Upper Extremity Peripheral Nerve Review PDF

Upper Extremity Peripheral Nerve Review CFS 6200 This review will serve as a reference to the slides in the Module: Neuroanatomy of the Upper Extremity. Here are the things you should focus on: 1) The brachial plexus roots, trunk, divisions, and cords, and their branches; 2) The names of the term...

Upper Extremity Peripheral Nerve Review CFS 6200 This review will serve as a reference to the slides in the Module: Neuroanatomy of the Upper Extremity. Here are the things you should focus on: 1) The brachial plexus roots, trunk, divisions, and cords, and their branches; 2) The names of the terminal nerves and their branches; 3) The names of the nerves that innervate the muscles of the extremities; 4) The distribution of the spinal nerve VPR to the individual muscles (segmental innervation); and 5) The indicator muscles and reflexes for the individual spinal nerve roots (MSR neurological levels). The actions of the muscles will NOT be reviewed here; use your gross anatomy resources for these. The formative and summative assessments may include a reference to the action of a muscle, but it wouldn’t be the focus of a question. Unless otherwise noted, all muscular branches of the nerves consist of GSE, GSA (high and low threshold fibers from the somatic components), GVA (high and low threshold fibers from vascular elements), and postganglionic GVE sympathetic fibers (to the vessels of the muscles); all cutaneous branches of the nerves consist of GSA (high and low threshold somatic fibers), GVA (high and low threshold fibers from vascular elements), and postganglionic sympathetic fibers to vascular elements, sweat glands, erector pili, and sebaceous glands. It is expected that once we finish this information, you may be expected to answer questions regarding the material on all subsequent assessments! The Brachial Plexus Basic Neuroanatomy: 1. The Brachial Plexus arises from the Ventral Primary Rami (VPR) of spinal nerve roots C5-T1. 2. The VPR re-assort themselves into several different arrangements (proximal to distal): a. “roots” (really the VPRs of C5-T1); b. trunks (upper: C5 and C6; middle: C7; and lower: C8 and T1); c. divisions (anterior and posterior from each VPR via the trunks); d. cords (lateral [anterior divisions of the upper and middle trunks], medial [anterior 1|Page  divisions of the lower trunk], and posterior [posterior divisions all three trunks]— labelled in relationship to the axillary artery); and the e. terminal branches/nerves (Musculocutaneous [lateral cord], Axillary [posterior cord], Radial [posterior cord], Median [lateral and medial cords], and Ulnar [medial cord]). 3. Several important nerves branch off of the roots, trunks, and cords, prior to the terminal nerves. 4. The terminal nerves have many important branches that you should be aware of. The Brachial Plexus: This diagram helps you to understand that the spinal nerve contributions are distributed by the names peripheral nerves, given the color coding. If you have difficulty seeing the colors, please le me know and I will help provide a different resource. The major branches of the Brachial Plexus: 2|Page Supraclavicular Branches: 1. Those nerves arising from the roots (VPR of the spinal nerves before the plexus is formed): a. Dorsal Scapular Nerve: C5. Functionally, a posterior division nerve. Innervates the rhomboid major and minor, and occasionally supplies a branch to the levator scapulae (though in that case, a branch of the cervical plexus C3-4 joins the dorsal scapular nerve). The nerve is accompanied by branches of the transverse cervical artery. b. Long Thoracic Nerve: C5, 6, 7. Functionally, the long thoracic nerve is a posterior division nerve. Innervates the serratus anterior. As this nerve passes between the anterior and middle scalene, it is possible that compression of the nerve could occur with muscle spasm of the scalenes (as could occur to the whole brachial plexus as well) resulting in weakness of the serratus. Poorly fitted crutches, carrying heavy backpacks, axillary surgery, and other trauma can also contribute to long thoracic nerve damage. Scapular winging is a significant sign of weakness. 2. Those nerves arising from the trunks of the BP: a. Nerve to the Subclavius: C5. Functionally, this is an anterior division nerve, from the upper trunk of the BP. Innervates the subclavius muscle. b. Suprascapular Nerve: C5, C6. Functionally, an anterior division nerve, arising from the upper trunk. Innervates the supraspinatus muscle (mainly the C5 portion) and the infraspinatus muscle (C5 and 6); it also transmits sensory fibers from the acromioclavicular joint as well as the glenohumeral joint. Anatomy: the nerve passes downward, laterally (deep to the omohyoid and trapezius & then posteriorly to pass under the trapezius. With the suprascapular vein and artery, it reaches suprascapular notch. Interestingly, the nerve travels beneath the suprascapular notch, whereas the vessels travel above the notch. After giving off 2 branches to supraspinatus, it passes around lateral border of the scapular spine and ends in the infraspinatus fossa to supply infraspinatus. From: http://www.wheelessonline.com/ortho/suprascapular_nerve Infraclavicular Branches: The rest of the branches of the brachial plexus are derived from the cords of the plexus. These include the major terminal branches, as well as a few smaller branches: 1. Nerves derived from the lateral cord (anterior divisions): a. Lateral Pectoral Nerve: C5, 6, 7. Innervates the upper and lower fibers of the pectoralis major. 3|Page  2. Nerves derived from the medial cord (anterior divisions): a. Medial Pectoral Nerve: (C6,7), C8, T1. Innervates the lower fibers of the pectoralis major and the pectoralis minor. 3. Nerves derived from the posterior cord (all posterior divisions): a. Upper subscapular nerve: C5, 6. Innervates the subscapularis muscle. Muscle Test: Internal rotation of the shoulder. b. Lower subscapular nerve: C5, 6 (C7). Innervates the teres major (C6) and subscapularis muscles (C5). c. Thoracodorsal nerve: C6, 7, 8. Innervates the latissimus dorsi muscle. Musculocutaneous Nerve: Musculocutaneous nerve is a terminal branch of the Lateral Cord, made up of VPR of C5, 6, and 7. Muscles innervated: Biceps (C5, 6), Brachialis (C5, 6), Coracobrachialis (C5, 6, 7) Neurological Level Indicators: Biceps: C6; Biceps reflex: C5 4|Page Cutaneous Contribution: Lateral Antebrachial Cutaneous Nerve (LACN). Distribution to the lateral forearm, largely from C6. The LACN distribution does NOT include the thumb. It continues in the lateral forearm to the wrist, but not into the thum. The C6 dermatome continues down to the thumb and includes the web. Clinical Notes: The musculocutaneous nerve is rarely injured directly. The more vulnerable upper trunk is more often damaged. Tennis players who repeatedly and forcefully execute overhead smashes may injury the lateral antebrachial cutaneous portion of the nerve at the elbow. However, this may be accompanied by lateral epicondylitis, making the diagnosis more complicated. Axillary Nerve: Regarding the figure above, anterior and posterior terminal divisions should perhaps better be called the terminal “portions”, so as not to be confused with the fact that the axillary nerve is a posterior division nerve. The Axillary Nerve is a terminal branch of the Posterior Cord, made up of VPR from C5 and C6. Muscles innervated: Deltoid (C5, 6), and Teres minor (C6) Neurological Level Indicated: Deltoid, C5. Cutaneous Contribution: Superior Lateral Cutaneous Nerve: “Regimental badge” area. Clinical Notes: -the axillary nerve is accompanied by the posterior humeral circumflex artery as it traverses the surgical neck of the humerus. 5|Page  -Humeral fracture at the surgical neck could compromise both the nerve and the vessel. -Anterior humeral dislocation may compromise the axillary nerve to the deltoid, but not the vessel. -Quadrangular Space Syndrome: Weakness of the deltoid and teres minor is noted. Paresthesia in the “regimental badge” area is noted. No loss of biceps reflex. Cutaneous Distribution of the Axillary Nerve: This distribution is referred to as the “regimental badge” distribution. Contrast this distribution to that of the C5 dermatome. Notes: 6|Page  Anterior interosseus nerve Notes: 7|Page The Median Nerve Cutaneous Distribution of the Median Nerve: The Median nerve is a large branch of brachial plexus, arising from both the lateral and medial cords, and receiving contributions from the VPR of C6-T1. The cutaneous GSA (somatic high and low threshold fibers) and GVA (vascular high and low threshold fibers) components are distributed to the areas outlined above (palm associated with the thenar eminence, the anterior surfaces of the thumb and lateral three and a half digits, and the distal tips of the posterior surfaces of the thumb and lateral two digits) via the palmar and digital cutaneous branches of the median nerve. Along with the GSAs, the postganglionic GVE sympathetic axons will be distributed to the sweat glands (there are no hair follicles on the palmar surfaces of the hand) and the cutaneous vascular smooth muscle. Superficial Muscles of the Anterior Forearm Innervated by the Median Nerve: -Pronator teres: C5-6 -Flexor carpi radialis: C6-7 -Palmaris longus: C7-8 -Flexor digitorum superficialis: C7-T1 8|Page The pronator teres represents an important entrapment site of the median nerve as the nerve passes through the two heads of the muscle. Here is a very nice video reviewing the pronator teres syndrome: https://www.youtube.com/watch?v=ZqhO1dzqTtY One important difference between pronator teres syndrome and carpal tunnel syndrome is that the median nerve gives two cutaneous branches to the palm: the common proper digital branch (blue in the picture above) which branches under the tunnel and the palmar cutaneous branch (yellow in the picture above) which branches over the tunnel. In pronator teres syndrome, the palmar cutaneous branch as well as the common proper digital branch would be symptomatic, in CTS, only the common proper digital branch would be affected. Deep Muscles of the Anterior Forearm Innervated by the Anterior Interosseus Branch of the Median Nerve: -Flexor digitorum profundus (the median nerve portion, digits 2/3): C7-T1 -Flexor pollicis longus: C7-T1 -Pronator quadratus: C8-T1 Muscles of the Hand Innervated by the Recurrent Branch of the Median Nerve (C8-T1): -Abductor pollicis brevis -Flexor pollicis brevis (superficial head) -Opponens pollicis NOTE**** Recall then, that within the thenar eminence, the Median Nerve DOES NOT innervate the Adductor pollicis: the Ulnar Nerve does. The Palmar Digital Branch of the Median Nerve (C8-T1) innervates the: -Lumbricals I and II (of digits II and III: the thumb does not have lumbricals) 9|Page  The recurrent branch of the median nerve innervates the opponens pollicis, abductor pollicis brevis, and the superficial part of flexor pollicis brevis. A more proximal branch of the median nerve (the palmer digital branch) also supplies the lumbricals 1 & 2. The Ulnar Nerve The Ulnar nerve first innervates the flexor carpi ulnaris and the ulnar portion of the flexor digitorum profundus in the antebrachium. There is no cutaneous innervation of the ulnar nerve until the hand. 10 | P a g e The Ulnar Nerve arises as the terminal branch of the medial cord, receiving contributions from VPR of C8 and T1 via the lower trunk of the brachial plexus. The muscular branch of the ulnar nerve in the anterior forearm innervates: Flexor carpi ulnaris: C8-T1 Flexor digitorum profundus (ulnar portion): C8-T1 The muscular branches of the ulnar nerve to the hand (reach their destination by passing through the Tunnel of Guyon) innervate: Thenar eminence: C8-T1 Adductor pollicis Flexor pollicis brevis (deep head) Hypothenar Eminence: C8-T1 Palmaris brevis Abductor digiti minimi Flexor digiti minimi Opponens digiti minimi Lumbricals III and IV Palmar interossei: (PAD: Palmar interossei produce adduction of the fingers) Dorsal Interossei: (DAB: Dorsal interossei produce abduction of the fingers) The Cutaneous Branches: The Palmar Cutaneous Branch: medial half of the palm The Superficial Branch: anterior aspects of the medial 1 ½ fingers The Dorsal Cutaneous Branch: posterior aspects of the medial 1 ½ fingers and palm. 11 | P a g e Clinical Notes: -The Ulnar Nerve is commonly entrapped at the medial epicondylar groove in the cubital fossa and within the Tunnel of Guyon in the medial carpus. -Tunnel of Guyon Syndrome: Entrapment at the Tunnel of Guyon results in mainly hypothenar weakness and weakness in adduction of the thumb. -Cubital Tunnel Syndrome: Entrapment at the cubital fossa results in weakness of ulnar wrist flexion as well as hypothenar weakness, due to the loss of all of the muscular innervation (adduction weakness of the thumb, hypothenar weakness, and weakness in finger flexion due to loss of the flexor carpi ulnaris and the ulnar portion of the profundus [digits 3 and 4]). Here is a video review of the cubital tunnel syndrome: https://www.youtube.com/watch?v=HQyw-tJKmjA&index=7&list=PL2B7044E940F74D15 12 | P a g e The Radial Nerve General information: The Radial Nerve is the terminal branch of the posterior cord. It is a large nerve, comprised of posterior division axons from C5-T1. It innervates all the muscles in the posterior brachium and antebrachium. It consists of several motor branches and several cutaneous branches. It also innervates one flexor of the forearm: the brachioradialis, and often contributes a branch to the brachialis muscle. Muscles innervated in the brachium: Triceps: C6, C7, 8, T1. The triceps is used as an indicator of the integrity of C7, both by testing the strength of the muscle and the reflex. Muscle test: resist the patient’s attempt to extend the forearm. NOTE: a key indicator of whether or not the patient’s symptoms are due to a peripheral nerve loss or a spinal nerve root loss is to note the reflex associated with the neurological level. If the reflex is diminished, the likely loss is of the spinal nerve root. If the reflex is normal, the loss is more likely to be in the course of the peripheral nerve. Anconeus: C7, 8. Muscles innervated in the antebrachium by the radial nerve: Brachioradialis: C5, 6 Supinator: C6 Extensor carpi radialis longus: C6, 7 Muscles innervated in the antebrachium by the deep radial nerve (aka, the posterior Interosseus nerve) Extensor carpi radialis brevis: C6, 7 Extensor carpi ulnaris: C6, 7, 8 Extensor digitorum: (C6) C7 (C8) Extensor digiti minimi: (C6) C7 (C8) Extensor indicis: C7 (C8) Extensor pollicis longus: C7, C8 Extensor pollicis brevis: C6, 7 Abductor pollicis longus: C6, 7 13 | P a g e 14 | P a g e The Cutaneous Innervation of the Radial Nerve: In the brachium: The Lower Lateral Cutaneous Nerve The Posterior Brachial Cutaneous Nerve In the antebrachium: The Posterior Antebrachial Cutaneous Nerve The Superficial Radial Nerve 15 | P a g e Clinically Important Innervation: The Muscles of the Thumb Median Nerve Proper: Flexor pollicis longus Recurrent Branch of the Median Nerve in the Thenar Eminence: Abductor pollicis brevis Opponens pollicis Flexor pollicis brevis (superficial portion) Ulnar nerve: Flexor pollicis brevis (deep head) Adductor pollicis Radial Nerve: Extensor pollicis longus Extensor pollicis brevis Abductor pollicis longus 16 | P a g e