Ulnar nerve entrapment at the elbow is the second most frequently encountered nerve entrapment in neurosurgical practice. Neurosurgeons should be familiar with the anatomy of the ulnar nerve at the elbow, the diagnostic hallmarks of the entrapment disorder, and the indications for surgical intervention. When surgical intervention is necessary, the neurosurgeon may choose from three surgical approaches: simple decompression of the nerve, subcutaneous transposition of the nerve, and submuscular transposition of the nerve. The literature does not provide conclusive support for any of these surgical approaches relative to the others, with most studies finding no significant outcome difference when comparing each of the different modalities. ^{1,​ 2} Several studies do suggest, however, that in patients with a history of elbow fracture or dislocation leading to the cubital tunnel syndrome, subcutaneous transposition is superior to in situ nerve release. ² Nonetheless, until there is concrete evidence, it is incumbent upon surgeons to be competent with the three main approaches. This chapter describes the surgical technique for subcutaneous transposition of the ulnar nerve. In addition, it discusses the anatomy, diagnosis, surgical indications, and perioperative considerations that are pertinent to the management of the disorder regardless of the surgical approach chosen.

62.2 Patient Selection

The diagnosis of ulnar nerve entrapment at the elbow is usually established easily by careful patient history, physical examination, and electrodiagnostic studies. Patients typically report the gradual onset of paresthesias in the ulnar half of the affected hand. The little finger is usually affected more than the ring finger. When the ring finger is affected, the medial half is usually affected more than the lateral half. If the lateral and medial halves of the ring finger are affected equally, careful consideration of neurogenic thoracic outlet syndrome must be made. As the disorder progresses, the paresthesias will advance to include frank pain in the medial hand. Medial elbow pain in the form of sensitivity to pressure over the ulnar nerve is also frequently present at this stage. The pain and paresthesias are usually aggravated by activities that require repetitive or prolonged elbow flexion. Patients may or may not report weakness with the hand. When weakness is reported, it is usually described as clumsiness. Patients with neck pain or upper arm pain should be evaluated for cervical radiculopathy.

The most common finding on physical examination is decreased subjective sensation in the medial hand to light touch and objective decreased sensation to two-point discrimination. ¹ One should carefully determine whether this decreased sensation honors the midline of the ring finger, which is quite specific for ulnar neuropathy versus radiculopathy or thoracic outlet syndrome. The next most common physical finding is nerve irritability elicited by tapping over the course of the nerve at the elbow. A Tinel’s sign is present if this tapping produces paresthesias in the medial hand. Careful motor testing will usually demonstrate some weakness of the ulnar innervated intrinsic hand muscles. Challenging the strength of the abductor digiti minimi relative to the contralateral side is perhaps the simplest test of this function. Froment’s sign, if present, indicates weakness of the adductor pollicis. The presence of this sign is evaluated by having the patient grasp a piece of paper between the straightened thumb and forefinger. The examiner then pulls the paper away against the patient’s resistance. The sign is present if the distal thumb flexes, which is compensatory action of the unaffected median nerve–innervated flexor pollicis brevis. The intrinsic hand muscles are usually affected before the flexor digitorum profundus of the ring and little finger. The strength of the flexor carpi ulnaris is rarely affected. In severely advanced cases, ulnar intrinsic muscle atrophy and ulnar clawing may be present.

Electrodiagnostic testing is usually helpful to confirm the diagnosis of ulnar nerve entrapment at the elbow that was made on the basis of history and physical examination. A surgeon should carefully reconsider all the clinical and historical findings if a patient with suspected ulnar nerve entrapment at the elbow has an electrodiagnostic evaluation that reveals no evidence of ulnar neuropathy at the elbow. A normal electrodiagnostic evaluation should not be considered an absolute contraindication to intervention in a patient whose history and physical examination are highly suggestive of the disorder, however. The most common electrodiagnostic finding is slowing of the nerve conduction velocity. ² This velocity is generally considered abnormal if the absolute velocity across the elbow is less than 50 m/s or if the velocity below the elbow is 10 m/s slower than the velocity above the elbow. More severe cases are marked by signs of denervation on electromyography. ³

Nonoperative therapies to consider before surgical intervention include splints to minimize elbow flexion, pads and pillows to prevent direct pressure on the ulnar nerve, and nonsteroidal anti-inflammatory medications. These measures, combined with patient education and physical therapy, have been successful in treating mild and moderate disease in up to 80% of patients in one series. ² Surgical intervention is indicated for patients for whom nonoperative management fails or who have with moderate to severe dysfunction marked by significant sensory loss or muscle weakness.

Subcutaneous transposition of the ulnar nerve to treat cubital tunnel syndrome was first described by Benjamin Curtis in 1898. ³ Many modern surgical series have investigated the benefits of this technique. ² Subcutaneous ulnar nerve transposition can be accomplished using regional anesthesia, and studies have demonstrated improved postoperative pain and patient satisfaction when regional anesthesia is used. ³ The subcutaneous transposition requires slightly more operating time to perform than does a simple decompression of the cubital tunnel but requires considerably less operating time than submuscular transposition. It may therefore be more suitable for some medically infirm patients than the submuscular transposition procedure. Comorbid conditions, such as coronary artery disease or chronic respiratory ailments, should be addressed before starting the procedure. Patients who regularly take anticoagulation medications must be evaluated by the prescribing physician to ensure that it is safe to stop those medications and return the patient to a normal coagulable state before surgery. Screening for untoward reactions to anesthesia, drug allergies, and the ability to participate in the postoperative plan of care should be accomplished before surgery.

62.3 Preoperative Preparation and Operative Procedure

The patient is positioned supine on the operating table. Intravenous access is established in the contralateral arm. A pneumatic tourniquet may be used if the surgeon prefers; however, meticulous attention to hemostasis throughout the procedure makes the use of a tourniquet unnecessary. The tourniquet also poses some risk of additional injury of the ulnar nerve or other nerves in the arm. This added risk probably outweighs the potential benefit of tourniquet-assisted hemostasis. The patient is adequately sedated by the anesthesiologist, and the affected arm is prepared and draped in a sterile fashion from the fingers to the proximal arm. The arm is extended on an attached arm table with the shoulder externally rotated in such a manner that the medial epicondyle directly faces the surgeon, who sits on a stool caudal to the extended arm. The distal arm is elevated slightly with folded towels. The elbow is mildly flexed. Overhead lighting may be augmented with headlamp illumination, and visualization may be augmented with loupe magnification. Hemostasis is obtained with bipolar cautery.

A 10-cm curvilinear incision centered 2 cm posterior to the medial epicondyle and along the anticipated course of the ulnar nerve is used to begin the exposure. As the surgeon gains familiarity with this approach, the incision can be reduced to 6 cm long. The skin incision is deepened through the subcutaneous connective tissue with scissor dissection. As this dissection proceeds, great care is taken to identify and preserve the medial antebrachial cutaneous nerve as it courses from anterior to posterior across the distal surgical field. ⁴ Dissection is carried farther to the plane of the fascia of the medial head of the triceps, where it joins the intermuscular septum at the medial epicondyle. The ulnar nerve is identified just posterior to the intermuscular septum and proximal to the cubital tunnel. ⁴ With the nerve safely identified, the surgeon may now bluntly develop the dissection plane just superficial to the fascia of the flexor–pronator complex using blunt finger dissection. This dissection should be carried to the distal extent of the incision. A vessel loop should be placed around the ulnar nerve proximal to the elbow. The nerve should then be released from any surrounding tissue. The nerve at this location is usually deep to the arcade of Struthers, a fine aponeurotic band extending from the medial triceps to the medial intermuscular septum. This arcade of Struthers is a normal anatomical finding not to be confused with the more unusual ligament of Struthers, which is a fibrous band stretching from anomalous humeral bone spur to the medial epicondyle and is a rare cause of entrapment of the median and ulnar nerve in the arm. An army–navy retractor can be used at the proximal end of the incision to provide additional exposure to completely release the ulnar nerve from the overlying arcade of Struthers.

The roof of the olecranon groove is now sharply incised to expose and release the underlying ulnar nerve. The nerve is then followed distally as it travels deep to the fibrous band of fascia between the heads of the flexor carpi ulnaris muscle. This band is also a frequent site of entrapment and should be incised to at least the distal length of the incision. This is accomplished by placing the blades of dissecting scissors on either side of the band and advancing the scissors distally. Both the fascia and the muscle fibers overlying the nerve need to be released in this fashion to expose the underlying nerve ( ▶ Fig. 62.1). The next goal of the procedure is to accomplish the transposition of the nerve from the tunnel to a position anterior to the medial epicondyle with maximal preservation of nerve branches and vascular supply. The superior ulnar collateral artery is the main vascular supply of the nerve above the elbow, with the posterior ulnar collateral artery providing the main supply below the elbow. Collateral vascular supply to the nerve should be preserved as much as possible. A randomized trial by Nakamura et al demonstrated that artery ligation results in 28 to 55% less blood flow to the nerve. ¹ This is a technical error that can lead to a procedural failure despite adequate decompression and transposition of the nerve. In addition to avoiding excessive dissection and cautery of the collateral circulation, care must be taken to avoid an excess transposition distance, which can put the nerve and its collateral circulation under tension. Cadaveric anatomical studies suggest an ideal transposition distance range of 1.8 ± 0.6 cm (1.1 to 2.5 cm) to maintain tension-free vascular supply to the transposed nerve. ⁵

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