CLINICAL INFORMATION

32yo female presenting with persistent thenar eminence discomfort and ache 3 months post Carpal Tunnel Release (CTR).

 ULTRASOUND FINDINGS

The palmar cutaneous branch of the median nerve (PCBMN) is identified deep to the released and thickened transverse carpal ligament (TCL). Just proximal to penetrating the thickened TCL the nerve is thickened suggesting compression and irritation of the nerve (see below video). This may explain the prolonged discomfort at the thenar eminence post CTR.

DISCUSSION

The PCBMN is the last branch of the median nerve in the forearm and usually arises from the median nerve 5-6cm proximal to the TCL. The PCBMN generally arises from the radial margin of the median nerve (MN)  and can be seen running alongside the median nerve between the palmaris longus tendon and flexor carpi radialis (FCR) tendon . A vast majority of PCBMNs run superficial to the TCL with only a small percentage running deep to the ligament before penetrating it to run its customary superficial course.

CTR is a common surgery performed to reduced pressure with the carpal tunnel and involves surgically releasing the transverse carpal ligament (TCL) which form the roof of the carpal tunnel. Post surgical complications are rare but widely reported and scarring of the ligament with entrapment of the PCBMN is one of these potential complications.

TEACHING NOTES

The median nerve supplies sensation in the radial 3.5 fingers but NOT the thenar eminence region which is supplied by the PCBMN. If there is sensory deficit or discomfort of the thenar eminence, particularly post CTR, this sensory branch should be identified and assessed along its visible length.

PCBMN seen deep to TCL between the Median Nerve and FCR. Thickening of PCBMN is noted just before it penetrates the thickened post release TCL.

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