Joints - Shoulder Joint Flashcards
What other name is the shoulder joint known by?
What type of joint is the GHJ?
Glenohumeral joint (GHJ).
It is the most mobile joint, at the cost of joint stability.
This is known as a ball and socket joint.
What are the articuating surfaces of the GHJ?
Formed by the head of the humerus and the glenoid fossa of the scapula.
Like most articulating surfaces the GHJ is lined with hyaline cartilage.
The glenoid fossa is deepened by a fibrocartilage rim, called the glenoid labrum.
What are the features of the joint capsule of the GHJ?
The joint capsule is fibrous shear that encloses the structures of the joint.
It extends form 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.
WhaT clinically relevant bursae are present in the GHJ?
1) Subacromial - located deep to the deltoid and acromion, and superficial to the supraspinatus and joint capsule. This bursa serves to reduce friction beneath the deltoid, promoting free motion of the rotator cuff tendons.
Clinical relevance - subacromial bursitis (i.e. inflammation of the bursa) can be a cause of shoulder pain.
2) Subscapular - located between the subscapularis tendon and the scapula. It reduces wear and tear on the tendon during movement at the shoulder joint.
There are other minor bursae present between the tendons of the muscles around the joint.
What are the ligaments of the GHJ?
1) Glenohumeral ligaments (superior, middle and inferior) - the joint capsule is formed by this group of ligaments connecting the humerus to the glenoid fossa. They are the main source of stability for the shoulder, holding it in place and preventing it from dislocating anteriorly. They act to stabilise the anterior aspect of the joint.
2) Coracohumeral joint - attaches the base of the coracoid process to the greater tubercle of the humerus. It supports the superior part of the joint capsule.
3) Transverse humeral ligament - spans the distance between the two tubercles of the humerus. This holds the tendon of the long head of the biceps in the intertubercular groove.
4) Coraco-clavicular ligament - composed of the trapezoid and conoid ligaments and runs from the clavicle to the coracoid process of the scapula. They work alongside the the AC ligament to maintain the alignment of the clavicle in relation to the scapula. They have significant strength but larges forces (e.g. after a highe energy fall) can rupture these ligaments as part of the ACJ injury. In severe ACJ injury, the coraco-clavicular ligaments may require surgical repair.
5) Coraco-acromial ligament - runs between the acromion and the coracoid process of the scapula it formed the coraco-acromial arch. This structure overlies the shoukder joint, preventing superior displacement of the humeral head.
What are the movements of the GHJ?
1) Extension (upper limb backwards in saggital plane) - posterior deltoid, latissimus dorsi and teres major.
2) Flexion (upper limb forwards in saggital plane) - pectoralis major, anterior deltoid and coracobrachialis. Biceps brachii weakly assists the forward flexion.
3) Abduction (upper limb away from the midline in coronal plane):
i) First 15 degrees - supraspinatus
ii) 15 - 90 degrees - middle fibres of deltoid
iii) >90 degrees - scapular needs to rotate to achieve abduction - trapezius and serratus anterior.
4) Adduction (upper limb towards midline in coronal plane) - pectoralis major, latissimus dorsi and teres major.
5) Internal rotation - subscapularis, pectorlais major, latissimus dorsi, teres major and anterior deltoid.
6) External rotation - infraspinatus and teres minor.
What are the factors contributing to mobility?
1) Type of joint - ball and socket joint
2) Bony surfaces - shallow glenoid cavity and large humeral head. 1:4 disproportion in surfaces. Analogous to a golf ball and tee.
3) Inherent laxity of the joint capsule
What are the factors contributing to stability?
1) Rotator cuff muscles - surround the shoulder joint, attaching to the tuberosities fo the humerus, whilst also fusing with the joint capsule. The resting tone of these muscles act to compress the humeral head into the glenoid cavity.
2) Glenoid labrum - a fibrocartilaginous ridge surrounding the glenoid cavity. It deepens the cavity and creates a seal with the head of humerus, reducing the risk of dislocation.
3) Ligaments - acts to reingorce the joint capsule, and form the coraco-acromial arch.
4) Biceps tendon - it acts as a minor humeral head depressor, thereby contributing to stability.
What is the neurovasculature of the GHJ?
Supplied by:
1) Anterior and posterior circumflex humeral arteries (branches of the axillary artery).
2) Branches of the suprascapular artery and a branch of the thyrocervical trunk contribute.
1) Axillary
2) Suprascapular
3) Lateral pectoral
nerves provide innervation to the GHJ.
Clinical relevance: dislocation of the shoulder joint
Anterior dislocations are most prevalent (95%), but there are posterior (4%) and inferior (1%) dislocations.
Superior displacement of the humeral head is prevented by the coraco-acromial arch.
Anterior dislocation is caused by excessive extension and external rotation of the humerus. The head of the humerus is forced anteriorly and inferiorly - into the weakest part of the joint capsule.
Tearing of the joint capsule is associated with an increased risk of future dislocations.
Hill-Sachs lesion (impactiion of the posterolateral humeral head against the anteroinferior glenoid)
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Bankart lesions (detachment of the antero-inferior labrum with or without an avulsion fracture) can also occur following anterior dislocation.
‘Reverse Hill-Sachs lesion’ and ‘reverse Hill-Sachs lesion’ can be seen in posterior dislocations.
The axillary nerve runs in close proximity to the shoulder joint and around the surgical neck of the humerus, and so it can be damaged in the dislocation of with attempted reduction. Injury to the axillary nerve causes paralysis of the deltoid, and loss of sensation over regimented badge area.
Clinical relevance: rotator cuff tendonitis
The rotator cuff muscles have a very important rle in stablising the GHJ. They are often under heavy strain, and therefore injuries of these muscles are relatively common.
The spectrum of rotator cuff pathology comprises tendinitis, shoulder impingement and sub-acromial bursitis. Tendinitis refers to the inflammation of muscle tendons - usually due to overuse. Over time, this causes degenerative changes in the subacromial bursa and the suprasinatus tendon, potentially causing bursitis and impingement.
The characteristic sign of supraspinatus tendinitis is the ‘painful arc’ pain in the middle of abduction between 60-120 degrees, where the affected area comes into contact with the acromion. This sign may also suggest a partial tear of supraspinatus.
