Updated: 5/18/2021

PIN Compression Syndrome

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  • 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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(SBQ17SE.44) A 75-year-old female presents with difficulty extending her fingers and thumb. Her exam is notable for subcutaneous nodules, ulnar deviation of the metacarpophalangeal joints, and swan neck deformities. The wrist radially deviates with extension. Extension cannot be actively initiated or maintained when her fingers are passively manipulated. Tenodesis is normal. What pathology would best explain her symptoms?

QID: 211589
1

Attenuation of the sagittal bands

42%

(792/1902)

2

Tendon rupture

20%

(382/1902)

3

Peri-elbow synovitis causing nerve compression

28%

(530/1902)

4

Intersection syndrome

5%

(90/1902)

5

Distal radioulnar joint synovitis

4%

(82/1902)

L 5 A

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(OBQ12.274) Compressive injury to the posterior interosseous nerve will lead to EMG fibrillations in which of the following muscles?

QID: 4634
1

Extensor Carpi Radialis Longus/Extensor Carpi Radialis Brevis/Brachoradialis

7%

(358/5220)

2

Extensor Carpi Radialis Longus/Supinator/Abductor Pollicis Longus

6%

(338/5220)

3

Extensor Pollicis Longus/Supinator/Abductor Pollicis Longus

68%

(3559/5220)

4

Brachoradialis/Supinator/Extensor Pollicis Longus

5%

(252/5220)

5

Extensor Pollicis Longus/Supinator/Abductor Pollicis Brevis

13%

(663/5220)

L 3 C

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