Shoulder

Anatomy and Biomechanics of the Rotator Cuff Matsen Ch. 1 / Burkhart et al.

From a clinical standpoint, the shoulder gains its remarkable range of motion by accepting relatively little bony constraint. The glenoid is shallow in relation to the much larger humeral head, so stability cannot depend on bone shape alone. Instead, normal joint control relies on the combined contribution of the capsulolabral and ligamentous restraints, coordinated muscle forces, and preserved osseous anatomy [1]. Dynamic compression from the rotator cuff helps keep the humeral head centered on the glenoid during motion, complementing the static restraints and allowing mobility without sacrificing functional stability [26] [28].

Clinically, shoulder motion is described in six principal directions. Flexion elevates the arm anteriorly, whereas extension carries it posteriorly. Abduction moves the arm away from the trunk, while adduction returns it toward the body. Internal rotation rotates the humerus medially and external rotation rotates it laterally. These movements are best understood as motions of the shoulder complex rather than of the glenohumeral articulation in isolation, because coordinated scapular and clavicular motion contributes progressively as the arm is elevated [1] [5].

Range of motion should therefore be interpreted as a clinical spectrum rather than as a single fixed value. In a large community-based cohort of adults without shoulder pain or stiffness, mean active right-shoulder flexion was approximately 159–162° and mean active abduction approximately 150–152°, with both measures declining with age; external rotation also showed age-related variation [45]. Extension and adduction are assessed as smaller posterior and medial arcs, while internal- and external-rotation measurements are particularly dependent on the starting position and examination technique. All six directions—flexion, extension, abduction, adduction, internal rotation, and external rotation—are routinely quantified during clinical shoulder range-of-motion assessment [46]. These movements can be viewed directly in Figure 1.1 — General Movements of the Shoulder.

Osteological Foundations

A practical understanding of shoulder disease begins with three bones that shape the shoulder complex: the scapula, clavicle, and proximal humerus.

The Scapula provides the mobile base on which much of shoulder function depends [1]. Important landmarks include the glenoid cavity, which has been described as having slight retroversion and superior tilt [17]; the coracoid process, which gives attachment to several muscles and the coracoclavicular ligaments [18]; and the spine of the scapula, which continues laterally into the acromion [1]. The shape of the acromion also influences the available space beneath it [2].

A

B

C

D

A complete three-dimensional view of the scapula can be appreciated in the rotating model below; see Figure 1.2A — 3D Rotation of the Human Scapula.

The Clavicle acts as an S-shaped strut between the upper limb and the axial skeleton, articulating medially with the sternum at the sternoclavicular joint and laterally with the acromion at the acromioclavicular joint [1] [19]. It also provides attachment for several important muscles of the shoulder girdle and neck [1]. Medially, the clavicular head of the sternocleidomastoid arises from the superior surface of the clavicle, while the clavicular head of the pectoralis major originates from its anterior surface [1]. Laterally, the clavicular fibers of the deltoid arise from the anterior aspect of the lateral clavicle, whereas the trapezius attaches along its posterior aspect [1]. These major muscular attachment sites are illustrated in (Figure 1.8). Its inferior surface contains several clinically important landmarks, including the conoid tubercle and trapezoid line, which provide attachment for the two components of the coracoclavicular ligament, as well as the costoclavicular impression and subclavian groove [18]. These landmarks can be appreciated in the inferior view of the clavicle shown below (Figure 1.7). They are particularly relevant when considering clavicular fractures and surgical approaches, especially because the subclavian vessels and brachial plexus lie immediately deep to the clavicle [1] [20].

Proximal Humerus: Anatomy and Clinical Relevance

The humerus forms the bony foundation of the arm, and its proximal end forms the humeral side of the glenohumeral joint [1] [9]. The rounded humeral head articulates with the glenoid cavity, while the anatomical neck marks the margin of the articular surface [1]. Immediately adjacent to it are the greater tubercle laterally and the lesser tubercle anteriorly [9]. These tubercles are particularly important in shoulder anatomy because they provide the bony attachment sites for the rotator cuff tendons: the supraspinatus, infraspinatus, and teres minor attach to the greater tubercle, whereas the subscapularis attaches to the lesser tubercle [1] [11]. Between the two tubercles lies the intertubercular groove, or bicipital groove, which provides a passage for the tendon of the long head of the biceps [1] [4]. Distal to the tubercles, the proximal humerus narrows at the surgical neck before continuing into the shaft [9]. These major landmarks are shown in (Figure 1.9).

These landmarks are not simply descriptive anatomy; they repeatedly become important when evaluating shoulder pathology [1]. The tubercles are directly related to rotator cuff function and may be involved in proximal humeral fractures [9], while the intertubercular groove is closely related to disorders of the long head of the biceps [4]. The surgical neck is also a clinically important region in proximal humeral fractures, where displacement may be associated with injury to nearby neurovascular structures, particularly the axillary nerve [9] [10].

The region around the intertubercular groove is also an important site of muscular attachment [1]. The pectoralis major inserts along the lateral lip of the intertubercular groove, the latissimus dorsi attaches within the floor of the groove, and the teres major inserts along its medial lip [10]. Their close relationship to the proximal humerus is useful when interpreting tendon injuries and when identifying surgical anatomy around the anterior humerus [10]. These insertion sites are illustrated in (Figure 1.10).

Rotator Cuff: Functional Anatomy, Innervation and Vascular Supply

Functional Myology and Force Couples

Around the humeral head, the rotator cuff tendons blend into a continuous musculotendinous covering that contributes to dynamic control of the joint [5]. Burkhart and colleagues used the “suspension bridge” concept to describe the biomechanical role of the rotator cable within this system [6].

Glenohumeral Joint Capsule, Glenohumeral Ligaments and Labrum

Glenoid Cavity of the Scapula

The glenoid cavity is a shallow, pear-shaped articular surface on the lateral aspect of the scapula. Its contour is generally narrower superiorly and broader inferiorly, creating the characteristic pear-shaped appearance of the glenoid [1]. The characteristic pear-shaped outline and location of the glenoid cavity can be appreciated in the animation below.

Functionally, the glenoid cavity forms the socket of the glenohumeral joint by articulating with the humeral head. Its relatively shallow geometry permits the extensive range of motion that characterizes the shoulder, but it provides little stability through bony shape alone. Glenohumeral stability therefore also depends on the glenoid labrum, joint capsule, glenohumeral ligaments, and the coordinated action of the surrounding musculature [1].

Other Clinically Important Ligaments of the Shoulder

Several additional ligamentous structures become important when interpreting acromioclavicular injury, subacromial anatomy, and pathology of the long head of the biceps. Their importance is less about acting as one single stabilizing unit and more about how each structure supports a particular region of the shoulder.

The positions of the AC, coracoclavicular, and coracoacromial ligamentous structures can be reviewed in Figure 1.14.

Periarticular Bursae of the Shoulder: Anatomy and Clinical Relevance

The shoulder contains several synovial-lined bursae and recesses positioned at interfaces where tendons, muscles, bone, and ligamentous structures move against one another. Their principal mechanical role is to reduce friction and permit smooth tissue gliding during the shoulder's large range of motion. The clinically most important structures include the subacromial-subdeltoid (SASD) bursa, subscapular recess, subcoracoid bursa, coracoclavicular bursa, and supra-acromial bursa [40].

Subacromial-Subdeltoid Bursa (SASD)

The subacromial-subdeltoid bursa is the largest and most clinically important bursa around the shoulder. It lies superficial to the rotator cuff, particularly the supraspinatus tendon, and deep to the acromion, coracoacromial arch, acromioclavicular region, and deltoid. Its subacromial and subdeltoid portions form a broad gliding plane that reduces friction as the greater tuberosity and rotator cuff pass beneath the coracoacromial arch during elevation of the arm [40].

In the normal shoulder, the SASD bursa does not communicate with the glenohumeral joint. Distension or inflammatory change may occur with subacromial bursitis, rotator cuff disease, mechanical subacromial impingement, infection, trauma, or reactive inflammatory processes. In a full-thickness rotator cuff tear, disruption of the intervening cuff can establish communication between the glenohumeral joint and the SASD bursa, allowing joint fluid to enter the bursal space [40].

Subscapular Recess

The subscapular recess, often termed the superior subscapularis recess, is a synovial extension of the glenohumeral joint related to the superior portion of the subscapularis. This distinction is important because the recess normally communicates with the joint cavity and should not be confused on imaging with the adjacent subcoracoid bursa, which ordinarily does not communicate with the glenohumeral joint [41].

Fluid within the recess may therefore reflect glenohumeral joint fluid rather than primary bursitis. Marked fluid distension of the superior subscapularis recess has also been described as an MRI sign associated with adhesive capsulitis, particularly during the painful freezing phase, although it should be interpreted together with the other clinical and imaging features of frozen shoulder [42].

Subcoracoid Bursa

The subcoracoid bursa occupies the anterior shoulder beneath the coracoid process and is closely related to the anterior surface of the subscapularis. Unlike the subscapular recess, it does not normally communicate with the glenohumeral joint, although an anatomic communication with the SASD bursa may occasionally occur. Its position allows it to reduce friction around the subscapularis and adjacent coracoid structures during shoulder motion [40] [43].

Pathologic distension of the subcoracoid bursa may represent subcoracoid bursitis and can accompany anterior shoulder pathology. MRI studies have demonstrated an association between subcoracoid effusion and tears of the anterior rotator cuff, including lesions involving the rotator interval. Correctly distinguishing this bursa from the communicating subscapular recess is therefore important when interpreting fluid in the subcoracoid region [44].

Coracoclavicular and Supra-acromial Bursae

The coracoclavicular bursa and supra-acromial bursa are smaller and less frequently encountered than the SASD bursa. The coracoclavicular bursa lies in the coracoclavicular region, while the supra-acromial bursa is superficial to the acromion. Both are recognized components of the normal periarticular bursal anatomy of the shoulder [40]. Because these bursae are small and are not routinely conspicuous on imaging, their pathologic distension is much less commonly encountered; when enlarged, a focal bursal process such as inflammation, repetitive mechanical irritation, or trauma should be considered in the appropriate clinical context rather than assuming that all superior shoulder fluid represents SASD bursitis.

Clinical perspective: Bursal fluid should be interpreted according to its precise anatomic compartment. SASD fluid may accompany bursitis, impingement, or rotator cuff tearing; subcoracoid fluid may point toward anterior cuff or rotator-interval disease; and fluid in the subscapular recess can simply track from the glenohumeral joint or become conspicuous in conditions such as adhesive capsulitis [40] [42] [44].

Shoulder Joint Articulations

Rotator Cuff Biomechanics

Concept 1 — Concavity–Compression and Dynamic Humeral Head Centering

Concavity–compression is a central mechanism of dynamic glenohumeral stability. Because the rounded humeral head articulates with a relatively shallow glenoid, stability depends not only on the geometry of the joint but also on compressive forces that keep the articular surfaces opposed [26] [27]. In the classic quantitative model of concavity–compression, increasing compression of the humeral head into the glenoid concavity increases the tangential force required to translate the head across the glenoid rim [26]. Experimental work further demonstrated that the glenoid labrum deepens the effective concavity and contributes measurably to the stabilizing effect of concavity–compression [27].

The rotator cuff provides an important muscular source of this dynamic compression. When the supraspinatus, infraspinatus, teres minor, and subscapularis contract, their combined force components compress the humeral head toward the glenoid and resist unwanted translation while motion continues [28] [26]. Cadaveric analysis has shown that the individual cuff muscles make substantial contributions to dynamic stability in both the mid-range and end-range of motion, with their relative importance changing according to joint position [28]. Functionally, this coordinated compression helps maintain humeral-head centering while preserving the large rotational and elevational excursions required of the shoulder [26] [28]. The concavity–compression mechanism is demonstrated in Figure 1.17.

Concept 2 — Coronal Plane Rotator Cuff Force Couple

During arm elevation, the glenohumeral joint must generate enough torque to raise the humerus while simultaneously limiting excessive superior translation of the humeral head [5] [31]. In the coronal plane force-couple model, the superiorly directed action of the deltoid is balanced by the inferiorly directed stabilizing components of the rotator cuff, particularly the infraspinatus, teres minor, and subscapularis [30] [31]. The resulting balance allows the deltoid and cuff to contribute to elevation while maintaining a stable glenohumeral fulcrum [28] [31].

The deltoid is a major motor of arm elevation, but its line of pull also produces a superior translational tendency at the humeral head [31]. The inferior cuff supplies a counteracting component that limits superior migration and helps preserve humeral-head centering throughout elevation [28] [31]. In a cadaveric shoulder model, simulated abduction with the deltoid alone—or without the stabilizing contribution of the infraspinatus, teres minor, and subscapularis—produced significantly greater superior displacement of the humeral head than conditions in which the cuff was functionally intact [31]. The interaction between the superiorly directed deltoid vector and the counterbalancing inferior cuff force is illustrated in Figure 1.18 [32].

Concept 3 — Rotator Cable–Crescent Complex

The rotator cable–crescent complex describes a distinctive structural organization within the posterosuperior rotator cuff. Burkhart, Esch, and Jolson described the rotator crescent as the relatively thin, crescent-shaped distal portion of the supraspinatus and infraspinatus tendons and the rotator cable as a thicker band of fibers forming the proximal margin of this crescent [6]. In their cadaveric description, the cable was substantially thicker than the adjacent crescent and was proposed to function as a load-transmitting structure across the cuff [6].

This arrangement led to the influential “suspension bridge” model, in which the rotator cable was proposed to transfer tensile load between its anterior and posterior attachments while partly stress-shielding the thinner crescent [6]. Later cadaveric testing supported an important load-bearing role for the anterior cable insertion: tears involving the anterior cable produced greater tear gapping and altered regional tendon strain compared with equivalently sized crescent tears [33].

The suspension-bridge interpretation should not, however, be presented as mechanically absolute. A more recent cadaveric study found that releasing the rotator cable did not measurably change cable or crescent strain during abduction and concluded that the crescent itself remained important for transmitting abduction force to the greater tuberosity [34]. The cable–crescent concept therefore remains highly useful for describing cuff anatomy and tear location, while the exact degree to which the cable stress-shields the crescent remains an area of ongoing biomechanical investigation [33] [34].

Concept 4 — Transverse Force Couple

In the transverse plane, the anterior rotator cuff and posterior rotator cuff generate opposing rotational forces around the humeral head. The subscapularis forms the anterior component, while the infraspinatus and teres minor form the principal posterior component. Their balanced activity permits internal and external rotation while helping maintain the humeral head centered against the glenoid rather than allowing uncontrolled anterior or posterior translation [35] [36].

The functional importance of this balance has been demonstrated experimentally. In a cadaveric deficiency model, glenohumeral ball-and-socket kinematics were maintained when the transverse force couple—subscapularis anteriorly and infraspinatus/teres minor posteriorly—remained intact, whereas disruption of this force couple produced significant alterations in glenohumeral motion [35]. Imaging-based studies provide complementary anatomic support: CT assessment found no significant difference between the muscle volumes of the anterior and posterior components in nonpathologic shoulders [36], while MRI measurements demonstrated significant correlations between the cross-sectional areas of the muscles forming the transverse force couple, supporting the concept of a dynamically balanced shoulder [37].

The transverse force couple can be visualized from complementary perspectives. Figure 1.19 demonstrates this concept from a lateral view, showing the relationship between the anterior subscapularis and the posterior infraspinatus/teres minor around the humeral head [38]. Figure 1.20 shows the transverse force-couple concept from a posterior view, emphasizing the posterior component formed by the infraspinatus and teres minor [39].

Chapter 1 · Self-Assessment

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Innervation, vascular supply, and clinical links.

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Shoulder Impingement Syndromes Neer / Bigliani / Gerber

Shoulder impingement is better viewed as a group of mechanical conflicts rather than a single disorder. The tissues involved and the site of contact vary according to the anatomic space and the position of the arm.

Section 1 — Subacromial Impingement Syndrome

In subacromial impingement, the supraspinatus tendon and subacromial bursa may become compressed beneath the coracoacromial arch, a mechanism classically described by Neer [1]. Bigliani and colleagues later described three commonly cited acromial shapes: Type I (flat), Type II (curved), and Type III (hooked) [2].

Section 2 — Internal Impingement

Internal impingement is seen particularly in overhead activity, where the articular side of the rotator cuff can contact the posterosuperior glenoid-labral region and the greater tubercle [3].

Section 3 — Coracoid Impingement

Coracoid impingement is different: the conflict occurs anteriorly when the subcoracoid space becomes reduced [4].

Rotator Cuff Tears Ellman / Cofield / Goutallier

Rotator cuff disease is best understood as a spectrum rather than as one uniform lesion. Tendon change may begin with degeneration and tendinopathy, progress to a defect involving only part of the tendon thickness, or become a full-thickness tear that crosses the entire tendon. A tear may remain limited to one tendon or extend into neighboring cuff tendons. Longitudinal observations of degenerative cuff disease also show that some tears enlarge with time, although progression is not inevitable and differs considerably between patients [4].

As a tear becomes larger or more chronic, the problem may no longer be confined to the tendon defect itself. The torn tendon can retract medially, while the muscle attached to it may lose volume and develop fatty infiltration. These findings describe different features of the musculotendinous unit: tear size describes the dimensions of the defect, retraction describes how far the detached tendon has moved from its insertion, and atrophy and fatty infiltration describe changes within the muscle. They should therefore be assessed separately rather than used interchangeably [3] [11].

This distinction matters clinically because the anatomy of the tear, tendon mobility, chronicity, and muscle quality all contribute to treatment planning and to the surgeon's assessment of whether an anatomic repair is likely to be achievable and durable. None of these features should be considered in isolation, and a large tear is not automatically irreparable simply because of its measured size [11] [12].

Section 1 — Partial Rotator Cuff Tear

Definition and Morphologic Patterns

A partial-thickness rotator cuff tear disrupts only a portion of the tendon thickness, leaving some tendon fibers intact. This differs from a full-thickness tear, in which the defect extends completely through the tendon. Partial tears are commonly described according to the surface or layer in which the defect is located. An articular-sided tear involves the deep surface facing the glenohumeral joint, a bursal-sided tear involves the superficial surface adjacent to the subacromial-subdeltoid bursa, and an intrasubstance or interstitial tear lies within the tendon without initially reaching either surface [1].

A commonly used term for an articular-sided partial tear of the supraspinatus is a PASTA lesion (partial articular-sided supraspinatus tendon avulsion). The label identifies the side and tendon involved; it does not by itself describe the depth, chronicity, or overall size of the lesion.

Ellman Classification

Ellman proposed an arthroscopic system that describes partial-thickness tears by both location and depth [1]. In this framework, type A is articular-sided, type B is bursal-sided, and type C is interstitial. Depth is graded separately: grade I tears are less than 3 mm deep, grade II tears measure 3 to 6 mm, and grade III tears extend more than 6 mm into the tendon. These measurements were intended to standardize arthroscopic description and should be interpreted together with the tendon involved, tissue quality, and the clinical context rather than as a complete description of the lesion.

Etiology and Pathogenesis

Partial-thickness tearing can arise in more than one setting. Degenerative change within the tendon may reduce the ability of collagen fibers to tolerate repeated loading, while mechanical contact and repetitive overhead use can add further stress in susceptible shoulders. The relative contribution of intrinsic tendon degeneration and extrinsic mechanical factors varies between patients, so these mechanisms are better viewed as overlapping influences rather than mutually exclusive causes [1] [8] [9].

Clinical Presentation

Symptoms are variable. Patients may describe pain over the lateral or superolateral shoulder, discomfort with elevation or overhead activity, and difficulty with tasks that repeatedly load the cuff. The clinical picture does not reliably reveal the exact depth or surface of a partial tear, and similar symptoms can occur with subacromial bursitis, tendinopathy, or other shoulder disorders. History, examination, and imaging therefore need to be interpreted together.

Physical Examination

Examination usually combines assessment of active and passive motion with strength testing and selected provocative maneuvers. The Jobe (Empty Can) test places the supraspinatus under resisted elevation and is used clinically when supraspinatus dysfunction is suspected [7]. The Neer impingement sign provokes the subacromial region during forced forward elevation [8], while the Hawkins-Kennedy test uses forward elevation with internal rotation to reproduce symptoms associated with subacromial contact [9]. A positive result contributes to the overall clinical picture, but no single one of these maneuvers establishes the presence, side, or depth of a partial-thickness tear on its own.

Imaging

Ultrasound and MRI are both used to evaluate rotator cuff integrity. In a prospective comparison using arthroscopy as the reference standard, Teefey and colleagues found that experienced ultrasonography and MRI could both identify partial- and full-thickness cuff tears, while MRI also provides broader assessment of adjacent bone, muscle, labrum, and joint structures [9]. MR arthrography can provide additional detail for articular-sided partial tears, although its performance varies with tear type and small defects may remain difficult to characterize [10]. Imaging findings should be correlated with symptoms and examination rather than interpreted in isolation.

Natural History

Partial tears do not follow a single predictable course. In the classic arthrographic follow-up study by Yamanaka and Matsumoto, some articular-sided tears enlarged and some progressed to full-thickness defects, while others decreased in size or were no longer visible on follow-up imaging [6]. More recent longitudinal work on degenerative cuff disease likewise found that enlargement can occur over time, but the risk is not identical for every tear [4]. For this reason, the presence of a partial tear should not be presented as an inevitable pathway to a complete rupture.

Management Overview

Initial management is commonly guided by symptoms, functional limitation, tear characteristics, patient activity, and previous treatment. A nonoperative program may include activity modification and structured rehabilitation aimed at restoring motion, cuff and scapular muscle function, and tolerance of daily or overhead loading. Surgery may be considered when clinically meaningful symptoms persist despite an appropriate nonoperative trial or when the structural pattern and functional demands make operative treatment reasonable. The decision is individualized rather than determined by one imaging measurement alone.

Section 2 — Total Rotator Cuff Tear

Definition

A full-thickness rotator cuff tear extends through the complete thickness of the involved tendon, creating a pathway between its articular and bursal surfaces. The defect can be focal or broad, may involve one tendon or several tendons, and can differ substantially in shape, retraction, tissue quality, and chronicity. For this reason, the words “full thickness” define the depth of the tear but do not by themselves describe its overall severity.

Tear Size and Cofield Classification

Cofield's commonly used size-based system groups full-thickness tears according to the greatest measured dimension of the tendon defect [2]. In this framework, tears are described as small when they measure less than 1 cm, medium at 1 to 3 cm, large at 3 to 5 cm, and massive when the measured defect exceeds 5 cm. Tear size is useful descriptive information, but it does not show how far the tendon has retracted or what condition the corresponding muscle is in.

Tendon Retraction and Chronicity

Once a tendon is completely detached, its free edge may move medially away from the greater or lesser tuberosity. This tendon retraction is a separate feature from the width or length of the tear itself. With chronic tears, retraction may coexist with progressive changes in the musculotendinous unit, making assessment of tendon mobility and tissue quality increasingly relevant when planning repair [11].

Muscle Atrophy and Fatty Infiltration

Chronic cuff tears may be accompanied by loss of muscle bulk and replacement of normal muscle tissue by fat. These changes are clinically important because they reflect the condition of the muscle attached to the torn tendon and can persist even after the tendon is repaired. In longitudinal studies, enlargement of degenerative tears has been associated with progression of muscle degeneration [4], while surgical series have shown that more advanced fatty degeneration is associated with less favorable structural and functional results after repair [12].

Goutallier Classification

Goutallier and colleagues described a five-stage system for grading fatty degeneration of the rotator cuff muscles on cross-sectional imaging [3]. Grade 0 indicates no visible fat; grade 1 shows a few fatty streaks; grade 2 contains less fat than muscle; grade 3 contains approximately equal amounts of fat and muscle; and grade 4 contains more fat than muscle. This system describes muscle quality, not tear size.

Massive Tears and Reparability

The term massive rotator cuff tear has not always been defined in the same way. Size-based descriptions have used a defect greater than 5 cm, whereas other shoulder literature has emphasized complete involvement of at least two cuff tendons [2] [11]. “Massive,” however, does not mean the same thing as “irreparable.” Reparability is a surgical judgment that considers whether the tendon can be mobilized back to an acceptable insertion without excessive tension, together with the degree of retraction, tissue quality, chronicity, and the condition of the cuff muscles.

Clinical perspective: A complete rotator cuff tear should therefore be described in several dimensions rather than by a single label: which tendon or tendons are involved, the size and configuration of the defect, the degree of retraction, the chronicity of the lesion, and the amount of muscle atrophy or fatty infiltration. These features answer different clinical questions and should not be collapsed into one measure of “severity.”

Biceps Pathology Snyder / Walch / Biceps Pulley

The long head of the biceps tendon (LHBT) is closely related to the superior labrum, the rotator interval, and the structures of the bicipital pulley. Because these structures function together, pathology in this region can present as a significant source of anterior shoulder symptoms and may coexist with rotator cuff disease [1] [2].

Section 1 — Biceps Tear

A Superior Labrum Anterior to Posterior (SLAP) lesion involves the superior labral region around the attachment of the long head of the biceps. Snyder and colleagues described the classic Types I through IV according to the pattern of superior labral and biceps-anchor involvement [3]. The active compression test is one of the historically described provocative maneuvers used in the clinical assessment of superior labral and acromioclavicular pathology [4].

Section 2 — Biceps Subluxation

Definition and Mechanical Concept

Subluxation of the long head of the biceps is a form of tendon instability in which the LHBT no longer remains normally centered within the intertubercular (bicipital) groove throughout shoulder motion. The tendon may ride onto or over the medial rim of the groove while retaining some contact with it. This differs from a true dislocation, in which the tendon loses contact with the groove and lies outside its normal osseous track [5].

Why the Tendon Subluxates: The Bicipital Pulley

The LHBT is not stabilized by the bony groove alone. At the rotator interval and the superior entrance to the groove, the tendon is restrained by the bicipital reflection pulley, formed principally by the superior glenohumeral ligament and coracohumeral ligament in continuity with the superior border of the subscapularis [1] [6]. Disruption of this stabilizing complex can permit abnormal medial translation or subluxation of the LHBT and can be associated with subsequent tendon degeneration [6]. In Walch and colleagues’ surgical series, LHBT subluxation was closely associated with partial tearing of the subscapularis and frequently accompanied supraspinatus tearing [5].

Clinical Presentation

The classic symptomatic pattern is anterior shoulder pain associated with a mechanical sensation such as painful snapping, popping, or shifting of the tendon during shoulder rotation or elevation. Athletic descriptions of LHBT subluxation emphasize tenderness over the bicipital groove and a reproducible pop during humeral rotation [7]. In strength athletes, the same mechanical symptoms may become particularly noticeable during loaded upper-body movements that repeatedly stress the anterior shoulder. Resistance-training literature documents shoulder pain and shoulder injury as clinically important problems in weight-training athletes, while proximal biceps disorders in athletic populations are characteristically aggravated by activity [8] [9].

Examination may reproduce pain with palpation of the bicipital groove and with maneuvers that load the biceps, including resisted elbow flexion or forearm supination. Speed, Yergason, upper-cut, and related tests can support the clinical suspicion, but their diagnostic performance varies; they should therefore be interpreted together with the history and imaging rather than used as stand-alone proof of a biceps lesion [10].

Imaging: What to Look for on Axial MRI

On axial MRI, the normal LHBT is seen as a low-signal round or oval tendon related to the bicipital groove [11] [12]. Suspicion for subluxation increases when the tendon is displaced toward or over the medial rim of the groove and when this abnormal relationship persists across sequential axial cuts; arthroscopy-correlated MRI work has specifically used displacement of the tendon over the inner rim of the bicipital groove with some remaining groove contact as an imaging criterion for subluxation [13]. MRI assessment should also include the superior subscapularis, the superior glenohumeral ligament, the adjacent supraspinatus, and the remainder of the pulley complex [14]. In an arthroscopy-correlated study, medial LHBT subluxation on transverse MR arthrographic images was a useful sign of a pulley lesion, while the complete diagnosis benefited from assessment of the SGHL and adjacent cuff structures [14].

Ultrasound provides an additional method of assessing the long-head biceps and can be particularly useful when instability is suspected. In a prospective comparison with arthroscopy, ultrasound demonstrated high diagnostic performance for LHBT subluxation or dislocation [15].

Associated Tenosynovitis

Mechanical instability and tendon-sheath inflammation can coexist. MRI findings associated with bicipital tenosynovitis include abnormal tendon signal or contour and abnormal fluid or synovial change around the tendon sheath; these findings must be interpreted in the context of the complete examination because biceps-sheath fluid can accompany other shoulder pathology [16]. The teaching case below demonstrates the relationship between the clinical history, sequential axial MRI, and an annotated image of the associated inflammatory change.

Acromioclavicular Joint Diseases Rockwood / Shaffer / Walton

Disorders of the acromioclavicular (AC) joint include both acute traumatic injuries and longer-term degenerative conditions. The clinical picture therefore ranges from ligament injury after trauma to symptomatic osteoarthritis.

Section 1 — Dislocations

The Rockwood classification groups traumatic AC joint injuries into six types according to the pattern and severity of disruption [1].

Section 2 — AC Joint Inflammation

The acromioclavicular (AC) joint is a small synovial articulation that can become painful through several different mechanisms. In clinical practice, the phrase AC joint inflammation is best used as an umbrella description rather than as a single diagnosis: symptomatic inflammation may accompany primary or post-traumatic osteoarthritis, repetitive-load injury such as distal clavicle osteolysis, systemic inflammatory or crystal arthropathy, and—much less commonly—infection. Degenerative change on imaging is common and may be asymptomatic, so the diagnosis should always correlate the patient's pain pattern, focused examination, and imaging rather than relying on an isolated radiographic abnormality [4].

Major Inflammatory and Painful AC Joint Patterns

Clinical Presentation

Symptomatic AC joint inflammation most often produces focal superior shoulder pain centered directly over the AC joint. The discomfort may be a persistent ache at rest and become sharper when the arm is brought across the chest, when the patient pushes through the upper extremity, performs pressing exercises, reaches to the opposite shoulder, or lies directly on the affected side. Pain that is diffuse, extends well below the elbow, or is dominated by weakness or cervical symptoms should broaden the differential diagnosis beyond the AC joint [10].

Physical Examination

• Inspection: look for focal swelling, erythema, a chronic step deformity from previous AC separation, or asymmetry of the distal clavicle.
• Direct palpation: reproduce the patient's familiar pain by palpating the joint line rather than the surrounding deltoid or trapezius. Local AC tenderness is sensitive but not highly specific for an injection-confirmed AC pain source [10].
• Cross-Body Adduction (Scarf) Test: with the shoulder elevated to approximately 90°, the arm is passively adducted horizontally across the chest. Reproduction of the patient's focal superior AC pain is considered positive. The maneuver loads and compresses the AC joint, but it should be interpreted with the rest of the examination rather than used alone [11].
• Paxinos sign: compression of the distal clavicle and acromion can reproduce AC pain and may complement other provocative maneuvers. No single special test has sufficient diagnostic strength in every clinical setting, so combinations of findings are more useful than an isolated positive maneuver [12].
• Active Compression (O'Brien) test: this maneuver may be used as an adjunct when AC-joint pain is suspected, but—as with other AC provocative tests—its value is greater when interpreted together with the history, focal tenderness, and the rest of the examination rather than in isolation [12].
• Complete shoulder examination: assess active and passive motion, rotator cuff strength, subacromial provocative signs, biceps/labral features, scapular mechanics, cervical screening, and neurovascular status so that concomitant or alternative sources of shoulder pain are not missed.

Clinical principle: degenerative AC findings on radiographs or MRI do not automatically prove that the AC joint is the pain generator. Concordant focal tenderness, symptom reproduction during AC-loading maneuvers, and—when uncertainty remains—a carefully performed diagnostic local-anesthetic injection can strengthen the clinical attribution [4].

Imaging

Plain radiographs remain useful for evaluating joint-space narrowing, osteophytes, distal-clavicle resorption, chronic deformity, and other osseous abnormalities. A Zanca view provides a focused radiographic assessment of the AC joint [2]. MRI is particularly useful when the diagnosis is uncertain or when associated soft-tissue and marrow abnormalities must be assessed. In symptomatic AC osteoarthritis, reported MRI features include bone-marrow edema, inferior joint distension, inferior osteophytes, and impression on the supraspinatus; bone-marrow edema was strongly associated with symptomatic disease in one comparative study [13].

Management Principles

Management is directed at the underlying cause. For noninfectious mechanical or degenerative AC pain, initial care commonly includes temporary modification of painful loading, analgesic or anti-inflammatory medication when medically appropriate, ice or other symptom-modifying measures, and rehabilitation aimed at restoring comfortable shoulder motion and scapular/shoulder mechanics [4] [5]. Distal clavicle osteolysis often requires specific modification of provocative training loads [6].

A targeted AC joint injection containing local anesthetic with or without corticosteroid may be used selectively for diagnostic clarification and short-term symptom control in appropriately selected noninfectious cases. Ultrasound guidance improves the accuracy of AC joint infiltration compared with palpation-guided placement [14]. Persistent, well-localized symptomatic osteoarthritis or distal clavicle osteolysis that fails appropriate nonoperative treatment may be considered for distal clavicle excision; the classic procedure is associated with the name Mumford [3] [5].

Calcific Tendinitis Uhthoff & Loehr

Calcific tendinitis is a cell-mediated disorder in which deposits composed largely of hydroxyapatite develop within a rotator cuff tendon [1].

Pathophysiological Phases and Interventions

Uhthoff described the condition as progressing through pre-calcific, calcific, and post-calcific stages. The calcific stage itself includes formative and resorptive phases, reflecting changes in the deposit over time [1].

Frozen Shoulder Neviaser / Zuckerman

Frozen shoulder, or adhesive capsulitis, develops through a combination of inflammation and progressive capsular tightening. Synovial inflammation is followed by fibrosis and contracture, with prominent involvement of structures such as the rotator interval and axillary recess [1].

Clinical Course and Management

Diabetes mellitus is one of the best-recognized clinical conditions associated with adhesive capsulitis [2].

Shoulder Instability Anterior / Posterior / Bipolar Bone Loss

Shoulder instability describes symptomatic loss of normal glenohumeral centering and may present as a frank dislocation, recurrent subluxation, or position-dependent apprehension. The direction of abnormal translation is clinically important because anterior and posterior instability have different injury mechanisms, characteristic soft-tissue and osseous lesions, examination findings, and reconstructive strategies.

Section 1 — Anterior Shoulder Instability

Anterior glenohumeral dislocation is the classic traumatic instability pattern of the shoulder. In the usual mechanism, the arm is forced into a vulnerable combination of abduction and external rotation, often with extension, allowing the humeral head to translate anteroinferiorly beyond the glenoid rim. The event is not simply a temporary loss of joint congruity: it can permanently deform or detach the capsulolabral stabilizers and can injure both the anterior glenoid and the posterolateral humeral head. Experimental work has shown that anterior dislocation can produce non-recoverable strain within the glenohumeral capsule, providing a biomechanical explanation for persistent laxity after the joint has been reduced [16].

Mechanism and Pathoanatomy

The principal static restraint that fails during traumatic anterior instability is commonly the anteroinferior capsulolabral complex. Detachment of the anteroinferior labrum from the glenoid rim is the classic Bankart lesion [1]. Capsular stretching or tearing may coexist with the labral lesion, and in some patients the injury extends to the glenoid rim as a bony Bankart lesion. On the humeral side, the posterolateral humeral head may impact against the anterior glenoid during dislocation, producing the characteristic Hill-Sachs lesion [2].

These lesions should be considered together rather than as isolated findings. Repeated instability can progressively enlarge anterior glenoid bone loss and humeral-head impaction damage, reducing the effective articular arc available to contain the humeral head. Clinical series of failed arthroscopic Bankart repair demonstrated that substantial glenoid deficiency and engaging Hill-Sachs lesions are powerful structural causes of recurrent instability [13]. Cadaveric work likewise showed that an anterior glenoid defect can significantly compromise anteroinferior stability even after Bankart repair [14].

Clinical Pattern and Risk of Recurrence

Patients with anterior instability often describe a traumatic event followed by pain, loss of motion, visible deformity when the shoulder is dislocated, or a subsequent sense that the shoulder may "come out" when the arm is brought into abduction and external rotation. After reduction, some shoulders become clinically stable, whereas others progress to recurrent subluxation, recurrent frank dislocation, or persistent apprehension. Age is one of the strongest clinical modifiers of recurrence: long-term prospective follow-up has shown particularly high recurrence in adolescents and young adults after a first-time traumatic anterior dislocation treated nonoperatively [12].

Imaging and Bone-Loss Assessment

Initial imaging confirms the direction of dislocation, excludes associated fracture, and documents the quality of the reduction. In recurrent instability, imaging must move beyond simply asking whether a Bankart or Hill-Sachs lesion is present. The clinically important questions are how much anterior glenoid articular surface has been lost, how large and how medially positioned the Hill-Sachs defect is, and whether the humeral defect can interact with the remaining glenoid during functional positions of risk. Three-dimensional CT is particularly useful for defining glenoid and humeral bone morphology, while MRI or MR arthrography can characterize the labrum, capsule, cartilage, rotator cuff, and associated soft-tissue injury.

The glenoid-track concept provides a biomechanical framework for understanding the interaction between the glenoid and a Hill-Sachs lesion. Yamamoto and colleagues mapped the zone of contact between the glenoid and the humeral head during abduction, external rotation, and horizontal extension, emphasizing that the functional significance of a humeral defect depends on its relationship to the available glenoid track rather than on humeral defect size alone [15]. This concept reinforces why anterior glenoid loss and humeral-head loss should be evaluated as a bipolar instability problem.

Lesion Characteristics and Surgical Management

Management is individualized according to whether the episode is first-time or recurrent, the patient's age and activity demands, the presence of apprehension or recurrent subluxation, the quality of the capsulolabral tissue, and the amount and interaction of glenoid and humeral bone loss. A repairable Bankart lesion in a shoulder without clinically important bone deficiency may be treated with arthroscopic capsulolabral repair when operative stabilization is indicated. In contrast, structural bone loss changes the mechanical problem: Burkhart and De Beer demonstrated markedly higher failure when significant glenoid or humeral defects were ignored during Bankart repair [13].

When anterior instability is accompanied by substantial glenoid bone loss, soft-tissue repair alone may be insufficient. The Latarjet coracoid transfer is one established reconstructive option for selected patients with clinically important anterior glenoid deficiency [3]. When a clinically important Hill-Sachs lesion contributes to instability, the humeral defect may also require treatment; the exact strategy depends on the amount of glenoid loss, the humeral defect, prior surgery, sport or occupational demand, and the overall pattern of instability. The aim is not merely to repair a visible labral tear, but to restore a stable relationship between the humeral head and the effective glenoid articular arc.

Remplissage vs Latarjet — Which Procedure Fits the Bone-Loss Pattern?

Both procedures are used to reduce recurrence in anterior shoulder instability, but they solve different mechanical problems. Remplissage primarily addresses the humeral-sided defect—the Hill-Sachs lesion—whereas the Latarjet primarily reconstructs deficient anterior glenoid bone and adds a dynamic stabilizing effect. Procedure selection therefore depends on the combined or bipolar pattern of bone loss rather than on the presence of a Hill-Sachs lesion alone [13] [15].

Section 2 — Posterior Shoulder Instability

Posterior shoulder instability is less common than anterior instability and spans a spectrum from an acute traumatic posterior dislocation to recurrent posterior subluxation. Acute dislocation may follow direct trauma or a powerful internally rotating muscular contraction, including during seizure, while recurrent posterior instability may also develop through repetitive loading. In a large clinical series of acute posterior dislocations, traumatic accidents were the most frequent cause and recurrent instability developed in a clinically important minority of shoulders [4].

Reverse Hill-Sachs Lesion: How Posterior Dislocation Produces the Defect

During a posterior dislocation, the humeral head translates behind the glenoid. As the humeral head impacts against the posterior glenoid rim, an impression fracture may be created on the anteromedial aspect of the humeral head. This is the reverse Hill-Sachs lesion. It is the posterior-instability counterpart of the classic posterolateral Hill-Sachs lesion seen after anterior dislocation. MRI series of first-time traumatic posterior dislocations have demonstrated a high frequency of reverse Hill-Sachs defects and associated posterocaudal labrocapsular injury [5]. Modern three-dimensional CT analysis also localizes the reverse Hill-Sachs lesion to the anteromedial humeral head [11].

The clinical importance of the defect is not simply its presence but whether its size, depth, orientation, and relationship to the posterior glenoid permit the defect to engage the glenoid rim. Engagement can promote recurrent posterior translation and may make isolated soft-tissue stabilization insufficient. Defect assessment must therefore be integrated with posterior capsulolabral pathology, glenoid morphology or bone loss, chronicity, and the patient's functional demands [8].

Physical Examination

Examination begins with comparison of active and passive motion, scapular mechanics, generalized laxity, and direction-specific instability. Posterior translation can be assessed with posterior load-and-shift or posterior stress maneuvers, while the jerk test and Kim test are commonly used provocative tests for symptomatic posterior or posteroinferior instability [6]. The Kim test was originally described for posteroinferior labral lesions, and combining it with the jerk test improved sensitivity in the original diagnostic cohort [7]. No single examination maneuver should be interpreted in isolation; the clinically relevant finding is reproduction of the patient's pain, apprehension, posterior shift, or symptomatic clunk in a pattern consistent with the history and imaging.

Imaging

Acute posterior dislocation requires careful radiographic assessment because the injury can be missed on an isolated anteroposterior view. Axillary or equivalent orthogonal imaging is important for confirming humeral-head position. CT is useful for quantifying humeral and glenoid bone defects, while MRI evaluates the posterior capsulolabral complex, marrow edema, rotator cuff, cartilage, and associated soft-tissue injuries. In traumatic posterior dislocation, MRI may demonstrate a reverse Hill-Sachs lesion, posterior labral or capsular injury, joint effusion, and associated fracture or cuff pathology [5].

Management

Management is determined by whether the shoulder is acutely dislocated or reduced, whether instability persists, and the extent of capsulolabral and bony injury. After an acute posterior dislocation has been recognized, reduction and post-reduction stability assessment are essential. Stable shoulders with small, non-engaging reverse Hill-Sachs defects may be treated nonoperatively with protected immobilization followed by progressive rehabilitation. Recurrent symptomatic instability, a repairable posterior capsulolabral lesion that fails appropriate rehabilitation, clinically important glenoid bone loss, or a larger/engaging reverse Hill-Sachs lesion may require operative stabilization or reconstruction. Treatment algorithms are not based on one universal defect-size threshold; patient demand, chronicity, lesion size and location, engagement, and associated injuries all influence the choice of procedure [8].