Scapula Bone
Anatomy and Location
Introduction to the Scapula
The scapula joins the clavicle to form the shoulder (pectoral) girdle, which connects the humerus (upper arm bone) to the thorax.
Because much of the scapula is relatively flat, it is commonly known as the shoulder blade. Scapulae is the Latin word for the “shoulder blades.” This term was likely derived from the Greek verb “skaptein,” meaning “to dig,” because the bone’s flattened shape resembles a trowel or small shovel.
Several prominent anatomical landmarks are on the scapula. Most provide surface area for the 17 muscles that attach to it.
Location of the Scapula Bone
Borders and Angles
The triangular scapula has three edges called the superior, medial, and lateral borders (or margins). The three corners of the scapula, where the edges converge, are called angles. The superior angle is formed by the convergence of the superior and lateral borders. This area provides attachment for muscles that move the neck. The inferior angle is formed by the convergence of the medial and lateral borders. The bone in this region is thick because it is the attachment site for several powerful muscles that move the shoulder and upper limb. The remaining corner of the scapula, the lateral angle, is where the superior and lateral borders intersect.
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Tubercles, Notches, & Cavities
Along the lateral angle, a shallow depression called the glenoid cavity (or glenoid fossa) is present. This area articulates with the humerus bone to form the glenohumeral joint (shoulder joint).
A small, bump-like projection, the supraglenoid tubercle, is located above the glenoid cavity and is most easily observed from the lateral view. A second bump-like projection, the infraglenoid tubercle, is below the glenoid cavity. The supraglenoid tubercle is an attachment site for the biceps brachii muscle, and the infraglenoid tubercle is an attachment site for the triceps brachii. Both of these muscles contribute to the movement of the arm and forearm.
An indentation, the suprascapular notch, appears on the superior border, medial to the base of the coracoid process. The superior transverse scapular ligament converts the notch into a foramen, through which the suprascapular nerve passes.
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Projections, Ridges, & Depressions
A prominent projection, the coracoid process, emerges from the lateral end of the scapula’s superior border, inferior to the clavicle. It is hook-like in shape, extending anteriorly and curving laterally. Coracoid is a Greek word meaning “crow” or “raven”, and it is used because the process resembles a crow’s beak. Ligaments that reinforce the acromioclavicular joint anchor the coracoid process to the underside of the clavicle. The surface of the process is also the attachment site for muscles that move the scapula, arm, and forearm.
On the posterior side of the scapula is a prominent ridge called the scapular spine, which runs obliquely across the upper part of the bone. It primarily serves as an attachment point for several muscles that move the scapula (shoulder).
The acromion (acromial process) is a flattened and expanded lateral projection from the spine. It articulates with the lateral end of the clavicle at the acromioclavicular joint and provides a protective bony cover over the top of the shoulder joint. It is also the attachment site for the deltoid muscle, which spans the shoulder joint to move the arm.
The scapula has three depressions, each called a fossa (plural = fossae). Two are on the posterior scapula, above and below the scapular spine. Superior to the spine is the narrow supraspinous fossa, and inferior to the spine is the broad infraspinous fossa. The scapula’s anterior (deep) surface forms the broad subscapular fossa. These fossae are the attachment sites for muscles that cross the shoulder joint to act on the humerus.
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Assessment
Anterior Scapula Flip Card Quiz
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Lateral Scapula Flip Card Quiz
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Posterior Scapula Flip Card Quiz
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References and Attributions
NIH: National Library of Medicine – “Anatomy, Back, Scapula.”
NIH: National Library of Medicine – “Anatomy, Thorax, Scapula.”
OpenStax – “The Pectoral Girdle” (Access for free at https://openstax.org/books/anatomy-and-physiology-2e/pages/1-introduction).