Scapula
The scapula, commonly known as the shoulder blade, is a flat triangular bone that plays a critical role in upper limb movement and shoulder stability. It serves as an attachment site for multiple muscles and forms articulations that allow a wide range of motion. Understanding its anatomy and landmarks is essential for clinical evaluation and surgical procedures.
Anatomy
General Structure
The scapula is a flat, triangular bone located on the posterior aspect of the thoracic cage. It has two surfaces: the anterior or costal surface, which faces the ribs, and the posterior or dorsal surface, which provides attachment for muscles and forms the prominent spine of the scapula. The scapula also has three borders (superior, medial, and lateral) and three angles (superior, inferior, and lateral) that serve as important anatomical landmarks.
Landmarks
- Spine of scapula: A prominent ridge on the posterior surface that divides it into the supraspinous and infraspinous fossae.
- Acromion process: An extension of the spine that articulates with the clavicle at the acromioclavicular joint.
- Coracoid process: A hook-like projection on the anterior surface serving as a muscular and ligamentous attachment.
- Glenoid cavity: A shallow socket that articulates with the humeral head to form the glenohumeral joint.
- Suprascapular notch: A notch on the superior border for passage of the suprascapular nerve.
Muscular Attachments
The scapula provides attachment points for numerous muscles that control shoulder and arm movements. Key muscles include:
- Trapezius
- Deltoid
- Rhomboid major and minor
- Serratus anterior
- Levator scapulae
- Rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis)
Articulations
- Glenohumeral joint: Ball-and-socket joint with the humeral head
- Acromioclavicular joint: Connects the acromion to the clavicle
- Scapulothoracic articulation: Functional joint where the scapula glides over the thoracic wall
Development and Variations
Embryology
The scapula develops from mesenchymal condensations in the limb bud during the fifth to sixth week of gestation. Ossification begins in the body of the scapula and proceeds through multiple centers including the coracoid, acromion, and inferior angle, completing by adolescence.
Anatomical Variations
- Variations in the shape and size of the scapula
- Presence of accessory ossicles or abnormal bony processes
- Differences in the angle and orientation of the glenoid cavity
Blood Supply and Innervation
Arterial Supply
- Suprascapular artery: Supplies the supraspinatus and infraspinatus regions.
- Dorsal scapular artery: Supplies the rhomboids and levator scapulae.
- Circumflex scapular artery: Branch of the subscapular artery that supplies the infraspinous fossa and scapular borders.
Venous Drainage
Venous return follows the arterial supply and drains primarily into the subclavian and external jugular veins.
Nerve Supply
- Suprascapular nerve: Innervates the supraspinatus and infraspinatus muscles.
- Dorsal scapular nerve: Innervates the rhomboid muscles and levator scapulae.
- Axillary nerve contributions: Provides sensory fibers to the acromial region and motor fibers to the deltoid and teres minor.
Function
Movements
- Elevation: Lifting the scapula superiorly
- Depression: Lowering the scapula inferiorly
- Protraction (abduction): Moving the scapula away from the spine
- Retraction (adduction): Bringing the scapula toward the spine
- Upward rotation: Rotating the glenoid cavity superiorly for arm abduction
- Downward rotation: Returning the glenoid cavity to a neutral position
Role in Shoulder Stability
The scapula provides a stable base for humeral movement and acts as a fulcrum for shoulder muscles, facilitating coordinated upper limb motion.
Muscle Coordination
Scapular movement is controlled by the coordinated activity of multiple muscles, including the trapezius, serratus anterior, and rhomboids, which maintain optimal glenohumeral alignment during arm movements.
Clinical Significance
Fractures
- Common fracture sites include the scapular body, spine, acromion, and coracoid process
- Mechanisms of injury often involve high-energy trauma such as motor vehicle accidents or falls
- Management may be conservative with immobilization or surgical in severe displaced fractures
Disorders and Syndromes
- Scapular winging: Protrusion of the medial border due to serratus anterior or trapezius dysfunction
- Snapping scapula syndrome: Painful crepitus during scapulothoracic motion
- Osteoarthritis or degenerative changes: Less common but can affect acromioclavicular or glenohumeral articulation
Surgical Considerations
- Scapular fixation or reconstruction in fractures or deformities
- Landmark identification for shoulder arthroscopy and rotator cuff repair
Imaging and Diagnostic Evaluation
- X-ray: Standard anteroposterior, lateral, and scapular Y views for fracture assessment
- CT scan: Detailed evaluation of complex fractures and bony anatomy
- MRI: Assessment of soft tissue attachments, rotator cuff muscles, and labral pathology
- Ultrasound: Dynamic evaluation of scapular motion and detection of muscle or tendon abnormalities
References
- Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. London: Elsevier; 2020.
- Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2020.
- Netter FH. Atlas of Human Anatomy. 7th ed. Philadelphia: Elsevier; 2018.
- Wang T, Liu J, Li Y, Li J. Clinical anatomy and variations of the scapula: a review. J Anat. 2019;235(3):419-432.
- Warner JP, Micheli LJ. Scapular fractures and dislocations. Orthop Clin North Am. 2001;32(3):423-435.
- Flinkkila T, Lehtinen J, Paakkala T. Imaging of the scapula: anatomy and clinical relevance. Radiographics. 2014;34(6):1796-1815.
- Kibler WB, Sciascia A. Evaluation and management of scapular disorders in athletes. Br J Sports Med. 2010;44(5):301-308.
- Kim SH, Ha KI. Scapular fractures: diagnosis, management, and surgical considerations. Clin Orthop Surg. 2012;4(2):97-105.
