In general, the surgical approach should be chosen sufficiently large to provide a good overview and to avoid injury to the median nerve and the superficial palmar arch.
The approach for simple carpal roof splitting (red line) runs longitudinally starting approximately 5 mm distal to the wrist crease, towards the third interdigital space, and ends before the so-called Kaplan's line.
The approach is chosen so that the median nerve lies far radially and is thus safely protected.
Kaplan's line serves as a topographical orientation line and to protect the superficial palmar arch, which is typically found approximately 10 mm distal to Kaplan's line in depth. It runs parallel to the proximal transverse palmar crease, from the ulnar pole of the flexion crease over the thumb's metacarpophalangeal joint to the ulnar edge of the hand.
To avoid iatrogenic injury, the numerous variants of the motor branch's origin must be considered.
a most common variant, extraligamentous origin of the motor branch,
b subligamentous course of the motor branch,
c transligamentous course of the motor branch,
d ulnar origin of the motor branch.
e high division of the median nerve with the median artery,
f accessory motor branch with origin proximal to the carpal tunnel from the ulnar edge of the median nerve,
g accessory motor branch with origin proximal to the carpal tunnel, perforating the retinaculum,
h high division of the median nerve.
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