The Shoulder

Clavicle

The clavicle or collar bone is a long, curved bone on the upper portion of the shoulder that connects with the scapula and the sternum.

Learning Objectives

Describe the characteristics of the clavicle

Key Takeaways

Key Points

  • The clavicle is a long, doubly curved bone that connects the arm to the body, located directly above the first rib. It acts as a strut to keep the scapula in place so the arm can hang freely.
  • The clavicle is an attachment point for several muscles.
  • Structurally, the clavicle can be divided into three parts: medial end, lateral end, and shaft.
  • There are sex differences in clavicle shape—female clavicles are shorter and thinner than male clavicles.

Key Terms

  • acromion: The outermost point of the shoulder blade.

The clavicle, or collarbone, is a slender s-shaped bone that extends between the sternum and the scapula and is located directly above the first rib. It functions to attach the upper arm to the trunk and provides support to allow free movement around the shoulder.

This is a drawing of the left clavicle, viewed from above. Thee muscle attachment sites pectoralis major, subclavius muscle, deltoid, and sterno-hyoid are highlighted.

Left Clavicle: The left clavicle, viewed from above. Muscle attachment sites (pectoralis major, subclavius muscle, deltoid, and sterno-hyoid) are highlighted.

Medially the clavicle is quadrangular in shape and articulates with the manubrium of the sternum forming the sternoclavicular joint.  Laterally, the clavicle is flattened and attaches to the acromion process of the scapula forming the acromioclavicular joint.

The shaft of the clavicle acts as the origin and attachment point for numerous muscles and ligaments. At the medial end of the shaft the pectoralis major originates from the anterior surface, the posterior surface gives origin to the sternohyoid muscle and the superior surface the sternocleidomastoid muscle.

The costoclavicular ligament attaches to the inferio≠r surface. Laterally the deltoid muscle originates from the anterior surface and the trapezius muscle attaches to the posterior surface at the trapezoid line. Adjacent to this is the conoid tubercle which is an attachment point for the conoid ligament.

The clavicle in males is typically thicker and longer than a female’s clavicle to account for the larger muscle mass operating through it.

Scapula

The scapula, or shoulder bone, is a flat, triangular bone that connects to the humerus and the clavicle.

Learning Objectives

Describe the shape and function of the scapula in humans

Key Takeaways

Key Points

  • The scapula articulates with the humerus and the clavicle.
  • The scapula is flat and triangular.
  • The scapula articulates with the humerus at the glenoid fossa and the clavicle at the acromion process.
  • The scapula provides attachment sites for many muscles including the pectoralis minor, coracobrachialis, serratus anterior, triceps brachii, biceps brachii, and the subscapularis.
  • The scapula has two main surfaces: the costal (front facing) surface and the dorsal (rear facing) surface.

Key Terms

  • acromion: The outermost point of the shoulder blade.
  • glenoid: A shallow depression in a bone, especially in the scapula.

The scapula, or shoulder blade, is a flat, triangular bone located to the posterior of the shoulder. The scapula articulates with the clavicle through the acromion process, a large projection located superiorly on the scapula forming the acromioclavicular joint. The scapula also articulates with the humerus of the upper arm to form the shoulder joint, or glenohumeral joint, at the glenoid cavity.

Due to its flat nature, the scapula presents two surfaces and three borders; the front-facing costal surface and the rear-facing dorsal surface, as well as the superior, lateral, and medial borders.

This is a drawing of the costal surface of the left scapula. The subscapular fossia for subscapularis, serratus, pector minor regions are highlighted.

Costal surface: Costal surface of the left scapula. The subscapular fossia for subscapularis, serratus, pector minor regions are highlighted.

The serratus anterior originates from the costal surface, which also provides an attachment for the subscapularis muscle. The dorsal surface gives origin to the supraspinatus and infraspinatus muscles, and inferiorly to the teres minor and major. It is divided by a ridge-like structure called the spine of the scapula, from which the deltoid and trapezius muscles originate.

This is a drawing of the dorsal surface of the left scapula. It highlights the supraspinatus and infraspinatus muscles, spine, teres major, and teres minor regions.

Dorsal surface: Dorsal surface of the left scapula.

The lateral border is the thickest border of the scapula and extends downwards from the glenoid cavity. Immediately below the glenoid cavity is the infraglenoid tuberosity, which is the origin for the long head of the triceps brachii.

Immediately above the glenoid cavity is the supraglenoid tubercle and its associated hook-like coracoid process, from which the long and short heads of the biceps brachii originate.

Four muscles attach to the medial border of the scapula. To the anterior side the serratis anterior attaches, whilst posteriorly the levator scapulae and rhomboids minor and major attach.