Fig. 14.1
Schematic demonstrating scapula anatomy in the axial plane. Two major bursae, the supraserratus and infraserratus bursae, the source of pathology in the majority of cases in the scapulothoracic bursitis, can be identified. (Reproduced with permission from Gaskill T, Millett PJ, Snapping Scapula Syndrome: Diagnosis and Management. J Am Acad Orthop Surg. 2013; 21(4): 214–224)
Muscular dysfunction can also be attributable to SSS [5] and can take the form of either abnormal biomechanics, anatomical variants, or both. The synchrony of the periscapular muscles may be disrupted by muscle weakness, glenohumeral pathology, trauma, or iatrogenic nerve injury leading to a disruption of the force couples about the scapula and abnormal scapula motion, which can subsequently cause abnormal contact between the scapula and the thoracic cavity [3, 6]. In this setting, arm forward flexion may induce a posterior tilting of the scapula, thereby compressing the space between the inferior pole and the rib cage [7]. Conversely, abnormal anterior tilt due to a pathologically tight pectoralis minor muscle, for example, may compress the space between the superior scapula and the thoracic wall [8]. Atrophied or fibrotic muscle or anomalous insertions can produce abnormal scapular biomechanics potentially leading to painful “snapping.”
Finally, soft tissue anatomic variations, including thinner muscle bulk of the subscapularis on the medial border of the scapula, may lead to a predisposition to abrasive forces against the rib cage [9, 10]. A superomedial bare area on the costal surface of the scapula between the origin of the subscapularis and the insertion of the serratus anterior has recently been described in a cadaveric study and may play a role in some cases [6, 11]. Skeletal abnormalities that contribute to SSS include anatomic variations, posttraumatic conditions, and mass lesions. A review of 89 cases of snapping scapula syndrome determined that a skeletal abnormality was present in 43% of cases [12]. Anatomic variations are the most common subgroup and involve the bony structures of the scapula, thoracic cage, or the spine. A recent imaging analysis demonstrated that a “curved-type” scapular morphology, anteriorly angled medial border of the scapula, and decreased scapulocostal distance might be associated with SSS [13]. Luschka’s tubercle, which is a prominence of bone or fibrocartilage at the superomedial angle of the scapula, has also been shown to contribute [14]. Additionally, removal of the first rib for treatment of thoracic outlet syndrome has led to SSS in some cases [15]. With regard to spinal abnormalities, excessive thoracic kyphosis or scoliosis may be implicated as the cause of an abnormal scapulothoracic articulation [4]. Despite these associations, many patients with anatomic variations are asymptomatic, so the clinical context of their presentation must be taken into account [16]. Posttraumatic conditions including malunion of the scapula or underlying ribs and reactive bone spurs from repetitive periscapular muscle trauma can also disrupt the normal articulation [9, 17–19]. Furthermore, musculoskeletal tumors such as osteochondromas, elastofibroma dorsi, and rarely chondrosarcoma can be the cause and must be excluded [20]. Osteochondromas in particular are the most common benign tumor of the scapula [21] and have been well-documented as a cause of SSS in the literature with one report accounting 16% of cases as due to these mass lesions [12]. Elastofibroma dorsi may specifically affect the ventral surface of inferomedial angle of the scapula causing a mass effect and abnormal biomechanics [22].
Clinical Presentation
Patients with SSS can present with a spectrum of complaints from mild discomfort to severely painful pseudoparalysis of the shoulder with an audible crepitus. This wide variety of presentations is largely due to the diversity of underlying causes.
History
Patients with scapulothoracic bursitis or snapping scapula typically complain of pain, palpable crepitus, and/or audible noise with arm movement, especially with overhead activities. These symptoms can significantly vary between individuals. As such, the patient should be questioned on the precise location, quality, and intensity of the associated pain or discomfort along with its chronicity, associated symptoms, and aggravating and alleviating factors. A family history of similar symptoms may be important as Cobey et al. suggested that there may be an inherited predisposition for scapular crepitus [18]. In addition, the patient’s prior as well as desired type and level of activity should also be noted for appropriate goal setting and management of expectations.
Physical Examination
Physical examination should begin with a visual inspection of posture because significant kyphoscoliosis is known to reduce scapulothoracic congruity and may induce scapular snapping with or without painful bursitis [4]. Evaluation of the cervical spine should be performed in all patients to exclude a referred pain syndrome resulting from nerve compression between the C5 and C8 nerve root levels [23, 24]. Dynamic evaluation of both scapulae is then undertaken, noting any evidence of asymmetry, dyskinesis, winging, or audible snapping as the arms are moved through a range of active and passive motion. It is important to note that overhead athletes will often have depression, protraction, and downward rotation of their dominant scapula, which may be unrelated to their primary complaint [25].
Additionally, scapular dyskinesis is a common finding in patients with scapulothoracic bursitis and may be the result of unbalanced periscapular muscle kinematics such as weakness or tightness of the serratus anterior, trapezius, levator scapulae, or pectoralis minor muscles. Scapular winging can result from serratus anterior muscle weakness, most commonly caused by a long thoracic nerve palsy, or weakness or atrophy of the trapezius muscle, which may be caused by a spinal accessory nerve palsy. Superomedially, tightness of the trapezius and levator scapulae muscle may present with neck stiffness and can be diagnosed via muscle length testing. Anteriorly, pectoralis minor tightness, which can result in scapular depression and protraction, can be diagnosed by visualization of the difference in the height of the shoulders off the examination table with the patient in a supine position. The affected shoulder girdle will rise higher off the table than the unaffected shoulder [26, 27]. In addition, an alternative method to assess pectoralis minor tightness in the same position is to place a hand on the anterior aspect of the affected shoulder and apply a moderate anteroposterior force. Significant resistance in flattening the shoulder against the examination table likely indicates a shortened pectoralis minor muscle-tendon complex. The presence of SICK (scapular malposition, inferomedial border prominence, anterior coracoid pain, and scapular dyskinesis) scapula in overhead athletes should alert the clinician to other associated diagnoses such as a glenohumeral internal rotation deficit (GIRD), posterosuperior impingement, or superior labral anterior to posterior (SLAP) tears, which may be contributing to snapping through scapular malpositioning or a dyskinetic pathophysiology [1].
Palpation of the periscapular region may reveal areas of localized tenderness consistent with adventitial infraserratus or supraserratus bursal inflammation. The superomedial angle and the inferomedial angle of the scapula are the most common locations for painful bursae [28]. Deeper palpation of these sites may be achieved by placing the arm in the “chicken-wing” position, in which the humerus is internally rotated and the dorsum of the hand is placed over the lumbosacral junction, a movement which tilts the scapula laterally [28, 29]. Some patients may be able to reliably produce scapulothoracic crepitus with provocative movements. In these cases, palpating the scapula while the patient performs these movements may help localize the site of pathology [30]. Additionally, applying posterior-to-anterior compressive forces over the scapular body during range of motion testing may also precipitate or accentuate crepitation between the scapula and the posterior thorax and exacerbate the patient’s symptoms [31].
Periscapular muscle strength testing should also be performed on individual muscle groups to identify any weakness that may result in biomechanical force imbalance, scapular dyskinesia or winging, and subsequent snapping. The examiner should apply varying levels of resistance, and all resistance testing should be compared to the contralateral side. The trapezius musculature is evaluated by having the patient shrug the shoulders against resistance, while the levator scapulae and rhomboid musculature are best examined with the patient’s hands on the ipsilateral iliac crests and subsequently having the patient force the elbows posteriorly against resistance. The serratus anterior muscle is tested by having the patient perform a wall push-up while the examiner simultaneously visualizes and palpates the medial border of the scapula. Weakness will exacerbate medial border prominence. The latissimus dorsi muscle can be isolated by having the patient push posteriorly against resistance with the arm at the side while the examiner palpates the inferomedial angle of the scapula.
Imaging
Radiographs
Standard radiographs should always be obtained when a diagnosis of snapping scapula syndrome is suspected. A combination comprising of true anteroposterior, tangential Y, and axillary views gives the clinician the best chance to exclude skeletal abnormalities. Despite adequate plain radiographs, bony anatomic abnormalities may still be missed [32].
Computed Tomography
When a skeletal lesion is identified on plain radiographs or suspected based on clinical exam, a CT scan, ideally including three-dimensional optimization, should be obtained to further characterize the lesion [32]. Routine CT scanning should be avoided in young patients unless indicated by radiographic evidence of an osseous or cartilaginous lesion that alters the congruency of the scapulothoracic articulation.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is most useful to identify soft tissue structures that may be responsible for scapulothoracic crepitus or bursitis such as fibrotic scar tissue (Fig. 14.2), inflamed tissue, or musculotendinous disease. Additionally, tissue component analysis can be used to distinguish between malignant and benign soft tissue lesions [33].
Fig. 14.2
Preoperative MRI (T2 weighted) of a patient with SSS showing inflamed fibrotic scar tissue between the superomedial scapula angle and the thorax (white arrow). HH humeral head, S scapula
Electromyograms
An electromyogram is indicated to evaluate the integrity of the nervous supply to the musculature in patients with unexplained scapular winging or periscapular muscle weakness. In particular, medial scapular winging may be caused by atrophy or weakness of the serratus anterior muscle following long thoracic nerve injury, and lateral scapular winging may be caused by trapezius muscle atrophy or weakness or spinal accessory nerve dysfunction. Whereas the majority of long thoracic nerve palsies are posttraumatic, the majority of spinal accessory nerve palsies are iatrogenic following neck or facial surgery [34]. Aberrant arthroscopic portal placement superior to the level of the scapular spine is an extremely rare cause of spinal accessory nerve dysfunction but should be considered in the appropriate circumstances [2].
Diagnostic Injections
In general, injections with local anesthetic agent and steroid can be both diagnostic and therapeutic. The temporary resolution of pain after the injection confirms the diagnosis of bursitis while also precisely localizing the pathological bursa. Despite a high likelihood of immediate success in these patients, the effect is rarely long-lasting although there have been reports of extended success [35]. The patient is positioned prone with the shoulder extended, internally rotated, and adducted in a “chicken-wing” position. The skin overlying the medial scapula is prepared in a sterile fashion, and the needle is inserted parallel to the anterior border of the scapula at the spot of maximal tenderness. Clinicians must be aware of the potential risk of intrathoracic penetration with an inappropriate vector of injection. Use of ultrasound has been described to aid localization of scapulothoracic injection with good results [36].
Nonoperative Treatment
With the exception of the situation in which there is a malignant mass lesion, a trial of nonoperative therapy is warranted regardless of the underlying of etiology of SSS. When caused by chronic overuse in the absence of anatomic abnormalities, nonoperative treatment should be attempted for 6 months to 1 year prior to considering surgery and can be expected to have high success rates [37, 38]. If symptoms are caused by an anatomic lesion, a trial of conservative treatment is still warranted [4]; however, the threshold for considering surgery is lower as surgical excision or correction of the abnormality has a high cure rate [14, 39]. A nonoperative protocol consists of activity modification, nonsteroidal anti-inflammatory medications, physical therapy, and therapeutic injections of steroids and/or local anesthetic into the inflamed bursae. With overuse and biomechanical imbalances being the major etiologic factors, the patient must initially modify activities to abate the cycle of bursitis and scarring. Physical therapy should focus on periscapular muscle strengthening and improving shoulder girdle biomechanics. In cases where poor posture is contributory, training to minimize kyphosis, promote upright posture, and strengthen upper thoracic musculature is indicated. Because the scapula is responsible for static stability of the shoulder girdle, endurance training is crucial for scapular stability. This type of training comprises of low-intensity exercises with high repetitions. Strengthening of the subscapularis and serratus anterior reduces anterior tilt of the scapula alleviating bursal compression. Scapular adduction and postural shoulder shrug exercises are critical to strengthen the scapular stabilizers, including the serratus anterior, rhomboids, and levator scapulae. Specific beneficial exercises include scaption, press-up and push-up plus, rowing and machine rowing, and ball isometric scapular stabilization exercises. Abduction and elevation of the scapula cause increased pressure and strain on the underlying musculature and therefore should be avoided [40].
Operative Treatment
Indications
Surgical treatment is considered in patients who have failed nonoperative therapy. Surgery may provide more reliable results in patients who experience temporary relief with injections or in those patients with anatomic abnormalities contributing to their symptoms [38, 41]. In most cases, an arthroscopic approach may be successful; however, with larger mass lesions, open techniques may offer superior visualization and direct access and prevent the inadvertent spread of malignant cells. Arthroscopic treatment offers a quicker postoperative recovery and rehabilitation process [30, 42]. Specific surgical methods are variable depending on the individual patient’s complaints and anatomic abnormalities, but typically surgery entails bursectomy of the pathologic bursa with or without partial scapulectomy of the superomedial scapula. Good results have been demonstrated with bursectomy alone in some reports [43]; however, partial scapulectomy with bursectomy is more commonly performed, particularly in the setting of mechanical crepitus [29, 44].
Arthroscopic Technique
Prior to surgery, the most painful areas should be confirmed with the patient to maximize success of surgery. These can be indicated with an indelible marker prior to induction of anesthesia in counsel with the patient. With regard to positioning, the patient is positioned prone with the nonoperative arm tucked to the side (Fig. 14.3a). The posterior thorax is draped widely, and the operative extremity is placed into a sterile stockinette. The dorsum of the operative hand is positioned on to the small of the back, effectively placing the glenohumeral joint into extension and near maximal internal rotation in the “chicken-wing” position. This position aids portal placement by increasing the potential space between the scapula and the chest wall. Additional separation may be accomplished by placing a medially directed force on the lateral shoulder to cause bayonet apposition of the scapular body. Bony landmarks are marked including the medial border and the spine of the scapula. Portals (Fig. 14.3b) are established 3 cm medial to the medial scapular border and kept inferior to the scapular spine to reduce the risk of injury to the main branches of dorsal scapular nerve and artery. This medial portal placement also allows a trajectory into the bursae that is more parallel to the chest wall, thereby decreasing the risk of thoracic penetration.
Fig. 14.3
(a) Intraoperative photograph of a right scapula and arm, placed in the “chicken-wing” position. Preoperatively, the point of maximum tenderness (white arrow) is marked. (b) Intraoperative photograph of the right scapula. The bony landmarks including the medial border of the scapula are marked. Portals are placed 3 cm medially to the scapula to minimize the risk of injury to neurovascular structures
An initial viewing portal is made 3 cm medial to the inferomedial angle of the scapula, and a 30° arthroscope is introduced (Fig. 14.3b). Fluid pressure is routinely maintained at or below 50 mmHg. A second medial portal (Fig. 14.3b) is placed by triangulation, located 3 cm medial to the scapula just inferior to the medial confluence of the scapular spine. Once adequate visualization is established, a diagnostic bursoscopy is performed. The intercostal muscles and ribs are visualized inferiorly, the subscapularis is visualized laterally, and the rhomboid and levator muscles are identified medially. A spinal needle is placed along the superomedial scapular border for additional orientation. Red muscle fibers of the subscapularis are not resected because a shaver or radiofrequency (RF) ablator is used to clear bursal tissue and fibrous bands in order to skeletonize the superomedial scapular border. Next, the supraserratus bursa is accessed similarly by bluntly penetrating the serratus posterior superior (Fig. 14.4a).
