What Is Ape Hand and What Causes It?
Ape hand is a condition in which movements of the thumb are severely limited.
The thumb may have limited extension and flexion. This means the thumb can only be moved away from and towards the hand in the plane of the palm.
The thumb will also have very limited or no ability to abduct or oppose. This means it cannot be moved in and out of the palm to pinch or grasp.
Abduction of the thumb is its ability to move towards an angle of 90 degrees in relationship to the palm. Opposition of the thumb is its ability to swing over the palm to touch the tip of the little finger.
What causes ape hand?
Ape hand is usually the result of median nerve palsy, which is commonly caused by deep injury to the wrist or forearm. This can impair the function of the thenar muscles.
The median nerve runs down the length of the arm, starting near the shoulder. It runs through the forearm, traveling through the carpal tunnel into the hand.
While the median nerve provides only motor function to the forearm, it provides both motor and sensory function to the wrist and hand, including the:
- index finger
- middle fingers
- half of the ring finger
It does not typically affect the little finger.
According to a 2018 study, the most common peripheral nerve neuropathy is median nerve mononeuropathy. This is damage that occurs to a single nerve. Although the nerve can be entrapped in the elbow, the carpal tunnel is the most common site of compression.
The thenar muscles of the thumb allow for power gripping and precision pinching. The four muscles are the:
- abductor pollicis
- adductor pollicis
- opponens pollicis
- flexor pollicis brevis
Why is it called ape hand?
When the thumb loses its ability to pinch against a finger (pincer grasp), muscles in the hand begin to atrophy. Because of the inability to oppose the thumb, the hand has an appearance that some think resembles the hand of an ape.
Since apes have opposable thumbs, ape hand is a bit of a contradictory name.
Ape hand vs. claw hand
Ape hand involves a limited range of motion in the thumb. Claw hand, however, is a condition in which the fingers are noticeably curved or bent. This can make it difficult to pick up or grasp objects with your hand. It can affect one or more fingers on one or both hands.
Like ape hand, claw hand can be caused by injuries to the arm or hand. Other common causes of claw hand include a congenital defect, a defect present at birth, and certain disorders such as diabetic neuropathy.
Conditions similar to ape hand
There are a number of other hand conditions similar to or associated with the ape hand:
Carpal tunnel syndrome
Carpal tunnel syndrome is the result of the median nerve being compressed as it travels through the carpal tunnel in the wrist.
It’s a relatively common condition characterized by pain, tingling, or numbness in the thumb, index finger, middle finger and ring finger. Sometimes these sensations can travel up the forearm.
De Quervain’s tendinosis
De Quervain’s tendinosis, also called Quervain’s tenosynovitis, is an inflammation of certain tendons in the thumb. It’s often caused by trauma to the thumb, repetitive grasping, or certain inflammatory conditions such as rheumatoid arthritis.
This condition typically causes pain and tenderness at the base of the thumb. According to the Cleveland Clinic, women are affected with De Quervain’s tendinosis 8 to 10 times more than men.
Trigger finger or trigger thumb, also known as stenosing tenosynovitis, occurs when a finger or thumb becomes stuck while in a bent position.
Trigger finger is often characterized by soreness at the base of the thumb or finger. You might also feel a popping or snapping when moving the thumb or finger. The stiffness tends to be worse in the morning, easing as the thumb and fingers are used.
Trauma to or compression of your median nerve can lead to a number of conditions, including ape hand and carpal tunnel syndrome. If you have pain in your fingers, wrists or forearms, see your doctor.
After a diagnosis, your doctor can create a treatment plan to relieve symptoms and avoid future damage.
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