The Brachial Plexus PDF 2023

THE BRACHIAL PLEXUS 1 of 117 The brachial plexus is anetwork of nerve fibres thatsupplies the skin and musculature of the upper limb. It begins in the root of the neck, passes through the axilla, and enters the upper arm. The plexus is formed by the anterior rami (divisions) of the cervical spinal n...

THE BRACHIAL PLEXUS 1 of 117 The brachial plexus is anetwork of nerve fibres thatsupplies the skin and musculature of the upper limb. It begins in the root of the neck, passes through the axilla, and enters the upper arm. The plexus is formed by the anterior rami (divisions) of the cervical spinal nerves C5, C6, C7 and C8, and the first thoracic spinal nerve, T1. 2 of 117 3 of 117 4 of 117 The brachial plexus is divided into five parts; roots, trunks, divisions, cords and branches. There are no functional differences between these divisions – they are simplyused to aid explanation of the brachial plexus. 5 of 117 Agood mnemonic for this is Randy Travis Drink Cold Bear! 6 of 117 Roots The ‘roots’ refer the beginning of thebrachial plexus. They are formed by the spinal nerves C5, C6, C7, C8and T1. At each vertebral level, paired spinal nerves arise. They leave the spinal cord via the intervertebral foramina of the vertebral column. 7 of 117 8 of 117 Each nerve then divides into anterior and posterior nerve fibres. The roots of the brachial plexus are formed by the anterior divisions of spinal nerves C5-T1 (the posterior divisions go onto innervate the skin and musculature of the trunk). After their formation, these nerves pass between the anterior and medial scalene muscles toenter the base of the neck. 9 of 117 Trunks At the base of the neck, the roots of the brachial plexus converge, forming three trunks. These structures are named by their anatomical position: Superior trunk: A combination of C5and C6roots. Middle trunk: A continuation of C7. Inferior trunk: A combination of C8 andT1 roots. The trunks begin to move laterally, crossing the posterior triangle ofthe neck. 10 of 117 Divisions Within the posterior triangle of the neck, each trunk divides into two branches. One division travels anteriorly (toward the front of the body) and the other posteriorly (towards the back of the body). Thus, they are known as the anterior and posterior divisions. We now have three anterior andthree posterior nerve fibres. These divisions leave the posterior triangle and pass into the axillaregion. They recombine in the next part of the brachial plexus. 11 of 117 12 of 117 13 of 117 Cords Once the anterior and posterior divisions have entered the axilla, they combine together to formthree nerves. These nerves are named by their position relative to theaxillary artery. The lateral cord is formed by: The anterior division of thesuperior trunk The anterior division of the middle trunk 14 of 117 The posterior cord is formed by: The posterior division of the superior trunk The posterior division of the middle trunk The posterior division of the inferior trunk 15 of 117 The medial cord is formed by: The anterior division of theinferior trunk. The cords give rise to themajor branches of the brachialplexus. 16 of 117 17 of 117 18 of 117 19 of 117 Major Branches In the axilla and the proximal aspect of the upper limb, the three cords give rise to five major branches. These nerves continue into the upper limb to provide innervation to the muscles and skin present. 20 of 117 Minor Branches In addition to the five major branches of the brachial plexus, there are a number of smaller nerves that arise. They do so from all five parts of the brachial plexus, and are listed below: 21 of 117 Clinical Relevance: Injury to the Brachial PlexusUpper Brachial Plexus Injury – Erb’s Palsy Erb’s palsy commonly occurs where there is excessiveincrease in the angle between the neck and shoulder – this stretches(or can even tear) the nerveroots, causing damage. It can occur as a result of resultof a difficult birth or shoulder trauma. Nerves affected: Nervesderived from solely C5 or C6roots; musculocutaneous, axillary, suprascapular and nerve to subclavius. 22 of 117 Clinical Relevance: Injury to the Brachial PlexusUpper Brachial Plexus Injury – Erb’s Palsy Muscles paralysed: Supraspinatus, infraspinatus, subclavius, biceps brachii, brachialis, coracobrachialis, deltoid andteres minor. Motor functions: The following movements are lost or greatly weakened – abduction at shoulder, lateral rotation of arm, supination of forearm, andflexion at shoulder. 23 of 117 Clinical Relevance: Injury to the Brachial PlexusUpper Brachial Plexus Injury – Erb’s Palsy Sensory functions: Loss of sensation down lateral side ofarm, which covers the sensory innervation of the axillary and musculocutaneous nerves. The affected limb hangs limply, medially rotated by theunopposed action of pectoralismajor. The forearm is pronated due to the loss of biceps brachii. This is position is known as ‘waiter’s tip’, and is characteristic of Erb’spalsy. 24 of 117 25 of 117 Clinical Relevance: Injury to the Brachial PlexusLower Brachial Plexus Injury – Klumpke Palsy A lower brachial plexus injury results from excessive abduction of the arm (e.g person catching a branch as they fall from atree). It has a much lower incidence than Erb’spalsy. Nerves affected: Nerves derived from the T1 root – ulna and median nerves. 26 of 117 Clinical Relevance: Injury to the Brachial PlexusLower Brachial Plexus Injury – Klumpke Palsy Muscles paralysed: All the small muscles of the hand (the flexors muscles in the forearm aresupplied by the ulna and median nerves, but are innervated by different roots). Sensory functions: Loss of sensation along medial side of arm. The metacarpophalangeal joints are hyperextended, and the interphalangeal joints are flexed. This gives the hand a clawed appearance. 27 of 117 28 of 117 29 of 117 30 of 117 THEMUSCULOCUTANEOUSNERVE Nerve roots: C5-C7. Motor functions:Innervates the muscles in the anterior compartment of the arm – the coracobrachialis, biceps brachii and the brachialis Sensory functions: Gives rise to the lateral cutaneous nerve of forearm, which innervates skin on the lateral surface of the forearm. 31 of 117 Anatomical Course The musculocutaneous nerve arises from the lateral cord of the brachial plexus, and therefore contains fibres from spinal roots C5, C6 andC7. After originating from the brachial plexus, the musculocutaneous nerve leaves the axilla, and pierces the coracobrachialis muscle, near its point of insertion on the humerus. 32 of 117 Anatomical Course It then passes down the arm, anterior to the brachialis muscle but deep to the biceps brachii, innervating them both. The musculocutaneous nerve emerges laterally to thebiceps tendon, and continues into the forearm as the lateral cutaneous nerve. It provides sensory innervation to the lateral aspect of the forearm. NB: The musculocutaneous nerve is well recognised to havea varied anatomical course. It can interact with the median nerve, adhering to the nerve and exchanging fibres. 33 of 117 34 of 117 Motor Functions The musculocutaneous nerve innervates the muscles in the anterior compartment of thearm – the biceps brachii, brachialisand coracobrachialis. These muscles flex the upperarm at the shoulder and theelbow. In addition, the biceps brachiialso performs supination of the forearm. A good memory tool to helpyou remember these muscles isBBC. 35 of 117 Sensory Functions The musculocutaneous nerve gives rise to thelateral cutaneous nerve of forearm. This nerve initially enters the deep forearm, but then pierces the deep fascia to become subcutaneous. In this region, it can be found in close proximity to the cephalicvein. The lateral cutaneous nerve of forearm innervates the skin of the lateral aspect of the forearm. 36 of 117 37 of 117 Clinical Relevance: Lesions of the Musculocutaneous Nerve How it commonly occurs: An injury to the musculocutaneous nerve is relatively uncommon, as it is well protected within the axilla. The most common cause is a stab wound to the axilla region. Motor functions: The coracobrachialis, biceps brachii and brachialis muscles are paralysed. Flexion at the shoulder is weakened, but can still occur due to the pectoralis major. Flexion at the elbow is also affected, but can still be performed because ofthe brachioradialis muscle. Also, supination of the affected limb is greatly weakened, butis produced by the supinator muscle. Sensory functions: Loss of sensation over the lateral side of the forearm. 38 of 117 THEAXILLARYNERVE The axillary nerve is a major peripheral nerve of theupper limb. Spinal roots: C5andC6. Sensory functions: Gives rise to superior lateral cutaneous nerve of arm, which innervates the skin over the lower deltoid(‘regimental badge area’). Motor functions: Innervates the teres minor and deltoidmuscles. 39 of 117 40 of 117 Anatomical Course The axillary nerve is formed within the axilla region. It is a direct continuation of the posterior cord of the brachial plexus, and therefore contains fibres from the C5and C6nerve roots. Immediately after its formation, the axillary nerve lies posteriorlyto the axillary artery and anteriorlyto the subscapularis muscle. 41 of 117 It descends to the inferior border of thesubscapularis muscle, and then exits the axilla posteriorly via the quadrangular space. It is accompanied by the posterior circumflex humeral artery. 42 of 117 In the posterior scapular region, the axillary nerve terminates by dividing into two branches: Posterior terminal branch – Provides motor innervation to the teres minor muscle, and innervates the skin over the inferior part of the deltoid. Anterior terminal branch – Provides motor innervation to the deltoid muscle The axillary nerve also provides articular branches to the shoulder joint itself. 43 of 117 The Quadrangular Space The quadrangular space is a gap in the muscles of the posterior scapular region. It is a pathway for neurovascular structures to move from the axilla to the posterior shoulder and arm. 44 of 117 The Quadrangular Space Its boundaries are: Superior – Subscapularis and teres minor. Inferior – Teresmajor. Laterally – Surgical neck of humerus. Medially – Long head of triceps brachii. The axillary nerve and posterior circumflex humeral artery pass through the quadrangularspace. 45 of 117 Motor Functions The axillary nerve innervatesthe teres minor and the deltoid muscles. The teres minor is part ofthe rotator cuff muscles of the shoulder. This set of muscles acts to stabilise the glenohumeraljoint. 46 of 117 Acting individually, the teresminor externally rotates the upperlimb. The muscle is innervated the posterior terminal branch of the axillarynerve. The deltoid is situated at thesuperior aspect of the shoulder. It performs abduction of the upper limb at the glenohumeral joint. The muscle is innervated by the anterior terminal branch of the axillarynerve. 47 of 117 Sensory Functions The sensory component of the axillary nerve is delivered viaits posterior terminal branch. After the posterior terminal branch of the axillary nervehas innervated the teres minor, it continues as the upper lateral cutaneous nerve of the arm. 48 of 117 This nerve innervates the skinover the inferior portion of the deltoid (known as the ‘regimental badge area’). In a patient with axillary nerve damage, sensation at the regimental badge area may be impaired or absent. The patient may also report paraesthesia (pins and needles) in the distribution of the axillary nerve. 49 of 117 50 of 117 Clinical Relevance: Injury to the AxillaryNerve The axillary nerve is most commonlydamaged by trauma to the shoulder or proximal humerus – such as a fracture of the humerus surgical neck. Motor functions: Paralysis of the deltoid and teres minor muscles. This renders the patient unable to abduct the affected limb. 51 of 117 Sensory functions: The upper lateral cutaneous nerve of arm will be affected, resulting in loss ofsensation over the regimental badgearea. Characteristic clinical signs: In long standing cases, the paralysed deltoid muscle rapidly atrophies, and the greater tuberosity can be palpatedin that area. 52 of 117 53 of 117 THEMEDIANNERVE Nerve roots: C6 – T1. (Also contains fibres from C5 in some individuals). Motor functions: Innervates the flexor muscles in the anterior compartment of the forearm(except the flexor carpi ulnaris and part of the flexor digitorum profundus, innervated by the ulnarnerve). Also supplies innervation to the thenar muscles and lateral two lumbricals in the hand. 54 of 117 55 of 117 Sensory functions: Gives rise to the palmar cutaneous branch, which innervates the lateral part of the palm, and the digital cutaneous branch, which innervates the lateral threeand a half fingers on the anterior (palmar) surface of thehand. 56 of 117 Anatomical Course The median nerve is derived from the medial and lateral cords ofthe brachial plexus. It contains fibres from all five roots (C5T1). After originating from thebrachial plexus in the axilla, the median nerve descends down the arm, initiallylateral to the brachialartery. Halfway down the arm, thenerve crosses over the brachial artery,and becomes situated medially. The median nerve enters the anterior compartment of the forearm via the cubital fossa. 57 of 117 In the forearm In the forearm, the nervetravels between the flexor digitorum profundus and flexor digitorum superficialis muscles. The median nerve gives rise to two major branches in the forearm: Anterior interosseous nerve – Supplies the deep muscles inthe anterior forearm. Palmar cutaneous nerve – Innervates the skin of thelateral palm. 58 of 117 The median nerve enters the hand via the carpal tunnel, where it terminates by dividing into two branches: Recurrent branch – Innervates the thenar muscles. Palmar digital branch –Innervates the palmar surface and fingertips of the lateral three and half digits. Also innervates the lateral two lumbrical muscles. 59 of 117 60 of 117 Clinical Relevance: Carpal Tunnel Syndrome Compression of the median nerve within the carpal tunnel can cause carpal tunnel syndrome (CTS). It is the most common mononeuropathy and can be caused by thickened ligaments and tendon sheaths. Its aetiology is,however, most often idiopathic. 61 of 117 If left untreated,CTScan cause weakness and atrophy of the thenar muscles. Clinical features include numbness, tingling and painin the distribution of the median nerve. The pain will usually radiateto the forearm. 62 of 117 Symptoms are often associated with waking the patient from their sleep and being worse in the mornings. Tests for CTScan be performed during physical examination: Tapping the nerve in thecarpal tunnel to elicit pain in median nerve distribution (Tinel’s Sign) Holding the wrist in flexion for 60 seconds to elicit numbness/pain in median nerve distribution (Phalen’s manoeuvre) 63 of 117 Treatment involves the useof a splint, holding the wrist in dorsiflexion overnight to relieve symptoms. If this is unsuccessful, corticosteroid injections into the carpal tunnel can beused. In severe case, surgical decompression of the carpal tunnel may be required. 64 of 117 Motor Functions - The Anterior Forearm The median nerve innervates the majority of the muscles in the anterior forearm, and some intrinsic handmuscles. In the forearm, the median nerve directly innervates muscles in the superficial and intermediate layers: 65 of 117 Superficial layer: Pronator teres, flexorcarpi radialis and palmaris longus. Intermediate layer: Flexordigitorum superficialis. The median nerve also gives rise to theanterior interosseous nerve, which supplies the deep flexors. (volar interosseousnerve) 66 of 117 Deep layer: Flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus (the medial half of the muscle is innervated by the ulnar nerve). In general, these muscles perform pronation of the forearm, flexion of the wrist and flexion of the digits of the hand. 67 of 117 Motor Functions - TheHand The median nerve innervates some of the muscles in the hand via two branches. The recurrent branch of the median nerve innervates the thenar muscles – muscles associated with movements of thethumb. The palmar digital branch innervates the lateral two lumbricals – these muscles perform flexion at the metacarpophalangeal joints of the index and middle fingers. The remaining muscles in the anterior forearm and hand are innervated by the ulnar nerve. 68 of 117 69 of 117 70 of 117 Sensory Functions The median nerve is responsible for the cutaneous innervation of part of the hand. This is achieved via two branches: Palmar digital cutaneous branch– Arises in the hand. Innervates the palmar surface and fingertips of the lateral three and half digits. 71 of 117 Palmar cutaneous branch –Arises in the forearm and travels into thehand. It innervates the lateral aspect of the palm. This nerve does not pass through the carpal tunnel, and is spared in carpal tunnel syndrome. 72 of 117 73 of 117 Clinical Relevance: Lesions of the Median Nerve - Damaged at the Elbow How it commonly occurs: Supracondylar fracture ofthe humerus. Motorfunctions: The flexors and pronators in the forearm are paralysed, with the exception of the flexor carpi ulnaris and medial half of flexor digitorum profundus. The forearm constantly supinated, and flexion is weak (often accompanied by adduction, because of the pull of the flexor carpi ulnaris). Flexion at the thumb is also prevented, as both the longus and brevis muscles are paralysed. The lateral two lumbricals are affected, and the patient will not be able to flex at the MCP joints or extend at IP joints of the index and middle fingers. 74 of 117 Sensory functions: Lack of sensation over the areas that the median nerve innervates. Characteristic signs: The thenar eminence is wasted, due to atrophy of the thenarmuscles. If patient tries to make a fist, only the littleand ring fingers can flex completely. This results in a characteristic shape of the hand, known as hand of benediction. 75 of 117 76 of 117 77 of 117 78 of 117 Clinical Relevance: Lesions of the Median Nerve - Damaged at the Wrist How it commonly occurs: Lacerations just proximal to the flexor retinaculum. Motor functions: Thenar muscles paralysed, as are the lateraltwo lumbricals. This affects opposition of the thumb and flexion of the index and middle fingers. Sensory functions: Same as an injury at the elbow. Characteristic signs: Same as an injury at the elbow. 79 of 117 THERADIALNERVE Nerve roots: C5-T1. Sensory: Innervates most of theskin of the posterior side of forearm, and the dorsal surface of the lateral side of the palm, and lateral three and a half digits. Motor: Innervates the tricepsbrachii (extends at the elbow), and the majority of the extensor muscles in the forearm (extends the wrist and fingers and supinates the forearm). 80 of 117 Anatomical Course The radial nerve is a continuation of the posterior cord of the brachial plexus. It thereforecontains fibres from nerve roots C5–T1. The nerve arises in the axilla region, where it is situated posteriorly to the axillary artery. 81 of 117 82 of 117 It exits the axilla inferiorly (via the triangular interval), and supplies branches tothe long and medial heads of the tricepsbrachii. The radial nerve then descends down the arm, travelling in a shallow depression within the surface of the humerus – known as the radial groove. 83 of 117 84 of 117 As it descends, the radial nervewraps around the humerus laterally, and supplies a branch to the medial head of the tricepsbrachii. During much of its course within the upper arm, it is accompanied by the deep branch of the brachialartery. To enter the forearm, the radial nerve moves anteriorly over the lateral epicondyle of the humerus, through the cubital fossa. 85 of 117 The nerve then terminatesby dividing into two branches: Deep branch (motor) – innervates most of themuscles in the posterior compartment of the forearm. Superficial branch (sensory) – contributes to the cutaneous innervation of the hand and fingers. 86 of 117 87 of 117 Motor Functions The radial nerve innervates the muscles located in the posterior upper arm and posterior forearm. In the upper arm, it innervates the three heads of the triceps brachii – which acts to extend the arm at the elbow. The radial nerve also gives rise to branches that supply the brachioradialis and extensor carpi radialis longus (muscles of the posterior forearm). Aterminal branch of the radial nerve, the deep branch, innervates the remaining muscles of the posteriorforearm. As a generalisation, these muscles act to extend at the wrist and finger joints, and supinate the forearm. 88 of 117 When the deep branch of the radial nerve penetrates the supinator muscle of the forearm, it is termed the posterior interosseousnerve for the remainder of its course. 89 of 117 Sensory Functions 90 of 117 There are four branches of the radial nerve that provide cutaneous innervation tothe skin of the upperlimb. Three of these branches arise in theupper arm: Lower lateral cutaneous nerve of arm – Innervates the lateral aspect of the upper arm, below the deltoid muscle. Posterior cutaneous nerve of arm –Innervates the posterior surface of the upper arm. Posterior cutaneous nerve of forearm – Innervates a strip of skin down the middle of the posterior forearm. 91 of 117 The fourth branch – the superficial branch – is a terminal division of theradial nerve. It innervates the dorsal surface of the lateralthree and half digits, and their associated palm area. 92 of 117 93 of 117 Clinical Relevance: Injury to the RadialNerve Injury to theradial nerve can be broadly categorised into four groups – depending on where the damage has occurred (and thus which components of the nerve have been affected). 94 of 117 95 of 117 In the Axilla The radial nerve can be damaged in the axilla region by a dislocation at the shoulder joint,or a fracture of the proximalhumerus. Occasionally, it is injured via excessivepressure on the nerve withinthe axilla (e.g. a badly fitting crutch). Motor functions – the triceps brachiiand muscles in posterior compartment are affected. The patient is unable to extend at the forearm, wrist and fingers. Unopposed flexion of wrist occurs, knownas wrist-drop. 96 of 117 In the Axilla Sensory functions – all four cutaneous branches of theradial nerve are affected. There will be a loss of sensation over the lateral and posterior upper arm, posterior forearm, and dorsal surface of thelateral three and a half digits. 97 of 117 In the RadialGroove The radial nerve is tightly bound withinthe spiral groove of the humerus. Thus, it is most susceptible to damage with a fracture of thehumeral shaft. Motor functions The triceps brachii may be weakened, but is not paralysed (branches to the long and lateral heads of the triceps arise proximal to the radial groove). Muscles of the posterior forearm are affected. The patient is unable to extend at the wrist and fingers. Unopposed flexion of wrist occurs, known as wrist-drop. 98 of 117 In the RadialGroove Sensory functions – the cutaneous branches to the arm and forearm have already arisen. The superficial branch of theradial nerve will be damaged, resultingin sensory loss on the dorsal surface of the lateral three and half digits, and their associated palmarea. 99 of 117 In the Forearm There are two terminal branches of the radial nerve located within the forearm: 100 of 117 THEULNARNERVE Spinal roots: C8-T1. Motor functions: Innervates the muscles of the hand (apart fromthe thenar muscles and two lateral lumbricals), flexor carpi ulnaris and medial half of flexor digitorum profundus. Sensory functions: Innervates the anterior and posterior surfaces ofthe medial one and half fingers, and the associated palm area. 101 of 117 102 of 117 Anatomical Course The ulnar nerve is derivedfrom the brachial plexus. It is a continuation of the medial cord, containing fibres from spinal roots C8andT1. After arising from the brachial plexus, the ulnar nerve descends down the medialside of the upperarm. 103 of 117 At the elbow, it passes posterior to the medial epicondyle of the humerus, entering the forearm. At the medial epicondyle,the nerve is easily palpable and vulnerable to injury. In the forearm, the ulnar nerve pierces the two heads of the flexor carpi ulnaris, and travels alongside the ulna. 104 of 117 Three branches arise in the forearm: Muscular branch: innervates some muscles in the anterior compartment of the forearm. Palmar cutaneous branch: innervates the skin of themedial half of the palm. Dorsal cutaneous branch: innervates the skin of the medial 1 and 1/2 fingers, and the associated palm area. 105 of 117 At the wrist, the ulnar nerve travels superficially to theflexor retinaculum. It enters the hand via the ulnar canal (or Guyon’s canal). In the hand the nerve terminates by giving rise to superficial and deep branches. 106 of 117 Motor Functions - The Anterior Forearm In the anterior forearm, the muscular branch of the ulnar nerve supplies two muscles: Flexor carpi ulnaris – Flexes and adducts the hand at thewrist. Flexor digitorum profundus (medial half) – Flexes thefingers. The remaining muscles in the anterior forearm are innervated by the median nerve. 107 of 117 Motor Functions - TheHand The majority of the intrinsic hand muscles are innervated by the deep branch of the ulnar nerve. The hypothenar muscles (a group of muscles associated with the little finger) are innervated by the ulnar nerve. It also innervates some other muscles of the hand: Medial two lumbricals Adductor pollicis Interossei of the hand Palmaris brevis The other muscles in the hand (such as thethenar eminence) are innervated by the mediannerve. 108 of 117 109 of 117 Sensory Functions There are three branches of the ulnar nerve that are responsible for its cutaneous innervation. Two of these branches arise in the forearm, and travel into the hand: Palmar cutaneous branch: Innervates the skin of the medial half of the palm. Dorsal cutaneous branch: Innervates the skin of the medial one and a half fingers, and the associated dorsal handarea. The last branch arises in the handitself: Superficial branch – Innervates the palmar surface of the medial one and a half fingers. 110 of 117 111 of 117 Clinical Relevance: Lesions of the Ulnar Nerve – Damaged at the Elbow The ulnar nerve is most susceptible to injury at the elbow and the wrist. How it commonly occurs: The nerve is most vulnerable to injury at the medial epicondyle, but it can also be compressed in the cubital tunnel. This is known as cubital tunnel syndrome. 112 of 117 Clinical Relevance: Lesions of the Ulnar Nerve – Damaged at the Elbow Motor functions: Flexorcarpi ulnaris and medial half of flexor digitorum profundus paralysed. Flexion of the wrist can still occur, but is accompaniedby abduction. The interossei are paralysed, so abduction and adduction of the fingers cannot occur. 113 of 117 Movement of the little and ring fingers is greatly reduced, dueto paralysis of the medial two lumbricals. Sensory functions: All sensory branches are affected, sothere will be a loss of sensation over the areas that the ulnar nerve innervates. Characteristic signs: Patient cannot grip paper placed between fingers 114 of 117 Damaged at the Wrist How it commonly occurs: Lacerations to the wrist Motor functions: The interosseiare paralysed, so abduction and adduction of the fingers cannot occur. Movement of the little and ring fingers is greatly reduced, due to paralysis of the medial two lumbricals. The two muscles in theforearm are unaffected Sensory functions: The palmar branch and superficial branch are usually severed,but the dorsal branch isunaffected. Sensory loss over palmar side of medial one and a half fingers only. 115 of 117 Characteristic signs: Patient cannot grip paper placedbetween fingers. For long-term cases, a hand deformity called ‘Ulnar Claw’develops. Ulnar claw consists of: Hyper-extension of the metacarpophalangeal joints of the little and ring fingers – this is because of the paralysis of the medial two lumbricals, and the now unopposed action of the extensor muscles Flexion at the interphalangeal joints (if the lesion has occurred close to the elbow, this might not be evident, as the flexor digitorum profundus will beparalysed) 116 of 117 117 of 117