The movement of the shoulder joint involves the combined movement of several joints. For example, the sternoclavicular joint, the acromioclavicular joint, the scapular joint and the glenohumeral joint. The glenohumeral joint is the main joint of the shoulder.
I. Active movements of the shoulder joint
Flexion/extension (160-180 degrees/50-60 degrees)
Abduction/adduction (170-180 degrees/50-75 degrees)
Abduction in the scapular plane (170-180)
External rotation/internal rotation (80-90 degrees/60-100 degrees)
Abduction/adduction in horizontal position (45 degrees/130 degrees)
II. Scapulohumeral rhythm
Scapula: humerus = 2:1
Phase I: In the first 30 degrees of shoulder joint abduction, mainly done by the glenohumeral joint
Stage 2: After 30 degrees of shoulder joint abduction, the scapula begins to rotate upward on the chest wall and the subscapular angle moves forward.
Sternoclavicular joint: Clavicle elevation of approximately 30 degrees (or 25 degrees)
Acromioclavicular joint: 5 degrees of superior rotation
Glenohumeral joint: 60 degrees of abduction
Stage 3: Sternoclavicular joint: clavicle remains elevated 30 degrees and rotates approximately 45 degrees (or 25 degrees) posteriorly about the long axis
Acromioclavicular joint: 30 degrees of supination (or 35 degrees)
Glenohumeral joint: 120 degrees of abduction
III. Motor muscles of the shoulder joint
Scapula
Upward lift: scapularis elevator, rhomboid muscle
Lowering: lower trapezius, latissimus dorsi, pectoralis minor, subclavian muscle (role is not determined)
Upper rotation: superior trapezius, inferior trapezius, serratus anterior
Inferior rotation: scapularis elevator, rhomboid, pectoralis minor
Anterior extension: pectoralis major, pectoralis minor, serratus anterior
Posterior extension: lesser rhomboids, middle trapezius, latissimus dorsi
Glenohumeral joint
Abduction: middle bundle of deltoid, rotator cuff
Adduction: anterior deltoid, posterior deltoid, latissimus dorsi, pectoralis major, rostrum brachii, rhomboid, triceps longus
Flexion: pectoralis major clavicularis, anterior deltoid, rostrum brachii, long head of biceps brachii
Extension: triceps long head, posterior deltoid, teres minor, latissimus dorsi
Internal rotation: pectoralis major, anterior deltoid bundle, vastus lateralis, latissimus dorsi, subscapularis
External rotation: posterior deltoid, infraspinatus, teres minor
4.Stability of the shoulder joint
The stability of the shoulder joint is mainly maintained by the ligaments of the joint capsule, the joint components, the negative pressure in the joint cavity, and the glenoid lip.
The ligamentous complex of the joint capsule consists of the superior glenohumeral ligament, the middle glenohumeral ligament, the anterior inferior glenohumeral ligament, the posterior inferior glenohumeral ligament, and the rostro-humeral ligament.
1. Superior glenohumeral ligament: restricts external rotation and inferior displacement of the humeral head
2. Middle glenohumeral ligament: restricts external rotation and anterior displacement of the humeral head
3.Inferior glenohumeral ligament.
Anterior branch: restricts external rotation, upward and forward movement of the humeral head
Posterior branch: restricts internal rotation and anterior movement of the humeral head
When the upper limb is on both sides of the trunk, the superior glenohumeral ligament and the middle glenohumeral ligament have the greatest restrictive effect.
The middle glenohumeral ligament and inferior glenohumeral ligament have the greatest restrictive effect when the upper extremity is abducted at 45 degrees.
When the upper limb is abducted 90 degrees, the inferior glenohumeral ligament has the greatest restrictive effect.
4.Rostral humeral ligament: It starts from the rostral process and is attached to the humerus together with the joint capsule after mixing. During external rotation of the shoulder, this ligament is tensed and prevents shoulder subluxation.
Dynamic stabilization
The dynamic elements of the shoulder joint are maintained by the muscles surrounding the shoulder joint. The rotator cuff is the key to maintaining dynamic stability. The rotator cuff is composed of the supraspinatus, infraspinatus, teres minor, and subscapularis muscles. The supraspinatus maintains the stability of the shoulder by pulling the humeral head toward the glenoid; the infraspinatus and the lesser circular muscle can externally rotate the humeral head when the supraspinatus is activated and stabilize the shoulder joint by putting pressure on the joint; the subscapularis functions similarly to the internal rotators.
V. Nerve structure
The motor and sensory branches of the glenohumeral joint are mainly derived from the C5 and C6 levels
The glenohumeral capsule is mainly innervated by the suprascapular nerve (C5,C6) and axillary nerve (C5,C6)
the brachial plexus nerve is encapsulated and vulnerable to compression: the cervical foramen; the anterior and middle oblique muscles; the clavicle and the first costal space