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In Depth: Deep muscles

The deep muscles of the hand are those underneath major tendons and muscles. They are also closest in proximity to the bones of the hand.

The deep muscles of the hand have very particular functions, such as flexing or pulling the hand away from the body. Together with the hand’s other muscles, tendons, ligaments, vessels, and bones, they create one of the evolutionary tools that sets humans on top of the food chain.

  • Lumbricals: The lumbricals are four deep muscles of the hand that fan out from the center of the back of the hand out to each finger. They flex and extend the joints and bones of the fingers, both at the knuckles and the distal joints.
  • Dorsal interossei: These four muscles lie between the metacarpal bones in the palm of the hand. They assist the lumbricals. And also function in the flexion and extension of the finger.
  • Abductor pollicis longus: This forearm muscle helps abduct and extend the wrist and the thumb. It is important in holding small objects such as a pencil.
  • Abductor digiti minimi: This muscle on the pinkie side of the palm is the outermost muscle in the hand. It pulls the little finger into the hand. It is important in carrying large objects with outspread fingers, such as when palming a basketball.
  • Extensor pollicis brevis: Another important forearm muscle, this one acts in conjunction with the abductor pollicis longus to extend and abduct the thumb.

Several tendons woven together form sheaths around the three bones of each finger. They connect the muscles to the bones, which allows for finger movement when the muscles flex and extend. The deep muscles and tendons work together to produce hand strength and fine motor skills.

Repetitive stresses to these muscles, created by activities such as gripping a baseball bat for too long or sewing, can cause temporary pain or permanent damage. These pains can be fixed in numerous ways, from rest to surgery.

Extensive damage to these muscles and surrounding structures, such as tendon detachment, typically happens during major accidents or traumas. These can lead to loss of movement in an area, great pain, and often require surgery to repair the damage.

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