Posterior Interosseous Nerve Compression Syndrome

- See: PIN

- Inciting causes:
    - radiocapitellar joint ganglions and synovitis
    - congenital tightness of ligamentous arcade of Frohse;
    - include poorly placed screws for fracture fixation
           - PIN is vulnerable during ORIF of proximal radius;
           - in 25% of pts, PIN lies in direct contact w/ periosteum of radius just dorsal to the biciptial tuberosity;
           - fixation device applied to radius, which might have its proximal screw at level of bicipital tuberosity, could cause PIN syndrome by entrapment beneath plate;
           - to avoid this complication, the nerve should be directly exposed;
    - idiopathic compression syndrome:
           - sites of compression:
                  - fibrous bands anterior to the radial head at the entrance of radial tunnel (uncommon cause of compression);
                  - radial recurrent vessels (leash of Henry);
                  - tendinous origin of ECRB: the ECRL is more superficial and is not a source of compression;
                  - arcade of Froshe:
                        - tendinous proximal border of supinator (arcade of Frohse):
                        - this is the most common location of nerve compression in radial tunnel syndrome;
                        - lies deep to the extensor carpi radialis brevis
                        - references: 
                              - The arcade of Frohse and its relationship to posterior interosseous nerve paralysis.
                              - Anatomic and morphometric study of the arcade of Frohse in cadavers
                  - distal edge of the supinator at exit: this is the least common site of compression;
           - reference:
                  - Radial nerve entrapment at the elbow: surgical anatomy.
                  - Peripheral nerve compression.  

- Diff Dx: of Post Interosseous Nerve Syndrome:
    - C7 radiculopathy:
          - unlike PIN, there will be weakness of triceps and wrist flexors;
    - lateral epicondylitis (ECRB)
          - it is often misdiagnosed as resistant tennis elbow or PIN Syndrome;
          - unlike tennis elbow, there is tenderness about 4 cm distal to the lateral humeral epicondyle;
    - distal PIN syndrome:
          - pts w/ distal posterior interosseous nerve syndrome have pain with repetitive dorsiflexion & tenderness centered over the 4th extensor compartment;
    - trigger finger (no passive movement possible);
    - extensor tendon rupture:
          - may be differentiated by tenodesis effect of passive flexion of wrist: if the tendons are intact, the digits will extend (ie., tenodesis effect is lost);
    - failure of digit extension from chronic dislocation of MCP (see MP joint in RA)
          - pt can maintain extension achieved passively
          - Bouvier's Test
- Exam:
    - following muscles are intact with PIN syndrome:
         - BR, ECRL , often ECRB, & supinator;
    - pts commonly have tenderness over lateral epicondyle & almost always have tenderness more distally over the arcade of Froshe;
    - pain is almost always experienced w/ resisted supination of the forearm and frequently w/ resisted pronation;
          - full pronation of forearm produces pressure on PIN by sharp tendinous edge of the origin of ECRB  muscle;
          - PIN may be compressed by the tendinous origin of the ECRB;
          - active supination from a pronated position (tightening supinator) along w/ wrist flexion (which tighens the ECRB) may reproduce the patient's symptoms;
    - most will have pain w/ resisted extension of extension of middle finger;
    - pt will unable to extend thumb or other digits at MCP joints;
          - w/ complete palsy, pts will continue to have wrist extension (ECU) but they are unable to extend wrist at neutral or in ulnar deviation;
          - they can extend the digits at the interphalangeal joints, but not at MP joints;
    - pain is relieved by blocking the posterior interosseous nerve 3 cm proximal to the wrist joint;
          - performed by injecting approx 1 cm ulnar to Lister's tubercle;

- Injection Test:
    - lidocaine injection 4 finger breadths distal to the lateral epicondyle will result in temporary PIN palsy and, in the case of PIN syndrome, will result in temporary relief of pain;
    - w/ lateral epicondylitis, the patient should note pain relief following injection at the origin of the ECRB tendon (which is usually more proximal than the site of injection for PIN compression);

- Succinylcholine test:
    - diagnostic aid for differentiation of loss of function due to nerve injury from muscle or tendon rupture;
    - succinylcholine paralyzes normal skeletal muscles by blocking transmission at myoneural junction;
           - in denervated muscle, however, sustained muscle contractions are seen lasting several minutes (so-called denervation hypersensitivity);
    - w/ muscle or tendon disruption, fasciculations last only seconds;

- Operative Decompression

Anatomic dissections relating the posterior interosseous nerve to the carpus, and the etiology of dorsal wrist ganglion pain.

The terminal branch of posterior interosseous nerve: a useful donor for digital nerve grafting.

Posterior interosseous nerve palsies

Posterior interosseous nerve: an anatomic study of potential nerve grafts.

A study of the posterior interosseous nerve (PIN) and the radial tunnel in 30 Thai cadavers.

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Monday, January 21, 2013 12:32 pm