Musculoskeletal Ultrasound is also able to clearly visualise nerves, characteristically appearing in the transverse view best as a 'Pepper Pot' appearance. There is a building library of research regarding MSK Ultrasound appearances of nerve pathology, with a significant amount regarding the median nerve at the carpal tunnel. Indications of potential nerve pathology include thickening, and increased cross-sectional area. Rob Mast, Extended Scope Physiotherapist, has provided the following case study. This will hopefully be the first of a selection of peripheral nerve pathologies that we can post on the site.
This lady in her 30's , presented with sensory loss and pain in an ulnar distribution. This webpage provided by Washington University School of Medicine, provides an excellent overview of ulnar nerve anatomy, with good diagrams for the dermatomal distribution affected.
The case was interesting, predominantly as musculoskeletal ultrasound was able to help with the clinical diagnosis and help with the differential diagnosis. This lady had been referred to me by the GP with a 'Cubital tunnel syndrome'.
Examination ruled out a cervical source of symptoms. I then performed an ultrasound scan of the ulnar nerve at the cubital tunnel. I assessed the nerve by slowly flexing and extending the elbow whilst scanning the cubital tunnel to see if any subluxation of the ulnar nerve at the cubital tunnel was occurring. Subluxation of the ulnar nerve at the cubital tunnel in my opinion is not uncommon and can often cause pain and sensory disturbance in the distribution of the ulnar nerve. There was no sign that this was occurring on visualisation with the ultrasound. Volpe et al (2009) have produced a free text article which reviews the relationship of ulnar nerve thickness with severity of symptoms. They found a correlation, that was significant and also suggested the severity of the complaint. The ultrasound in this case showed that the cross sectional area of the nerve in the cubital tunnel was identical to the CSA on the non- symptomatic site.
Not only was there no subluxation at the elbow, but clinically I could not provoke the symptoms when palpating the nerve in the cubital tunnel which made it less likely that this was the site of dysfunction.
I then focussed my attention to Guyons canal in the wrist. The Guyon's canal is a space at the wrist between flexor retinaculum and the palmar carpal ligament (which runs between the pisiform bone and the hamate bone), through which the ulnar artery and the ulnar nerve travel into the hand. I find this a less common site for dysfunction than the elbow. Clinically this did fit, as palpation of the nerve at the Guyons canal reproduced her symptoms suggestive of ulnar nerve irritation. Whilst preparing this case study, I found this interesting case of an aneurysm at the Guyon's Canal. This provides a useful reminder for all of us involved with MSK assessments, that vascular conditions should always be considered.
Reproduced from www.orthogate.org
I then scanned the ulnar nerve in the Guyon's canal. It was very clear that the calibre of the nerve was significantly bigger than on the non-symptomatic site. This useful article by Peeters et al (2004) Sonography of the Normal Ulnar Nerve at the Guyons canal, offers further information on this condition.
This provides a useful case study on the use of ultrasound to add a further level of detail to help distinguish the site of neural pathology.
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