Muscular-Ligamentous-Fascial Layers of the Glenohumeral Joint
Introduction
Subacromial bursitis and soft tissue pathologies are common problems associated with the shoulder. A review of the functional anatomy of the muscles, ligaments, fascia and subacromial bursa show relationships not commonly associated that can account for a variety of different clinical symptoms and inform choice of treatment. Examples of these considerations from the following text are:
Subacromial bursitis: soft tissue attachments to the subacromial bursa include the subdeltoid fascia, coracoacromial ligament and supraspinatus tendon. In cases of a subacromial bursitis treatment to any one of these tissues that could be the cause of the bursitis may be warranted. Even just considering the coracoacromial ligament, there are anatomical connections to the supraspinatus, clavipectoral fascia, subdeltoid fascia, conjoint tendon of the short head of biceps/coracobrachialis, deltoid fascia and rotator interval capsule. Therefore a knowledge of the local anatomy can inform treatment choices beyond the immediate source of pain.
Subdeltoid fascia pain: as well as being a potential cause for subacromial bursitis the subdeltoid fascia is a meeting point, or a union, for the fascia of all the rotator cuff and costocoracoid membrane. It has muscular attachments pulling on it from the conjoint tendon of the coracobrachialis and short head of biceps, deltoid muscle and short head of biceps. It also has a ligamentous attachment to the coracoacromial ligament. Even if you was to treat just the subdeltoid fascia when treating subacromial bursitis or lateral shoulder pain a more global approach with specific reference to certain muscles can be adopted with a knowledge of the local anatomy.
Rotator Interval and rotator interval capsule pathology: the rotator interval and its capsule is anatomically formed and reinforced externally by the coracoacromial veil and the coracohumeral ligament. It is contains the rotator cuff and long head of bicep. By reviewing the broader anatomical attachments of these ligaments and how to stretch them a more detailed treatment can be applied for rotator cuff tendonitis, long head of bicep tendonitis and adhesive capsulitis.
For convenience the four muscular-ligamentous-fascial layers of the shoulder has been described according to Cooper et al (1993). However sometimes anatomical structures from one layer are associated with the next layer so there is some duplication of work.
Also not all the anatomical structures listed in Cooper et al (1993) work has been described, only the parts of particular interest for osteopathic practice. Any parts of the different layers that are listed in the title of each section, but not described in the ensuing text, is because on reviewing these anatomical structures they were found to have no clinical significance to osteopathic practise.
Four muscular-ligamentous-fascial layers supporting the glenohumeral joint
Cooper et al (1993) identified four muscular-ligamentous-fascial layers supporting the glenohumeral joint. Each one of these layers forms a continuous sheet wrapping around the shoulder.
Layer 1: consists of the deltoid and pectoralis major muscle and its overlying fascia.
Layer 2: consists of anteriorly the clavipectoral fascia, conjoined tendon of the short head of the biceps and coracobrachialis, coracoclavicular and the coracoacromial ligaments. Laterally the subdeltoid fascia (Nauta & Landsmeer 1948). Posteriorly the scapular fascia that overlies the infraspinatus and teres minor.
Layer 3: consists of the deep layer of the subdeltoid bursa and the rotator cuff.
Layer 4: is the capsule of the glenohumeral joint, glenohumeral ligaments and coracohumeral ligament.
Layer 1: muscle and fascia of the deltoid and pectoralis major
Deltoid
Fascial relations of the deltoid:
Fascia covering the trapezius: via the superficial deltoid fascia.
Spine of scapula and clavicle via the deep deltoid fascia.
Coracoacromial ligament (Rothenberg et al 2017).
Lateral intermuscular septum: via the deltoid tendon and fibrous aponeurosis (Rispoli et al 2009).
Lateral aspect of the brachialis and deep brachial fascia (Rispoli et al, 2009 & Stecco et al, 2008) via the deltoid tendon and fibrous aponeurosis.
Subdeltoid fascia: Nauta & Landsmeer (1948) found the subdeltoid fascia to attach to the deltoid proximally. This prevents folds in the subdeltoid fascia during abduction (refer subdeltoid fascia, layer 2).
The architecture of the lateral deltoid is designed to optimise strength. This could be associated with its function in preventing folds in the subdeltoid fascia during abduction. The muscle has short fiber length, complex multipennate structure and high cross sectional area (Peterson & Rayan 2011). Four fibrous intramuscular bands descend from 4 to 5 tendinous insertions (Moatshe et al 2018) from the acromion to interdigitate with three septa ascending from the deltoid tubercle. The septa are connected by short muscle fibers that provide powerful traction. This powerful traction can prevent folds in the subdeltoid fascia (refer subdeltoid fascia, layer 2).
Pectoralis Major
Pectoralis major is covered by a thin enveloping pectoral fascia (also called thoracic fascia), which originates from the clavicle and sternum and is in continuity with the facial layer that covers the muscles of the shoulder, thorax, abdomen, and back.
The pectoral fascia creates individual fascial beds for the clavicular, sternocostal and abdominal portions. These fascial beds are separated from each other by connective septa. This connective tissue space allows the three portions to move separately and to glide against each other.
These different beds of the pectoralis major can be stretched in different ways:
Clavicular portion: abduction and depression of the arm. The sternoclavicular portion can be stretched mostly with abduction with external rotation.
Sternocostal portion: abduction.
Abdominal portion: elevation of the arm.
At the caudal border of the pectoralis major, the fascia divides into a superficial and a deeper layer: the superficial fascia covers the superficial part of the pectoralis major, the deeper layer rolls back the muscle and intercommunicates with the fascia of the pectoralis minor and the coracoclavicular fascia (clavipectoral fascia)
The muscles of the pectoral girdle, especially the pectoralis major, interact with each other through the fascial fibers.
The fascial interaction is between the pectoralis major and supraspinatus, as well as the infraspinatus, the teres minor, latissimus dorsi and the deltoid. The deltoid sends fascial and tendinous bridges to the pectoralis major tendon. Moreover, the humeral capsule can communicate with other muscles of pectoral girdle through the fascial fibers (Larionov et al 2018).
Fascia attachments of the clavicular part of the pectoralis major:
Clavicle via the deep layer of the pectorlais fascia.
Superficial lamina of the deep cervical fascia via superficial layer of pectoralis fascia.
Anterior brachial fascia.
Fascia attachments of the costal part of the pectoralis major:
Sternum via deep layer of the pectoralis fascia.
Contralateral pectoral fascia via the superficial layer of the pectoral fascia.
Rectus abdominis muscle.
Contralateral external oblique fascia.
Medial brachial fascia.
Medial intermuscular septum.
Latissimus Dorsi fascia: Stecco et al (2009) found laterally the deep and superficial layers of the pectoralis major fascia unites and continue with the fascia of the latissimus dorsi.
Layer 2: (anteriorly) clavipectoral fascia, conjoined tendon of the short head of the biceps & coracobrachialis, coracoclavicular ligaments, coracoacromial ligament; (posteriorly) scapular fascia (infraspinatus and teres minor); (circumferential) subdeltoid fascia,
Clavipectoral fascia
The clavipectoral fascia is a deep layer of fascia in the pectoral region. It acts to suspend the floor of the axilla and protect the axillary nerve, artery and vein. Its boundaries are:
Laterally:
Coracoid process of scapula.
Coracoclavicular ligament. The fascia divides into (i) anterior sheet attaches to the trapezoid ligament; (ii) posterior sheet attaches to the conoid ligament. The small space between these two sheets is part of the coracoclavicular joint (Nakazawa et al 2011).
Short head of bicep.
Suspensory ligament of the axilla.
Medially:
First costal cartilage.
External intercostal membrane of the first two intercostal spaces.
The portion extending between the first rib and coracoid process is often thicker and called the costocoracoid membrane.
Superiorly:
The fascia splits anteriorly and posteriorly to enclose the subclavis and attaches to the clavicle. The posterior part of the fascia that encloses the subclavis fuses with the prevertebral fascia and the axillary sheath.
Inferiorly:
Invests the pectoralis minor.
Deep:
Extends in continuity with the axillary sheath.
Superficial:
Blends with the deep fascia of the pectoralis major (Larionov et al 2018).
Coracobrachialis
Origin: coracoid process with a conjoint origin with the short head of biceps. It is formed of two fused heads.
Insertion: antebrachial fascia and the medial epicondyle of the humerus.
Variations include the coracobrachialis brevis. This muscle can insert proximally to the capsule of shoulder joint, root of coracoid process or conoid ligament of clavicle. It can insert distally into the medial intermuscular septum, medial supracondylar ridge, medial epicondyle and ligament of Struthers.
Subdeltoid fascia (Nauta & Landsmeer 1948)
The subdeltoid fascia is a tough sheet of connective tissue stretched out over the greater tubercle and surgical neck of the humerus.
It is merely the junction of several fascia being formed from the union of the:
Infraspinatus and teres minor fascia: a retinacular sheet of fascia extends deep to the posterior deltoid and superficial to the infraspinatus and teres minor as they approach the proximal humerus (Moccia et al 2016). Cooper et al (1993) found this fascia continuous with the clavipectoral fascia. This shows the continuity of the infraspinatus/teres minor fascia and clavipectoral fascia (part of which is the costocoracoid membrane) via the subdeltoid fascia.
Supraspinatus fascia.
Subscapularis fascia.
Costocoracoid membrane: subdeltoid fascia extends laterally over the conjoint tendon of the coracobrachialis and short head of biceps.
It blends with the surgical neck of the humerus a small distance above the deltoid insertion and acromion process.
It receives direct muscle insertions that pull on the fascia from the:
Deltoid: connects to the subdeltoid fascia proximally to prevent formation of folds in the fascia during abduction (refer deltoid, layer one).
Short head of biceps.
The subdeltoid fascia has ligamentous attachments to the:
Coracoacromial ligament.
Coracoclavicular ligament
Coracoclavicular ligaments are composed of the lateral coracoclavicular ligament providing superior and posterior stability to the acromioclavicular joint (Kurata et al 2021):
Conoid ligament: coracoid process of scapula to the clavicle (around the conoid tubercle). Posterior sheet of clavipectoral fascia attaches onto the ligament (Nakazawa et al 2011).
Trapezoid process: coracoid process of scapula (trapezoid ridge) to the clavicle (trapezoid ridge). Anterior sheet of clavipectoral fascia attaches onto the ligament (Nakazawa et al 2011).
And the medial coracoclavicular ligament providing again superior and posterior stability to the acromioclavicular joint (Moya et al 2018).
It extends from the coracoid process (i. anterior to the lateral coracoclavicular ligament and posterior to the pectoralis minor; ii. medial edge of the coracoid process. Pectoralis minor runs through these two bundles) to the anterior lip of the subclavian channel on the clavicle (fusing with the subclavian muscle).
Fascial expansions run from the ligament medially and inferiorly to rib 1, posteriorly to the back of the pectoralis minor joining the retropectoralis fascia and superiorly attaches to the subclavian sheath (Moya et al 2018).
Coracoacromial ligament
Rothenberg et al (2017) described the coracoacromial ligament as extending superolateraly from the coracoid process to the acromion. Near the coracoid, the coracoacromial ligament usually bifurcates into an anterolateral band and posteromedial band, which is often separated by a thin membrane.
Coracoacromial arch: is formed from the coracoacromial ligament, inferior aspect of the acromion and the coracoid process. It limits superior displacement of the humeral head.
The coracoacromial ligament is continuous with:
Medially: supraspinatus fascia (Nauta & Landsmeer 1948); clavipectoral fascia (Rothenberg et al 2017).
Laterally: subdeltoid fascia (Nauta & Landsmeer 1948); conjoined tendon of the short head of the biceps and coracobrachialis (Rothenberg et al 2017).
Superiorly: deltoid fascia at its insertion to the acromion.
Rotator interval capsule: via the coracoacromial veil, refer below (Rothenberg et al 2017).
When the pectoralis minor inserts into the glenohumeral joint capsule and not the coracoid process, its tendon passes between the bands of the coracoacromial ligament (Standring, 2016).
The coracoacromial ligament functions in (Rothenberg et al 2017):
Restricting upward displacement of the humeral head.
Transmiting loads across the scapula.
Acting as a tension band: forces exerted on the coracoid process by the coracobrachialis, pectoralis minor, and short head of biceps are transmitted to the acromion via the coracoacromial ligament. Likewise acromial distortion due to forces exerted by the deltoid and trapezius muscles is limited by the action of the coracoacromial ligament.
Acting as a dynamic brace within the shoulder girdle.
Proprioceptive function: a high density of mechanoreceptors within the coracoacromial ligament seems to indicate an originator of afferent static and dynamic proprioceptive signals.
Coracoacromial veil: is a ligamentous connection between the coracoacromial ligament and the rotator interval capsule (Rothenberg et al 2017) (refer rotator interval & rotator interval capsule, layer 3). It prevents inferior migration of the glenohumeral joint.
The subacromial bursa facilitates movement between the supraspinatus, glenohumeral joint and coracoacromial ligament.
Infraspinatus and teres minor fascia
The fascia of the Infraspinatus has six components (Moccia et al 2016):
Medial band: a band of fascia extending from the midspine of the scapula towards the inferior angle.
Superomedial band: a band of fascia extending from the medial border of the scapula, near the origin of the spine of the scapula, toward the lateral border. In the three divisions of the Infraspinatus noted by Fabrizio and Clemente (2014) this band of fascia maybe the one cited in the article as separating the superior from the middle portion of the Infraspinatus.
Inferomedial band: a band of fascia extending from the inferior angle of the scapula toward the scapular neck and glenoid fossa. The Infraspinatus fibers originate most strongly from the deep aspect of the inferomedial band. In the three divisions of the Infraspinatus noted by Fabrizio and Clemente (2014) this band of fascia maybe the one cited in the article as separating the middle and the inferior portions of the Infraspinatus.
Posterior deltoid: the insertion of the posterior belly of the deltoid muscle is inserted into the infraspinatus fascia inferior to the scapular spine.
Transverse fascia: A band of fascia extending transversely from the posterior deltoid to anchor near the teres minor and teres major muscles.
A retinacular sheet of fascia deep to the posterior deltoid and superficial to the infraspinatus and teres minor muscles as they approach the proximal humerus. Cooper et al (1993) claimed this fascia ran continuous with the clavipectoral fascia around the lateral aspect of the proximal humerus. This is most likely via the subdeltoid fascia (Nauta & Landsmeer 1948).
Layer 3: deep layer of the subacromial bursa and rotator cuff
Subacromial bursa
The Subacromial bursa has anatomical connections to:
Subdeltoid fascia: attaches to the bursa wall.
Coracoacromial ligament: the subacromial bursa facilitates movement between the supraspinatus, glenohumeral joint and coracoacromial ligament.
Acromion.
Supraspinatus tendon: forms part of the bursa wall.
The muscles that pull on the subdeltoid fascia (the deltoid and short head of biceps) as well as the adjoining rotator cuff fascia and costocoracoid membrane (first intercostal, subclavis, pectoralis minor/major and short head of biceps), pulls on the subacromial bursa (Nauta & Landsmeer 1948). Could these muscles be a cause of subacromial bursitis?
Rotator cuff
The rotator cuff interval: a triangular space between the subscapularis and supraspinatus and coracoid process. Jost (2000) found it composed of and represents a complex interaction of the supraspinatus, subscapularis, coracohumeral ligament, superior glenohumeral ligament, and glenohumeral joint capsule.
The fibers of the coracohumeral ligament cannot be separated from those of the anterior supraspinatus and superior subscapularis tendons with which it interdigitates or from the rotator interval capsule.
Layer 4: glenohumeral joint capsule, glenohumeral ligaments and coracohumeral ligament.
Whilst the articular side of the capsule has a synovial lining the key elements to the joint capsule are the glenohumeral ligaments which represent either discreet thickenings of the joint capsule or well-defined cord like structures. Remaining slack in most positions the joint capsule only stabilises the joint at extreme ranges of motion.
Innervation of the capsule (i) posteriorly: axillary and musculocutaneous nerve; (ii) middle and anteriorly: subscapular nerve: (iii) inferiorly, anteriorly and posteriorly: axillary nerve; (iv) laterally: axillary and musculocutaneous nerve.
Transverse Humeral Ligament
The transverse humeral ligament: consists of a few collagen fibers. Greater tuberosity —> lesser tuberosity. Stabilises the long head of bicep in the bicipital groove.
Anterior glenohumeral ligament: superior glenohumeral liogament, medial glenohumeral ligament and inferior glenohumeral ligament
Superior glenohumeral ligament
The superior glenohumeral ligament is a fold–focal thickening of the glenohumeral joint capsule. It is variable in origin (supraglenoid tubercle, superior labrum, long head biceps tendon, middle glenohumeral ligament, or any combination thereof). The superior glenohumeral ligament is anterior to and maintains a close relationship with the biceps tendon along its course before it inserts into a small depression above the lesser tuberosity (Petchpapra et al 2010) and semicircular band. It blends with coracohumeral and coracoglenoid ligament (Merila 2004).
The superior glenohumeral ligament plays a minor role in the stability of the shoulder joint and its biomechanical properties parallel that of the coracohumeral ligament (Merila 2004).
Medial glenohumeral ligament
Originates from the supraglenoid tubercle, anterosuperior labrum, scapular neck, superior glenohumeral ligament and extends to the antero-lateral joint capsule, subscapularis tendon and lesser tubercle. It connects to the spiral glenohumeral ligament. At 45° – 90° of abduction it limits external rotation and is a secondary stabiliser for inferior translation (Merila 2004).
Inferior glenohumeral ligament
The inferior glenohumeral ligament is the largest and the most important of the glenohumeral ligaments acting as a primary stabiliser for inferior translation when the shoulder is abducted (Merila 2004). The inferior glenohumeral ligament is divided into the:
anterior band: anterior scapular neck and labrum —> anatomical neck of humerus. Restricts external rotation and anterior translationof the humeral head.
posterior band: posterior scapular neck and labrum —> anatomical neck of humerusRestricts internal rotation and posterior translation of the humeral head
interposed axillary pouch: inferior 2/3 of the anterior glenoid —> inferior 1/3 of the humeral head.
Coracohumeral ligament
The Coracohumeral ligament is a dense fibrous structure that runs from the coracoid process to the lesser tubercle (deep band) and greater tubercle (superficial band) as well as the intertubercle attachment of the semicircular band. It blends with and strengthens the upper part of the shoulder joint capsule (refer rotator interval capsule, layer 3). Along with the coracoglenoid ligament some authors believe it is formed, and is a remnant of, the pectoralis minor tendon (Merila 2004).
The coracohumeral ligament encloses (superficial band) the supraspinatus and infraspinatus, and (deep band) transverse humeral ligament and subscapularis tendon. It also encloses the long head of biceps at the proximal end of the bicipital groove forming part of the biceps pulley. It reinforces the roof of the rotator interval capsule. It cannot be separated from the anterior supraspinatus and superior subscapularis tendons with which it interdigitates or from the rotator interval capsule. Blends with the coracoglenoid and superior glenohumeral ligament (Merila 2004).
The coracohumeral ligament is most effectively stretched in external rotation with either lower shoulder elevations, extension or extension with adduction (Izumi et al 2011), in adduction it also limits inferior translation and external rotation, and in flexion, adduction, and internal rotation it limits posterior translation (Merila 2004).
Coracoglenoid ligament
Extends from the coracoid process —> supraglenoid tubercle covering the long head of bicep and scapula neck. Blends with the coracohumeral and superior glenohumeral ligaments and medial boarder of the rotator interval capsule to form part of the anterosuperior capsuloligamentous complex of the shoulder. Along with the coracohumeral ligament some authors believe it is formed, and is a remnant of, pectoralis minor tendon (Merila 2004).
Spiral glenohumeral ligament
Extends from the subscapularis fascia and posterior surface of the subscapularis tendon, which joins the medial glenohumeral ligament —> infraglenoid tubercle (long head of tricep). Forms an anterior capsular ligament. Restricts flexion and external rotation (Merila 2004).
Semicircular band (rotator cable)
Thick fibrous band of the deep layer of the coracohumeral ligament. Extends from the greater tuberosity (coracohumeral ligament, anterior fibers of the supraspinatus and rotator interval capsule) and lesser tuberosities (between infraspinatus & teres minor) & intertubercle attachment of the coracohumeral ligament. It posteriorly courses within the joint capsule attaching to the superior glenohuermal ligament (Merila 2004).
Resists anterior translation of humeral head and external rotation, adduction/inferior translation, flexion and adduction. Forming the biceps pulley it stabilises the long head of biceps tendon with the coracohumeral ligament and superior glenohumeral ligament (Huri et al 2019).
The rotator interval capsule
The rotator interval capsule is the anterosuperior aspect of the glenohumeral joint capsule (Petchprapa et al 2010). It forms the roof of the rotator cuff interval linking the (superiorly) supraspinatus tendon where it is reinforced by the anterior supraspinatus tendon; (inferiorly) subscapularis, (laterally) semicircular band; (medially) medial glenohumeral ligament, coracoid process/coracoglenoid ligament/coracohumeral ligament (rotator interval capsule was originally described as a deep band of the coracohumeral ligament); (anteriorly) coracohumeral and superior glenohumeral ligament. It is reinforced externally by the coracoacromial veil (ligament between the coracoacromial ligament and rotator interval capsule, Rothenberg et al 2017), coracohumeral ligament, spiral glenohumeral ligament, coracoglenoid ligament, semicircualr band; internally it is reinforced by the superior and medial glenohumeral ligaments.
The rotator interval capsule acts as a acts as a loaded cable of the suspension bridge (Merila 2004)
The biceps pulley
The soft tissue component of the biceps pulley include:
Subscapularis.
Supraspinatus.
Coracohumeral ligament.
Superior glenohumeral ligament.
The insertions of the coracohumeral and superior glenohumeral ligaments to the rotator interval capsule are medial and lateral to the bicipital groove.
The coracohumeral ligament is a dense fibrous structure extending from the coracoid process to the greater and lesser tuberosities enveloping the long head of biceps.
The superior glenohumeral ligament, as well as following the biceps tendon anteriorly and folding into a sling to support it, attaches to the lesser tubercle. These two ligaments stabilise the long head of biceps in the bicipital groove (Petchpapra et al 2010).
The subscapularis has superficial and deep fibers that envelope the bicipital groove, creating the “roof” and “floor,” respectively. These fibers also blend with those from the supraspinatus and superior glenohumeral ligament/coracohumeral ligament complex.
These structures attach intimately at the lesser tuberosity to create the proximal and medial aspect of the pulley system, with soft tissue extensions serving to further envelope the long head of biceps tendon in the bicipital groove.
Posterior joint capsule
In flexion, adduction and internal rotation it limits posterior translation of the humerus (Merila 2004).
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