The little finger is the 5th number of our finger. It is surrounded by muscles, supplied with blood flow, and innervated by nerves. There are situations when this particular part of our finger becomes weak, and can’t move medially with wrist extended.
Adductor palmar interosseous palsy is the weakness or paralysis of the adductor palmar interosseous muscle. This muscle surrounds the fifth finger & together with the hypothenar muscles, they are innervated by the ulnar nerve. The adductor palmar interosseous adducts the fifth finger.
Ulnar neuropathy is a term that best describes any damages to the ulnar nerve. This can be caused by either of the followings:
- Cerebral stroke,
- Ulnar nerve lesion by insufficient blood flow.
- Hyper-activity of the hypothenar muscles after surgical repair,
- Syringomyelia.
Ulnar neuropathy involves palsy of both adductor palmar interosseous and hypothenar muscles from ulnar nerve damage. This then causes exclusive abduction of the fifth finger by the extensor digiti mini, innervated by the radial nerve.
It is common for most patients to complain of adductor palmar interosseous palsy during freezing temperatures. Constriction of blood flow to this muscle would also affect the muscle & ulnar nerve innervating it. This results in lateral displacement of the fifth finger even when you try to align them together medially
Diagnosis, treatment & management of ulnar neuropathy
Testing for adductor palmar interosseous palsy and ulnar neuropathy require the Warternburg sign. This tests for the motor function of the ulnar nerve. To do this:
- Pronate the forearm and fully extend the wrist.
- Intermittently abduct and adduct all fingers.
- A positive Warternburg sign indicates little finger abduction.
Treatment and management require identifying the true cause of fifth finger abduction. Little finger abduction can also be due to ligament tear. A proper way to manage adductor palmar interosseous palsy in the cold is through warming the hands. This condition is self-limiting & reversible if blood flow to tissue is quickly restored.
Muscle paralysis from ulnar neuropathy may require radialization of the extensor digiti mini. This is done to reroute this muscle from the 5th to 4th extensor compartment of the metacarpophalangeal joint.