The scapula spans superoinferiorly from the second to the seventh rib and is connected to the axial skeleton via the acromioclavicular and sternoclavicular joints.

The scapula is composed of borders (medial, lateral, and superior) and four angles (inferomedial, medial, lateral, and superomedial) which serve as important arthroscopic landmarks.

The scapula is concave on its anterior surface as it articulates with the convex thoracic cage.

The osseous anatomy of the scapulothoracic articulation can vary considerably,¹ although some of these nonpathologic variations may be related to snapping scapula³⁹:

The suprascapular notch occurs just medial to the take-off of the coracoid process and its shape has been categorized into six types (I-VI) by Rengachary³⁴:

The transverse scapular ligament, which spans the suprascapular notch, can also vary in morphology. There are three types as described by Polguj et al³³:

Trapezius muscle

Serratus anterior muscle

Subscapularis muscle

Levator scapulae muscle

Rhomboid major muscle

Rhomboid minor muscle

A thorough understanding of surrounding neurovascular structures is necessary to prevent iatrogenic injury.

The dorsal scapular nerve and artery run superoinferiorly 1 to 2 cm medial to the medial scapular border and deep to the rhomboid musculature (Ruland). Portal placement less than 3 cm from the medial scapular border endangers these structures.

The spinal accessory nerve is located in the central portion of the levator scapulae muscle deep to the trapezius muscle.³⁶ Portal placement superior to the level of scapular spine endangers this structure.

The long thoracic nerve travels along the anterior belly of the serratus anterior muscle. This nerve is infrequently in danger unless portals are placed in an extraordinarily lateral position.

The suprascapular nerve branches from the brachial plexus and runs posterosuperiorly with the suprascapular artery. The nerve passes through the suprascapular notch below the transverse scapular ligament, whereas the artery passes above this ligament. These structures are endangered with superomedial portal placement or when superomedial scapular resection is performed. It is important to place arthroscopic portals 2 to 3 cm lateral to the suprascapular notch to avoid iatrogenic injury.¹,⁴

Anatomic bursae

Adventitial bursae

Smooth scapulothoracic stability and motion occurs as a result of the coordinated contraction of periscapular musculature and the function of various bursae that lie within muscular planes to allow gliding between surfaces. The scapulothoracic articulation effectively positions the glenoid to maximize range of motion capacity at the glenohumeral joint.

Most commonly arise as an overuse syndrome of the shoulder

Bursal tissue becomes irritated when gliding over uneven surfaces.

Most commonly occurs at the superomedial, medial, and inferior angles of the scapula

Fibrosis can occur if chronic inflammation is present. Fibrotic bursal tissue can produce recurrent bursitis and snapping scapula in the absence of a distinct scapulothoracic mass.¹⁷,³²

Most commonly results from soft tissue entrapment between the scapula and underlying thorax. Very uncommonly, snapping scapula can also be due to an osseous or soft tissue mass with or without concurrent bursitis. Crepitus can also occur in asymptomatic individuals; thus, it should not be considered pathologic unless accompanied by pain and/or shoulder dysfunction.

Masses are rare in clinical practice. However, the most frequent scapulothoracic masses that result in crepitation include osteochondromas at the superomedial angle,¹³,⁴⁰ elastofibroma dorsi⁸ at the inferomedial angle, and chondrosarcoma (especially in older patients). Resection of these masses is curative in the majority of cases.¹³,⁴⁰

Other mechanical causes of “snapping” include bursal fibrosis,²³,²⁴ malunion of scapular or rib fractures,³⁸ variations in anatomy of the scapula or posterior chest wall,¹,¹²,³⁹ scoliosis/kyphosis,²⁰ first rib resection,⁴¹ and, rarely, anomalous musculature.