Background

Avulsion or rupture of the triceps tendon has been described as "the least common of all tendon injuries."^[1] In their analysis of 1014 cases of muscle and tendon injuries at the Mayo Clinic, Anzel et al reported that only eight cases involved the triceps tendon.^[2]

Partridge documented the first case of avulsion of the triceps tendon. Only 13 cases had been reported before 1975, when Pantazopoulos et al described two cases and stressed the importance of having diagnostic awareness of this injury.^[3] Their report suggested that the lesion may be more common than was previously thought.

Triceps tendon avulsion may be overlooked during an evaluation of injuries to the upper extremity, especially when it is associated with fractures of the wrist or radial head or neck.

Farrar and Lippert emphasized the importance of determining whether a complete or an incomplete rupture of the distal triceps tendon has occurred.^[4]

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Anatomy

As its name suggests, the triceps muscle has three heads of origin, as follows:

• The long head arises from the infraglenoid tubercle of the scapula
• The lateral head arises from the posterior surface of the humerus above the radial groove and partly from the lateral intermuscular septum
• The medial head originates from the entire posterior surface of the humerus below the radial groove—from the medial and lower parts of the lateral intermuscular septum; it joins the deep surface of the combined long and lateral heads and forms the strong and broad triceps tendon

The triceps tendon inserts, for the most part, into the posterior portion of the upper surface of the olecranon. However, a band of fibers continues downward, on the lateral side, over the anconeus, to blend with the deep fascia of the forearm. This entire muscle complex is the only real extensor at the elbow joint.

Pathophysiology

Disruption of the triceps can occur in one of the following three anatomic locations, listed in decreasing order of frequency:

• Attachment of the tendon to bone
• Musculotendinous junction
• Muscle substance

Tarsney stated that disruption of the triceps at its insertion into the olecranon is most accurately termed avulsion of the triceps and that the term rupture should be used to describe intramuscular or musculotendinous disruption of the triceps.^[5]

Clinical evidence suggests that avulsion fracture of the olecranon is related to olecranon ossification center healing.^[6]

Etiology

Avulsion or rupture of the distal triceps tendon most often occurs after trauma. Indirect trauma is the most common cause of injury and usually involves a fall onto an outstretched arm, with resultant pain about the elbow. This mechanism places a deceleration stress on a contracted triceps muscle, with or without a concomitant blow to the posterior aspect of the elbow. The result is a distal avulsion at the tendo-osseous insertion. The tendon usually retracts, and bone from the proximal olecranon becomes embedded in it.^{[7, 4]}

Avulsion has also been reported after an isolated blow to the elbow alone.^[4] In rare instances, ruptures of the midsubstance belly and musculotendinous junction have occurred.^[8] Spontaneous avulsion of the distal triceps tendon has been reported in patients with hyperparathyroidism, osteogenesis imperfecta, Marfan syndrome, systemic lupus erythematosus, or systemic treatment with steroids.^{[4, 9, 10, 11]}

In addition, review of the literature reveals a growing population of patients with chronic renal failure who are receiving dialysis, have secondary hyperparathyroidism, or both. These patients appear to be at increased risk for tendon injury after minor trauma.^{[4, 12]}

The mechanism described above for distal triceps tendon avulsion may also cause the relatively less common transverse or oblique avulsion fracture through the proximal olecranon. A high incidence of fractures of the proximal olecranon is noted among javelin throwers and baseball pitchers.^[13] Fractures of the proximal olecranon are not uncommon in children, who are more inclined than adults to have a fracture rather than a tendo-osseous avulsion due to the triceps mechanism.

Ring and Jupiter proposed a ring theory of elbow stabilizers and mentioned the posterior column, including the triceps.^[14] Most of their patients had either an olecranon fracture or no injury. Hence, they suggested that avulsion of the triceps can occur with elbow dislocation, perhaps as an alternative to an olecranon fracture.^[15]

Epidemiology

Nearly 75% of triceps tendon ruptures reported in the literature occurred in male patients, with a male-to-female ratio of 3:1.^[7]  Although the mean age at injury was approximately 26 years, patients described in case reports have had an age range of 7-72 years. The dominant and nondominant extremities appear to be injured with equal frequency, and cases of bilateral avulsion have been reported.^{[7, 9]}

Clinical Presentation