Bones and Joints of Pectoral Girdle

Terminology for the Upper Limb

• Pectoral girdle refers to the scapula and clavicle and is part of the appendicular skeleton

• Arm refers to the region between shoulder and elbow

• Forearm refers to the region between elbow and wrist

Clavicle

• An S-shaped bone that connects the upper limb to the trunk

• Medial half of the bone is convex anteriorly

• Lateral half of the bone is concave anteriorly

• Articulates with the manubrium of the sternum medially

• Articulates with the acromion of the scapula laterally

• Superior surface is smooth

• Inferior surface is rough due to bone markings from ligaments and muscles

Scapula

A triangular shaped bone that lies on the posterior aspect of the rib cage

• Acromion of the scapula articulates with the lateral end of the clavicle

• Glenoid fossa/cavity articulates with the head of the humerus

• Provides surface area for muscle attachments

Humerus

Figure 4.2

• A long bone found in the arm

• Head of the humerus articulates with the glenoid fossa/cavity of the scapula

• Proximal humerus has 2 necks, 2 tubercles, and an intertubercular sulcus (bicipital groove)

• The intertubercular sulcus (bicipital groove) consists of a medial lip, a lateral lip, and a floor 

Classification of Ligaments 

• Ligaments are classified as being either intrinsic or extrinsic

• Intrinsic ligaments are thickenings of portions of the joint capsule

• Extrinsic ligaments provide support to a joint but are located some distance away from the joint capsule 

Sternoclavicular Joint

• Sternal end of the clavicle articulates with the manubrium of the sternum

• Structurally, the sternoclavicular (SC) joint is classified as a saddle joint

• Functionally, the SC joint acts like a ball and socket joint

• Within the joint capsule there is an articular disc  

Ligaments of the Sternoclavicular Joint

•  Intrinsic ligaments:

  • Anterior sternoclavicular ligament

  • Posterior sternoclavicular ligament

• Extrinsic ligaments:

  • Interclavicular ligament

  • Costoclavicular ligament

Movements of the Sternoclavicular Joint 

• SC joint is very strong and also very mobile

• During abduction of the arm, the clavicle elevates to an angle of approximately 60°

• During protraction and retraction of the scapula, the lateral end of the clavicle swings anteriorly and posteriorly

• During flexion of the arm, the clavicle rotates on its own longitudinal axis

Clavicle Fracture

• The sternoclavicular joint is so strong, it very rarely dislocates

• Instead, the clavicle is a commonly fractured bone

Acromioclavicular Joint

•  Acromion of the scapula articulates with the acromial end of the clavicle

• Classified as a plane joint

• Within the joint capsule, there is an articular disc 

Ligaments of the Acromioclavicular Joint

•  Intrinsic ligament: 

  • Acromioclavicular ligament

• Extrinsic ligaments: 

  • Coracoclavicular ligament

  • Conoid ligament

  • Trapezoid ligament 

Dislocation of the Acromioclavicular Joint

•  Dislocation of the AC joint is usually referred to as a shoulder separation

• Can occur due to falling on an outstretched upper limb or by a direct blow to the shoulder 

• The coracoclavicular ligaments may or may not rupture 

Glenohumeral Joint

•  Head of the humerus articulates with the glenoid cavity/fossa of the scapula

• Classified as a ball and socket joint

• The shallow glenoid cavity is deepened slightly by the glenoid labrum

• Tendon of long head of biceps brachii passes through the capsule to reach the supraglenoid tubercle 

• Rotator cuff muscles assist in maintaining shoulder joint stability

• Inferior aspect of the joint capsule is loose and weak but this allows for full abduction of the arm

Ligaments of the Glenohumeral Joint

•  Intrinsic ligaments:

  • Glenohumeral ligaments

    • Superior

    • Middle

    • Inferior

  • Coracohumeral ligament

  • Transverse humeral ligament

• Extrinsic ligaments:

  • Coracoacromial ligament 

Glenohumeral Dislocation

•  Dislocation of the GH joint is usually referred to as a shoulder dislocation

• Joint is highly mobile at the expense of stability

• Dislocations tend to happen inferiorly due to the protective nature of the coracoacromial arch superiorly 

Scapulohumeral Rhythm 

• The scapula has no direct attachment to the rib cage 

• However, the scapulothoracic joint is described as a physiological joint

• Movement of the scapula permits and contributes to movement of the humerus in extreme flexion and abduction

• For every 3° of rotation, 2° comes from the glenohumeral joint and 1°comes from the scapulothoracic joint