The shoulder joint (glenohumeral joint) is a ball and also socket joint between the scapula and the humerus. That is the significant joint connecting the upper limb to the trunk.
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It is one of the many mobile joints in the human body, at the price of joint stability. In this article, we shall look at the anatomy the the shoulder joint and also its necessary clinical correlations.
Structures the the Shoulder Joint
The shoulder share is formed by the coupling of the head of the humerus through the glenoid cavity (or fossa) of the scapula. This gives rise to the alternating name because that the shoulder share – the glenohumeral joint.
Like many synovial joints, the articulating surfaces are covered with hyaline cartilage. The head that the humerus is much larger than the glenoid fossa, giving the joint a wide variety of activity at the cost of natural instability. To reduce the disproportion in surfaces, the glenoid fossa is deepened by a fibrocartilage rim, referred to as the glenoid labrum.
Fig 1 – The articulating surface of the shoulder joint.
Joint Capsule and also Bursae
The joint capsule is a fibrous sheath which encloses the frameworks of the joint.
It extends from the anatomical neck of the humerus come the border or ‘rim’ of the glenoid fossa. The joint capsule is lax, permitting higher 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 alleviate friction in the shoulder joint, several synovial bursae are present. A bursa is a synovial fluid filled sac, i m sorry acts as a cushion in between tendons and other joint structures.
The bursae the are necessary clinically are:Subacromial – situated deep to the deltoid and also acromion, and superficial come the supraspinatus tendon and also joint capsule. The subacromial bursa to reduce friction beneath the deltoid, promoting totally free motion of the rotator cuff tendons. Subacromial bursitis (i.e. Inflammation the the bursa) have the right to be a cause of shoulder pain.Subscapular – located between the subscapularis tendon and also the scapula. That reduces wear and tear on the tendon during movement at the shoulder joint.
There are various other minor bursae present in between the tendons that the muscles roughly the joint, however this is past the border of this article.
Fig 2 – The significant bursae the the shoulder joint.
In the shoulder joint, the ligaments pat a key role in stabilising the bony structures.Glenohumeral ligaments (superior, middle and also inferior) – the share capsule is formed by this group of ligaments connecting the humerus to the glenoid fossa. They are the main resource of stability for the shoulder, holding it in place and also preventing it from dislocating anteriorly. Lock act come stabilise the anterior aspect of the joint.Coracohumeral ligament – attaches the basic of the coracoid process to the greater tubercle that the humerus. It support the superior component of the joint capsule.Transverse humeral ligament – spans the distance between the two tubercles of the humerus. The holds the tendon that the lengthy head of the biceps in the intertubercular groove.>Coraco–clavicular ligament – written of the trapezoid and conoid ligaments and also runs from the clavicle to the coracoid procedure of the scapula. They job-related alongside the acromioclavicular ligament to preserve the alignment that the clavicle in relation to the scapula. They have far-reaching strength but huge forces (e.g. After a high power fall) have the right to rupture these ligaments as part of one acromio-clavicular share (ACJ) injury. In major ACJ injury, the coraco-clavicular ligaments may require surgical repair.
The other significant ligament is the coracoacromial ligament. Running between the acromion and coracoid procedure of the scapula it develops the coraco-acromial arch. This framework overlies the shoulder joint, staying clear of superior displacement of the humeral head.
Fig 3 – The ligaments the the shoulder joint. The transverse humeral ligament is not shown on this diagram
As a ball and socket synovial joint, there is a wide selection of activity permitted:Extension (upper limb backwards in sagittal plane) – posterior deltoid, latissimus dorsi and also teres major.Flexion (upper body forwards in sagittal plane) – pectoralis major, anterior deltoid and also coracobrachialis. Biceps brachii weakly assists in front flexion.Abduction (upper limb far from midline in coronal plane):The first 0-15 levels of kidnapping is produced by the supraspinatus.The center fibres of the deltoid space responsible for the following 15-90 degrees.Past 90 degrees, the scapula demands to be rotated to accomplish abduction – the is brought out by the trapezius and also serratus anterior.Adduction (upper limb towards midline in coronal plane) – pectoralis major, latissimus dorsi and teres major.Internal rotation (rotation towards the midline, so the the thumb is pointing medially) – subscapularis, pectoralis major, latissimus dorsi, teres major and anterior deltoid.External rotation (rotation far from the midline, so that the ignorance is pointing laterally) – infraspinatus and also teres minor.
Mobility and also Stability
The shoulder joint is among the many mobile in the body, in ~ the price of stability. Here, we shall think about the factors the permit movement, and those that add towards share structure.
Factors that add to mobility:Type that joint – ball and socket joint.Bony surfaces – shallow glenoid cavity and huge humeral head – there is a 1:4 disproportion in surfaces. A frequently used analogy is the golf ball and tee.Inherent laxity that the joint capsule.
Factors that contribute to stability:Rotator cuff muscles – surround the shoulder joint, attaching to the tuberosities the the humerus, whilst also fusing with the share capsule. The resting tone of this muscles act come compress the humeral head into the glenoid cavity.Glenoid labrum – a fibrocartilaginous ridge surrounding the glenoid cavity. It deepens the cavity and creates a seal v the head that humerus, reduce the risk of dislocation.Ligaments – act come reinforce the joint capsule, and type the coraco-acromial arch.Biceps tendon – it acts as a boy humeral head depressor, in order to contributing come stability.
Fig 4 – The rotator cuff muscles, i beg your pardon act come stabilise the shoulder joint.
The shoulder joint is supplied by the anterior and posterior circumflex humeral arteries, which are both branches of the axillary artery. Branches that the suprascapular artery, a branch the the thyrocervical trunk, likewise contribute.
Innervation is detailed by the axillary, suprascapular and lateral pectoral nerves.
Clinical Relevance: typical Injuries
Dislocation that the Shoulder Joint
Clinically, dislocations at the shoulder are explained by wherein the humeral head lies in relation to the glenoid fossa. Anterior dislocations space the most prevalent (95%), although posterior (4%) and inferior (1%) dislocations have the right to sometimes occur. Premium displacement the the humeral head is impede by the coraco-acromial arch.
An anterior dislocation is usually led to by excessive extension and lateral rotation of the humerus. The humeral head is required anteriorly and also inferiorly – into the weakest part of the joint capsule. Tearing the the share capsule is connected with an raised risk the future dislocations. Hill-Sachs lesions (impaction fracture the posterolateral humeral head versus anteroinferior glenoid) and also Bankart lesions (detachment of antero-inferior labrum through or there is no an avulsion fracture) can also occur following anterior dislocation.
Indeed, so-called ‘reverse Hill-Sachs lesions’ (impaction fracture of anteromedial humeral head) and also ‘reverse Bankart lesions’ (detachment the posteroinferior labrum) have the right to be watched in posterior dislocations.
The axillary nerve runs in close proximity come the shoulder joint and also around the operation neck that the humerus, and so it have the right to be damaged in the dislocation or through attempted reduction. Injury to the axillary nerve reasons paralysis that the deltoid, and loss that sensation end regimental argorial area.
Fig 5 – Anterior dislocation of the shoulder joint.
Rotator Cuff Tendonitis
The rotator cuff muscles have actually a an extremely important function in stabilising the glenohumeral joint. Lock are frequently under hefty strain, and therefore injuries of these muscles are fairly common.
The spectrum that rotator cuff pathology comprises tendinitis, shoulder impingement and also sub-acromial bursitis. Tendinitis advert to inflammation of the muscle tendons – usually as result of overuse. End time, this causes degenerative changes in the subacromial bursa and also the supraspinatus tendon, potentially leading to bursitis and also impingement.
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The characteristic sign of supraspinatus tendinitis is the ‘painful arc’ – ache in the middle of abduction between 60-120 degrees, wherein the influenced area comes into contact with the acromion. This authorize may likewise suggest a partial tear that supraspinatus.