Dominic Stone
The glenohumeral (GH) joint is a ball-and-socket joint that connects the upper extremity to the trunk. It is formed by the combination of the humeral head and the glenoid fossa of the scapula. The GH joint is the most mobile and least stable joint in the body, allowing for a wide range of movements, including flexion, extension, abduction, adduction, and internal/external rotation. The muscles that enable GH flexion include the anterior deltoid, coracobrachialis, pectoralis major, and biceps brachii. These muscles work in synergy with the joint capsule and ligaments to provide stability and facilitate the impressive range of motion associated with the GH joint.
| Characteristics | Values |
|---|---|
| Joint type | Ball-and-socket diarthroidal joint |
| Function | Connects upper extremity to trunk |
| Mobility | High |
| Stability | Low |
| Ligaments | Glenohumeral, coracoglenoid, coracohumeral, transverse humeral, coracoacromial, coracoclavicular, acromioclavicular |
| Bursae | Subacromial, subscapular, subcoracoid, subdeltoid-subacromial, coracobrachial |
| Prime flexors | Deltoid (anterior fibres), pectoralis major (clavicular fibres) |
| Weak flexor muscles | Coracobrachialis, long head of biceps brachii |
| Prime extensors | Posterior deltoid, latissimus dorsi, teres major |
| Internal rotators | Subscapularis, pectoralis major, latissimus dorsi, teres major, anterior deltoid |
| External rotators | Infraspinatus, teres minor |
| Circumduction | Combination of movements |
| Stabilizers | Osseous articular anatomy, joint congruity, glenoid labrum, glenohumeral ligaments, joint capsule, negative intraarticular pressure, LHBT, rotator cuff muscles, rotator interval, periscapular muscles |
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What You'll Learn
Glenohumeral joint flexion
The glenohumeral joint, or shoulder joint, is a true synovial ball-and-socket style diarthroidal joint. It is the most mobile joint in the human body, exhibiting a vast range of motion across multiple planes. It is also the least stable joint in the body and is the most commonly dislocated diarthroidal joint.
The joint is formed from the combination of the humeral head and the glenoid fossa of the scapula. The glenoid fossa is a shallow pear-shaped pit on the superolateral angle of the scapula. The humeral head is three to four times larger than the glenoid fossa, meaning that only a third of the humeral head is ever in contact with the fossa.
The glenohumeral joint's main flexors are the anterior deltoid, coracobrachialis, and pectoralis major. The biceps brachii weakly assists in this action. The anterior portion limits extension, while the posterior portion limits flexion. The joint capsule and the ligaments of the GH joint work together to provide a passive restraint to keep the humeral head in contact with the glenoid fossa.
The scapulohumeral and thoracohumeral muscles are responsible for producing movement at the glenohumeral joint. The prime flexors of the joint are the deltoid (anterior fibres) and pectoralis major (clavicular fibres) muscles. The coracobrachialis and the long head of the biceps brachii assist as weak flexor muscles.
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Muscles involved
The glenohumeral (GH) joint is a ball-and-socket joint that connects the upper extremity to the trunk. It is formed by the combination of the humeral head and the glenoid fossa of the scapula. The GH joint is the most mobile and least stable joint in the body, and it is the most commonly dislocated diarthrodial joint. The joint capsule and the ligaments of the GH joint work together to keep the humeral head in contact with the glenoid fossa.
The muscles involved in GH flexion, or forward flexion, are the pectoralis major, anterior deltoid, coracobrachialis, and biceps brachii. The biceps brachii only weakly assist in this action. The scapulohumeral and thoracohumeral muscles are responsible for producing movement at the GH joint. The prime flexors of the GH joint are the deltoid (anterior fibres) and pectoralis major (clavicular fibres) muscles. The coracobrachialis and the long head of the biceps brachii assist as weak flexor muscles.
The rotator cuff muscles, including the supraspinatus, subscapularis, infraspinatus, and teres minor, are important dynamic stabilizers of the GH joint. They attach to the humeral head within the glenoid fossa and maintain a centralized positioning of the humeral head within the glenoid fossa. The rotator cuff muscles are often under heavy strain and are therefore susceptible to injury. Tendinitis, or inflammation of the muscle tendons, is a common pathology of the rotator cuff.
The larger muscles involved in shoulder movements include the trapezius, levator scapula, deltoids, serratus anterior, latissimus dorsi, rhomboids, teres major, biceps, coracobrachialis, and triceps muscles. These muscles work synergistically to enable gross motor movements of the upper quadrant.
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Shoulder flexors
The shoulder joint is a ball-and-socket joint, with the head of the humerus fitting into a shallow cavity on the scapula, called the glenoid fossa. It is the most mobile joint in the body, but also one of the most unstable due to the shallow cavity, which provides little support to the head of the humerus. The shoulder musculature not only moves the joint but also plays a crucial role in maintaining its stability.
The prime flexors of the glenohumeral joint are the deltoid (anterior fibres) and pectoralis major (clavicular fibres) muscles. The deltoid muscle has three parts: the clavicular, acromial, and spinal. The deltoid muscle is responsible for a strong superior translation force on the humerus, which is counterbalanced by the rotator cuff muscles, preventing superior humeral dislocation. The pectoralis major is also one of only three muscles that act as prime movers for arm movements, along with the latissimus dorsi and the deltoid muscles. The other six muscles crossing the shoulder joint are used as synergists or fixators.
The coracobrachialis and the long head of the biceps brachii are also involved as weak flexor muscles. The biceps brachialis muscle originates with its long head from the supraglenoid tubercle of the scapula and with its short head from the coracoid process of the scapula. The triceps brachii is formed from three parts: the long head, lateral head, and medial head.
The latissimus dorsi muscle is another large muscle in the posterior shoulder area, with four parts: vertebral, iliac, costal, and scapular. It is the most important internal rotator at the level of the shoulder, playing a crucial role in adduction and flexion. The trapezius muscle indirectly helps the shoulder in adduction and flexion in the first degree.
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Shoulder extension
The shoulder is a complex joint that controls our arm movements, and it includes many small but important muscles. The shoulder muscles are skeletal muscles, meaning they are attached to bones by tendons. Tendons connect the shoulder muscles to the scapula (shoulder blade), humerus (bone between the shoulder and elbow), and clavicle (collarbone).
The shoulder's principal extensors are the posterior deltoid, latissimus dorsi, and teres major. The latissimus dorsi forms the posterior pillar and the posterior wall of the axillary cavity, covering the lower and lateral sides of the back (lumbar region) and the lateral part of the chest. The teres major provides internal rotation, extension, and adduction of the shoulder. The deltoid muscle intervenes in the flexion of the shoulder, in the internal rotation, and in the front adduction on a horizontal plane.
The supine position is commonly used to emphasise the shoulder flexors and to provide scapular stability. Conversely, the prone position is used to emphasise the shoulder extensors and challenge the scapula-stabilizing muscles. A standing modified unilateral push-up activity performed isokinetically can mimic the function of the serratus anterior performing a wall push-up manoeuvre. This can be used concentrically and eccentrically for serratus strengthening.
The rotator cuff muscles also play a role in lifting and rotating the arm. The four muscles that constitute the rotator cuff are the supraspinatus, infraspinatus, subscapularis, and teres minor. The rotator cuff muscles act as the glenohumeral joint's dynamic stabilizers. The subscapular bursa lies between the subscapularis tendon and the capsule, reducing frictional damage to the subscapularis muscle during internal shoulder rotation.
To strengthen the shoulder extensors, one can perform a shoulder extension exercise with a resistance band. Secure the centre of the resistance band overhead and take the two ends of the band in your hands. Pull the two sides of the band down and back to work the muscles around your shoulder blades. Hold for a few seconds and repeat for up to 15 reps or until you feel a burn in your muscles.
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Shoulder instability
The glenohumeral joint is a ball-and-socket joint that connects the upper extremity to the trunk. It is the most mobile joint in the human body, allowing us to lift our arms, rotate them, and reach up over our heads. The joint has a wide range of motion across multiple planes, including flexion, extension, abduction, adduction, and internal/external rotation.
However, this great range of motion comes at a cost: the shoulder joint is the least stable in the body. The bony surfaces offer little support, and the shoulder relies on strong tendons, muscles, and ligaments to keep it stable. Shoulder instability occurs when the head of the upper arm bone (humeral head) is forced out of the shoulder socket (glenoid). This typically happens as a result of a sudden injury, fall, or accident. Once a shoulder has dislocated, it becomes vulnerable to repeat episodes.
There are two main types of shoulder dislocations: subluxation and complete dislocation. A subluxation occurs when the humerus partially slides in and out of place quickly, while a complete dislocation means the ball comes all the way out of the socket. Shoulder instability can also occur when the labrum is torn or peeled off the glenoid, either after a dislocation, trauma, or repetitive motion such as throwing a baseball. Some people are born with loose shoulder ligaments, and for them, instability can occur without any trauma or following a minor injury.
Chronic shoulder instability is the persistent inability of the shoulder's tissues to keep the arm centred in the shoulder socket. It is characterised by repeated episodes of the shoulder "giving way," which is often associated with pain. Treatment for shoulder instability includes both non-operative and surgical options.
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Frequently asked questions
The glenohumeral joint (GH) is a ball-and-socket joint that connects the upper extremity to the trunk. It is formed by the combination of the humeral head and the glenoid fossa of the scapula.
The GH joint allows for a wide range of movements, including flexion, extension, abduction, adduction, and internal/external rotation. It is the most mobile joint in the human body.
The shoulder's main flexors are the anterior deltoid, coracobrachialis, and pectoralis major. The biceps brachii also weakly assists in this movement.
The GH joint is stabilised by static and dynamic structures. Static stabilisers include the glenoid labrum, glenohumeral ligaments, and the joint capsule. Dynamic stability is provided by the rotator cuff muscles, rotator interval, and periscapular muscles.
Due to its high mobility, the GH joint is prone to dislocations and impingement issues. Rotator cuff injuries are common due to the heavy strain these muscles undergo to stabilise the joint.
