Canine Elbow Dysplasia: Anatomy and Pathogenesis*

Canine elbow dysplasia is a complex of diseases that includes ununited anconeal process, fragmented medial coronoid process, osteochondrosis of the medial humeral condyle, and elbow incongruity. Three causes of elbow dysplasia have been proposed: osteochondrosis, trochlear notch dysplasia, and asynchronous growth of the radius and ulna. Genetics, nutritional imbalance, growth disturbances, and trauma may influence the development and expression of elbow dysplasia. Canine elbow dysplasia (CED) is a term that causes controversy and confusion among veterinarians. In its broadest sense, CED is used to describe all developmental abnormalities involving the elbow joint. The International Elbow Working Group adopted the term elbow dysplasia to describe all conditions resulting in arthrosis of the elbow joint regardless of the underlying cause. CED now typically means a complex of developmental abnormalities of the elbow, including ununited anconeal process (UAP), fragmented medial coronoid process (FMCP), osteochondrosis (OC) of the medial humeral condyle, and elbow incongruity. This article reviews the basic anatomy of the elbow joint and the proposed causes of CED. ANATOMY The elbow (cubital joint) includes the humeroradial joint, humeroulnar joint, and proximal radioulnar joint (Figure 1). A common joint capsule encompasses all three articulations. The capitulum of the humeral condyle articulates with the radial head to form the humeroradial joint, which supports most of the weight transmitted through the elbow joint. The trochlea of the humeral condyle articulates with the trochlear (semilunar) notch of the ulna to form the humeroulnar joint. The olecranon fossa of the humeral condyle articulates with the anconeal process of the ulna during joint extension beyond 90 ̊ and restricts movement of the elbow to the sagittal plane (Figure 2). The proximal radioulnar joint allows limited rotation of the elbow. The medial collateral ligament limits abduction n Three separate articulations make up the elbow (cubital)