Last Updated on March 12, 2025
The scapula is a triangular, flat bone of shoulder girdle located on either side of the spine in the upper back between ribs 2 to 7. It is also called a shoulder blade. It articulates with the head of the humerus at the glenohumeral joint, popularly called the shoulder joint, and with the lateral end of the clavicle at the acromioclavicular joint, thus connecting the upper limb to the trunk.
Along with the clavicle and the manubrium of the sternum, it forms a pectoral girdle or shoulder girdle that functions to connect the upper limb to the axial skeleton. The scapula serves as an attachment to many muscles and due to its own mobility gliding over the back provides greater mobility for the upper limb.
Quick Summary
- Bony Structure:
- 3 borders- superior, lateral, and medial
- 3 angles- lateral, superior, and inferior
- 2 surfaces- anterior or costal(abuts thorax), posterior
- 2 processes- coracoid, acromion
- Muscles:
- Origin – Deltoid, supraspinatus, infraspinatus, long head of triceps, teres minor and major, omohyoid, latissimus dorsi, coracobrachialis, biceps, subscapularis
- Insertion- Trapezius, levator scapulae, rhomboid major, rhomboid minor, serratus anterior, pectoralis minor muscles
- Ligaments: Coracoacromial, coracoclavicular ligament, suprascapular ligament and spinoglenoid ligament
- Blood supply: Suprascapular, posterior circumflex humeral, circumflex scapular, and transverse cervical arteries
Bony Structure of Scapula
The scapula has two surfaces, three borders, three angles, and three processes. The scapula serves as a site for attachment for many important muscles around the shoulder.
Surfaces
Two surfaces – a costal surface that abuts the thorax and the dorsal surface which can be felt when we palpate the bone from behind.
- Costal surface: The costal surface of is concave and is directed medially and forward. A concave depression over most of its surface is called the subscapular fossa. The subscapularis muscle, one of the rotator cuff muscles, originates from the subscapular fossa.
The costal surface has three longitudinal ridges. These serve as attachments to tendinous subscapularis. Another thick ridge adjoins the lateral border. This part of the bone is almost rod-like. It acts as a lever for the serratus anterior in the overhead abduction of the arm. - Dorsal Surface: This surface is rougher than the anterior surface. It provides attachment to the spine of the scapula, a ridge that divides the surface into a smaller supraspinous fossa and a larger infraspinous fossa. Its posterior border is called the crest of the spine. The crest has upper and lower lips. The two fossae are connected by the spinoglenoid notch, situated lateral to the root of the spine. The acromion is a projection of the spine that arches over the glenohumeral joint and articulates with the clavicle.
Borders
- Superior border is thin and short. It has a suprascapular notch near the root of the coracoid process.
- Lateral border is the thickest of the three and presents the infraglenoid tubercle and glenoid cavity at the upper end. It is also called the axillary border as it runs superolaterally towards the apex of the axilla. It also has the glenoid cavity or socket along this border, a shallow fossa that articulates with the head of the humerus, forming the glenohumeral joint.
- Medial border is thin extends from the superior angle to the inferior angle. It also called the vertebral border or vertebral margin.
Angles
The scapula has three angles formed at junctions of borders.
- Lateral Angle: It is formed when the superior border meets the lateral border. The lateral angle is broad and bears the glenoid cavity which is directed forwards, laterally and slightly upwards. The glenoid cavity articulates with the head of the humerus to form shoulder joint.
- Superior angle: The superior border meets the medial border at the superior angle. The superior angle is covered by the trapezius.
- Inferior angle: Inferior angle is formed where the medial and lateral borders meet. The inferior angle is covered by the latissimus dorsi and moves forward around the chest when the arm is abducted.
Processes
- Acromion process: It is a lateral extension of the posterior spine of the scapula that projects anterolaterally. It articulates with the acromial end of the clavicle to form acromioclavicular joint. It is superior to the glenohumeral joint of the shoulder. The acromioclavicular joint is stabilized by the acromioclavicular ligament.
- Coracoid process: It is a beak-like structure that is directed forwards and slightly laterally from the superior border. It plays an important role in shoulder stabilization by providing attachments to ligaments and muscles. it lies superior to the glenoid cavity and inferior to the clavicle.
How to Determine the Side?
- The lateral angle is large and bears the glenoid cavity.
- The dorsal surface is convex and is divided by the triangular spine into the supraspinous and infraspinous fossae.
- The costal surface is concave to fit on the convex chest wall.
- The lateral thickest border runs from the glenoid cavity above to the inferior angle below.
Ligaments
- Capsule: The margin of the glenoid cavity gives attachment to the capsule of the shoulder joint and to the glenoid labrum. The margin of the facet on the medial aspect of the acromion gives attachment to the capsule of the acromioclavicular joint.
- Coracoacromial Ligament: The coracoacromial ligament extends between the coracoid process and the acromion. It is attached to the lateral border of the coracoid process, and the medial side of the tip of the acromion process. This ligament protects the head of the humerus from dislocating during motion.
- Coracohumeral ligament: It is attached to the root of the coracoid process.
- Coracoclavicular ligament: It is attached to the coracoid process. The trapezoid part attaches to the superior aspect and the conoid part near the root.
- Suprascapular ligament: It is a ligament that bridges across the suprascapular notch. and converts it into a foramen. The suprascapular nerve passes through the foramen and the suprascapular artery is above the ligament.
- Spinoglenoid ligament: It bridges the spino-glenoid notch. The suprascapular vessels and nerves pass deep to it.
Muscles
There are a total of 17 muscles that attach to the scapula. These muscles function to fix the scapula to the thoracic wall during shoulder movement and also cause movements of the scapula. Four of these muscles, namely subscapularis, infraspinatus, teres minor, and supraspinatus arise from the surface of the scapula and are called intrinsic muscles. Together these form rotator cuff that stabilizes the glenohumeral joint.
Trapezius, levator scapulae, serratus anterior, rhomboid major and rhomboid minor are major stabilizers of the scapular bone.
Following is the list of muscles that originate from and are inserted into the scapula.
The following diagram shows the arrangements of the muscles’ origins and insertions on the scapular bone. 
Muscles originating from the Scapula
(After each nerve supply, the cord segments are mentioned like C3, C4, and so on. These denote the spinal segments responsible for supply for that particular muscle. This is done as the nerve may carry fiber from many segments but to a particular muscle only the designated segments supply. For example, a nerve may carry C4, C5, C6, C7 fibers but for a particular muscle, it may only provide input from C3, and C4. Hence, after the nerve name (C3, C4) would be written.
- Deltoid Muscle: Deltoid muscle arises from the lower border of the crest of the spine and the lateral border of the acromion. There is a clavicular origin also. The insertion is at the deltoid tuberosity of the humerus. It causes flexion and medial rotation(anterior fibers), abduction of the shoulder (middle fibers)of the arm, and extension and lateral rotation of the arm. It is innervated by axillary nerve (C5, C6)
- Supraspinatus Muscle: It arises from the medial two-thirds of the supraspinous fossa (including the upper surface of the spine). It is inserted into the greater tubercle of the humerus. It initiates the abduction of the arm and also stabilizes the glenohumeral joint. The suprascapular nerve supplies it.
- Infraspinatus Muscle: It arises from the medial two-thirds of the infraspinous fossa (including the lower surface of the spine). It inserts on the greater tubercle of the humerus, between the supraspinatus and teres minor insertion. It causes external rotation of the arm and is supplied by the suprascapular nerve.
- Triceps: The long head of the triceps arises from the infraglenoid tubercle while the other two heads originate from the humerus. The muscle inserts at the olecranon process of the ulna and fascia of the forearm. It is supplied by the radial nerve.(C6, C7, C8)
- Teres Minor: Teres minor arises from the upper two-thirds of the rough strip on the dorsal surface along the lateral border. It inserts into the inferior aspect of the greater tubercle of the humerus. It is an external rotator or lateral rotator of the arm. It is supplied by the axillary nerve (C5, C6).
- Teres Major: It arises from the lower one-third of the rough strip on the lateral aspect of the lateral border. The insertion is on the medial aspect of the intertubercular groove. It causes adduction and medial rotation of the arm. Nerve supply is by the lower scapular nerve (C5, C6).
- Latissimus Dorsi: It originates from the spinous processes of T6 to T12, iliac crest, thoracolumbar fascia, the inferior three ribs, and the inferior angle of the scapula. It inserts into the intertubercular sulcus of the humerus. It extends, adducts, and medially rotates the upper limb. It is supplied by the thoracodorsal nerve (C6, C7, C8)
- Coracobrachialis: The coracobrachialis arises from the medial part of the tip of the coracoid process. Coracobrachialis inserts into the medial aspect of the middle of the humerus. It causes flexion and adduction of the arm. It is supplied by the musculocutaneous nerve (C5, C6, C7)
- Biceps Brachii: The long head of the biceps brachii arises from the supraglenoid tubercle. The short head from the lateral part of the tip of the coracoid process. It inserts into radial tuberosity and bicipital aponeurosis. It flexes and supinates the forearm. The musculocutaneous nerve (C5, C6) supplies it.
- Subscapularis Muscle: It arises from the medial two-thirds of the subscapular fossa and inserts into the lesser tubercle of the humerus. It causes adduction and medial rotation of the arm. It is supplied by subscapular nerves (C5, C6, C7)
- Omohyoid: The inferior belly of the omohyoid arises from the upper border near the suprascapular notch and inserts into the inferior edge of the hyoid bone. It pulls the hyoid bone down during talking and swallowing. The nerve supply is from ansa cervicalis (C1, C2, C3), a loop formed by the joining of brachial plexus roots.
Muscles inserted into the scapula
- Trapezius: The Trapezius muscle originates from, the nuchal ligament, and the spinous processes of C7 to T12. It is inserted into the upper border of the crest of the spine and the medial border of the acromion and clavicle. Its upper fibers elevate the scapula and cause it to rotate during abduction of the arm in 90 to 180 degrees range. The middle fibers retact the scapula whereas the lower fibers pull the scapula inferiorly. It is supplied by the accessory nerve or Cranial nerve XI.
- Levator Scapulae: It originates from transverse processes of the C1 to C4 vertebrae and is inserted along the dorsal aspect of the medial border, from the superior angle up to the root of the spine. It elevates the scapula. It is supplied by ventral rami of C3, C4, and the dorsal scapular nerve (C5)
- Rhomboid Minor: It originates from the spinous processes of C-T1. It is inserted into the medial border (dorsal aspect) opposite the root of the spine of the scapula. Rhomboid minor retracts and rotates the scapula and is supplied by the dorsal scapular nerve (C5).
- Rhomboid Major: It originates from the spinous process of T2-T5. Rhomboideus major is inserted into the medial border (dorsal aspect) between the root of the spine and the inferior angle. It has action and nerve supply same as rhomboid minor.
- Serratus Anterior: The Serratus anterior muscle originates from the upper eight ribs at the side of the chest and is inserted along the entire medial border of the costal surface-one digitations to the superior angle, two digitations to the medial border, and five digitations to the inferior angle. Serratus anterior fixes the scapula into the thoracic wall, and aids in rotation and abduction of the arm from 90 to 180 degrees. It is supplied by long thoracic nerve (C5, C6, C7).
- Pectoralis Minor: Pectoralis minor originates from the third, fourth, and fifth ribs and is inserted into the medial border and superior surface of the coracoid process. It acts to cause depression of the shoulder and protraction of the scapula. It is supplied by medial pectoral nerve (C8, T1)
[Learn more about shoulder muscles]
Movements of Scapula
There is a total of six movements of the scapula and are discussed in pairs
- Elevation-depression: These movements occur when we shrug our shoulders or raise our arm
- Abduction-adduction: Abduction of the scapula is also called protraction adduction is also called retraction. Abduction movement occurs when scapulae are drawn away and adduction when these are brought together. In abduction, the scapula is drawn away from vertebrae whereas in adduction the bone moves towards vertebrae. When we bring arm in front of the body, it results in the abduction of the scapula whereas if the arm is taken behind, it causes adduction.
- Upward-downward rotation: When we raise our arm the scapula participate in the movement by rotating upward. On lowering, the scapula rotates downwards.
The scapula also rotates upward and downward as the arm raises and lowers,
Blood Supply, Lymphatics, and Nerve Supply
Scapular anastomosis is mainly responsible for the blood supply. It is formed by branches of the axillary artery and subclavian artery. The participating vessels are
- Suprascapular artery- a branch of the thyrocervical trunk, a branch of the subclavian artery
- Posterior circumflex humeral artery – a branch of the axillary artery
- Circumflex scapular artery – originates from the subscapular artery, a branch of the axillary artery
- Transverse cervical artery – a branch of the thyrocervical trunk, a branch of the subclavian artery
The venous drainage is via the axillary vein and the suprascapular veins. The right scapular lymphatics go to the right lymphatic duct. those of the left side into the thoracic duct.
Dorsal scapular, upper and lower subscapular, and suprascapular nerves are mainly responsible for the innervations.
Clinical Significance
Anatomical Variations
Os acromiale is a condition due to the unfused center of secondary ossification in the acromion. it may lead to pain and tenderness. It is also thought to increase the risk of impingement and rotator cuff tears.
Sprengel deformity is also called as congenital elevation of the scapula or congenital high riding scapula. This abnormal position causes a decrease in the functionality of the scapula. Surgical release may be required.
Scapulohumeral Rhythm
In shoulder abduction, the scapulohumeral movement is in the ratio of 2:1. A disturbance in this rhythm results in scapular dyskinesia. This may occur as a result of trauma, joint pathologies or muscular issues.
Winging of Scapula
The scapula needs to be kept close to the posterior chest wall by muscle forces. A break in forces as in paralysis of the serratus anterior causes ‘winging’ where the medial border of the bone becomes unduly prominent, and the arm cannot be abducted.
Winging may also be caused by trapezius muscle paralysis due to spinal accessory nerve injury.
Facioscapulohumeral dystrophy is an autosomal dominant condition that leads to muscular paralysis and winging could be seen in these patients.
Injury
Scapula bone is not frequently injured as it sits quite protected but scapular fractures can occur in high-energy motor vehicle injuries.
Scapular Dysplasia
It is an abnormal morphology that can either be primary or acquired and is often secondary to obstetric brachial plexus palsy. it may have varied presentation as the center of ossification affected may be different.
Snapping Scapula Syndrome
For good motion, the scapula has to glide over the chest wall. The snapping syndrome occurs when there is non-smooth motion. the most common causes are scapulothoracic bursitis and osteochondroma.
References
- Bonz J, Tinloy B. Emergency department evaluation and treatment of the shoulder and humerus. Emerg Med Clin North Am. 2015 May;33(2):297-310. [PubMed]
- J.P. Iannotti, R.D. Parker: The Netter collection of medical illustrations (Frank H. Netter, MD). Musculoskeletal system, Part 1: Upper Limb, 2nd Edition, Elsevier Saunders (2013), p. 2-3.
- R.L. Drake, W. Vogl, A.W.M Mitchell et al.: Gray’s anatomy for students, 3rd Edition, Churchill Livingstone/Elsevier (2010), p. 685 – 837.
