Nerves Part 1: 

Upper Extremity Compression Syndromes: 
Nerve Anatomy:

• Pacinian corpuscles: detect vibration in subcutaneous tissue, myelinated A-beta fibers
• C fibers: burning pain
• A-delta fibers: sharp pain
• Meissner’s corpuscles: intermediate dermal ridge–> moving two point discrimination a beta
• Merkel cell: static two point discrimination (sweat ducts) interdermal ridge a beta

Nerve Injury:

• Grade of Injury: Sunderland Classification 
• I – neuropraxia that is characterized by segmental demyelination 
• II, III, IV – axonotmesis with complete then variable recovery 
• V – complete transection neuronotmesis no recovery 
• VI – segmental nerve injury

• Studies: 
• EMG findings occur after 3 weeks

• Nerve Repair: 
• Primary repair: clean lacerations less than 1cm gap 
• Conduit: use to reinforce primary repair, or if unable to perform primary repair 1-3cm 
• Allograft: if the gap if 3-7cm (although we do still get tested on 3cm as the cut off as the upper limit of a allograft) 
• Autograft if the gap if >7 cm 

**Age is the best predictor of outcomes for nerve repair

• Nerve injuries and open wounds: 
• Sharp Injury: If it is a clean wound and a sharp injury repair immediately 
• Crush Injury or GSW: 
• Explore the nerve at the time of the injury if it appears intact then assume all neuropathy postoperatively to be neuropraxia. 

Compression Neuropathy is nerve entrapment- disproportion between volume of nerve and space through which it passes

• Pathophysiology: 
• elevated extraneural pressure inhibits intraneural microvascular blood flow which leads to decreased axonal transport and endoneurial edema. This eventually leads to demyelination, distal axon degeneration, and nerve fibrosis
• Overall, the degree of axonal injury is proportional to duration and magnitude to compression

• Compression Pressure: 
• 30mmHg- paresthesias
• 50-60mmHg- complete motorsensory block
• Local nerve ischemia prevents depolarization (-90 is resting)

• Diagnosis: 
• Diagnosis of upper extremity nerve compressions is often clinical however, electrodiagnostic testing is confirmatory. 
• Two Types of electrodiagnostic testing:
• Nerve conduction study: This measures the strength and velocity of a signal traveling through a nerve. 
• Electromyography: measures the response of the muscles to the nerve input 

ANATOMY REVIEW: 
When discussing compression neuropathy of the upper extremity we do need to review the anatomy of the three major nerve of the forearm: 

• Median Nerve 
• Ulnar Nerve 
• Radial Nerve 

Median Nerve Anatomy: 

• Upper Arm: The median nerve arises from the lateral and medial cords of the brachial plexus. It then passes down the medial part of the upper arm with the brachial artery between the biceps muscles and brachialis 
• Forearm: It passes into the forearm with the brachial artery under the lacertus fibrosis at the AC fossa. It then separates from the artery and passes between the two heads of the pronator teres. 
• Distally: Travels between the FDS above and FDP below. About 5cm proximal to the TCL it becomes more superficial and basses between the FDS medially and the FCR laterally and then travels under the palmaris longus and into the carpal tunnel. 
• Branches of the median nerve:
• AIN: branches proximally and travels within the interosseous membrane between the ulna and radius. This provides motor branches to the FDP of the index and little fingers, FPL, and the pronator quadratus. The most distal branches of the AIN provide sensory innervation to the wrist capsule.  
• Palmar Cutaneous Branch: provides sensation to the thenar eminence and branches about 5cm proximal to the carpal tunnel
• Median Recurrent Motor Branch: this innervates the thenar muscles including APB, opponens pollicis and the superficial belly of the FPB. This nerve typically branches distal to the tranverse carpal ligament but does have a variable anatomy and can branch earlier or through the TCL. 

• One way to remember the innervation of the median recurrent motor branch is FOAL : innervated by recurrent median nerve: FPB (one head), opponens pollicis, abductor pollicis brevis, lateral two lumbricals

Median Nerve Compression Syndromes: 

• Carpal Tunnel Syndrome:  most common compressive neuropathy 

• Anatomy of the carpal tunnel: 
• Nine tendons (FPL, 4 FDS, and 4 FDP) and the median nerve all pass through the carpal tunnel 
• Roof is TCL, floor is radiocarpal ligaments, borders include scaphoid and trapezium radially, triquetrum and hamate ulnarly

• History: patients presenting with carpal tunnel complain of intermittent to constant paresthesia in median distribution (particularly at night), pain frequent (may radiate proximally), decreased dexterity, weakness/atrophy late
• Associated: DM, HT, pregnancy, renal disease, inflammatory arthritis, trauma, masses, amyloidosis
• Staging: Early (mild): intermittent paresthesias, pain, night symptoms; Intermediate (moderate): more frequent paresthesias, worse with use, numbness, clumsiness; Advanced (severe): constantly impaired sensibility, severe pain, thenar atrophy, pinch opposition weakness
• Physical Exam: 
• Sensibility: sever nerve- 2 point, compression- semmes weinstein (more sensitive and specific- 85-90%)
• Provocative tests: 
• Durkans: compression at the carpal tunnel leading to symptoms is the most sensitive and specific 
• Phalens: wrist flexion leading to symptoms 
• Tinel’s: tapping on the nerve distal to proximal leading to symptoms 
• Other diagnostics: 
• EMG/NCS: Abnormal nerve latency >4ms
• Diagnostic Ultrasound: look at transverse images (look at area of median nerve in carpal tunnel and median nerve proximal) and takes a ratio of the two. If the nerve is enlarged at the carpal tunnel it suggests compression at that location

• Treatment: 
• Nonoperative: night splints (wrist neutral), steroid injections
• Steroid Injection: When injecting you aim to inject slightly ulnar to the median nerve. 40-80% of patients get relief – however the relief is variable and lasts from only days in some patients to months in others. CSI injection in these patients is not a long term treatment but generally used as a temporizing measure until surgery or as a diagnostic tool. If the patient gets relief from a CSI injection into the carpal tunnel in general they will see similar relief from a carpal tunnel release. 
• Surgery: 
• Technique:  Open TCL (on the ulnar side)
• Endoscopic CTR (rehabs faster)
• Open technique for carpal tunnel has decreased recurrent median nerve injury
• Postoperative Care: 
• Splints and rehab are not necessary unless the patient has thenar muscle weakness 
• Abx are not indicated pre or postoperatively unless the patient has DM or is immunocompromised 
• Complications: incomplete release, damage to palmar cutaneous branch, hypertrophic painful scar, bowstringing of tendons, and CRPS 
• Revision carpal tunnel release
• This refers to two distinct patients populations: (1) those who had an incomplete release and have persistent symptoms (2) those who had relief initially but have developed recurrent symptoms. 
• In the 1^st group – release generally have the same efficacy as a complete initial release
• In the 2^nd group – they generally re-developed symptoms of carpal tunnel due to scarring of one of the leaflets of the TCL to the median nerve. Adjunctive procedures such as hypothenar fat pad flap, radial forearm fascial flap, radial artery perforator based flap have been use to prevent scarring 
• Acute CTS: This is slightly different than chronic CTS. This can occur after fracture or due to pyogenic infection. This requires urgent release of the carpal tunnel to prevent long term damage to the nerve. In this situation a  delay of 36 hours of release may result in poor prognosis

• AIN: Anterior interosseous nerve compression
• Anatomy: The AIN is mainly a motor neve that divides from the median nerve 4-6cm distal to the elbow and passes between the two heads of the PT and then in the interosseous membrane. It gives off branches that innervate the FDP of the index and long, the FPL and the PQ. 
• Sites of compression: There are several places that the median nerve can be compressed along its couse. Most commonly it gets compressed at the deep head PT, the edge of lacertus fibrosis, or the FDS arcade. Other areas of compression include enlarged bicipital tendon bursa, accessory head of FPL (Gantzer’s muscle), aberrant radial artery, thrombosed ulnar artery
• Symptoms of compression of the AIN: motor loss without sensory involvement, inability to perform OK sign due to loss of FPL. 
• Surgery: lacertus fibrosis release, PT release, FDP fibrous arch release

• Prontator Syndrome: 
• Anatomy: compression of the median nerve (not just the AIN) 
• Sites of compression: lacertus fibrosis, pronator teres, arch of the FDS, entrapment beneath the ligament of Struthers between the supracondylar process of the distal humerus and the fascia of the pronator teres 
• Presentation: pain proximal forearm +/- weakness, paresthesias in median nerve distribution (including thenar eminence)
• Physical exam: Tinels over the pronator teres. Motor weakness in the distribution of the median nerve. Diminished sensation over the thenar eminence. This is differentiated from carpal tunnel due to numbness in the palm from involvement proximal to the palmar cutaneous branch. Also in stems these can be differentiated by carpal tunnel without + provocative tests. 
• Diagnosis: generally clinical given that EMG/NCV: usually normal
• Treatment: 
• Non-operative: splinting, activity modification
• Surgery: 90% successful –> release ligament of struthers, supracondylar process of humerus, lacertus fibrosis, fascia of superficial head of pronator arch of proximal FDS

Ulnar Nerve Anatomy: 

• Upper arm: terminal branch of the medial cord. In the upper arm, the ulnar nerve runs ulnar and volar to the ulnar artery. 
• Elbow: the ulnar nerve is covered by the arcade of struthers 8cm proximal to the medial epicondyle. The nerve passes through the cubital tunnel and is then covered by the FCU tendon 
• Forearm: The ulnar nerve lies on the top of the FDP. The FDS lies on top of the nerve 
• Wrist: the nerve tracks radial to the FCU tendon and ulnar to the hook of the hamate to enter Guyon’s canal. 

• Branches of the Ulnar Nerve 

• Before the wrist 
• Motor branches innervate the FDS of the ring and small and FCU 
• Dorsal cutaneous nerve which gives off sensation to the dorsoulnar hand is 5-7cm proximal to the ulnar styloid 
• Palmar cutaneous branch gives sensation to the palmar ulnar hand and comes off proximal to the wrist 
• After the wrist 
• Deep motor branch – this innervates the hypothenar muscles, adductor muscles, intrinsics and thenar (deep head of the FPB) 
• Superficial sensory nerve gives sensation to the common and proper digital nerve for the ulnar digits 

Ulnar Nerve Compression: 

• Cubital Tunnel Syndrome: 
• Anatomy/Potential Sites of Compression: arcade of struthers, medial intermuscular septum, medial epicondyle, cubital tunnel (osbornes ligament or the fibrous band between the two heads of the FCU), triceps, aconenous epitrochlearis (anomalous muscle)
• Presentation: 
• Early: intermittent paresthesia in the ulnar 2 digits, extrinsic/intrinsic motor weakness (FDP to ring and small)
• Late symptoms include:: Froment’s sign – inability to activate  adductor pollicis leading to weakness in pinch.  Wartenburg sign – clawing of the hand.  
• Cubital tunnel should have some sensory loss on dorsum of hand (differentiate from Guyon’s Canal Compression 

• Physical exam: 
• Provocative Testing: 
• Tinel’s at the elbow 
• Elbow flexion test 
• Other Physical Exam Findings: atrophy and decreased motor strength
• Treatment: 
• Nonoperative: elbow splint (45 extension) and ulnar nerve glides 
• Operative: in situ decompression, anterior transposition (subcutaneous, submuscular, intramuscular), medial epicondylectomy (none are superior to the other)
• In situ decompression: safe and simple (release the sites of compression only, do not change its position), do not perform if nerve subluxates
• Transposition: severe ulnar neuropathy, failure of in situ, throwing athlete, angular deformities, subluxation of the nerve ** must remove some medial intramuscular septum if you transpose
• Complications: elbow flexion contracture, medial epicondylitis, neuroma of the (MABCN), elbow instability, persistent m/s deficits, failed decompression
• MABC can be injured during ulnar nerve neuroplasty, best identified and corrected by excision of neuroma and nerve stump implantation

• Ulnar Tunnel Syndrome (Guyon’s canal): 
• Presentation: numbness/paresthesias in palmar aspect ring and small (NOT DORSAL- dorsal hand divides proximal to wrist crease); weakness/atrophy (ulnar intrinsics)
• Areas of compression: as the ulnar nerve passes through Guyons canal it can be compressed in three places leading to specific presenting symptoms
• 1: proximal to the ulnar nerve bifurcation – usually both sensory and motor 
• 2: at the ulnar nerve deep motor branch as it passes the hook of the hamate – usually an isolated motor finding. Normally due to a ganglion cyst. 
• 3: proximal to the bifurcation of the ulnar nerve – normally sensory only for ulnar artery thrombosis 
• Causes of compression: palmaris brevis, fibrous origin of FDM, ulnar artery aneurysm or thrombosis, hook of hamate fracture, ganglion cyst (most common)
• Evaluation: Xrays with carpal tunnel view to evaluate the hook of the hamate, CT/MRI, EMG/NCV 
• Treatment: 
• Conservative including splinting if it is due to repetitive trauma without a mass or other cause of compression seen 
• Surgery: refractory or identifiable cause

Radial Nerve Anatomy 

• Upper Arm: terminal branch of the posterior cord. It runs posterior to the brachial artery and anterior to the triceps. It transects the lateral intramuscular septum with the radial collateral artery about 10cm proximal to the distal humerus. It then run between the brachialis and the brachioradialis 
• Forearm: the nerve then divides into superficial and deep branches (PIN and SBRN). 
• PIN: The PIN passes under the arcade of Froshe, splitting the supinator muscle and then travels within the 4^th extensor compartment to innervates the extensors including ECU, EDM, EDC, EIP (most distal), and the EPL, EBP and APL terminates under fourth extensor compartment to innervate wrist capsule
• SBRN: between brachioradialis and ECRL. In the midforearm it runs below the brachioradialis and then becomes subcutaneous 8-9cm proximal to the radial styloid.  It provides sensation to dorsal radial aspect of hand 

Radial Nerve Compression: 

• Radial Tunnel Syndrome: 
• Presentation: pain during movement of the elbow radiating distally along with weakness of grip due to repetitive elbow extension and rotation 
• Points of Compression:  fibrous bands, vascular leash, ECRB, proximal supinator, distal supinator, arcade of Frohse (pin entrapment)
• Diagnosis: 
• Physical exam: pain over ECRB during forced extension of the middle finger while the elbow is in extension 
• Radial nerve block is diagnostic 
• EMG is not typically helpful
• Treatment: 
• Conservative management: NSAID, resting splint, activity modification 
• Surgical: release only provides relief in 50% of cases 

• PIN Syndrome: 
• Presentation: weakness (and some pain) during finger and wrist extension without sensory loss 
• Differential diagnosis: includes RA tendon ruptures
• Area of compression: entrapment of elbow, masses (ganglion, lipoma, bursa), radial head dislocation, traction neuropraxia like from a tourniquet on the forearm 
• Diagnosis: 
• Xray to r/o radial head dislocation
• EMG 
• U/S to evaluate for a soft tissue mass compressing the nerve 
• Treatment: 
• Conservative 8-12 weeks –> activity modification, splint, steroid
• Surgery: address the areas of potential compression including the radiocapitellar joint, Leash of Henry (radial recurrent vessel bundle), ECRB lateral edge, Arcade of Froshe (anterior edge of the supinator muscle) 

• Wartenberg Syndrome: 
• Presentation: pain and numbness at the dorsal radial aspect of the distal forearm and hand
• Cause: SBRN entrapment at the point of exit from the brachioradialis fascia. This can be due to external compression or compression from BR/ECRL with pronation of forearm
• Diagnosis: Provocative Tests: tinel’s over nerve, pain with pronation
• Treatment: 
• conservative management –> modification, no jewelry, steroid injection
• Surgery: 80-85% successful, release deep fascia around nerve +/- Dequervain’s release

Miscellaneous: 
CRPS

• Reflex sympathetic dystrophy or complex regional pain syndrome: progressive complex pain syndrome –> swelling stiffness and discoloration of hand (vasomotor instability of sympathetic nervous system), hyperhidrosis, osteoporosis, trophic changes may occur (acute subacute chronic); can occur as soon as 10 days with burning pain
• Diagnosis is helpful with bone scan: type I has no etiology, two has neural causality
• Ascorbic acid or vitamin C has been used prophylactically to treat CRPS
• Stellate ganglion blocks reduce sympathetic tone
• C sensory fibers are responsible fibers in CRPS