What’s the Diagnosis – Case 186
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Findings Radiographs show no abnormality. An additional radiograph was obtained and will be shown later. MRI demonstrates edema and fracture along the radial border of the pisiform. There is a loss of the fascicular architecture of the ulnar nerve, ganglion formation of the nerve, and loss of the fat plane surrounding the ulnar nerve within the ulnar tunnel/Guyon’s canal.
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Diagnosis: Ulnar tunnel/Guyon’s canal syndrome This case demonstrates a number of odd clinical scenarios. The first is a pisiform fracture. A very uncommon carpal bone fracture with ulnar sided carpal bone fractures much more commonly involving the hamate and especially the hook of the hamate. Pisiform and hamate fractures most commonly occur from direct impact but especially pisiform fractures occasionally may be seen in a fall on an outstretched hand. The ulnar nerve and artery traverse in the adjacent Guyon’s canal which is bordered by the hamate, pisiform, volar carpal ligament, and transverse carpal ligament. Any process which effaces the fat of the ulnar nerve/causes mass effect upon the nerve or a chemical irritation may produce symptoms of the ulnar nerve or an ulnar tunnel syndrome. This can be related to ganglia, ulnar artery thrombosis, anomalous musculature, fracture, or trauma with inflammation and chemical irritation of the nerve. The ulnar nerve more proximally has motor and sensory components but further distally has a deep, motor and more superficial, sensory component as shown in the above case, particularly in the axial images. Depending on where the nerve is involved, different symptoms may ensue. In our case, there was not only an effacement of the fat plane around the nerve but typical findings of injury such as loss of the normal polk-a-dot axial fascicular architecture and ganglion formation.
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References Kieran O’Shea MB, FRCSI and Andrew J. Weiland MD. Fractures of the Hamate and Pisiform Bones. Hand Clinics, 2012-08-01, Volume 28, Issue 3, Pages 287-300, Copyright © 2012 Elsevier Inc. Chang MK, Yap RTJ. Acute ulnar nerve compression associated with pisiform fracture - a case report and literature review. Case Reports Plast Surg Hand Surg. 2019 Jan 28;6(1):1-6. doi: 10.1080/23320885.2018.1522959. PMID: 32550255; PMCID: PMC6968647. Daniel Hatch MD. Ulnar Tunnel Syndrome. https://www.orthobullets.com/
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