Jon J. P. Warner and Bassem Elhassan
DEFINITION
The snapping scapula syndrome first was described by Boinet in 1867.14
It is characterized by painful scapular motion with associated crepitus during scapulothoracic motion, with or without a clear history of injury or trauma.
It has also been referred to as scapulothoracic bursitis, retroscapular creaking, superior scapular syndrome, and retroscapular pain.3,7,11,14
The associated audible crepitus, which can be tactile in most instances, has been described by Milch and Burman11 as a tactile-acoustic phenomenon, possibly generated secondary to an abnormality in the scapulothoracic interval.
This crepitus is divided into three classes, based on the volume of the sound produced.10
The first group is considered physiologic, with what is described as a “gentle friction” sound.
The second group, which includes most patients with the snapping scapular syndrome, features a louder grating sound.
The third group is defined by a loud snapping noise that is considered pathologic in most cases.
ANATOMY
The scapulothoracic articulation consists of the interface between the anterior aspect of the scapula and the ribs in the posterior aspect of the convex thoracic chest wall (FIG 1).
This articulation is cushioned by several muscles, specifically the subscapularis and the serratus anterior.
In addition, two major and four minor bursae have been described in the scapulothoracic articulation6,7,23 (Fig 1).
The two major bursae are the infraserratus bursa, located between the serratus anterior muscle and the chest wall, and the supraserratus bursa, located between the serratus anterior and the subscapularis muscles.
The four minor bursae are distributed as follows: two at the superomedial angle of the scapula, one at the inferior angle of the scapula, and one at the medial base of spine of the scapula, underlying the trapezius muscle.
While the major bursae have been found consistently in cadaveric and clinical studies, those of the minor bursae were not.3,19,20
PATHOGENESIS
Incongruence of the scapulothoracic articulation has been postulated to be the main cause of the snapping scapular syndrome, which may or may not be associated with bony anomalies of this region.13,17
Maltracking or dynamic compression of the scapulothoracic articulation has been postulated as a main etiology of this syndrome, because it leads to irritation of the bursa secondary to pathologic contact between the ribs and the superior angle of the scapula.4,22
This maltracking is considered to be a soft tissue cause of snapping scapula syndrome, which has been reported in cases of subscapularis atrophy secondary to glenohumeral fusion and long thoracic nerve palsy.11,24
Clinical studies and histologic findings of muscle intrafascicular fibrosis, bursitis, edema, and shoulder girdle muscle atrophy support this hypothesis.7,17
Bony or skeletal causes of snapping scapula syndrome are rare. These include scapular osteochondromas and exostoses (FIG 2), anterior angulation of the scapula, scapula fracture, scapular tubercle of Luschka, skeletal abnormalities of the vertebrae (omovertebral bone), and abnormal angulations and tumors of the ribs.10,11,21
FIG 1 • Four different bursae are shown—two infraserratus, one supraserratus, and one trapezoid bursae.
NATURAL HISTORY
Patients with snapping scapula syndrome usually complain of pain around the shoulder girdle.
This pain most often is secondary to bursitis in the scapulothoracic articulation. Constant motion irritates the soft tissues, leading to inflammation and a cycle of chronic bursitis and scarring.
FIG 2 • An osteochondroma (arrow) of the superomedial angle of the scapula may, rarely, be the cause of snapping scapula syndrome.
The chronic inflammation of the bursae will lead to fibrotic, scarred, and tough bursal tissues that can lead to mechanical impingement and pain with motion, resulting in further inflammation.
Once the patient reaches this level of chronic bursal inflammation, the symptoms rarely subside by themselves without trial of rest and physical therapy.
In many cases, especially when the cause of snapping is skeletal, surgical intervention becomes essential to manage this problem.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patients with scapulothoracic bursitis report a history of pain in the shoulder or neck with overhead activities for months or years and often have a history of repetitive overuse in work or recreation or a history of trauma.
A history of neck injury, shoulder injury or fracture, or previous shoulder surgery should be ruled out.
Audible or palpable crepitus may accompany the symptoms with scapulothoracic motion; this is another indication for the location of the symptomatic inflamed bursa.
Some patients report a family history of the disorder and have bilateral symptoms.
Localized tenderness is an indication for the site of scapulothoracic bursitis.
Improvement of symptoms by lifting the scapula off the chest wall helps localize the source of pathology to the scapulothoracic articulation.
Diagnosis is confirmed if significant relief or even elimination of the pain occurs when local anesthetic and corticosteroids are injected in the scapulothoracic bursa under the superomedial border of the scapula.
The examiner also must assess soft tissue tightness, muscle strength, and flexibility around the involved shoulder.
Special attention should be directed to rule out tight trapezius, pectoralis minor, or levator scapula muscles, as well as weakness of any of the scapular muscles, specifically the serratus anterior and the trapezius.
In patients with winging of the scapula, a careful neuromuscular examination should be performed to differentiate true winging from compensatory pseudo-winging that might originate from a painful scapulothoracic articulation.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Radiologic studies should include an anterior-posterior (AP) and tangential (Y) views of the shoulder, to identify bony abnormalities in the scapula and ribs (FIG 3A).
A CT scan may be needed for more bony definition. Its role, with or without three-dimensional reconstruction, is still debated,9,13 but in patients with suspected bony skeletal abnormality, the CT scan might be helpful (FIG 3B).
Fluoroscopy could be used to visualize the snapping during simulated shoulder motion.
MRI can identify the location and size of the inflamed bursa, but its usefulness is debated. The senior author does not believe that the MRI is necessary and has never ordered it in any of his cases.
Nerve conduction and electromyography studies are useful if a neurologic injury is suspected as the reason for scapula winging.
DIFFERENTIAL DIAGNOSIS
Soft tissue lesions, such as atrophied muscle
Fibrotic muscle
Anomalous muscle insertion
Subscapular elastofibroma. This tumor is nonneoplastic and appears to form in response to repetitive injury or microtrauma. Most patients who have this tumor complain of a palpable mass rather than pain.
Cervical spondylosis and radiculopathy
Periscapular muscle strain
Glenohumeral pathology
NONOPERATIVE MANAGEMENT
The initial management of snapping scapula syndrome, once the diagnosis has been made, is conservative.
Rest, activity modification, and nonsteroidal anti-inflammatory medications should be started.
Next, physical therapy should be initiated to restore the normal kinematics of the shoulder and prevent it from sloping.
Weakness in the serratus anterior, even if subtle, may lead to tilting of the scapula forward, thus increasing the friction and rubbing of the upper medial pole of the scapula on the thoracic ribs. This will cause irritation and inflammation of the scapulothoracic bursae.
Therapy should emphasize periscapular muscle strengthening, particularly the serratus anterior and subscapulari, which can elevate the scapula off the chest wall when they are hypertrophied.1,17
Taping, a figure-8 harness, scapulothoracic bracing, or postural training can serve to minimize shoulder sloping and thoracic kyphosis.
Injection of corticosteroid and local anesthetic into the scapulothoracic bursa can be diagnostic and also may be therapeutic and helpful in the rehabilitation program.
There is no consensus on how long the patient should be kept on trial of physical therapy. The underlying diagnosis is important. In general, a 3to 6-month trial is a good estimate.
If the diagnosis is certain, no structural anatomic lesion is present, and the patient has failed 3 to 6 months of appropriate conservative treatment, then surgical options should be considered.
The threshold to proceed to surgical intervention also should be much lower if the patient has a real structural lesion such as a bony exostosis or an osteochondroma.
FIG 3 • A. A Y-scapular view showing a prominent osteochondroma (arrow) of the body of the scapula, causing symptomatic snapping. B. A three-dimensional CT scan shows the bony anatomy in more detail. The arrow points to the same osteochondroma.
SURGICAL MANAGEMENT
Preoperative Planning
All radiographs are reviewed before surgery.
The decision to operate is made based on relief of pain with anesthetic injection into the scapulothoracic region in patients who failed conservative management, or in patients who have symptomatic snapping scapula syndrome secondary to structural lesion.
The different surgical approaches, as well as the technique that the surgeon decides to perform, are discussed with the patient before surgery.
Positioning
The patient is positioned in the prone position for both arthroscopic and open techniques (FIG 4).
The involved arm is placed in internal rotation against the patient’s lower back (chicken-wing position). This will cause the scapula to wing out from the thorax and make the superomedial angle more prominent.
The surgeon stands on the side opposite the scapula to be operated to get the best access to the surgical field.
Approach
Multiple surgical approaches are available that can decompress the impingement in the superomedial region of the scapula.
These include open surgical decompression, arthroscopic surgical decompression, or a combination of the two approaches.
Each of these approaches may include bursectomy alone, bony resection of the superomedial aspect of the scapula alone, or a combination.
FIG 4 • The operating room setup for arthroscopic scapulothoracic bursectomy. The patient is positioned prone with the hand of the involved shoulder placed behind the back in order to lift the scapula off the chest wall.
TECHNIQUES
OPEN DECOMPRESSION
A longitudinal incision is made along the medial scapular edge (TECH FIG 1A).
Subcutaneous undermining is performed to expose the superior portion of the scapula, from the level of the scapula spine to the superomedial angle of the scapula.
Splitting and elevation of the trapezius in line with its fibers is performed at the level of the scapular spine, and the superomedial edge of the scapula is exposed (TECH FIG 1B).
The levator scapulae and rhomboids are detached from the superior and medial edge of the scapula to expose the upper scapula border (TECH FIG 1C).
Care is taken not to dissect into the rhomboids or fully detach them so as not to injure the dorsal scapular nerve, which usually is located 2 cm medial to the medial scapular edge.
TECH FIG 1 • A. Patient positioned prone with hand positioned behind back to lift the scapula off the chest wall. The surgical incision is placed over the medial border of the scapula, centered over the level of the scapula spine. B. The trapezius is split along its fibers, and the levator scapulae, the rhomboids, and the posterior surface of the scapula are exposed. C. The levator scapulae, rhomboid major, and rhomboid minor are detached from their insertion on the scapula and tagged with sutures. (continued)
TECH FIG 1 • (continued) D,E. Resection of the superomedial border of the scapula. F. The detached muscles are reattached to the scapula through drill holes. G. The final repair of the detached levator scapulae and rhomboids.
The serratus anterior muscle is left intact.
A retractor is placed underneath the scapula to lift it away from the thoracic ribs.
The scapulothoracic bursa is identified against the ribs, underneath the serratus anterior muscle.
A clamp is used to grasp the bursa, and sharp excision of it is performed from superior to inferior.
Subperiosteal elevation of the muscles around the superomedial border of the scapula, including the supraspinatus, infraspinatus, subscapularis, and serratus anterior muscles, is performed with the use of electocautery to expose 1 to 2 cm of bone (TECH FIG 1D).
This exposed portion of the superomedial portion of the scapula is resected with use of an oscillating saw (TECH FIG 1E).
Once the bony resection is accomplished, drill holes are placed into the upper-medial border of the scapula in order to reattach the muscles to their anatomic insertion (TECH FIG 1F) using a no. 2 nonabsorbable braided suture (TECH FIG 1G).
The skin is closed with absorbable subcuticular suture.
ARTHROSCOPIC BURSECTOMY
Positioning is the same as in open decompression.
Placement of the arm in the chicken-wing position results in scapula winging and protraction off the posterior thorax, which facilitates the entry of the arthroscopic instruments in the bursal space.
Standard arthroscopic portals are used.
The initial “safe” portal is placed at the level of the scapular spine, 2 cm medial to the scapular edge, to avoid injury to the dorsal scapular nerve and artery (TECH FIG 2A).
The scapulothoracic space is localized with a spinal needle and distended with approximately 30 mL of saline, and the portal is created.
A blunt obturator is inserted into the scapulothoracic (subserratus) bursa between the posterior thoracic wall and the serratus anterior muscle.
Care should be taken to avoid overpenetration through the serratus anterior into the subscapular space or through the chest wall.
A 30-degree arthroscope is inserted into the scapulothoracic space, which was distended with fluid infiltration.
Use of a fluid pump is optional. Our preference is to use an arthroscopy pump but keep the pressure low, at around 30 mm Hg, to minimize fluid extravasation.
A spinal needle is used to localize the second portal under direct visualization.
This portal is inserted, in most instances, in line with and approximately 4 cm distal to the first portal.
A bipolar radiofrequency device and a motorized shaver are introduced into a 6-mm cannula through the lower portal, and used to resect the bursal tissue. Because the inflamed scapulothoracic bursa is a potential source of bleeding during arthroscopic shaving, the radiofrequency device becomes particularly useful to minimize bleeding in these tissues (TECH FIG 2B).
A methodic approach to resection should be followed, because there are no real landmarks.
Ablation of tissues should be performed from medial to lateral and then from inferior to superior.
The surgeon should be ready to switch portals and should have a 70-degree athroscope ready to facilitate visualization. A probe can be used to palpate the scapula and serratus muscle superiorly and the ribs and intercostal muscles inferiorly.
An additional superior portal may be placed as needed. We prefer not to use this portal, because it may place the accessory spinal nerve, transverse cervical artery, and dorsal scapular neurovascular structures at risk.
After complete bursectomy is performed, the arthroscopic instruments are withdrawn, and skin closure is performed with absorbable subcuticular sutures.
TECH FIG 2 • A. Locations of the arthroscopic portals. A proximal (safe) portal (black arrow) is placed 2 cm medial to the spine of the scapula. A distal portal (white arrow) is placed in line with and 4 cm distal to the proximal portal. B. Sites of portal placement. The shaver and the camera can be placed interchangeably in either portal for viewing and shaving.
ARTHROSCOPIC BURSECTOMY AND PARTIAL SUPEROMEDIAL SCAPULECTOMY
First, all the steps for arthroscopic bursectomy are followed.
After the bursa has been completely resected, the superomedial angle of the scapula is localized by palpation through the skin.
Detachment of the conjoined insertion of the levator scapulae, supraspinatus, and rhomboids is performed with the use of the radiofrequency device.
A motorized shaver and a burr are used to perform a partial scapulectomy. We do not attempt to repair the periosteal sleeve; it is allowed to heal through scarring.
The rest of the steps are the same as those for arthroscopic bursectomy.
ARTHROSCOPIC BURSECTOMY AND OPEN PARTIAL SUPEROMEDIAL SCAPULECTOMY
The decision to perform the superomedial scapular bony resection through a small skin incision rather than through the arthroscope may be made either before surgery or at the time of surgery.
If full definition of the superomedial border of the scapula becomes difficult because of swelling from the arthroscopic fluid, then bony resection is performed through a small skin incision.
A 4to 6-cm incision is performed obliquely over the superomedial border of the scapula (see Tech Fig 1A).
The trapezius muscle is split, and the levator scapulae and rhomboids are detached from the superomedial angle (see Tech Fig 1B,C).
The superomedial angle of the scapula is resected. Then the levator scapulae and rhomboids are repaired to the superior scapula through drill holes (see Tech Fig 1D).
Skin closure is performed with absorbable subcuticular sutures.
PEARLS AND PITFALLS
POSTOPERATIVE CARE
After open decompression and a combined arthroscopic and open approach:
The patient is kept in a sling, and gentle, passive range of motion is started early after surgery and continued for 4 weeks.
After 4 weeks, active range of motion is started.
Strengthening is allowed at 8 to 12 weeks.
After arthroscopic decompression:
The patient is kept in a sling and allowed passive and active assisted range-of-motion exercises immediately after surgery.
After 4 weeks, isometric exercises are started.
Strengthening of the periscapular muscles begins by 8 weeks.
OUTCOMES
No published reports have compared the outcomes of different surgical techniques of scapulothoracic decompression.
The outcome of open decompression, as reported in the literature, has been good.7,12,17,18
No large series have been published reporting the outcome of arthroscopic scapulothoracic decompression for symptomatic snapping scapular syndrome.
Early results from small series of patients who underwent arthroscopic decompression seem promising, with minimal morbidity and early return to work.2,5,8,15,16
COMPLICATIONS
Recurrence of symptoms secondary to incomplete resection
Pneumothorax
Iatrogenic injury to the neurovascular structures around the superomedial border of the scapula
Aggressive bony resection risking injury to the suprascapular nerve through the notch
Insufficiency of the scapular muscles due to detachment after surgery
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