Ulnar Neuropathy in the Distal Ulnar Tunnel DAVID W. SHUPE, PT, ATC' Journal of Orthopaedic & Sports Physical Therapy A brief anatomical review of the ulnar nerve and areas of ulnar nerve entrapment is discussed. The importance of the dorsal cutaneous nerve is presented with regard to localizing a lesion to the ulnar nerve in the forearm. A classification system is described for ulnar entrapment that occurs distal to the wrist. The case of a nine-yearold girl with a fibrous entrapment of the ulnar nerve in the distal ulnar tunnel is presented. The clinical and diagnostic procedures required for localizing the level of the ulnar nerve entrapment are described, along with the operative findings of this case report. When evaluating and treating patients with trauma to the upper extremity, a vital part of the assessment is the basic neurological examination. One component of this examination is the evaluation of peripheral nerve function. If ulnar nerve involvement is suspected, then particular assessment of this nerve is warranted. Conclusions derived from this assessment will allow the physical therapist to develop more realistic treatment goals and to enhance communication with patients and others in the medical community. The purpose of this article is to give a brief anatomical review of the ulnar nerve and potential areas of ulnar nerve entrapment, with emphasis on the distal ulnar tunnel. A case report of a patient with a fibrous entrapment of the ulnar nerve in the distal ulnar tunnel is presented. ANATOMY OF THE ULNAR NERVE An anatomical review of the ulnar nerve shows that after originating from the medial cord of the brachial plexus, it descends along the medial aspect of the arm with the median nerve. In the distal aspect of the arm, it becomes more superficial after passing through the intermuscular sep tum of the triceps brachii (Arcade of Struthers). At the elbow, the nerve passes through a fibroosseous tunnel, known as the cubital tunnel. Laterally, this tunnel is bordered by the elbow joint, ' Director. Swrtsmed Center. 325 N. 25th Street. Lafavette. IN 47904. 0190-601 1 PI11 301 -OOO6$03.OO/O THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAW Copyight 0 1991 by The OrWqwdc and Sports Physical Therapy Sectis of the Americen Physical Therapy Associati medially by the heads of the flexor carpi ulnaris, and anteriorly by the medial epicondyle (1). After passing through the cubital tunnel. the nerve enters the forearm, taking a less superficial course when it descends between the two heads of the flexor carpi ulnaris muscle (7). The ulnar nerve then takes a straight course along the medial aspect of the forearm after giving muscular branches to the flexor carpi ulnaris and the flexor digitorum profundus to the ring and little fingers (barring any anomalies). It is important to note that entrapments may occur at the Arcade of Struthers, in the cubital tunnel, and within the fibrous tunnel formed by the two heads of the flexor carpi ulnaris. Approximately eight to ten centimeters proximal to the ulnar styloid process, the dorsal cutaneous nerve branches from the ulnar nerve (Figure 1). Four to five centimeters proximal to the styloid process, the dorsal cutaneous nerve crosses the medial aspect of the ulna to take a position dorsal to the ulna (4, 7). This branch provides sensory innervation to the ulnar portion of the dorsum of the hand and parts of the dorsal aspect of the little and ring fingers (Figure 2). The ulnar nerve enters the hand through the distal ulnar tunnel (2, 5). This tunnel is four to four and one-half centimeter long, beginning at the proximal edge of the palmar carpal ligament and extending to the fibrous arch of the hypothenar muscles (Figure 3). As described by Gross and Gelberman (2), the roof of the tunnel from proximal to distal is composed of the palmar carpal ligament, palmaris brevis muscle, and hypothenar fat and fibrous tissue. Kleinert and Hayes (5) reported that this roof is multilayered, with the palmar 6 SHUPE JOSPT 13: 1 January 199 1
carpal ligament blending distally with the hypothenar fascia, radially with the palmar aponeurosis, and proximally with the volar forearm fascia. The floor of the tunnel is formed by the tendons of the flexor digitorum prcifundus, the transverse carpal ligament, the pisohamate and pisometacarpal ligaments, and the opponens digiti minimi (2). The flexor carpi ulnaris, the pisiform, Dorsal Cutaneous Branch Ulnaris Figure 1. Course of the dorsal cutaneous nerve. Figure 2. Sensory distribution of the dorsal cutaneous branch of the ulnar nerve. and the abductor digiti minimi comprise the ulnar wall. The radial wall is formed by the tendons of the extrinsic flexors, the transverse carpal ligament, and the hook of the hamate. Along with the ulnar nerve, the ulnar artery lies within the distal ulnar tunnel. Within the distal ulnar tunnel, the ulnar nerve divides into a superficial branch and a deep branch (5). The superficial branch supplies the skin on the palmar aspect of the little finger and the medial half of the ring finger. Motor fibers to the palmaris brevis also take their origin from the superficial branch. After innervating the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi muscles, the deep palmar branch turns laterally to supply the dorsal and palmar interossei, the third and fourth lumbricals, the adductor pollicis, and the deep head of the flexor pollicis brevis muscles. In their anatomical study of the distal ulnar tunnel, Gross and Gelberman (2) used an anatomical basis for dividing the tunnel into three zones. Zone one is the portion of the tunnel proximal to the bifurcation of the nerve. Any lesion of the ulnar nerve in this zone would lead to both motor and sensory deficits. Zone two encompasses the deep motor branch of the nerve. Any involvement of the nerve in this zone would lead to motor deficits only. The superficial branch is located in zone three. Any lesion at this level would lead to sensory involvement and a motor deficit of the palmaris brevis. SENSORY AND MOTOR EVALUATION Understanding the distribution of the dorsal cutaneous branch of the ulnar nerve is extremely important in helping to differentiate the approximate level of any lesion of the ulnar nerve in the distal one-half of the forearm. Any problem proximal to the dorsal cutaneous branch would result in a sensory disturbance to the dorsal and ulnar aspect of the hand, parts of the dorsal aspect of the ring and little fingers, and a sensory deficit on the palmar surface of the little finger and medial aspect of the ring finger. A lesion distal to the origin of this small cutaneous branch would only produce a sensory deficit in the little finger and medial aspect of the ring finger (7). Regardless of where an ulnar nerve lesion in the distal forearm would be located, the same motor deficit would exist. A thorough assessment of the motor function of the hand, fingers, and thumb is an essential component of the evaluation process. Along with any functional tests, a detailed manual muscle test should always be performed. Strength deficits in the hand muscles innervated by the ulnar nerve can result directly from an ulnar motor branch dysfunction as discussed. However, these JOSPT 13: 1 January 199 1 ENTRAPMENT AT DISTAL ULNAR TUNNEL 7
Opponens Digiti Minimi Flexor Digiti Minimi Deep Branch Ulnar Nerve Superficial Branch Abductor Digiti Minimi Hamate Transverse Carpal Ligament Palmar Carpal Ligament Pisohamate Ligament Flexor Carpi Ulnaris Journal of Orthopaedic & Sports Physical Therapy strength deficits may also arise from other sources that should not be ignored, even in the presence of known trauma to the ulnar nerve. Other sources of dysfunction may include motor neuron diseases, nerve root compression, brachial plexopathy from various etiologies, diseases of peripheral nerves, mechanical abnormalities as a result of a disease process, and nerve entrapments (3). CASE REPORT A nine-year-old girl fell from a balance beam during gymnastics practice. She landed on her right hand with the wrist extended and the elbow in a fully extended position (Figure 4). Immediate pain and disability were reported in the right elbow. After x-ray examination revealed a displaced fracture of the medial epicondyle of the right humerus, an open reduction and internal fixation of the displaced fragment were performed (Figure 5). Stabilization was maintained with percutaneous pinning, and a posterior plaster splint was applied with the elbow at 60' of flexion. After five weeks, the Steinman pins were removed and the patient was referred to physical therapy for rehabilitation. Active range of motion (AROM) of the right elbow was 50-1 05'; supination was 0-45'; and pronation was 0-73'. An AROM and gravity-assisted, static-stretching program was begun. At the seventh postoperative week, elbow AROM was 48-1 13O, with supination and pronation showing normal ROM measurements. The patient, now less focused on the elbow, reported Figure 3. Diagram of the distal ulnar tunnel. SHUPE that her ring and little fingers 'felt cold at times." Examination of the right hand revealed an abnormal resting finger position that consisted of clawing of the fourth and fifth fingers (6). Atrophy of the intrinsic hand muscles innervated by the ulnar nerve was noted. Trophic changes were present in the ring and little fingers, consisting of a white, leathery appearance to the skin and a brittie, ridged look to the nails. A sensory evaluation was normal to light touch and pinprick. Two-point discrimination was also normal at five millimeters. Manual muscle testing revealed normal function of all muscles innervated by the median nerve. Normal function of the flexor carpi ulnaris and flexor digitorum profundus to all fingers was present. No function of the intrinsic hand muscles innervated by the ulnar nerve was noted, although a minimal degree of abduction of the little finger was present. This was in the presence of no palpable contraction of the abductor digiti minimi and was thought to have resulted from aponeurotic attachments from the flexor carpi ulnaris to the abductor digiti minimi. Finger tip prehension (thumb to index) was possible, but lateral prehension was not. A negative Tinel's sign was present at the elbow and wrist over the ulnar and median nerves. Marked tenderness was found with palpation in the area of the hook of the hamate. A positive Tinel's sign was also present at this location. These findings were documented and reported to the referring physician. After carpal tunnel views of the right wrist ruled out a fracture of the hook of the hamate (6), JOSPT 13: 1 January
Figure 4. Mechanism of injury for nine-yearsld patient in case study. the decision was made in favor of nonsurgical management to see if spontaneous recovery of function would occur. At five months postinjury, ROM measurements of the right, elbow, along with supination and pronation of the forearm, were normal. The neurological status, however, remained unchanged. At this time, further evaluation was requested by her physician. Motor and sensory nerve conduction studies of the right median nerve were normal. Ulnar nerve studies using a needle electrode showed no response from the abductor digiti minimi or the first dorsal interosseous muscles. No evoked sensory action potential was elicited when recording from the little finger using an antidromic testing technique. Ulnar sensory testing for the dorsal cutaneous nerve showed significant slowing, with the amplitude of evoked sensory action potential somewhat decreased compared to the contralatera1 side. Over a six centimeter segment, the latency on the left was 1.8 msec with an amplitude Figure 5. Postoperative radiographs of right elbow: A) lateral view; B) anterior-posterior view. of 21.0 pv. The values on the right were 4.2 msec and 11.3 pv, respectively. This was a somewhat surprising finding since sensory testing of the dorsal cutaneous nerve was normal. The slowing, thought to result from a retrograde demyelination rather than from a more proximal process, seemed to be supported by the electromyographic (EMG) findings. Electromyographic sampling of the right a b ductor pollicus brevis and the flexor carpi ulnaris muscles showed normal, insertional activity with electrical silence at rest. Motor units were normal for shape, amplitude, and duration, and there was a normal interference pattern in the abductor pollicus brevis with a slightly reduced interference pattern in the flexor carpi ulnaris. The decreased interference pattern in the flexor carpi ulnaris was associated with subjective complaints of pain at the sampling site. When the abductor digiti minimi and the first dorsal interosseous muscles were sampled, minimal insertional activity with 2+ denervation potentials at rest was noted in both muscles. No JOSPT 13: 1 January 1991 ENTRAPMENT AT DISTAL ULNAR TUNNEL 9
motor units were located at multiple sampling sites in either of the latter muscles. A surgeon localized the ulnar nerve lesion and performed surgery at a level distal to the wrist. The hook of the hamate was found to be stable, but a significant fibrosis of the motor branch of the ulnar nerve and a lesser degree of fibrosis of its sensory branch was observed. Dissection, release of the entrapment, and an external neurolysis were performed in all three zones (2). At two weeks postsurgery, the patient reported that the fourth and fifth fingers "felt warmer." According to the surgeon, some interossei muscle function was noted at four weeks following surgery. After this time, objective information and the opportunity for further evaluation of the patient were no longer available to the author. However, at four months postsurgery, an uncomplicated recovery was reported by the surgeon. 0 SUMMARY Peripheral nerve injury can be a common sequelae in trauma involving the upper extremity. Recognizing an orthopaedic injury and its soft tissue and/or neurological components is critical. Neurological assessment should be a routine part of a thorough physical therapy examination in any orthopaedic and sports rehabilitation practice. Appreciation is extended to Hospital Services. Inc. for all of their assistance. REFERENCES 1. Green DP: Operative Hand Surgery. Vd 2. Churchill/Livingstm: New York. 1982 2. Gross MS. Gelbennan RH: The Anatomy of the Distal Unar Tunnel. Clin Orthop 196:238-247. 1985 3. Hogue RE: Compression of the deep palmar branch of the ulnar nerve: A case report. Phys Ther 65203-205.1985 4. Jabre JF: Unar nerve lesions at the wrist: new technique for recording from the sensory dorsal branch of the ulnar nerve. Neurology 30373-876. 1980 5. Klemert HE. Hayes JE: The Unar Tunnel Syndrwne. Plast Reconstr Surg 47:21-24. 1971 6. Parker RD. Berkowitz MS. Brahrns MA. Bohl WR: Hook of the harnate fractures in athletes. Am J Sports Med 14517-523. 1986 7. Spmner M: Injuries to the Major Branches of Peripheral Nwes of the Forearm, pp 114-127. Philadelphia: WE Saunders SHUPE JOSPT 13: 1 January 1991