Preservation of the Medial Cutaneous Nerve of the Forearm During Carpal Tunnel Release
Critical Clarification
The medial cutaneous nerve of the forearm does not traverse the carpal tunnel and is not at risk during standard carpal tunnel release surgery. The nerve at risk is the palmar cutaneous branch of the median nerve (PCBMN), which provides sensation to the thenar eminence and palm. This is the most commonly injured nerve during carpal tunnel surgery and causes postoperative pillar pain and scar hypersensitivity 1, 2, 3.
Surgical Technique to Preserve the Palmar Cutaneous Branch
Optimal Incision Placement
Position your skin incision over the distal third of the transverse carpal ligament, as this area has the lowest frequency of sensory branches crossing the surgical field 3.
The subcutaneous layer overlying the distal third of the transverse carpal ligament is relatively devoid of sensory branches and represents the safest surgical zone 3.
Terminal branches of the PCBMN cross the surgical field in approximately 40-47% of cases, originating an average of 1.05 cm distal to the proximal border of the carpal tunnel 2, 3.
Make your incision at least 0.5 cm ulnar to the palmaris longus tendon to avoid the radial branches of the PCBMN, which average 0.81 cm radial to this landmark 4.
Intraoperative Nerve Identification and Protection
Actively identify and preserve crossing cutaneous branches through careful subcutaneous dissection before dividing the transverse carpal ligament 2.
Use loupe magnification to identify sensory branches in the subcutaneous tissue 4.
Branches cross the incision with either transverse (52%) or oblique proximal-distal radio-ulnar (48%) courses 3.
When branches are identified and preserved, patients experience no postoperative pillar pain or scar hypersensitivity 2.
Alternative Technique for Proximal Visualization
Consider a biportal technique with a second proximal incision if you need better visualization of the proximal transverse carpal ligament and antebrachial fascia, while keeping the main incision in the safe distal zone 3.
A minimally invasive approach using a small transverse incision proximal to the wrist fold with a grooved guide directed toward the fourth finger can achieve 99.8% symptom resolution with minimal complications 5.
Common Pitfalls to Avoid
Avoid incisions that extend too far proximally or radially, as the PCBMN typically originates 4.5 cm proximal to the distal wrist crease and branches radially 4.
Do not assume the subcutaneous layer is safe throughout the entire surgical field—40-47% of patients have crossing branches that require identification 2, 3.
Avoid blind division of subcutaneous tissue without first identifying potential nerve branches under magnification 4.
Anatomic Considerations
The motor branch of the median nerve (recurrent branch) is extraligamentous in 60%, subligamentous in 34%, and transligamentous in only 6% of cases 1.
The palmar cutaneous innervation pattern is highly variable, with five distinct anatomic types described based on contributions from median and ulnar nerves 1.