- 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.