Case: A 76-year-old male presents after falling down a long flight of stairs. On exam the patient has multiple obvious external injuries, including a grossly deformed right shoulder with a large overlying hematoma. His chest x-ray and shoulder x-ray demonstrate a superiorly and laterally displaced right scapula, as well as a comminuted right scapular fracture and clavicle fracture. On further CT imaging, the patient has subtle widening of the scapulothoracic articulation.
Answer: Scapulothoracic dissociation
What is scapulothoracic dissociation?
Scapulothoracic dissociation is a complete disruption of the scapulothoracic articulation, and is associated with profound musculoskeletal and neurovascular injuries. In its most severe form, it can be consdiered a closed forequarter amputation, where the overlying skin remains intact, but all of the important underlying neurovascular structures are damaged or destroyed.
Mechanism, morbidity, and mortality
First described in 1984, scapulothoracic dissociation usually results from high-energy trauma and is frequently found in conjunction with multiple other traumatic injuries. As a result, this injury is frequently missed, leading to potentially devastating consequence.
Scapulothoracic dissociation is associated with significant morbidity and mortality. Approximately 10% of patients die due to concomitant traumatic injuries, though the actual mortality rate may be even higher due to prehospital deaths. More than 50% of surviving patients have a resulting flail extremity, with early amputation required in 21%.
This injury is thought to occur when high traction forces are applied to the shoulder girdle (e.g. a motorcyclist attempting to hold onto the handlebars while being violently thrown from the motorcycle). Approximately 50% of cases reported in the literature result from motorcycle accidents.
Anatomy and classification
The shoulder girdle connects the upper limb to the axial skeleton by means of the scapula and clavicle, in conjunction with surrounding muscle attachments. The sternoclavicular joint is, in fact, the only “true” joint that connects the upper limb to the axial skeleton. The scapulothoracic articulation is a “physiological” joint describing simply a muscular connection and does not actually create a bony link between the scapula and axial skeleton. This anatomy makes the upper limb particularly vulnerable to traction forces and the ensuing consequences.
Osseous injuries to the shoulder girdle are common with scapulothoracic dissociation and include acromioclavicular dislocation, sternoclaviclular dislocation, and displaced clavicular fractures.
The shoulder also contains important neurovascular structures, including the brachial plexus and subclavian and axillary vessels. Damage to these structures can be devastating, leading to hemorrhage, thrombosis, limb ischemia, and/or denervation. Complete avulsion of the brachial plexus is the worst prognostic indicator for recovery of limb function, and some surgeons recommend primary above elbow amputation to avoid the further sequelae of a flail, anesthetic limb.
Exam should begin with a visual inspection of the shoulder. Gross deformity caused by massive soft tissue swelling due to hematoma or edema should clue the examiner in to the potential for scapulothoracic dissociation.
If the patient is not obtunded, palpation of the shoulder may elicit tenderness, and the patient may complain of weakness and numbness in the affected extremity.
Careful attention should be given to the vascular exam. Coldness and mottling may be present along with a pulse deficit in severe cases of vascular compromise. Doppler ultrasound and measurement of brachial-brachial indices (systolic blood pressures with Doppler in the injured versus uninjured arm) may be useful in evaluating for arterial compromise.
On neurological exam, the examiner should inspect dermatomal sensation, DTRs and motor strength in order to evaluate for nerve root and/or peripheral nerve involvement. The examiner should also pay close attention to any other neurologic abnormalities present on secondary survey. For example, the presence of a Horner’s syndrome suggests a preganglionic injury at the level of T1.
Lateral displacement of the scapula on chest x-ray is pathognomonic for scapulothoracic dissociation. The degree of lateral displacement can be quantified by the scapula-index. The distance between the spinous process of the vertebral column to the medial border of the scapula is measured bilaterally. The value of the injured side is then divided by the value of the non-injured side. In the normal population, the scapula index should be 1.07 +/- 0.04. Higher values should raise suspicion for scapulothoracic dissociation. This method naturally requires a well-centered and non-rotated radiograph, with an absence of any confounding injuries.
CT imaging may demonstrate widening of the scapulothoracic articulation, hematoma, muscle rupture, or other soft-tissue abnormalities.
Management of these patients entails trauma resuscitation in the ED, diagnostic imaging as appropriate, and involvement of vascular and orthopedic surgery services for definitive operative repair.
Unstable patients should be taken directly to the OR. While it is rare for a patient to exsanguinate from uncontrolled hemorrhage as a direct result of this injury, it has been reported and may necessitate gaining proximal control of bleeding vessels surgically through high lateral thoracotomy or a supraclavicular incision.
For stable patients, dedicated angiography of subclavian, axillary or brachial vessels should be obtained to evaluate for hemorrhage or limb-threatening ischemia. If vascular compromise is present, repair should be performed within 4-6 hours of injury for optimal results. Timing of orthopedic stabilization depends upon associated neurovascular injuries and any further reconstructive surgeries that may be performed on the affected limb.
Scapulothoracic dissociation is an overlooked and easily missed injury in the high-energy mechanism polytrauma patient. It is a limb-threatening and potentially life-threatening injury, and is associated with grave morbidity and mortality.
Careful visual inspection and neurovascular exam should clue the clinician into the potential for this diagnosis.
Lateral displacement of the scapula on CXR, quantified by the scapula-index, is pathognomonic for scapulothoracic dissociation but requires adequate, non-rotated films.
Trauma resuscitation follows the same principles as per any other trauma patient.
Unstable patients should go to the OR for exploration and proximal control of hemorrhage.
Stable patients should undergo dedicated angiography of the affected extremity, with a goal of vascular repair within 4-6 hours.
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Faculty Reviewer: Dr. Feden