Ape hand also called Simian hand is a deformity of thumb characterized by an inability to abduct the thumb or by extension of thumb parallel to the plane of the fingers (thumb normally extends perpendicular to the palm)
It is caused by Median Nerve injury (also called Median claw lesion) which causes wasting of the muscles of the thenar eminence. So the palm appears flattened with an extended thumb.
Why is it named so?
Supposedly this name is derived due to its resemblance to an ape’s hand. But the term “Ape Hand Deformity” is a misnomer since apes have opposable hands.
The opposable thumb is indispensable to men. The opposition of the thumb refers to the rotation of the thumb along its long axis such that it can touch each fingertip of the same hand.
Median Nerve & Median Nerve Injury:
Median Nerve (C5-T1) is a peripheral nerve of the hand which originates from the brachial plexus around the axilla. It begins near the shoulder and runs down the arm length supplying flexors of the forearm and muscles of the hand, including the thenar muscles and two lateral lumbrical. It also supplies sensory innervations to the lateral palm and three and three and a half fingers.
According to research, Median nerve mononeuropathy is the most common peripheral neuropathy in the world. It can occur due to the myriads of causes. The two most common etiologies of median nerve injury are:
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- Traumatic e.g., fractures or penetrating injuries
- Chronic compression e.g., carpal-tunnel syndrome or tumor (Schwannoma)
As the nerve runs through the entire length of the hand, the nerve lesion can be a
- Proximal lesion (above elbow)
- Distal lesion (below elbow)
The motor and sensory deficits produced due to median nerve injury depend on the site of the lesion.
Ape hand deformity is caused due to a distal nerve lesion either near the elbow or wrist. Thumb is rotated and adducted. The lesion causes a wasting of the following thenar muscles.
- Adductor pollicis
- Abductor pollicis brevis
- Flexor pollicis brevis
- Opponens pollicis
These above mentioned four thumb muscles dynamically allow for power gripping and pinching of objects. Hence due to muscle atrophy in Ape Hand Deformity, these abilities are lost.
Hand deformities similar to Ape Hand Deformity:
There are a few other hand deformities akin to Ape hand deformity. These include:
Carpal Tunnel Syndrome:
If the median nerve gets compressed in the carpal tunnel in the wrist, it causes the Carpal tunnel syndrome.
Tingling, numbness, and pain in the thumb, index finger, Middle finger, and ring finger sometimes even in the forearm.
Impaired flexion of the thumb, index, and middle finger and thenar muscle atrophy similar to Ape hand deformity.
Tinel test and Phalen test are used to diagnose Carpal tunnel syndrome.
Hand of Benediction:
Also known as Preacher’s hand, it occurs due to a proximal lesion of the median nerve i.e., if the nerve is compressed in the forearm or at the elbow.
Often confused with ape hand deformity, Claw hand is a condition that is characterized by curved or bent fingers. This may affect one or both hands.
Claw hands can be caused later in life due to any injury to the arm, diabetic neuropathy, or can be present at birth.
Like Ape hand this condition also makes it difficult to grasp or pick up any object with your hand.
Trigger finger occurs when a finger or thumb gets stuck in a bent position. Tendons in the thumb or fingers get inflamed due to repetitive or forceful movement, which causes stiffening.
Signs and symptoms include soreness at the base of a thumb or finger.
De Quervain’s Tendinosis:
Inflammation of certain tendons of the thumb due to repetitive movement or rheumatoid arthritis causes a condition called Quervain tenosynovitis.
It is characterized by pain and tenderness at the base of the thumb.
Pronator syndrome occurs when the “Pronator teres” muscle compresses the median nerve in the forearm.
The patient complains of loss of sensation over thenar eminence and discomfort in the forearm during activity.
Diagnosis and Evaluation:
On physical examination, one may find a “bottle sign,” i.e., when a person grasps a long cylindrical object (e.g., a bottle) in his hand, there is some gap present between the skin of the hand and the object.
Bottle sign is related to the weakness of the thenar muscles due to nerve injury.
After the history and physical examination, the following diagnostic procedures can be used.
- Nerve conduction velocity- This can detect any impairment in the median nerve conductance
- Electromyography (EMG) – Any pathology of the muscles innervated by the median nerve can be determined. This will also help to exclude other causes such as polyneuropathy.
Treatment and Management:
Management mainly depends upon the etiology of median nerve injury. In the case of Carpal tunnel syndrome, splints can be used.
Some other conservative therapies are:
- Physiotherapy (gentle exercises and massage help in the rapid recovery of nerve injury)
- Avoidance of repetitive hand and wrist movements
Prognosis is usually good. It depends upon the severity of nerve injury and the younger the patient, the better the prognosis. Conservative therapies help in the speedy improvement of symptoms. Symptoms get improved within two to six weeks. The complete healing time varies from four months to two and a half years.
In case of a nerve injury, it is crucial to consult a specialist. Stick to the treatment plan your doctor prescribes you. Precautions must be taken to prevent further injuries.