DEFINITION

Scapulothoracic crepitus first was described by Boinet4 in 1867.

It is characterized by painful scapular motion with associated crepitus during scapulothoracic motion, with or without a clear history of injury or trauma.20,21

Snapping scapula syndrome has also been referred to as scapulothoracic bursitis, retroscapular creaking, superior scapular syndrome, retroscapular pain, washboard syndrome, and rattling of the

shoulder blade.8,14,20,21,28

The associated audible crepitus, which can be tactile in most instances, has been described by Milch

and Burman21 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.20

 

 

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).

 

The mean superomedial angle of the scapula is has been estimated to be 139 to 154 degrees and the average thickness of the superior poles is a mean1,17,36 of 3.4 to 3.9 mm.

 

The osseous anatomy of the scapula is variable.1 The scapulothoracic articulation is cushioned by several muscles, specifically the subscapularis and the serratus anterior. The serratus anterior has both a broad origin on the chest wall and a broad insertion along the majority of the ventral surface of the medial scapula (FIG 2).

 

A bare area devoid of muscular attachments has been described between the origins of the subscapularis and serratus anterior averaging 22.3 × 10.8 mm and has been implicated as a possible source of pathologic

scapulothoracic impingement.5

 

 

 

FIG 1 • Four different bursae are shown—two infraserratus, one supraserratus, and one trapezoid bursae.

 

 

In addition, two major and four minor bursae have been described in the scapulothoracic articulation13,14,37 (see 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.

 

Although the major bursae have been found consistently in cadaveric and clinical studies, those of the minor bursae were not.8,33,34

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 osseous anomalies of this region.25,31

 

Maltracking or dynamic compression of the scapulothoracic articulation has been postulated as an 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.9,37

 

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.21,38

 

Clinical studies and histologic findings of muscle intrafascicular fibrosis, bursitis, edema, and shoulder girdle muscle atrophy support this hypothesis.14,31

 

 

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FIG 2 • The serratus anterior has both a broad origin on the chest wall and a broad insertion along the majority of the ventral surface of the medial scapula.

 

 

Osseous causes of snapping scapula syndrome are rare. These include scapular osteochondromas and exostoses (FIG 3), anterior angulation of the scapula, scapular fracture, scapular tubercle of Luschka, skeletal abnormalities of the vertebrae (omovertebral bone), and abnormal angulations and tumors of the ribs.20,21,35

 

Several osseous anatomic variants on the ventral surface of the scapula have been implicated as a potential cause of snapping scapula syndrome.

 

The tubercle of Luschka is a ventral osseous prominence at the superomedial angle of the scapula, which was found in 3% of cadaveric specimens. A teres major tubercle was found in 43.2%, and a teres major process

was found in 6.8%.36

 

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 at the superomedial border. Constant motion irritates the soft tissues, leading to inflammation and a cycle of chronic bursitis and scarring.

 

 

 

FIG 3 • 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.12

 

Alternatively, some patients report a history of relatively painless shoulder crepitation that has only recently become painful.

 

 

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.

 

Patients can often reproduce their symptomatic crepitation on command, which often involves exaggerated shrugging of the shoulders.

 

Some patients report a family history of the disorder and have bilateral symptoms.

 

Improvement of symptoms by lifting the scapula off the chest wall helps localize the source of pathology to the

scapulothoracic articulation.

 

Alternatively, the scapula assistance test (SAT) may improve the patient's symptoms by increasing the posterior tilt of the scapula in cases of snapping scapula syndrome due to dyskinesia. This test is performed by the examiner manually placing inferomedial directed pressure on the scapular body in an attempt to manually correct/assist scapular maltracking. A positive test is an improvement in the patient's symptoms with

this maneuver.11 A positive SAT often indicates that a

 

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patient's symptoms may significantly improve with intensive physical therapy to correct scapular dyskinesia.

 

 

 

FIG 4 • A. A scapular Y 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.

 

 

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.

 

Altered scapula motion is often due to tightness in the scalene muscles, pectoralis minor, or pectoralis major. Dyskinesia and winging can be caused by weakness in the serratus anterior or lower trapezius. Finally, upper trapezius hypertrophy may contribute to altered scapular kinematics due to anterior tilting of the scapular body

on the chest wall.11

 

In patients with winging of the scapula, a careful neuromuscular examination should be performed to differentiate true winging from compensatory pseudowinging that might originate from a painful scapulothoracic articulation.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Radiologic studies should include an anteroposterior (AP) and tangential (Y) views of the shoulder to identify bony abnormalities in the scapula and ribs (FIG 4A).

 

A computed tomography (CT) scan may be needed for more bony definition. Its role, with or without three-dimensional reconstruction, is still debated,19,25 but in patients with suspected bony skeletal abnormality, the CT scan might be helpful (FIG 4B).

 

Fluoroscopy could be used to visualize the snapping during simulated shoulder motion.

 

Magnetic resonance imaging (MRI) can identify the location and size of the inflamed bursa, but the authors do not use this modality to diagnose bursitis.

 

MRI is often useful in the evaluation of soft tissue masses around the shoulder girdle. Specifically, the elastofibroma dorsi can easily be diagnosed due to pathognomonic location and MRI features.27

 

Nerve conduction and electromyography studies are useful if a neurologic injury is suspected in patients with scapular winging.

 

DIFFERENTIAL DIAGNOSIS

Soft tissue malignancies or benign tumors Atrophied or fibrotic muscle

Anomalous muscle insertions

Subscapular elastofibroma dorsi—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.27

Cervical spondylosis and radiculopathy Periscapular muscle strain Glenohumeral or subacromial pathology

 

 

NONOPERATIVE MANAGEMENT

 

The initial management of snapping scapula syndrome 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 subscapularis, which can elevate the scapula off the chest wall when they are hypertrophied.6,31

 

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.

 

 

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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 3- to 6-month trial is a good estimate.

 

If the diagnosis is certain, no structural anatomic lesion is present, and if 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.

 

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 surgeon must be conscious of patient-specific negative prognostic factors that may be associated with poor outcomes. These include chronic narcotic use, prior surgery, worker's compensation status, or any secondary gain issue.

 

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 5).

 

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.

 

 

 

FIG 5 • 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.

 

 

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.

 

The senior author routinely uses a combination approach of an arthroscopic bursectomy followed by an open superomedial scapulectomy.

 

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). Depending on the size of bony resection, the levator scapulae and upper serratus insertion are almost always detached with possible detachment of small portion of the upper part of the rhomboid minor.

 

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.

 

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 electrocautery 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.

 

 

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TECH FIG 1 • A. Patient positioned prone with hand positioned behind the 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)

 

 

P.3866

 

 

 

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.

 

 

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• Arthroscopic Bursectomy

   

  Positioning is the same as in open decompression.

   

  Placement of the arm in the chicken wing position results in scapular winging and protraction off the posterior thorax, which facilitates the entry of the arthroscopic instruments in the bursal space.16

   

  The initial “safe” portal is placed at the level of the scapular spine, just 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.

   

   

   

  TECH FIG 2 • A. Locations of the arthroscopic portals. A proximal (safe) portal (black arrow) is placed just 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.

   

   

  Alternatively, a superior scapular portal (Bell portal) may be developed as a working portal.7 The superior portal is localized between the medial and middle third of the scapula. The authors do not routinely use this portal due to its proximity and theoretical risk of injury to the spinal accessory, long thoracic, and suprascapular nerves.

   

  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 arthroscope 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.

   

  P.3868

• 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.22

   

  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.

   

  Spinal needles are often used to mark the outline of the superomedial angle of the scapula and estimated extent of the resection.23

   

  Bell et al2 defined a safe zone for arthroscopic resection of the superomedial angle. The medial border of the resection is defined by the medial scapular boarder and scapular spine. The lateral boarder is defined a line between the junction of the medial and middle third of the scapula (Bell portal) and an

  arthroscopic resection target localized at the junction of the scapular spine and inferior angle.2 The authors do not routinely use this portal due to its proximity and theoretical risk of injury to the spinal accessory, long thoracic, and suprascapular nerves.

   

  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.15

 

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 4- to 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
	Indications ▪ Appropriate history, physical examination, and review of radiographs should be done. Diagnostic injection is very helpful to confirm the diagnosis and predict a

 

	good surgical outcome.     Contraindications to Symptoms that originate from the trapezoid bursa. This bursa is superficial arthroscopic to the scapulothoracic space, and, therefore, removing it will not remove decompression the pathologic tissue.     Positioning ▪ Patient prone, with hand of the affected shoulder behind the back to elevate and protract the scapula. Surgeon should be standing by the opposite shoulder.     Open ▪ Avoid suprascapular notch during bony resection. decompression ▪ It is essential to reattach the detached muscles to the scapula through bony drill holes.     Arthroscopic ▪ Use a spinal needle for localization of the scapulothoracic space. decompression ▪ Care should be taken to avoid overpenetration through the serratus anterior into the subscapular space or through the chest wall. Use of a bipolar radiofrequency device is essential to avoid bleeding from the inflamed bursa. Complete bursectomy should be performed.

 

 

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 activeassisted range-of-motion exercises immediately after surgery.

 

After 4 weeks, isometric exercises are started.

 

Strengthening of the periscapular muscles begins by 8 weeks.

OUTCOMES

Historically, the outcome of open decompression as reported in the literature has been good.14,24,31,32

Nicholson and Duckworth26 reported improved functional shoulder scores and pain relief in the open treatment of snapping scapular syndrome at a mean 2.5-year follow-up.

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Lien et al18 reported similar results with combined endoscopic bursectomy and mini-open partial

 

 

scapulectomy.

There have been multiple recent publications on the arthroscopic management of snapping scapula syndrome, but the majority of these reports are technique guides and anatomic cadaveric studies.

Early results from small series of patients who underwent arthroscopic decompression were promising, with minimal morbidity and early return to work.7,10,15,29,30

Pearse et al30 reported 70% satisfactory outcomes in patients undergoing arthroscopic management of the snapping scapula syndrome.

Millett et al22 demonstrated functional improvement in 21 shoulders undergoing arthroscopic scapulothoracic bursectomy and partial scapulectomy at a mean follow-up of 2.5 years. However, the resultant functional scores were lower than expected with only modest patient satisfaction and a 13%

revision rate.22

Recently, Blønd and Rechter3 prospectively analyzed 20 shoulders with a mean follow-up of 2.9 years and demonstrated a 95% satisfaction rage and functional improvement in 90% of the patients.

Currently, there is no compelling evidence to suggest one specific technique over another.

 

COMPLICATIONS

Recurrence of symptoms secondary to incomplete resection Pneumothorax

Iatrogenic injury to the neurovascular structures around the superomedial border of the scapula.3 The spinal accessory, long thoracic, and suprascapular nerves are specifically at risk.

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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2. Bell SN, van Riet RP. Safe zone for arthroscopic resection of the superomedial scapular border in the treatment of snapping scapula syndrome. J Shoulder Elbow Surg 2008;17(4):647-649.

    

    

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