Lanz prospectively recorded median nerve anatomy in 246 carpal tunnel explorations and synthesized case reports from the literature to build a four-group classification of nerve variants. The study asks: how often do dangerous anatomical variants occur, what forms do they take, and what surgical approach minimizes injury risk?
Carpal tunnel release seems straightforward until you cut something you shouldn't. Before Lanz, variant median nerve anatomy was known only from isolated case reports, leaving surgeons without a framework for anticipating or categorizing what they might encounter.
The 12% variant rate means roughly 1 in 8 of your carpal tunnel releases will have an anatomical surprise. The Lanz classification gives you a mental checklist: look for an aberrant thenar branch (Group I), accessory branches off the distal tunnel (Group II, usually sensory — preserve them), a bifid nerve with a median artery between the divisions (Group III), and rare proximal accessory branches that perforate the ligament (Group IV).
The single most protective technical habit this paper supports is approaching from the ulnar side of the median nerve. Variant branches arise from the ulnar aspect of the nerve at every level. Proximal to, within, and distal to the tunnel. A radially centered incision puts all of them at risk before you even see them.
If you see a bifid nerve and an artery running between the two divisions, that is a persistent median artery. Do not mistake it for a nerve trunk, and do not divide it without recognizing what it is.
Lanz prospectively recorded median nerve anatomy in 246 carpal tunnel explorations and synthesized case reports from the literature to build a four-group classification of nerve variants. The study asks: how often do dangerous anatomical variants occur, what forms do they take, and what surgical approach minimizes injury risk?
Carpal tunnel release seems straightforward until you cut something you shouldn't. Before Lanz, variant median nerve anatomy was known only from isolated case reports, leaving surgeons without a framework for anticipating or categorizing what they might encounter.
The 12% variant rate means roughly 1 in 8 of your carpal tunnel releases will have an anatomical surprise. The Lanz classification gives you a mental checklist: look for an aberrant thenar branch (Group I), accessory branches off the distal tunnel (Group II, usually sensory — preserve them), a bifid nerve with a median artery between the divisions (Group III), and rare proximal accessory branches that perforate the ligament (Group IV).
The single most protective technical habit this paper supports is approaching from the ulnar side of the median nerve. Variant branches arise from the ulnar aspect of the nerve at every level. Proximal to, within, and distal to the tunnel. A radially centered incision puts all of them at risk before you even see them.
If you see a bifid nerve and an artery running between the two divisions, that is a persistent median artery. Do not mistake it for a nerve trunk, and do not divide it without recognizing what it is.