Chapter 200 Management of Ulnar Nerve Compression
The ulnar nerve arises from the medial cord of the brachial plexus and innervates the muscles of both the forearm and parts of the hand. It also carries sensory neurons supplying the skin of the back of the forearm, the palm, and the fourth and fifth digits. Entrapment of the ulnar nerve at the elbow is the second most common neuropathy in adults, after entrapment of the median nerve at the carpal tunnel.1–3
History
Before surgical options were explored, conservative treatments employed included hydrotherapy, immobilization,4 electrotherapy/application of electric current,5,6 massage, and application of ointments and solutions.7 In 1818, Granger8 described a patient with ulnar palsy after fracture of the medial condyle of the humerus and advised nonsurgical management with anatomic repositioning and immobilization. The earliest known report of surgical treatment of ulnar nerve entrapment dates to 1816 when Henry Earle (1789–1838)5,9 attempted to alleviate pain caused by ulnar entrapment in a 14-year-old girl by nerve sectioning.
In the Archives Générales de Médecine,10 in 1878, Photinos Panas was the first to describe the relationship between ulnar nerve compression at the elbow and clinical ulnar nerve palsy, what has been called “tardy ulnar palsy.” He presented three cases in which either prior trauma or osteoarthritis gradually caused damage to the ulnar nerve and eventually clinical manifestations. The term tardy was applied to this scenario where deficits appeared late after an injury. Panas attempted to improve the “bed” for the ulnar nerve by deepening the epicondylar groove.
In 1888, Poncet11 performed the first definitive surgical treatment for a subluxed ulnar nerve by creating a groove or a sulcus in the bone, placed the ulnar nerve in it, and then sutured the periosteum over the nerve to create a roof over the tunnel. Benjamin Farquhar Curtis(1857–1924)12 in 1898 developed the technique that is known today as the anterior subcutaneous transposition.5 Albert Mouchet (1869–1963)13 in 1914, described ulnar neuropathy secondary to a fracture of the humerus (maladie de Mouchet), and developed the technique of supracondylar cuneiform osteotomy of the humerus for ulnar neuritis from cubitus valgus. Rudolf Klauser in 1917 described a technique of transposing the nerve in a muscular bed to prevent repetitive direct trauma to the relatively superficially placed nerve from a simple subcutaneous transposition and was the first to describe anterior “intramuscular” transposition.14 Decompression or “liberation” of the ulnar nerve (without transposition) was first suggested by Sir Edward Farquhar Buzzard, a British physician in the year 1922. In 1942, James Rögnvald Learmonth15 described the anterior “submuscular” transposition placing it deep to the flexor pronator group of muscles alongside the median nerve.16 Feindel and Stratford defined the cubital tunnel anatomically in 1958.17,18
In 1959, Geoffrey Vaughan Osborne19 postulated that a fibrous band bridging the two heads of the flexor carpi ulnaris and directly laying over the ulnar nerve may be responsible for compressing the ulnar nerve leading to ulnar neuritis rather than by the previously postulated friction or traction on nerve. This fibrous band later came to be known as “Osborne’s band.”5 King and Morgan20 proposed medial epicondylectomy as another surgical option for the treatment of this problem.
Anatomy
Arm
The ulnar nerve descends in the arm posterior to the pectoralis major muscle and medial or posteromedial to the brachial artery. At the inferior border of the pectoralis major, the nerve moves medially and pierces the medial intermuscular septum about 8 cm above the medial epicondyle. It descends medially on the anterior surface of the medial head of the triceps muscle and then enters the interval between the medial epicondyle of the humerus and the olecranon. As it descends the nerve is usually invested by some triceps fibers that are given the name “Struther’s arcade.”21–23 The arcade, located about 8 cm proximal to the medial epicondyle is a musculofascial band and is about 1.5 to 2 cm wide. Its anterior border is the medial intermuscular septum, and its lateral border is formed by the deep fibers of the medial head of the triceps. The arcade typically passes obliquely and superficial to the nerve. The Struthers’ arcade should not be confused with “Struthers’ ligament,” a rare finding that bridges the supracondylar spur on the medial aspect of the humerus to the junction of the medial epicondylar ridge and medial epicondyle.24 Struthers’ ligament is usually associated with compression of the median nerve.
Cubital Tunnel
The nerve passes into the ulnar groove on the dorsal aspect of the medial epicondyle, at the entrance to the so-called cubital tunnel, the term first coined by Feindel and Stratford in 1958.5,17,18
The nerve is most superficial here during its entire course down the length of the arm. Laying over a bony floor it is therefore most susceptible to trauma in this location. The nerve is surrounded by fat throughout the cubital tunnel except adjacent to the medial epicondyle. The roof of the cubital tunnel is formed by a fibrous aponeurosis that thickens to form the cubital tunnel retinaculum or the arcuate ligament of Osborne25 (also called triangular ligament, arcuate ligament, or humero-ulnar arch or humero-ulnar arcade/HUA) which connects the tendinous origin of the humeral and ulnar heads of the flexor carpi ulnaris. This fibrous band is approximately 4 mm wide and extends from the medial epicondyle to the tip of the olecranon. Its fibers are oriented transversely and are taut in elbow flexion. The walls of the cubital tunnel are formed by the medial epicondyle and the olecranon and the floor is formed by the medial collateral ligaments and the joint capsule. The proximal and mid-portions of the cubital tunnel alter with flexion from round to elliptical.1,26 Studies show that the pressure within the cubital tunnel rises up to 7-fold with elbow flexion and further up to 20-fold with contraction of the flexor carpi ulnaris muscle causing microvascular ischemia and pressure injury to the nerve.27 As it traverses through the cubital tunnel, the ulnar nerve passes from the extensor surface of the arm to the flexor surface of the forearm and the nerve gives off branches to the elbow joint. Anatomical and vascularization pattern studies demonstrate a consistent but segmental extraneural and intraneural vascular supply from the superior ulnar collateral, inferior ulnar collateral and posterior ulnar recurrent arteries. The inferior ulnar collateral artery which is typically sacrificed with ulnar nerve transposition procedures provides the only direct vascularization to the nerve in the region just proximal to the cubital tunnel.28
Wrist
Approximately 9 cm proximal to the wrist the ulnar nerve gives off the dorsal cutaneous sensory branch leaving the terminal motor and palmar sensory branches to traverse the wrist into the hand. The dorsal cutaneous nerve passes posteriorly, deep to the tendon of the flexor carpi ulnaris, pierces the deep fascia, and continues distally along the dorsomedial side of the wrist. It supplies sensation to the dorsal surface of the ulnar innervated fingers, that is, the fifth digit and medial half of the fourth digit. The remainder of the ulnar nerve continues into the wrist, traveling with the ulnar artery and vein as it passes lateral to the pisiform bone. Guyon’s canal, named after French surgeon Jean Casimir Félix Guyon (1831–1920), and also known as the ulnar canal or ulnar tunnel, is a space at the wrist between the pisiform bone and the hook of the hamate bone through which the ulnar artery and the ulnar nerve travel into the hand. In 1861, Guyon proposed that compression can occur in one of three zones. Zone 1 is in the most proximal portion of the canal, where the nerve is a single structure in one epineural sheath containing both motor and sensory fascicles. Zones 2 and 3 are further along the canal where the ulnar nerve has already bifurcated into motor and sensory branches. This lies just distal to the fibrous arch of the hypothenar muscles. The clinical picture will correlate with the zone in which compression is occurring.24 In some cases a fibrous arch overlying the motor branch of the ulnar nerve as it passes beneath the origin of the hypothenar muscles in Guyon’s canal is encountered. Awareness of this fibrous arch facilitates appropriate surgical management of ulnar-innervated intrinsic muscle weakness or wasting associated with ulnar compression at the wrist.24 In some cases a fibrous arch overlying the motor branch of the ulnar nerve as it passes beneath the origin of the hypothenar muscles in Guyon’s canal is encountered. Awareness of this fibrous arch facilitates appropriate surgical management of ulnar-innervated intrinsic muscle weakness or wasting associated with ulnar compression at the wrist.29
The nerve fibers cross beneath the pisohamate ligament and the fibrous arch of the hypothenar muscles. They then split off into sensory palmar digital nerves to the fifth and fourth digits, motor branches to the hypothenar muscles, deep branches to the interossei muscles, and a communicating branch to the median nerve. The ulnar nerve in the hand supplies motor function to the abductor digiti minimi, opponens digiti minimi, and flexor digiti minimi muscles of the fifth digit as well as the lumbricales III and IV. It also supplies the interossei, both dorsal and palmar, and finally the adductor pollicis and flexor pollicis brevis muscles.30
The sensory distribution of the nerve includes the palmar and dorsal medial aspects of the hand, including the fifth digit and half of the fourth digit. As the ulnar nerve crosses the extensor aspect of the elbow in a superficial site with little supporting epineurium, it is prone to injury after upper extremity trauma. The motor fibers that supply the intrinsic muscles of the hand occupy a more superficial location, and those that supply the flexor carpi ulnaris and ulnar half of the flexor digitorum profundus a deeper location. This fact is offered as an explanation of why intrinsic weakness of the hand muscles is a more often seen in patients with cubital tunnel syndrome. It then follows that as the sensory fibers are also located more superficially as the ulnar nerve traverses the extensor elbow, that paresthesias and sensory disturbances are the most common early features of cubital tunnel syndrome (Table 200-1).31
| MOTOR |
| Forearm, via the muscular branches of the ulnar nerve: |
Anatomic Variations
Numerous anatomic variations have been reported in the literature mainly between the median and the ulnar nerve in the forearm. The Martin-Gruber anastomosis is the most commonly encountered anatomical variation and was first described by the Swedish anatomist Martin32 in 1763 and later by Gruber33 in 1840. Here an anomalous neural pathway is seen in the proximal forearm where motor fibers from the median nerve cross over to the ulnar nerve. Another rare entity in the distal forearm, the Riche-Cannieu anomaly consists of the abnormal connection between the motor branch of the ulnar nerve and the recurrent motor branch of the median nerve.34
Etiology of Ulnar Nerve Compression
The ulnar nerve responds in a proportional manner by exhibiting increasingly altered intraneural microvascular blood flow, axonal transport and nerve function as the pressure exerted upon it increases.35 The main etiologies of ulnar nerve damage at the elbow joint are thought to be compression,17–1936 ischemia,1,37–40 traction,13,38,41 longitudinal strain, and friction.42 In previous studies25,43 increased cubital tunnel pressures up to 6 times have been reported with elbow flexion, wrist extension and shoulder abduction.1 Apfelberg in 1973 demonstrated that with elbow flexion, due to the increasing tension of the arcuate ligament and the bulging of the medial collateral ligament, there is change in the cross-sectional contour of the cubital tunnel from a smooth, round configuration to a flattened triangle, narrowing by approximately by 55%.1,17,40 Friction on the nerve may result from subluxation or dislocation of the nerve because of congenital or developmental laxity of the soft-tissue restraints that normally hold the ulnar nerve in its groove at the cubital tunnel.
Along its path around the elbow, five anatomic sites of potential entrapment/compression of the ulnar nerve exist.44 The Arcade of Struthers,22,24,45 the medial intermuscular septum,24 the cubital tunnel, the arcade of the flexor carpi ulnaris and the flexor-pronator aponeurosis have all been described. In the wrist, the motor branch of the ulnar nerve can also be compressed by the arch of origin of the adductor pollicis muscle. A well-defined band of tissue either at the point where the nerve crosses the third metacarpal or where it penetrates the adductor muscle46 can be found. Another potential site of ulnar compressive neuropathy, especially in cases of anterior dislocation of the nerve, is found as the nerve passes over the edge of the intermuscular septum. Compression can also develop as a postoperative complication of ulnar nerve transposition when the septum has not been excised or excised incompletely.
Constricting fascial bands, compression while under general anesthetic with inadequate padding, presence of an anomalous anconeus muscle (anomalous anconeus epitrochlearis muscle),47 a hypertrophied medial head of triceps as seen in some bodybuilders, ganglion cysts, subluxation of the ulnar nerve over the medial epicondyle,48 cubitus valgus, malunited supracondylar fracture, bony spurs and osteophytes, joint deformity in osteoarthritis or rheumatoid arthritis or gouty tophus,49 osteoarthritic or rheumatoid narrowing of the ulnar groove, constriction of the ulnar nerve as it passes behind the medial epicondyle causing frictional neuritis, medial epicondylitis (“golfer’s elbow”), tumors, postradiation,50 direct compression, repetitive strain, perineural adhesions, multiple intraneural hemangiomas,51 fractures, elbow dislocation, venepuncture, and severe hematoma are all additional described causes of ulnar neuropathy. Iatrogenic injuries to the nerve such as after total elbow replacement are also well described.52–54 Compression of the ulnar nerve in the ulnar groove is common in people who lean on their elbows, particularly in the flexed position (e.g., truck drivers leaning their arms on the edge of the window frame, people working on computers). Ulnar compressive neuropathy is also seen after suboptimal intraoperative padding to on the medial side of the arm and in patients confined to bed for acute55 or chronic illnesses.24 Chronic subluxation of the ulnar nerve in and out of the epicondylar groove, especially during extension and flexion of elbow, can result in friction neuritis and cause ulnar neuropathy.
The common causes of compression at the wrist at Guyon’s canal are repeated blunt trauma to the hypothenar region (e.g., bicycle riders) ganglionic cysts56 arising from the underlying carpus (usually from the triquetrohamate joint), lipoma,57 use of bilateral forearm crutches,58 vascular lesions,59 fractures of distal ulna or of carpal bones and fracture of the hook of the hamate.24
Diagnosis
Clinical Presentation
Cubital tunnel syndrome has been stratified by McGowan60 into three grades: grade I, sensory alteration only; grade II, muscle weakness/wasting of the interossei muscles; grade III, complete intrinsic muscle paralysis. Ulnar nerve palsy whether acute, subacute, or chronic, can cause wasting and weakness of the small muscles of the hand and partial clawing of the ring and little finger. The extent of the deformity and disability depends on the site of the lesion and the severity of the compression. Patients often have numbness and tingling along the fifth digit and the medial half of the fourth finger, often associated with a weakness of grip, and particularly when the patient rests on or flexes the elbow. Patients may experience pain and tenderness at the level of the cubital tunnel. The severity of pain is very variable and the distribution of pain may spread proximally and/or distally. Symptoms may be intermittent at first and then become more constant. Patients with chronic ulnar neuropathy may complain of loss of grip and pinch strength and loss of fine dexterity. Severe prolonged compression may present with intrinsic muscle wasting and clawing or abduction of the fifth digit at rest. The weakness is more pronounced in the intrinsic muscles of the hand than of the muscles of the forearm. This is due to the somatotopic organization of the fibers in the ulnar nerve. The motor fibers to the intrinsic muscles along with the sensory fascicles are situated more medially and more superficial therefore more likely to suffer physical trauma/friction or influence of compressive forces.61
Physical exam consists of a thorough inspection of the arm for any deformity, an abnormal mass and for any signs of a hyper mobile or subluxation of the ulnar nerve. On examination, the patient is asked to flex his/her elbow with full wrist extension for up to 3 minutes, and if this maneuver reproduces pain, numbness, or tingling symptoms, it can be considered a positive sign, analogous to Phalen’s test62 for carpal tunnel syndrome.
Froment’s sign may also be seen in the clinical examination of a patient with ulnar nerve entrapment. The patient holds a piece of paper between the thumb and the side of the adjacent index finger as the paper is pulled away. A patient with an ulnar nerve palsy will flex the thumb at the interphalangeal joint to try to keep hold of the paper due to the weakness of the adductor pollicis muscle.63
Imaging
The diagnosis of ulnar neuropathy is primarily associated with electrophysiologic testing and therefore routine imaging is not warranted. However in some cases plain x-rays, magnetic resonance imaging (MRI),64 computed tomography scan, or high-resolution ultrasonography65 at the elbow may be obtained to rule out an osteophyte, cyst, vascular anomaly, or any mass compressing the nerve. MRI with short tau inversion recovery (STIR) sequences, otherwise known as MR neurography,66,67 may show an increased signal in the nerve or denervation changes in the affected muscles. In ulnar entrapment at the elbow, however, electrophysiologic studies remain the gold standard for diagnosis.
Electromyography/Nerve Conduction Studies
The use of electrodiagnostic techniques to evaluate compression neuropathies was first described by Simpson68 in 1956. Preoperative electromyography (EMG) and nerve conduction velocities (NCVs) should be obtained on all patients. This information allows for confirmation of the entrapment as well as localization of the entrapment site. The test also serves to document the baseline conduction which can be especially useful to document recovery (or lack thereof) and for comparison for any future recurrence. Motor studies are more sensitive than mixed sensory studies at localizing ulnar neuropathy to the elbow.31,69
Recordings from the abductor digiti minimi and first dorsal interossei, which is the most distal muscle supplied by the ulnar nerve, give some of the most useful information to diagnose ulnar nerve entrapment.70–72 Measurements should be taken with both the elbow flexed and extended. The EMG typically shows low ulnar sensory amplitudes and slowed ulnar motor conduction velocities across the elbow.3 The median sensory/motor distal latencies are normal. Short-segment stimulation or “the inching technique”73,74 studies done at 1- to 2-cm intervals across the elbow give the most useful information, and with this technique and focal changes in amplitude or a waveform morphology change or conduction delay of more than 0.7 milliseconds across each 2 cm are considered abnormal.75 A decrease in amplitude of the ulnar sensory nerve action potential (SNAP) helps in the diagnosis. If both the ulnar and median conduction velocities are abnormal, the contralateral elbow as well as lower extremity NCVs should be performed to rule out a peripheral neuropathy.72
In cases of suspected ulnar neuropathy at the elbow, needle EMGs from abductor digiti minimi and first dorsal interossei should be performed even if the NCVs are within normal limits.70,72 There are, however, instances where the patient exhibits a clinical picture of ulnar nerve entrapment with normal EMG/NCV studies. It is up to the judgment of the clinician in these rare cases whether to offer surgical intervention. This decision is then based on the clinical examination.
