Shoulder Region Flashcards
How is the shoulder joint formed (articulation)?
The shoulder joint is formed by the articulation of the head of the humerus with the glenoid cavity (or fossa) of the scapula. This gives rise to the alternate name for the shoulder joint – the glenohumeral joint.
Both the articulating surfaces are covered with hyaline cartilage – which is typical for a synovial type joint. The head of the humerus is much larger than the glenoid fossa, giving the joint inherent instability. To reduce the disproportion in surfaces, the glenoid fossa is deepened by a fibrocartilage rim, called the glenoid labrum.
Describe the joint capsule and bursae of the shoulder joint
The joint capsule is a fibrous sheath which encloses the structures of the joint. It extends from the anatomical neck of the humerus to the border of the glenoid fossa. The joint capsule is lax, permitting greater mobility (particularly abduction). The synovial membrane lines the inner surface of the joint capsule, and produces synovial fluid to reduce friction between the articular surfaces.
To reduce friction in the shoulder joint, several synovial bursae are present. A bursa is a synovial fluid filled sac, which acts as a cushion between tendons and other joint structures.
The bursae that are important clinically are:
Subacromial – Located inferiorly to the deltoid and acromion, and superiorly to the supraspinatus tendon and the joint capsule. It supports the deltoid and supraspinatus muscles. Inflammation of this bursa is the cause of several shoulder problems.
Subscapular – Located between the subscapularis tendon and the scapula. It reduces wear and tear on the tendon during movement at the shoulder joint.
Describe the ligaments of the shoulder
Glenohumeral ligaments (superior, middle and inferior) – Consists of three bands, which runs with the joint capsule from the glenoid fossa to the anatomical neck of the humerus. They act to stablise the anterior aspect of the joint.
Coroacohumeral ligament – Attaches the base of the coracoid process to the greater tubercle of the humerus. It supports the superior part of the joint capsule.
Transverse humeral ligament – Spans the distance between the two tubercles of the humerus. It holds the tendon of the long head of the biceps in the intertubecular groove.
The other major ligament is the coracoacromial ligament. Unlike the others, it is not a thickening of the joint capsule. It runs between the acromion and coracoid process of the scapula, forming the coraco-acromial arch. This structure overlies the shoulder joint, preventing superior displacement of the humeral head.
Describe neurovascular supply to the shoulder joint
Arterial supply to the glenohumeral joint is via the anterior and posterior circumflex humeral arteries, and the suprascapular artery. Branches from these arteries form an anastamotic network around the joint.
The joint is supplied by the axillary, suprascapular and lateral pectoral nerves. These nerves are derived from roots C5 and C6 of the brachial plexus. Thus, an upper brachial plexus injury (Erb’s palsy) will affect shoulder joint function.
Describe movements of the shoulder joint
Extension (upper limb backwards in sagittal plane). Produced by the posterior deltoid, latissimus dorsi and teres major.
Flexion (upper limb forwards in sagittal plane). Produced by the biceps brachii (both heads), pectoralis major, anterior deltoid and corocobrachialis.
Abduction (upper limb away from midline in coronal plane) The first 0-15 degrees of abduction is produced by the supraspinatus. The middle fibres of the deltoid are responsible for the next 15-90 degrees. Past 90 degrees, the scapula needs to be rotated to achieve abduction – that is carried out by the trapezius and serratus anterior.
Adduction (upper limb towards midline in coronal plane). Produced by contraction of pectoralis major, latissimus dorsi and teres major.
Medial Rotation (rotation towards the midline, so that the thumb is pointing medially). Produced by contraction of subscapularis, pectoralis major, latissimus dorsi, teres major and anterior deltoid.
Lateral Rotation (rotation away from the midline, so that the thumb is pointing laterally). Produced by contraction of the infraspinatus and teres minor.
What factors contribute to shoulder joint stability?
Type of joint – It is a ball and socket joint.
Bony surfaces – Shallow glenoid cavity and large humeral head – there is a 1:4 disproportion in surfaces. A commonly used analogy is the golf ball and tee. Laxity of the joint capsule.
What factors contribute to shoulder joint mobility?
Rotator cuff muscles – These muscles surround the shoulder joint, attaching to the tubercles of the humerus, whilst also fusing with the joint capsule. The resting tone of these muscles act to ‘pull’ the humeral head into the glenoid cavity.
Glenoid labrum: This is a fibrocartilaginous ridge surrounding the glenoid cavity. It deepens the cavity, reducing the risk of dislocation.
Ligaments – The ligaments act to reinforce the joint capsule, and forms the coraco-acromial arch.
What is the difference between the extrinsic and intrinsic muscles of the shoulder?
Extrinsic – originate from the torso, and attach to the bones of the shoulder (clavicle, scapula or humerus). Intrinsic – originate from the scapula and/or clavicle, and attach to the humerus.
What are the superficial extrinsic muscles?
the trapezius and latissimus dorsi
Give the attachments, actions and innervation of the trapezius
Attachments: Originates from the skull, ligamentum nuchae and the spinous processes of C7-T12. The fibres attach to the clavicle, acromion and the scapula spine.
Innervation: Motor innervation is from the accessory nerve. It also receives proprioceptor fibres from C3 and C4 spinal nerves.
Actions: The upper fibres of the trapezius elevates the scapula and rotates it during abduction of the arm. The middle fibres retract the scapula and the lower fibres pull the scapula inferiorly.
Give the attachments, actions and innervation of latissimus dorsi
Attachments: Has a broad origin – arising from the spinous processes of T6-T12, iliac crest, thoracolumbar fascia and the inferior three ribs. The fibres converge into a tendon that attaches to the intertubecular sulcus of the humerus.
Innervation: Thoracodorsal nerve.
Actions: Extends, adducts and medially rotates the upper limb.
What are the deep extrinsic muscles?
There three muscles in this group – the levator scapulae and the two rhomboids. They are situated in the upper back, underneath the trapezius.
Give the attachments, actions and innervation of the levator scapulae
Attachments: Originates from the transverse processes of the C1-C4 vertebrae and attaches to the medial border of the scapula.
Innervation: Dorsal scapular nerve.
Actions: Elevates the scapula.
Give the attachments, actions and innervation of rhomboid major
Attachments: Originates from the spinous processes of T2-T5 vertebrae. Attaches to the medial border of the scapula, between the scapula spine and inferior angle.
Innervation: Dorsal scapula nerve.
Actions: Retracts and rotates the scapula.
Give the attachments, actions and innervation of rhomboid minor
Attachments: Originates from the spinous processes of C7-T1 vertebrae. Attaches to the medial border of the scapula, at the level of the spine of scapula.
Innervation: Dorsal scapula nerve.
Actions: Retracts and rotates the scapula.
Can you label the extrinsic muscles of the shoulder?
Can you label the rotator cuff muscles?
