Bilateral extensor pollicis et indicis accessorius: clinical and anatomical perspectives

Area of Science:

• Anatomy
• Human Anatomy
• Musculoskeletal System

Background:

• The extensor muscles of the hand are vital for thumb and finger extension.
• Thumb extension involves the extensor pollicis longus and brevis muscles.
• Index finger extension is facilitated by the extensor indicis and digitorum muscles.

Purpose of the Study:

• To describe a rare bilateral anatomical variation: the extensor pollicis et indicis accessorius.
• To document a single tendon bifurcating to insert on both the thumb and index finger.

Main Methods:

• Bilateral dissection of a 92-year-old female donor.
• Embalmment using a formaldehyde-based fixation method.

Main Results:

• An accessory extensor pollicis et indicis accessorius muscle was found bilaterally in the deep posterior forearm compartment.
• A single tendon from this muscle bifurcated distally, inserting on the thumb and index finger.
• Bilateral descriptions of this anomaly are rare in existing literature.

Conclusions:

• The term extensor pollicis et indicis accessorius muscle is recommended for this configuration.
• Existing classification systems for accessory extensor muscles should be revised.
• Accessory extensor muscles originating from extensor pollicis longus, extensor indicis, or ulna should be included in revised classifications.