BMS MSK Lecture 9 Fall 2023 PDF

BMS Anatomy Lecture 9 Upper Limb Nerves , Dermatomes & Myotomes (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) Moore's Clinically Oriented Anatomy, by Arthur F. Dalley II Ph.D. FAAA (Author), Anne M. R. Agur BSc (O...

BMS Anatomy Lecture 9 Upper Limb Nerves , Dermatomes & Myotomes (In-Person Class) Presented By: Dr. K. Lumsden; [email protected] (Toronto Campus) Dr. M. Doroudi; [email protected] Boucher Campus) Moore's Clinically Oriented Anatomy, by Arthur F. Dalley II Ph.D. FAAA (Author), Anne M. R. Agur BSc (OT) MSc Ph.D. FAAA (Author), 9th ed. Upper Limb Chapter; Pages: 165 – 174 RECALL: The Brachial Plexus Supraclavicular Branches: Branches that exit the brachial plexus “superior” to the clavicle Largely located in the cervical region Important branches: Long Thoracic Nerve Suprascapular Nerve Dorsal Scapular Nerve ANTERIOR, Right side Infraclavicular Branches (terminal Branches) Branches exit plexus inferior to clavicle Primarily located in axilla / armpit Musculocutaneous (C5,6,7) Axillary (C5/6) Radial (C5 – T1) Median (C5 – T1) Ulnar (C8/T1) 2 Musculocutaneous Nerve Origin: terminal branch of lateral cord Functions: Motor to anterior arm: Coracobrachialis Biceps Brachialis Sensory to : Skin of anterolateral forearm ANTERIOR, Right side Musculocutaneous Nerve - Terminal Branch of lateral cord within axilla - Travels through the coracobrachialis muscle belly *Most likely site of injury - Innervates muscles of the anterior compartment of the arm - Continues after passing the cubital fossa as the Lateral. Cutaneous N. of forearm 4 Axillary Nerve Origin: terminal branch of posterior cord Function: Motor to lateral shoulder: Deltoid Teres minor Sensory to: Skin of lateral shoulder ANTERIOR, Right side Axillary Nerve - Pathway: heads posteriorly in axilla - Travels through the quadrangular axillary space - Wraps around posterior aspect of humeral neck - Relationship with the surgical neck of humerus *Most likely site of injury - Innervates deltoid and Teres minor 6 Axillary Nerve Injury MOI: Fracture of Surgical neck of Humerus 7 Radial Nerve Radial nerve (C5, C6, C7, C8 and T1) Origin: terminal branch of posterior cord Function: Motor To: Extensor muscles of posterior arm Extensor muscles of posterior forearm Brachioradialis Supinator muscle Sensory to: Skin of posterior arm, forearm and hand Dorsal surface of digits 1, 2, 3 and lateral ½ of digit 4 (typically written as lateral 3.5 digits, dorsal surface) “Great extensor nerve” Posterior View Radial Nerve - Pathway: heads posteriorly in axilla - Travels posteriorly, inferior to the quadrangular axillary space - wraps around posterior aspect of humeral shaft - Relationship with the radial groove of humerus *Most likely site of injury - Innervates extensors of arm and forearm and supinator 9 Radial Nerve in Cubital Fossa 10 Radial Nerve - Sensory branches in posterior arm: - Post. Cutaneous Nerve of Forearm - Lower lateral cutaneous nerve of arm 11 Radial Nerve Terminal branches of radial N. Deep branch (motor) – innervates the muscles in the posterior compartment of the forearm. Superficial branch (sensory) – contributes to the cutaneous innervation of the dorsal hand and fingers. 12 Radial N. Palsy (Wrist Drop) MOI: Fracture of radial groove of Humerus 13 Median Nerve Median nerve (C5, C6, C7, C8 and T1) Origin: terminal branch of lateral and medial cords Function: Motor to Muscles of the anterior forearm and hand: Flexors of wrist Pronators of forearm Flexors of Digits 1, 2, 3 Lumbricals 1 and 2 Thenar muscles Sensory to: Palmer surface of digits 1, 2, 3 and lateral ½ of digit 4 (typically written as lateral 3.5 digits, palmer surface) Palmer View ANTERIOR, Right side Pathway: heads inferiorly from axilla, travelling down antero-medial arm (within layers of muscle) crosses anterior elbow within cubital fossa *likely site of injury travels down anterior forearm enters hand via carpal tunnel *likely site of injury Median Nerve injury Carpal Tunnel Syndrome: Compression of the median nerve as it passes through the carpal tunnel Typing Mechanics Pregnancy Obesity Will first impact function of median nerve in the hand (motor and sensory) Patient often complains of numbness and tingling in the first 3.5 digits and weakness of thumb movement As the condition progresses, sensory changes can radiate into the forearm, and even the axilla. To relieve symptoms, partial or complete surgical division of the flexor retinaculum may be necessary – this is known as ‘carpal tunnel release’. 16 Ape hand deformity (Median nerve lesion) 17 Ulnar Nerve ANTERIOR, Right side Ulnar nerve (C8 and T1) Origin: terminal branch of medial cord Function: Motor to medial forearm and hand: Medial ½ of flexor digitorum profundus Hand intrinsics Lumbricals 3&4 Hypothenar group Palmer and Dorsal Interossei Sensory to: Palmer and Dorsal surface of medial ½ of digit 4 And all if digit 5 (typically written as medial 1.5 digits) Dorsal Palmer Pathway: heads inferiorly from axilla, travelling down antero-medial arm (protected by muscle) passes posterior to medial epicondyle, *Most likely site of injury travels down medial forearm enters hand external to carpal tunnel 19 Ulnar Claw Hand MOI: Fracture of medial epicondyle of Humerus 20 Axillary C5-C6 Cutaneous Supply from Brachial Plexus: Radial C5, C6, C7, C8, T1 Medial Brachial Cutaneous Medial Antebrachial Cutaneous Musculocutaneous C5, 6, 7 Radial C5, C6, C7, C8, T1 Median C5, C6, C7, C8, T1 Ulnar C8 - T1 Cutaneous Supply from Brachial Plexus: Median Palmer surface of lateral 3.5 digits Ulnar Palmer and dorsal surface of medial 1.5 digits Radial Dorsal surface of lateral 3.5 digits RECALL: Anatomy of the Spinal Nerves There are 31 pairs of spinal nerves exiting off spinal cord Nerves are WHITE matter pathways that provide a route for motor and sensory signals to travel between PNS and CNS Spinal nerves are IPSILATERAL and will carry signals to and from targets/receptors on the same side of the body Posterior/Dorsal root carries sensory/afferent information into CNS so it can ascend in the cord to reach the cortex Ventral/Anterior root carries motor/efferent information out of CNS that has descended from the cortex to the cord Swelling/bulb contains the soma/cell bodies of incoming sensory cells Ventral & Dorsal roots come together to form a spinal nerve in the intervertebral foramen 23 Dermatomes and Myotomes Dermatome is a specific area on the skin innervated by a specific spinal root Myotome is a specific group of muscles innervated by a particular spinal root. Testing both dermatome and myotomes can provide important clinical feedback about the function of spinal nerves 24 25 Dermatomes of the Upper Limb Dermatomes of the Upper Limb 27 Nerve Root Myotome Function C5 Deltoid muscle Abduction of the arm at the shoulder C6 Biceps Flexion of the arm at the elbow C7 Triceps Extension of the arm at the elbow C8 Small muscles of the hand Finger flexion T1 Small muscles of the hand Finger Abduction 28 Myotomes of the Upper Limb https://www.youtube.com/watch?v=8UcSvosgKWA 29 Clinical Test: C5 Dermatome = sensation of skin of anterior/lateral arm (skin over deltoid) Myotome = muscle strength of deltoid (arm abduction) 30 Clinical Test: C6 Dermatome = sensation of anterior skin of thumb Myotome = muscle strength of biceps (elbow flexion) 31 Clinical Test: C7 Dermatome = sensation of anterior skin of digits 2 and 3 Myotome = muscle strength of triceps (elbow extension) 32 Clinical Test: C8 Dermatome = sensation of skin of digits 4 and 5 Myotome = muscle strength of finger flexors 33 C8 Motor Nerve 34 Clinical Test: T1 Dermatome = sensation of skin of antero/medial elbow Myotome = muscle strength of finger abductors 35 The Reflex Arc. Simplest of all neural responses Automatic Predictable Acquired Summary of Deep Tendon Reflexes of Upper Limb 37