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|LETTER TO EDITOR
|Year : 2013 | Volume
| Issue : 3 | Page : 311-312
Transligamentous thenar branch of the median nerve: The million dollar nerve
Prasad Krishnan1, Rohit Mishra1, Manaranjan Jena1, Ashis Das2
1 Department of Neurosurgery, National Neurosciences Centre, Peerless Hospital Complex, Kolkata, West Bengal, India
2 Department of Neurology, National Neurosciences Centre, Peerless Hospital Complex, Kolkata, West Bengal, India
|Date of Submission||12-Apr-2013|
|Date of Decision||16-Apr-2013|
|Date of Acceptance||07-Jun-2013|
|Date of Web Publication||16-Jul-2013|
Department of Neurosurgery, National Neurosciences Centre, Peerless Hospital Complex, Kolkata, West Bengal
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Krishnan P, Mishra R, Jena M, Das A. Transligamentous thenar branch of the median nerve: The million dollar nerve. Neurol India 2013;61:311-2
Sectioning of the thenar branch of the median nerve has been called the "million dollar injury" due to the compensation awarded in lawsuits as a consequence of loss of thenar function. We have described herein a transligamentous thenar branch of the median nerve - a rare anatomical variant in a patient with carpal tunnel syndrome.
A 37-year-old euthyroid lady presented with troublesome paresthesias, nocturnal pain, tingling, and numbness in the outer aspect of the right hand of 9-months duration. On examination, she had decreased pin-prick sensation in the tips of the outer three fingers of the right hand. Nerve conduction study revealed prolonged motor distal latency of the right median nerve with reduced amplitude of compound action potential and absent median sensory nerve action potential, consistent with the diagnosis of right carpal tunnel syndrome. She underwent median nerve decompression by classical palmar skin incision and sectioning of the transverse carpal ligament (TCL). Intraoperatively, an anomalous branch was seen piercing the TCL and was spared. The branch was found to enter the thenar muscles and was arising from the anterior aspect of the median nerve [Figure 1].
|Figure 1: Operative photograph showing a cut-edge of the transverse carpal ligament [black arrows], the median nerve [deep blue arrow], and the transligamentous thenar branch perforating the ligament [light blue arrow]|
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According to Vashishtha, the first branch arising from the median nerve trunk in the hand is taken to be the thenar nerve.  This nerve supplies the opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis and is eponymously called the "million dollar nerve"  due to litigation-related compensation that may occur if it is transected, resulting in loss of function of the hand muscles. The variations of the muscular (thenar) branch of the median nerve in the carpal tunnel as described  are extraligamentous (46%), subligamentous (31%), and transligamentous (23%). The transligamentous variant is the rarest of these, and the most treacherous from the operative standpoint as it may get sacrificed inadvertently during surgery even before the nerve is exposed. In a study of 50 hands from 25 adult cadavers in an Indian population, this variant was found in only 9.09% of cases where a single thenar branch was present.  Its incidence goes up if multiple thenar branches are present.
The incidence of this complication cannot be known as the event will remain undiagnosed if there is preoperative thenar muscle wasting. This complication was first reported in two cases out of 662 patients by Lilly and Magnell.  Candal-Couto and Sher  attempted to find the "best practice" to deal with the possibility of finding this nerve during decompression by a questionnaire to 220 surgeons who were members of the British Society for Surgery of the Hand and 71% of the respondents had seen the anomaly in less than 5% of the cases, while 10% had seen it in more than 5% of the cases. Also, 34% of the respondents had never seen an iatrogenic injury and 5% had seen more than 5 cases. Furthermore, 71% of the surgeons felt that there was no need to formally explore and identify the branch intraoperatively to avoid iatrogenic damage.
We feel that surgeons must be aware of this anomaly and, as the thenar nerve progresses laterally from its origin,  reiterate that the median nerve must be decompressed from its ulnar side during surgery without disturbing the transligamentous branch if present.
| » References|| |
|1.||Vashishitha K. Variations of the median nerve in the carpal tunnel and its distribution in the hand. J Anat Soc India 2011;60:193-8. |
|2.||Jordan C, Mirzabeigi E, editors. Atlas of Orthopedic Surgical Exposures. New York: Theime; 2000. p. 68. |
|3.||Candal-Couto JJ, Sher JL. The thenar motor branch during carpal tunnel decompression: The expert opinion. Arch Orthop Trauma Surg 2007;127:431-4. |
|4.||Lilly CJ, Magnell TD. Severance of the thenar branch of the median nerve as a complication of carpal tunnel release. J Hand Surg Am 1985;10:399-402. |
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