Published in:
Open Access 01-11-2017 | Musculoskeletal
Ultrasound imaging of the thenar motor branch of the median nerve: a cadaveric study
Published in: European Radiology | Issue 11/2017
Login to get accessAbstract
Introduction
Anatomic variations of the median nerve (MN) increase the risk of iatrogenic injury during carpal tunnel release surgery. We investigated whether high-frequency ultrasonography could identify anatomic variations of the MN and its thenar motor branch (MBMN) in the carpal tunnel.
Methods
For each volar wrist of healthy non-embalmed cadavers, the type of MN variant (Lanz classification), course and orientation of the MBMN, and presence of hypertrophic muscles were scored by 18-MHz ultrasound and then by dissection.
Result
MBMN was identified by ultrasound in all 30 wrists (15 subjects). By dissection, type 1, 2 and 3 variants were found in 84%, 3%, and 13% of wrists, respectively. Ultrasound had good agreement with dissection in identifying the variant type (kappa =0.9). With both techniques, extra-, sub-, and transligamentous courses were recorded in 65%, 31%, and 4% of cases, respectively. With both techniques, the bifid nerve, hypertrophic muscles, and bilateral symmetry for variant type were identified in 13.3%, 13.3%, and 86.7% of wrists, respectively. Agreement between ultrasound and dissection was excellent for the MBMN course and orientation (kappa =1).
Conclusion
Ultrasound can be used reliably to identify anatomic variations of the MN and MBMN. It could be a useful tool before carpal tunnel release surgery.
Key Points
• Ultrasound can identify variations of the motor branch of the median nerve.
• Ultrasound mapping should be used prior to carpal tunnel release surgery.
• All sub-, extra-, and transligamentous courses were accurately identified.
• Type 3 variants (bifid nerve), hypertrophic muscles, and bilateral symmetry were accurately identified.