Ulnar Neurolysis (Simple Decompression) for Cubital Tunnel Syndrome

The first description of surgical treatment for ulnar neuropathy around the elbow occurred in 1816 when Henry Earle described transecting the ulnar nerve before it enters the cubital tunnel in a 14-year-old girl suffering from painful ulnar neuropathy. Although this method relieved her pain, it resulted in paralysis of the ulnar innervated muscles and loss of sensation in the ulnar sensory distribution. ¹ Surgical treatment of ulnar neuropathy around the elbow has gone through a number of iterations through the years before arriving at our current approach, including ulnar neurolysis, with or without transposition. Recent iterations have not really changed these approaches per se, but rather they have sought to make the approaches more minimally invasive with smaller incisions or the use of the endoscope without significant change in outcomes.

Compressive ulnar neuropathy around the elbow—cubital tunnel syndrome—is second only to carpal tunnel syndrome in frequency of compressive neuropathies. There are approximately 75,000 new cases of cubital tunnel syndrome annually. ²^, ³ Four main surgical options are currently used for cubital tunnel syndrome: open in situ decompression, endoscopic in situ decompression, anterior submuscular transposition, and anterior subcutaneous transposition. ⁴ We review here our approach to patients presenting with cubital tunnel syndrome and the open in situ decompressive approach to neurolysis of the ulnar nerve.

61.2 Patient Selection

61.2.1 Clinical Presentation

The typical presentation for patients with cubital tunnel syndrome is pain or paresthesias in the ulnar one and one half digits. Similar to carpal tunnel syndrome, patients may complain of nocturnal exacerbation of the pain. The sensory field of the ulnar nerve extends only a few centimeters proximal to the wrist crease, so symptoms should be limited to the hand. Altered sensation proximal to this should prompt workup for an alternative diagnosis. Patients may also report weakness of hand grip or dropping objects.

On physical examination, light touch and two-point discrimination may be reduced over both the dorsal and palmar surface of the ulnar one and one half digits. There may be weakness of the hand intrinsic muscles, particularly the palmar and dorsal interossei and third and fourth lumbricals. Atrophy of the hypothenar eminence may be present. Tinel’s test over the ulnar nerve near the medial epicondyle will typically elicit pain or paresthesias in the ulnar distribution and recreate the patient’s symptoms. Wartenberg’s sign (i.e., abduction of the fifth digit at rest secondary to weakness of the palmar interossei) may be present. Froment’s sign also may be present; when attempting to grasp a piece of paper between the thumb and radial side of the index finger, the interphalangeal joint of the thumb is flexed owing to weakness of the adductor pollicis and activity of the flexor pollicis longus innervated by the anterior interosseous nerve, which is median nerve derived. The elbow flexion test is a provocative maneuver that may reproduce the patient’s symptoms. The patient is asked to flex the elbow past 90 degrees with the forearm in supination and the wrist in extension. The test is positive if pain or paresthesias are experienced in the ulnar distribution. The ulnar nerve should also be palpated while the elbow is flexed and extended, and subluxation of the ulnar nerve over the medial epicondyle should be noted when present.

Examination of the median nerve hand intrinsics, including the first and second lumbricals, opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis should be performed when considering ulnar neuropathy as the diagnosis, as testing these muscles helps differentiate a C8–T1 radiculopathy, such as seen in thoracic outlet syndrome or lesions of the lower trunk from ulnar neuropathy. Although these muscles are innervated by C8–T1, the innervating nerve fibers travel via the median nerve and consequently these muscles should not be affected in cases of ulnar neuropathy. When there is atrophy of the thenar eminence in addition to the hypothenar eminence (often the thenar eminence atrophy is more severe than the hypothenar atrophy), because of involvement of the median-innervated muscles, this places the lesion more proximal, such as at the thoracic outlet. Testing of the sensory loss can also help localize the lesion. The dorsal cutaneous branch arises just before the ulnar nerve entering Guyon’s canal. Thus, the dorsal sensation is spared when the ulnar nerve is affected at the level of Guyon’s canal. When sparing of the dorsal ulnar distribution is seen, consideration should be given to compression of the ulnar nerve at Guyon’s canal rather than at the cubital tunnel. Data show that spine surgeons do a poor job of differentiating C8–T1 radiculopathy from ulnar neuropathy; so each diagnosis should be considered and the appropriate physical examination maneuvers performed to differentiate the two. ⁵

61.2.2 Electrodiagnostic Testing

With compression of the ulnar nerve at or about the elbow, electrodiagnostic testing will reveal denervation changes in the ulnar innervated muscles and delayed motor conduction velocity across the elbow. The American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM) has put together a set of practice parameter guidelines for the diagnosis of ulnar neuropathy using electrodiagnostic testing. The AANEM suggests performing surface stimulation and recording with the elbow in moderate flexion measuring across a 10-cm section of the ulnar nerve. Using these measurement guidelines, a nerve conduction velocity across the elbow of less than 50 m/s is considered abnormal. Additionally, if the nerve conduction velocity across the elbow is greater than 10 m/s slower than the conduction velocity of the ulnar nerve from below the elbow to the wrist, this is also considered an abnormal finding consistent with ulnar neuropathy. A decrease in compound muscle action potential (CMAP) negative peak amplitude of greater than 20% across the elbow or a significant change in the CMAP configuration above the elbow compared with below the elbow are also consistent with ulnar neuropathy. The AANEM also recommends that needle examination should include the first dorsal interosseous muscle, as this is the most frequently abnormal muscle. The ulnar innervated forearm flexors should also be part of the needle examination, however. To rule out brachial plexopathy, examination should also include nonulnar C8/medial cord/lower trunk innervated muscles. Cervical paraspinal muscles should also be included to help exclude a C8/T1 radiculopathy. ⁶^, ⁷

61.2.3 Imaging Studies

X-rays or computed tomography (CT) scans of the elbow can be useful for defining the bony anatomy, particularly if there is a history of trauma or fracture of any of the bones surrounding the cubital tunnel that can be consistent with tardy ulnar palsy. These imaging modalities can also be useful to examine any surgical hardware that may be in place. Aside from these specific indications, magnetic resonance imaging (MRI) or ultrasound is more useful for examining the ulnar nerve.

We favor ultrasound imaging over MRI for the detection of compressive ulnar neuropathy. Ultrasound has been shown to have a superior sensitivity (93% versus 67%) compared with MRI with an equivalent specificity (86%). ⁸ In addition, ultrasound allows for dynamic imaging, which provides an advantage over MRI.

The hallmark feature of cubital tunnel syndrome on ultrasound is hypoechoic enlargement of the ulnar nerve around the elbow with return to normal size distal to the elbow ( ▶ Fig. 61.1). The diagnostic criteria for ulnar neuropathy vary but the upper limit of normal area of the ulnar nerve ranges from 7.5 to 10 mm². Ulnar nerve measurements above this level or a change in area by 1.5 times is consistent with cubital tunnel syndrome. ⁹^, ¹⁰^, ¹¹ In addition to imaging the nerve directly, ultrasound can be useful for detection of lesions such as ganglion cysts or tumors that are secondarily compressive of the ulnar nerve. Ultrasound can also help identify an anconeus epitrochlearis when present that may compress the ulnar nerve ( ▶ Fig. 61.2).

Fig. 61.1 Ultrasound over the cubital tunnel region: (a) short axis and (b) long axis to the ulnar nerve show marked hypoechoic enlargement of the ulnar nerve (arrows) with a transition to normal size as it enters the cubital tunnel distally beneath the arcuate ligament (curved arrow). Note the fascia of Osborn (arrow) in (a). E, medial epicondyle of humerus; O, olecranon process of ulna.

Fig. 61.2 Ultrasound over the cubital tunnel region: (a) short axis and (b) long axis to the ulnar nerve shows an accessory anconeus muscle (arrows) overlying the hypoechoic and enlarged ulnar nerve (arrowheads). E, medial epicondyle of humerus; O, olecranon process of ulna.

Dynamic assessment of the ulnar nerve adds to the utility of ultrasound in the diagnosis of cubital tunnel and increases its sensitivity and specificity. The ulnar nerve should be assessed for subluxation over the medial epicondyle throughout range of motion. If subluxation is present, this may alter the treatment plan. Transducer pressure over the ulnar nerve may elicit pain or paresthesias in the ulnar distribution and when this occurs should be reported. When the medial head of the triceps is abnormally displaced during elbow range of motion, two palpable snaps may be observed, termed snapping triceps syndrome. ¹² This can also be visualized by ultrasound. This observation may guide the clinician to pay particular attention to the ulnar nerve around the intermuscular septum.

61.3 Preoperative Preparation

61.3.1 Nonsurgical Management

For patients without a progressive neurologic deficit, we typically recommend a trial of conservative management before offering surgical decompression. Initial management typically consists of behavioral modification to reduce repetitive flexion–extension of the elbow, padding the elbow if there is frequent pressure on the elbow, and splinting the arm, particularly at night. Approximately 35% of patients will have improvement in symptoms, simply with patient education and activity modification, though symptoms may not completely resolve. ¹³ Night splinting adds to the success of conservative treatment. In one study, the combination of patient education, activity modification, and nighttime splinting in patients resulted in successful treatment without the need for operative decompression in 79% of patients with mild symptoms, 67% of patients with moderate symptoms, and 38% of patients with severe symptoms. ¹⁴ Steroid injections have not been shown to be beneficial. ¹⁵^, ¹⁶ Thus, for patients without a progressive neurologic deficit, we typically recommend a course of conservative therapy for a period of 3 to 6 months consisting of patient education, activity modification, and nighttime splinting. This regimen is less likely to be successful in pediatric and adolescent patients but is nonetheless reasonable to try in the absence of a progressive neurologic deficit. ¹⁷

61.3.2 Decision for Operative Management

We offer surgical intervention for cubital tunnel syndrome for patients with a progressive neurologic deficit, those for whom a course of conservative therapy fails and who continue to experience symptoms that affect daily life, and those who have a lesion with secondary ulnar nerve compression. Our decision to operate is based primarily on the neurologic examination and clinical symptoms rather than solely on electrodiagnostics.

61.3.3 Consideration of Operative Approach

Studies comparing outcomes for open and endoscopic in situ decompression versus anterior submuscular or subcutaneous transposition have not demonstrated that any technique is superior to open in situ decompression. ⁴^, ¹⁸^, ¹⁹^, ²⁰^, ²¹ Thus, we favor open ulnar neurolysis for patients with cubital tunnel syndrome. The exception to this is patients who have subluxation of the ulnar nerve over the medial epicondyle in whom we favor decompression and anterior subcutaneous transposition, although there is no strong evidence to support this practice.

61.4 Operative Procedure

61.4.1 Surgical Anatomy

The ulnar nerve originates as the terminal branch of the medial cord of the brachial plexus ( ▶ Fig. 61.3). In the upper arm, the ulnar nerve passes through the intermuscular septum and through the arcade of Struthers. The point at which the nerve passes through the arcade occurs approximately 8 cm proximal to the medial epicondyle. ²² There is controversy as to whether or not this structure actually exists. ²³ In one anatomical study, most specimens had a thickening consistent with an arcade of Struthers, although controversy may exist based on how this is defined. ²³ The components that make up this arcade include the brachial fascia, the internal brachial ligament, and the medial intermuscular septum. ²³ The nerve then descends through the upper arm between the medial intermuscular septum and the medial head of the triceps. The medial intermuscular septum attaches on the humerus from the lesser tubercle to the medial epicondyle and separates the brachialis muscle from the triceps brachii muscle.

Fig. 61.3 The ulnar nerve arises from the C8 and T1 nerve roots, which join to form the lower trunk, which gives off its anterior division becoming the medial cord. The medial cord ultimately continues as the ulnar nerve after it gives off its contribution to the median nerve. The approximate takeoff of each of the branches (both sensory and motor) is shown in this diagram. Note the origin of the dorsal cutaneous branch proximal to Guyon’s canal.

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