First Lumbrical Muscle of Hand

Origin

The first lumbrical muscle of hand originates from the lateral aspect of the tendon of flexor digitorum profundus that travels to the index finger.

Insertion

The fibers of the first lumbrical muscle of hand travel inferiorly to the index finger and insert, via a short tendon, onto the lateral aspect of the extensor expansion of the index finger.

Key Features & Anatomical Relations

The first lumbrical muscle of hand is found in the central compartment of the hand. It is a short, wormlike, unipennate skeletal muscle. It is located:

- anterior to the adductor pollicis muscle and the first dorsal interosseous muscle of hand;

- posterior to the palmar aponeurosis;

- lateral to the tendon of flexor digitorum profundus that travels to the index finger.

Actions & Testing

The first lumbrical muscle of hand simultaneously flexes the second metacarpophalangeal joint and extends the interphalangeal joints of the index finger, which occurs when the first palmar and first dorsal interosseous muscles of hand contract simultaneously with it.

The first lumbrical muscle of hand can be tested by simultaneously flexing the second metacarpophalangeal joint and extending the interphalangeal joints of the index finger. While holding this position, an examiner tries to either extend the metacarpophalangeal joint or flex the interphalangeal joints of the same finger (Sinnatamby, 2011).

References

Sinnatamby, C. S. (2011) Last's Anatomy: Regional and Applied. ClinicalKey 2012: Churchill Livingstone/Elsevier.