Ultrasound (US) of the posterior interosseous nerve (PIN) around the distal edge of the supinator tunnel. Poster No.: C-0024 Congress: ECR 2013 Type: Scientific Exhibit Authors: C. Rolla Bigliani 1, G. Russo 2, E. Fisci 1, B. Bignotti 1, A. Tagliafico 1, Keywords: DOI: C. Martinoli 2 ; 1 Genova/IT, 2 Genoa/IT Inflammation, Localisation, Ultrasound, Neuroradiology peripheral nerve 10.1594/ecr2013/C-0024 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 7
Purpose The posterior interosseous nerve (PIN) is a deep motor branch of radial nerve serving the extensor muscles of the forearm, except for the ECRL. PIN passes through the supinator muscle in its course from the anterior to the posterior surface of the forearm and supplies ECRB and the supinator muscle before entering the Arcade of Frohse, a fibrotendinous arch formed by the superficial belly of the supinator muscle [1]. This fibrous structure, absent in the newborn, may develop in response to repeated rotatory movements of the forearm [2]. The most common site of PIN entrapment is at the Arcade of Frohse [2]; other possible causes of nerve entrapment are the Leash of Henry [3,6] i.e. arterial branches arising from the recurrent radial artery that cross over the PIN few centimeters proximal to the Arcade of Frohse, and the compression within the supinator tunnel [1,4,5]. Few patients can develop nerve entrapment also at the end of the supinator tunnel. At this level the nerve sends a recurrent branch for the EDC [1],(fig 1). The purpose of this study was to assess the value of ultrasound (US) to detect the entrapment of the posterior interosseous nerve (PIN) around the distal edge of the supinator tunnel. Images for this section: Fig. 1: Fig 1. A-B. After exiting the supinator tunnel, the PIN sends a recurrent branch for the EDC it then descends the forearm supplying the extensor muscles and ends at the wrist sending sensory fibers to the carpal ligaments and joints Page 2 of 7
Methods and Materials A dissection study was performed on n=3 cadavers to assess the regional anatomy of the divisional branches of the PIN beyond the distal edge of the supinator. We examined n=20 consecutive patients with posterior interosseous neuropathy with a 12-5MHz and 17-5MHz probe (Fig. 2). The nerve was evaluated from the radial nerve bifurcation down to its divisional branches in the forearm. The US diagnosis of PIN entrapment was based on nerve shape changes and loss of the fascicular pattern. Patients were subdivided in three groups based on the location of nerve entrapment at zone I (incl. leash of Henry area and arcade of Froshe), zone II (within the supinator tunnel) and zone III (at the distal edge of the supinator muscle or beyond it in the forearm). All patients underwent MRI and had surgical decompression. Images for this section: Fig. 2: Fig.2 A-B Scanning technique can be performed starting from proximal to distal (A), sweeping the probe down from anterior to posterior while pronating the forearm; or from distal to proximal (B), sweeping the probe up from posterior to anterior while supinating the forearm Page 3 of 7
Results The divisional branches of the PIN distal to the supinator tunnel can be reliably identified with US. In our series, PIN entrapment was observed at zone I in 35%, (fig 3) at zone II in 50% (fig 4), and at zone III in 15% of cases (fig 5). In this last localization, US was reliable to depict pathologic findings affecting the distal PIN and its divisional branches. Two-thirds of these cases went undetected at MR imaging [6,7]. Images for this section: Fig. 3: Fig. 3. A-B Possible sites of nerve compression at the Arcade of Frohse and at the Leash fo Henry: prominent vessels (hypertrophic leash #6 vessels) may cause PIN compression. Fig 2. B. US longitudinal scan demostrates PIN compression at the Arcade of Frohse Page 4 of 7
Fig. 4: Fig 4. A-B-C. PIN entrapment at the level of the supinator tunnel: comparative US transverse scan of right side, affected, and the normal left side(a; note the normal appeareance of the sensory branch of the radial nerve also demostrated in the intraoperatory photograph(c). MRI T2 Fat-Sat scan (B) shows hyperintense, thickened PIN beteween the two heads of the supinator. Page 5 of 7
Fig. 5: Fig. 5. A-B. US scan demonstrates PIN entrapment at the distal edge of the supinator tunnel(a). US transverse scan of the extensor muscles of the forearm(b), shows atrophyc denervation of the EDC supplied by the recurrent branch of PIN at this level. Note the normal aspect of ECU and ECRB. Page 6 of 7
Conclusion Ultrasound (US) is an accurate technique to identify the entrapment of the posterior interosseous nerve (PIN) around the distal edge of the supinator tunnel. When examining the supinator area for a suspected PIN neuropathy, the area around the distal edge of the supinator tunnel should be included routinely in the standard US examination for its clinical and surgical implications. References 1. Bianchi S, Martinoli C, et al. Ultrasound of the Musculoskeletal System, Springer- Verlag Berlin Heidelberg 2007. 2. Spinner M. The arcade of Frohse and its relationship to posterior interosseous nerve paralysis. J Bone Joint Surg Br 1968;50;809-812. 3. Rosenberg ZS, Bencardino J, Beltran J. MR featurese of nerve disorders at the elbow. Magn Reson Imaging Clin N Am 1997;5:545-565. 4. Wein TH, Albers JW. Electrodiagnostic approach to the patient with suspected peripheral polyneuropathy. Neurol Clin 2002;20: 503-526, vii. 5. Rosenberg ZS, Bencardino J, Beltran J. MR imaging of normal variants and interpretation pitfalls of the elbow. Magn Reson Imaging Clin N Am 1997;5:481-499. 6. Husarik DB, Saupe N, Pfirrmann CW, Jost B, Hodler J, Zanetti M. Elbow nerves: MR findings in 60 asymptomatic subjects--normal anatomy, variants, and pitfalls. Radiology 2009 Jul;252(1):148-56. 7. Aagaard BD, Maravilla KR, Kliot M. Magnetic resonance neurography: magnetic resonance imaging of peripheral nerves. Neuroimaging Clin N Am 2001;11:viii, 131-146. Personal Information Page 7 of 7