Structures at Risk in Carpal Tunnel Release
A carpal tunnel release looks like a simple ligament cut, but four named structures sit within millimeters of that incision, and a slip in either direction leaves a lasting deficit.
Takeaways
- Carpal tunnel syndrome carries a lifetime risk near 10%. Reported prevalence in the general population runs about 2.7%, with an annual incidence near 0.1% among adults, so most residents manage several cases before a sub-I rotation ends (Hirata, Rinsho Shinkeigaku 2007;47:761-765, PMID 18210793).
- The recurrent motor branch runs extraligamentous in about 80% of hands. A cadaveric study of 30 hands classified the branch as extraligamentous in 24, transligamentous in 4, and subligamentous or preligamentous in 1 each, the high-risk transligamentous and subligamentous courses a TCL incision can catch (Kanazuka et al, J Hand Surg Asian Pac Vol 2025;30:172-180, PMID 39800356).
- The palmar cutaneous branch can arise as much as 11 cm proximal to the wrist crease. It runs radially just after its origin so it lies against the flexor carpi radialis tendon in the distal forearm, the reason a curved incision extended toward FCR risks cutting it (Naff et al, J Hand Surg Br 1993;18:316-317, PMID 8345258).
- An injection just ulnar to the FCR border sits only 1.74 mm from the palmar cutaneous branch. The traditional approach, needle ulnar to palmaris longus at the wrist crease, stays a safer 9.47 mm from that branch though it comes closer to the median nerve itself, a trade-off to weigh before any landmark-based wrist injection or incision (MacLennan et al, J Hand Surg Am 2009;34:875-879, PMID 19410990).
- The superficial palmar arch lies roughly 15 mm distal to Kaplan's cardinal line. A cadaveric series measured the arch at 15.3 mm (±8.6 mm) distal to the line, and hand surgeons do not agree on the line's exact course, so it functions as an estimate rather than a fixed boundary for how far a release can safely extend (McLean et al, Plast Reconstr Surg 2008;121:181-185, PMID 18176219; Vella et al, J Hand Surg Am 2006;31:912-918, PMID 16843150).
- The ulnar artery courses radial to the hook of hamate in over half of wrists. Cadaveric dissection of 9 wrists found the artery radial to the hamate hook in 5 and palmar to it in 4, so the classic pisiform-to-hamate boundary of Guyon's canal understates how far radially the ulnar neurovascular bundle can sit, a real hazard when a release extends too far ulnarly (Cobb et al, J Hand Surg Br 1994;19:24-26, PMID 8169471).
- A superficial nerve connection crosses between the median and ulnar nerves in roughly 44% of hands. Dissection of 27 cadaveric palms found this Berrettini connection in 12, concentrated in a reproducible high-risk zone, and cutting it causes lasting numbness rather than a clean recovery (Marton et al, J Hand Surg Eur Vol 2022;47:851-856, PMID 35473393).
- 9 flexor tendons share the carpal tunnel with the median nerve. Four tendons of flexor digitorum superficialis, four of flexor digitorum profundus, and one of flexor pollicis longus cross under the transverse carpal ligament alongside the nerve, 10 structures compressed in the same tight space that carpal tunnel syndrome narrows (StatPearls, NBK545198).