The Effect of the Lumbrical Muscle Position on Carpal Tunnel Syndrome

Carpal tunnel syndrome (CTS) is a compressive neuropathy of the median nerve at the wrist, yet the role of lumbrical muscles in CTS remains unclear. This study investigates the impact of lumbrical muscle position on the outcomes of open carpal tunnel release in CTS patients.

Patients with CTS indicated for surgical release underwent pre-operative ultrasound to dynamically assess lumbrical positioning, followed by open carpal tunnel release with flexor tenosynovectomy. Intra-operative assessment of lumbrical position was recorded relative to the transverse carpal ligament (TCL), and patients completed the Boston Carpal Tunnel Questionnaire pre-and post-operatively.

A total of 147 wrists in 114 patients were included in the study. On pre-operative ultrasound assessment, the most proximal lumbrical position in maximal passive finger flexion was distal to the TCL in 13 cases, at the level of the TCL in 19 cases, and proximal in 115 cases. Intra-operatively, the most proximal lumbrical muscle position was distal in 19 cases, at the level of the TCL in 69 cases, and proximal in 59 cases. Patients with more proximal lumbrical positioning had poorer clinical outcomes, with less improvement in manual workers compared to non-manual workers. Intra-operatively, greater excursion was observed in manual workers compared with non-manual workers. Manual workers were seen to have less clinical improvement post-operatively.

This study suggests that greater lumbrical excursion into the carpal tunnel is associated with worse outcomes following release, especially in manual workers. These findings may assist in patient discussions on surgical expectations and outcomes.