Determination of the Mechanical Axis and Joint Orientation Lines in the Canine Humerus: A Radiographic Cadaveric Study

Abstract

To describe a radiographic method for determination of the mechanical axes and joint orientation lines in orthogonal planes for the canine humerus and establish a range of normal joint orientation angles in a population of large breed dogs. Radiographic study. Humeri (n = 50) of skeletally mature, nonchondrodystrophic canine cadavers, weighing 20-40 kg with no evidence of orthopedic disease. Mediolateral and craniocaudal digital radiographs were used to establish anatomic landmarks for determination of the mechanical axis in both frontal and sagittal planes, the joint orientation lines of both shoulder and elbow and measurement of the resulting mechanical lateral distal humeral angle (mLDHA) in the frontal plane, and the mechanical caudal proximal humeral angle (mCaPHA), and mechanical cranial distal humeral angle (mCrDHA) in the sagittal plane. Means (± SD) for the joint orientation angles were: mLDHA, 86.92 ± 1.24°, mCaPHA, 43.28 ± 5.44°, and mCrDHA, 71.86 ± 3.97°. The 95% CI ranges for the joint orientation angles were mLDHA, 86.58-87.86°, mCaPHA, 41.77-44.79°, and mCrDHA, 70.76°-72.96°. A method for measurement of the mechanical axis and associated joint angles of the normal canine humerus in the frontal and sagittal planes was established and reference intervals reported. In the frontal plane, it was determined that the canine humerus is not perpendicular to the elbow joint; therefore, elbow mechanical axis deviation is normal and requires further assessment.