Surgical Anatomy of the Supraretinacular Fat Pad: Sensory Innervation and Preservation in Open Carpal Tunnel Release.

Background and objectives: Postoperative pain may occur following open carpal tunnel release (OCTR). Various causes have been postulated. During OCTR, adipose tissue located between the palmar aponeurosis and the flexor retinaculum is exposed. It is unknown whether damage to this pad of supraretinacular fat (SRF) might contribute to postoperative palmar pain or tenderness. We studied the sensory innervation of the SRF exposed in OCTR to assess whether SRF damage could potentially generate pain.

Methods: A microanatomic dissection of the innervation and vascular supply of the SRF was performed in 25 embalmed human cadaveric upper limbs. Eight fat pads were removed en bloc for histological evaluation. Three-dimensional reconstructions were made based on immunohistochemically stained sections using computer-assisted microscopy.

Results: The SRF is the radial continuation of the hypothenar fat pad that covers the neurovascular bundle in the Guyon canal. The fat pad is richly innervated and contains Pacinian corpuscles. The sensory innervation originates exclusively from the ulnar nerve (palmar branch) and its vascular supply from the ulnar artery. The integrity of the SRF can be preserved by detaching it from the flexor retinaculum in a radial to ulnar fashion.

Conclusion: The SRF, which is exposed during OCTR, is richly innervated by sensory fibers from the ulnar nerve. It is the radialmost extension of the hypothenar fat pad. In view of its rich innervation, damage to the SRF during OCTR might generate postoperative pain. Preserving its integrity during OCTR is technically possible and even simplifies the procedure. Clinical trials are needed to corroborate whether preservation of the SRF during OCTR indeed makes a clinical difference in postoperative pain generation.