Ape Hand Deformity

Ape hand deformity is a condition in which the thumb is permanently rotated and adducted, resulting in loss of its ability to oppose the other fingers. The deformity occurs following injury to the distal median nerve, which supplies the muscles that control the thumb.[1] Thumb abduction refers to the ability to move the thumb at a 90° angle away from the plane of the palm. Opposition involves movement of the first metacarpal across the palm so that the thumb can meet the tip of the little finger. In ape hand deformity, thumb flexion and extension may also be limited.

Illustration: Ape Hand Deformity.

The term "ape hand" is misleading, however, because apes do in fact have opposable thumbs. Because of the functional limitations of the thumb in this deformity, some consider the hand to resemble an ape's hand.

Mechanism of Injury / Pathological Process

The mechanism of injury involves deep injuries to the arm, forearm, or wrist that damage the median nerve. This nerve injury impairs the function of the thenar muscles and the opponens pollicis, leading to loss of thumb opposition and contributing to the development of ape hand deformity.[2]

Clinical Presentation

The condition is part of median nerve palsy and typically presents with difficulty moving the thumb in different planes. The patient has a limited range of motion of the thumb, particularly for opposition and abduction. This may make daily activities requiring a precision grip difficult, such as holding a pen or picking up small objects.

Typical symptoms include:

• Permanent adduction and rotation of the thumb.

• Reduced strength in the thenar muscles, including the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis.

• Inability to bring the thumb toward the little finger (opposition).

• Possible thenar muscle atrophy in long-standing injury.

• Limited thumb flexion and extension.

• Sensory changes in the distribution of the median nerve, which may include numbness or tingling in the thumb, index finger, middle finger, and radial half of the ring finger, depending on the extent of the injury.

Treatment and Interventions

Treatment of ape hand deformity depends on the severity of the condition and the cause of the median nerve injury. The following interventions may be considered:

Surgery

In severe cases, surgery may be recommended to repair damaged nerves or relieve pressure on the median nerve. This may include decompression surgery or nerve grafting.

Medical Treatment

• Anti-inflammatory medication: Used to reduce inflammation and pain.

• Corticosteroid injections: May be effective in relieving symptoms caused by nerve compression or inflammation.

Physiotherapy and Occupational Therapy

• Muscle-strengthening exercises: Focus on strengthening the thenar muscles and improving thumb range of motion, particularly opposition and abduction.

• Neural mobilization: Techniques intended to improve nerve gliding and reduce pressure on the median nerve.

• Functional training: Assistance with returning to daily activities that require a precision grip.

Dynamic Splinting

• Dynamic splints (C-splints) can be used to position the thumb in opposition, helping to prevent further deformity and support rehabilitation.

Prognosis

Ape hand deformity may improve without surgery in some cases, particularly when the condition is mild. Regular physiotherapy has been reported to help restore muscle strength and function, as indicated by a 2017 study. A combination of splinting and physiotherapy may support faster recovery and help prevent secondary complications such as stiffness or further atrophy.[3][4][5]

Differential Diagnoses

When a patient presents with signs of ape hand deformity, it is important to exclude other conditions that can produce similar clinical findings:

1. Carpal Tunnel Syndrome

   • Caused by compression of the median nerve within the carpal tunnel.

   • Symptoms: Tingling, numbness, and weakness in the thumb, index finger, middle finger, and radial side of the ring finger.

   • Typically associated with nocturnal pain and a positive Tinel or Phalen test.

2. De Quervain's Tenosynovitis

   • Inflammation of the tendon sheaths of the abductor pollicis longus (APL) and extensor pollicis brevis (EPB).

   • Symptoms: Pain and swelling at the base of the thumb, particularly during gripping or twisting movements.

   • Positive Finkelstein test.

3. Trigger Finger

   • Caused by thickening of the tendon or tendon sheath, which interferes with smooth movement of the finger.

   • Symptoms: Pain at the base of the finger; the finger may "lock" in a flexed position before clicking back into extension.

   • Often associated with overuse or inflammatory conditions such as diabetes or rheumatoid arthritis.

Assessment of Differential Diagnoses

A thorough clinical examination, including history taking, palpation, and specific tests such as the Finkelstein test or Tinel sign, combined with diagnostic imaging and, when indicated, electrophysiological testing such as EMG, may be required to establish an accurate diagnosis.

Sources:

1. Dydyk AM, Negrete G, Cascella M. Median nerve injury.[1]

2. Gross Anatomy - The Brachial Plexus. Available from; https://web.archive.org/web/20090904141914/http://www.upstate.edu/cdb/grossanat/limbs2.shtml (Last accessed 11/Oct/2020)

3. Washington State Department of Labor and Industry. Work-Related Proximal Median Nerve Entrapment (PMNE) Diagnosis and Treatment (PDF). 2009.

4. US National Library of Medicine. MedlinePlus.  Distal median nerve dysfunction. Available from; https://medlineplus.gov/ency/article/000691.htm (Last accessed 11/10/2020)

5. Amelot A, Lechanoine F, François P, Terrier LM. Bilateral ape hand deformity. Neurology. 2017 Aug 8;89(6):638-9. [2]

6. FSUMedMedia | Claw Hand, Ape Hand, and the Sign of Benediction: Animated Review | Available at: https://www.youtube.com/watch?v=0AAligXLJ1A [Last accessed: 11/17/2021]