13.2 Anatomy

The humerus has unique features that make it a challenging bone to approach and repair, in part due to its proximal location with a large surrounding muscle mass. Accurate knowledge of the relevant anatomy is essential for successful reduction of fracture fragments and application of a fixation apparatus (Figure 13.1). Differences in anatomy between dogs and cats can dictate the choice of fracture repair technique, along with the actual position of the chosen implants. Specific factors that are relatively unique to the humerus are the S‐shaped nature with a twist moving distally. There are ridges proximally and distally, which make accurate plate contouring especially challenging. The radial nerve is located on the distolateral aspect, with the canine median and ulnar nerves being located on the medial aspect. The feline humerus differs in three ways. First, there is a supracondylar foramen; second, the median nerve and a branch of the brachial artery pass through the supracondylar foramen; and third, the communication between the olecranon fossa caudally and the radial fossa cranially is interrupted by bone across the supratrochlear foramen.

Supracondylar humeral fractures can be especially challenging due to the complex anatomy of the distal humerus. There are several important factors, the most notable being the presence of the supratrochlear foramen in the dog; a thin lateral epicondylar ridge; irregular surfaces of the metaphysis; and finally, the proximity to the elbow joint [4]. These factors in combination lead to challenging surgical repairs and a very small area for safe and effective implant placement.

13.3 Surgical Approach

It is possible to approach the humerus from lateral, cranial, and medial surfaces. The approaches are challenging because of the plethora of neurovascular structures that can be encountered during dissection, along with the significant muscle bellies [5].

It is the opinion of the author that diaphyseal fractures are generally best approached from the medial aspect, with the exception of proximal fractures, which may be more accessible through a lateral approach. Medially, the humeral diaphysis is relatively straight and flat and the medial epicondylar crest is less pronounced than that of the lateral epicondyle. These features permit less plate contouring and thus a simpler application of a plate on the medial surface; particularly given that locking plates need not fit perfectly to the shape of the bone [1].

Medial approaches to the feline humerus are advantageous for visualization and protection of the median nerve and the brachial artery within the supracondylar foramen [1, 6]. (See Figure 13.2). This medial approach in itself is relatively straightforward. Depending on the patient and injury factors, it might require cutting of the pectoral muscle origins proximally, reflecting the biceps brachii muscle caudally and the brachiocephalicus muscle cranially. It is the author’s experience that the overall soft tissue trauma and subsequent morbidity is significantly less when utilizing this particular approach. It is imperative to identify and protect the median and ulnar nerves along with the brachial vessels when performing a surgical approach to the medial aspect of the humerus in both species.

13.4 Biomechanics

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