Upper Limb Anatomy and Function

• The upper limb is important for precise movements necessary for daily tasks like grasping, gripping, pinching, and manipulating objects, essential for eating, writing, typing, buttoning clothes, and using tools.
• Provides sensory perception for safe interactions, enabling tactile and stereognosis.
• The shoulder joint and its muscles enable mobility and reach, allowing upper limbs to reach, lift, and move objects in various directions.
• The elbow joint and its muscles position the hand, allowing shortening (flexion) or elongation (extension), and orientation during tasks like pronation and supination.
• Hands and fingers enable precise movements.
• The upper limbs aid in maintaining balance and stability during weight-bearing activities.
• Neural organization is important to understand the function and clinical conditions leading to upper limb dysfunction.

Brachial Plexus Anatomy

• The brachial plexus includes roots, trunks, divisions, cords, and branches.
• Roots: C5, C6, C7, C8, and T1.
• Trunks: superior, middle, and inferior.
• Divisions: anterior and posterior.
• Cords: lateral, posterior, and medial.
• Branches include the long thoracic nerve, dorsal scapular nerve, suprascapular nerve, lateral pectoral nerve, medial pectoral nerve, medial brachial cutaneous nerve, medial antebrachial cutaneous nerve, upper subscapular nerve, thoracodorsal nerve, lower subscapular nerve, axillary nerve, musculocutaneous nerve, ulnar nerve, radial nerve and median nerve.

Brachial Plexus Relations

• The plexus passes through the intervertebral foramina, located between the anterior and middle scalene muscles.
• In the posterior triangle of the neck, the plexus is lateral and behind the sternocleidomastoid.
• Below the clavicle.
• The axillary artery is named according to its relationship to the artery.

Clinical Conditions

• Roots (proximal trunks) travel through intervertebral foramina and can be affected by compressed foraminal stenosis from osteophytes, between the anterior and middle scalene muscles and can be compressed due to scalene muscle hypertrophy.
• C8/T1 roots (lower trunk) pass over the first rib behind the subclavian vessels and can be affected in thoracic inlet pathologies (e.g., cervical rib) and apical lung tumors.
• Divisions may be affected by clavicle fractures.

Motor Innervation

• Anterior Compartment of Upper Limb
  • Flexors of the elbow are innervated by the Musculocutaneous Nerve.
  • Flexors of the wrist are innervated by the Median Nerve.
  • The Hand is innervated by the Ulnar Nerve.
• Posterior Compartment of Upper Limb
  • Extensors of the elbow and wrist are innervated by the Radial Nerve.
• Myotomes.
  • C5 is responsible for shoulder abduction.
  • C5/6 is for elbow flexion.
  • C7/8 is for elbow extension.
  • T1 controls finger adduction/abduction.
• Some dermatomes
  • C5: Lateral arm and upper forearm.
  • T2 is top of the axilla

Patterns of Sensory Deficits

• Lesions above the pons lead to contralateral hemisensory loss.
• Damage to a single spinal root or dorsal horn affects the dermatome (supply area of that root), affecting all sensory modalities.
• Lesions in the peripheral nerves cause a deficit distribution that follows the nerve's sensory territory.

Shoulder Associated Muscles

• Scapulothoracic muscles attach the scapula to the axial skeleton.
• Scapulohumeral and Pectoral muscles attach the upper limb to the shoulder girdle

Scapulo-Thoracic Muscles

• The trapezius is a superficial muscle that attaches superiorly to the nuchal line and inferiorly to the spine and acromion of scapula. Its superior fibres elevate the scapula, and the whole muscle retracts the shoulder. It is innervated by the spinal accessory nerve.
• Rhomboids are located under the trapezius and attach from the supraspinous ligament to the medial border of the scapula. It retracts of scapula and is innervated by the dorsal scapular nerve (C5).
• Serratus anterior holds the scapula against the rib cage during shoulder movements, protracts the shoulder girdle, and upwardly rotates the glenoid. It is innervated by the long thoracic nerve (C5,6,7).
  • Paralysis of the serratus anterior results in scapular winging due to the backward displacement of the medial border of the scapula.

Posterior Scapulo-Humeral Muscles

• Latissimus Dorsi is a superficial muscle attached to the thoracolumbar fascia, iliac crest, inferior angle of scapula and bicipital groove. It enables extension, internal rotation, and adduction at the GH joint and is innervated by the thoracodorsal nerve.
• Teres Major is under the latissimus dorsi and attaches to the lateral border of the scapula and bicipital groove on the proximal humeral shaft. It enables internal rotation and adduction at the GH joint.

Anterior Scapulo-Humeral Muscles

• Pectoralis major is a superficial muscle in the anterior chest that attaches to the clavicle, manubrium, sternum, and the anterior of the proximal humerus. It enables Clavicular fibres - Flexion at GH (Glenohumeral) joint, Sternocostal fibres – Adduction at GH joint, and Sternocostal fibres – Internal rotation at GH joint. Medial and Lateral pectoral nerves innervate this muscle.
• Deltoid comprises anterior, lateral, and posterior fibres attached to the clavicle, spine of the scapula, acromion, and the deltoid tuberosity on the humerus. They enable flexion, abduction, and extension of the GH joint respectively and the axillary nerve innervates this.

Axillary Nerve

• The axillary nerve originates from the posterior cord of the brachial plexus and passes back through the quadrangular space. It provides motor innervation to the deltoid and teres minor, and sensory innervation to the skin over the lower part of the deltoid.

Scapulo-Humeral Muscles - Rotator Cuff

• Supraspinatus:
  • The scapular attachment in the supraspinous fossa with a humeral attachment on the greater tuberosity (superior) with a function of Abduction.
• Infraspinatus: - The scapular attachment in the infraspinous fossa with a humeral attachment on the greater tuberosity (middle) with a function of External Rotation.
• Teres Minor:
  • The scapular attachment is Upper Lateral and a humeral attachment on the greater tuberosity (Inferior) with a function of External Rotation and also Lateral rotation
• Subscapularis: - The scapular attachment in the subscapular fossa and a humeral attachment on the lesser tuberosity function is Internal Rotation.
• The suprascapular nerve arises from the superior trunk (C5,6) and supplies motor innervation to the supraspinatus and infraspinatus. It goes through the suprascapular notch to enter the supraspinous fossa then passes through spinoglenoid notch to enter the infraspinous fossa.

Muscles of the Arm

• The anterior compartment enables more proximal joint muscles in glenoid, forearm
• The posterior compartment Radial has muscles that have a further affect on the shoulder and elbow

Posterior Compartment of the Arm

• The triceps brachii is in the posterior compartment of the arm. Its long head originates from the infraglenoid tubercle and inserts into the olecranon process of the ulna. It enables extension at the GH joint and at the elbow joint. The radial nerve innervates the triceps brachii.
• The radial nerve originates from the posterior cord of the brachial plexus and passes back through the triangular interval, supplying Teres major, long head triceps, Humeral shaft/lateral head triceps

Anterior Compartment of the Arm

• The biceps brachii is the most anterior muscle of the arm, crossing both the GH joint and elbow joints. The muscolocutaneous nerve innervates this muscle.