Radial Nerve Anatomy and Function

• Class notes from 2025-03-07.

Radial Nerve

• Originates from the posterior cord of the brachial plexus (C5-T1).
• Travels through the triangular interval/triceps hiatus, bordered by teres major, the long head of triceps, and the humerus.
• Follows the medial head of the triceps, moving through the posterior axilla along the spinal groove of the humerus.
• Runs anteriorly between the brachialis and brachioradialis muscles.
• Located beneath the ECRL & ECRB.
• Crosses the elbow laterally to the olecranon process.
• It divides into a posterior motor branch and a superficial sensory branch.

Radial Nerve Motor Function

• Innervates the Triceps, Anconeus, Brachioradialis, ECRL, ECRB, Extensor digitorum, Extensor carpi ulnaris, Extensor digiti minimi, Abductor pollicis, and Extensor indicis.

Radial Nerve Sensory Function

• Provides sensation to the dorsum of digits 1-3, not including the fingertips.
• The focus of study is on the motor and superficial sensory branches in the forearm.

Causes of Radial Nerve Lesions

• Humerus fractures, especially at the spiral groove, can cause lesions.
• Radius fractures, mainly in the proximal 1/3, can lead to "radial nerve palsy".
• Elbow dislocations can cause lesions.
• Compression at the Arcade of Frohse or Radial Tunnel, involving the supinator muscle.
• Prolonged pressure on the arm during surgery.
• Crutch Palsy, Saturday Night Palsy, or Honeymoon Palsy due to prolonged compression of the radial nerve at the axilla, potentially leading to neuropraxia, axonotmesis, or Wallerian degeneration.

Signs and Symptoms of Radial Nerve Lesions

• Altered sensation in the radial nerve distribution.
• Complete lesions result in wrist drop.
• Lesions proximal to the elbow affect both sensory and motor branches.
• Distal to the elbow, lesions usually affect either sensory OR motor function, not both.
• Muscle wasting and swelling on the dorsum of the hand.
• Aesthesia in the webbing between digits 1 & 2.

Radial Nerve Palsy

• Commonly caused by humerus fractures.
• Results in weakness or paralysis of wrist/finger extensors and forearm supinators (wrist drop).
• May cause weakness in triceps depending on the injury location.
• Parasthesia in the dorsum of the hand, lateral 3.5 digits, and lateral forearm.

Saturday Night/Crutch/Honeymoon Palsy

• Due to prolonged compression at the posterior axilla or spiral groove.
• Can occur in intoxicated individuals passing out with their arm over a chair or surface, falling asleep with someone on your arm, or incorrect crutch use.
• Depending on the duration of compression, it can be a neuropraxia or axonotmesis.
• Results in wrist drop.
• Potential weakness to the triceps.
• Parasthesia in the dorsum of the hand, lateral 3.5 digits, and lateral forearm.

Posterior Interosseus Nerve (PIN) Syndrome

• Also known as Supinator or Radial Tunnel Syndrome.
• Distal to the elbow, the radial nerve splits into the superficial radial nerve (sensory) and the posterior interosseus nerve (motor).
• The posterior interosseous nerve travels through the Arcade of Frohse in the Supinator, a possible compression site.
• After the Arcade of Frohse, the PIN runs through the Radial Tunnel, where the Supinator, Brachioradialis, ECRL, and ECRB are located.
• Compression can occur from repetitive use of these muscles.
• Causes pain distal to the lateral condyle.
• Weakness/paralysis of wrist and finger extensors.
• Symptoms worsen with elbow extension and pronation.
• No sensory deficits.

Superficial Radial Nerve Syndrome

• Also known as Wartenberg's Syndrome or Cheiralgia Paraesthetica.
• Involves compression of the sensory branch which occurs at the brachioradialis.
• Risk factors include Trauma, Direct pressure on the nerve from watches, handcuffs, or Hypertoned/overused muscles like the Brachioradialis and ECRL.
• causes Pain over the distal radial forearm and Paresthesia in the dorsal hand.
• No motor deficits.

Radial Nerve Lesion DDx

• Differential diagnoses include Radiculopathy, Brachial plexus injuries, and other compression sites along the radial path.
• If pain is present, consider Lateral epicondylitis and DeQuarvain's syndrome.

Radial Nerve Lesion Assessments: History

• Includes Location(s) of symptoms, Onset, and Nature of symptoms being Intermittent/chronic/episodic.
• Quality of symptoms include Pain/NWT/coordination, Skin changes and Temperature changes.

Radial Nerve Lesion Assessments: Obvs/Palp/Mvmt

• Includes Postural scan for waiters tip, palpate for tenderness, HT mm, fascial restrictions
• Temperature changes/edema
• Shoulder/elbow/wrist ROM
• MMTs for mm weakness or imbalances such as wrist extensors, finger extensors or ABD pollicis

Assessments & Special Tests

• DTRs of the Triceps and brachioradialis.
• Sensory testing on the back of hand and digits 1, 2, 3, ½ 4.
• ULTT 3.
• TOS tests, Finkelsteins and Lateral epicondylitis tests

Ulnar Nerve

• Originates from the medial cord of the brachial plexus (C8 – T1).
• Runs from the axilla to the medial humerus.
• Passes posterior to the medial epicondyle.
• Runs through the forearm between FCU & FDP.
• Beneath ECRL & ECRB.
• Over the flexor retinaculum between pisiform and hook of hamate.
• Passes through Guyon's Canal/Unal Tunnel.
• Ends through palm to digits 1, 4 and 5

Ulnar Nerve Motor Function

• Innervates the Flexor carpi ulnaris, Flexor digitorum profundus, Abductor, flexor, opponens digiti minimi, 3rd and 4th lumbricals, Palmar and dorsal interossei, Adductor pollicis and Flexor pollicis brevis

Ulnar Nerve Sensory Function

• Provides sensation to Digits 5 and ½ of 4 and the Ulnar aspect of palm

Ulnar Nerve Lesion

• Results in Claw Hand with Passive hand position in 5th MCP/IP and 4th MCP/IP.
• Resuls in Benediction Hand with loss of lumbrical function and digits 4 & 5 IPs & DIPs flex unopposed.
• A complete lesion results in Claw hand, Loss of thumb ADD, Muscle wasting in hypothenar and interosseous spaces and Anhydrosis and vasomotor changes.

Causes of Ulnar Nerve Lesion

• Fractures to the Medial epicondyle, forearm or wrist (Colles').
• Elbow dislocation.
• Prolonged compression or Repetitive use.
• Trauma such as contusion or laceration.
• The nerve is most vulnerable at the elbow & wrist.

Ulnar Nerve Lesion Signs & Symptoms

• Complete lesion will result in claw hand
• 5th digit MCP EXT, ABD; IP FLX
• 4th digit MCP EXT; IP FLX
• Loss of thumb adduction.
• Muscle wasting in hypothenar eminence & interosseous spaces.
• Anhidrosis, vasomotor changes possible.
• Altered sensation in 5th & ½ of 4th digits & palm and Anesthesia in 5th digit.

Classic Deformities from Ulnar Nerve Lesions

• Bishop's hand aka Benediction hand – resting due to Loss of ulnar lumbricals leads to digits 4 & 5 resting in a position opposite to the lumbricals action.
• Claw hand – resting like bishop's hand but with abduction of digits 4 & 5.
• Froment's sign - Active, involves Loss of adductor pollicis leading to compensatory recruitment of flexor pollicis longus

Conditions related to Ulnar Nerve Lesions

• Tardy Ulnar Palsy can arise years after fracture due to Callus formation or Valgus deformity of elbow and Gradually stretches the nerve in the ulnar groove of the medial epicondyle.

Cubital Tunnel Syndrome

• Occurs with the Passage between heads of FCU and FDP
• Elbow flexion flattens the tunnel, putting pressure on the nerve and its compression is provoked with sustained elbow flexion.

Ulnar Tunnel/Guyon's Tunnel Syndrome

• Due to pressure on the hypothenar eminence from Cycling, Jack hammers or other heavy tools, or Keyboard use.
• Can be caused by Trauma/swelling, Carpal fractures or Arthritis.
• It is formed by the Pisiform, Hook of hamate, Volar carpal ligament and Transverse carpal ligament.
• Contains the Ulnar nerve and Ulnar artery.

Ulnar Nerve Lesion DDx

• Differential diagnoses include Radiculopathy, Brachial plexus injuries, and TOS.
• Consideration for Triangular Fibrocartilage Complex (TFCC) injuries
• Ulnar collateral ligament (wrist) sprain and UCL (elbow) sprain.
• Consideration for Elbow/wrist mm strains/tendinopathies

Ulnar Nerve Lesion Assessments: History

• Location(s) of symptoms, Onset, Nature of symptoms being Intermittent/chronic episodic Related patterns relating to Work, sleep, hobbies and exercise.
• Quality of symptoms such as Pain/NWT/coordination, Skin changes and Temp changes.

Ulna Nerve Lesion Assessments: Obvs/Palp/Mvmt

• Postural Scan for claw hand.
• Palpate for tenderness, HT mm, and fascial restrictions and for temperature changes, edema, and sweating.
• Elbow/wrist/finger/thumb ROM assessments.
• MMTs for weakness or imbalances in the FCU, FDP, Hypothenar group, Interossei, Adductor pollicis and flexor pollicis brevis

Ulnar Nerve Special Assessments and Tests

• Tinel's Test to determine amount of regeneration, tapping the nerve will elicit tingling.
• Test Ulnar nerve at medial epicondyle to tests how far the regeneration has gone by testing how far the zinging goes down their arm
• Froment's sign that involves the patient grasp paper between 1st and 2nd digit while the examiner tries to pull paper. A positive result means the patient will flex their IP to recruit flexors to maintain grasp because of weakness in ADD pollicis.
• Sensory testing for Ulnar distribution.
• ULTT 4

Regenerating Nerve Treatment Goals

• Reduce fascial restrictions, manage edema reduce TrPs and reduce HT in Proximal to lesion or compensatory mm.

Treatment Modalities for Regenerating Nerves

• Segmental strokes proximal to lesion, perpendicular to the nerve.
• Blocking/stabilization proximal to the nerve to prevent tissue drag.
• PROM that slacken/don't bias the affected nerve.
• Stretching – passive/PNF/pin and stretch

Treatment Considerations & Homecare

• Positioning in a neutral position using pillows, avoid tractioning a regenerating nerve and do not stretch deservated tissue/muscles.
• Splint/brace as well as multiple stimulus sensory re-education.
• Mild hydro is CI'd if autonomic nerve symptoms.
• Neural mobilizations and ADL modifications with Canes or hand/crutches.
• Homecare should be based on compression site/symptoms