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Snapping scapula

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Originally described in 1867, snapping scapula syndrome (also known as scapulothoracic crepitus or bursitis) results from an imbalance of the scapulothoracic articulation that causes a distinct sound as the scapula is moved across the chest[1-3].  The air-filled thoracic cavity acts as noise amplifier, although noise alone is not pathognomonic of snapping scapula syndrome.  The syndrome is not only characterized by crepitus, it is also associated with pain, scapular winging, or other disorders of the scapulothoracic articulation.  Although the disorder is relatively uncommon in the general population, it is not infrequently seen in the athletic and military population.

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The scapula is a flat, triangular shaped bone, positioned on the posterior surface of the thoracic cage, spanning ribs 2-7.  At rest, the scapula is rotated relative to the trunk approximately 30 degrees[8, 9].  It is comprised of the scapular body, neck, spine, acromion, glenoid, and coracoid process.  It has superior, axillary and vertebral borders, and superomedial, inferomedial, and lateral angles. The scapula’s only attachments to the axial skeleton are muscular and ligamentous (acromioclavicular and coracoclavicular). Although the scapulothoracic articulation is one of the most incongruent in the body, it plays a crucial role in movement and function of the upper extremity as part of the superior shoulder suspensory complex[10, 11]. Seventeen muscles originate or insert on the scapula, including the subscapularis on the ventral surface, and the supraspinatus, infraspinatus, teres major and minor from the dorsal surface. Scapulothoracic and glenohumeral motion are involved in almost every functional upper extremity movement[12].  Abnormalities, including alterations or prominences of the inferomedial or superomedial angle of the scapula, called Luschka tubercles, can disrupt the otherwise smooth contour of the scapula, and alter scapulothoracic motion.

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Two distinct types of disorders exist[4]:

  • Scapulothoracic crepitus, typically the more painful type, results from as osseous lesion in the scapulothoracic space, most commonly an osteochondroma (the most prevalent benign tumor of the scapula) [5, 6]. 
  • Scapulothoracic bursitis results from some soft-tissue disorder, often an inflamed bursa.  It includes those resulting from a single insult, and those resulting from repetitive scapulothoracic motion. 

Six distinct bursae, two major and four minor, have been described for the scapulothoracic articulation[7].  The bursae allow for smooth motion of the scapula on the chest wall.

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Little is known of the epidemiology of this rare condition, and little is known of the natural history if untreated. Patients with snapping scapula may relate the onset of symptoms to a single traumatic event, or may be involved in sports or activities that require repetitive overhead movements[12, 14-16].  Pain is often activity related.  Lesions can develop from chronic repetitive action of the shoulder mechanism, resulting in microtears in the periosteum along the medial border of the scapula and ultimately causing osteophytes or bone spurs.  Similarly, a change in the musculature or mechanics of the scapulothoracic articulation can result in one of the previously described bursae becoming irritated and inflamed.  Whether treated operatively or nonoperatively, the prognosis for patients with snapping scapula is generally good, specifically with respect to decreased pain and increased motion.

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As with any orthopaedic condition, a careful history and physical exam are paramount in making the correct diagnosis.  This is especially true for snapping scapula,  as up to 31% of asymptomatic people have scapular crepitus[13].  The patient may be able to localize the location of the pain and crepitus, typically at the superomedial or inferior angle of the scapula. 

As mentioned, snapping scapula can result from scapular winging and from incongruence of the scapulothoracic articulation.  Thoracic kyphosis, common in athletes, and scoliosis can both result in incongruence and cause scapulothoracic crepitus[17-19].  Scapular winging in athletes is most commonly a result of a neurologic deficit involving the fifth cervical root, the spinal accessory nerve, or the long thoracic nerve.

Physical exam should include a complete neurovascular exam to assess for weakness or nerve deficits.  In addition to physical examination of the scapula, a full exam of the glenohumeral joint and cervical myotomes is essential to rule out the two most common causes of periscapular referred pain[8].

  • Visually inspect the spine and scapula, noting any kyphosis or scoliosis as well as scapular and shoulder positioning at rest.
  • Palpate the periscapular region for masses and/or focal areas of tenderness.
  • Move the shoulder and scapula through a full range of motion, noting the position of the scapula during ascending and descending motions. 
  • Auscultate during scapular range of motion.  The typical provocative position to reproduce the ‘thumping’ or ‘clunking’ is with the arm abducted 90 to 180 degrees.  If that fails, remember that symptomatic patients can typically reproduce their symptoms.
  • Assess the strength and size of the scapular musculature including the trapezius, rhomboids, levator scapulae, serratus anterior, and latissimus dorsi[20].
  • Scapular winging often only becomes evident with motion and stress testing.  One option is to observe scapular motion and symmetry while the patient pushes against a wall[10].

Imaging and Diagnostic Studies

Plain radiographs remain the imaging modality of choice in the initial evaluation of the snapping scapula.  To assess the scapula in all planes, radiographs should include a true anteroposterior view, a tangential transscapular view ( scapular Y) and an axillary lateral view.  Look for any osseous abnormalities including a rib or scapular fracture, osteochonrroma, or alterations or prominence of the inferomedial or superomedial angle of the scapula (Luschka tubercle)[7, 8, 10].

Additional imaging modalities including fluoroscopy, MRI, and CT have been suggested as an adjunct to radiographs.  CT has not proven to be a valuable tool in the assessment of snapping scapula, with the possible exception of pre-operative planning in the presence of a bone or cartilage lesion[10, 21].  MRI has been shown to be more valuable in characterizing associated soft-tissue masses, specifically fluid-filled bursal tissue, and for distinguishing snapping scapula from other disorders including an elastofibroma[22].

Classification

Again, two distinct types of disorders exist, scapulothoracic crepitus, and scapulothoracic bursitis.  Overhead athletes, specifically pitchers, can develop SICK syndrome (Scapular malposition, Inferior medial border prominence, Coracoid pain and malposition, and dysKinesis of scapular movement), a muscular fatigue syndrome with many features similar to scapulothoracic bursitis. True snapping (crepitus) can be caused by prominence of the surperomedial border, as well ad tumors such as osteochondromas and elastofibromas.

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There are operative and nonoperative treatment options for the snapping scapula.  Fortunately, the majority of patients with snapping scapula, especially those with a soft tissue disorder, can successfully be treated with nonoperative modalities including physical therapy, non-steroidal medications, and corticosteroid injections[5, 8, 10].  Because poor posture can cause scapular muscle weakening and result in imbalance, physical therapy is focused on improving muscle strength and balance, addressing and improving postural conditions, and core strengthening[10, 20].  Corticosteroid injections (typically with a local anesthetic) into the scapulothoracic bursa can be used for diagnosis and treatment, though care must be taken to match the trajectory of the scapula in relation to the chest wall (stay parallel to chest wall) to prevent pnuemothorax[7, 10].

While nonoperative management should be attempted in patients with a clearly defined osseous abnormality, resection of the lesion is often necessary to alleviate all their symptoms[7, 23].  Additionally, surgical resection of a persistently symptomatic bursa, although not as common, is sometimes necessary.  Both open and arthroscopic excision of symptomatic bursae have been described, with mostly good to excellent results[7, 24, 25].

The most common surgical treatment for those patients without a clearly defined bursa or osseous lesion as the source of their pain is resection of the superomedial or inferomedial angle of the scapula[3-5, 7, 17].  The best candidates for resection can localize their pain to the superomedial or inferomedial angle, and experience some level of relief with injection into the localized area[26].  The procedure is typically performed with the patient prone on the operating table.  Using a vertical or oblique skin incision in line with the medial border of the scapula (inferior or superior depending on symptoms), the trapezius is split parallel with its fibers, taking care to protect the spinal accessory nerve[10].  The supraspinatus, rhomboid, and levator scapulae muscles are then elevated off the spine of the scapula subperiosteally.  Once exposed, the superomedial angle of the scapula is resected with an oscillating saw, taking care not to injure the suprascapular nerve and artery as you move laterally toward the suprascapular notch (Figure 1).  The elevated muscles are then repaired back to the spine with suture through drill holes[7].  Patients are typically immobilized in a sling for up to 4 weeks post operatively to protect the repair of the elevated muscles.  Physical therapy is then focused on range of motion and strengthening [3, 25, 26].


Figure 1. Intraoperative photograph of open superomedial border resection performed in the beach-chair position. Note the significant size of the resected portion of scapula.

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