Accessory first lumbrical muscle within the carpal tunnel: a case report

Area of Science:

• Anatomy
• Neurology
• Orthopedics

Background:

• Carpal tunnel syndrome is the most prevalent upper extremity entrapment neuropathy.
• While uncommon, muscles like palmaris longus, flexor digitorum superficialis, and lumbricals can cause nerve compression.
• Understanding anatomical variations is crucial for diagnosing and treating nerve entrapment.

Observation:

• Anatomical dissection of Korean cadavers revealed an unusual variant of the first lumbrical muscle within the carpal tunnel.
• This aberrant musculature was present in both wrists.
• The anomalous muscle originated from the radial side of the flexor digitorum superficialis in the distal forearm.

Findings:

• The identified anomaly was an additional muscle belly of the first lumbrical muscle.
• This aberrant muscle ran separately across the wrist, beneath the flexor retinaculum.
• The presence of this muscle variant can potentially lead to median nerve compression at the wrist.

Implications:

• This finding highlights the importance of recognizing rare anatomical variations in the carpal tunnel.
• Surgeons must be aware of such anomalies to avoid complications during carpal tunnel release surgery.
• Modified surgical approaches may be necessary when encountering this first lumbrical muscle variant.