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Updated: Dec 18 2023

PIN Compression Syndrome

Images tunnel syndrome_moved.jpg tunnel lateral_moved.jpg
  • Sumary
    • PIN compression syndrome is a compressive neuropathy of the PIN which affects the nerve supply of the forearm extensor compartment.
    • Diagnosis is made clinically with weakness of thumb and wrist extensors without sensory deficits.
    • Treatment is a course of conservative management with splinting and surgical decompression reserved for persistent cases lasting > 3 months.
  • Epidemiology
    • Incidence
      • ~ 3 per 100,000 annually
    • Demographics
      • more common in manual laborers, males and bodybuilders
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • microtrauma
          • from repetitive pronosupination movements
        • trauma
          • fracture/dislocation (e.g., monteggia fx, radial head fx, etc)
        • space filling lesions
          • e.g. ganglion, lipomas, etc
        • inflammation
          • e.g. rheumatoid synovitis of radiocapitellar joint
        • iatrogenic (surgery)
      • pathoanatomy:
        • five potential sites of compression include
          • fibrous tissue anterior to the radiocapitellar joint
            • between the brachialis and brachioradialis
          • “leash of Henry”
            • are recurrent radial vessels that fan out across the PIN at the level of the radial neck
          • extensor carpi radialis brevis edge
            • medio-proximal edge of the extensor carpi radialis brevis
          • "arcade of Fröhse"
            • which is the proximal edge of the superficial portion of the supinator
          • supinator muscle edge
            • distal edge of the supinator muscle
  • Anatomy
    • PIN
      • origin
        • PIN is a branch of the radial nerve that provides motor innervation to the extensor compartment
      • course
        • passes between the two heads of origin of the supinator muscle
        • direct contact with the radial neck osteology
        • passes over abductor pollicis longus muscle origin to reach interosseous membrane
        • transverses along the posterior interosseous membrane
      • innervation
        • motor
          • common extensors
            • ECRB (often from radial nerve proper, but can be from PIN)
            • Extensor digitorum communis (EDC)
            • Extensor digiti minimi (EDM)
            • Extensor carpi ulnaris (ECU)
          • deep extensors
            • Supinator
            • Abductor pollicis longus (APL)
            • Extensor pollicus brevis (EPB)
            • Extensor pollicus longus (EPL)
            • Extensor indicis proprius (EIP)
        • sensory
          • sensory fibers to dorsal wrist capsule
            • provided by terminal branch which is located on the floor of the 4th extensor compartment
          • no cutaneous innervation
  • Presentation
    • Symptoms
      • insidious onset, often goes undiagnosed
      • defining symptoms
        • pain in the forearm and wrist
          • location depends on site of PIN compression
            • e.g., pain just distal to the lateral epicondyle of the elbow may be caused by compression at the arcade of Frohse
        • weakness with finger, wrist and thumb movements
    • Physical exam
      • inspection
        • chronic compression may cause forearm extensor compartment muscle atrophy
      • motion
        • weakness
          • finger metacarpal extension weakness
          • wrist extension weakness
            • inability to extend wrist in neutral or ulnar deviation
            • the wrist will extend with radial deviation due to intact ECRL (radial n.) and absent ECU (PIN).
      • provocative tests
        • resisted supination
          • will increase pain symptoms
        • normal tenodesis test
          • tenodesis test is used to differentiate from extensor tendon rupture from RA
  • Evaluation
    • Radiographs
      • indications
        • not commonly needed for the diagnosis of PIN compression syndrome
    • MRI
      • indications
        • not commonly needed for the diagnosis of PIN compression syndrome
        • may be help to site and delineate the soft tissue mass responsible for compression
        • helpful for surgical planning of mass resection
  • Studies
    • EMG
      • indications
        • may help identify the level of nerve compression
        • may be used to rule out differential diagnoses of neuropathy
  • Differential
    • Cervical spine nerve compression
    • Brachial plexus compression
    • Peripheral neuropathy
  • Diagnosis
    • Clinical 
      • diagnosis is made with careful history and physical examination
  • Treatment
    • Nonoperative
      • rest, activity modification, stretching, splinting, NSAIDS
        • indications
          • recommended as first-line treatment for all cases
      • lidocaine/corticosteroid injection
        • indications
          • a compressive mass, such as lipoma or ganglion, has been ruled out
          • isolated tenderness distal to lateral epicondyle
          • trial of rest, activity modification, anti-inflammatories were not effective
        • technique
          • single injection 3-4 cm distal to lateral epicondyle at site of compression
      • surgical decompression
        • indications
          • symptoms persist for greater than three months of nonoperative treatment
          • compressive mass detected on imaging
        • outcomes
          • results are variable
          • spontaneous recovery of motor function was seen in 75 - 97% of non-traumatic case series
          • may continue to improve for up to 18 months
  • Technique
    • Surgical decompression
      • approach
        • anterolateral approach to elbow is most common approach
        • may also consider posterior approach
      • decompression
        • decompression should begin with release of
          • fibrous bands connecting brachialis and brachioradialis
          • leash of Henry
          • fibrous edge of ECRB
          • radial tunnel, including arcade of Frosche and distal supinator
  • Complications
    • Neglected PIN compression syndrome
      • muscle fibrosis of PIN innervated muscles
      • resulting in tendon transfer procedures to re-establish function
    • Chronic pain
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