Ulnar Nerve Submuscular Transposition

Ulnar nerve entrapment (UNE) at the elbow, also known as cubital tunnel syndrome, is the second most common upper extremity focal neuropathy after carpal tunnel syndrome. The cubital tunnel is the most common location for ulnar neuropathy. Surgical intervention is an effective treatment for many of these patients after conservative measures fail. Compared with a subcutaneous transposition, the submuscular transposition affords less risk of scarring, less risk of trauma related to superficial positioning, and less severe angulation. The submuscular transposition places the ulnar nerve parallel to the median nerve by relocating it deep to pronator teres and flexor carpi ulnaris.

63.2 Patient Selection

63.2.1 Relevant Anatomy

At the elbow, the ulnar nerve courses through the cubital tunnel. This area is bound by the medial epicondyle medially and the olecranon process laterally. Distal to the medial epicondyle, the ulnar collateral ligament forms the floor. The roof is composed of a fascial aponeurosis, which thickens distally, between the two heads of flexor carpi ulnaris (FCU), known as Osborne’s band. The arcade of Struthers is an aponeurosis between the medial head of the triceps and the medial intermuscular septum. Its presence is controversial but may be of more relevance in revision surgeries. During elbow flexion, the cubital tunnel cross-sectional area decreases in size by approximately half; consequently, compression occurs. ¹ Entrapment can occur at multiple sites along the course of the ulnar nerve and may be due to compression, trauma, traction, adhesions, hypertrophy, deformity, or joint changes.

63.2.2 Clinical Presentation

Risk factors for UNE include prolonged elbow flexion, localized pressure, prior fracture, prior dislocation, arthritis, swelling, and female gender. Ulnar nerve entrapment may manifest with a combination of pain and sensory or motor symptoms and signs. Pain may be localized to the medial aspect of the hand, or it may occur in the elbow or forearm, typically at night. Sensory disturbance, such as numbness and paresthesia, is localized within the medial hand and typically the medial one and a half digits. Motor symptoms may result in weakness of the hand, particularly with fine activities, such as removing coins from a pocket, opening jars, or doing up buttons. Clinical examination may demonstrate motor changes, including atrophy of hand intrinsic muscles (hypothenar and interossei), weakness of these muscles, clawing of the hand, or sensory dysfunction in the medial hand and one and a half digits. The ulnar nerve may demonstrate subluxation at the elbow. Simple clinical maneuvers include Froment’s sign, that is, weak adductor pollicis seen as flexion of the interphalangeal joint of the thumb by the median nerve (anterior interosseous branch) when removing a sheet a paper from a pinch grip between the first and second digits and Wartenberg’s sign, that is, unopposed abduction of the fifth digit.

Other clinical tests may assist with clinical diagnosis and can be particularly helpful for mild cases. Tinel’s sign may be elicited by percussing over the ulnar nerve and, if positive, will cause paresthesia in the hand (sensitivity = 54%, negative predictive value = 98%). ² The elbow flexion test is performed bilaterally: with the shoulder fully externally rotated, elbow maximally flexed, and wrist neutral, a positive result will cause numbness or paresthesia (sensitivity = 46%). ³ In the scratch collapse test, the elbow is kept at 90 degrees, the patient externally rotates the shoulder against resistance, and the skin over the ulnar nerve at the elbow is scratched and then the external shoulder rotation against resistance is repeated; weakness or collapse unilaterally denotes a positive test (sensitivity = 69%). ⁴

Differential diagnosis includes cervical disk disease, especially C7–T1, peripheral demyelinating diseases, motor neuron disease, or pathology of the brachial plexus. It is also important to differentiate UNE at the elbow from distal entrapment at Guyon’s canal.

63.2.3 Electrophysiological Findings

Although the diagnosis of UNE is often made clinically, confirmation is made with electrophysiological testing. Loss of conduction velocities of the ulnar nerve at the elbow of less than an absolute value of 50 m/s or a loss of greater than 20% compound muscle action potential amplitude are an indication of UNE. ⁵ Electrophysiological study performance and interpretation can be user dependent, and published evidence suggests that a negative electrophysiologic test does not necessarily exclude the diagnosis (specificity = 95%; sensitivity = 37 to 86%).

63.2.4 Imaging Studies

X-rays may demonstrate bone spurs, arthritis, deformities, or bony compression. Ultrasound can be used to assess nerve cross-sectional area, in which an abnormal nerve will have an area greater than 0.10 cm² (sensitivity 93%, specificity 98%). ⁶ Comparison with the contralateral side could also be helpful. Magnetic resonance imaging may demonstrate nerve thickening or swelling and may show signal hyperintensity on T2-weighted images. ⁷

63.2.5 Indications

Submuscular ulnar transposition is indicated for patients refractory to previous simple decompression (neurolysis) or medial epicondylectomy, refractory to conservative treatment of over 3 months, have significant motor deficit, or have conduction velocities of less than 50 m/s across the elbow. Additionally, transposition is indicated when there is nerve compression by osteophytes, tumors, ganglion cysts, or other masses or in the presence of significant subluxation of the nerve at the elbow. This technique decompresses the nerve, and eliminates physiological stretching of the ulnar nerve during elbow flexion; however, the procedure is more complex than simple decompression, and requires particular nerve surgery expertise to be performed well.

63.3 Preoperative Preparation

The operation is performed with the patient under general anesthesia with laryngeal mask or endotracheal intubation. The patient is positioned supine, with the head on a head ring and the arm outstretched on an arm board, and supinated. The skin is prepared from the wrist to the upper third of the arm. The arm is draped, and the wrist/hand are wrapped in sterile towel and wrapped with a crepe bandage ( ▶ Fig. 63.1). The elbow is elevated by resting on a tower of three or four folded towels. Local anesthesia (0.5% bupivacaine with 1:200,000 epinephrine) is infiltrated into the subcutaneous tissue.

Fig. 63.1 Left upper limb, prepared, draped, and planned skin incision marked. Note the elevation of the elbow on a small tower of folded towels.

63.4 Operative Procedure

63.4.1 Exposure (Video 63.1)

The procedure is typically done using surgical loupes for magnification. A curvilinear incision is symmetrically placed about the medial epicondyle, extending from medial arm between the biceps and triceps to medial forearm, at least 10 to 12 cm total length. The middle third of the incision may curve anterior to the epicondyle ( ▶ Fig. 63.1).

The subcutaneous dissection proceeds carefully, with identification, neurolysis and mobilization of the medial antebrachial cutaneous nerve(s). These nerves are encircled with vessel loops, and sufficient nerve mobilization is required to enable the nerve to be swung from posterior to anterior.

The ulnar nerve dissection begins just proximal to the epicondyle, with division of the overlying fascia and deroofing the nerve proximally into the arm. Once a sufficient length of nerve has been exposed, the ulnar nerve is encircled with a Penrose drain or a vessel loop, and the more proximal dissection continues, with division of the medial intermuscular septum. Often, a length of the intermuscular septum will need to be excised, and this is best judged by gently running the surgeon’s gloved finger along the path that the transposed nerve will take and feeling for any fibrous bands that will require division or excision. At the proximal aspect of the dissection, a Langenbeck retractor is placed subcutaneously to allow the surgeon to visualize the longitudinal path of the ulnar nerve from elbow level to mid arm level ( ▶ Fig. 63.2). Here it is essential to divide all fibrous bands overlying the ulnar nerve and to complete the 360-degree external neurolysis of the ulnar nerve. Often, gliding the surgeon’s gloved finger just superficial to the nerve, toward the mid arm level, will enable the surgeon to feel such fibrous bands and ensure complete freedom for the nerve. It is failure to completely free the nerve proximally (and distally) that can result in kinking of the nerve and subsequent postoperative failure.

Fig. 63.2 Exposure of the proximal aspect of the ulnar nerve, from the distal arm to the elbow. The medial intermuscular septum has been divided, and residual fascial band identified proximally. This residual band requires division. The Penrose drain encircles the ulnar nerve at the elbow, and the yellow vessel loop encircles the medial antebrachial cutaneous nerve. Flexor carpi ulnaris and Osborne’s band identified at the distal end of the exposure.

Only gold members can continue reading. Log In or Register to continue