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Shoulder Anatomy & Biomechanics

Glenohumeral stability mechanisms, including static and dynamic stabilizers, and the biomechanical adaptations associated with overhead athletic activity.

90 citationsUpdated Sep 2026

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Overview

The shoulder possesses the greatest range of motion of any joint in the human body [4], a capacity enabled by anatomy that permits more mobility than any other articulation [12]. This extreme mobility is balanced by a reliance on both static and dynamic stabilizers, particularly the rotator cuff, to maintain joint integrity [12]. The bony architecture does not provide inherent stability [27]; instead, the glenohumeral joint depends on the synchronized action of the rotator cuff and deltoid muscle for normal function [12]. The rotator cuff stabilizes the joint while allowing freedom of motion and fixing the fulcrum against which the deltoid contracts to elevate the humerus [12].

Four basic mechanical characteristics are essential to shoulder function: mobility, stability, strength, and smoothness [16]. Normal glenohumeral motion requires appropriate capsular laxity, concentric articular surfaces, and the absence of unwanted contact between the proximal humerus and lateral scapula [16]. In healthy shoulders, the capsule remains lax through most of the functional range, with tension increasing sharply only at the limits of motion [16]. The articular surfaces serve to distribute joint reaction forces across the broadest possible contact area and optimize stability without compromising motion [80].

The glenohumeral joint utilizes a mechanism known as concavity compression, where the rotator cuff embraces the humeral head and compresses it into the glenoid fossa [35]. This dynamic stabilization is effective in any arm position, unlike ligaments which are active only in extreme positions [35]. The anterior and posterior glenoid labra deepen the fossa to facilitate this centering mechanism [35]. Contact between the proximal humeral convexity and the coracoacromial arch represents normal stabilization against superiorly directed forces rather than pathological impingement [35].

Osseous Anatomy

Proximal Humerus

The articular head of the proximal humerus is spherical, with a diameter ranging from 37 to 57 mm [1]. The articular surface is covered by cartilage over an arc of approximately 160 degrees [12]. The radius of curvature averages approximately 25 mm, a value slightly larger in men than in women [12]. Specific measurements indicate a humeral head radius of curvature between 23 and 28 mm, with smaller values in women [12]. The humeral head surface area ranges from 11 to 19 mm, and the cartilage thickness is 1.44 mm [12]. The best fit circle serves as a surrogate for normal proximal humeral bony articular anatomy; while the native circle is significantly larger on average, the differences are clinically irrelevant [49].

Humeral version and inclination vary by measurement method. Humeral version averages 29.8 degrees, with a range of 10 to 55 degrees [1]. Proximal humeral retroversion is highly variable, ranging from 0 to 55 degrees depending on the measurement method [12]. Other data report an average retroversion of 19° and inclination of 41° [42], or a retroversion of 30 degrees relative to the transepicondylar axis [121]. The average neck-shaft angle is 45 degrees (±5 degrees), with a range of 30 to 50 degrees [12]. Broader ranges for the head-shaft angle are cited as 30 to 55 degrees [12]. The superior margin of the humeral head articular surface is normally positioned 8 to 10 mm superior to the top of the greater tuberosity [12]. The humeral head height is approximately 5.6 cm above the superior border of the pectoralis major tendon [121].

The proximal humerus develops from three centers of ossification: the humeral head (4 to 6 months), the greater tuberosity (1 to 3 years), and the lesser tuberosity (3 to 5 years) [42]. These centers fuse to the shaft at age 17 to 20 years [42]. The proximal humeral physis closes by 14 to 17 years in girls and 16 to 18 years in boys [127]. This physis contributes 80% of subsequent humeral growth, accounting for approximately 40% of the growth of the entire upper extremity [127]. Humeral retroversion averages 65 degrees in infants and young children, gradually decreasing to approach adult values by 11 years of age [127].

The surgical neck represents an indistinct metadiaphyseal junction below the tuberosities but above the humeral shaft [1]. Fractures involving the anatomic neck carry a worse prognosis than fractures in other regions due to potential disruption of vascular supply and the development of avascular necrosis [1]. The greater tuberosity is located posterior-superior to the humeral shaft and serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons [1]. The lesser tuberosity is located on the anterior aspect of the proximal humerus and serves as the attachment site for the subscapularis tendon [1].

The humeral shaft extends from the level of the pectoralis major muscle insertion proximally to the supracondylar ridge distally [2]. The upper portion of the shaft is cylindrical and becomes more flattened in an anteroposterior direction as it proceeds distally [2].

Glenoid and Scapula

The glenoid fossa is a shallow, inverted, comma-shaped articular surface one-fourth the size of the humeral head [20]. The subchondral bone is relatively flat, with articular concavity augmented by cartilage and a circumferential labrum [42]. The glenoid articular surface radius of curvature is 2 to 3 mm larger than that of the humeral head [12]. Specific measurements report a glenoid radius of curvature between 22 and 28 mm [12]. The glenoid cartilage thickness is 2.16 mm [12]. The glenoid surface area is 4 to 6 mm [12].

Glenoid dimensions and orientation are defined as follows: Glenoid Diameter: Ranges from 18 to 30 mm superior anteroposterior, 21 to 35 mm inferior anteroposterior, and 30 to 48 mm superoinferior [12]. Glenoid Inclination: Averages 4.2 degrees, with a range of –7 to 20 degrees [12]. Glenoid Version: Averages 5° of retroversion in relation to the axis of the scapular body [42]. Other data indicate a normal position ranging from 2 degrees of anteversion to 7 degrees of retroversion [12], or approximately 5 degrees relative to the scapular body [121]. A specific measurement reports 1.5 degrees retroversion, with a range of 10.5 to 9.5 degrees anteversion [12].

The scapula is a thin sheet of bone that mainly functions as a site of muscle attachment [120]. It is thicker at its superior and inferior angles and at its lateral border [120]. The scapula spans the second through seventh ribs and serves as an attachment for 17 muscles [121]. It is anteverted on the chest wall approximately 30 degrees relative to the body [121]. The scapula has only one true diarthrodial articulation, the acromioclavicular (AC) joint [42]. Ossification of the scapular body begins at the eighth week of gestation [42].

The scapular spine is an osseous ridge that separates the supraspinatus and infraspinatus fossae [42]. It functions as part of the insertion of the trapezius on the scapula and as the origin of the posterior deltoid [120]. The spine suspends the acromion in the lateral and anterior directions, serving as a prominent lever arm for the function of the deltoid [120]. The dimensions of the spine are regular, with less than 1.5-cm variation from the mean in any dimension [120].

The acromion has three ossification centers: the metacromion (base), the mesoacromion (middle), and the preacromion (tip) [42]. Failure of fusion of these centers results in os acromiale, which is most commonly located between the mesoacromion and meta-acromion [121].

The coracoid process functions as the origin of the short head of the biceps and coracobrachialis tendons [120]. It serves as the insertion of the pectoralis minor muscle [120]. Additionally, it serves as the insertion for the coracoacromial, coracohumeral, and coracoclavicular ligaments [120].

Clavicle

The clavicle is the first bone to ossify, occurring in the fifth week of gestation [42]. It is the only long bone to ossify by intramembranous ossification [42]. The medial (sternal) epiphysis is the last ossification center to fuse, occurring at age 20 to 25 years [42]. The primary blood supply of the clavicle is periosteal, and no nutrient artery is present [42].

The clavicle articulates medially with the sternum at the sternoclavicular joint and laterally with the acromion of the scapula at the acromioclavicular joint [20]. It rotates on its long axis and acts as a strut, serving as the only bone connecting the appendicular upper extremity to the axial skeleton [20]. Fracture of the clavicle is the most common musculoskeletal birth injury [121].

Vascular Anatomy

The anterior humeral circumflex artery (AHCA) arises from the axillary artery at the inferior border of the subscapularis [1]. The AHCA provides vascular inflow to the humeral head by way of its terminal anterolateral branch, known as the artery of Laing (also known as the arcuate artery) [1]. The anterolateral ascending branch of the anterior humeral circumflex artery provides the primary blood supply to the humeral head [42]. The terminal intraosseous portion of the anterior humeral circumflex artery enters at the proximal aspect of the intertubercular groove as the arcuate artery [42]. The ascending branch of the AHCA courses parallel to the lateral aspect of the long head biceps tendon and enters the humeral head at the interface of the bicipital groove and greater tuberosity [1]. Quantitative assessment has shown that 64% of the humeral head blood supply arises from the posterior humeral circumflex artery [127].

Anthropometric and Measurement Data

The distance from the lateral base of the coracoid process to the lateral margin of the greater tuberosity is called the lateral humeral offset [12]. A significant decrease in lateral humeral offset reduces the lever arms for the deltoid and supraspinatus muscles, weakening abduction and impairing function [12]. Conversely, a significant increase in lateral humeral offset causes excessive tension on the soft tissues ("overstuffing" of the joint), resulting in loss of motion and likely accelerating polyethylene wear [12].

Humeral articular malposition of more than 4 mm led to increased subacromial contact [12]. An offset of 8 mm in any direction significantly decreased passive range of motion [12]. Anatomic reconstruction of the humeral head/humeral shaft offset should be within 4 mm of normal to minimize subacromial contact and maximize glenohumeral motion [12].

Additional anthropometric measurements include: Medial (Coronal) Humeral Offset: 4 to 14 mm [12]. Posterior (Transverse) Humeral Offset: –2 to 10 mm [12].

There are no significant side-dependent differences in the osseous anatomy of the glenohumeral joint [45].

Ligaments and Joint Capsule

Glenohumeral Capsule

The glenohumeral joint capsule is a large, thin, and redundant structure possessing nearly twice the surface area of the humeral head to facilitate a wide range of motion [20]. It is lined by synovium and extends from the glenoid neck or labrum to the anatomic neck and proximal shaft of the humerus [32]. The capsule typically accepts approximately 28 to 35 mL of fluid, with a greater volume in women than in men [32]. Superiorly, the capsule often extends and attaches to the coracoid process via the coracohumeral ligament, while on either side of the scapular body it forms anterior and posterior recesses [32].

Capsular thickness varies significantly by location and specimen. In cadaveric specimens, thickness ranges from 1.3 to 4.5 mm [91]. The inferior pouch is the thickest at 2.8 mm, followed by the anterior portion at 2.4 mm and the posterior portion at 2.2 mm [91]. The posterior capsule is much thinner than the anterior capsule, measuring less than 1 mm, and lacks the glenohumeral ligaments or thickenings found in the anterior counterpart [90]. The cross-sectional area of the posterior capsule increases with posterior instability, a finding not present with anterior instability [90].

Biomechanically, the capsule remains lax through most of the functional range of motion, with tension increasing sharply as the joint approaches its limits [16]. In normal shoulders, the capsule remains essentially free of tension until a terminal degree of motion is reached [34]. With the arm at the side, the superior portion of the capsule is taut and the inferior portion is lax; this relationship reverses with overhead elevation [20]. The inferior region becomes tighter with increasing abduction [34], while the posterior capsule becomes tight in internal rotation with the arm at the side [34]. A contracted capsule reduces glenohumeral motion and increases the torque required to achieve an elevated position [34]. Asymmetric tightness of the posterior capsule can cause obligate anterosuperior translation of the humeral head during forward flexion [34]. Chronic contracture of the anterior aspect of the shoulder results in greater joint reaction forces directed toward the posterior portion of the glenoid, causing excessive posterior glenoid articular cartilage wear and osteoarthritis [34].

Capsular elongation and laxity, whether preexisting or acquired, play a role in certain instability conditions of the shoulder [95]. A recent cadaveric study demonstrated diminished tensile behavior of the glenohumeral capsule in patients with anterior instability [32]. The anatomical structure of passive shoulder restraints has no impact on the difference in passive joint position sense values between external and internal rotation [51].

Superior Glenohumeral Ligament (SGHL)

The superior glenohumeral ligament is a fairly constant structure present in 97% of shoulders in the classic anatomic study by DePalma and in 26% to 90% of specimens in an anatomic study conducted at the authors' institution [65]. It attaches to the glenoid rim near the apex of the labrum conjoined with the long head of the biceps [27]. On the humerus, it is attached to the anterior aspect of the anatomic neck [27] and inserts into the fovea capitis just superior to the lesser tuberosity [65]. The ligament travels from the anterosuperior glenoid labrum to the humerus, forming a pulley/sling medial to the bicipital groove [90]. It helps prevent medial or anterior-inferior translation of the long head of the biceps tendon from the groove [90].

The superior glenohumeral ligament is the primary restraint to inferior humeral subluxation in 0 degrees of abduction [24]. It is also the primary stabilizer to anterior and posterior stress at 0 degrees of abduction [24]. Tightening of the rotator interval, which includes the superior glenohumeral ligament, decreases posterior and inferior translation [24]. Its contribution to stability is best demonstrated with the arm in the dependent position, where it helps keep the humeral head suspended [65]. Conversely, the superior glenohumeral ligament contributes very little to the static stability of the glenohumeral joint in the abducted shoulder [65]. Selective cutting of the ligament did not significantly affect translation either anteriorly or posteriorly in the abducted shoulder [65]. The anatomic superior capsule has a negligible role in preventing the superior translation of the humeral head [86].

Middle Glenohumeral Ligament (MGHL)

The middle glenohumeral ligament originates from the anterior glenoid labrum and inserts on the lesser tuberosity [90]. On the humerus, it is attached to the anterior aspect of the anatomic neck [27]. This ligament shows great variability, existing as a thin wisp of tissue or as thick as the biceps tendon [54]. When quite thick, it can act as an important secondary restraint to anterior translation if the anterior portion of the inferior glenohumeral ligament is damaged [65].

The middle glenohumeral ligament limits external rotation of the adducted humerus [18]. It limits inferior translation of the adducted and externally rotated humerus [18]. Additionally, it limits anterior and posterior translation of the partly abducted (at 45 degrees) and externally rotated arm [18]. It serves as the primary constraint against anterior and posterior translation with the shoulder in 45° to 60° of abduction [90]. The middle glenohumeral ligament and the anterior band of the inferior glenohumeral ligament become taut with maximal external rotation at 45 degrees and 90 degrees of abduction, respectively [34].

Inferior Glenohumeral Ligament (IGHL)

The inferior glenohumeral ligament is a complex structure that serves as the main static stabilizer of the abducted shoulder [54]. The complex consists of an anterior band, a posterior band, and an axillary pouch lying in between [54]. The anterior band originates from various areas between the 2 o'clock and 4 o'clock positions on the glenoid [54]. The posterior band originates from areas between the 7 o'clock and 9 o'clock positions on the glenoid [54].

The anterior band of the inferior glenohumeral ligament is important in external rotation [18] and acts as the primary restraint to anterior and inferior translation with the arm in 90° of abduction and external rotation [90]. The posterior band is important in internal rotation [18] and acts as the primary restraint to posterior and inferior translation at 90° of flexion and internal rotation [90]. With external rotation, the hammock-like inferior glenohumeral ligament slides anteriorly and superiorly, the anterior band tightens, and the posterior band fans out [24]. With internal rotation, the posterior band fans out to support the head, and the anterior band becomes cord-like [24]. The inferior glenohumeral ligament provides the principle static constraint to anteroinferior instability when the arm is in extreme abduction, extension, and external rotation [40].

Coracohumeral Ligament (CHL)

The coracohumeral ligament is a strong band that originates from the base and lateral border of the coracoid process just below the origin of the coracoacromial ligament [32]. It is directed transversely and inserts on the greater tuberosity [32]. The ligament travels from the lateral coracoid, posterior to the coracoacromial ligament, to the humerus where it crosses both tuberosities bridging the bicipital groove and inserting into the rotator cable [90].

The primary function of the coracohumeral ligament is a restraint to inferior translation in 0° of abduction and external rotation [90]. The fibers of the coracohumeral ligament are arranged in a fashion to unwind with external rotation [90]. It also serves as a stabilizer to the long head of the biceps tendon [90].

Transverse Humeral Ligament

The transverse humeral ligament consists of a few transverse fibers of capsule that extend between the greater and lesser tuberosities [32]. It helps contain the long head of the biceps tendon in its groove [32].

Glenoid Labrum

The glenoid labrum is a circumferential fibrocartilage structure that functions to provide an increased depth to the glenoid cavity up to 50% [90]. It increases the depth of the glenoid socket by nearly 50% [20]. The triangular cross-section of the labrum acts as a chock-block to help prevent subluxation [20]. The labrum serves as an attachment site for the capsuloligamentous structures and as an extension of the articular cavity [20].

The glenoid labrum is approximately 4 to 6 mm wide and 4 mm thick [89]. It is intimately associated with capsular ligaments and the long head of the biceps tendon anchor [89]. The vast majority of the labrum consists of dense fibrous tissue with a few elastic fibers [61]. The posterosuperior portion of the glenoid labrum is continuous with the tendon of the long head of the biceps [61]. Anteriorly, the glenoid labrum is continuous with the inferior glenohumeral ligament [61].

Labral vascularity emanates from an anastomotic network receiving contributions from the suprascapular, anterior humeral circumflex, and posterior humeral circumflex arteries without any direct vascularity emanating from the glenoid bone [89]. The superior labrum has limited inherent healing potential due to its relative vascular deprivation [89]. It shows great variability in its attachment morphology, often having a more meniscal-type, loose attachment consisting of thin elastic connective tissue [89]. In contrast, the inferior labrum consists of more firm inelastic tissue compared to the superior labrum [89]. The glenocapsular ligament and the posterosuperior part of the joint capsule of the shoulder are well vascularized [8].

Resection of the labrum was found to decrease the stability ratio of cadaveric shoulders by 9.6% [61]. Loss of the labrum can reduce the stabilizing effect of concavity compression by 20% [27].

Capsuloligamentous Biomechanics and Stability

The glenohumeral joint capsular ligaments are lax in mid-range shoulder positions and only provide static constraint when they become taut at the extremes of motion [40]. In healthy adult shoulders, ligamentous structures are not fully elongated in many positions but function as restraints at the extremes of motion [44]. The glenohumeral ligaments play important stabilizing roles only at the extremes of motion and are lax and relatively ineffectual in most functional positions of the joint [37]. The primary passive stabilizers of the glenohumeral joint are the capsule and the scapulohumeral ligaments, which play a primary role in positions near the extremes of the allowed range of motion [91]. The capsule and its ligaments act as checkreins when they come under tension as the joint approaches the limits of its range of motion [91]. In the midrange of shoulder motion, the center of the humeral head remains within 2.2 mm of the center of the glenoid on magnetic resonance imaging [91].

Specific ligaments tension under distinct movements. The superior glenohumeral ligament and coracohumeral ligament come under tension with external rotation in adduction [91]. The middle glenohumeral ligament is tensioned by external rotation when the humerus is abducted to 45 degrees [91]. The superior glenohumeral ligament, coracohumeral ligament, and rotator interval capsule come under tension with glenohumeral flexion, extension, external rotation, and adduction [91]. When these superior structures are under tension, they resist posterior and inferior displacement of the humeral head [91]. Releasing or surgically tightening the rotator interval capsule increases or decreases the allowed posterior and inferior translational laxity, respectively [91].

The superior capsular complex forms a suspension sling with anterior and posterior limbs that function similarly to the inferior glenohumeral ligament complex, with the posterior limb restricting internal rotation [64]. The tendinous insertions of the rotator cuff muscles, the articular capsule, the coracohumeral ligament, and the glenohumeral ligament complex blend into a confluent sheet before insertion into the humeral tuberosities [24]. The coracohumeral ligament is deep to the tendinous insertion of the cuff and blends with the capsule and supraspinatus tendon to form part of the roof of the biceps sheath [24]. A 1-cm wide thickening of fibrous tissue extends posteriorly from the coracohumeral ligament origin on the coracoid to the posterior margin of the subscapularis tendon [24].

The superior shoulder suspensory complex is a bony and soft tissue ring composed of the glenoid process, coracoid process, coracoclavicular ligament, distal end of the clavicle, acromioclavicular joint, coracoacromial ligament, and acromial process [38]. The coracoacromial ligament is a component of the superior shoulder suspensory complex and the coracoacromial arch [38]. The pectoralis minor tendon provides sufficient tissue length, excursion, and width, and is biomechanically as strong as the coracoacromial ligament [9].

Muscles and Tendons

Rotator Cuff Muscles

The rotator cuff comprises the subscapularis, supraspinatus, infraspinatus, and teres minor muscles [2]. These muscles function as depressors of the humeral head, enabling the deltoid to efficiently abduct the humerus [2]. The infraspinatus and teres minor act as external rotators of the humerus [2], while the subscapularis serves as an internal rotator [2]. The infraspinatus is the second most active rotator cuff muscle, contributing up to 60% of the external rotation force [105]. It also functions as a depressor of the humeral head [105]. In the passive state, the infraspinatus stabilizes against posterior subluxation [105]. During internal rotation, it creates a forward force to stabilize against posterior subluxation [105]. Conversely, its posterior line of pull stabilizes against anterior subluxation when the shoulder is in abduction–external rotation [105]. Anatomically, the infraspinatus is a pennate muscle with a median raphe covered by a fat stripe, which can be mistaken for the gap between the infraspinatus and teres minor during surgery [105]. The infraspinatus is innervated by the suprascapular nerve [105]. Its blood supply generally derives from two large branches of the suprascapular artery [105]. However, in two-thirds of specimens, the subscapular artery, via its dorsal or circumflex scapular branch, supplied the greater portion of the muscle’s circulation [105]. The infraspinatus bare area broadens as the humeral head is evaluated from a superior to inferior direction [146].

Supraspinatus

The supraspinatus fossa and muscle have changed little in size or shape over evolutionary time [15].

Subscapularis

The subscapularis inserts on the lesser tuberosity, causing medial displacement of fracture fragments [1]. The subscapularis footprint is broad proximally and tapered distally, exhibiting a comma shape [150]. It consists of a proximal tendinous part and a distal muscular part [150]. The upper 60% of the footprint provides the major surface area for tendon insertion [128]. The first facet of the subscapularis tendon area comprises approximately one third of the entire footprint [145, 151]. The first two facets of the subscapularis tendon consist of 60% of the entire footprint [145, 151].

Biceps Brachii

The long head of the biceps originates from the bicipital tubercle at the superior rim of the glenoid and along the posterior superior rim of the glenoid and labrum [126]. Much of this origin is via the superior labrum [126]. The short head originates from the coracoid tip, lateral to and in common with the coracobrachialis [126]. The size of the bicipital tubercle does not reflect the size of the biceps tendon [126]. The long head exits the shoulder through a capsular defect between the greater and lesser tuberosities, passing distally in the bicipital groove [126]. The tendon does not move vertically within the groove; instead, the humerus moves relative to the tendon during adduction and abduction [126]. A pulley composed of fibers from the coracohumeral and superior glenohumeral ligaments, reinforced by adjacent tendons, retains the tendon within the groove [126]. Loss of long head attachment results in a 20% loss of supination strength and an 8% loss of elbow flexion strength [126]. Rupture of the long head causes a 20% loss of elevation strength in external rotation [126]. The long head contributes to joint stability, which is increased in external rotation and decreased in internal rotation [126]. The biceps is innervated by branches of the musculocutaneous nerve (C5 and C6) [126]. Its blood supply derives from a single large bicipital artery from the brachial artery (35%), multiple very small arteries (40%), or a combination of both [126].

Triceps Brachii

The long head of the triceps originates from the infraglenoid tubercle [112]. Its insertion is intimately related to the labrum over a 2 cm distance centered on the tubercle [112]. Fibers adjacent to the capsule radiate into and reinforce the inferior capsule [112]. The long head functions in shoulder adduction against resistance to offset shear forces generated by primary adductors [112]. In violent activities such as throwing, triceps electromyographic activity may reach 200% of that generated by a maximal muscle test [112]. The triceps is innervated by the radial nerve with root innervation from C6 to C8 [112]. Arterial supply derives mainly from the profunda brachii artery and the superior ulnar collateral artery [112]. Near its origin, the long head receives branches from the brachial and posterior humeral circumflex arteries [112].

Pectoralis Major

The pectoralis major inserts on the humeral shaft, displacing it medially [1]. The muscle also inserts onto the medial coracoid process [42]. A cadaveric study quantified the anatomic dimensions of the pectoralis major tendon, its humeral head insertion, and its location relative to nearby vital structures [141].

Pectoralis Minor

The pectoralis minor tendon provides sufficient tissue length, excursion, and width for acromioclavicular joint reconstruction [9]. Biomechanically, the pectoralis minor tendon is as strong as the coracoacromial ligament [9].

Deltoid

The deltoid and rotator cuff counterbalance moderate loads on the shoulder girdle [1]. The deltoid has an increasing role in shoulder function due to the enlargement of the acromion and broader attachment [15]. The broader acromial attachment and more distal humeral insertion have increased the deltoid’s mechanical advantage in shoulder motion [15]. No accessory motor branches to the anterior deltoid cross the tendinous raphe between the anterior and lateral deltoid [14].

Nerve Supply to Muscles

The axillary nerve passes beneath the conjoined tendon, anterior to the subscapularis, 3 to 5 mm medial to the musculotendinous junction [14]. The suprascapular nerve arises from the superior lateral aspect of the upper trunk shortly after its formation at Erb’s point [41]. It passes below the transverse scapular or suprascapular ligament to innervate the supraspinatus through two branches [41]. The nerve innervates the infraspinatus through two branches after passing inferiorly around the base of the scapular spine [41]. The motor branch to the supraspinatus branches within 1 cm of the suprascapular notch in all specimens [41]. The suprascapular nerve innervates the infraspinatus within 1 cm of the base of the scapular spine in nearly 90% of cases [41]. The distance from the midline of the posterior glenoid rim to the nerve at the base of the scapular spine averages 1.8 cm, with some as close as 1.4 cm [41]. The safe zone for the suprascapular nerve is 2.1 cm from the supraglenoid tubercle to the nerve at the scapular notch and 1.1 cm from the midline of the posterior glenoid rim [41]. Entrapment at the superior transverse scapular ligament causes denervation of both the supraspinatus and infraspinatus [42]. Entrapment, traction, or compression at the spinoglenoid ligament causes denervation of the infraspinatus [42].

Muscle-Tendon Interactions and Biomechanics

Displacement of proximal humeral fracture fragments results from the pull of muscles attaching to various bony components [1]. The subscapularis inserts on the lesser tuberosity, causing medial displacement [1]. The supraspinatus and infraspinatus insert on the greater tuberosity, causing superior and posterior displacement [1]. Broadening of the infraspinatus fossa has shifted the vector of muscle pull from the axillary border of the scapula to the glenoid fossa [15]. Shoulder anatomy influences rotator cuff tear formation mechanisms, with greater tuberosity area, coracoacromial space, acromial index, lateral acromial angle, and footprint dimensions playing a more significant role in L-shaped tears than in other tear shapes [43]. Access to the rotator cuff from almost every portal is influenced by acromial shape [140]. The acromiohumeral distance was no longer measured intra-articularly or within the supraspinatus footprint above approximately 70 degrees of arm elevation [149].

Neurovascular Anatomy

Nerve Supply and Innervation

The shoulder receives innervation primarily from C5, C6, and C7 nerve roots, with minor contribution from C4 [93]. The axillary nerve, a terminal branch of the posterior cord, passes beneath the conjoined tendon anterior to the subscapularis, 3 to 5 mm medial to the musculotendinous junction [14]. It enters the quadrilateral space posteriorly and divides into anterior and posterior branches [14]. The anterior branch solely innervates the anterior and middle deltoid muscles [14]. In 89.1% of cases, the posterior deltoid receives supply from both the anterior and posterior branches [14]. The posterior branch supplies the teres minor and terminates as the superior lateral brachial cutaneous nerve [14].

The suprascapular nerve passes below the transverse scapular ligament to innervate the supraspinatus via two branches [41]. It then passes around the base of the scapular spine to innervate the infraspinatus through two additional branches [41]. The motor branch to the supraspinatus branches within 1 cm of the suprascapular notch in all specimens studied by Bigliani et al. [41]. The distance from the midline of the posterior glenoid rim to the nerve at the scapular spine base averages 1.8 cm, with some cases as close as 1.4 cm [41]. The nerve is furthest from the posterior glenoid edge when the shoulder is at 90 degrees of external rotation [39].

The subscapular nerves innervate the subscapularis, teres major, and latissimus dorsi, with the thoracodorsal nerve formerly referred to as the middle subscapular nerve [106]. The closest innervation point of either the upper or lower subscapular nerve to the medial coracoid was 11 mm [133]. The radial nerve is commonly injured in humeral shaft fractures, particularly at the junction of the middle and distal third [2]. Axillary nerve injury from proximal humeral fractures or fracture-dislocations results in deltoid paralysis and anesthesia over the “badge” region of the lateral proximal arm [2]. Anterior shoulder dislocations can injure the brachial plexus and axillary artery [2].

Joint innervation involves medullary and nonmedullary fibers from the axillary, suprascapular, subscapular, and musculocutaneous nerves [93]. The axillary and suprascapular nerves provide most supply to the anterior capsule and glenohumeral joint [93]. The suprascapular nerve provides two articular branches: one to the acromioclavicular and superior glenohumeral joints, and one to the posterior superior glenohumeral joint [41]. Sensory branches to the shoulder joint are more common and numerous than previously described [98]. The suprascapular, lateral pectoral, and axillary nerves are the most common parent nerves supplying articular branches [131]. Thinly myelinated or unmyelinated sensory neurons innervate the long head of the biceps tendon [93].

Vascular Supply

The anterolateral ascending branch of the anterior humeral circumflex artery supplies the majority of the humeral head [114]. This artery travels laterally at the inferior border of the subscapularis tendon, marking the border between the upper tendinous and lower muscular insertions [114]. The posterior humeral circumflex artery descends into the quadrilateral space with the axillary nerve and divides into anterior and posterior branches after emerging on the posterior side [114]. The anterior branch of this vessel supplies the anterior two-thirds of the deltoid [114].

The subscapular artery originates in the third part of the axillary artery, giving off the circumflex scapular and thoracodorsal arteries [114]. The circumflex scapular artery passes under the inferior edge of the subscapularis and medial to the long head of the triceps through the triangular space [114]. The axillary artery travels an average of 1-1.8 cm from the inferior glenoid margin [147]. The brachial plexus and axillary artery were within 2 cm of the glenoid rim, with the plexus as close as 5 mm in some cases [134].

The main vascular supply of the proximal long head of the biceps tendon comes from the anterior-dorsal direction [136]. The subacromial space is highly vascularized, with a consistent blood supply pattern found in 60% of dissected shoulders [129]. The main blood supply of the humeral head enters anterolaterally above the surgical neck [142]. Preserving posterior vessels at the lower end of the humeral head is crucial for fragment viability [142]. Significant intraosseous anastomoses exist between the arcuate artery and posteromedial vessels from the posterior humeral circumflex artery [114].

Anatomical Relationships and Surgical Landmarks

The axillary nerve can be palpated in the anterior deltopectoral approach by sweeping a finger inferiorly across the subscapularis muscle tendon interface [14]. The distance from the coracoid process to neurovascular structures was closest in the beach-chair position with 90 degrees of arm abduction [123]. The brachial plexus and axillary artery lie anterior to the coracoid process and humeral head [2].

The axillary space contains the brachial plexus and its branches, the axillary artery and vein, and major lymphatic drainage [106]. The clavipectoral fascia continues medially to the first rib as the costocoracoid membrane, forming the anterior boundary of this space [106]. The posterior boundary is formed by the subscapularis, teres major, and latissimus dorsi muscles [106]. Adipose tissue indicates the position of enclosed nerves or arteries [106]. The largest adipose deposit is the axillary space [106]. A second important body of adipose tissue lies posteriorly, deep to the deep fascia, inferomedial to the medial border of the posterior deltoid, lateral to the trapezius, and superior to the latissimus dorsi [106]. The third deep deposit lies between the supraspinatus tendon and the overlying clavicle and acromioclavicular joint [106].

The transhumeral portal for arthroscopic glenohumeral resurfacing traversed within 5 mm of a small terminal branch of the main anterior branch of the axillary nerve in 20% of specimens [138]. The safe zone for avoiding suprascapular nerve injury is defined as 2.1 cm from the supraglenoid tubercle to the nerve at the scapular notch and 1.1 cm from the midline of the posterior glenoid rim [41]. The axillary artery and vein have an at-risk zone between the medial quarter and midpoint of the clavicle where neurovascular structures lie beneath the bone [143]. Two or three branches of the supraclavicular nerve cross the clavicle 97% of the time [144].

Biomechanics and Function

Joint Articulation and Mobility

The shoulder is the most mobile joint in the body, a characteristic resulting from the minimal containment of the large humeral head by the shallow, smaller glenoid fossa [20]. This articulation functions as a modified ball-and-socket joint where the humeral head articulates against, rather than within, the glenoid cavity [12, 20]. The bony anatomy contributes little to stability, often compared to a golf ball on a tee [24]. Consequently, the tradeoff for this mobility is reduced structural restraint against undesirable and potentially damaging movements [20].

Shoulder function relies on the coordinated movement of four distinct articulations: the sternoclavicular, acromioclavicular, glenohumeral, and scapulothoracic joints [24]. The humeroscapular motion interface, described as a "fifth shoulder joint," is lined by the subacromial and subdeltoid bursa and lies between the proximal humerus and the acromion-deltoid layer [14]. Smooth, unrestricted motion at this interface is vital to overall shoulder mobility [14].

The normal ratio of glenohumeral motion to scapulothoracic motion is 2:1 [34]. During shoulder elevation, the first 20 degrees represent pure glenohumeral motion, after which combined movement occurs in a 2:1 ratio [96]. When the scapula is immobilized, pure glenohumeral elevation is approximately 90 degrees [96].

Static Stabilizers

The shoulder is stabilized by both static and dynamic restraints [18, 19]. Static restraints include the glenoid labrum, articular version, articular conformity, negative intraarticular pressure, capsule, and glenohumeral ligaments [18, 19]. The glenoid labrum increases the depth of the glenoid concavity by nearly 50% and serves to anchor the glenohumeral ligaments [18, 19, 20]. Combined with the articular surface, the labrum creates a socket approximately 9 mm deep superoinferiorly and 5 mm deep anteroposteriorly [24]. Adding the labrum increases the glenoid surface to 75% of the humeral head vertically and 57% horizontally [24].

The glenohumeral ligaments do not offer isometric stability like hinge-like joints; they are lax and relatively ineffectual in most functional positions, playing important stabilizing roles only at the extremes of motion [37]. Specific ligament functions include: * Superior and Coracohumeral Ligaments: Limit inferior translation and external rotation when the arm is adducted [18, 19]. * Middle Glenohumeral Ligament: Has little effect on stability when the arm is in 90 degrees of abduction [24]. * Inferior Glenohumeral Ligament: Composed of an anterior band, posterior band, and axillary pouch forming a hammock-type sling; provides the principal static constraint to anteroinferior instability when the arm is in extreme abduction, extension, and external rotation [24, 40].

The rotator interval is central to normal glenohumeral kinematics; any insult to its integrity alters shoulder motion throughout abduction [23]. Imbrication of the rotator interval decreases inferior and posterior translation, while release produces greater forward flexion and external rotation [18, 19]. Additionally, the coracoid process can mechanically limit anterior translation of the humerus relative to the glenoid when the shoulder is in 90 degrees of abduction [15].

Dynamic Stabilizers

Dynamic restraints include joint concavity compression produced by synchronized contraction of the rotator cuff, increased capsular tension from direct cuff-capsule attachments, and scapular stabilizers that maintain a stable glenoid platform [18, 19]. The scapular stabilizers maintain a stable glenoid platform described as a "ball on a seal's nose" [18, 24]. Rotator cuff and biceps activity stiffen the capsule and decrease glenohumeral translation [24].

The rotator cuff acts as depressors of the humeral head, allowing the deltoid to efficiently abduct the humerus by fixing the fulcrum of the upper extremity [2, 12]. The subscapularis and posterior rotator cuff provide a compressive force that centers the humeral head in the glenoid cavity [24]. Specific muscle contributions include: * Infraspinatus and Teres Minor: Account for approximately 80% of external rotation strength in the adducted position [20]. * Supraspinatus: Active during the entire arc of scapular plane abduction; paralysis of the suprascapular nerve results in an approximately 50% loss of abduction torque [20]. * Teres Minor: Activates mainly with the shoulder in 90 degrees of elevation [20].

The deltoid and cuff muscle forces maintain the net humeral joint reaction force within the balance stability angle [37]. The basic law of glenohumeral stability dictates that the joint will not dislocate as long as the net humeral joint reaction force is directed within the effective glenoid arc; if this force passes outside the arc, the joint becomes unstable [37]. The balance stability angle varies around the face of the glenoid, with superior and inferior angles greater than anterior and posterior angles in a normal glenoid [37].

Biomechanical testing shows that the labrum affects the distribution of contact stresses when a compressive load is applied to the shoulder at 90 degrees of abduction [24]. External loads transferred to the shoulder girdle are initially offset by joint surface anatomy, joint volume, atmospheric pressure, and joint fluid cohesion and adhesion [1]. Moderate and large loads are counterbalanced by the deltoid and rotator cuff, and by the capsulolabral and bone structures, respectively [1].

Capsular Mechanics and Range of Motion

The normal surface area of the capsule is nearly twice that of the humeral head, and the capsule is inherently loose [34]. In cadaveric tests, the capsule remained essentially free of tension until a terminal degree of motion was reached [34]. As the joint approaches the limit of its range, tension in the capsule and its ligaments increases sharply [16].

Tension distribution shifts with position: * Anterosuperior Capsule: Assumes tension with increasing external rotation with the arm in 0 degrees of abduction [34]. * Middle Glenohumeral Ligament: Becomes taut with maximal external rotation at 45 degrees of abduction [34]. * Anterior Band of Inferior Glenohumeral Ligament: Becomes taut with maximal external rotation at 90 degrees of abduction [34]. * General Elevation: With increasing angles of elevation, tension is shifted inferiorly in the capsule [34].

Asymmetric tightness of the capsule can cause an obligate translation of the humeral head [34]. Tightening of the posterior capsule can lead to anterosuperior translation of the humeral head during forward flexion, which can lead to impingement of the rotator cuff against the coracoacromial arch [34]. Conversely, overtightening of anterior structures can result in greater joint reaction forces directed toward the posterior portion of the glenoid, potentially causing excessive posterior glenoid articular cartilage wear and posterior bony erosion from chronic anterior capsular contracture [34].

The term "stuffing" refers to additional tightening of the capsule resulting from the insertion of prosthetic components that take up more space than the available joint volume [16]. Joint stuffing limits joint motion and requires greater torque to move the arm; less than 10 mm of overstuffing can reduce normal capsular laxity [16]. Humeral articular malposition of more than 4 mm led to increased subacromial contact in a biomechanical cadaver study [12]. An offset of 8 mm in any direction significantly decreased passive range of motion [12]. A significant decrease in lateral humeral offset reduces the lever arms for the deltoid and supraspinatus muscles, weakening abduction, while a significant increase causes excessive tension on soft tissues, resulting in loss of motion and likely accelerating polyethylene wear [12].

Throwing Biomechanics

Significant forces generated during throwing can result in anatomic variation and injury [18, 19]. The dominant shoulder typically exhibits greater external rotation and a loss of internal rotation compared with the nondominant shoulder, referred to as glenohumeral internal rotation deficit (GIRD) [18, 19]. In the throwing shoulder, the anterior capsule is selectively stretched while the posterior capsule is tightened [18, 19]. Bony changes in the dominant throwing shoulder include increased humeral head retroversion and glenoid retroversion [18, 19].

Maximal torque is generated during maximal external rotation (late cocking) and just after ball release (deceleration) [18, 19]. Injuries to the thrower’s shoulder joint occur most commonly in the late cocking or early acceleration phases [29]. Phase-specific pathologies include: * Late Cocking: Associated with superior labrum from anterior to posterior (SLAP) tears and internal impingement [18, 19]. * Deceleration: Associated with tensile failure of the posterior aspect of the supraspinatus and anterior half of the infraspinatus; the rotator cuff must offset high-energy forces during this phase [18, 19].

The scapula retracts during the late cocking phase and protracts during the acceleration phase [18, 19]. Scapular dyskinesis is extremely common in patients with a disabled throwing shoulder, resulting in scapular protraction, anterior tilt, and excessive internal rotation [18, 19]. Anterior scapular tilt results in external impingement, while excessive internal rotation of the scapula results in internal impingement [18, 19].

The SICK scapula is an extreme form of scapular dyskinesis characterized by scapular malposition, inferior medial border prominence, coracoid pain, and dyskinesis of scapular movement [111]. This condition predisposes the shoulder to labral and rotator cuff tears by positioning the glenoid to face more anteriorly and superiorly [111]. Glenoid protraction tightens the anterior band of the inferior glenohumeral ligament, limiting anterior translation of the humeral head [111]. Excessive external rotation in the setting of scapular protraction can result in posterosuperior glenoid impingement [111]. A study of throwers with proven posterosuperior labral tears found that 94% showed patterns of dynamic scapular dyskinesis [111]. The study demonstrates abnormal kinematics and path of glenohumeral motion throughout a rotational range of motion in the thrower's model compared with an intact shoulder [63].

Pathomechanics and Kinematic Alterations

Partial-thickness articular-sided rotator cuff tears with a thickness >50% involving the rotator cable increased glenohumeral translation and changed kinematics in a cadaveric biomechanical model [74]. Simulated anterosuperior rotator cuff tears involving the superior half of the subscapularis significantly alter shoulder biomechanics and lead to increased anterosuperior and superior glenohumeral translation under higher loads [79]. Asymptomatic rotator cuff pathology is associated with a plausible mechanical progression of kinematic and strength changes [33].

Alterations of scapular kinematics in symptomatic subjects are multifactorial [30]. Small but significant asymmetries exist between the dominant and nondominant shoulders in terms of kinematics [55]. Clavicle shortening of >10% greatly affects scapular kinematics in vivo [71], and shortening of the clavicle affects the kinematics in the shoulder girdle [59].

Kinematics of reverse total shoulder arthroplasty shoulders are significantly altered, with more scapulothoracic motion used to achieve shoulder elevation compared to healthy subjects [66]. At a shoulder abduction between 40° and 90° on the scapular plane, internal rotation of the humeral component was significantly less with a load than without a load in reverse total shoulder arthroplasty patients [78]. Superior capsular reconstruction only partially restored native glenohumeral joint loads in a dynamic biomechanical shoulder model [56]. The observed changes in scapular kinematics after rotator cuff repair are associated with an increased overall range of motion and suggest restored function of shoulder muscles [26]. The biomechanical shoulder model is consistent with clinical observations regarding the effects of glenoid inclination and acromion index on humeral head translation and glenoid articular cartilage strain [5]. A clinical evaluation of altered shoulder kinematics is still complicated [10].

Common Sites of Injury

Proximal Humerus

The proximal humerus comprises four main anatomic parts: the humeral head, greater tuberosity (GT), lesser tuberosity (LT), and humeral shaft [1]. The articular head is spherical with a diameter of 37 to 57 mm, and its most superior portion averages 8 mm above the GT [1]. The bicipital groove lies between the GT and LT, serving as a pathway for the long head of the biceps [1]. The GT is located posterior-superior to the humeral shaft and serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons [1]. The LT is located on the anterior aspect of the proximal humerus and serves as the attachment site for the subscapularis tendon [1].

Following a proximal humeral fracture, displacement of each anatomic part occurs in a predictable manner based on deforming forces created by the tendinous insertions of the pectoralis major, subscapularis, supraspinatus, and infraspinatus [1]. Specifically, the supraspinatus and infraspinatus insert on the greater tuberosity and cause superior and posterior displacement of fracture fragments [1]. Fractures involving the anatomic neck are prognostically worse than fractures involving other regions of the proximal humerus due to the potential disruption of the vascular supply to the humeral head and subsequent development of avascular necrosis [1]. The ascending branch of the anterior humeral circumflex artery (AHCA) courses parallel to the lateral aspect of the long head biceps tendon and enters the humeral head at the interface of the bicipital groove and GT [1].

Glenoid and Capsulolabral Structures

The glenoid articulates with the humeral head and serves as the attachment for the labrum and joint capsule [1].

Acromioclavicular Joint

The most common mechanism for injury to the acromioclavicular joint (ACJ) is a direct force applied to the superior aspect of the acromion process, such as a fall onto the outer aspect of the shoulder with the upper limb in an adducted position [92]. A falling object or a deliberate blow striking the superior acromion is a rarer mechanism of direct injury to the ACJ [92]. Indirect mechanisms of ACJ injury are exceedingly rare [92]. The AC ligaments offer the weakest resistance to forces that push the acromion inferiorly and medially, while stronger resistance is afforded by the intact clavicle and sternoclavicular joint (SCJ) [92]. AC injuries that occur in conjunction with clavicle fractures or SCJ injuries have been reported [92].

An inferiorly directed force acting upon the superior lateral clavicle can cause more damage when the upper limb is abducted and the scapula is retracted [92]. This specific mechanism can result in an inferior dislocation of the clavicle beneath the coracoid process [92]. A fall onto the adducted upper limb is apt to drive the humeral head into the inferior aspect of the acromion, subjecting the ACJ to variable degrees of injury [92]. The integrity of the acromion process and glenohumeral stability is risked when extremely high superiorly directed forces are encountered [92]. The ACJ may also be injured by pulling or traction-like forces applied to the upper limb [92].

In type I ACJ injuries, the AC ligaments sustain a mild-to-moderate sprain while maintaining ACJ integrity [92]. In these injuries, the coracoclavicular (CC) ligaments and the deltoid and trapezius muscles are normal [92].

Throwing Shoulder

Typical sites of pathoanatomy in the throwing shoulder include the superior and posterosuperior labrum, the articular surface of the supraspinatus and infraspinatus, and the posterior capsule [29]. Injury to the thrower’s shoulder joint occurs most commonly in the late cocking or early acceleration phases [29]. A combination of abnormal scapulothoracic and glenohumeral motion can injure the superior and posterosuperior labrum as well as the undersurface of the rotator cuff and posterior capsule [29].

Adaptive pathology of osseous and soft tissue structures in the throwing shoulder allows accommodation of extremes of horizontal extension and external rotation [116]. This adaptive pathology can result in a shoulder that is relatively “loose in the front” and “tight in the back” [116]. Corresponding pathology often includes anterior inferior capsular laxity, posterior inferior capsular contracture, humeral retroversion, altered range of glenohumeral rotation, scapular drooping and protraction, PASTA tears, PAINT tears, and SLAP tears [116]. As many as 50% of asymptomatic, professional-level pitchers have a partial-thickness rotator cuff tear and/or a SLAP lesion on MRI [116]. Furthermore, as many as 80% of asymptomatic, mature pitchers had MRI changes and 45% had a labral tear [116]. Reduced humeral retroversion may be accompanied by morphological changes in the posterior glenoid rim, which may be associated with an increased risk of throwing shoulder injury [73].

Surgical Anatomy

Bony Anatomy

The bicipital groove is situated between the greater and lesser tuberosities, serving as the pathway for the long head of the biceps tendon [1]. Fractures involving the anatomic neck carry a worse prognosis than those affecting other regions of the proximal humerus, owing to potential disruption of the vascular supply to the humeral head and subsequent avascular necrosis [1]. Medial and lateral intermuscular septae divide the arm into anterior and posterior compartments [2].

Soft Tissue Anatomy

The greater tuberosity serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons of the rotator cuff [1]. The long head of the biceps tendon traverses from its intraarticular origin at the superior glenoid–labral complex into the proximal arm via the bicipital groove [1]. Within this groove, the biceps tendon is covered by the transverse humeral ligament [2].

The anterior compartment of the arm contains the biceps brachii, coracobrachialis, and brachialis muscles, along with the neurovascular bundle coursing along the medial border of the biceps [2]. The posterior compartment of the arm contains the triceps brachii muscle and the radial nerve [2].

Vascular Anatomy

The anterior humeral circumflex artery arises from the axillary artery at the inferior border of the subscapularis [1]. It provides vascular inflow to the humeral head by way of its terminal anterolateral branch, known as the artery of Laing or arcuate artery [1]. In surgical neck fractures, the blood supply to the head is preserved [2].

Neurovascular Anatomy

The brachial plexus and axillary artery are located anterior to the coracoid process of the scapula and humeral head [2]. The radial nerve originates off of the posterior cord of the brachial plexus and travels through the triangular space, bounded by the teres minor, humeral shaft, and long head of the triceps [107]. It travels distally and trifurcates along the medial border of the humerus, giving off a large branch to the medial head of the triceps and the posterior antebrachial cutaneous branch [107].

The radial nerve courses distally along the middle third of the humeral shaft from 21 cm proximal to the medial epicondyle to 14 cm proximal to the lateral epicondyle, where it pierces the lateral intermuscular septum [107]. The radial nerve proper diverges from the posterior antebrachial cutaneous branch and enters the interval between the brachialis and brachioradialis [107]. This nerve is vulnerable as it runs in the spiral groove intimate with the humeral cortex and distally where it is bound by the lateral intermuscular septum [107].

The axillary nerve can be found approximately 63 mm from the anterolateral tip of the acromion during an anterolateral deltoid splitting approach [107]. Evaluation of radial nerve function should include sensation of the dorsal web space between the thumb and index finger, independent digital extension, and wrist extension [2].

Key Evidence

• [L5] The biomechanical shoulder model is consistent with clinical observations. [5] (10.1016/j.jse.2016.05.031)
• [L5] The glenocapsular ligament is a constant anatomical structure that consists of one or two different parts. [8] (10.1007/s00167-017-4603-x)
• [L5] Anatomically, it provides sufficient tissue length, excursion, and width, and biomechanically, it is as strong as the coracoacromial ligament. [9] (10.1016/j.jse.2006.09.007)
• [L2] A clinical evaluation of altered shoulder kinematics is still complicated. [10] (10.3390/ijerph17082974)
• [L5] The rotator interval is central to normal glenohumeral kinematics, and any insult to its integrity alters shoulder motion throughout abduction. [23] (10.1186/s12891-016-0898-x)
• [L4] The observed changes in scapular kinematics are associated with an increased overall range of motion and suggest restored function of shoulder muscles. [26] (10.1016/j.jse.2015.10.021)
• [L4] Alterations of scapular kinematics in symptomatic subjects are multifactorial. [30] (10.1016/j.jse.2015.04.007)
• [L3] Furthermore, these findings suggest a plausible mechanical progression of kinematic and strength changes associated with the development of rotator cuff pathology. [33] (10.1016/j.jse.2016.11.048)
• [L5] The suprascapular nerve is furthest away from the posterior edge of the glenoid with the shoulder at 90 of external rotation. [39] (10.1007/s00167-014-2900-1)
• [L3] Shoulder anatomy affects the mechanisms of rotator cuff tear formation, with GTA, CSA, AI, LAA, and footprint dimensions playing a more significant role in L-shaped tears compared to other tear shapes. [43] (10.1186/s12891-024-07829-9)
• [L5] In healthy adult shoulders, ligamentous structures are not fully elongated in many positions but function as restraints at the extremes of motion. [44] (10.1186/1749-799x-7-29)
• [L4] There are no significant side-dependent differences in the osseous anatomy of the glenohumeral joint. [45] (10.1016/j.jse.2015.12.024)
• [L4] This study validates the best fit circle (BFC) as a surrogate of the normal proximal humeral bony articular anatomy in most shoulders, noting that while the native circle is significantly larger on average, differences are usually small and clinically irrelevant. [49] (10.1016/j.jseint.2025.10.005)
• [L3] The anatomical structure of passive shoulder restraints has no impact on the difference in passive joint position sense values between external and internal rotation. [51] (10.1186/s12891-016-0971-5)
• [L5] Small but significant asymmetries exist between the dominant and nondominant shoulders in terms of kinematics. [55] (10.1016/j.jse.2013.08.020)
• [L5] In this dynamic shoulder model, SCR only partially restored native glenohumeral joint loads. [56] (10.1016/j.arthro.2023.02.019)
• [L5] The findings of this study clearly indicated that shortening of the clavicle affects the kinematics in the shoulder girdle. [59] (10.1177/0363546509355143)
• [L5] The study demonstrates abnormal kinematics and path of glenohumeral motion throughout a rotational range of motion in the thrower's model compared with an intact shoulder. [63] (10.1177/0363546506287740)
• [L5] The superior capsular complex forms a suspension sling with anterior and posterior limbs that function similarly to the inferior glenohuminal ligament complex, with the posterior limb restricting internal rotation. [64] (10.1016/j.jse.2007.02.138)
• [L4] Kinematics of the rTSA shoulders are significantly altered, and more scapulothoracic motion is used to achieve shoulder elevation compared to healthy subjects. [66] (10.1016/j.jse.2011.07.031)
• [L4] Clavicle shortening of >10% greatly affects scapular kinematics in vivo. [71] (10.1016/j.jse.2017.03.013)
• [L4] Reduced humeral retroversion may be accompanied by morphological changes in the posterior glenoid rim, which may be associated with an increased risk of throwing shoulder injury. [73] (10.1002/ksa.70334)
• [L5] Partial-thickness articular-sided rotator cuff tears with a thickness >50% involving the rotator cable increased glenohumeral translation and changed kinematics in our cadaveric biomechanical model. [74] (10.1016/j.jse.2016.12.063)
• [L4] At a shoulder abduction between 40° and 90° on the scapular plane, internal rotation of the humeral component was significantly less with a load than without a load. [78] (10.1186/s42836-023-00207-1)
• [L5] Simulated anterosuperior rotator cuff tears involving the superior half of the subscapularis significantly alter shoulder biomechanics and lead to increased anterosuperior and superior glenohumeral translation under higher loads. [79] (10.1016/j.arthro.2008.10.005)
• [L5] The anatomic superior capsule has a negligible role in preventing the superior translation of the humeral head. [86] (10.1016/j.arthro.2018.06.025)
• [L4] Our results reinforce the concept that capsular elongation and laxity, either preexisting or acquired, play a role in certain instability conditions of the shoulder. [95] (10.1177/0363546507311603)
• [L5] The cadaveric results indicate that sensory branches to the shoulder joint are more common and numerous than previously described and therefore should be considered in shoulder surgery and nerve blocks to this area. [98] (10.1016/j.jse.2007.10.008)
• [L5] The distance from the coracoid process to the neurovascular structures was closest in the beach-chair position with 90 degrees of arm abduction. [123] (10.1016/j.arthro.2018.09.031)
• [L5] The upper 60% of the footprint provided by far the major surface area for tendon insertion, consistent with prior findings of superior load transmission at the superior aspect of the footprint. [128] (10.1016/j.arthro.2006.11.023)
• [L5] The subacromial space is highly vascularized, and the pattern of blood supply was found to be consistent in 60% of the shoulders dissected. [129] (10.1016/j.arthro.2007.03.093)
• [L4] Current literature supports the presence of a common sensory innervation pattern for the human shoulder joint, with the suprascapular, lateral pectoral, and axillary nerves being the most common parent nerves supplying articular branches. [131] (10.1016/j.jse.2020.07.017)
• [L5] The closest that the innervation point of either the upper or lower subscapular nerve came to the medial aspect of the coracoid was 11 mm. [133] (10.1016/j.arthro.2013.02.005)
• [L5] The brachial plexus and axillary artery were within 2 cm of the glenoid rim, with the brachial plexus as close as 5 mm in some cases. [134] (10.1177/03635465010290061001)
• [L5] The main vascular supply of the proximal long head of the biceps tendon comes from the anterior-dorsal direction. [136] (10.1016/j.jse.2020.07.014)
• [L5] However, this transhumeral portal did traverse within 5 mm of a small terminal branch of the main anterior branch of the axillary nerve in 20% of our specimens. [138] (10.1016/j.arthro.2015.06.003)
• [L5] The access to the rotator cuff from almost every portal is influenced by the acromial shape. [140] (10.1186/s13018-019-1486-1)
• [L5] This study successfully quantifies anatomic dimensions of the PM tendon, its humeral head insertion (SH and CH), and its location relative to nearby vital structures. [141] (10.1177/23259671221121333)
• [L5] The main blood supply of the humeral head enters anterolaterally above the surgical neck, and preserving posterior vessels at the lower end is crucial for fragment viability. [142] (10.2106/00004623-195638050-00013)
• [L5] The study defines the anatomic relationship of the axillary artery and vein to the clavicle, identifying an at-risk zone between the medial quarter and midpoint of the clavicle where neurovascular structures lie beneath the bone. [143] (10.1016/j.jse.2009.01.021)
• [L5] There were two or three branches of the supraclavicular nerve crossing the clavicle 97% of the time and a wide variability of the location of these branches outside the safe zones. [144] (10.1007/s11999-010-1608-x)
• [L5] The first facet of subscapularis tendon area consists of approximately 1/3 of the entire footprint area, and the first two facets consist of 60% of its entire footprint. [145] (10.1016/j.arthro.2013.07.104)
• [L5] The infraspinatus bare area broadens as one evaluates the humeral head in a superior to inferior fashion. [146] (10.1177/17585732241229068)
• [L5] The axillary artery travels an average of 1-1.8 cm from the inferior glenoid margin, which puts the artery at significant risk. [147] (10.1016/j.jse.2020.09.018)
• [L5] The acromiohumeral distance was no longer measured intra-articularly or within the supraspinatus footprint above approximately 70 degrees of arm elevation. [149] (10.1016/j.jse.2011.11.023)
• [L5] The subscapularis footprint was broad proximally and tapered distally, exhibiting a comma shape, and consisted of a proximal tendinous part and a distal muscular part. [150] (10.1016/j.arthro.2008.02.009)
• [L2] The first facet of the subscapularis tendon footprint consists of approximately one third of the entire footprint, and the first 2 facets consist of 60% of the entire footprint. [151] (10.1016/j.arthro.2014.08.015)

See Also

• Rotator Cuff
• Fractures
• Os Acromiale
• Total shoulder arthroplasty
• Rotator cuff repair
• Soft Tissue Structures

References

[1] Rockwood And Matsen S The Shoulder. Shoulder and Elbow Specialty Clinic Workers’ Survey > ANATOMY.

[2] A Lange Medical Book Current Diagnosis Treatment In Orthopedics Fifth Edition. 2Musculoskeletal Trauma Surgery > SHOULDER AND ARM INJURIES.

[4] Chapter 23 Shoulder Anatomy and Biomechanics, Clinical Evaluation, Imaging. 2020.

[5] Effects of glenoid inclination and acromion index on humeral head translation and glenoid articular cartilage strain. Journal of Shoulder and Elbow Surgery. 2017. DOI: 10.1016/j.jse.2016.05.031

[8] The glenocapsular ligament and the posterosuperior part of the joint capsule of the shoulder are well vascularized. Knee Surgery, Sports Traumatology, Arthroscopy. 2017. DOI: 10.1007/s00167-017-4603-x

[9] Anatomy of the pectoralis minor tendon and its use in acromioclavicular joint reconstruction. Journal of Shoulder and Elbow Surgery. 2007. DOI: 10.1016/j.jse.2006.09.007

[10] Scapular Dyskinesis: From Basic Science to Ultimate Treatment. International Journal of Environmental Research and Public Health. 2020. DOI: 10.3390/ijerph17082974

[12] Campbell S Operative Orthopaedics 4 Volume Set. RECONSTRUCTIVE PROCEDURES OF THE SHOULDER AND ELBOW IN ADULTS > ANATOMY AND BIOMECHANICS.

[14] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > EDITOR COMMENTARY.

[15] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Development of Individual Regions.

[16] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > Mechanics of Anatomic Arthroplasty.

[18] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > SECTION 3 SHOULDER.

[19] Miller S Review Of Orthopaedics. SECTION 3 SHOULDER.

[20] A Lange Medical Book Current Diagnosis Treatment In Orthopedics Fifth Edition. 3Sports Medicine > Image SHOULDER INJURIES.

[21] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Bursae.

[23] The effect of the rotator interval on glenohumeral kinematics during abduction. BMC Musculoskeletal Disorders. 2016. DOI: 10.1186/s12891-016-0898-x

[24] Campbell S Operative Orthopaedics 4 Volume Set. ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION WITH BONE-PATELLAR TENDON-BONE GRAFT > SHOULDER INJURIES > ANATOMY AND BIOMECHANICS.

[26] Three-dimensional shoulder kinematics normalize after rotator cuff repair. Journal of Shoulder and Elbow Surgery. 2016. DOI: 10.1016/j.jse.2015.10.021

[27] Campbell S Operative Orthopaedics 4 Volume Set. POSTERIOR SURGICAL APPROACH FOR QUADRILATERAL SPACE SYNDROME > SHOULDER > NORMAL FUNCTIONAL ANATOMY.

[29] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > THROWING SHOULDER CONDITIONS.

[30] 3D scapular orientation on healthy and pathologic subjects using stereoradiographs during arm elevation. Journal of Shoulder and Elbow Surgery. 2015. DOI: 10.1016/j.jse.2015.04.007

[32] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Shoulder Capsule.

[33] Effects of asymptomatic rotator cuff pathology on in vivo shoulder motion and clinical outcomes. Journal of Shoulder and Elbow Surgery. 2017. DOI: 10.1016/j.jse.2016.11.048

[34] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > NORMAL MOTION AND PATHOMECHANICS > Glenohumeral Articulation.

[35] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > SENIOR EDITOR COMMENTARY.

[37] Rockwood And Matsen S The Shoulder. Fractures, Dislocations, and Acquired Problems of the Shoulder in Children > MECHANICS OF GLENOHUMERAL STABILITY.

[38] Rockwood And Matsen S The Shoulder. Shoulder and Elbow Specialty Clinic Workers’ Survey > Double Disruptions of the Superior Shoulder Suspensory Complex.

[39] The safe zone for avoiding suprascapular nerve injury in bone block procedures for shoulder instability. A cadaveric study. Knee Surgery, Sports Traumatology, Arthroscopy. 2014. DOI: 10.1007/s00167-014-2900-1

[40] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > EDITOR COMMENTARY—cont’d.

[41] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Suprascapular Nerve.

[42] Aaos Comprehensive Orthopaedic Review 3. Anatomy of the Shoulder, Arm, and Elbow > I. Shoulder.

[43] The relationship between the shape of rotator cuff tears and shoulder anatomical parameters. BMC Musculoskeletal Disorders. 2024. DOI: 10.1186/s12891-024-07829-9

[44] In-vivo glenohumeral translation and ligament elongation during abduction and abduction with internal and external rotation. Journal of Orthopaedic Surgery and Research. 2012. DOI: 10.1186/1749-799x-7-29

[45] The osseous morphology of nondegenerated shoulders shows no side-related differences in elderly patients: an analysis of 102 computed tomography scans. Journal of Shoulder and Elbow Surgery. 2016. DOI: 10.1016/j.jse.2015.12.024

[49] Is the circle perfect? Radiographic validation of the best fit circle in nonarthritic shoulders. JSES International. 2026. DOI: 10.1016/j.jseint.2025.10.005

[51] Shoulder proprioception – lessons we learned from idiopathic frozen shoulder. BMC Musculoskeletal Disorders. 2016. DOI: 10.1186/s12891-016-0971-5

[54] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Inferior Glenohumeral Ligament.

[55] Dominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations. Journal of Shoulder and Elbow Surgery. 2014. DOI: 10.1016/j.jse.2013.08.020

[56] Superior Capsular Reconstruction Partially Restores Native Glenohumeral Joint Loads in a Dynamic Biomechanical Shoulder Model. Arthroscopy. 2023. DOI: 10.1016/j.arthro.2023.02.019

[59] Effect of Shortening Deformity of the Clavicle on Scapular Kinematics. The American Journal of Sports Medicine. 2010. DOI: 10.1177/0363546509355143

[61] Rockwood And Matsen S The Shoulder. Fractures, Dislocations, and Acquired Problems of the Shoulder in Children > Glenoid Concavity and Labrum.

[63] Path of Glenohumeral Articulation Throughout the Rotational Range of Motion in a Thrower's Shoulder Model. The American Journal of Sports Medicine. 2006. DOI: 10.1177/0363546506287740

[64] Variations in the superior capsuloligamentous complex and description of a new ligament. Journal of Shoulder and Elbow Surgery. 2007. DOI: 10.1016/j.jse.2007.02.138

[65] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Glenohumeral Ligaments.

[66] Kinematic analysis of dynamic shoulder motion in patients with reverse total shoulder arthroplasty. Journal of Shoulder and Elbow Surgery. 2012. DOI: 10.1016/j.jse.2011.07.031

[71] Effects of short malunion of the clavicle on in vivo scapular kinematics. Journal of Shoulder and Elbow Surgery. 2017. DOI: 10.1016/j.jse.2017.03.013

[73] Shoulder morphology and throwing shoulder pain: Associations with humeral retroversion angle and posterior glenohumeral distance. Knee Surgery, Sports Traumatology, Arthroscopy. 2026. DOI: 10.1002/ksa.70334

[74] Partial-thickness tears involving the rotator cable lead to abnormal glenohumeral kinematics. Journal of Shoulder and Elbow Surgery. 2017. DOI: 10.1016/j.jse.2016.12.063

[78] Analysis of in vivo humeral rotation of reverse total shoulder arthroplasty patients during shoulder abduction on the scapular plane with a load. Arthroplasty. 2023. DOI: 10.1186/s42836-023-00207-1

[79] The Effect of Anterosuperior Rotator Cuff Tears on Glenohumeral Translation. Arthroscopy. 2008. DOI: 10.1016/j.arthro.2008.10.005

[80] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > OVERVIEW.

[86] The Superior Glenohumeral Joint Capsule Alone Does Not Prevent Superior Translation of the Humeral Head: An In Vitro Biomechanical Study. Arthroscopy. 2018. DOI: 10.1016/j.arthro.2018.06.025

[89] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > Normal Anatomy.

[90] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Shoulder Anatomy and Biomechanics, Clinical Evaluation, Imaging > Anatomy > Joints.

[91] Rockwood And Matsen S The Shoulder. Fractures, Dislocations, and Acquired Problems of the Shoulder in Children > Rotator Cuff > Scapulohumeral Ligaments.

[92] Rockwood And Matsen S The Shoulder. Shoulder and Elbow Specialty Clinic Workers’ Survey > Mechanism of Injury.

[93] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Innervation.

[95] An Analysis of Capsular Area in Patients with Anterior, Posterior, and Multidirectional Shoulder Instability. The American Journal of Sports Medicine. 2008. DOI: 10.1177/0363546507311603

[96] Tachdjian S Pediatric Orthopaedics From The Texas Scottish Rite Hospital For Children E Book. Appendix 3.2 Manual Muscle Tests of the Lower and Upper Extremities > The Shoulder.

[98] The sensory branch distribution of the suprascapular nerve: An anatomic study. Journal of Shoulder and Elbow Surgery. 2008. DOI: 10.1016/j.jse.2007.10.008

[105] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Infraspinatus.

[106] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Adipose Tissue.

[107] Rockwood And Green S Fractures In Adults. 29: Principles of Nonunion and Bone Defect Treatment > Pathoanatomy and Applied Anatomy Related to Periprosthetic Humeral Fractures About Shoulder Arthroplasty.

[111] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > SICK Scapula and Scapular Dyskinesis.

[112] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Triceps Brachii.

[114] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Axillary Artery > Third Portion.

[116] Rockwood And Matsen S The Shoulder. Arthroscopic Management of Prearthritic and Arthritic Conditions of the Shoulder and the Postarthroplasty Shoulder > INTRODUCTION.

[120] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Scapula.

[121] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > UPPER EXTREMITY > SHOULDER.

[123] Proximity of the Coracoid Process to the Neurovascular Structures in Various Patient and Shoulder Positions: A Cadaveric Study. Arthroscopy. 2019. DOI: 10.1016/j.arthro.2018.09.031

[126] Rockwood And Matsen S The Shoulder. Developmental Anatomy of the Shoulder and Anatomy of the Glenohumeral Joint > Biceps Brachii.

[127] Rockwood And Matsen S The Shoulder. Fractures, Dislocations, and Acquired Problems of the Shoulder in Children > FRACTURES OF THE PROXIMAL HUMERUS.

[128] The Subscapularis Footprint: An Anatomic Description of Its Insertion Site. Arthroscopy. 2007. DOI: 10.1016/j.arthro.2006.11.023

[129] Vascular Anatomy of the Subacromial Space: A Map of Bleeding Points for the Arthroscopic Surgeon. Arthroscopy. 2007. DOI: 10.1016/j.arthro.2007.03.093

[131] Sensory innervation of the human shoulder joint: the three bridges to break. Journal of Shoulder and Elbow Surgery. 2020. DOI: 10.1016/j.jse.2020.07.017

[133] Relationship of the Subscapular Nerves to the Base of the Coracoid. Arthroscopy. 2013. DOI: 10.1016/j.arthro.2013.02.005

[134] The Anatomic Relationship of the Brachial Plexus and Axillary Artery to the Glenoid. The American Journal of Sports Medicine. 2001. DOI: 10.1177/03635465010290061001

[136] Effects of type II SLAP lesion repair techniques on the vascular supply of the long head of the biceps tendon: a cadaveric injection study. Journal of Shoulder and Elbow Surgery. 2021. DOI: 10.1016/j.jse.2020.07.014

[138] Transhumeral Portal for Arthroscopic Glenohumeral Resurfacing Procedures: A Cadaveric Study of the Safety and Accuracy. Arthroscopy. 2015. DOI: 10.1016/j.arthro.2015.06.003

[140] Angle of approach to the superior rotator cuff of arthroscopic instruments depends on the acromial morphology: an experimental study in 3D printed human shoulders. Journal of Orthopaedic Surgery and Research. 2019. DOI: 10.1186/s13018-019-1486-1

[141] Qualitative and Quantitative Anatomy of the Humeral Attachment of the Pectoralis Major Muscle and Structures at Risk: A Cadaveric Study. Orthopaedic Journal of Sports Medicine. 2022. DOI: 10.1177/23259671221121333

[142] The Arterial Supply of the Adult Humerus. The Journal of Bone & Joint Surgery. 1956. DOI: 10.2106/00004623-195638050-00013

[143] The anatomic relationship of the axillary artery and vein to the clavicle: A cadaveric study. Journal of Shoulder and Elbow Surgery. 2009. DOI: 10.1016/j.jse.2009.01.021

[144] The Anatomy of the Supraclavicular Nerve During Surgical Approach to the Clavicular Shaft. Clinical Orthopaedics & Related Research. 2011. DOI: 10.1007/s11999-010-1608-x

[145] Paper #100: Subscapularis Footprint Anatomy Revisited With 3‐Dimensional Perspective and its Relationship With Supraspinatus 1st Facet. Arthroscopy. 2013. DOI: 10.1016/j.arthro.2013.07.104

[146] Describing the infraspinatus bare area of the proximal humerus: An anatomic cadaveric study. Shoulder & Elbow. 2024. DOI: 10.1177/17585732241229068

[147] Surgical anatomy of the axillary artery: clinical implications for open shoulder surgery. Journal of Shoulder and Elbow Surgery. 2021. DOI: 10.1016/j.jse.2020.09.018

[149] The effects of arm elevation on the 3-dimensional acromiohumeral distance: a biplane fluoroscopy study with normative data. Journal of Shoulder and Elbow Surgery. 2012. DOI: 10.1016/j.jse.2011.11.023

[150] An Anatomic Study of the Subscapularis Insertion to the Humerus: The Subscapularis Footprint. Arthroscopy. 2008. DOI: 10.1016/j.arthro.2008.02.009

[151] Subscapularis Tendon Tear Classification Based on 3‐Dimensional Anatomic Footprint: A Cadaveric and Prospective Clinical Observational Study. Arthroscopy. 2014. DOI: 10.1016/j.arthro.2014.08.015