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Anatomy, Shoulder and Upper Limb, Shoulder Muscles
Cassidy McCausland; Ethan Sawyer; Benjamin J. Eovaldi; Matthew Varacallo.Author Information
The shoulder joint, also known together the glenohumeral joint, is a ball and socket joint with the most extensive range of motion in the person body. The shoulder muscles have a wide range of functions, including abduction, adduction, flexion, extension, internal and external rotation.<1> The main bony framework of the shoulder is the scapula, where every one of the muscle interact. At the lateral facet of the scapula is the articular surface ar of the glenohumeral joint, the glenoid cavity. The glenoid cavity is peripherally surrounded and reinforced by the glenoid labrum, shoulder share capsule, sustaining ligaments, and also the myotendinous attachments that the rotator cuff muscles. The muscles of the shoulder play a vital role in giving stability come the shoulder joint. The primary muscle group that support the shoulder joint is the rotator cuff muscles. The 4 rotator cuff muscles incorporate the supraspinatus, infraspinatus, teres minor, and also subscapularis.<2><1> Other muscles that form the shoulder girdle encompass the pectoralis major, pectoralis minor, the deltoids, trapezius, and the serratus anterior.
Structure and Function
The upper extremity is attached to the axial skeleton by method of the sternoclavicular joint. The three joints the the pectoral girdle room the sternoclavicular joint, coracoclavicular joint, and acromioclavicular joint. The bones of the pectoral girdle space the clavicle, scapula, and also humerus. The clavicle is positioned instantly superior to the first rib. The distal aspect of the clavicle articulates v the acromial process and coracoid process of the scapula, forming the acromioclavicular joint and coracoclavicular joints, respectively. The most important structural ligaments that the shoulder joint space the glenohumeral ligaments and the coracoacromial ligament.<3>
The scapula is a flat bone v multiple muscular attachments. The glenoid fossa serves the articulating function with the humeral head at the lateral edge of the scapula. The glenohumeral share is the point of articulation between the humerus, the scapula, and the thoracic cavity, with the last occurring through the scapulothoracic articulation. The scapula connects to the clavicle via the coracoclavicular joint and the acromioclavicular joint.
The coracoclavicular joint is strengthened by the coracoclavicular ligament that unites the undersurface of the clavicle to the coracoid process of the scapula. The acromioclavicular share is in ~ the lateral facet of the clavicle and does not provide much structural support to the shoulder joint. The coracoid process, the acromion process, and the coracoacromial ligament administer peripheral reinforcement for the shoulder joint in addition to the muscle of the shoulder. The shoulder muscles and peripheral structures of the shoulder function to rise the structure integrity of the shoulder joint.<4>
Embryologic advance of the limbs starts at the end of the fourth week of fetal development. By the 6th week, the fetus establishes hand plates and footplates. During limb development, the shape of the body is formed by mesenchymal cells condensing and also differentiating into chondrocytes which will ultimately identify into the bones and cartilage the the upper and also lower extremity. The upper and also lower extremities undergo very similar embryological breakthrough patterns. Body musculature is first seen roughly the saturday week. The mesenchyme migrates from the dorsolateral cells of somites out to the limb and is differentiated into muscle cells. The shoulder muscles construct earlier 보다 the distal muscle of the top extremity.<5>
Blood Supply and also Lymphatics
The arterial it is provided to the upper extremity originates indigenous the subclavian artery. These vessels exist on both sides of the body to carry out upper extremity blood supply. Both arteries obtain their blood supply from the arch that the aorta. The subclavian artery branches ~ above both political parties of the body incorporate the vertebral artery, internal thoracic artery, thyrocervical trunk, and dorsal scapular artery.
The subclavian artery becomes the axillary artery as soon as it will the lateral border that the first rib.
There room three components to the axillary artery, with each portion having arterial branches to it is provided the shoulder muscles. Multiple arteries branch indigenous the axillary artery, consisting of the remarkable thoracic artery, thoracoacromial artery, circumflex humeral artery, and also the lateral thoracic artery. The subscapular artery is a department of the third part of the axillary artery. The subscapular artery provides off the circumflex scapular artery and the thoracodorsal artery. In general, the muscles of the shoulder get vascular it is provided by called arteries linked with the muscle they supply.<6>
Efferent lymphatic vessels arise native the distal top extremity and pass with the shoulder. Additionally, axillary lymph nodes add to efferent lymphatic vessels in the shoulder region and happen proximally with the shoulder. Deep lymphatic ship accompany superficial lymphatic vessels. The deep lymphatic vessels drain lymph indigenous the joint capsule, tendons, and nerves. The lymphatics the the shoulder and axillary an ar are drained by the subclavian lymphatic trunk. On the right, the subclavian stems drains into the right lymphatic duct. top top the left, the subclavian tribe drains right into the thoracic duct.<7>
The upper and also lower branches that the subscapular nerve innervate the subscapularis muscle. The suprascapular nerve innervates the supraspinatus and also infraspinatus muscles. The posterior branch that the axillary nerve gives the teres minor. The axillary nerve additionally innervates the deltoid muscle. The nerve supply to the trapezius is by the spinal accessory nerve/11th cranial nerve through some direct branches native the cervical plexus. Innervation come levator scapula is by C3-C5. The nerve supply to the rhomboids is the dorsal scapular nerve. The nerve supply to the serratus anterior is the lengthy thoracic nerve. The pectoralis major muscle receives its nerve it is provided via the medial and also lateral pectoral nerves.<8>
The main muscle team that support the shoulder joint is the rotator cuff muscles. The 4 rotator cuff muscles room the supraspinatus, infraspinatus, teres minor, and also subscapularis. Together the rotator cuff muscles kind a musculotendinous cuff together they insert on the proximal humerus.
The rotator cuff muscles connect to the proximal humerus anteriorly at the greater tuberosity. The rotator cuff muscles administer considerable structural support to the glenohumeral joint and also keep the humeral head in a firm position by articulating with the scapula in ~ the glenoid cavity. The muscles of the chest also administer structural assistance to the shoulder joint.<8>
The beginning of the supraspinatus is indigenous the supraspinatus fossa above the spine that the scapula crossing the shoulder joint, happen under the coracoacromial arch, and above the glenohumeral joint where it inserts at the higher tubercle of the humerus. The supraspinatus muscle functions by abbot of the humerus approximately 30 degrees and stabilizing the glenohumeral joint.<8>
The infraspinatus muscle originates from the infraspinatus fossa listed below the spine that the scapula and also inserts ~ above the higher tubercle that the proximal humerus listed below the supraspinatus tendon. The infraspinatus muscle functions by externally rotating the humerus.
The teres minor muscle is positioned automatically inferior to infraspinatus, originating at the inferior element of the dorsal scapula at the lateral border the the scapula. The teres young inserts top top the higher tubercle of the humerus below the infraspinatus. The Teres boy acts to externally rotate the humerus and also assists through abduction the the humerus.
The subscapularis originates indigenous the subscapular fossa that the scapula and inserts top top the lesser tubercle the the humerus as well as a portion of the anterior capsule that the shoulder joint. A big bursa off the muscle indigenous the neck of the scapula—the subscapularis functions by internally rotating and also abducting the humerus.
The rhomboid boy originates from the nuchal ligament and spinous processes of C7-T1. The rhomboid significant originates indigenous the spinous procedures of T2-T5. The rhomboid muscle insert on the medial border that the scapula and work in combination with the levator scapulae muscles to elevate the medial border of the scapula. The just muscle which action to depress the shoulder is the reduced trapezius, which is aided by gravity in the upright position.<8>
The trapezius is a large triangular-shaped muscle that overlies the shoulder posteriorly. The trapezius originates from the superior aspect of the nuchal heat in the occipital, cervical, and also upper thoracic region and inserts at the lateral aspect of the clavicle, the acromion, and also spine the the scapula. The role of the trapezius muscle is both elevation and depression of the shoulder depending upon whether the top or reduced muscle fibers room activated. as soon as the whole trapezius muscle contracts, the fibers room geometrically opposed, and also the forces are balanced, resulting in no shoulder movement.
The deltoid muscle overlies the shoulder superficially and also functions to abduct the humerus. The deltoid muscle has actually three origins; the human body of the clavicle, the spine that the scapula, and the acromion. The deltoid muscle has actually its insertion on the deltoid tuberosity that the humerus. The role of the deltoid muscle is variable depending upon which muscle fibers space activated. The anterior deltoid flexes and medially rotations the humerus, the middle deltoid abducts the humerus, and the posterior deltoid performs the action of extension and also external rotation the the humerus.<9>
The quick head that the biceps brachii originates native the coracoid process, and the long head originates native the supraglenoid tubercle, passing with the intertubercular groove the the proximal humerus. The biceps brachii is not actually considered a shoulder muscle, but the tendon the its long head originates ~ above the superior lip of the glenoid labrum.
The infraspinatus muscle tendon is periodically separated from the capsule that the shoulder share by a bursa. One accessory muscle the the biceps brachii might be confused with a separation tear follow me the biceps tendon. There is some variability the the location that the rotator cuff muscle insert on the proximal humerus.<10>
Rotator cuff injuries and tendon degeneration result from multifactorial processes and pathological changes, both of which impact the quality of tendons.<11> A pathology affecting the rotator cuff muscle is common, and also surgical treatment is regularly performed in patients who have actually failed conservative therapy for various pathologies, including full and partial-thickness rotator cuff tears and also subacromial impingement syndrome. Subacromial decompression with rotator cuff debridement and acromioplasties are performed in situations of subacromial impingement and administer increased clearance because that the supraspinatus tendon.<12>
Arthroscopic procedures deserve to be supplied to accessibility the shoulder joint and repair the rotator cuff muscles. Number of port web page are provided to accessibility the joint, and also they room made family member to bony landmarks and also pass in between or v the muscle of the shoulder. Posterior accessibility is attained by making a port site that allows access to the joint by passing between the infraspinatus muscle and also the teres minor muscle or directly through the infraspinatus muscle. Anterior accessibility is derived by passing a portal v the pectoralis major and the deltoid muscle. Lateral access is derived by placing a portal straight through the deltoid muscle.
Surgical repair of individuals with partial-thickness rotator cuff tears refractory come conservative management as well as full-thickness cuff tears is generally done arthroscopically. The take it tendon(s) are repaired through anchoring them back to the humerus, their original insertion site.
Tendinopathies the the long head the the biceps tendon typically co-occurs with rotator cuff pathologies and often add to shoulder pain. As the tendon attaches to the remarkable lip that the glenoid labrum, the is encountered during arthroscopic shoulder operations and is often contained as a component of the operation. Biceps tendon tenotomy, or tendon release, is a common an approach that clinicians have the right to use to relieve pain led to by biceps tendinopathies. Tenodesis that the biceps tendon, or release and re-anchoring, is another method used. Over there is part debate about which an approach is superior.<13>
The usability of the shoulder muscles is vital when considering total shoulder instead of options. For example, reverse full shoulder arthroplasties are typically used in people with bad rotator cuff function, however successful procedure necessitates a sensible deltoid muscle to enable for shoulder abduction.<14>
Rotator Cuff Injury
Rotator cuff tears room either partial-thickness or full-thickness tears. Partial-thickness tears most commonly occur at the articular or bursal next of the rotator cuff tendons. Full-thickness tears often involve some degree of tendon retraction. The patient"s age, baseline shoulder function, tear size, chronicity, and degree of tendon retraction room several crucial elements to be thought about when deciding just how to manage each patient many appropriately.<15><12>
The supraspinatus tendon is the most generally injured tendon that the rotator cuff muscles, followed by infraspinatus, subscapularis, and teres minor. The teres young tendon is just rarely affiliated in rotator cuff injuries. The subscapularis tendon tear have the right to be connected with a biceps tendon dislocation native the bicipital tendon groove moving right into the subscapularis tendon medially. Confirmation of intra-articular tendon tears is through the lack of the biceps tendon in the north bicipital groove.<10>
Labral Injuries and also Dislocations
Multiple species of shoulder labral injuries can occur in various patient populations. One an especially common injury subgroup consists of young athletes afflicted v a traumatic shoulder dislocation. In the setting of glenohumeral instability, clinicians must recognize the prestige of not just a recurrent dislocation however the threat of raised bone loss and also soft organization compromise, which may ultimately impact the outcome adhering to surgical repair.
Glenohumeral instability, specifically in the setting of trauma, is most commonly seen anteriorly. Posterior shoulder instability have the right to be watched in weightlifters or football linemen. Rarely dislocation patterns encompass the superior and inferior glenohumeral dislocation (luxatio erecta).
It is necessary to note that in the setting of multidirectional instability (MDI), specifically in cases of bilateral ligamentous laxity or in a patient through a an individual or family history of a connective tissue disorder, the probability of recurrent instability is fairly common. The mainstay therapy for this injuries centers on physical therapy and also shoulder strengthening programs.
Para-labral cysts are most often seen in association v glenoid labral tears. Para-labral cyst development can cause subsequent nerve compression and denervation that shoulder muscles. The suprascapular nerve is susceptible to compression from a para-labral cyst as result of its place as it passes through the suprascapular and also spinoglenoid notches nearby to the anterior-inferior labrum. The subscapular nerve is likewise susceptible come compression from a para-labral cyst in the subscapular recess. Diverted atrophy of the teres minor indicates injury come the axillary nerve.<16>
The reason of frozen shoulder is the deposition the hydroxyapatite crystals into the muscle-tendon. The shoulder is the most common site of hydroxyapatite calcification in the human body. The supraspinatus tendon is the most usual site of hydroxyapatite decision deposition. Frozen shoulder is associated with diabetes mellitus but may likewise be associated with coronary artery disease, cerebral vascular disease, rheumatoid arthritis, and also thyroid disease.<17>
Subacromial bursitis, especially the acute phase, outcomes in painful overhead movement. This is as result of friction in between the acromion and deltoid superiorly and the humeral head and supraspinatus inferiorly. Chronic bursitis leads to chronic pain due to the fact that there is inflammation within the bursa. This inflammatory process can cause weakness and also rupture of the nearby ligaments and also tendons. When challenged with chronic bursitis cases, it is likewise important to consider tendinitis since it can present simultaneously v bursitis.
Subacromial bursitis have the right to be caused by repeated steroid injections as they boost the threat of infection within the shoulder and also can additionally lead to damage to the rotator cuff muscles. Therapy most typically consists the avoiding tasks that encompass repetitive overhead movements, taking oral NSAIDs, and rest.
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An important imaging factor to consider in patients through previous orthopedic surgical fix of the shoulder and proximal humerus is metallic MRI artifacts. Performing MRIs at lower magnetic fields can decrease artefacts from implanted steel hardware.<19>