Anatomy of the Extensor Indicis Muscle

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

The extensor indicis muscle is part of the fourth dorsal extensor compartment of the forearm.
It lies deep to the extensor digitorum communis muscle.
It has the most distal muscle belly within the fourth dorsal compartment.
This distal muscle belly is clinically important, as it helps in identification of the extensor indicis muscle during tendon lacerations involving multiple extensor tendons.
The tendon of the extensor indicis lies ulnar to the extensor digitorum communis tendon to the index finger.

The muscle is examined by:
- Asking the patient to make a fist
- Then asking the patient to extend the index finger independently

Two tendons contribute to extension of the index finger:
- Extensor indicis muscle
- Extensor digitorum communis tendon to the index finger

Indications for Tendon Transfer Using Extensor Indicis

Rupture of the extensor pollicis longus tendon
- Extensor pollicis longus tendon may rupture following a nondisplaced fracture of the distal radius
- This results in inability to extend the thumb
- The extensor indicis tendon can be transferred to restore thumb extension
Median nerve injury
- Extensor indicis opponensplasty may be performed to restore thumb opposition

During tendon transfer:
- The extensor indicis tendon should be sectioned proximal to the sagittal hood
- This preserves independent extension of the index finger through the extensor digitorum communis

In cases of rheumatoid arthritis:
- The extensor digitorum communis tendon to the index finger may already be ruptured
- In such situations, transfer of the extensor indicis tendon is contraindicated, as it would eliminate index finger extension

Extensor indicis provides independent extension of the index finger
It is a reliable donor tendon for reconstruction
Proper identification and preservation of index finger extension are essential during tendon transfer