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Supraspinous fossa

The supraspinous fossa is a concave bony depression on the posterior surface of the scapula, situated superior to the scapular spine and serving as the primary origin site for the supraspinatus muscle, a key component of the rotator cuff responsible for initiating shoulder abduction.^[1]^[2]^[3] This fossa is broader medially and narrows laterally, forming a smaller superior compartment of the scapula's posterior aspect, distinct from the larger infraspinous fossa below the spine.^[1]^[4] Its boundaries include the scapular spine inferiorly, the acromion process laterally, and the superior angle of the scapula cranially, with the suprascapular notch providing entry for neurovascular structures.^[1] The fossa houses the supraspinatus muscle, which originates from its medial two-thirds and features a fusiform structure with an internal tendinous core, as well as the suprascapular nerve, artery, and vein that course through it after passing the suprascapular notch.^[1]^[2] Clinically, the supraspinous fossa is significant for shoulder stability and mobility, as pathologies here—such as supraspinatus muscle atrophy from tendon tears, suprascapular nerve compression by paralabral cysts, or rare tumors like chondrosarcoma—can lead to pain, weakness in arm abduction, and reduced range of motion.^[1] The region's anatomy also informs surgical approaches, including rotator cuff repairs and nerve decompression procedures, emphasizing the need to preserve the delicate neurovascular elements within the fossa.^[1]

Anatomy

Location and Borders

The supraspinous fossa is a concave depression located on the posterior surface of the scapula, positioned superior to the spine of the scapula.^[1] It is smaller and shallower compared to the infraspinous fossa, with a shape that is broader at the medial (vertebral) end and narrower laterally.^[1]^[5] The boundaries of the supraspinous fossa are defined inferiorly by the spine of the scapula, laterally by the acromion process, superiorly by the superior angle of the scapula, and medially it remains open toward the suprascapular notch.^[1]^[6] These spatial limits provide a foundational framework for understanding the fossa's position within the scapular anatomy.^[5] In adults, the dimensions of the supraspinous fossa vary based on individual scapular size.^[7]

Attachments and Relations

The supraspinous fossa serves primarily as the origin site for the supraspinatus muscle, which arises from the medial two-thirds of the fossa's floor and the adjacent superior surface of the scapular spine.^[2]^[8]^[9] This attachment provides a broad base for the muscle's fusiform anterior belly and unipennate posterior belly, enhancing its mechanical leverage within the scapular framework.^[2] A secondary muscular attachment involves the distal fibers of the levator scapulae muscle, which insert along the medial border of the scapula from the superior angle to the root of the spine, forming the medial boundary of the supraspinous fossa.^[10]^[11] This insertion lies in close proximity to the fossa's medial aspect, contributing to the structural continuity of the posterior scapular region.^[12] The supraspinous fossa maintains key relations to adjacent scapular features, including its medial and superior proximity to the suprascapular notch, a bony defect in the superior border that accommodates passage of the suprascapular nerve and vessels.^[12] Indirectly, the fossa connects to the coracoid process through the supraspinatus tendon's course, which passes superior to the coracoid and integrates with the rotator cuff mechanism.^[2] These relations underscore the fossa's integration within the scapula's posterior surface, bounded superiorly by the superior border, medially by the medial border, and inferiorly by the scapular spine.^[6] Overlying the supraspinous fossa and its contents is the supraspinous fascia, a thin connective tissue layer that blends with the periosteum of the scapula and provides attachment points for the supraspinatus muscle, thereby enclosing the fossa in an osseofibrous compartment for added stability.^[13]^[14] This fascia extends from the superior border of the scapula to the spine, reinforcing the region's tensile strength.^[15] Anatomical variations in the supraspinous fossa's attachments are infrequent but notable, including an aponeurotic expansion from the anterior supraspinatus tendon observed in approximately 50% of cases on MRI, which may reinforce tendon integrity.^[2] Additionally, the supraspinatus muscle may exhibit distinct anterior and posterior bellies with varying origins, where the posterior belly arises partly from the scapular spine and glenoid neck adjacent to the fossa.^[2]

Function

Supraspinatus Muscle Support

The supraspinous fossa serves as the primary site of origin for the supraspinatus muscle, which acts as a key abductor of the arm at the glenohumeral joint.^[2] This muscle originates from the medial two-thirds of the fossa's floor, enabling it to initiate the first 15 degrees of arm abduction before the deltoid muscle assumes the primary role in further elevation.^[16] Through this attachment, the fossa supports the supraspinatus in providing initial lift and dynamic control during shoulder movements. As part of the rotator cuff, the supraspinous fossa's structure contributes to the supraspinatus tendon's ability to compress the humeral head firmly against the glenoid cavity, thereby enhancing glenohumeral joint stability, particularly during overhead activities.^[16] This compressive mechanism counters superior translation of the humeral head, maintaining central positioning within the glenoid and facilitating smooth articulation.^[17] Biomechanically, the fossa's shallow concavity accommodates a broad, flat muscular origin that distributes contractile forces evenly across the supraspinatus fibers, thereby minimizing localized shear stress on the tendon during tension.^[1] The resulting force vectors from this origin align horizontally to counterbalance the superior pull of the deltoid, forming a force couple that optimizes abduction efficiency and joint congruence.^[18] In the context of scapulohumeral rhythm, the supraspinatus, anchored in the supraspinous fossa, coordinates with scapular upward rotation to ensure progressive arm elevation without superior humeral migration, thus preventing subacromial impingement.^[19] This integration allows for a 2:1 ratio of glenohumeral to scapulothoracic motion, promoting fluid overhead function.^[16]

Neurovascular Supply

The supraspinous fossa receives its primary arterial supply from the suprascapular artery, which originates as a branch of the thyrocervical trunk from the subclavian artery and enters the fossa after passing superior to the superior transverse scapular ligament.^[20] Once in the fossa, the artery branches to provide blood to the supraspinatus muscle and the overlying fascia, ensuring adequate perfusion for the region's muscular and connective tissues.^[21] The neural supply to the supraspinous fossa is provided by the suprascapular nerve, which arises from the upper trunk of the brachial plexus with contributions from the C5 and C6 spinal roots.^[22] This nerve passes through the suprascapular notch inferior to the superior transverse scapular ligament, then travels deep to the supraspinatus muscle within the fossa, where it delivers motor innervation to the muscle via two primary branches.^[20] The superior transverse scapular ligament serves as a key anatomical divider in the suprascapular notch, with the suprascapular artery typically coursing superior to it and the nerve (accompanied by the suprascapular vein) passing inferiorly, thereby separating the neurovascular elements and potentially influencing their vulnerability to compression.^[20] In some individuals, the artery may traverse a separate bony foramen or pass inferior to the ligament, representing anatomical variants that occur in approximately 10-20% of cases.^[23] Additional minor arterial contributions to the supraspinous fossa and supraspinatus muscle can come from the dorsal scapular artery, which arises from the subclavian or transverse cervical artery and provides collateral supply in some cases.^[21] The suprascapular nerve also includes sensory branches that extend to the acromioclavicular joint, contributing to proprioception and pain sensation in the shoulder region.^[20] Anatomical variations, such as ossification of the superior transverse scapular ligament, can result in the formation of a bony suprascapular foramen, which alters the spatial dynamics of the artery and nerve passages and has been observed with varying prevalence (e.g., 4% to 18% partial ossification) in different populations and studies.^[24]

Clinical Aspects

Rotator Cuff Pathology

Rotator cuff tears most commonly involve the supraspinatus tendon, which originates from the supraspinous fossa, and are classified as partial-thickness (incomplete disruption) or full-thickness (complete tendon rupture).^[25] These tears often result from degenerative changes or acute trauma, leading to progressive tendon failure.^[25] In chronic cases, tears cause supraspinatus muscle atrophy and fatty infiltration, manifesting as a visible hollowing or concavity in the supraspinous fossa due to reduced muscle bulk.^[25]^[1] Suprascapular nerve entrapment, frequently at the suprascapular notch or due to compression by supraglenoid cysts arising from labral tears, results in denervation of the supraspinatus muscle.^[26]^[27] This leads to muscle atrophy and weakness, particularly during shoulder abduction, as the nerve's compression disrupts innervation to the fossa's contents.^[26]^[1] Other pathologies affecting the supraspinous fossa include tendinopathy from overuse, which induces degeneration in the supraspinatus tendon through repetitive microtrauma, often progressing to tears.^[28]^[1] Calcific deposits commonly form in the supraspinatus tendon near its insertion, causing inflammation and potential extension into the fossa.^[29] Paralabral cysts, associated with superior labral tears, can erode the fossa floor or extend into the suprascapular notch, exacerbating nerve compression and muscle denervation.^[1] Symptoms of these conditions typically include shoulder pain exacerbated by overhead activities or at night, along with weakness and impingement sensations during arm elevation.^[25]^[26] Risk factors encompass age over 40, repetitive overhead motions in athletes or laborers (such as throwing or painting), smoking, and traumatic injuries.^[25]^[28]^[26] Epidemiologically, rotator cuff tears affect approximately 20-30% of individuals over 60 years, with prevalence rising to approximately 20% in those aged 60-69 years and 31% in those aged 70-79 years (asymptomatic individuals per 1999 ultrasonography study), particularly involving the supraspinatus.^[30]^[31] Higher incidence occurs in overhead athletes and those with occupational repetitive strain.^[28]^[26]

Diagnostic and Surgical Considerations

Magnetic resonance imaging (MRI) serves as the gold standard for diagnosing rotator cuff tears and assessing muscle atrophy in the supraspinous fossa, particularly for the supraspinatus tendon, where T2-weighted sequences reveal high signal intensity indicative of edema or partial tears.^[32] Ultrasound provides dynamic evaluation of tendon integrity during shoulder motion, offering high sensitivity (up to 95%) and specificity (up to 93%) for detecting supraspinatus injuries and impingement by visualizing real-time tendon displacement relative to the acromion.^[33] Computed tomography (CT) is utilized to identify bony variants, such as ossification of the superior transverse scapular ligament, which can narrow the suprascapular notch and affect the supraspinous fossa.^[1] Diagnostic confirmation of nerve entrapment involves electromyography (EMG), which detects denervation patterns in the supraspinatus muscle through fibrillation potentials and positive sharp waves, with sensitivity ranging from 70% to 90%.^[34] Clinical evaluation includes the empty can test, performed by resisting internal rotation and abduction at 90 degrees with the thumb down; weakness or pain suggests supraspinatus involvement.^[35] Arthroscopic repair of rotator cuff tears originating in the supraspinous fossa employs the subacromial portal for visualization and instrument access, allowing suture anchor placement and tendon mobilization with minimal tissue disruption.^[36] Cyst debridement within the fossa is similarly performed arthroscopically to alleviate pressure on the supraspinatus. For confirmed suprascapular nerve entrapment, decompression involves releasing the superior transverse scapular ligament to restore nerve function.^[37] Postoperative rehabilitation emphasizes gradual restoration of abduction strength, beginning with passive range-of-motion exercises at 4-6 weeks and progressing to active strengthening by 12 weeks, achieving healing rates of 85-91% in isolated supraspinatus repairs.^[38] Emerging techniques include ultrasound-guided injections of corticosteroids or platelet-rich plasma into the supraspinatus tendon for tendinopathy, reducing pain and improving function in 70-80% of cases without surgery.^[39] Minimally invasive endoscopic approaches facilitate cyst excision in the supraspinous fossa by accessing paralabral or ganglion cysts through small portals, minimizing morbidity compared to open methods.^[40]

References

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Supraspinous fossa – the area above the spine of the scapula, it is much smaller than the infraspinous fossa, and is more convex in shape. The supraspinatus ...Costal Surface · Lateral Surface · Posterior SurfaceMissing: dimensions | Show results with:dimensions
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