osteology of the shoulder

Osteology of the ShoulderOverview of the Shoulder ComplexThe 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:

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

    • 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:

    • Teres Minor & Major: Lateral border of scapula.

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

  • Anterior Aspects:

    • Subscapularis Fossa: Space for the subscapularis muscle.

    • Serratus Anterior: Attaches at the medial border.

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

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

Glenohumeral Joint Details

  • Structure of the Humerus:

    • Head: Articular surface connecting to glenoid.

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

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

  • Ligaments of the GH Joint:

    • 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.

    • 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.

    • 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.

    • 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.

    • 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:

    • 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:

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

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

  • Subacromial Space:

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

    • 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.