Ulnar nerve compression is the second most common upper extremity compressive neuropathy (only secondary to median nerve compression neuropathy), with an incidence of 25 and 19 cases per 10 000 person-years in men and women, respectively.3
Approximately 70% involve entrapments at the elbow level, 12% lacerations, 8% stretches/contusions, and 10% other (ie, gunshot wounds [GSW], fractures, tumors.)2
Typically affects males in working age group (18-45 years) with a median income of $36 0001
From 1993 to 2006, ulnar nerve injury was the most frequent major upper extremity peripheral nerve injury resulting in hospital admission when compared with median, radial, and brachial plexus injuries.1
Healthcare costs associated with ulnar nerve injuries range from $10 563 to $42 000 per individual.1
Mechanism of injury
Entrapment/compression (most common cause of ulnar nerve injury)
Multiple causes (intrinsic versus extrinsic) and sites of compression in the upper extremity (Table 39.1)
Usually because of penetrating trauma, GSW, fractures
Blunt trauma, iatrogenic (ie, instrument positioning, prolonged tourniquet use), heterotrophic ossification, fractures, fracture malunion
Anatomic course of the ulnar nerve throughout the upper extremity predisposes the nerve for injury as it passes through constricting areas of the elbow and wrist and becomes very superficial at other areas along its course.
Basic understanding of ulnar nerve anatomy and innervation patterns guides identification of the source of pathology.
Ulnar nerve consists of nerve fibers from C7 to T1 nerve roots and lies medial to brachial artery in the upper arm and exits the
posterior compartment as it descends down the humerus to enter the anterior compartment through the medial intermuscular septum.
Enters the cubital tunnel posterior to medial epicondyle, medial to elbow joint capsule and medial collateral ligament
After exiting the cubital tunnel, it gives off muscular branches to flexor carpi ulnaris (FCU) and enters volar aspect of the forearm through heads of FCU, supplying ulnar half of flexor digitorum profundus (FDP).
In the forearm, it continues its course between FDP and flexor digitorum superficialis (FDS) and gives off the dorsal cutaneous branch (DCB) approximately 8 cm proximal to the pisiform bone. The DCB provides sensory innervation to small finger, ulnar aspect of ring finger, and ulnar aspect of carpus and hand.
At the level of the wrist, the nerve bifurcates into superficial sensory and deep motor branches at the distal aspect of Guyon canal. Deep motor branch innervates the intrinsic and thumb adductor muscles and superficial sensory gives off the fourth common digital nerve and ulnar proper digital nerve to the small finger.
TABLE 39.1 Sites of Ulnar Nerve Compression in the Upper Extremity
Paresthesias and numbness of the volar and dorsal sides of the small finger and the ulnar half of the ring finger
Hand weakness secondary to intrinsic muscle weakness, which leads to reduced grip and pinch strength, difficulty opening bottles, or a loss of coordination during fine manipulation
Occasionally, patients might complain of pain along the course of ulnar nerve from elbow into the ulnar forearm or hand
Chronicity of the symptoms should be ascertained along with exacerbating and alleviating factors, comorbidities (ie, diabetes, hemophilia), and occupation (ie, person working with vibrating tools).
Positions of the shoulder, elbow, and wrist that cause or exacerbate symptoms should be recorded.
Elbow flexion—compression of cubital tunnel
Overhead elevation—thoracic outlet syndrome
Wrist flexion—entrapment in Guyon canal
A systematic approach from the proximal origin of the nerve to the most distal aspect is required along with a through sensory and motor examination.
Inspection of the upper extremity may reveal cysts/masses along the course of ulnar nerve, deformities about the elbow joint (ie, carrying angle), atrophy of muscles of the hand.
Atrophy is most readily appreciated in the first dorsal interosseous muscle in the first web space.
Sensory examination reveals impaired sensation in little and ring fingers as quantified by two-point discrimination or Semmes-Weinstein monofilament testing.
Note—ulnar nerve injury distal to branching of DCB may present with normal sensation along the dorsal aspects of little and ulnar side of ring finger. Injuries at Guyon canal may also have varying presentation depending on zone of injury (see Table 39.1 for details).
Motor examination findings vary depending on the exact nature and chronicity of the injury, as motor function is usually not associated with mild compression. Moderate to severe or prolonged compression can cause muscle weakness and atrophy, whereas a complete transection presents with paralysis.
Resistive testing of FDS to the ring and little finger as well as ulnar nerve innervated small muscles in the hand must be performed.
Examiner should be aware of anomalous innervation patterns as seen in Martin-Gruber communication (seen in 7.5% of the population) or Riche-Cannieu anastomosis that may blur the clinical presentation.6,7,8
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