shoulder osteology

The shoulder consists of four primary joints:

·       Glenohumeral Joint

·       Scapulothoracic Joint

·       Acromioclavicular Joint

·       Sternoclavicular Joint

Primary elements of the GH joint include:

·       Humerus

·       Glenoid Fossa of the Scapula

·       Clavicle (anterior side)

Anatomy of the Scapula

·       Posterior Aspects:

o   Spine of the Scapula: Runs from medial root to lateral aspect of the acromion. Divides supraspinatus (above) and infraspinatus (below).

o   Fossae Present:

§  Infraspinatus Fossa: Area below the spine of the scapula for muscle attachment.

§  Supraspinatus Fossa: Area above the spine of the scapula for muscle attachment.

·       Muscle Attachments:

o   Teres Minor & Major: Lateral border of scapula.

o   Rhomboids Major and Minor, Levator Scapulae: Medial border of scapula.

·       Anterior Aspects:

o   Subscapularis Fossa: Space for the subscapularis muscle.

o   Serratus Anterior: Attaches at the medial border.

o   Coracoid Process: Bony protrusion above the glenoid fossa, attachment site for short head of biceps.

o   Long Head of Biceps: Attachment site superior to glenoid fossa.

Glenohumeral Joint Details

·       Structure of the Humerus:

o   Head: Articular surface connecting to glenoid.

o   Greater and Lesser Tubercles: Bony prominences for rotator cuff muscle attachments.

o   Articular surface of glenoid covers only one-third of the humeral head, allowing significant movement.

·       Ligaments of the GH Joint:

o   Glenohumeral Ligaments:

§  Three fibrous bands (superior, middle, and inferior glenohumeral ligaments) that run from the glenoid rim to the humerus.

§  These ligaments provide stability to the shoulder, particularly against anterior translation and external rotation of the humeral head.

§  The inferior glenohumeral ligament has significant importance during arm abduction and external rotation, acting as the primary stabilizer in these positions.

o   Coracohumeral Ligament:

§  Connects the coracoid process of the scapula to the greater tubercle of the humerus.

§  Provides stability by restricting inferior movement of the humeral head and supports the biceps tendon in the subacromial space.

o   Transverse Humeral Ligament:

§  A small ligament that holds the biceps tendon in the bicipital groove during joint motion.

§  Helps to prevent dislocation of the tendon from its groove.

o   Coracoclavicular Ligament:

§  Comprises trapezoid and conoid ligaments, connecting the coracoid process to the clavicle.

§  Prevents superior subluxation of the clavicle and contributes to the overall stability of the shoulder girdle.

o   Coracoacromial Ligament:

§  Forms an arch over the humeral head, connecting the coracoid process to the acromion.

§  Acts as a protective arch, preventing superior displacement attachment of the Glenoid and contributing to joint stability.

Additional Considerations

·       Scapula Position:

o   Orientation: Positioned at a 30–40-degree angle anterior to the frontal plane. The glenoid fossa faces approximately 35 degrees anteriorly from the frontal plane, referred to as the scapular plane.

·       Humeral Position:

o   In anatomical position, the humeral head is directed medially, superiorly, and posteriorly (retroverted) into scapular plane

o   Normal resting position involves slight internal rotation of the humerus compared to anatomical position.

·       Subacromial Space:

o   Location: Underneath the coracoacromial ligament and above the humeral head.

o   Contains:

§  Supraspinatus Muscle and Tendon

§  Subacromial Bursa: Facilitates movement of the supraspinatus tendon located under coracoacromial arch and of the deltoid over the joint capsule of the GH joint and greater tuberacle of the humerus.

Clinical Relevance: This closed space can become inflamed, especially affecting the function and movement of the shoulder.