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The glenohumeral (GH) joint is a ball-and-socket joint that connects the upper extremity to the trunk. It is the most mobile and least stable joint in the body. The primary muscles that produce adduction of the GH joint are the teres major, latissimus dorsi, and pectoralis major. These muscles work closely with the scapular downward rotators to produce adduction of the shoulder as a whole. The deltoid muscle is also engaged in abduction and carries the arm through a full 180-degree range of motion.
| Characteristics | Values |
|---|---|
| Muscles that produce adduction of the GH joint | Teres major, latissimus dorsi, pectoralis major |
| Muscles that produce internal rotation of the GH joint | Teres major, pectoralis major, subscapularis, latissimus dorsi, anterior deltoid |
| Muscles that produce external rotation of the GH joint | Infraspinatus, teres minor, posterior fibres of the deltoid |
| Muscles that produce extension of the GH joint | Latissimus dorsi, teres major, pectoralis major, posterior deltoid, long head of the triceps |
| Muscles that produce flexion of the GH joint | Pectoralis major, anterior deltoid, coracobrachialis, biceps brachii |
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What You'll Learn
- The latissimus dorsi, teres major, and pectoralis major are the primary muscles
- The deltoid, coracobrachialis, and triceps brachii are also active
- The rotator cuff muscles are important stabilisers
- The supraspinatus is key for movement initiation
- The scapulothoracic retractor and downward rotator muscles are essential for functional movements
The latissimus dorsi, teres major, and pectoralis major are the primary muscles
The latissimus dorsi is the largest muscle of the upper body, originating from the lumbar vertebra and pelvis. It inserts under the deltoid on the humerus (upper arm bone), with a small additional insertion on the scapula (shoulder blade). This muscle is crucial for shoulder extension and adduction, and it may also contribute to shoulder internal rotation (medial rotation) and lumbar movements. It is an important muscle for activities such as rowing, swimming, and chopping, as it assists in pulling the trunk upwards and forwards relative to the arms.
The teres major is located inferior to the teres minor muscle and has a tendon that inserts on the upper arm near the insertion of the latissimus dorsi and subscapularis. It performs similar functions to the latissimus dorsi, including shoulder joint extension, adduction, and internal rotation.
The pectoralis major is a large muscle on the anterior surface of the chest wall, composed of a sternocostal head and a clavicular head. It is a prime flexor of the glenohumeral joint and contributes to adduction, flexion, and internal rotation. Injuries to this muscle, such as partial tears, are typically managed non-surgically, with surgical repair reserved for complete ruptures.
Together, these three muscles are known as the "climbing muscles" due to their powerful adduction capabilities. They also play a crucial role in lifting the trunk upwards towards a fixed arm, as seen in activities like chin-ups or using crutches. Proper coordination between these muscles is essential for smooth and fluid movements of the upper extremities.
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The deltoid, coracobrachialis, and triceps brachii are also active
The glenohumeral (GH) joint is a ball-and-socket joint that connects the upper extremity to the trunk. It is the most mobile and least stable joint in the body. The GH joint is capable of a wide range of motions, including abduction, adduction, internal rotation, and external rotation.
The prime flexors of the GH joint are the deltoid and pectoralis major muscles. The deltoid muscle is engaged from approximately 20° of abduction and can carry the arm through a full 180° of abduction. Contraction of the deltoid muscle applies a strong superior translation force to the humerus, which is countered by the action of the rotator cuff muscles, preventing superior humeral dislocation.
The coracobrachialis muscle lies deep to the biceps brachii in the arm. It originates from the coracoid process of the scapula, passes through the axilla, and attaches to the medial side of the humeral shaft at the level of the deltoid tubercle. The coracobrachialis is a weak flexor muscle and is active during adduction movements, depending on the position of the arm.
The triceps brachii is the only muscle in the posterior compartment of the arm. It has three heads: the long head, the lateral head, and the medial head. The superior portion of the long head of the triceps is covered by the posterior border of the deltoid muscle. The long head of the triceps can be palpated as an elevation parallel and medial to the posterior border of the deltoid muscle when the elbow is extended. The medial head of the triceps is active in all forms of forearm extension, while the long and lateral heads are only significantly active during extension at the elbow that occurs against resistance. Due to its attachment to the scapula, the long head of the triceps can also act on the GH joint, producing an extension of the arm and contributing to joint stability.
Thus, the deltoid, coracobrachialis, and triceps brachii muscles are all active during GH joint movements, specifically in abduction and adduction. The deltoid is a prime flexor and plays a crucial role in abduction, while the coracobrachialis and triceps brachii assist as weak flexors and are involved in adduction, depending on the arm's position.
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The rotator cuff muscles are important stabilisers
The rotator cuff muscles originate from the scapula and insert into the humerus, forming a musculotendinous collar around the shoulder joint. They play a major role in the internal and external rotation of the arm, with the subscapularis muscle acting as a powerful internal rotator and the teres minor muscle primarily responsible for external rotation and adduction of the arm. The supraspinatus muscle initiates abduction of the arm, while the infraspinatus and teres minor muscles contribute to external rotation.
The primary biomechanical role of the rotator cuff is to stabilise the glenohumeral joint by compressing the humeral head against the glenoid cavity. This joint is a ball-and-socket style diarthroidal joint, considered the most mobile and least stable joint in the body. The rotator cuff muscles prevent the sliding of the head of the humerus during arm movements, allowing a full range of motion while maintaining stability.
The rotator cuff muscles are susceptible to injuries such as tears and impingements due to their involvement in the movement and stabilisation of the shoulder. These injuries can occur from lifting heavy objects, repetitive motions, or trauma to the shoulder. MRI examinations can provide key information about the extent of muscle tears and guide treatment approaches, which may include physical therapy or surgical intervention.
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The supraspinatus is key for movement initiation
The supraspinatus muscle is the most superiorly located of the four rotator cuff muscles, which also include the infraspinatus, teres minor, and subscapularis. The supraspinatus resides in the supraspinous fossa of the scapula, superior to the scapular spine, and is considered key for movement initiation.
The supraspinatus is involved in abduction of the arm, pulling the head of the humerus medially towards the glenoid cavity. It prevents the head of the humerus from slipping inferiorly and works with the deltoid muscle to perform abduction. The deltoid becomes the main propagator of this action beyond 15 degrees of abduction. The supraspinatus is also believed to contribute weakly to the lateral rotation of the humerus.
The supraspinatus is one of the most frequently damaged components of the rotator cuff, with tears being a common injury. Bad posture and age are leading risk factors for supraspinatus tears, and these injuries are associated with acromial impingement, frozen shoulder, and poor sleep. A 2016 study found that arthroscopic surgery for rotator cuff tears was effective for improving shoulder functionality and reducing pain.
The supraspinatus is also important for stabilising the shoulder joint. It helps resist the gravitational forces acting on the shoulder joint and keeps the head of the humerus firmly pressed against the glenoid fossa of the scapula. This dynamic stabilisation helps maintain the structural integrity of the joint.
In summary, the supraspinatus muscle is key for movement initiation, particularly in the abduction of the arm. It also plays a crucial role in stabilising the shoulder joint and preventing injuries.
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The scapulothoracic retractor and downward rotator muscles are essential for functional movements
The scapulothoracic joint is a ball-and-socket style diarthroidal joint that is responsible for connecting the upper extremity to the trunk. It is formed from the combination of the humeral head and the glenoid fossa of the scapula. The glenohumeral joint is considered the most mobile and least stable joint in the body.
The scapula is an important bone that allows for multiple types of motion, including protraction, retraction, elevation, depression, upward rotation, and downward rotation. This enables us to have a fully functional upper extremity area. The scapulothoracic retractor and downward rotator muscles are, therefore, essential for functional movements.
The trapezius, rhomboids, and latissimus dorsi muscles are responsible for retraction. The trapezius and serratus anterior muscles are responsible for upward rotation. Gravity, and the latissimus dorsi, levator scapulae, rhomboids, and pectoralis major and minor muscles, assist in downward rotation.
Scapular retractions involving a resistance band are highly effective as warm-ups and can help strengthen the middle and upper back muscles. This exercise focuses on the upward and downward movements of the scapulars.
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Frequently asked questions
The primary muscles that produce adduction of the GH joint are the teres major, latissimus dorsi, and pectoralis major.
The GH joint is responsible for connecting the upper extremity to the trunk. It is one of four joints that comprise the shoulder complex.
Larger muscles involved in shoulder movements include the trapezius, levator scapula, pectoralis, deltoids, serratus anterior, latissimus dorsi, rhomboids, teres major, biceps, coracobrachialis, and triceps muscles.
