Third Lumbrical Muscle of Hand

Origin

The third lumbrical muscle of hand consists of two heads:

- the lateral head, which originates from the medial aspect of the tendon of flexor digitorum profundus that travels to the middle finger;

- the medial head, which originates from the lateral aspect of the tendon of flexor digitorum profundus that travels to the ring finger.

Insertion

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

Key Features & Anatomical Relations

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

- anterior to the second palmar and third dorsal interossei muscles of hand;

- posterior to the palmar aponeurosis;

- medial to the tendon of flexor digitorum profundus that travels to the middle finger;

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

Actions & Testing

The third lumbrical muscle of hand simultaneously flexes the fourth metacarpophalangeal joint and extends the interphalangeal joints of the ring finger, which occurs when the second palmar and fourth dorsal interossei muscles of hand contract simultaneously with it.

The third lumbrical muscle of hand can be tested by simultaneously flexing the fourth metacarpophalangeal joint and extending the interphalangeal joints of the ring 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.