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 muscluar 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 conveinience 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 and the coracoacromial ligament. 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
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).
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: clavipectoral fascia, conjoined tendon of the short head of the biceps & coracobrachialis, coracoacromial ligament, subdeltoid fascia, scapular fascia (infraspinatus and teres minor)
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:
- Coracoid process of scapula.
- Coracoclavicular ligament.
- Short head of bicep.
- Suspensory ligament of the axilla.
- 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.
- 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.
- Invests the pectoralis minor.
- Extends in continuity with the axillary sheath.
- Blends with the deep fascia of the pectoralis major.
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:
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
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.
- 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?
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 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 subscapularis and supraspinatus tendon. It is reinforced externally by the coracoacromial veil (ligament between the coracoacromial ligament and rotator interval capsule, Rothenberg et al 2017), coracohumeral ligament and the spiral glenohumeral ligament; internally it is reinforced by the superior glenohumeral ligament.
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.
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). It blends with and strengthens the upper part of the shoulder joint capsule (rotator interval capsule, refer layer 3).
The coracohumeral ligament encloses the supraspinatus, infraspinatus and subscapularis tendon. It also enclodes 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.
Izumi et al (2011) found the coracohumeral ligament most effectively stretched in external rotation with either lower shoulder elevations, extension or extension with adduction.
Superior Glenohumeral ligament (Petchpapra et al 2010)
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 some combination). 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.
The biceps pulley
The soft tissue component of the biceps pulley include:
- 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 attaches to the greater and lesser tuberosities and 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.
The coracohumeral ligament is a dense fibrous structure connecting the base of the coracoid process to the greater and lesser tuberosities. Laterally, the coracohumeral ligament separates into two distinct bands that envelopes the long head of biceps at the proximal end of the bicipital groove.
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