Orientated superiorly (140º) and posteriorly (30º)
Covered in hyaline cartilage
Glenoid fossa (cavity)
Situated on the lateral aspect of scapula
Typically pear shaped
Covered in hyaline cartilage
In anatomical position faces antero-laterally
Note difference in size of articular surfaces (size ratio of 1:4) and poor congruence - poor stability
Glenoid Labrum
Glenoid fossais deepened by the fibrocartilage glenoid labrum – improves size ratio
Triangular in X-section
Labrum is complete (compare with acetabular labrum in the hip)
Capsule
Loose cylindrical sleeve passing from just beyond glenoid articular margins
On humerus extends to
Anatomical neck and tubercles anteriorly, posteriorly and superiorly
Medial shaft of humerus inferiorly
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
Opening for Biceps Tendon
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
Ligaments
The anterior capsule is reinforced anteriorly by 3 weak ligaments
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
Coracohumeral ligament
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
Synovial Membrane
Lines Capsule:
attached to the articular margins of both the glenoid fossa and head of humerus
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
Subacromial Bursa
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
Stability of the Glenohumeral Joint (GHJ)
Inherently unstable - poor congruency of articular surfaces, poor size ratio, lax capsule and weak or absent ligaments
Stability is increased by
Glenoid labrum
Rotator cuff tendons
Tendon of long head of biceps
Larger muscles overlying joint
Stability is predominantly offered by muscles
Surface Markings
Anteriorly
A line (concave laterally) passing through a point 1cm lateral to the tip of the corocoid porocess
Laterally
A line passing through the apex of the greater tubercle (concave inferiorly)
Ligaments
Glenohumeral Joint ligamentscan 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
Movements at the Shoulder Joint
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