Supraglenoid tubercle fractures

Fractures of the supraglenoid tubercle occur in young adult horses and may also develop as an avulsion injury. These are the most frequently diagnosed scapular fractures.

Fractures of the equine scapula occur rarely and are usually encountered in foals and horses younger than 3 years of age. These injuries are generally caused by direct trauma, such as a kick by another horse...

...or bumping in a solid stationary object.

The body of the scapula is covered by cuticular shoulder muscles in addition to the supra- and infraspinatus muscles.

The supraglenoid tubercle represents a separate center of ossification in foals that unites with the neck of the scapula at approximately 2 years of age. This represents a locus of decreased resistance relative to external forces. The biceps tendon, which transforms to the very strong biceps muscle, originates at the supraglenoid tubercle.

The scapular nerve courses around the scapular neck on its way to innervate the supra- and infraspinatus muscles. The muscles provide stability to the shoulder region, maintain the shoulder region proximity to the chest, and assist in the protraction of the limb.

Trauma to this nerve induces a rapid atrophy of the supra- and infraspinatus muscles, resulting in an outward rotation of the shoulder region during weight bearing and a mechanical lameness with a shortened protraction phase.

The image shows massive atrophy of the supra- and infraspinatus muscles as a result of a suprascapular nerve injury. The arrow points at the very prominent spine of the scapula.

Clinically, patients affected with a fracture of the scapula will present with acute onset, severe lameness. They will usually be grade 3-5/5 lame.

The degree of soft tissue swelling in the area will vary depending on the inciting trauma and secondary fracture displacement.

The image shows an adult Thoroughbred horse with moderate swelling of the scapular region (left) and another adult horse with a massive swelling in the scapular region (right).

The lameness will significantly improve within days, but will not resolve. The fact that the lameness improves rapidly leads to a delay in a correct diagnosis and a timely state-of-the-art management providing the best prognosis for the patient.

The patient will usually present with a somewhat dropped elbow stance with extended phalanges. Patients with fractures of the scapular neck region may assume a more pronounced dropped elbow stance. Also the patient may not be able to protract the limb. This may be the result of instability, pain or involvement of the suprascapular nerve.

The image shows the type of stance the patient may show. The young horse shown suffered from tendonitis which was treated with bolster.

The differential diagnosis for a patient that presents with a dropped elbow stance includes fractures of the ulna, humerus (left) as well as radial nerve injuries (right). It is often possible to differentiate humerus and olecranon fractures through meticulous clinical examination. Occasionally the scapular body fracture can be palpated by pushing onto the scapular region and in doing so elicit some crepitation sounds. The location and character of the soft-tissue swelling can also help differentiate a humerus or olecranon fracture from a scapula fracture. Humerus fractures, especially those affecting the diaphyseal region, are usually accompanied by an apparent swelling of the brachial region when viewed from the front of the patient (left).

Diagnostic images are best obtained in the standing patient by directing the beam from medial to lateral and slightly cranial to caudal with the leg held in extension by an assistant.

A cranial to caudal projection is required to rule out additional injury, especially of the radius.

The fracture is best diagnosed radiographically. This is relatively easily accomplished in foals but may cause some difficulties in heavily muscled adult horses, such as Warmbloods and American Quarter Horses. Ideally different radiographic views (ML and CC) should be taken.

Left: Lateromedial radiographic view of a supraglenoid tubercle fracture in an 18-month old filly. Right: Lateromedial radiographic view of a scapular neck fracture (arrow) in a 1-month old thoroughbred colt.

Good quality radiographic images are required to arrive at the correct diagnosis.

Radiographic images from the same horse:
Left: The radiograph taken by the referring practitioner in the field shows an incomplete fracture of the supraglenoid tubercle. Right: The repeat radiograph taken at the clinic with a high power x-ray unit reveals a complete supraglenoid tubercle fracture. It is potentially possible that the initially incomplete fracture turned into a complete fracture between the initial diagnosis and the referral to the clinic.

In adult horses radiography may not be conclusive because of the large body mass and the superimposition of different bones and structures. In these cases the use of ultrasonography may show the location and to some extent the configuration of the fracture.

The image shows three fracture lines (arrows). They can be identified ultrasonographically, representing a multi fragment fracture of the scapula. If available, nuclear scintigraphy may be also helpful in identifying the lesion(s).

In foals and ponies the fracture may also be diagnosed with the help of computed tomography, because depending upon their size and gantry diameter the entire foal fits into the tube.

The CT images show the facture configuration and displacement of the fragments of the scapular body fracture.

Articular fractures usually also traumatize the articular cartilage of the glenoid. This fact has to be kept in mind when discussing treatment options with the owner.

The image shows a post-mortem articular view of a supraglenoid tubercle fracture with displacement.