Capsule and Ligaments of the Shoulder Joint
Capsular Ligament (Joint Capsule)
The fibrous capsule is thin and very loose, permitting free movement.
Medial attachment: margins of the glenoid cavity, beyond the glenoid labrum (enclosing the supraglenoid tubercle and thus the long head of biceps brachii within the joint cavity)
Lateral attachment: anatomical neck of the humerus, with exceptions:
- Inferiorly: extends down to the surgical neck (1.5 cm below anatomical neck)
- Superiorly: deficient to allow passage of the tendon of the long head of biceps brachii
The capsule is lined internally by synovial membrane, which forms a tubular sheath around the tendon of the long head of biceps brachii in the bicipital groove.
Apertures in the capsule:
- Between the tubercles of humerus — for passage of long head of biceps tendon
- Anteriorly, below the coracoid process — communicates with subscapular bursa
- Posteriorly — communicates with infraspinatus bursa
The capsule is least supported inferiorly, which is why dislocations most commonly occur downward (subglenoid).
Glenohumeral Ligaments
Three thickenings on the anterior part of the fibrous capsule, visible only from inside the joint:
| Ligament | Position |
|---|---|
| Superior glenohumeral ligament | Upper anterior capsule |
| Middle glenohumeral ligament | Mid anterior capsule |
| Inferior glenohumeral ligament | Lower anterior capsule |
A defect exists between the superior and middle glenohumeral ligaments — the Foramen of Weitbrecht — which is a common site of anterior dislocation of the humeral head.
Coracohumeral Ligament
- Strong band from the base/root of the coracoid process to the anterior aspect of the greater tubercle of the humerus
- Strengthens the capsule superiorly
- Reinforces the capsule where it would otherwise be weak
Transverse Humeral Ligament
- Broad fibrous band bridging the bicipital groove between the greater and lesser tubercles
- Converts the groove into a canal
- Retains the tendon of the long head of biceps brachii (surrounded by its synovial sheath) within the groove
Accessory Ligaments (Outside the Joint)
Coracoacromial Ligament
- Triangular ligament from the lateral border of the coracoid process to the tip of the acromion
- Forms the coracoacromial arch with these two bony processes
- Protects the superior aspect of the joint
Coracoacromial Arch
- Formed by: coracoid process + coracoacromial ligament + acromion process
- Acts as the secondary socket for the head of the humerus
- Prevents superior displacement of the humeral head
- The supraspinatus tendon passes beneath this arch