The thenar eminence refers to the bulge that can be seen at the base of your thumb. It's made up of three separate muscles that work to control the fine motions of the thumb.
We'll take a closer look at the thenar eminence, its function, and conditions that may affect it.
Opponens pollicis
The opponens pollicis is the largest of the muscles found in the thenar eminence.
Its function is very important to what makes human thumbs opposable. The opponens pollicis works to move the thumb away from the other fingers of the hand. During this motion, the thumb rotates so that it opposes, or is across from, the other four fingers of the hand.
This motion is very important for tasks such as gripping and grasping objects.
Abductor pollicis brevis
The abductor pollicis brevis is located above the opponens pollicis along the outside of the thumb. Its function is to help move the thumb away from the index finger.
This movement can be illustrated if the hand is laid flat on a surface and the thumb is moved away from the hand.
Flexor pollicis brevis
The flexor pollicis brevis is also located above the opponens pollicis but is located on the inside of the thumb. It's responsible for bending the thumb toward the pinky finger.
This movement can be demonstrated by bending the first joint of the thumb. When this occurs, the thumb should bend so that it points toward the pinky finger.
Click on the muscles of the thumb to see the opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis.
The median nerve supplies nerves to all three muscles in the thenar eminence. This median nerve originates from a group of nerves called the brachial plexus.
The median nerve runs along the inside of the arm where it eventually crosses over the elbow, supplying nerves to the muscles of the forearm, wrist, and hand.
A small portion of the flexor pollicis brevis, referred to as the deep head, is supplied with nerves by the ulnar nerve. Additionally, the opponens pollicis is supplied with nerves by the ulnar nerve in about 20 percent of people.
Like the median nerve, the ulnar nerve originates from the brachial plexus. It moves down the arm, crosses the elbow along the inner aspect and then moves along the inside of the forearm. It also gives nerves to parts of the forearm, wrist, and hand.
The scientist John Napier once said, 'The hand without a thumb is at worst nothing but an animated spatula and at best a pair of forceps whose points don't meet properly.' Indeed, the thumb is very important for the ways in which we interact with objects in the environment.
The thenar eminence helps to control the fine movements of the thumb, including being able to grab, grip, and pinch objects.
The abductor pollicis brevis and the flexor pollicis brevis allow for movement of the thumb away or towards the other fingers of the hand. The opponens pollicis enables the thumb to be opposable. These movements allow us to carefully handle and manipulate items and objects.
There are several conditions that can affect the thenar eminence, leading to a decrease in function or even atrophy of the muscles.
You may be experiencing an issue with the muscles of the thenar eminence if you notice:
- Numbness or 'pins and needles' in your thumb. These sensations are typically due to pinching or pressure on the median nerve.
- Muscle weakness. People with weakened thenar eminence muscles may grip objects less soundly and be more prone to dropping them.
- Pain. Most related pain may radiate from the base of the thumb.
- Deformity. If you notice this around the base of your thumb, it can be due to atrophy of the muscles of the thenar eminence.
Some examples of conditions that may affect the thenar eminence include:
- Carpal tunnel syndrome. This condition is caused by a compression or pinching of the median nerve as it runs through the wrist. Common symptoms include numbness, tingling, and weakness.
- Basal thumb arthritis. This condition is due to breakdown of cartilage around the lower thumb joint. While affecting the joints around the thenar eminence and not the muscles themselves, the condition can cause loss of motion or weakness of the thumb.
- Trauma to the forearm, wrist, or thumb. Injury to the lower arm can predispose people to nervous or arthritic conditions that may affect the thenar eminence. For example, a forearm fracture that damages the median nerve may lead to a decrease in sensation in the area of the thumb.
- Mass or tumor. A mass or tumor at or around the thenar eminence is very rare. Where present, this can cause symptoms similar to carpal tunnel syndrome.
- Amyotrophic lateral sclerosis (ALS). ALS is a disease of the nervous system that progressively weakens the muscles of the body. Atrophy of parts of the thenar eminence is an early clinical sign of ALS.
Try the exercises below to maintain the strength of the thenar eminence. If you're unsure about any of these exercises or have recently injured or had surgery on your forearm, wrist, or hand, talk to your doctor first.
Thumb flex and extension
Raise your hand, making sure that your thumb is positioned away from your fingers. Move your thumb across your palm so that it's touching just below your pinky finger.
Hold each position for 10 to 15 seconds, performing 10 reps with each hand.
Thumb extension with rubber band
Lay your hand flat on a table or other hard surface. Place a rubber band around your hand so it sits at the base of your finger joints. Gently move your thumb away from your other fingers as far as it can go. Hold this position for 30 to 60 seconds and then release.
Repeat 10 to 15 times with each hand.
Hand grip exercise
Pick up a tennis or similar-sized ball in one hand. Squeeze the ball as hard as you can for between 3 and 5 seconds before slowly relaxing your grip.
Repeat this 10 to 15 times in the same hand and then with the other hand.
Pinch strength exercise
Pick up a soft foam ball between your thumb and index finger. Pinch the ball, holding the position between 30 and 60 seconds. Slowly release the pinch.
Repeat 10 to 15 times with the same hand and again with the other hand.
Thumb-to-finger touch
Hold your hand up in front of you. Gently touch your thumb to each of your other four fingers, holding each position for 30 to 60 seconds.
Repeat at least 4 times for each of your hands.
The thenar eminence is a group of three small muscles at the base of the thumb. Despite their small size, they're very important for controlling fine thumb movements such as grabbing and pinching.
The thenar eminence can be affected by a variety of conditions that can lead to a decrease in range of movement or muscle function. If you believe you're experiencing symptoms consistent with one of these conditions, make an appointment to see your doctor.