Clinical manifestations

Presentation and course

Ulnar nerve lesions can occur at various sites (see Table 1 below), and the clinical manifestations depend in large part on the level of the lesion. The most common lesions occur at the elbow; most of these are in the retroepicondylar groove, although a significant proportion of them occur at the humeroulnar aponeurotic arcade (19; 18; 24). Compression neuropathies may rarely involve the main trunk in the forearm or the dorsal ulnar cutaneous nerve. Many ulnar lesions occur at the base of the palm where the nerve enters the hand through Guyon canal; such lesions may cause either purely motor, purely sensory, or mixed abnormalities. Lesions more distally in the palm itself usually spare all sensory branches, resulting in a pure motor syndrome that sometimes spares the hypothenar muscles.

Table 1. The Sites of Ulnar Nerve Lesions

Site of compression	Etiology
Erb point	Idiopathic conduction block
Axilla	External pressure (crutch palsy)
Upper arm	External pressure, entrapment by medial intramuscular septum (arcade of Struthers)
Ulnar groove	External pressure flexion, (elbowing), intragroove pressure, eg, repetitive elbow deformity with chronic stretch (true tardy ulnar palsy), osteoarthritic spurs, Epitrochleoanconeus muscle or ligament, proximal humeroulnar aponeurotic arcade, mass (ganglion, sesamoid bone, etc.), idiopathic
Humeroulnar aponeurotic Arcade	Entrapment by aponeurosis
Flexor carpi ulnaris exit	Entrapment by deep flexor pronator, aponeurosis
Forearm	Entrapment by hypertrophic flexor carpi ulnaris and vascular bundle
Wrist	External pressure (eg, mass bicyclist palsy), (eg, ganglion)
Palm	External pressure, entrapment by pisohamate ligament

Peripheral nerve trunks are not a random, homogeneous collection of fibers. They exhibit a complex, internal fascicular arrangement wherein fibers bound for particular targets travel together in a bundle. The internal location of a particular fascicle at the level of a compressive lesion determines the likelihood of its involvement, especially if the lesion is mild or partial. Unfortunately, a compression syndrome may not behave as a simple transverse lesion with equal involvement of all fibers distally. Selective fascicular vulnerability can result in spotty involvement and a confusing, complex clinical and electrodiagnostic picture. For example, it is not at all rare for the forearm flexor muscles or even the dorsal ulnar cutaneous nerve to be spared, even though the lesion is in the ulnar groove well proximal to the origin of these branches (47; 10; 51).

As an overview, if considering lesions as transverse "sections" (this is often not valid), pathology at different levels would produce the following five types of deficits:

(1) A lesion at the medial intermuscular septum would cause weakness of ulnar hand intrinsics plus forearm flexors, sensory loss on both dorsal and volar aspects of the hand and the fingers including the palm, and perhaps focal tenderness or a Tinel sign several centimeters above the elbow with motor conduction block at the midarm (38).

(2) A lesion in the ulnar groove would produce the same deficits but with the tenderness and Tinel sign in the groove.

(3) A lesion at the humeroulnar aponeurotic arcade might spare some forearm flexor function, depending on the individual anatomy.

(4) A lesion at the flexor carpi ulnaris exit site, or at any point more distal, would spare forearm muscles.

(5) A lesion involving the nerve in the forearm causes a deficit that mirrors its exact placement. If distal to the takeoff of the palmar sensory branch, the sensory loss may spare the palm. If distal to the takeoff of the dorsal ulnar cutaneous nerve, the sensory loss may spare both the palm and the dorsum of the hand, involving only the volar aspect of the fingers.

Ulnar neuropathy at the elbow is discussed in a separate chapter.

Ulnar nerve lesions in the wrist and hand can cause a variety of different clinical findings, depending on precise location. Findings might range from a pure sensory deficit to pure motor syndromes with weakness that may or may not involve the hypothenar muscles. This depends on whether the lesion involves the main trunk, the sensory branch only, or the deep palmar branch at different sites from just at the hypothenar muscles to the lateral palm. Wrist level lesions, if distal to the take-off of the branch to the palmaris brevis, can sometimes be localized by the presence of a palmaris brevis sign (43). This small muscle is useful to examine both clinically and electromyographically (21; 30). As a general rule, "high" ulnar lesions cause less hand clawing than "low" ones. The high lesion may also produce forearm flexor weakness that lessens the deforming pull on the lumbrical muscles.

Compression of the ulnar nerve within the forearm is rare, because the nerve is not confined within anatomical passageways as at the elbow and wrist. Harrelson and Newman reported ulnar compression in the distal forearm associated with a tender, nonpulsatile mass overlying the ulnar aspect of the forearm (27). Surgical exploration revealed that the mass consisted of hypertrophied fibers of the flexor carpi ulnaris extending along the normally tendinous distal third of the muscle; work-induced hypertrophy may have been responsible. Holtzman and colleagues managed a patient with complete conduction block 5 cm proximal to the ulnar styloid, in whom surgery revealed compression and grooving of the ulnar nerve by two fibrovascular bands crossing from the ulnar artery to the distal belly of the flexor carpi ulnaris (28). Campbell reported a similar case wherein a professional golfer developed work-induced flexor carpi ulnaris hypertrophy. The nerve was compressed by a large vascular pedicle coursing from the ulnar artery to supply the excessive muscle tissue (10). The abnormality was localized by a short segment nerve conduction study and confirmed with intraoperative electroneurography. In the latter two cases, complete resolution followed resection of the fibrovascular band.

Of the different lesions of the ulnar nerve near the wrist, the most common and extensively reported is a compression of the deep palmar branch (12). Shea and McClain classified ulnar compression syndromes of the wrist and hand into three types (46):

(1) In type I, the lesion is proximal to or within Guyon canal, involves both the superficial and deep branches, and causes a mixed motor and sensory deficit with weakness involving all the ulnar hand muscles.

(2) In type II, the lesion is within Guyon canal or at the pisohamate hiatus, involves the deep branch, and causes a pure motor deficit with a variable pattern of hypothenar weakness depending on the precise site of compression.

(3) A type III lesion is in Guyon canal or in the palmaris brevis, involves the superficial branch only, and causes a purely sensory deficit.

In the type I and III lesions, sensory loss should spare the dorsum of the hand (innervated by the dorsal ulnar cutaneous branch), as well as the hypothenar eminence, because its innervation is via the palmar cutaneous branch that arises proximal to the wrist.

Wu and colleagues reclassified 55 published cases of ulnar neuropathy at the wrist into five groups according to clinico-anatomic presentations (52). Their type I lesion corresponds to Shea and McClain type I, and their type II corresponds to Shea and McClain type III. Their types III through V all describe pure motor syndromes. Type III is caused by a lesion proximal to the branch to the hypothenar muscles, and causes global ulnar hand weakness. Type IV is caused by a lesion distal to the hypothenar branches, and causes weakness of all muscles except the hypothenars. Type V is caused by a far distal lesion just proximal to the termination of the palmar branch, and causes weakness limited to the first dorsal interosseous and adductor pollicis, but spares the other interossei and the ulnar innervated lumbricalis. The Wu classification system seems more precise and more useful than Shea and McClain system. A Wu type I lesion is the most common, and type V is the most rare.

Prognosis and complications

The prognosis depends on a number of factors, but most prominently on the severity of the neuropathy (11).

Biological basis

Etiology and pathogenesis

The etiology of cubital tunnel syndrome is hypothesized to involve compression by the surrounding soft-tissue structures and tension on the ulnar nerve created by elbow flexion. Previous studies evaluating pressures within the cubital tunnel have shown increased pressure within the cubital tunnel with elbow flexion. The combination of increased pressure and tension on the ulnar nerve will produce chronic nerve compression; thus, both will contribute to the patient’s symptoms. This compression can also be caused by "elbowing" or entrapment by some pathoanatomic structure, such as the humeroulnar aponeurotic arcade or the pisohamate ligament. It is unknown why these structures are present throughout life but suddenly cause an entrapment neuropathy. Simple decompression of the ulnar nerve at the cubital tunnel may relieve isolated pressure at that point, but it will not alter the tension placed on the ulnar nerve with elbow flexion. Simple decompression of the nerve and release of the structures maintaining the ulnar nerve in the cubital tunnel may predispose the ulnar nerve to subluxation over the medial epicondyle. Anterior transposition of the ulnar nerve will decompress the nerve and, by placing the nerve anterior to the medial epicondyle, will decrease tension on the ulnar nerve with elbow flexion.

Some neuropathies occur as a complication of underlying metabolic processes, which cause demyelination, edema, and ischemia such as diabetes mellitus, alcoholism, malnutrition, vitamin deficiency, or paraneoplastic syndromes (44). Friction may also play a role in the development of neuritis at the cubital tunnel, causing an ulnar neuropathy at the elbow (07). Less common causes include inflammation, rheumatoid synovitis, lipomas, bone fragments, ganglion in a Guyon canal (25), synovial chondromatosis of the pisotriquetral joint (36), arthropathy of the pisotriquetral joint (45), and osteophytes (07). The incidence and causes of perioperative ulnar neuropathy were examined in a series of 203 consecutive patients. In the entire prospective series, 3% of patients developed ulnar neuropathy. The incidence was 6% in patients having total hip arthroplasty. There was a significant association between a tilted body position on the operating table and development of ulnar neuropathy on the contralateral side. This position rotates the arm internally and places the ulnar nerve at risk for direct compression (32).

A review of the relevant clinical anatomy helps in understanding ulnar neuropathies. The ulnar nerve exits the thorax as a continuation of the medial cord of the brachial plexus. In the axilla it lies in close anatomical relationship to the median and ulnar nerves, and to the axillary artery. Descending through the arm, it slants posteriorly to pierce the medial intermuscular septum (the arcade of Struthers) and gains entrance to the posterior compartment. There is debate regarding whether the medial intermuscular septum can cause de novo entrapment. Most cases of compression at the arcade of Struthers are seen in failed transpositions, and are due to inadequate proximal release of the septum, resulting in secondary kinking of the nerve. The arcade of Struthers may be more an artifact of inept ulnar transposition than a natural pathoanatomic entrapment site.

As the nerve runs distally, it passes through the ulnar groove in a superficial position, covered only by skin and subcutaneous tissue, where it is especially vulnerable to external pressure. Dynamic anatomical changes occur with elbow movement that may damage the nerve, particularly when there are structural derangements due to trauma or degenerative changes (03). After traversing the ulnar groove, the nerve passes beneath the humeroulnar aponeurotic arcade. After passing under the arcade, the nerve runs through the belly of the flexor carpi ulnaris, and exits from the muscle through the deep flexor pronator aponeurosis. This thick connective tissue originates from the common flexor tendon at the medial epicondyle and lines the deep surface of the flexor carpi ulnaris. The nerve is vulnerable to entrapment both where it enters the flexor carpi ulnaris under the humeroulnar aponeurotic arcade and where it exits through the deep flexor-pronator aponeurosis (35; 02; 17; 16).

After exiting the muscle belly, the nerve runs distally just lateral to the flexor carpi ulnaris tendon. The palmar cutaneous branch separates from the main trunk in the mid to distal forearm and pursues a separate course anterior to the ulnar artery. It enters the hand superficial to Guyon canal and supplies sensation to the skin of the hypothenar region. The dorsal ulnar cutaneous branch leaves the main trunk 5 cm to 10 cm proximal to the wrist, curves dorsally to gain the back of the hand, and innervates the skin of the ulnar aspect of the dorsum of the hand and fingers. Isolated lesions of the dorsal ulnar cutaneous nerve have been reported (12). After giving off these sensory branches, the nerve enters the hand through Guyon canal.

The transverse carpal ligament roofs the carpal tunnel and dips downward to form the floor of Guyon canal. The pisohamate ligament runs from the pisiform bone to the hook of the hamate and forms the distal part of the floor of the canal. The volar carpal ligament and the thin palmaris brevis muscle form the roof of the canal. Emerging from beneath the volar carpal ligament, the nerve sends a twig to innervate the palmaris brevis muscle, and then bifurcates into the superficial terminal division and the purely motor deep palmar division. The deep palmar branch exits Guyon canal through a slit-like opening, the pisohamate hiatus. The deep branch arcs laterally to traverse the palm. These innervate the interossei and then break up into terminal branches on reaching the adductor pollicis and first dorsal interosseous. The nerve may become compressed at several different points in either the Guyon canal or in the palm.

Prevention

Prevention hinges on avoiding acute or chronic repetitive trauma.

Differential diagnosis

The differential diagnosis of ulnar neuropathies includes a number of neurologic and non-neurologic conditions. These are discussed in more detail in the chapter on ulnar neuropathy at the elbow. Particularly problematic is the distinction from motor neuron disease in patients with pure motor syndromes due to compression in the wrist and palm (29). Spinal cord pathologies must also be considered. “Numb and clumsy hands” could be a sign of lesions, such as intramedullary tumors, syringomyelia, amyotrophic lateral sclerosis, and spondylitic myelopathy. Other causes could include cervical radiculopathies or pancoast tumors (07).

Dupuytren contracture is a painless thickening characterized by fibroblastic proliferation and disorderly collagen deposition of tissue beneath the skin on the palm of the hand and fingers. Subsequently, nodules will form due to contraction of fibroblasts in the superficial palmar fascia. The possibility of a T-cell mediated autoimmune disorder as a cause of Dupuytren contracture is suggested by the demonstration of the presence of CD3-positive lymphocytes and the expression of MHC class II proteins along the affected areas. The flexor tendons are not intrinsically involved, but invasion of the dermis occurs, resulting in the characteristic puckering and tethering of the skin. Progressive contracture results in deformity and loss of function of the hand. This disorder is usually observed in white males over the age of 50 and, curiously, appears to have a pronounced genetic predisposition with up to 68% of male relatives of affected patients developing the disease at some time. Although the treatment of choice is surgery, indications for the timing of surgery exist. In general, operative management should be performed on the affected MCP joint if the contracture is 30 degrees or greater. Usually, a limited fasciectomy of the pretendinous cord is sufficient to establish normal function in the corresponding joint. Techniques for this are also varied. McFarlane favors the use of a regional fasciectomy of the pretendinous cord to prevent recurrence. Since its initial description during the sixteenth century, Dupuytren disease has been exhaustively researched. However, controversy corresponding to the exact cause of the disease is ongoing. Future nonoperative therapies may include percutaneous needle fasciotomy, skeletal traction, therapy with calcium channel blockers, and treatment with gamma interferon. The last of these treatments shows the most promise. Until any of these treatments is proven to be therapeutic, surgery is the only option for a cure.

Diagnostic workup

The primary test for workup of these conditions is electrodiagnosis (12; 13). Short segment studies similar to those employed at the elbow may help to localize wrist lesions (34). In the presence of ulnar neuropathy, the upper arm segment should be included in a routine nerve conduction study to screen for the rare but important entrapment neuropathy caused by the arcade of Struthers (39). Traumatic ulnar neuropathy at or distal to the wrist is characterized by motor symptoms and sensory and motor axonal loss by electromyography, whereas cumulative stress cases have sensory symptoms and electromyographic findings that are highly variable and noncharacteristic. Patients with no motor symptoms are more apt to show sensory distal latency abnormalities on electromyography, whereas those with motor symptoms show motor-evoked amplitude and needle electromyography abnormalities (20).

Once localization has been established by the clinical and electrodiagnostic features, imaging studies ranging from plain films to MRI may be useful. The most critical consideration is to image the correct area. An increase of nerve T2-signal of distal ulnar nerve branches and in particular of the deep/motor branch is highly accurate for the diagnostic determination of Guyon canal syndrome (31). In a study of 56 patients with clinical and electrodiagnostic evidence of ulnar neuropathy, 12 cases were non-localizable. High resolution ultrasound added value as it helped in localizing ten of twelve cases to the elbow area; one was at the wrist and another at the retrocondylar groove with a tandem lesion higher in the proximal arm (01). In another ultrasound study focusing on shear-wave elastography, 46 patients with clinical and electrodiagnostic evidence of compression at Guyon canal were compared to 39 healthy controls (41). As compared to the control group, patients with ulnar neuropathy at the wrist had increased ulnar nerve stiffness at Guyon canal, and the ratios of Guyon canal stiffness to that measured at either the distal forearm or the mid forearm were ≥ 1.5.

Table 2. Synopsis of the Recommendations of the American Association of Electromyography and Electrodiagnosis Practice Parameter on Ulnar Neuropathy at the Elbow

(1) When using moderate-elbow flexion (70° to 90° from horizontal), a 10 cm across elbow distance, and surface stimulation and recording the following abnormalities suggest a focal lesion involving the ulnar nerve at the elbow:
	• Absolute motor nerve conduction velocity from above elbow to below elbow of less than 50 m/sec.
	• An above elbow to below elbow segment greater than 10 m/sec slower than the below elbow to wrist segment.
	• A decrease in CMAP negative peak amplitude from below elbow to above elbow greater than 20%.
	• A significant change in CMAP configuration at the above elbow site compared to the below elbow site.
	• Multiple internally consistent abnormalities.
(2) If routine motor studies are inconclusive, the following procedures may be of benefit:
	• Nerve conduction study recorded from the first dorsal interosseous muscle.
	• An inching study.
(3) Needle examination should include the first dorsal interosseous, the most frequently abnormal muscle, and ulnar innervated forearm flexors. Neither changes limited to the first dorsal interosseous nor sparing of the forearm muscles exclude an elbow lesion. If ulnar innervated muscles are abnormal, the examination should be extended to include non-ulnar C8/medial cord/lower trunk muscles to exclude brachial plexopathy and the cervical paraspinals to exclude radiculopathies.
From (12).

Management

If the conduction velocity is more than 39 m per second, a period of conservative treatment is recommended. Many mild ulnar neuropathies at the elbow respond to conservative treatment (23). In general, if the patient’s motor conduction velocity across the elbow is less than 39 m per second they are offered surgery. In addition, those who do not respond to conservative treatment also require surgical exploration. Operative management is generally straightforward, except in the case of ulnar neuropathy at the elbow, where several different procedures are in common use (06). In the case of diabetic neuropathy, Aszmann and colleagues designed a study to evaluate whether decompression of a peripheral nerve at a known site of anatomic narrowing can restore sensitivity to that nerve in the diabetic. The study confirmed the observation that sensitivity can be restored to the diabetic extremity (04). In an outcome study performed by Taha and colleagues (49), results suggested that patients with cubital tunnel syndrome who have absent sensory nerve conduction seem to experience less improvement of sensory symptoms after surgery, compared with all patients with cubital tunnel syndrome described in the literature. In a series published by Murata and colleagues (37), the most common cause of ulnar tunnel syndrome was idiopathic, and most idiopathic ulnar tunnel syndrome cases were associated with carpal tunnel syndrome. The clinical symptoms of ulnar tunnel syndrome improved after surgery in all cases. Lastly, the review by Dellon (22) of the outcome after surgery for cubital tunnel syndrome presented an overview of published studies before 1989. He concluded that with a minimal amount of compression, any surgical intervention will achieve excellent results in 100% of patients. With moderate compression, anterior submuscular transposition had the best result and the least recurrence rate. Review of the studies since 1989 has shown good results using an anterior submuscular transposition of the ulnar nerve.

Table 3. Conservative Treatment of Ulnar Neuropathy at the Elbow

	• Minimization of elbow flexion • Elbow pads • Arms never crossed • Forearm supinated and resting on thigh while sitting • Telephone in asymptomatic hand only • Book stand for reading • Avoidance of external pressure • Elbow pads or night splints • Elbow resting on pillow during desk work • Nonsteroidal anti-inflammatory drugs when repetitive motion involved
Modified from: (23).

Table 4. Advantages and Disadvantages of the Surgical Procedures for Cubital Tunnel Syndrome

Decompressive procedures
	Simple decompression
		Advantages:
			(1) Simpler and quicker to perform with low risk of complications
			(2) Small linear incision avoids injury to medial antebrachial cutaneous nerve
			(3) No need to mobilize nerve from it bed and risk disrupting vascular supply (vasa nervorum) or injuring articular or muscular branches
			(4) Shorter postoperative recovery.
		Disadvantages:
			(1) Exposure not adequate to explore the proximal and distal extent of nerve for additional sites of entrapment
			(2) Does not address (and may predispose to) neuropathy from recurrent subluxation in advanced stages of disease.
			(3) Potential for entrapment in scar tissue from overlying incision
			(4) Possibly less efficacious
	Medial epicondylectomy
		Advantages:
			(1) Easy to perform
			(2) Does not require mobilization of the nerve
			(3) Relieves compressive effects of medial epicondyle in elbow flexion
			(4) Addresses recurrent subluxation over the medial epicondyle.
		Disadvantages:
			(1) Nerve is more vulnerable to external trauma both within the ulnar groove and its anterior position over the flexor-pronator origin
			(2) Potential for friction neuritis, elbow instability from injury to the ulnar collateral ligament, or flexor-pronator weakness related to detachment of its origin
			(3) Bone tenderness at site of epicondylectomy
			(4) Length of nerve visualized and explored may be inadequate.
Transposition procedures
	Subcutaneous transposition
		Advantages:
			(1) Removes the ulnar nerve away from the compressive agent at the elbow, even if the pathology is unidentified
			(2) Reduces tension on the nerve with elbow flexion
			(3) Allows complete visualization of the nerve from its proximal to distal extent.
		Disadvantages:
			(1) May devascularize the nerve
			(2) May constrict or kink the nerve proximally at the intermuscular septum, “arcade of Struthers”, or the medial head of the triceps or distally at or between the two heads of the flexor-pronator mass when elbow is fully extended
			(3) Fascial sling created to hold nerve into anterior position may entrap nerve
			(4) Nerve prone to injury due to its unprotected and superficial location
			(5) Longer and complex postoperative recuperation and rehabilitation
			(6) Longer incision and undermining of skin increases risk of bleeding and hematoma formation.
	Intramuscular transposition
		Advantages:
			Same as for subcutaneous transposition
		Disadvantages:
			Same as for subcutaneous transposition, but for significantly increased risk of scarring or fibrosis around transported nerve (cicatrix formation).
	Submuscular transposition
		Advantages:
			Same as for subcutaneous transposition, except for:
			(1) Ulnar nerve is better protected from external trauma angulation
			(2) Deeper position of nerve causes less anterior
			(3) Less risk for stretching, kinking, or constriction
			(4) Less risk for entrapment of nerve in scar tissue
From (07).

Patients with severe (grade IIB–III) cubital tunnel syndrome based on the modified McGowan classification were randomized to ulnar nerve decompression and anterior subfascial transposition, with or without supercharged end-to-side anterior interosseous nerve–to–ulnar motor nerve transfer (53). At 2 years, the anterior interosseous nerve–to–ulnar motor nerve transfer group did better on pinch strength, CMAP amplitudes (first dorsal interosseous and abductor digiti minimi muscles) and on fulfilling criteria for excellent to good results than the control group. On multivariate analysis, advanced in the interventional group predicted unsatisfactory outcome.

Special considerations

Anesthesia

The primary anesthetic consideration is to avoid ulnar compression at the elbow during general anesthesia.

During any operation, the elbows should be adequately padded and the forearm placed in supination to avoid pressure on the ulnar groove. Unfortunately, ulnar neuropathy at the elbow may occur after anesthesia in spite of seemingly adequate padding and positioning. Post anesthetic ulnar neuropathy at the elbow has a poor prognosis (35). Some patients who develop postanesthetic palsies have pre-existent ulnar nerve pathology and some postanesthetic neuropathies are subclinical (50).