Definition

By: Gregory R. Waryasz, MD

The opponens digiti minimi muscle of the musculoskeletal system is characterized by being used for opposition.

It is part of the hypothenar muscles.  It consists of skeletal muscle fibers.

Its unique structural features include it being a quadrangular muscle that is deep to the abductor and flexor of the 5th digit.

The origin is the hook of the hamate and flexor retinaculum.

The insertion is the medial border of the 5th metacarpal.

The blood supply is from the ulnar artery and venous drainage is from the accompanying veins.

The innervation is from the deep branch of the ulnar nerve.

The opponens digiti minimi muscle as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.

The function of the opponens digiti minimi is to draw the 5th metacarpal anteriorly and to rotate it.  This helps to bring the 5th digit into opposition with the thumb.  The synergists are the flexor digiti minimi brevis and the abductor digiti minimi.

Common diseases include ulnar nerve palsy.

Ulnar nerve palsy can occur at any point of the course of the ulnar nerve leading to weakness and sensory changes.  Numbness and tingling can occur in the distribution of the ulnar nerve.

Commonly used diagnostic procedures include clinical history, physical exam, EMG, and MRI.

It is usually treated with bracing, NSAIDs, physical therapy, and corticosteroid injections for ulnar nerve palsy syndrome.

References

Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.

Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.

Wheeless’ Textbook of Orthopaedics: Opponens Digiti Minimi (http://www.wheelessonline.com/ortho/opponens_digiti_minimi)