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Shoulder Anatomy & Biomechanics

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

71 citationsUpdated Oct 2026

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Overview

The shoulder possesses the most motion of any joint in the human body [3], a capacity enabled by anatomy that permits greater mobility than any other articulation [11]. Function depends on the coordinated movement of the glenohumeral, acromioclavicular, and sternoclavicular joints and the scapulothoracic articulation [12]. The "fifth shoulder joint," or humeroscapular motion interface, lies between the inner structures of the proximal humerus, rotator cuff, coracohumeral ligament, and biceps tendon sheath and the superficial layer of the acromion, deltoid, coracoacromial ligament, coracoid process, and conjoined tendon [12]. Smooth, unrestricted motion at this interface is vital to shoulder mobility [12]. The evolution of the shoulder exemplifies anatomical adaptation to environmental requirements [8], with the scapula suspended by muscles alone and shifted caudally from the cervical position seen in lower animals [13].

Biomechanically, the planar concept of shoulder motion must give way to a spherical frame of reference to describe complex motions [140]. The bony anatomy does not provide inherent stability [28]; instead, the glenoid fossa is a flattened, dish-like structure where only one fourth of the large humeral head articulates at any given time [28]. The glenoid is deepened by 50% by the presence of the glenoid labrum, which increases humeral contact to 75% [28]. The rotator cuff embraces the humeral head and compresses it into the glenoid fossa via concavity compression, a mechanism effective in any arm position [38]. Contact between the proximal humeral convexity and the coracoacromial arch is not "impingement" but rather the normal stabilization mechanism resisting superiorly directed forces [38].

The biomechanical shoulder model is consistent with clinical observations [4], although a clinical evaluation of altered shoulder kinematics remains complicated [7]. The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch, a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [1]. The rotator cuff, subacromial bursa, and subdeltoid bursa pass underneath this arch [1]. Detailed bony dimensions, soft tissue anatomy, and vascular and neural structures are addressed in subsequent sections.

Osseous Anatomy

Proximal Humerus

The proximal humerus comprises four main 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 [1]. The most superior portion of the articular surface averages 8 mm above the greater tuberosity [1], with the superior margin normally positioned 8 to 10 mm superior to the top of the greater tuberosity [11]. The humeral head height is approximately 5.6 cm above the superior border of the pectoralis major tendon [123].

Humeral Head Orientation: The humeral head averages 19° of retroversion and 41° of inclination (neck-shaft angle) [46]. It is retroverted 30 degrees relative to the transepicondylar axis of the humerus [123]. Proximal humeral retroversion is highly variable, ranging from 0 to 55 degrees depending on the measurement method [11]. The head-shaft angle ranges from 30 to 55 degrees [11].

Tuberosities and Shaft: The greater tuberosity is located in a posterior-superior location with respect to the humeral shaft [1], while the lesser tuberosity is located on the anterior aspect of the proximal humerus [1]. The bicipital groove lies between the greater and lesser tuberosities and serves as a pathway for the long head of the biceps [1]. The upper portion of the humeral shaft is cylindrical and becomes more flattened in an anteroposterior direction as it proceeds distally [2].

Ossification and Fracture Prognosis: The proximal humerus has 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) [46]. These ossification centers fuse to the shaft at age 17 to 20 years [46]. Fractures involving the anatomic neck are prognostically worse than fractures involving other regions of the proximal humerus regarding potential disruption of vascular supply and development of avascular necrosis [1].

Glenoid and Scapula

The glenoid fossa is a shallow inverted, comma-shaped, articular surface one fourth the size of the humeral head [21]. The subchondral bone of the glenoid is relatively flat, and the articular concavity is augmented by cartilage and a circumferential labrum [46]. The glenoid cartilage thickness is 2.16 mm [11], and the glenoid radius of curvature is 22-28 mm [11]. The glenoid surface area is 4-6 mm [11].

Glenoid Dimensions and Orientation: The glenoid diameter superior anteroposterior is 18-30 mm [11], and the glenoid diameter inferior anteroposterior is 21-35 mm [11]. The glenoid superoinferior height is 30-48 mm [11]. The glenoid inclination averages 4.2 degrees, with a range of –7 to 20 degrees [11]. The glenoid version is 1.5 degrees retroversion, with a range of 10.5-9.5 degrees anteversion [11]. The glenoid averages 5° of retroversion in relation to the axis of the scapular body [46], and is retroverted approximately 5 degrees relative to the scapular body [123]. The normal position of the glenoid surface in relation to the axis of the scapular body ranges from 2 degrees of anteversion to 7 degrees of retroversion [11].

Scapular Anatomy and Evolution: The scapula is a thin sheet of bone that mainly functions as a site of muscle attachment [122]. It is thicker at its superior and inferior angles and at its lateral border [122]. The scapula spans second through seventh ribs and serves as an attachment for 17 muscles [123]. The scapula is anteverted on the chest wall approximately 30 degrees relative to the body [123]. The scapular spine is an osseous ridge that separates the supraspinatus and infraspinatus fossae [46]. The scapula has only one true diarthrodial articulation, the acromioclavicular (AC) joint [46]. Normal shoulder motion is approximately two-thirds glenohumeral and one third scapulothoracic [46]. Ossification of the scapular body begins at the eighth week of gestation [46].

The scapular index, defined as the relationship between the length (measured along the base of the spine) and breadth (measured from superior to inferior angle) of the scapula, is extremely high in pronograde animals with a long, narrow scapula [13]. The scapula is broader in humans and other primates, with the most pronounced differences observed in the infraspinatus fossa [13]. Broadening of the infraspinatus fossa has resulted in a change in the vector of muscle pull from the axillary border of the scapula to the glenoid fossa [13]. The acromion is an extension of the spine of the scapula and has enlarged over time in humans compared to pronograde animals [13].

Clavicle and Acromion

The clavicle is the first bone to ossify, occurring in the fifth week of gestation [46]. It is the only long bone to ossify by intramembranous ossification [46]. The medial (sternal) epiphysis of the clavicle is the last ossification center to fuse, at age 20 to 25 years [46]. The primary blood supply to the clavicle is periosteal, and no nutrient artery is present [46].

Acromial Anatomy and Os Acromiale: The acromion has three ossification centers: the metacromion (base), the mesoacromion (middle), and the preacromion (tip) [46]. Failure of fusion of the acromial ossification centers results in os acromiale [46]. Os acromiale is most commonly between the mesoacromion and meta-acromion [123]. The acromion, the coracoacromial ligament, and the coracoid process form the coracoacromial arch [1]. This arch is a rigid bony-ligamentous structure that imparts stability to the shoulder girdle [1].

Acromiohumeral Offset: When viewed from the front, a 9- to 10-mm gap (6.6 to 13.8 mm in men and 7.1 to 11.9 mm in women) can be observed between the acromion and humerus [122]. Offset of 8 mm in any direction significantly decreased passive range of motion [11]. The medial (coronal) humeral offset is 4-14 mm [11], and the posterior (transverse) humeral offset is –2 to 10 mm [11].

Vascular Supply

The anterolateral ascending branch of the anterior humeral circumflex artery provides the primary blood supply to the humeral head [46]. The terminal intraosseous portion of the anterior humeral circumflex artery enters at the proximal aspect of the intertubercular groove as the arcuate artery [46]. 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 [129]. The low rate of osteonecrosis associated with anterior shoulder dislocations is explained by the contribution of the posterior humeral circumflex artery to humeral head blood supply [129].

Ligaments and Joint Capsule

Glenohumeral Capsule

The glenohumeral capsule is a synovium-lined structure extending from the glenoid neck or labrum to the anatomic neck and proximal humeral shaft [34]. It is inherently large, loose, and redundant, with a surface area nearly twice that of the humeral head to permit full range of motion [37, 95]. The capsule blends with ligamentous structures arising from nearby bony landmarks and contains the glenohumeral ligaments within its substance [34]. These ligaments are collagenous reinforcements not visible on the external surface and are best appreciated arthroscopically without distension [69]. Capsular thickness varies, ranging from 1.3 to 4.5 mm in cadaveric specimens, with the inferior pouch measuring 2.8 mm, the anterior portion 2.4 mm, and the posterior portion 2.2 mm [95]. The posterior capsule is significantly thinner at <1 mm due to the absence of glenohumeral ligaments or thickenings present in the anterior counterpart [94].

The capsule functions as a sheetlike ligament connecting the humerus and scapula, with collagen fibers that are not organized in a parallel fashion and lack distinct fold margins [21]. Functional studies indicate the capsule does not possess "band-like" properties, and the "ligaments" of the anterior capsule are described with variable prevalence due to differing identification success [21]. The capsule inserts into the glenoid labrum and glenoid bone [21]. In healthy shoulders, ligamentous structures are not fully elongated in many positions but act as restraints at the extremes of motion [48]. The glenohumeral ligaments are lax in mid-range positions and provide static constraint only when taut at the limits of motion [40, 44]. In cadaveric tests, the capsule remains essentially free of tension until terminal degrees of motion are reached, at which point increased tension in the static restraints checks the range of motion [37, 14].

Capsular tension shifts with arm position. With the arm at the side, the superior capsule is taut and the inferior portion is lax; this relationship reverses with overhead elevation, making the inferior portion taut and the superior portion lax [21]. The anterosuperior capsule in the rotator interval contains the coracohumeral and superior glenohumeral ligaments, which assume tension with increasing external rotation at 0 degrees of abduction [37]. 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 [37]. The inferior capsule tightens with increasing abduction, while the posterior capsule becomes tight in internal rotation with the arm at the side [37]. As elevation angles increase, tension shifts inferiorly within the capsule [37].

A contracted capsule reduces glenohumeral motion and increases the torque required to achieve elevated positions [37]. Asymmetric tightness can cause obligate translation of the humeral head; for example, surgical tightening of the posterior capsule results in consistent anterosuperior translation during forward flexion [37]. Chronic anterior contracture is almost always associated with an external rotation deficit compared to the contralateral shoulder [37]. Overtightening of anterior structures directs greater joint reaction forces toward the posterior glenoid, causing excessive posterior cartilage wear, bony erosion, and osteoarthritis, a process termed "capsulorrhaphy arthropathy" by Matsen and colleagues [37]. In overhead athletes, the posterior capsule can become thicker and contracted, leading to glenohumeral internal rotation deficit [94].

The embryologic origin of the anterior capsule influences its strength. In an embryologic study of 52 specimens, the anterior capsule inserted into the glenoid labrum in 77% and into the medial scapular neck in 23% [95]. A type I attachment, where fibers primarily originate from the labrum with some attaching to the glenoid, is seen in 80% of cases, while a type II origin from the glenoid neck occurs in 20% [95]. If the capsule arises at the labrum, few synovial recesses are present, resulting in a stronger anterior capsule; conversely, a more medial origin from the anterior scapular neck produces larger, more numerous synovial recesses and a thin, weak anterior capsule [95]. Many observers have described great variation in the size and number of these synovial recesses [95].

In conditions requiring shoulder arthroplasty, the capsule and ligaments are often contracted, prematurely limiting range of motion and increasing joint pressure at the limits of motion [14]. The term "stuffing" refers to additional tightening of the capsule resulting from prosthetic components that take up more space than the available joint volume [14]. Unless sufficient capsular releases are performed to accommodate this additional volume, the joint becomes "overstuffed," limiting motion and requiring greater torque to move the arm [14]. Cadaver studies indicate that less than 10 mm of overstuffing can reduce normal capsular laxity [14]. A more complete glenohumeral capsular release may be necessary in certain clinical situations [66].

Mechanoreceptors exist in a significant population of capsular and juxtalabral tissue, and capsular structures are believed to contribute to stability through proprioceptive functions [35, 95]. However, the anatomical structure of passive shoulder restraints has no impact on the difference in passive joint position sense values between external and internal rotation [54]. Posterior shoulder tightness results in scapular malposition, with muscular and capsular components affecting scapular position differently [80].

Superior Glenohumeral Ligament

The superior glenohumeral ligament (SGHL) is the most consistent capsular ligament, present in 97% of shoulders in the classic anatomic study by DePalma, though it was present in 26% to 90% of specimens in an anatomic study at the authors' institution [69, 95]. It crosses the rotator interval capsule and lies between the supraspinatus and subscapularis tendons [95]. The SGHL attaches to the glenoid rim near the apex of the labrum conjoined with the long head of the biceps [28]. Three common variations exist in its glenoid attachment: it can arise from a common origin with the biceps tendon, from the labrum slightly anterior to the tendon, or originate with the middle glenohumeral ligament [69]. On the humerus, it attaches to the anterior aspect of the anatomic neck [28]. The SGHL inserts into the fovea capitis and lies just superior to the lesser tuberosity [69]. Its size and integrity are variable, existing as a thin wisp of capsular tissue or as a thickening similar to the patellofemoral ligaments in the knee [69].

The SGHL travels from the anterosuperior glenoid labrum to the humerus, forming a pulley/sling medial to the bicipital groove [94]. It helps prevent medial or anterior-inferior translation of the long head of the biceps tendon from the groove [94]. The principal function of the SGHL is the primary static restraint to inferior translation at 0° of shoulder abduction [94]. It is also the primary stabilizer to anterior and posterior stress at 0 degrees of abduction [26]. Biomechanical studies show that the SGHL contributes very little to the static stability of the glenohumeral joint in other positions; selective cutting did not significantly affect translation either anteriorly or posteriorly in the abducted shoulder [69]. Its contribution to stability is contingent upon its thickness and collagenous integrity [69].

The SGHL and coracohumeral ligament are reinforcing structures of the rotator interval [19]. They come under tension with external rotation in adduction, as well as with glenohumeral flexion, extension, external rotation, and adduction [95]. When under tension, they resist posterior and inferior displacement of the humeral head [95]. They limit inferior translation and external rotation when the arm is adducted [19]. They also limit posterior translation when the arm is flexed forward, adducted, and internally rotated [19]. Tightening of the rotator interval, which includes the SGHL, decreases posterior and inferior translation [26]. Imbrication of the rotator interval decreases inferior and posterior translation [19]. Conversely, release of the rotator interval produces greater forward flexion and external rotation [19]. Tightening of the rotator interval may also decrease external rotation [28].

The anatomic superior capsule has a negligible role in preventing the superior translation of the humeral head [89]. The superior capsular complex forms a suspension sling with anterior and posterior limbs that function similarly to the inferior glenohuminal ligament complex [68]. The posterior limb of the superior capsular complex restricts internal rotation [68].

Inferior Glenohumeral Ligament Complex

The inferior glenohumeral ligament (IGHL) is a complex structure and the main static stabilizer of the abducted shoulder [57]. It is a hammock-like structure originating from the glenoid and inserting into the anatomic neck of the humerus [57]. The IGHL complex consists of an anterior band, a posterior band, and an axillary pouch lying in between [57]. The anterior and posterior bands are most clearly defined with the arm abducted [57]. In some shoulders, these bands can only be visualized grossly by internally and externally rotating the arm at 90 degrees of abduction [57]. With abduction and external rotation, the anterior band fans out to support the head, and the posterior band becomes cord-like [57]. With internal rotation, the posterior band fans out to support the head, and the anterior band becomes cord-like [57].

The IGHL was originally described as triangular, with its apex at the labrum and its base blending with the capsule between the subscapularis and the triceps area [57]. Turkel and colleagues identified the especially thickened anterior superior edge as the superior band of the inferior glenohumeral ligament [57]. They named the region between the superior band and the middle glenohumeral ligament the anterior axillary pouch, and called the remainder of the capsule posterior to the superior band the posterior axillary pouch [57]. The IGHL complex originates from either the glenoid labrum or the glenoid neck [57]. The inferior glenohumeral ligament is composed of an anterior band that is quite thick, a posterior band

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, while the subscapularis serves as an internal rotator [2]. The infraspinatus is the second most active rotator cuff muscle, contributing up to 60% of external rotation force [108]. It also functions as a depressor of the humeral head [108]. In the passive state, the infraspinatus stabilizes against posterior subluxation [108]. During internal rotation, it creates a forward force to stabilize against posterior subluxation, whereas its posterior line of pull stabilizes against anterior subluxation when the shoulder is in abduction–external rotation [108].

The infraspinatus is a pennate muscle with a median raphe covered by a fat stripe that may be mistaken at surgery for the gap between the infraspinatus and teres minor muscles [108]. It originates from the infraspinatus fossa of the scapula, the overlying dense fascia, and the spine of the scapula [108]. Its tendinous insertion is shared with the supraspinatus anteriorly and superiorly, and the teres minor inferiorly, at the greater tuberosity [108]. The infraspinatus is innervated by the suprascapular nerve [108]. Its blood supply generally derives from two large branches of the suprascapular artery [108]. In two-thirds of specimens, the subscapular artery, via its dorsal or circumflex scapular branch, supplied the greater portion of the infraspinatus circulation [108]. The infraspinatus bare area broadens as the humeral head is evaluated from a superior to inferior direction [148].

The greater tuberosity serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons, while the lesser tuberosity serves as the attachment site for the subscapularis tendon [1]. The subscapularis inserts on the lesser tuberosity and causes medial displacement of fracture fragments [1]. Conversely, the supraspinatus and infraspinatus insert on the greater tuberosity and cause superior and posterior displacement of fracture fragments [1]. The subscapularis footprint is broad proximally and tapers distally, exhibiting a comma shape [150]. It consists of a proximal tendinous part and a distal muscular part [150]. The upper 60% of the subscapularis footprint provides the major surface area for tendon insertion [130]. The first facet of the subscapularis tendon area comprises approximately one-third of the entire footprint, while the first two facets constitute 60% of the total footprint [147].

Shoulder anatomy influences rotator cuff tear formation mechanisms, with greater tuberosity area, coracoacromial space area, acromion index, lesser tuberosity area, and footprint dimensions playing a more significant role in L-shaped tears compared to other tear shapes [142]. Access to the rotator cuff from almost every portal is influenced by acromial shape [145]. The acromiohumeral distance is no longer measured intra-articularly or within the supraspinatus footprint above approximately 70 degrees of arm elevation [149].

Biceps Brachii

The biceps muscle has two origins in the shoulder, both rich in collagen [128]. The long head originates from the bicipital tubercle at the superior rim of the glenoid and along the posterior superior rim of the glenoid and labrum, with much of its origin via the superior labrum [128]. The short head originates from the coracoid tip, lateral to and in common with the coracobrachialis [128]. The size of the bicipital tubercle does not reflect the size of the biceps tendon [128]. Distally, the lateral insertion is to the posterior part of the tuberosity of the radius, while the medial insertion is aponeurotic, passing medially across and into the deep fascia of the volar forearm muscles [128]. Loss of long head attachment results mainly in a 20% loss of supination strength and a smaller 8% loss of elbow flexion strength [128].

The long head exits the shoulder through a capsular defect between the greater and lesser tuberosities and passes distally in the bicipital groove [128]. A shallow bicipital groove and supratubercular ridge above the lesser tubercle predispose to biceps tendon pathology [128]. The intra-articular portion of the tendon is broader than that within the groove [128]. The medial wall of the bicipital groove is higher, with an opening angle of 30 to 40 degrees in the largest fraction of patients [128]. The bicipital tendon does not move up and down in the groove; rather, the humerus moves down and up with adduction and abduction relative to the tendon [128]. The tendon is retained within the groove by a pulley composed of fibers from the coracohumeral and superior glenohumeral ligaments, with some reinforcement from adjacent tendons [128].

Under normal conditions, the biceps action is flexion and supination at the elbow [128]. When supraspinatus paralysis or rupture occurs, the long head of the biceps hypertrophies, likely because the patient uses the muscle as a depressor of the humeral head by placing the shoulder in external rotation [128]. Rupture of the long head results in a 20% loss of elevation strength in external rotation [128]. Loss of the long head depressor effect is unlikely to worsen impingement [128]. In internal rotation, no loss of strength is evident following rupture of the long head [128]. The long head contributes to joint stability, which is increased in external rotation and decreased in internal rotation [128]. Biceps innervation is supplied by branches of the musculocutaneous nerve (C5 and C6) [128]. The blood supply derives from a single large bicipital artery from the brachial artery (35%), multiple very small arteries (40%), or a combination of the two types [128].

Other Shoulder Muscles

The pectoralis major inserts on the humeral shaft and displaces it medially [1]. The triceps long head originates from the infraglenoid tubercle [113]. Its insertion is intimately related to the labrum over a distance of 2 cm centered on the tubercle [113]. Fibers of the triceps long head tendon adjacent to the capsule radiate into the inferior capsule and reinforce it [113]. The origin is bounded laterally by the quadrilateral space and medially by the triangular space [113]. The triceps long head functions in shoulder adduction against resistance to offset shear forces generated by primary adductors [113]. In violent activities such as throwing, the triceps long head may demonstrate electromyographic activity up to 200% of that generated by a maximal muscle test [113].

The pectoralis minor tendon provides sufficient tissue length, excursion, and width for acromioclavicular joint reconstruction [15]. It is biomechanically as strong as the coracoacromial ligament [15]. The pectoralis minor muscle inserts onto the medial coracoid process [46]. The coracobrachialis muscle and the short head of the biceps tendon also originate from the coracoid process [46].

Innervation and Vascular Supply

The posterior branch of the axillary nerve branches to supply the teres minor muscle and then terminates as the superior lateral brachial cutaneous nerve [12]. In the anterior deltopectoral approach, the axillary nerve can be palpated by sweeping a finger inferiorly across the subscapularis muscle tendon interface [12]. In the anterolateral deltoid splitting approach, the axillary nerve crosses approximately 5 cm inferior to the anterolateral acromial corner [12]. Shoulder abduction brings the axillary nerve closer to the acromion landmark [12]. No accessory motor branches to the anterior deltoid cross the tendinous raphe between the anterior and lateral deltoid [12]. In the posterior deltoid splitting approach, the axillary nerve is approximately 7 cm from the posterior acromial corner [12].

The suprascapular nerve arises from the superior lateral aspect of the upper trunk shortly after its formation at Erb’s point [45]. It passes below the transverse scapular or suprascapular ligament and enters the supraspinatus muscle, which it innervates through two branches [45]. The nerve innervates the infraspinatus muscle through two branches after inferiorly passing around the base of the spine of the scapula [45]. It provides two articular branches: one in the supraspinatus fossa to the acromioclavicular and superior glenohumeral joints, and one in the infraspinatus fossa to the posterior superior glenohumeral joint [45]. The suprascapular nerve is accompanied by the suprascapular artery, which passes over the transverse scapular ligament [45]. The motor branch to the supraspinatus branches within 1 cm of the suprascapular notch in all specimens [45]. From the base of the scapular spine, the nerve medially curves and innervates the infraspinatus muscle within 1 cm of the base of the scapular spine in nearly 90% of cases [45]. The distance from the midline of the posterior glenoid rim to the suprascapular nerve at the base of the scapular spine averages 1.8 cm, with some as close as 1.4 cm [45]. The safe zone for the suprascapular nerve is a distance 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 [45]. Compression of the suprascapular nerve by the spinoglenoid ligament near the base of the spine has been reported [45].

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 (also known as the arcuate artery) [1]. The ascending branch of the anterior humeral circumflex artery 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]. The triceps long head innervation is supplied by the radial nerve with root innervation through C6 to C8 [113]. The arterial supply of the triceps long head is derived mainly from the profunda brachii artery and the superior ulnar collateral artery [113]. Near its origin, the triceps long head receives branches from the brachial and posterior humeral circumflex arteries [113].

Neurovascular Anatomy

Nerve Supply and Innervation

The shoulder receives innervation from a network of nerve fibers primarily derived from the C5, C6, and C7 nerve roots, with a minor contribution from the C4 root [97]. The axillary nerve, a terminal branch of the posterior cord of the brachial plexus, passes beneath the conjoined tendon anterior to the subscapularis, 3 to 5 mm medial to the musculotendinous junction [12]. It enters the quadrilateral space posteriorly and splits into anterior and posterior branches within this space [12]. The anterior and middle deltoid muscles receive sole innervation from the anterior branch of the axillary nerve [12]. In 89.1% of cases, the posterior deltoid muscle receives innervation from both the anterior and posterior branches of the axillary nerve [12]. The posterior branch supplies the teres minor muscle and terminates as the superior lateral brachial cutaneous nerve [12].

The suprascapular nerve passes below the transverse scapular or suprascapular ligament to enter the supraspinatus muscle, which it innervates through two branches [45]. It innervates the infraspinatus muscle through two branches after passing inferiorly around the base of the spine of the scapula [45]. The nerve provides two articular branches: one to the acromioclavicular and superior glenohumeral joints in the supraspinatus fossa, and one to the posterior superior glenohumeral joint in the infraspinatus fossa [45]. In all 90 cadaveric specimens studied by Bigliani et al., the motor branch to the supraspinatus branches within 1 cm of the suprascapular notch [45]. The distance from the midline of the posterior glenoid rim to the suprascapular nerve at the base of the scapular spine averages 1.8 cm, with some cases as close as 1.4 cm [45]. The safe zone for the suprascapular nerve 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 [45].

The subscapular nerve branches to the anterior border of the glenoid may be as little as 1 cm from that border [43]. The closest distance that the innervation point of either the upper or lower subscapular nerve came to the medial aspect of the coracoid was 11 mm [135]. The radial nerve is commonly injured in humeral shaft fractures, particularly at the junction of the middle and distal third [2]. 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]. An axillary nerve injury from proximal humeral fracture or fracture-dislocation results in paralysis of the deltoid muscle and anesthesia over the “badge” region at the lateral proximal arm [2]. The brachial plexus and axillary artery can be injured with anterior shoulder dislocations [2].

The nerves supplying the ligaments, capsule, and synovial membrane of the shoulder are medullary and nonmedullary fibers from the axillary, suprascapular, subscapular, and musculocutaneous nerves [97]. The axillary nerve and suprascapular nerve provide most of the nerve supply to the anterior capsule and glenohumeral joint [97]. The primary nerves supplying the posterior shoulder joint are the suprascapular nerve in the upper region and the axillary nerve in the lower region [97]. The anterior portion of the inferior shoulder joint is primarily supplied by the axillary nerve, while the posterior portion is supplied by a combination of the axillary nerve and lower ramifications of the suprascapular nerve [97]. Sensory branches to the shoulder joint are more common and numerous than previously described [101]. The suprascapular, lateral pectoral, and axillary nerves are the most common parent nerves supplying articular branches to the human shoulder joint [133]. Thinly myelinated or unmyelinated sensory neurons provide innervation to the long head of the biceps tendon [97]. A significant population of mechanoreceptors exists in the capsular and juxtalabral tissue of the human shoulder [35].

Vascular Supply

The anterolateral ascending branch of the anterior humeral circumflex artery supplies the majority of the humeral head [116]. The anterior humeral circumflex artery travels laterally at the inferior border of the subscapularis tendon, marking the border between the upper tendinous insertion and lower muscular insertion of the subscapularis [116]. Significant intraosseous anastomoses exist between the arcuate artery and posteromedial vessels from the posterior humeral circumflex artery [116]. The anterior humeral circumflex artery constitutes the main nutrient vessel of the humeral head [137].

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 of the shoulder beneath the teres minor [116]. The anterior branch of the posterior humeral circumflex artery supplies the anterior two-thirds of the deltoid [116]. The subscapular artery originates in the third part of the axillary artery and runs caudally on the subscapularis muscle [116]. 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 [116]. The thoracodorsal artery runs with the thoracodorsal nerve toward the latissimus dorsi on the subscapularis, teres major, and latissimus dorsi [116].

The brachial plexus and axillary artery are located within 2 cm of the glenoid rim, with the brachial plexus as close as 5 mm in some cases [136]. The distance from the coracoid process to the neurovascular structures is closest in the beach-chair position with 90 degrees of arm abduction [125]. The subacromial space is highly vascularized, with a consistent pattern of blood supply found in 60% of dissected shoulders [131]. There is poor vascular supply to the anterosuperior portion of the glenoid [138]. An area of approximately 5 mm from the edge of the glenoid rim is completely devoid of vascularity, with no blood supply from either the capsule or local muscle [138].

Surgical Landmarks and Anatomical Relationships

In 19.6% of cadaveric shoulders, the main portion of the anterior division of the axillary nerve was closer than 5 cm from the palpable edge of the acromion at some point along its course [41]. The axillary nerve has an intimate relationship within the humeroscapular motion interface [12]. The axillary space contains the brachial plexus and its branches, the axillary artery and vein, and major lymphatic drainage from the anterior chest wall, upper limb, and back [109]. The axillary space is bounded posteriorly by the subscapularis, teres major, and latissimus dorsi muscles [109]. The anterior boundary of the axillary space is the pectoralis minor muscle and the clavipectoral fascia [109]. Adipose tissue in the shoulder serves to indicate the presence of vessels or nerves [109].

The subacromial bursa has a capacity of 5 to 10 mL when not compromised by adhesions or edema [22]. The subscapularis bursa usually connects with the glenohumeral joint, acting as a recess rather than a separate bursa [22].

Biomechanics and Function

Joint Mechanics and Stability

The glenohumeral joint is a modified ball-and-socket joint where the large humeral head articulates against, not within, the small glenoid cavity [11]. The bony anatomy contributes little to stability, often compared to a golf ball on a tee [26]. The glenoid articular surface and labrum combine to create a socket approximately 9 mm deep in the superoinferior direction and 5 mm deep in the anteroposterior direction [26]. The glenoid labrum increases the depth of the glenoid socket by nearly 50% around the humeral head [26]. The small arc of the glenoid captures relatively little of the humeral articular surface, thus avoiding neck-to-rim contact for a wide range of positions [40]. An acetabulum-like socket would limit motion by contact of the anatomic neck of the humerus with its rim [40].

The joint does not offer a deep stabilizing socket or isometric articular ligaments that provide stability throughout flexion around a defined anatomic axis [40]. Instead, the humeral head translates over the glenoid surface rather than simply rotating within the cavity [37]. The normal shoulder precisely constrains the humeral head to the center of the glenoid cavity throughout most of the arc of movement [40]. The glenohumeral joint allows humeral translation until the lax capsular ligaments become taught [44]. This differs from hinge-like joints by allowing translation until the lax capsular ligaments become taught [44].

The normal ratio of glenohumeral motion to scapulothoracic motion is 2:1 [37]. The normal surface area of the glenohumeral capsule is nearly twice that of the humeral head and is inherently loose [37]. The glenohumeral capsule remains essentially free of tension until a terminal degree of motion is reached [37]. Glenohumeral ligaments are lax and relatively ineffectual in most functional positions of the joint, providing static constraint only at the extremes of motion [40]. The glenohumeral joint capsular ligaments are lax in mid-range shoulder positions and only provide static constraint when they become taught at the extremes of motion [44].

The basic law of glenohumeral stability is that the joint will not dislocate as long as the net humeral joint reaction force is directed within the effective glenoid arc [40]. If the net humeral joint reaction force passes outside the effective glenoid arc, the joint becomes unstable [40]. The net humeral joint reaction force is the vector sum of all forces acting on the head of the humerus relative to the glenoid fossa [40]. It is the result of all muscular, ligamentous, inertial, gravitational, and other external forces applied to the head of the humerus [40]. The effective glenoid arc is the arc of the glenoid able to support the net humeral joint reaction force [40].

The balance stability angle is the maximal angle that the net humeral joint reaction force can make with the glenoid center line before dislocation occurs [40]. The balance stability angle varies around the face of the glenoid [40]. For a normal glenoid, the superior and inferior balance stability angles are greater than the anterior and posterior balance stability angles [40]. The shape of the bone, cartilage, and labrum all contribute to the effective glenoid arc and the balance stability angle [40]. The deltoid and cuff muscle forces maintain the net humeral joint reaction force within the balance stability angle [40].

The shoulder is stabilized by both static and dynamic restraints [19]. Static restraints: * Glenoid labrum * Articular version * Articular conformity * Negative intraarticular pressure * Capsule * Glenohumeral ligaments [19]

Dynamic restraints: * Joint concavity compression produced by synchronized contraction of the rotator cuff [19] * Increased capsular tension produced by direct attachments of the rotator cuff to the capsule [19] * Scapular stabilizers that maintain a stable glenoid platform [19] * Proprioception [19]

Concavity compression is a mechanism of stability involving the dynamic compression of the humeral head into the shallow glenoid-labral concavity by balanced rotator cuff contraction [44]. Weak contraction of the cuff muscles does not offset an applied translational force, resulting in an unbalanced net force and humeral translation from the center of the glenoid concavity [44]. Strong contraction of the rotator cuff provides an increased compressive force into the glenoid concavity, balancing the net force and centering the humeral head [44]. Scapulohumeral balance is a mechanism of stability involving neuromuscular control of coordinated scapular movement to keep the glenohumeral joint reaction force positioned within the glenoid [44]. Coordinated scapular movement repositions the glenoid concavity to balance the net humeral force within the glenoid concavity [44].

The rotator cuff acts as depressors of the humeral head to allow the deltoid to efficiently abduct the humerus [2]. The rotator cuff stabilizes the glenohumeral joint while allowing greater freedom of motion and fixes the fulcrum of the upper extremity against which the deltoid can contract [11]. The rotator cuff must act simultaneously and synergistically with the deltoid muscle for normal function [11]. The glenohumeral joint depends on static and dynamic stabilizers for movement and stability, especially the rotator cuff [11].

The scapula must rotate during throwing, retracting during the late cocking phase and protracting during the acceleration phase [19]. The scapula optimizes the position of the glenoid with respect to the rapidly rotating humeral head during throwing [112]. The scapula acts as a stable base for the origin of extrinsic and intrinsic shoulder muscles that provide glenohumeral compression and regulate arm motion [112].

The humeroscapular motion interface lies between the inner structures of the proximal humerus, rotator cuff, coracohumeral ligament, and biceps tendon sheath and the superficial layer of the acromion, deltoid, coracoacromial ligament, coracoid process, and conjoined tendon [12]. Smooth, unrestricted motion at the humeroscapular interface is vital to shoulder mobility [12]. Adhesions in the humeroscapular motion interface can limit shoulder mobility [12]. The coracoid process can mechanically limit anterior translation of the humerus relative to the glenoid when the shoulder is in 90 degrees of abduction [13].

Capsular and Ligamentous Kinematics

Different regions of the glenohumeral capsule have differing roles in joint function [21]. The glenoid labrum acts as an attachment site for the capsuloligamentous structures [21]. The glenoid labrum acts as an extension of the articular cavity [21]. The triangular cross-section of the labrum acts as a chock-block to help prevent subluxation [21].

The inferior glenohumeral ligament is composed of an anterior band that is quite thick, a posterior band that is less thick and distinct, and a thinner intervening axillary pouch, creating a hammock-type sling [26]. With external rotation, the hammock slides anteriorly and superiorly, the anterior band tightens, and the posterior band fans out [26]. With internal rotation, the opposite occurs to the inferior glenohumeral ligament bands [26]. The inferior glenohumeral ligament complex serves as the primary restraint to anterior, posterior, and inferior glenohumeral translation at 45 to 90 degrees of glenohumeral elevation [19]. The anterior band of the inferior glenohumeral ligament is important in external rotation [19]. The posterior band of the inferior glenohumeral ligament is important in internal rotation [19]. The anteroinferior glenohumeral ligament complex is the main stabilizer to anterior and posterior stresses when the shoulder is abducted 45 degrees or more [26]. The inferior glenohumeral ligament provides the principle static constraint to anteroinferior instability when the arm is in extreme abduction, extension, and external rotation [44].

The superior glenohumeral ligament is the primary stabilizer to anterior and posterior stress in 0 degrees of abduction [26]. The middle glenohumeral ligament limits external rotation when the arm is in the lower and middle ranges of abduction but has little effect when the arm is in 90 degrees of abduction [26]. The middle glenohumeral ligament limits external rotation of the adducted humerus [19]. The middle glenohumeral ligament limits inferior translation of the adducted and externally rotated humerus [19]. The middle glenohumeral ligament limits anterior and posterior translation of the partly abducted (at 45 degrees) and externally rotated arm [19].

The middle glenohumeral ligament becomes taut with maximal external rotation at 45 degrees of abduction [37]. The anterior band of the inferior glenohumeral ligament becomes taut with maximal external rotation at 90 degrees of abduction [37]. Normally, the glenohumeral joint displays ball-and-socket mechanics, and the humeral head remains centered within the glenoid fossa except at the extremes of range of motion [37].

The rotator interval is central to normal glenohumeral kinematics, and any insult to its integrity alters shoulder motion throughout abduction [24]. Tightening of the rotator interval decreases posterior and inferior translation [26]. Anterosuperior translation of the humeral head can lead to impingement of the rotator cuff against the coracoacromial arch [37]. Overtightening of the anterior structures can result in greater joint reaction forces directed toward the posterior portion of the glenoid [37]. Overtightening of the anterior structures can cause excessive posterior glenoid articular cartilage wear, posterior bony erosion, and osteoarthritis [37]. This process of arthrosis resulting from anterior capsular contracture is called capsulorrhaphy arthropathy [37]. Glenohumeral internal rotation deficit is associated with partial articular-sided rotator cuff tears, labral tears, and ulnar collateral ligament tears of the elbow [37].

Common Sites of Injury

Proximal Humerus

The greater tuberosity (GT) serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons of the rotator cuff, while the lesser tuberosity (LT) serves as the attachment site for the subscapularis tendon [1]. Following a fracture of the proximal humerus, displacement of each “part” occurs in a predictable manner based on the deforming forces created by the tendinous insertions of the pectoralis major, subscapularis, supraspinatus, and infraspinatus [1]. Specifically, the subscapularis inserts on the lesser tuberosity and causes medial displacement [1]. The supraspinatus and infraspinatus insert on the greater tuberosity and cause superior and posterior displacement [1]. A fracture involving the anatomic neck is prognostically worse than fractures involving other regions of the proximal humerus with respect to the potential disruption of the vascular supply to the humeral head and the subsequent development of avascular necrosis [1].

Displaced proximal humeral fractures can impede normal movement of the rotator cuff, subacromial bursa, and subdeltoid bursa, causing impingement and disruption of normal glenohumeral motion [1]. In proximal humeral fractures, the subdeltoid and subacromial bursae can become thickened and fibrotic, forming adhesions that can limit normal glenohumeral motion [1].

Glenohumeral Joint and Labrum

The glenoid serves as the attachment for the labrum and joint capsule [1]. Tears of the subscapularis have greater biomechanical consequences than do tears of the infraspinatus [56].

Acromioclavicular Joint

The most common mechanism for injury to the acromioclavicular joint 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 [96]. Indirect mechanisms of acromioclavicular joint injury are exceedingly rare [96]. A fall onto the adducted upper limb can drive the humeral head into the inferior aspect of the acromion, subjecting the acromioclavicular joint to variable degrees of injury [96].

The acromioclavicular ligaments offer the weakest resistance to forces that push the acromion inferiorly and medially [96]. Stronger resistance to forces pushing the acromion inferiorly and medially is afforded by the intact clavicle and sternoclavicular joint [96]. 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, resulting in an inferior dislocation of the clavicle beneath the coracoid process [96].

In type I acromioclavicular injuries, the acromioclavicular ligaments sustain a mild-to-moderate sprain while maintaining joint integrity [96]. In type I acromioclavicular injuries, the coracoclavicular ligaments and the deltoid and trapezius muscles are normal [96].

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 [31]. Injury to the thrower’s shoulder joint occurs most commonly in the late cocking or early acceleration phases [31]. Abnormal scapulothoracic and glenohumeral motion can injure the superior and posterosuperior labrum as well as the undersurface of the rotator cuff and posterior capsule [31].

Adaptive pathology of osseous and soft tissue structures in the throwing shoulder allows the shoulder to accommodate extremes of horizontal extension and external rotation, resulting in a shoulder that is relatively “loose in the front” and “tight in the back” [118]. Corresponding pathology in the throwing shoulder 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 [118]. As many as 50% of asymptomatic, professional-level pitchers have a partial-thickness rotator cuff tear and/or a SLAP lesion on MRI [118]. As many as 80% of asymptomatic, mature pitchers had MRI changes and 45% had a labral tear [118].

Surgical Anatomy

Bony Anatomy

The articular head of the proximal humerus is spherical with a diameter of 37 to 57 mm [1]. Humeral version averages 29.8 degrees, with a range of 10 to 55 degrees [1]. The bicipital groove lies between the greater and lesser tuberosities and serves as a pathway for the long head of the biceps tendon [1]. The surgical neck represents an indistinct region, or metadiaphyseal junction, below the tuberosities but above the humeral shaft [1]. The acromion, coracoacromial ligament, and coracoid process form the coracoacromial arch [1].

Soft Tissue Anatomy

The greater tuberosity serves as the attachment site for the supraspinatus, infraspinatus, and teres minor tendons [1]. The biceps tendon within the bicipital groove is covered by the transverse humeral ligament [2].

Vascular Anatomy

The anterior humeral circumflex artery provides vascular inflow to the humeral head by way of its terminal anterolateral branch, known as the artery of Laing or arcuate artery [1]. Fractures of the anatomic neck have a poor prognosis because of complete disruption of the blood supply to the head [2]. With surgical neck fractures, the blood supply to the head is preserved [2].

Nerve Anatomy

The brachial plexus and axillary artery are 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 [110]. 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 [110]. The radial 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 [110]. It is increasingly vulnerable as it 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 [110]. The radial nerve proper diverges from the posterior antebrachial cutaneous branch and enters the interval between the brachialis and brachioradialis [110]. The radial nerve is commonly injured in humeral shaft fractures, particularly at the junction of the middle and distal third (Holstein-Lewis fracture) [2].

Regarding the axillary nerve, in 19 of 102 cadaveric shoulders (19.6%), the main portion of the anterior division was closer than 5 cm from the palpable edge of the acromion at some point along its course [41]. The distance of the nerve branches to the anterior border of the glenoid may be as little as 1 cm [43]. Distances defining safe zones for the axillary nerve may be affected by humeral head size and are relevant for defining safe zones during shoulder surgery [64]. The axillary nerve can be found approximately 63 mm from the anterolateral tip of the acromion during an anterolateral deltoid splitting approach [110].

Key Evidence

• [L5] The biomechanical shoulder model is consistent with clinical observations. [4] (10.1016/j.jse.2016.05.031)
• [L2] A clinical evaluation of altered shoulder kinematics is still complicated. [7] (10.3390/ijerph17082974)
• [Paper] The evolution of the shoulder exemplifies anatomical adaptation to environmental requirements. [8] (10.1016/s1058-2746(96)80472-1)
• [L5] The glenocapsular ligament is a constant anatomical structure that consists of one or two different parts. [9] (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. [15] (10.1016/j.jse.2006.09.007)
• [L5] The rotator interval is central to normal glenohumeral kinematics, and any insult to its integrity alters shoulder motion throughout abduction. [24] (10.1186/s12891-016-0898-x)
• [L5] Our findings support the existence of a significant population of mechanoreceptors in capsular and juxtalabral tissue of the human shoulder. [35] (10.1016/s1058-2746(95)80028-x)
• [L5] In 19 of 102 cadaveric shoulders (19.6%) the main portion of the anterior division of the axillary nerve was closer than 5 cm from the palpable edge of the acromion at some point along its course. [41] (10.1016/s1058-2746(09)80014-1)
• [L5] The distance of the nerve branches to the anterior border of the glenoid may be as little as 1 cm. [43] (10.1016/s1058-2746(05)80009-6)
• [L5] In healthy adult shoulders, ligamentous structures are not fully elongated in many positions but function as restraints at the extremes of motion. [48] (10.1186/1749-799x-7-29)
• [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. [54] (10.1186/s12891-016-0971-5)
• [L5] Tears of the subscapularis have greater biomechanical consequences than do tears of the infraspinatus. [56] (10.1016/j.arthro.2009.09.007)
• [L4] Both sets of distances may be affected by humeral head size and are relevant for defining safe zones during shoulder surgery. [64] (10.1016/j.jse.2020.08.005)
• [L5] A more complete glenohumeral capsular release may be necessary in certain clinical situations. [66] (10.1016/j.jse.2007.02.117)
• [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. [68] (10.1016/j.jse.2007.02.138)
• [L5] Posterior shoulder tightness resulted in scapular malposition, with muscular and capsular components affecting scapular position differently. [80] (10.1016/j.jse.2019.05.040)
• [L5] The anatomic superior capsule has a negligible role in preventing the superior translation of the humeral head. [89] (10.1016/j.arthro.2018.06.025)
• [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. [101] (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. [125] (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. [130] (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. [131] (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. [133] (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. [135] (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. [136] (10.1177/03635465010290061001)
• [L4] Knowledge concerning these aberrant muscles is indispensable in minimizing confusion concerning surgical anatomy and in achieving adequate exposure of the shoulder during surgery while preserving the anterior circumflex artery, which constitutes the main nutrient vessel of the humeral head. [137] (10.1016/s1058-2746(99)90054-x)
• [L5] It demonstrates poor vascular supply to the anterosuperior portion of the glenoid, as well as the fact that circumferentially around the glenoid, there is an area of approximately 5 mm from the edge of the glenoid rim that is completely devoid of vascularity, with no blood supply from either the capsule or local muscle. [138] (10.1016/j.jse.2005.07.015)
• [Paper] The planar concept of shoulder motion must give way to a spherical frame of reference to meet the challenge of describing complex shoulder motions. [140] (10.1016/1058-2746(92)90017-w)
• [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. [142] (10.1186/s12891-024-07829-9)
• [L4] The anatomy of the rotator interval as viewed arthroscopically is complex and variable. [143] (10.1016/j.jse.2012.08.024)
• [L5] The access to the rotator cuff from almost every portal is influenced by the acromial shape. [145] (10.1186/s13018-019-1486-1)
• [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. [147] (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. [148] (10.1177/17585732241229068)
• [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)

See Also

• Rotator Cuff
• Fractures
• Os Acromiale
• Shoulder Arthroplasty
• Capsular Release for Frozen Shoulder
• Soft Tissue Structures

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[64] Defining the proximity of the axillary nerve from defined anatomic landmarks: an in vivo magnetic resonance imaging study. Journal of Shoulder and Elbow Surgery. 2021. DOI: 10.1016/j.jse.2020.08.005

[66] Glenohumeral joint volume reduction with progressive release and shifting of the inferior shoulder capsule. Journal of Shoulder and Elbow Surgery. 2007. DOI: 10.1016/j.jse.2007.02.117

[68] 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

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

[80] Posterior shoulder tightness can be a risk factor of scapular malposition: a cadaveric biomechanical study. Journal of Shoulder and Elbow Surgery. 2020. DOI: 10.1016/j.jse.2019.05.040

[89] 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

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

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

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

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

[101] 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

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

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

[110] 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.

[112] 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.

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

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

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

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

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

[125] 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

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

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

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

[131] 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

[133] 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

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

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

[137] Aberrant muscle anterior to the shoulder joint: Its clinical relevance. Journal of Shoulder and Elbow Surgery. 1999. DOI: 10.1016/s1058-2746(99)90054-x

[138] Arterial supply of the glenoid: An anatomic study. Journal of Shoulder and Elbow Surgery. 2006. DOI: 10.1016/j.jse.2005.07.015

[140] Codman's paradox: Sixty years later. Journal of Shoulder and Elbow Surgery. 1992. DOI: 10.1016/1058-2746(92)90017-w

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

[143] Variability of the capsular anatomy in the rotator interval region of the shoulder. Journal of Shoulder and Elbow Surgery. 2013. DOI: 10.1016/j.jse.2012.08.024

[145] 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

[147] 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

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

[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