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Ulnar Nerve Entrapment

by Whitney Lowe

There are two locations where the ulnar nerve is likely to be compressed in the upper extremity.The first is at the elbow in a region called the cubital tunnel; here the condition is called cubitaltunnel syndrome. The second is at the wrist as the nerve enters uyon!s canal "also known as thetunnel of uyon#. $ere% ulnar nerve entrapment is called uyon!s canal syndrome.

These two problems occur more often than we realie. 'n fact% cubital tunnel syndrome is considered the second(most(common upper(extremity peripheral(compression neuropathy% with carpal tunnel syndrome being the first. Luckily%identification of these conditions is not terribly difficult. )assage treatment is also generally effective.

Pathology

The cubital tunnel is formed by the two heads of the flexor carpi ulnaris muscle. *ne head originatesat the medial epicondyle of the humerus% while the other is derived from the olecranon process. Thetwo heads +oin to form the belly of the flexor carpi ulnaris. The ulnar nerve courses between the twoheads in a channel called the cubital tunnel. ,ubital tunnel syndrome occurs when the nerve iscompressed between the two heads of the muscle.

,ubital tunnel syndrome develops as either an acute or chronic in+ury. Though not common% acutecubital tunnel syndrome may occur from a blow directly to the posterior elbow. As a result% scartissue could develop in the tunnel% creating compression. 't is also possible that the blow coulddamage bones or ligaments in the region that press on the nerve. The blow might also sensitie thenerve to further pressure.

'n chronic compression in+uries% cubital tunnel syndrome usually develops from tightness in the flexor

carpi ulnaris muscle or prolonged periods with the elbow in flexion. -uring elbow flexion the twoheads of the flexor carpi ulnaris are pulled apart as the olecranon process moves slightly away fromthe humerus. The tunnel becomes narrower and conseuently increases pressure on the ulnarnerve. 't is common for people to experience the symptoms of ulnar nerve compression at night by

holding the elbow in flexion for long periods during sleep.

The mechanism of damage in uyon/s canal syndrome is somewhat different. uyon!s canal islocated in the wrist% ad+acent to the carpal tunnel. Like the carpal tunnel% uyon!s canal isbordered by the transverse carpal ligament "also called the flexor retinaculum#. There is adivision in the ligament near the ulnar side of the hand that creates uyon!s canal "see 0igure1#. The ulnar nerve and artery pass through uyon!s canal. 2nlike the carpal tunnel% there areno tendons that travel through uyon!s canal. Therefore pressure on the nerve fromtenosynovitis does not occur in uyon/s canal syndrome as it does in carpal tunnel syndrome.

 

3ecause there are no tendons in the canal to press on the nerve% pathological compression inuyon/s canal syndrome occurs from extrinsic factors. That means nerve compression occursfrom forces outside the canal as opposed to pressure from within. A condition like carpal tunnelsyndrome% on the other hand% involves intrinsic pressure because it comes from within the tunnel due to tendon swelling.

uyon!s canal syndrome may occur as either an acute or chronic compression neuropathy. Acute in+uries occur mostoften when the base of the hand is hit while the wrist is in hyperextension. 0alling on an outstretched hand is a goodexample. ,hronic compression in+uries occur from pressure maintained on the base of the hand for long periods. Acommon example is long(distance cycling% where the weight of the body is resting on the handlebars with the wrist inhyperextension. 'n the cycling community uyon/s canal syndrome is referred to as handlebar palsy.

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Assessment and evaluationThe symptoms of ulnar nerve compression in the two syndromes are similar even thoughthe pathologies occur in different locations. ,lients usually report pain% numbness and4orparesthesia in the ulnar nerve distribution of the hand "see hand illustration#. 't is importantto isolate the sensory symptoms to the ulnar nerve distribution because many peopleassume they have carpal tunnel syndrome with neurological symptoms in the hand.Weakness in muscles supplied by the ulnar nerve may also occur in both conditions.

While the ulnar nerve innervates a number of muscles in the forearm% motor weakness is

most evident in muscles of the hand% such as the adductor pollices. 't is an importantmuscle in grasping ob+ects. ,onseuently% the client may report difficulty in holding ob+ectsin the hand% or clumsiness when performing precision activities such as writing.

While many symptoms of these two peripheral neuropathies are similar% there are a number of factors that help distinguishthem in the evaluation process. 'f the symptoms started from an acute in+ury% identify whether the primary insult was to theelbow or the wrist. 'n chronic compression pathologies it is a little more complex% but a more thorough assessmentprovides valuable clues.

'f the symptoms are aggravated by long periods with the body weight resting on the wrist% especially if it is in ahyperextended position% uyon/s canal syndrome is implicated. 2sing a cane for walking is an example of how chroniccompression may occur in uyon!s canal. 'f the symptoms occur from long periods of resting the body weight on theelbows% or holding the elbows in a flexed position "not necessarily weight(bearing# for long periods% then cubital tunnel

syndrome is more likely.

There are a few visual indicators that may help identify ulnar nerve compression from either cubitaltunnel syndrome or uyon/s canal syndrome. As mentioned above% the ulnar nerve innervatesseveral muscles in the hand. ,ompression of the nerve in either condition may lead to atrophy of thehypothenar muscles "those located in the fleshy bundle on the ulnar side of the hand#. 'n somecases% cubital tunnel syndrome is aggravated by a postural distortion of the upper extremity calledcubital valgus "see 0igure 1#. 'n cubital valgus the nerve may be pulled taut against structuresbordering it within the cubital tunnel.

5alpation is helpful for identifying both conditions. 3ecause the region of entrapment is superficial inboth pathologies% palpating the involved area may increase symptoms. 'f manual pressure directlyover the cubital tunnel reproduces the primary complaint% then cubital tunnel syndrome is likely.

6imilarly% if pressure directly over uyon!s canal reproduces the complaint% uyon/s canal syndromeis implicated.

The neurological symptoms of cubital tunnel syndrome or uyon/s canal syndrome are apt to be reproduced with certainmotions of the upper extremity. 'f cubital tunnel syndrome is the primary problem% neurological sensations may bereproduced with elbow flexion either passively or actively. *ften the symptoms are not aggravated by simply moving theelbow into a flexed position. The elbow must be held in the flexed position for some time before symptoms recur.

 Attempting to recreate symptoms by holding the elbow in flexion is demonstrated during the elbow(flexion test describedbelow.

'f uyon/s canal syndrome is the problem% pain is common with wrist hyperextension% either actively or passively. 'nhyperextension the nerve is pulled taut across the carpal bones% and if damaged from compression% the increased tensionon the nerve will aggravate symptoms.

There are two special orthopedic tests commonly used to help identify ulnar nerve compression. The first is the elbow(flexion test. 't is primarily used to identify cubital tunnel syndrome.

This test begins with the client in a standing or seated position. With the shoulder laterally rotated% the client brings theelbow into full flexion while the forearm is supinated and the wrist is hyperextended. This is the position used whencarrying a tray% for example. 'f the condition is unilateral% it is helpful to have the client adopt the position with both sides atthe same time so a comparison with the unaffected side can be made. ,ubital tunnel syndrome is probable if symptomsare reproduced within about 78 seconds while holding this position.

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