INCIDENCE

The first report of STD was published in 1984 by Oreck and colleagues.² The literature on the topic consists mainly of case reports, small case series, and reviews.¹ One of the largest reported series consists of 25 patients, treated over a 24-year period.³ Thus, one can expect to see a case of STD approximately once a year at a major trauma center. Extremity degloving injuries, on the other hand, are much more common.

MECHANISM OF INJURY

Scapulothoracic dissociation is typically the result of a massive traction force to the upper extremity, usually accompanied by a severe blunt force directed over the shoulder. Osseus and ligamentous injuries include clavicle fractures and acromioclavicular and sternoclavicular dislocations. Soft tissue destruction may involve the deltoid, latissimus dorsi, levator scapulae, pectoralis minor, rhomboids, and trapezius muscles. The skin is generally intact. Vascular injuries to the subclavian or axillary vessels and complete or partial avulsion of the brachial plexus are very common, and when severe result in a functional forequarter amputation.

DIAGNOSIS

The diagnosis of STD is made on the basis of clinical findings and radiographic studies. The diagnosis can be difficult, as patients often have severe associated injuries that impede the conduct of complete physical examination or distract the clinician from the involved extremity. Furthermore, intact skin and normal bony anatomy of the arm may be misleading as to the extent of the underlying injury.

Physical findings consistent with STD include massive soft tissue swelling, tenderness to palpation, and gross instability of the involved shoulder. The involved extremity may manifest vascular or neurologic compromise. Vascular injuries may be evidenced by the “Six P’s”: pain, pallor, pulselessness, paresthesias, paralysis, and poikilothermia. However, owing to the extensive collateral vascular network around the shoulder, a patient may have subclavian artery occlusion and still have a pulse in the distal extremity with a normal brachial-brachial index. On the other hand, a patient may have a cold, mottled extremity with diminished pulses due to shock or environmental conditions, in the absence of a vascular injury. The findings related to vascular and neurologic compromise may overlap. Diagnostic ambiguity calls for further vascular assessment.

The pathognomonic radiographic finding in STD is lateral displacement of the scapula on an anteroposterior (AP) chest x-ray.⁴ The degree of displacement may be quantified by the scapula index. This is calculated by measuring the distance from the thoracic vertebral spinous processes to the medial border of the scapula, and dividing the distance on the injured side by that on the uninjured side (Figure 1). It requires an AP chest x-ray in a supine patient with nonrotated extremities, and an uninjured shoulder.⁵ In the uninjured population, the scapula index averages 1.07 (±0.04).⁶ Zelle and colleagues³ reported an average index of 1.29 (±0.19) in a series of 25 patients with STD, but the diagnostic threshold is not well established. They noted that five of their patients had a scapula index within two standard deviations of the “normal” mean, and cautioned that it be used as a screen but not a definitive diagnostic test. Lange and Noel⁷ suggested simply that a difference of greater than 1 cm suggests STD, while Ebraheim and colleagues⁸ described alternative measurements from the sternal notch to the coracoid or glenoid margin. Because the accurate measurement of the scapula index requires a standardized x-ray and is affected by patient positioning, it is prudent to look for other clues such as distracted clavicle fractures and acromioclavicular or sternoclavicular joint disruptions, and to consider the overall clinical picture, in determining the possibility of STD.

Figure 1 Anteroposterior chest x-ray demonstrating scapulothoracic dissociation. The scapula index is calculated by measuring the distance from the thoracic vertebral spinous processes to the medial border of the scapula, and dividing the distance on the injured side by that on the uninjured side (e.g., A/B in this image).

Associated vascular injuries are very common. In a review of the literature, Damschen and colleagues⁴ found that 88% of patients with STD had vascular injuries. More recently, in their large single-institution experience, Zelle and colleagues³ reported vascular injuries in 16 (64%) of 25 patients. Duplex ultrasonography may be employed to document arterial flow, but arteriography is indicated in stable patients in whom STD is diagnosed or suspected, as it provides more definitive imaging. The subclavian, axillary, and brachial arteries should be interrogated.

Neurologic injury is also very common with STD. Damschen and colleagues⁴ reported from their literature review that 94% of patients had a neurologic injury; in the series of Zelle and colleages,³ the incidence was 80%. The precise extent of injury can be difficult to determine initially. Complaints of severe pain in an anesthetic extremity are consistent with nerve root avulsion,¹ but a history and physical exam predict the site of injury in just 30%–50% of cases.⁹ Evidence of concomitant spinal cord injury should be sought when there are any neurologic abnormalities. Computed tomography (CT) scanning and magnetic resonance imaging (MRI) may be complementary in the evaluation of these patients. A CT scan demonstrating paraspinous hematoma would be consistent with nerve root avulsion, and suggests that cervical myelography should be done.⁶ In the case of incomplete motor deficits, MRI is preferred.¹⁰ The T1-weighted images highlight the fat content of the spinal cord and nerve roots; the T2-weighted images highlight the water content and can demonstrate a pseudomeningocele that would suggest nerve root avulsion.¹ Electromyography (EMG) studies are useful in identifying the involved nerve roots and showing evidence of denervation.⁹