated ulna and radial head to slide proximo-distally and load the sensor placed in the horizontal osteotomy site. A digital pressure sensor (Pliance® -â S2070 Germany) was positioned into the subchondral osteotomy site at the radial head and proximal ulna. The leg was mounted in the testing apaparatus and measurements were taken in the following sequence: (1) neutral, and (2) after 15° of external rotation. To rotate the distal humerus a mid-diaphysear humerus osteotomy was performed and stabilized with a locking plate.  [...]