Lanz analysed the branching pattern of the median nerve within the carpal tunnel in 246 hands. This paper details these results and compares them with other peer-reviewed literature.
Author: Ulrich Lanz, M.D, Wiirzburg, Germany
Journal: The Journal of Hand Surgery, January, 1977, Vol. 2 No. I, pp. 44-53
Presented at the Thirty-first Annual Meeting of the American Society for Surgery of the Hand, New Orleans, La., Jan. 28-30, 1976.
In this Review
- Aim: Describe median nerve variations to avoid "surgical misadventure"
- Methods: 300 explorations of a carpal tunnel over 4 years.
- Results: 29/300 variations of median nerve in carpal tunnel were identified and can be classified into 4 groups.
- Conclusion: "Important to approach median nerve from the ulnar side when opening the carpal tunnel"
- Discussion: 12% incidence of anatomical variations in this series is much higher than the current literature suggests ("current" is at the time of publication in 1977).
Classification of Median Nerve Variations
Lanz classified variations in the Median Nerve into 4 Main groups. These are explained below.
Group 1: Variations of the course of the thenar branch.
In 1974 Poisel1 studied the relationship of the thenar branch to the transverse carpal ligament in 100 cadaver hands. The results were:
- 46 % extraligamentous
- 31% subligamentous
- 23% transligamentous
In 1968, Entin2 showed that the thenar branch may leave the median nerve at its ulnar aspect. This is high-risk of iatrogenic injury during division of transverse carpal ligament.
Group 2: Accessory branches at distal Carpal Tunnel
This was discovered in 18/246 hands.
Multiple branches from the recurrent motor branch are more common than first thought. Lanz highlights two main points in regards to this group:
- True Double Motor Branches are rare
- Majority of accessory branches are sensory.
Group 3: High division of the median nerve
Lanz only discovered this in 7 hands. Of these 7, 5 were associated with a Median Artery. Other associations in the literature of a high division of the median nerve include:
- Both branches of the median nerve have approximately the same diameter.
- The size of the median artery is highly variable3.
- Accessory lumbrical muscle between the two branches4
Group 4: Accessory branches proximal to the carpal tunnel.
Lanz only discovered this in 4/246 hands. So it's rare.
This variation can be associated with:
- Branch ran within transverse carpal ligament joining a regular motor branch distally5
- Branch joins the common digital nerve to thumb and radial side of index finger6.
- In its course on top of the ligament a few fibers to the skin of the thenar7.
3 Take-Home Points
- It was in fact Poisel, not Lanz, who described the anatomical variations of the recurrent motor branch of the median nerve. These variations have been confirmed in more recent studies.
- Carpal Tunnel is not such a straightforward operation when you are aware of all the potential variations of anatomy. Injury to the thenar branch can result in significant morbidity.
- Articles were much quicker to read in 1977!
- Poisel, S.: Ursprung und Verlauf des R. muscularis des Nervus digitalis palmaris communis I (N. medianus), Chir. Praxis 18: 471-474, 1974.
- Entin, M. A.: Carpal tunnel syndrome and its variants. Surg. Clin. North Am. 48: 1097, 1968.
- Winkelman, N. Z., and Spinner, M.: A variant high sen- sory branch of the median nerve to the third web space, Bull. Hosp. Joint Dis. 34: 161-166, 1973.
- Schultz, R. J., Endler, P. M., and Huddleston, H. D.: Anomalous median nerve and an anomalous muscle belly of the first lumbrical associated with carpal-tunnel syndrome, J. Bone Joint Surg. 55A: 1744-1746, 1973.
- Ogden, J. A.: An unusual branch of the median nerve, J. Bone Joint Surg. 54A: 1779-1781, 1972.
- Linburg, R. M., and Albright, J. A.: An anomalous branch of the median nerve, J. Bone Joint Surg. 54A: 1779-1781,1972.
- Lanz, U.: Variationen des Nervus medianus im Bereich des Karpalkanals, Handchirurgie 7: 159-162, 1975