Canine Humeral Fractures and Internal Fixation

Humeral fractures are a common orthopedic injury in dogs, often resulting from high-impact trauma such as vehicular accidents, falls from heights, or direct blows. The incidence of humeral fractures is significantly higher in dogs compared to other domestic animals, making it a crucial area of veterinary orthopedic study. Understanding the anatomy of the humerus, the various types of fractures, and appropriate treatment methods, including internal fixation, are vital for successful outcomes.

Anatomy of the Canine Humerus:

The humerus, or brachium bone, is the long bone of the forelimb, situated between the scapula (shoulder blade) and the radius and ulna (forearm bones). Its structure can be divided into three parts: the proximal epiphysis (head), the diaphysis (shaft), and the distal epiphysis (condyle).

Proximal Epiphysis: This includes the rounded humeral head, which articulates with the glenoid cavity of the scapula forming the shoulder joint. The anatomical neck is a constricted area below the head. Two prominent bony projections, the greater tubercle (lateral) and lesser tubercle (medial), are located just distal to the head. The bicipital groove, a deep furrow between the tubercles, accommodates the tendon of the biceps brachii muscle.

Diaphysis: The shaft of the humerus is slightly curved and cylindrical. A spiral groove, the musculospiral groove, runs along the lateral aspect, providing attachment for the brachial muscles.

Distal Epiphysis: The distal end of the humerus consists of the medial and lateral condyles, which articulate with the radius and ulna to form the elbow joint. Above the condyles are the medial and lateral epicondyles, providing attachment sites for forearm muscles. The olecranon fossa, a deep depression on the posterior aspect of the distal humerus, receives the olecranon process of the ulna during elbow extension.

Types of Humeral Fractures in Dogs:

The specific type of fracture will dictate the appropriate treatment plan. Fracture patterns vary depending on the age and size of the dog and the mechanism of injury.

Adult Dogs: Adult dogs commonly experience fractures of the humeral shaft, often presenting as spiral, oblique, transverse, or comminuted fractures. Comminuted fractures involve multiple fracture fragments. These fractures often involve significant displacement and shortening of the limb due to the pull of the surrounding musculature, particularly the powerful triceps brachii muscle.

Puppies: In younger dogs, fractures are more likely to occur at the physis (growth plate) of the humeral head or distal humerus. These epiphyseal fractures can affect the growth and development of the limb. The less developed musculature in young dogs may result in less displacement of the fracture fragments compared to adult dogs.

Clinical Signs:

Clinical signs of a humeral fracture include:

Severe lameness (non-weight-bearing)

Swelling and pain at the fracture site

Deformity of the limb (shortening, angulation)

Crepitus (grating sensation) on palpation

Limited range of motion in the shoulder and/or elbow joint

Muscle atrophy if the fracture is not promptly addressed

Diagnosis:

Radiographic examination is essential for confirming the diagnosis, identifying the fracture type, and assessing the degree of displacement. Lateral and craniocaudal views of the humerus are typically required.

Treatment: Internal Fixation

The primary treatment for displaced humeral fractures in dogs is surgical internal fixation. Several techniques are available, depending on the fracture pattern and the surgeon’s preference.

Intramedullary Pins: These pins are inserted into the medullary canal (the hollow center of the bone) to provide axial stabilization. This technique is suitable for many shaft fractures.

Plates and Screws: Plates are applied to the outer surface of the bone and secured with screws to provide rigid fixation. This method is particularly useful for comminuted fractures or fractures with significant comminution.

External Skeletal Fixation: External fixators are used in certain cases where internal fixation is not feasible, such as severely comminuted fractures or open fractures with significant soft tissue damage.

Postoperative Care:

Postoperative care is crucial for successful healing and involves strict confinement, pain management (analgesics and/or NSAIDs), and regular monitoring for complications such as infection or delayed union. Physical therapy may be recommended later in the recovery process to help restore muscle function and range of motion. Strict adherence to the veterinarian’s instructions is vital for optimal results.

Conservative Management:

In some cases, particularly in young dogs with minimally displaced fractures, conservative management with a sling or cast may be considered. However, this approach is less frequently used due to the risk of malunion and delayed healing.

Complications:

Potential complications associated with humeral fractures and their treatment include:

Infection

Non-union (failure of the fracture to heal)

Malunion (healing of the fracture in an incorrect position)

Delayed union

Muscle atrophy

Avascular necrosis of the humeral head (death of bone tissue due to lack of blood supply)

Humeral Head Excision:

In cases of severe comminution or avascular necrosis of the humeral head, humeral head excision (removal of the humeral head) may be considered as a salvage procedure. While this results in permanent lameness, it relieves pain and allows for functional limb use.

Prognosis:

The prognosis for dogs with humeral fractures treated with appropriate surgical intervention is generally good, with most dogs regaining good function. However, the recovery process requires patience and diligent follow-up care. The severity of the fracture, the age of the dog, and the surgical technique used all influence the final outcome. The owner’s compliance with the veterinarian’s post-operative instructions is crucial for a successful recovery.