Ulnar Nerve Release

Ulnar nerve release is performed for cubital tunnel syndrome with positive clinical and instrumental signs (on nerve conduction studies and electromyography [EMG]) of compression at the elbow.

In 1957, Osborne described simple decompression of the ulnar nerve achieved by cutting the ligament subsequently named after him (the Osborne fascia or band). This ligament is part of the fibrous arcade, a fascia running between the two heads of the flexor carpi ulnaris (FCU). Osborne divided this fibrous band connecting the medial epicondyle and the olecranon and reported results favorable to those of the anterior transposition procedures, which at that time represented the standard of surgical care for compressive ulnar neuropathies at the elbow.

In his report, Osborne observed that the ulnar neuritis was a result of direct compression of the nerve within the tunnel and that the flexion of the elbow exacerbated this condition.

The compression causes progressive disruption of the vascular supply to the nerve.[1] In a normal elbow, the nerve undergoes tensile forces that increase the nerve strain; when the elbow is flexed, the nerve is pushed against its bed, and upon extension, the nerve diverges away from the elbow.

The ulnar nerve at the elbow could be compressed at different sites, as follows:

• Proximal to the cubital tunnel at the level of the medial epicondyle - The arcade of Struthers is a canal made up by the intermuscular septum, the internal brachial ligament, and the triceps; at this site, between the middle and distal thirds of the humerus, the ulnar nerve travels from the anterior to the posterior compartment of the arm
• Distal to the cubital tunnel - The compression might be caused by the arcuate ligament of Osborne that runs between the two heads of origin of the FCU and therefore between the medial epicondyle of the humerus and the medial aspect of the olecranon

Ulnar nerve compression at the elbow is the second most common compression neuropathy in the upper limbs (after median nerve compression in the carpal tunnel), with an incidence of 25 per 100,000 population per year. The condition is more common in men than in women, possibly as a consequence of the smaller coronoid process of the ulna and the more abundant subcutaneous fat tissue in women.

Nontraumatic ulnar nerve compressive neuropathy is usually associated with arthritis, and there are no other known causes.

Ulnar nerve release is indicated for cubital tunnel syndrome[2] with positive clinical and instrumental signs (on nerve conduction studies and EMG) of compression at the elbow.

Contraindications for ulnar nerve release include the following:

• Valgus deformity of the elbow
• Tumors
• Ganglion cyst
• Osteophytes
• Elbow instability or deformity

Relative contraindications include recurrent neuropathies.

A delayed diagnosis increases the risk of chronic neuritis and pain due to repeated injuries to the nerve, leading to intraneural scar formation. Surgical treatment in this case is less effective in the long term. Negative prognostic factors include severe, long-lasting neuropathy accompanied by diminished nerve conduction velocity (NCV).

A randomized controlled trial of 70 patients with mild or moderate but not necessarily electrophysiologically proven cubital tunnel syndrome sought to assess the efficacy of conservative therapy at 6 months.[3] The study subjects were divided into the following three groups:

• Nocturnal elbow splinting for 3 months plus written information
• Nerve gliding exercises plus written information
• Written information only

The attrition rates among the three groups were high and equal, with 13 patients unavailable for follow-up and six others requesting surgical decompression. The authors found that written information improved occupational activities and pain, but the addition of splinting or exercises did not confer any further benefit.[3]

Medial epicondylectomy versus anterior ulnar nerve transposition for ulnar neuropathy at the elbow was examined in a randomized controlled trial of 47 operations.[4] Neurologic assessment of the hand and elbow at a minimum of 1 year showed no clinical difference between the two groups, though mild hand pain was more common after transposition. Patient satisfaction seemed better after medial epicondylectomy.[4]

Several randomized controlled trials have compared clinical and nerve conduction outcomes of simple decompression versus anterior ulnar nerve transposition in patients with electrophysiologically proven ulnar neuropathy at the elbow.[5, 6, 7, 8]

Bartels et al compared simple decompression with anterior subcutaneous transposition in 152 patients.[5] At 1-year follow-up, equivalent good or excellent clinical improvement was noted in both groups (65% decompression, 70% subcutaneous), though the transposition group had significantly higher rates of complications (10% decompression, 31% subcutaneous). An economic analysis of this trial revealed that simple decompression cost significantly less than transposition, mainly owing to significantly shorter operative time and sick leave.[9]

Nabhan et al also examined simple decompression versus anterior subcutaneous transposition in a randomized controlled trial of 66 patients with 9-month follow-up.[8] The two procedures achieved similar improvements in clinical findings and NCVs across the elbow.

Biggs and Curtis[6] and Gervasio et al[7] compared simple decompression with anterior submuscular transposition. At 1-year follow-up, Biggs and Curtis reported a nonsignificant difference in neurologic improvement between groups in their cohort of 44 patients (61% decompression, 67% submuscular), with a trend for deep wound infection in the transposition group (0% decompression, 14% submuscular).[6]  At 6-month follow-up, Gervasio et al reported a nonsignificant difference in good or excellent clinical and electrophysiologic outcomes between groups in their cohort of 70 patients (80% decompression, 83% submuscular), with no major complications observed.[7]

The data from these studies were cumulatively evaluated in a 2011 Cochrane review. The meta-analysis found that both simple decompression and anterior transposition procedures improved symptoms and nerve function and that no significant difference in postoperative clinical or electrophysiologic outcomes existed; however, transposition resulted in higher rates of deep and superficial wound infection.[10]

These findings suggested that conservative therapy would be appropriate for patients with mild or moderate symptoms of ulnar neuropathy at the elbow. In more severe cases requiring surgical intervention, clinical improvement might be expected in approximately 70% of cases.[10] No one surgical technique was shown to be superior to another.

The evidence from these randomized controlled trials led to increasing advocacy for simple decompression as the operation of choice, in view of its shorter operating time, potential economic benefits, and association with fewer complications. 

In a 2014 study by Martin et al, 145 patients underwent retractor-endoscopic carpal tunnel release (n = 47), endoscopic in-situ decompression of the ulnar nerve (n = 55), or endoscopic anterior transposition of the ulnar nerve (n = 52) between 2000 and 2010; nine patients underwent bilateral procedures.[11] Both objective results (via independent examination at 24 months) and subjective results (via questionnaire) were recorded, as follows:

• Endoscopic carpal tunnel release - 59.6% had excellent objective results, 21.2% good results, 12.8% fair results, and 6.4% poor results; 85% had subjective improvement
• Endoscopic in-situ decompression - 56.4% had excellent objective results, 32.7% good results, 9.1% fair results, and 1.8% poor results; 72.7% had subjective improvement
• Endoscopic anterior transposition of the ulnar nerve - 48.1% had excellent objective results, 26.9% good results, 23.1% fair results, and 1.9% poor results; 65.4% had subjective improvement

The investigators found that the retractor-endoscopic approach yielded good long-term results after carpal tunnel release, in-situ decompression, and anterior subcutaneous transposition of the ulnar nerve, with outcomes showing some correlation with the duration of preoperative symptoms.[11]

A 2016 update of the aforementioned 2011 Cochrane review found that the available comparative treatment evidence was insufficient to support a multiple-treatment meta-analysis to identify the best treatment for idiopathic ulnar neuropathy at the elbow on the basis of clinical, neurophysiologic, and imaging characteristics.[12]  The study was unable to define when to treat this condition conservatively or surgically. Simple decompression and decompression with transposition appeared equally effective, even with severe nerve impairment, though the latter procedure was associated with more deep and superficial wound infections. Patients undergoing endoscopic surgery were more likely to have a hematoma.

A 2018 prospective study of 45 patients randomly assigned to undergo either endoscopic (n = 22) or open surgery (n = 23) for decompression of the ulnar nerve found the two methods to be equally effective in the treatment of cubital tunnel syndrome.[13]  Patients who underwent open decompression experienced notably higher levels of postoperative chronic scar pain; satisfaction with scarring was greater in the endoscopy group. Operating time was significantly longer in the endoscopy group.

In a 2018 review comparing outcomes of open decompression, endoscopic decompression, minimal incision, subcutaneous transposition, intramuscular transposition, and submuscular transposition for cubital tunnel syndrome, Carlton et al found that all of these approaches appeared to be effective, but none demonstrated universal superiority to the others.[14] The only consensus reached was that transposition seemed preferable where the ulnar nerve tends to subluxate on either preoperative or intraoperative examination.

Patient instructions

The patient should be instructed to keep the wound dry, gently compressed, and elevated in the immediate postoperative period. Early mobilization of the arm is strongly encouraged and will reduce stiffness.

Some surgeons prefer slings for a few days postoperatively. Strenuous heavy lifting or the performance of repetitive tasks involving the arm is discouraged until at least the initial follow-up with the operating surgeon. This will likely require modification of lifestyle or occupational activities. Exercises may be prescribed by a hand physiotherapist. Simple analgesia should be taken as required.

The patient should seek medical attention upon any sign of infection (fever, new pain, swelling, heat, redness or ooze from the operative site) or new sensorimotor deficit.

Elements of informed consent

The patient must be made aware of the risks of ulnar nerve release. General risks include pain, infection, bleeding, thromboembolic phenomena, pressure areas, adverse reaction to anesthetic, and death. Specific risks include temporary or permanent neurologic deficit, specifically of the ulnar or nearby medial antebrachial cutaneous nerves, failure of the procedure to relieve or prevent recurrence, or even symptom exacerbation.

The patient will be required to attend a preoperative clinic for assessment of fitness for surgery and anesthetic (general or local). This may include blood tests, electrocardiography (ECG), and chest radiography.

History and physical examination

Individuals with ulnar neuropathy present with sensorimotor deficits in the territory of the ulnar nerve. Typically, numbness and tingling of the fingers innervated by the ulnar nerve occur first, followed by weakness. Pain may occur behind the elbow. Symptoms may be exacerbated by elbow flexion; this is especially apparent at night.

In severe cases, atrophy of the intrinsic muscles of the hand at the hypothenar eminence may develop, from mild to severe, including the Froment sign, in which the abductor pollicis is weak, so the patient tends to flex the interphalangeal (IP) joint of the thumb and extend the distal phalanx while grasping between the thumb and index finger to overcome the weakness of the abduction.

The patient can also present with a positive Wartenberg sign, in which the little finger is abducted owing to interosseous weakness. The Tinel sign may be positive at the elbow.

In severe cases, the benediction hand sign may also be seen, in which the last two fingers are less extended than the others when the patient tries to extend them all.

Neuroradiologic investigation

Electromyography (EMG) is very useful in detecting peripheral neuropathies. A nerve conduction velocity (NCV) of less than 50 m/s across the elbow is highly suggestive of a compression at that level. Patients with significantly reduced NCV and clinical findings of advanced ulnar neuropathy may show enlargement of the ulnar nerve at the medial epicondyle, which may affect surgical decision-making.[15]

Radiography is still very important in the workup of cubital syndrome, in that it helps rule out trauma, bony tumors, and osteoarthritis.

Magnetic resonance imaging (MRI) is useful for ruling out compressions of the nerve by tumors and cystic pathologies of the soft tissue and joints.[16]

High-resolution ultrasonography (HRU) may improve preoperative evaluation of ulnar neuropathy at the elbow; it is better tolerated, less costly, and less time-consuming than MRI or electrodiagnostic testing.[17]

Amyotrophic lateral sclerosis, Guillain-Barré syndrome, Charcot-Marie-Tooth disease, and hereditary neuropathy with liability to pressure palsies (HNPP) can all present with symptoms of ulnar nerve weakness and must be ruled out, as well as cervical nerve palsies, thoracic outlet syndrome, and compression of the nerve at the canal of Guyon.

Preoperative antibiotic prophylaxis has not been shown to offer benefits for uncomplicated ulnar nerve release at the cubital tunnel.[18]

Anesthesia

Some surgeons may prefer general anesthesia or regional block, especially if anterior transposition or epicondylectomy is planned. Local anesthesia is used, with 0.9% bupivacaine to close over the incision site. The wide-awake, local anesthetic, no tourniquet (WALANT) approach has been used for endoscopic cubital tunnel release.[19]

Positioning

The patient is laid supine. The arm is externally rotated and the elbow flexed to approximately 90°. The arm is exsanguinated and a pneumatic tourniquet applied.

A follow-up appointment with the clinic or general practitioner is made for 1-2 weeks after the procedure to remove sutures (if they are nonresorbable) and to assess the wound site.

Progress assessment with the operating surgeon is usually arranged for 6-8 weeks. Improvement in symptoms and hand function is generally good but varies according to the extent and duration of deficits preoperatively.

Recovery may take as long as 12 months.

Current surgical strategies for treatment of cubital tunnel syndrome include the following[20, 21] :

• In-situ decompression
• Simple decompression
• Anterior subcutaneous transposition
• Anterior submuscular transposition
• Medial epicondylectomy
• Endoscopic cubital tunnel release

Intraoperative magnification with loupes and headlight or microscope is required, and intraoperative neuromonitoring is a valuable adjunct for localizing the nerve.

A well-defined and widely accepted algorithm for choosing among the various surgical treatment options for cubital tunnel syndrome has not been established.[22]

A 6- to 8-cm curvilinear incision centered over the course of the ulnar nerve is made between the medial epicondyle and the olecranon. The dissection includes the two heads of the flexor carpi ulnaris (FCU) distally and proximally to the arcade of Struthers. It is safer to identify the nerve proximal to the ligament of Osborne. The ligament becomes tighter as the elbow is brought into flexion, confirming a dynamic compression of the ulnar nerve.

The ligament is incised proximally to distally to minimize the chances of injury. The nerve is then followed along the postcondylar groove and between the two heads of the FCU to exclude other sites of compression. The nerve should not be mobilized from the groove; doing so would increase the risk of subluxation.

Another dynamic test of flexion of the elbow is performed to ensure that the nerve is not compressed or does not tend to subluxate from the cubital tunnel during flexion; in these cases, an anterior transposition would ensure a better long-term result.

Among the postoperative morbidities easily avoided with the minimalist approach are lesions to the medial antebrachial cutaneous (MABC) nerve.[23] The terminal branches of the MABC nerve usually lie medial to the elbow; therefore, a curvilinear skin incision is directed toward the MABC branches, volar and distal to the medial epicondyle, but not beyond, in order to avoid injuries to the MABC nerve. The ulnar nerve is localized proximal to the cubital tunnel under the medial epicondyle before it passes beneath the Osborne band.

The fascia is divided, and the nerve is followed to the arcuate ligament between the two heads of the FCU. The FCU is also divided to free the nerve. If an anomalous epitrochleoanconeus muscle stretches the nerve in the cubital tunnel instead of the thickened fascial roof,[24, 25] it has to be divided.

The arcade of Struthers cannot be explored during this approach, because it is too distant from the skin incision. A smooth blunt probe can be inserted along the course of the ulnar nerve subcutaneously to evaluate the resistance to its passage proximally at the intermuscular septum and at the arcade of Struthers. If resistance is encountered, the incision can be extended.

The skin incision is centered between the medial epicondyle and the medial aspect of the olecranon. The structures exposed with this approach include the arcade of Struthers, the medial triceps, the cubital tunnel retinaculum, the Osborne fascia, and the two heads of the FCU.

The medial triceps could also represent a site of compression, with the nerve being compressed between the belly of the muscle and the medial intermuscular septum (MIS). In this case, the MIS is dissected and excised. The FCU is also partially divided. The fascia of the flexor pronator origin is used to contain the mobilized nerve and attached to the superficial subcutaneous layer.

A variant of this technique has been described in which the ligament of Osborne is used as a ligamentofascial or ligamentodermal sling to create a smooth gliding surface without causing compression and thereby to avoid subluxation.[26]

Anterior transposition may also be accomplished via a submuscular approach (see below); the evidence to date has not indicated that eaither approach is superior to the other.[27]

The skin incision is centered along the posterior condylar groove of the humerus. The proximal cubital tunnel is opened and the ulnar nerve identified. The MIS is excised as described above. The two heads of the FCU are separated, and a musculofascial incision or Z-plasty is made on the common flexor-pronator fascia. The fascia is cut at a length of 1.5-2 cm to provide enough length to avoid tension once the ulnar nerve is transposed.

Two flaps are made—one based on the medial humeral epicondyle and the other on the muscle bellies of the pronator teres and the FCU. The FCU is detached from the ulna, and the nerve is mobilized from its groove on the condyle over the MIS and the ulnar attachment of the FCU and placed back under the FCU. The flaps prepared at the beginning are sutured to the superficial layers.

A skin incision centered over the medial epicondyle is made, and the ulnar nerve is identified before it enters the Osborne band and the cubital tunnel. The FCU is prepared as described above, and the medial epicondyle is exposed with care to leave the origin of the flexor and the pronator with the periosteum in one layer. An osteotomy of 1.5 cm of the medial epicondyle is performed, and the stump is drilled with a diamond burr to accommodate the ulnar nerve on a smooth surface. This procedure may be combined with in-situ decompression.

A standard 30° Perneczky scope is used, traveling into a specific trocar with a flat inferior surface that helps both mobilization and safe dissection along the nerve. A retractor system mounted on the cannula facilitates separation from the surrounding structures.

The skin incision is made just over the cubital tunnel behind the medial epicondyle, and the initial dissection is carried out with a spatula so as to establish a plane between the roof of the canal and the nerve. The trocar is then introduced in the same plane with the retractor system, keeping superficial nerves away from the ulnar nerve. The endoscope is inserted with the visor window pointing inferiorly though its entire course. After this is done, the roof of the canal is sectioned and the ulnar nerve followed again to confirm its release.

In a systematic review and meta-analysis of 20 studies (17 observational and three comparative) comprising a total of 981 patients with idiopathic cubital tunnel syndrome, Aldekhayel et al found endoscopic cubital tunnel release (n = 556) to be similar to open cubital tunnel release (n = 425) with respect to outcomes, complication profiles, and reoperation rates.[28]

The following are potential complications of ulnar nerve release[29] :

• Postoperative persistence of symptoms caused by incomplete or inadequate decompression of the nerve and/or entrapment at a different location ^[30]
• Scar formation around the nerve due to insufficient/inadequate hemostasis
• Subluxation of the nerve to or across the medial epicondyle
• Direct injury or traction injury to the ulnar nerve during dissection
• Lesion of the MABC nerve or of its terminal branches (hyperesthesia, hyperalgesia due to painful neuromas formed from disorganized regeneration of sensory nerve fibers)
• Local postoperative hematomas due to inadequate hemostasis
• Cosmetic problems in wound healing
• Wound infection or dehiscence