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

• Pathophysiology: Elevated extraneural pressure inhibits intraneural microvascular blood flow –> which decreases axonal transport –> causing endoneurial edema –> and eventual demyelination, distal axon degeneration –> and fibrosis
• Degree of axonal injury proportional to duration and magnitude to compression
• It can be acute or chronic. Symptoms and damage depend on amount and duration of increased pressure.
• At 30mmHg patients will experience paresthesias, and at 50-60mmHg they will experience complete motorsensory block
• Diagnosis:
• Nerve conduction study –> will pick up on the segmental demyelination –> by exhibiting slowed nerve conduction
• Electromyography is the primary study for detecting axonal loss
• Compression neuropathies are associated with multiple other comorbidities including diabetes, Hypothyroidism, Obesity, and Menopause

Specific Nerves – we’ll talk about the three main nerves in the arm, their anatomic course, and locations of compression for each.

• Median Nerve
• Anatomy:
• accompanies brachial artery through arm –> lies medial to brachial artery at the elbow where it dives between the two heads of the pronator teres –> continues down to under the flexor retinaculum of the hand (remember TAN- tendon-artery nerve)
• Branches of the median nerve all distal to the elbow and include the AIN (a motor nerve which comes off around 4-6cm distal to the elbow), the palmar cutaneous branch (which originates 5cm proximal to the wrist crease), and the thenar motor branch (which runs radially to the thenar muscles, and can go over, under, or through the transverse carpal ligament)
• Compressive locations:
• Prontator Syndrome: compression of the median nerve at or above the elbow beneath the ligament of struthers, lacertus fibrosis, pronator muscle, or fibrous arch of FDS
• Presents with pain proximal forearm +/- weakness, paresthesias in median nerve distribution (including thenar eminence)
• Physical exam: tinels, motor weakness, diminished sensibility
• EMG/NCV: usually normal
• Treatment: splinting, activity modification, surgery: Surgery is 90% successful if you release the compressive tunnel
• Anterior interosseous nerve syndrome: compression of the median nerve at or distal to the elbow via the two heads of the pronator teres, the edge of lacertus fibrosis, biceps tendon bursa, FDS arcade, accessory head of FPL, aberrant radial artery, or thrombosed ulnar artery.
• Innervates FDP index and long, FPL, PQ hard to test but can present with motor loss without sensory involvement.
• Presentation: can be complete vs incomplete and may be associated with brachial plexitis, but generally has unilateral spontaneous onset of pain or weakness in proximal forearm, inability to actively flex thumb IP and index long DIP, weakness in forearm pronation
• EMG/NCS can be helpful to localizes lesions and rule out other diagnosis
• Treatment: depends on etiology –> traction (observe), traumatic –> explore
• Wait 6-12 months prior to intervention
• Surgery:lacertus fibrosis release, PT release, FDP fibrous arch release
• Moving distally into the arm, the carpal tunnel contents include median nerve and 9 flexor tendons. Sometimes we get asked about the borders of the carpal tunnel. The roof is TCL, floor is radiocarpal ligaments, and borders include scaphoid and trapezium radially, triquetrum and hamate ulnarly
• Carpal Tunnel Syndrome is the most common compressive neuropathy affecting up to 10% population. It is often associated with diabetes, hypothyroidism, pregnancy, renal disease, arthritis or other inflammatory conditions
• Usually presents with intermittent to constant paresthesia in median distribution (particularly at night), pain which may radiate proximally, decreased dexterity, and weakness/atrophy later on
• Staging:
• Early (mild) carpal tunnel is characterized by intermittent paresthesias, pain, night symptoms
• Intermediate (moderate) carpal tunnel is characterized by more frequentparesthesias, worse with use, numbness, clumsiness
• Advanced (severe) carpal tunnel is characterized by constantly impaired sensibility, severe pain, thenar atrophy, pinch opposition weakness
• Acute CTS is different than chronic nerve compression because the onset is sudden often after fracture, spontaneous hemorrhage, thrombosis of persistent median artery, or pyogenic infection –> delay of 36 hours of release may result in poor prognosis
• Physical Exam will show thenar atrophy, test APB, pinch strength, decreased 2 pointsensation
• Durkans (manual compression of the canal) is the most sensitive and specific by assessing symptoms after compression at carpal tunnel
• Phalens (pressing the back of the hands together)
• Tinel’s (wrist flexion and tapping on nerve from distal to proximal)
• EMG will show distal latencies and slowed velocity, fibrillations, positive sharp waves, and decreased amplitude, but you can diagnose it without conduction studies
• MRI will show increased signal intensity indicating edema and demyelinization; alternativelyyou might see decreased signal indicating chronic fibrotic changes
• Ultrasound: look at transverse images (look at area of median nerve in carpal tunnel and median nerve proximal), and the ratio of the two can give you an idea of compression
• Treatment: Night splints, steroid injections (around half get relief from for around a month), surgery (in patients who have failed nonoperative treatment or who have severe disease)
• open TCL, Endoscopic CTR (rehabs faster)
• Complications: incomplete release, damage to PCB, hypertrophic painful scar, bowstringing of tendons
• Splints and therapy not necessary, abx only indicated for DM, immunocompromised
• Adjunctive procedures include hypothenar fat pad flap, radial forearm fascial flap, radial artery perforator based flap (to prevent scarring), release of TCL releases guyon’s canal (89%) with ulnar symptoms have relief

• Radial Nerve:
• Anatomy:
• originates from C5-8,T1; spirals around posterior aspect of humerus with profunda brachii artery 13cm proximal to trochlea –> pierces lateral intramuscular septum between brachialis and brachioradialis 7.5cm proximal to trochlea –> travels anterior to lateral epicondyle
• Divides into deep and superficial branches (PIN and SBRN). The deep PIN splits supinator muscle and innervates extensors from ulnar to radial (except mobile wad) and terminates at the wrist capsule. The superficial (SBRN) travels between brachioradialis and ECRL and provides sensation to dorsal radial aspect of hand.
• Compressive locations
• Radial Tunnel Syndrome:  Caused by compression from fibrous bands, the vascular leash of henry, ECRB, proximal supinator, distal supinator
• Presents with pain over anterolateral aspect of elbow, pain that increases with passive pronation/wrist flexion or active supination/wrist extension; but without sensory/motor disturbance, may co-exist with tennis elbow
• Exam: pain over PIN
• middle finger test- symptoms exacerbated by resisted extension of middle finger, resisted supination
• EMG/NCV not usually helpful
• Treatment: conservative –> activity modification, splinting, injection
• Surgical release: release everything
• Posterior Interosseous Nerve Syndrome (PINS):  Caused by entrapment at the elbow, neoplasms, or radial head dislocation
• Typically presents with progressive loss of extensors so the wrist extends in radial deviation, cannot actively extend at MCPs
• Differential diagnosis includes RA tendon ruptures
• Treatment: conservative (activity restrictions, splinting) 8-12 weeks
• Surgery: release the PIN via an anterior or transverse approach through extensor intervals (BR splitting, BR ECRL or EDC/ECRB)
• Cheralgia Paresthetica (Wartenberg’s Syndrome): SBRN entrapment caused by compression from external forces (jewelry), or narrowing of the interval BR/ECRL –> with pronation of forearm
• Radiodorsal hand: pain, numbness, paresthesias
• 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’srelease

• Ulnar Nerve:
• Anatomy:
• comes from C8-T1; runs medial to brachial artery then behind medial epicondyle –> where it enters forearm between 2 heads FCU –> then traveles between FCU/FDP –> crosses wrist in Guyon’s canal –> divides into superficial and deep branches. It runs ulnar and volar to ulnar artery
• DSBUN (DCBUN) branches 6cm proximal to the ulnar head to supply the ulnar dorsum of the hand
• Immediately Proximal to the wrist crease the palmar radial fibers become superficial branch and dorsal ulnar become deep motor branch
• The sensory component provides sensation to the ulnar half of the hand
• The deep motor branch innervates FCU, FDP (III and IV), PB, hypothenar muscles, 3/4 lumbricals, dorsal interossei, palmar interossei, thenar muscles AddP and deep head FPB
• Compression sites
• Cubital Tunnel Syndrome: caused by compression, traction, friction, or decreased size of cubital tunnel ie during flexion at the arcade of struthers, medial intermuscular septum, medial epicondyle, cubital tunnel (osbornes ligament), deep aponeurosis of FCU, triceps, aconenous (anomalous muscle)
• Presents with intermittent paresthesias in the ulnar 2 digits, sensory loss later, extrinsic/intrinsic motor weakness (FDP to ring and small), may have mild clawing. The dorsal sensory loss is what differentiatees this from Guyons canal compression which does not have sensory symptoms
• Physical exam: atrophy, motor strength, sensibility, tinel’s, elbow flexion test (provocative maneuver), look for nerve subluxation with elbow flexion (when it comes out of retrocondylar groove) Dorsal interossei wasting,
• wartenburg SIGN (ulnar clawing)
• froment sign (ask to grasp paper –> will grasp with IP joint of thumb instead of dorsal interossei)
• pyramid sign –> loss of intrinsics in the hand
• Treatment: conservative: elbow splint (45 extension)
• Surgery: in situ decompression (not a good technique if nerve subluxes), anterior transposition (better technique for subluxation and very severe disease – can be subcutaenous, submuscular, or intramuular, or intramuscular), medial epicondylectomy (eliminates compressive possibility by may cause elbow instability) (none are superior to the other)
• Ulnar Tunnel Syndrome (Guyon’s canal): compression of the ulnar nerve at the palmaris brevis, fibrous origin of FDM, ulnar artery aneurysm or thrombosis, hook of hamate, or ganglion cyst (ganglion cyst is most common)
• Presentation: numbness/paresthesias in palmar aspect ring and small fingers (NOT DORSAL HAND – dorsal sensory branch comes off proximal to wrist crease); weakness/atrophy (ulnar intrinsics).
• Exam: The nerve is anatomically divided into three zones which have different presentations based on etiology:
• Zone/type 1: presents with both motor and sensory weakness – usually due to a ganglion cyst or fracture of the hamate.
• Zone/type 2: presents with isolated motor weakness – usually due to ganglion cyst
• Zone/type 3: presents with isolated sensory weakness – usually due to ulnar artery thrombosis
• Evaluation: You can look for small apertures with Xrays in carpal tunnel view or CT/MRI, EMG/NCV may be abnormal
• –> if hamate hook is broken excision may be performed as treatment
• Treatment: conservative if it’s due to repetitive trauma, no mass, or idiopathic; surgery if it’s refractory or identifiable cause (ie excise the hook of hamate if it’s broken and impinging)

• The last thing to mention is Double Crush Syndrome: compression at the nerve root origin (ie the neck) and at another distal site –> should release distally anyway (treat peripherally first and it may relieve symptoms)