Preserving the superficial branch of the radial nerve during carpometacarpal and metacarpophalangeal joint arthroscopy: an anatomical study.

Background: The superficial branch of the radial nerve (SBRN) is potentially at risk during thumb carpometacarpal (TCM) or thumb metacarpophalangeal (TMP) joint arthroscopy. The aim of this anatomical study was to describe the different branching patterns of the SBRN and to optimize positioning of portals during TCM and TMP arthroscopy.

Methods: The SBRN was dissected in 30 forearms. Three branches of the nerve (SR1, SR2, and SR3) were recorded and distances between SBRN branches and portals used for carpometacarpal (TCM) and metacarpophalangeal (TMP) joints of the thumb arthroscopy were measured. Three main portals were used for TCM joint arthroscopy. These portals were an ulnar portal (1-U), a radial portal (1-R), and an accessory portal (D-2). A radial metacarpophalangeal (MCP-rad) and an ulnar metacarpophalangeal (MCP-uln) portal were used for TMP joint arthroscopy.

Results: In 24 cases (80%), the 1-R portal was inserted radially (volar) to SR3 at a mean distance of 4.8 mm (0-8). In the remaining six cases (20%) when 1-R portal was inserted ulnar (dorsal) to SR3, the distance was less than 2 mm in all cases. SR3 was always far from the 1-U portal at a mean 13 mm (7-22). The D-2 portal was always close to SR2-D1 at a mean distance of 1.7 mm (0-6). The distance from SR2-D2 and D-2 portal was also inferior by 5 mm. At the level of the metacarphalangeal joint of the thumb, the MCP-rad portal was always situated dorsally and very close to SR3, at a mean distance of 1 mm (0-5). The MCP-uln portal was also situated dorsal to SR2-D1 at a mean distance of 3.7 mm (1.5-6.5).

Conclusion: The results of this anatomical study confirm actual reported findings about the SR2 and SR3 branches. These two branches of the SBRN are the most at risk of injury during TCM and TMP joint arthroscopy. According to our measurements, the 1-U portal is a safer portal than 1-R and D-2 portal for TCM arthroscopy and should be preferred for surgery necessitating only one portal. Concerning TMP arthroscopy, the SBRN appears less at risk of injury when using a MCP-uln portal and safer than MCP-rad which is at risk at less than 5 mm from the extensor pollicis longus tendon.