1. How is the radial nerve usually injured in the axilla and how does this present?
2. How is the radial nerve usually injured in the spiral groove and how does this present?
3. What is the differential diagnosis of wrist drop?
4. How is the posterior interosseous nerve (PIN) usually injured and what is the presentation?
5. What is a Monteggia fracture?
6. How does superficial radial neuropathy present?
Answers:
1. The radial nerve can be compressed at the axilla by improper crutch use and involves all radial innervated muscles with decreased sensation over the posterior arm and forearm. SNAP and CMAP may or may not be abnormal.
2. Injury at the spiral groove (Saturday night palsy, Honeymooner's palsy) can be due to an injection or by compression (a chair or a person's head). There is weakness of all radial-innervated muscles except triceps brachii and anconeus. There is weakness of elbow flexion, wrist drop, and finger extension weakness. SNAP and CMAP may or may not be abnormal.
3. Diffuse polyneuropathy (lead), PIN, radial nerve, posterior cord, upper trunk, middle trunk, C6/C7 radiculopathy, SCI, TBI, CVA.
4. The PIN can be injured by compression at the Arcade of Frohse of the supinator, by a lipoma, ganglion cyst, synovitis from RA, or by a Monteggia fracture. PIN injury involves all radial nerve distal extensors (EDC, EIP, ECU, EPB, EPL, APL) with a pseudo claw hand and radial deviation with wrist extension. There are no sensory symptoms. SNAP is normal and CMAP is abnormal to all radial hand muscles.
5. A Monteggia fracture is a fx of the proximal 1/3 of the ulna and dislocation of the radial head, sometimes resulting in PIN injury. It occurs secondary to a fall on an outstretched hand with the forearm locked in pronation.
6. Superficial radial neuropathy (Cheiralgia Paresthetica, Wristwatch Syndrome) can occur from injury by compression from a tight wristwatch or handcuffs. Symptoms include numbness, burning or tingling on the dorsal radial aspect of the hand. SNAP is abnormal and CMAP is normal.
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1 comment:
PIN also innervate ERCB and Supinator. It provides no CUTANEOUS sensory innervation but DOES provide sensation to the interosseous membrane which is significant in Monteggia & Galeazzi fractures and if there is persistant vague pain following ORIF of the same or after both-bone forearm fractures where there may be interosseous strain or irritation from internal hardware.
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