Updated: 10/4/2016

PIN Compression Syndrome

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https://upload.orthobullets.com/topic/6023/images/pin_moved.jpg
https://upload.orthobullets.com/topic/6023/images/radial tunnel syndrome_moved.jpg
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Introduction
  •  A compressive neuropathy of the PIN which affects the nerve supply of the forearm extensor compartment 
  • Epidemiology
    • incidence
      • reported as 3 per 100,000 people yearly
    • demographics
      • more common in manual laborers, males and bodybuilders
  • 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
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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Questions (2)
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(OBQ12.274) Compressive injury to the posterior interosseous nerve will lead to EMG fibrillations in which of the following muscles? Review Topic

QID: 4634
1

Extensor Carpi Radialis Longus/Extensor Carpi Radialis Brevis/Brachoradialis

7%

(279/3844)

2

Extensor Carpi Radialis Longus/Supinator/Abductor Pollicis Longus

7%

(250/3844)

3

Extensor Pollicis Longus/Supinator/Abductor Pollicis Longus

67%

(2582/3844)

4

Brachoradialis/Supinator/Extensor Pollicis Longus

5%

(188/3844)

5

Extensor Pollicis Longus/Supinator/Abductor Pollicis Brevis

13%

(513/3844)

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