The Shoulder (Glenohumeral) Joint

Note difference in size of articular surfaces (size ratio of 1:4) and poor congruence - poor stability

Glenoid fossa is deepened by the fibrocartilage glenoid labrum – improves size ratio
Triangular in X-section
Labrum is complete (compare with acetabular labrum in the hip)

Capsule is reinforced posteriorly, anteriorly and superiorly by the tendons of the rotator cuff muscles
Note laxity of capsule and inferior fold when arm held in the anatomical position

The capsule is pierced anteriorly to allow the passage of the tendon of the long head of biceps from its origin to the muscle belly
At this point the capsule is thickened by a series of transverse fibres passing from the greater to the lesser tubercle - The Transverse Humeral ligament - to stabilise the tendon

Superior Glenohumeral Joint ligament passes to from the upper part of the glenoid and labrum to just superior to the lesser tubercle
Middle Glenohumeral Joint ligament - absent in up to 30% of individuals - passes from the anterior glenoid to just medial to the lesser tubercle
Inferior Glenohumeral Joint ligament - passes from the lower glenoid to the neck of the humerus - most important of the 3 ligaments as it tighten in abduction providing inferior stability

In addition to the 3 Glenohumeral Joint ligaments there is another ligament to consider at the shoulder joint - the coracohumeral ligament
Passes from the lateral border of the corocoid process to the greater tubercle (overlies the transverse humeral ligament)
Function - to stabilise the dependent arm

Note presence of supscapular bursa anteriorly to separate tendon of subscapularis from the anterior margin of the joint (communicating)
Also as the long head of biceps passes from its origin under over the head of humerus and in the intertubercular sulcus it is encased in a double layer of synovial membrane

Lies between the deltoid & the coracoacromial arch and the upper end of humerus
It is a non-communicating bursa whose function is to allow friction free movement between the humerus/upper rotator cuff tendon and the CA arch

Inherently unstable - poor congruency of articular surfaces, poor size ratio, lax capsule and weak or absent ligaments
Stability is increased by

A line (concave laterally) passing through a point 1cm lateral to the tip of the corocoid porocess

Glenohumeral Joint ligaments can be identified by finding the surface marking of the shoulder joint - their proximal attachments are just medial to the joint whereas their distal attachments can be found with reference to the lesser tubercle

When assessing the end of a joint range of motion each movement should have a specific end feel - soft tissue apposition, bony apposition, ligamentous tension, muscular tension
Multiaxial joint therefore movements are possible in all 3 planes
Flexion - (180∞) - limited by soft tissue tension (extensors)
Extension - (45∞) - limited by tension in the extracapsular ligaments and shoulder flexors
Abduction - (100∞) - limited by engagement of the greater tubercle into the coracoacromial arch and tension in adductors, inferior part of of capsule and inferior GHJ ligament - if the arm is externally rotated at this point the arm can move through abduction to 180∞ of elevation
Adduction - (45∞) - limited by soft tissue apposition
Medial Rotation - (90∞) - limited by tension in posterior capsule and lateral rotators
Lateral Rotation - (90∞) - limited by Glenohumeral Joint ligaments, anterior capsule and medial rotators