| Glenohumeral joint | |
|---|---|
| The right shoulder and Glenohumeral joint | |
| Latin | articulatio humeri |
| Gray's | subject #82 315 |
| MeSH | Glenohumeral+Joint |
The glenohumeral joint, (from ancient Greek glene, eyeball, puppet, doll + -oid, 'form of', + Latin humerus, shoulder) or shoulder joint, is a multiaxial synovial ball and socket joint and involves articulation between the glenoid fossa of the scapula (shoulder blade) and the head of the humerus (upper arm bone). Due to the very limited interface of the humerus and scapula, it is the most mobile joint of the human body.
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The glenoid fossa is shallow and contains the glenoid labrum which deepens it and aids in stability. With 120 degrees of unassisted flexion, the glenohumeral joint is the most mobile joint in the body.
Scapulohumeral rhythm helps to achieve further range of movement. The Scapulohumeral rhythm is the movement of the scapula across the thoracic cage in relation to the humerus. This movement can be compromised by anything that changes the position of the scapula. This could be an imbalance in the muscles that hold the scapula in place which are the upper and lower trapezium. This imbalance could cause a forward head carriage which in turn can affect the range of movements of the shoulder.
The rotator cuff muscles of the shoulder produce a high tensile force, and help to pull the head of the humerus into the glenoid fossa.
| Movement | Muscles | Origin | Insertion |
|---|---|---|---|
| Flexion (150°–170°) |
Anterior fibers of deltoid | Clavicle | Middle of lateral surface of shaft of humerus |
| Clavicular part of pectoralis major | Clavicle | Lateral lip of bicipital groove of humerus | |
| Long head of biceps brachii | Supraglenoid tubercle of scapula | Tuberosity of radius, Deep fascia of forearm | |
| Short head of biceps brachii | Coracoid process of scapula | ||
| Coracobrachialis | Coracoid process | Medial aspect of shaft of humerus | |
| Extension (40°) |
Posterior fibers of deltoid | Spine of scapula | Middle of lateral surface of shaft of humerus |
| Latissimus dorsi | Iliac crest, lumbar fascia, spines of lower six thoracic vertebrae, lower 3–4 ribs, inferior angle of scapula | Floor of bicipital groove of humerus | |
| Teres major | Lateral border of scapula | Medial lip of bicipital groove of humerus | |
| Abduction (160°–180°) |
Middle fibers of deltoid | Acromion process of scapula | Middle of lateral surface of shaft of humerus |
| Supraspinatus | Supraspinous fossa of scapula | Greater tuberosity of humerus | |
| Adduction (30°–40°) |
Sternal part of pectoralis major | Sternum, upper six costal cartilages | Lateral lip of bicipital groove of humerus |
| Latissimus dorsi | Iliac crest, lumbar fascia, spines of lower six thoracic vertebrae, lower 3-4 ribs, inferior angle of scapula | Floor of bicipital groove of humerus | |
| Teres major | Lower third of lateral border of scapula | Medial lip of bicipital groove of humerus | |
| Teres minor | Upper two thirds of lateral border of scapula | Greater tuberosity of humerus | |
| Lateral rotation (in abduction: 95°; in adduction: 70°) |
Infraspinatus | Infraspinous fossa of scapula | Greater tuberosity of humerus |
| Teres minor | Upper two thirds of lateral border of scapula | Greater tuberosity of humerus | |
| Posterior fibers of deltoid | Spine of scapula | Middle of lateral surface of shaft of humerus | |
| Medial rotation (in abduction: 40°–50°; in adduction: 70°) |
Subscapularis | Subscapular fossa | Lesser tuberosity of humerus |
| Latissimus dorsi | Iliac crest, lumbar fascia, spines of lower 3-4 ribs, inferior angle of scapula | Floor of bicipital groove of humerus | |
| Teres major | Lower third of lateral border of scapula | Medial lip of bicipital groove of humerus | |
| Anterior fibers of deltoid | Clavicle | Middle of lateral surface of shaft of humerus |
The glenohumeral joint has a loose capsule that is lax inferiorly and therefore is at risk of dislocation inferiorly. The long head of the biceps brachii muscle travels inside the capsule to attach to the supraglenoid tubercle of the scapula.
Because the tendon is inside the capsule, it requires a synovial tendon sheath to minimize friction.
A number of bursae in the capsule aid mobility. Namely, they are the subdeltoid bursa (between the joint capsule and deltoid muscle), subcoracoid bursa (between joint capsule and coracoid process of scapula), coracobrachial bursa (between subscapularis muscle and tendon of coracobrachialis muscle), subacromial bursa (between joint capsule and acromion of scapula) and the subscapular bursa (between joint capsule and tendon of subscapularis muscle, also known as subtendinous bursa of subscapularis muscle). The bursa are formed by the synovial membrane of the joint capsule. An inferior pouching of the joint capsule between teres minor and subscapularis is known as the axillary recess.
The shoulder joint is a muscle dependent joint as it lacks strong ligaments.
branches of the anterior & posterior circumflex humeral & suprascapular arteries.
The capsule can become inflamed and stiff, with abnormal bands of tissue (adhesions) growing between the joint surfaces, causing pain and restricting movement of the shoulder, a condition known as frozen shoulder or adhesive capsulitis.
The acromion ranks among the osseous structures which feature the highest variability. The lateral margin could have a smooth convex arch, but also present several knobs, spikes, sharp or diffuse fissures, or even a large flat depression. Those shape variations have no functional significance compared to the variations at the anterior third, which essentially affect the subacromial space for the rotator cuff. [2] Bigliani proclaimed 3 types:
The glenoid labrum is a wedge shaped fibro-cartilaginous structure that is fixed at the glenoid border of the scapula and surrounds the glenoid like a wreath. The labrum doubles the joint surface of the glenoid for the humeral head and is also responsible for a certain stability in the antero-posterior movements. The following variants from the norm can be mis-interpreted as so-called SLAP lesions. The transversal stratification from the lower edge of the acromion up to the lower edge of the glenoid fossa is mandatory in order to depict changes of the glenoid labrum. Furthermore are oblique coronal or oblique sagittal planes not necessary examinations. Yet can they help to depict precisely the rotator cuff or the shape of the humeral head.[4]
1. The sublabral superior recess:
Linear inflow of contrast agent between labrum and glenoid at the paracoronal sequence. Typically straightened medially towards the tuberculum supraglenoidale. The superior labrum often isn’t completely attached to the glenoid. There can be a variously deep sulcus which communicates with the joint cavity. This anatomical variation is depictable at the 12 o’clock position in the oblique sagittal MR projection and can be subdivided into 3 types.
Park et al. examined 95 asymptomatic shoulders using MRA and was able to demonstrate a recess in 30% of the cases.[5]
2. The sublabral foramen:
It can be found in around 11% of the cases and should not be confused with a sublabral superior recess. The range of the foramen is large. From only few millimeters up to a complete ablation of the antero-superior labrum. In contrast to the sublabral superior recess, is the sublabral superior foramen depictable in the oblique sagittal projection, positioned antero-superiorly at around 2 o’clock. And Inflow of contrast agent can be seen at the axial sequence between labrum and glenoid. It can sometimes be found combined with a sublabral superior recess. Enhanced MR imaging via an intraarticular contrast agent injection, can lead to a false positive interpretation as a labral injury. This variation of the norm is positioned antero-superiorly. Bankart lesions for example have an antero-inferior localisation.[6]
3. The Buford complex:
The Buford complex can be found in 1.5% of the population. It consists of a ribbon-like thickening of the medial gleno-humeral ligament (GHL) and is further characterized by a lack of anterior superior labrum. The medial GHL inserts just at the area of the antero-superior glenoid. A thickened medial GHL can be confused with a displaced labral fragment on the arthroscope.
And furthermore:
4. In 50% of the cases a triangular linear signal increasement can be found at the area of the anterior labrum through hyaline cartilage. This is the most common shape and accounts for 73% in the posterior area and for 45% in the anterior area.
5. In 20% of the cases the labrum is rounded.
6. In 7% of the cases the labrum is comma-shaped flattened.
7. In 15% of the cases the labrum is splitted.
8. In 8% of the cases the labrum is notched.
9. The labrum has a central signal increasement.
10. The labrum has a linear signal increasement.
There are four known anatomical variants of the anterior capsule and ligaments in the anterior region.
The complex composed of glenoid, labrum and gleno-humeral ligaments is essential for the shoulder stability. The glenoid labrum is not a morphological entity. It consists of different zones and features multiple anatomical variants. These are of special importance at the areas superior and antero-superior of the long biceps tendon insertion. A clear discrimination between physiological varieties and pathological findings is of great clinical significance. Not via imaging, but on corpses defined Barthel T. et al. anatomical structures of the glenoid labrum. The labrum is at the postero-inferior parts firmly adhered to the glenoid. However, the supero-anterior part is rather loose and can be subdivided into a cranial labrum-biceps-tendon complex and an anterior labrum-capsule-complex. The fibers of the long biceps tendon irradiate in different forms into the labrum. Subdivided into an anterior and a posterior rein. After Vangsness et al. there are 4 types, of which type 2 is the most common. [8]
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