Scapular Motion and Serratus Anterior

Scapular Motion

• Scapular abduction with upward rotation is performed by the serratus anterior muscle.
• Scapular elevation is performed by the upper trapezius and levator scapula muscles.
• Scapular adduction (retraction) is performed by the middle trapezius muscle.
• Scapular depression and adduction is performed by the lower trapezius muscle.
• Scapular adduction and downward rotation is performed by the rhomboid major and minor muscles.

Scapular Abduction & Upward Rotation

• The serratus anterior muscle is responsible for scapular abduction and upward rotation.

Serratus Anterior Muscle

• Originates from the lateral, anterior surface of the upper 8th-9th ribs.
• Inserts on the anterior aspect of the medial vertebral border of the scapula.
• When the origin is fixed, it abducts the scapula, rotates it so the glenoid cavity faces cranially.
• Holds the medial border of the scapula firmly against the thorax.
• Lower fibers may depress the scapula, while upper fibers may slightly elevate it.
• Innervated by the long thoracic nerve (C5-C7).

Serratus Testing

• Test the serratus anterior during shoulder flexion to minimize synergy with the trapezius.
• Normal scapular position at rest requires the patient to raise the test arm above the head in the sagittal plane.
• If the arm can be raised well above 90 degrees, glenohumeral muscles must be at least Grade 3.

Scapular Range of Motion

• Within a 180° arc of shoulder forward flexion, 120° is glenohumeral motion, and 60° is scapular motion.

Scapula Abnormal Position at Rest

• If the scapula is positioned abnormally at rest (adducted or winging), the patient may not be able to flex the arm above 90 degrees.

Factors Limiting Motion

• Tension of the trapezoid ligament limits forward rotation of the scapula upon the clavicle.
• Tension of the trapezius and rhomboid major and minor muscles also limits motion.

Fixation

• In strong scapular abduction, the pull of the external oblique abdominis on the same side aids in fixation.
• Weight of the thorax also contributes to fixation.

Scapular Elevation

• Upper trapezius and levator scapulae muscles perform this action.

Upper Trapezius

• Originates from occiput (external protuberance and medial 1/3 of superior nuchal line), ligamentum nuchae, and C7 vertebrae (spinous process).
• Inserts on the posterior aspect of the lateral 3rd of the clavicle.
• Innervated by the accessory nerve (C3-C4).
• Trapezius upper fibers elevate the scapula.
• With fixed insertion, unilateral action extends laterally, flexes, and rotates the head and cervical vertebrae so the face turns toward the opposite side.
• With fixed insertion, bilateral action extends the head and neck.

Levator Scapula

• Originates from C1-C4 vertebrae (transverse processes).
• Inserts on the medial border of the scapula.
• Innervated by the dorsal scapular nerve (C5).
• With the origin fixed, elevates the scapula and assists in rotation so the glenoid cavity faces caudally.
• With fixed insertion, unilateral action laterally flexes and rotates the cervical vertebrae to the same side.
• With fixed insertion, bilateral action may assist in extension of the cervical spine.

Factors Limiting Motion of Scapular Elevation

• Tension of the costoclavicular ligament.
• Tension of muscles that depress the scapula and clavicle: pectoralis minor, subclavius, and trapezius (lower fibers).
• Accessory muscles: rhomboids major and minor.

Fixation

• Flexor muscles of the cervical spine (for tests in sitting position).
• Weight of the head (for tests done in prone position).

Substitution by Rhomboids

• In patients with weak shoulder elevators, the rhomboids may attempt to substitute.
• During an unsuccessful attempt to shrug, the inferior angle of the scapula will move medially towards the vertebral spine (scapular adduction), and downward motion (rotation) also may occur.

Helpful Hints for Testing

• If the sitting position is contraindicated, tests for grade 5 and 4 are accurate in the supine position.
• For a grade 3 test in the supine position, manual resistance may be needed due to neutralized gravity.
• If the prone position is not comfortable, tests for grades 2, 1, and 0 may be performed supine, but palpation will be less optimal.
• In the prone position, a turned head has disadvantages, with more trapezius and less levator activity.

Scapular Adduction (Retraction)

• The middle trapezius muscle performs this action.

Middle Trapezius

• Originates from T1-T5 vertebrae (spinous processes) and supraspinous ligaments.
• Inserts on the medial border of the acromion process and the upper border of the scapular spine.
• Innervated by the XI accessory nerve.
• The trapezius middle fibers are mainly responsible for scapula adduction.
• Maintains stabilization during scapula downward rotation.

Factors Limiting Motion of Scapular Adduction

• Tension of the conoid ligament (limits backward rotation of the scapula upon the clavicle).
• Tension of the pectoralis major and minor and serratus anterior muscles.
• Contact of the vertebral border of the scapula with spinal musculature.
• Accessory Muscles: Trapezius upper and lower fibers and Rhomboid major and minor.

Substitution During Scapular Adduction

• Rhomboids can substitute for the trapezius in adduction of the scapula, but cannot substitute for the upward rotation component.
• This substitution leads to scapula adduction with downward rotation.
• Posterior deltoid: If the scapular muscles are absent and the posterior deltoid acts alone, horizontal abduction occurs at the shoulder joint but there is no scapular adduction.

Scapular Depression & Adduction

• Lower Trapezius muscle performs this action.

Lower Trapezius

• Originates from T6-T12 vertebrae (spinous processes).
• Inserts on the scapula (spine, medial end, and tubercle at lateral apex via aponeurosis).
• Innervated by the accessory nerve.
• The trapezius lower fibers mainly depress the scapula.
• Provides stabilization when the upper and middle fibers are working.

Factors Limiting Motion of Scapular Depression

• Tension of the interclavicular ligament and articular disc of the sternoclavicular joint.
• Tension of trapezius (upper fibers), levator scapulae, and sternocleidomastoid (clavicular head).
• Accessory muscles: trapezius middle fibers.

Fixation of Scapular Depression

• Contraction of spinal extensor muscles.
• Weight of trunk.

Scapular Adduction & Downward Rotation

• Rhomboid Major and Rhomboid Minor muscles perform this.

Rhomboid Major

• Originates from T2-T5 vertebrae (spinous processes) and supraspinous ligaments.
• Inserts on the medial border of the scapula inferior to the spine (between the root of the spine and inferior angle).
• Supplied by the dorsal scapular nerve.
• Action: Adducts and elevates the scapula, and rotates it so that the glenoid cavity faces caudally.

Rhomboid Minor

• Originates from C7-T1 vertebrae (spinous processes) and ligamentum nuchae (lower).
• Inserts on the medial border of the scapula at the root of the spine of the scapula.
• Supplied by the dorsal scapular nerve (C5).
• Action: Adducts and elevates the scapula, and rotates it so that the glenoid cavity faces caudally.

Factors Limiting Motion of Scapular Adduction & Downward Rotation

• Tension of the conoid ligament (limits backward rotation of the scapula upon clavicle).
• Tension of the pectoralis major and minor and serratus anterior muscles.
• Contact of the vertebral border of the scapula with spinal musculature.
• Fixation: Weight of the trunk.

Substitutions During Movement

• Middle trapezius can substitute for the adduction component of the rhomboids, but not for the downward rotation.
• With middle trapezius substitution, the patient's scapula will adduct with no downward rotation.

Effect of Weakness of Scapula Adductor, Depressor, and Downward Rotator Muscles

• Weakness causes the scapula to abduct and the inferior angle to rotate outward.
• The strength of adduction and extension of the humerus is diminished by the loss of the rhomboids fixation of the scapula.
• Ordinary function of the arm is affected less by the loss of rhomboids than by loss of either trapezius or serratus anterior muscles.

Effect of Contracture

• The scapula is drawn into a position of adduction and elevation.
• Contracture tends to accompany paralysis or weakness of serratus anterior muscle because the rhomboids are direct opponents of the serratus.

Shoulder Flexion

• Anterior Deltoid and Coracobrachialis muscles are involved
• Range of Motion: 0-90°

Anterior Deltoid

• Origin: Anterior lateral third of the clavicle.
• Insertion: Deltoid tuberosity on the lateral humerus.
• Nerve supply: Axillary nerve C5, C6.
• Action: Flexes and medially rotates the shoulder joint; acts as a stabilizer when abduction of shoulder is performed by the deltoid middle fibers.

Coracobrachialis

• Origin: Coracoid process of the scapula.
• Insertion: Middle 1/3 of the medial surface of the humerus.
• Action: Flexes and adducts the shoulder joint.
• Nerve supply: Musculocutaneous nerve C6, C7.

Limitations of Shoulder Flexion

• This range of motion may be limited by ankylosis of the shoulder joint.
• Accessory Muscles: Pectoralis major (clavicular fibers), Biceps brachii
• Fixation: Contraction of the trapezius and serratus anterior muscles (serratus anterior and upper trapezius assist in upward rotation of the scapula as well as in fixation).

Note

• The patient is asked to keep their forearm in pronation to prevent lateral rotation with substitution by biceps brachii when testing the shoulder flexor muscles with the elbow in extension.
• The coracobrachialis muscle cannot be isolated, nor is it readily palpable, but classically it is considered a shoulder flexors and adductor.

Substitutions

• In the absence of the deltoid muscle, the patient may attempt to flex the shoulder with the biceps brachii by first externally rotating the shoulder. To avoid this, the arm should be kept in the mid position between internal and external rotation.
• Attempted substitution by the upper trapezius results in shoulder elevation.
• Attempted substitution by the pectoralis major results in shoulder horizontal adduction.
• The patient may lean backward or try to elevate the shoulder girdle to assist in flexion.

Effect Weakness of Shoulder Flexor Muscles

• Weakness of these muscles decreases the strength of shoulder flexion.
• In addition: weakness of the coracobrachialis muscle will impair function, particularly in movements that involve shoulder flexion and adduction with complete elbow flexion and supination (for example, combing hair)

Shoulder Extension

• Involves Latissimus dorsi, Teres Major and Posterior fiber of Deltoid.
• Range of Motion: 0-50°

Latissimus Dorsi

• Origin: Spines of lower 6 thoracic vertebrae, the thoracolumbar fascia from the lumbar and sacral vertebrae, lower 3-4 ribs, the inferior angle of the scapula, the posterior 1/3 of the external lip of iliac crest.
• Insertion: Intertubercle groove of humerus.
• Nerve Supply: Thoracodorsal nerve C6, C7, C8.
• Action: With the origin fixed, it medially rotates, adducts and extends the shoulder joint. By continued action, it depresses the shoulder girdle, and assists in lateral flexion of the trunk. With the insertion fixed, it assists in tilting the pelvis anteriorly and laterally. Acting bilaterally, this muscle assists in hyper extending the spine and anteriorly tilting the pelvis, or in flexing the spine depending upon its relation to the axes of motion

Important Points on the Latissimus Dorsi

• Is extremely important in relation to movements such as climbing, walking with crutches, or hoisting the body up on parallel bars.
• Forceful arm movements in swimming, rowing and chopping are largely dependent on the strength of this muscle. All shoulder adductors and medial rotators act in these strong movements but the latissimus dorsi is probably of major importance.
• May act as an accessory muscle of respiration.

Teres Major

• Origin: Dorsal surfaces of the inferior angle and lower third of the lateral border of the scapula.
• Insertion: Crest of the lesser tubercle of the humerus.
• Action: Medially rotates, adducts and extends the shoulder joints.
• Nerve Supply: Lower subscapular nerve: C5, C6, C7

Deltoid “Posterior Fiber”

• Origin: Inferior lip of the posterior border of the spine scapula
• Insertion: Deltoid tuberosity of the humerus.
• Action: Extends and laterally rotates the shoulder joint, acting as a stabilizer when the medial fibers of the deltoid are performing abduction of the shoulder.
• Nerve Supply: Axillary Nerve: C5, C6.

Points on Shoulder Extension

• Accessory Muscles: Triceps (long head), Teres Minor
• Range of Motion: Beyond the midline is of 0° to 50°. This may be limited by the tension of shoulder flexor muscles.
• Fixation: Contraction of Rhomboid major and minor and Trapezius muscles and Weight of trunk.

Effect Weakness of Muscles Involved In Extension

• Latissimus Dorsi: Weakness interferes with many activities which involve mainly adduction of the arm toward the body or the body toward the arm. The strength of shoulder extension and lateral trunk flexion is diminished.
• Teres Major: Weakness diminishes the strength of medial rotation and extension of the humerus.
• -Deltoid Posterior Fibers: Weakness diminishes the strength of extension of Humerus.

Shoulder Abduction

• To 90° is perform by the Middle Deltoid and Supraspinatus muscles.
• Range of Motion: 0° TO 90°