JBJS | Compression of the Medial Half of the Deep Branch of the Ulnar Nerve by an Anomalous Origin of the Flexor Digiti Minimi. A Case Report*

The Journal of Bone & Joint Surgery, Volume 78, Issue 3

Articles | March 01, 1996

Compression of the Medial Half of the Deep Branch of the Ulnar Nerve by an Anomalous Origin of the Flexor Digiti Minimi. A Case Report*

R. J. SPINNER, M.D.†; R. E. LINS, M.D.‡, DURHAM, NORTH CAROLINA; M. SPINNER, M.D.§, BRONX, NEW YORK

View Disclosures and Other Information

Investigation performed at Duke University Medical Center, Durham, and Albert Einstein College of Medicine, Bronx

The Journal of Bone & Joint Surgery. 1996; 78:427-30

5 Recommendations (Recommend) | 3 Comments | Saved by 3 Users Save Case

Article

Figures

References

text A A A

Introduction

Introduction | Case Report | Discussion | References

We describe the case of a patient who had compression of the medial half of the deep branch of the ulnar nerve by an anomalous penetrating tendinous structure, resulting in an unusual pattern of ulnar neuropathy. When the patient was first seen, she had isolated weakness of the intrinsic muscles of the ring and little fingers as well as some of the hypothenar muscles, without evidence of additional ulnar innervated motor or sensory abnormality. To our knowledge, this lesion has not been reported previously.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Duke University Medical Center, Box 3000 DUMC, Durham, North Carolina 27710. Please address requests for reprints to Dr. Spinner.

‡The Hand Treatment Center, 980 Johnson Ferry Road, Suite 1020, Atlanta, Georgia 30342.

§557 Central Avenue, Cedarhurst, New York 11516.

*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.

†Duke University Medical Center, Box 3000 DUMC, Durham, North Carolina 27710. Please address requests for reprints to Dr. Spinner.

‡The Hand Treatment Center, 980 Johnson Ferry Road, Suite 1020, Atlanta, Georgia 30342.

§557 Central Avenue, Cedarhurst, New York 11516.

View Large | Download Slide(.ppt)
Add to My JBJS

Drawing showing the anatomy of the fibrotic arch and its relationship to the deep branch of the ulnar nerve.

View Large | Download Slide(.ppt)
Add to My JBJS

Drawing showing the anomalous tendinous extension of the flexor digiti minimi penetrating the deep branch of the ulnar nerve and creating a neural loop.

Case Report

Introduction | Case Report | Discussion | References

A twenty-year-old woman who worked in the retail industry had a one-year history of a deformity involving the right, dominant hand. She recalled no episode of trauma and related the onset of the problem to lifting hangers with heavy clothing. She had no sensory abnormality or symptoms referable to problems elsewhere in the limb or cervical area and was otherwise healthy.

Before the patient was seen by the senior one of us (M. S.), a number of investigations had been performed. The findings on standard radiographs as well as a magnetic resonance image of the hand and wrist were considered within normal limits. No abnormalities were identified on two sets of nerve-conduction and electromyographic studies that had been performed two months apart. Non-invasive vascular studies demonstrated a congenitally small ulnar artery, which was confirmed by magnetic resonance angiography. Despite immobilization, avoidance of exacerbating activities, and use of non-steroidal anti-inflammatory agents, no improvement was noted.

On examination, a claw deformity of the ring and little fingers was observed. The deformity was passively correctable. Atrophy of the intrinsic muscles was visible in the intermetacarpal region between the third and fourth web spaces. Testing of muscle strength against the hand of the examiner demonstrated intrinsic weakness in the third and fourth dorsal interossei, second and third palmar interossei, third and fourth lumbrical muscles, flexor digiti minimi, and opponens digiti minimi. The other intrinsic muscles that are typically innervated by the ulnar nerve (including the abductor digiti minimi, adductor pollicis⁷, first and second dorsal interossei, and first palmar interosseous) were normal, and the extrinsic muscles that are innervated by the ulnar nerve (the flexor carpi ulnaris and flexor digitorum profundus to the ring and little fingers) had normal tone and strength. The flexor pollicis brevis (innervated by the median and ulnar nerves), first and second lumbrical muscles, abductor pollicis brevis, and opponens pollicis (innervated by the median nerve) were normal. With digital extension, the little finger was noted to be abducted away from the ring finger (a positive Wartenberg sign²⁹). The findings of two-point discrimination and Semmes-Weinstein monofilament testing were within normal limits. Tenderness was elicited with percussion of the ulnar nerve at the wrist, but it was not elicited in the cubital tunnel. The Allen test revealed filling in the radial artery bilaterally at two seconds after release of compression, in the right ulnar artery at five seconds, and in the left ulnar artery at four seconds. Pulp-to-pulp or so-called tip-pinch dynamometry with the Preston pinch gauge (J. A. Preston, Jackson, Mississippi) revealed values of 8.4 kilograms in the right hand and 7.2 kilograms in the left.

A third electrodiagnostic study was done six months after the second, with specific attention to the intrinsic muscles. The findings revealed denervation and fibrillation potentials in the third and fourth dorsal interossei, second and third palmar interossei, third and fourth lumbrical muscles, opponens digiti minimi, and flexor digiti minimi. The remaining intrinsic and thenar muscles were normal on electrical testing. In addition, stimulation of the median nerve produced palmar abduction of the thumb.

An operation was performed with Bier-block anesthesia. An incision was centered on the hook of the hamate, with use of operative loupes (magnification, 5.5 times). The ulnar nerve was identified proximal to the wrist flexion crease. The deep branch and sensory branches to the third and fourth web spaces were identified. The deep branch of the ulnar nerve was traced through the hypothenar fibrotic arch (Fig. 1). A six-millimeter anomalous tendinous extension of the flexor digiti minimi, arising from the hook of the hamate, was identified and observed to penetrate the deep branch of the ulnar nerve. This resulted in a small neural loop (or a so-called ellipse¹²), by virtue of the division of the nerve into two halves (Fig. 2). The medial half of the deep motor branch was compressed distal to the branch innervating the abductor digiti minimi. When this anomalous tendinous penetration was released, the neural loop collapsed. The opponens digiti minimi was then released from its origin in order to visualize the deep branch in its entirety, passing into the depth of the mid-part of the palm. The deep branch, traced distally, appeared normal. With use of a hand-held battery-operated electrical stimulator (Xomed-Treace Pulsatron-II; Singer Medical Products, Bensenville, Illinois) that delivered 0.7 milliampere of current at eighty pulses per second, both halves of the deep branch of the ulnar nerve were examined. When the deep branch of the ulnar nerve was stimulated proximal to the site of the neural loop, there was no response in the ring and little fingers, but the thumb adducted and the index finger abducted. Stimulation of the medial half of the deep ulnar nerve distal to the neural loop resulted in flexion of the metacarpophalangeal joint of the ring and little fingers, with simultaneous extension of the distal and proximal interphalangeal joints of these fingers as well as opposition of the ring and little fingers toward each other. When the lateral half of the deep ulnar nerve was stimulated, the thumb adducted toward the ray of the index finger.

Immediately postoperatively in the recovery room, the clawing of the hand improved. Within three months, the patient regained normal function and muscle tone in the hand. She remained asymptomatic two years postoperatively.

Discussion

Introduction | Case Report | Discussion | References

The distal ulnar tunnel is a one and one-half-inch (approximately four-centimeter) confined space, with discrete anatomical limits and boundaries. It extends from the proximal edge of the palmar ligament to the fibrous edge of the hypothenar muscles and is traversed by the ulnar nerve and artery. The tunnel has been subdivided into three zones to correlate the anatomy of the ulnar nerve and its branches with clinical symptoms^11,24. Zone I consists of the ulnar nerve proximal to its bifurcation; zone II, the deep branch of the ulnar nerve; and zone III, the superficial branch. Although many variations occur, the deep branch of the ulnar nerve typically innervates the palmar and dorsal interossei, third and fourth lumbrical muscles, hypothenar muscles, adductor pollicis, and deep head of the flexor pollicis brevis.

Ulnar-nerve compression within Guyon's canal is most commonly within zone I. Involvement of the deep branch within zone II, which is also relatively common, is usually due to ganglia or anatomical abnormalities in the vicinity of the fibrotic arch at the origin of the hypothenar muscles^8,11. The fibrotic arch has been demonstrated in 40 per cent of cadavera⁴, and swelling or edema of the fibrotic arch plays a well recognized role in the development of compression of the deep branch¹⁶. When a patient has motor weakness alone, it is almost exclusively due to compression in zone II. However, posteromedial fascicular involvement of the ulnar nerve within zone I may also result in pure motor weakness^8,11.

The usual clinical presentation of pure motor involvement from compression of the ulnar nerve or its deep branch within the distal ulnar tunnel^8,11,28 includes paresis or paralysis of (1) all of the intrinsic muscles innervated by the ulnar nerve²⁴, (2) the intrinsic muscles innervated by the ulnar nerve except the hypothenar muscles¹³, (3) the intrinsic muscles innervated by the ulnar nerve except the abductor digiti minimi²⁸, or (4) the first dorsal interosseous and adductor pollicis muscles^6,22.

Dysfunction of the ulnar nerve has been associated with variations in neural anatomy either involving the ulnar nerve at a level just proximal to the wrist^17,19,25,30 or involving the deep branch of the ulnar nerve^2,6. Loops of the deep ulnar nerve^14,18 have been previously identified in the region of the hook of the hamate in several patients^2,6,10 as well as in 9 per cent (seven) of seventy-seven cadavera in an anatomical study²⁰. Although the internal topography of the deep branch of the ulnar nerve has not been fully defined, histological cross-sectional studies have demonstrated the nerve to be composed of one to six fascicles^3,9. The innervation of the hypothenar muscles is from the medial aspect of the deep branch of the ulnar nerve⁹. The clinical presentation and intraoperative findings in our patient suggest that the medial half of the deep branch of the nerve, distal to its branches to the abductor digiti minimi, supplied the other hypothenar muscles as well as the intrinsic muscles of the third and fourth interspaces. The lateral half of the deep branch of the ulnar nerve probably supplied the muscles of the first and second web spaces.

Although it is rare, innervation of the thenar, adductor, and first dorsal muscles was identified as coming from the median nerve in 5 per cent (six) of 124 patients in one study²¹. However, the preoperative electrical studies and intraoperative stimulation of nerves eliminated the possibility of cross innervation in our patient.

The intraoperative response to stimulation of the medial half of the deep branch of the ulnar nerve after release indicated a neurapraxia and suggested that a good clinical recovery could be expected. This was confirmed by the immediate improvement in the clawing of the hand noted in the recovery room.

To our knowledge, penetration of the deep branch of the ulnar nerve by a tendinous structure has not been reported previously, although analogous neural penetration has been demonstrated elsewhere in the upper limb. One ramus of an ulnar neural loop may pass through the flexor carpi ulnaris just proximal to the wrist and entrap the ulnar nerve with resultant neuropathy^19,25,30. An anomalous flexor digitorum superficialis tendon¹ has also been reported to split the median nerve, resulting in neural dysfunction.

Anatomical variations within Guyon's canal⁵ or related to the flexor digiti minimi are common²⁷. An accessory flexor digiti minimi, arising in the forearm and passing through Guyon's canal, has presented as a mass in the hypothenar region¹⁵ or with nerve compression^23,26 at the level of the wrist, but not at the level of the fibrotic arch as was seen in our patient.

References

Introduction | Case Report | Discussion | References

Baruch, A., and |and |Hass, A.: Anomaly of the median nerve [letter]. J. Hand Surg.,2: 331-332, 1977.2331 1977

Bergfield, T. G., and |and |Aulicino, P. L.: Variation of the deep motor branch of the ulnar nerve at the wrist. J. Hand Surg.,13A: 368-369, 1988.13A368 1988

Bonnel, F.: Histologic structure of the ulnar nerve in the hand. J. Hand Surg.,10A: 264-269, 1985.10A264 1985

Dellon, A. L., and |and |Mackinnon, S. E.: Anatomic investigations of nerves at the wrist: II. Incidence of fibrous arch overlying motor branch of ulnar nerve. Ann. Plast. Surg.,21: 36-37, 1988.2136 1988 [PubMed][CrossRef]

Dodds, G. A. III; Hale, D.; and |and |Jackson, W. T.: Incidence of anatomic variants in Guyon's canal. J. Hand Surg.,15A: 352-355, 1990.15A352 1990

Fenning, J. B.: Deep ulnar-nerve paralysis resulting from an anatomical abnormality. A case report. J. Bone and Joint Surg.,47-A: 1381-1382, Oct. 1965.47-A1381 1965

Froment, M. J.: La paralysie de l'adducteur du pouce et le signe de la préhension. Rev. Neurol. (Paris),28: 1236-1240, 1914-1915.281236 1914-1915

Gelberman, R. H.: Ulnar tunnel syndrome. In Operative Nerve Repair and Reconstruction, pp. 1131-1143. Edited by R. H. Gelberman. Philadelphia, J. B. Lippincott, 1991.

Gonzalez, M. H.; Brown, A.; Goodman, D.; and |and |Black, B.: The deep branch of the ulnar nerve in Guyon's canal: branching and innervation of the hypothenar muscles. Orthopedics,19: 55-58, 1996.1955 1996 [PubMed]

Greenberg, J. A., and |and |Mosher, J. F., Jr.: Distal ulnar neuropathy: coexisting anatomic variants. J. Hand Surg.,17A: 303-305, 1992.17A303 1992

Gross, M. S., and |and |Gelberman, R. H.: The anatomy of the distal ulnar tunnel. Clin. Orthop.,196: 238-247, 1985.196238 1985 [PubMed]

Hartmann, H.: Note sur l'anatomie des nerfs de la paume de la main. Bull. mem. soc. anat. Paris,62: 860, 1887.62860 1887

Hayes, J. R.; Mulholland, R. C.; and |and |O'Connor, B. T.: Compression of the deep palmar branch of the ulnar nerve. Case report and anatomical study. J. Bone and Joint Surg.,51-B(3): 469-472, 1969.51-B(3)469 1969

Lassa, R., and |and |Shrewsbury, M. M.: A variation in the path of the deep motor branch of the ulnar nerve at the wrist. J. Bone and Joint Surg.,57-A: 990-991, Oct. 1975.57-A990 1975

Lipscomb, P. R.: Duplication of hypothenar muscles simulating soft-tissue tumor of the hand. Report of a case. J. Bone and Joint Surg.,42-A: 1058-1061, Sept. 1960.42-A1058 1960

Lotem, M.; Gloobe, H.; and |and |Nathan, H.: Fibrotic arch around the deep branch of the ulnar nerve in the hand. Anatomical observations. Plast. and Reconstr. Surg.,52: 553-556, 1973.52553 1973 [CrossRef]

McCarthy, R. E., and |and |Nalebuff, E. A.: Anomalous volar branch of the dorsal cutaneous ulnar nerve: a case report. J. Hand Surg.,5: 19-20, 1980.519 1980

Mannerfelt, L.: Studies on the hand in ulnar nerve paralysis. A clinical-experimental investigation in normal and anomalous innervation. Acta Orthop. Scandinavica,Supplementum 87: 19-53, 1966.Supplementum 8719 1966

O'Hara, J. J., and |and |Stone, J. H.: Ulnar neuropathy at the wrist associated with aberrant flexor carpi ulnaris insertion. J. Hand Surg.,13A: 370-372, 1988.13A370 1988

Rogers, M. R.; Bergfield, T. G.; and |and |Aulicino, P. L.: A neural loop of the deep motor branch of the ulnar nerve: an anatomic study. J. Hand Surg.,16A: 269-271, 1991.16A269 1991

Rowntree, T.: Anomalous innervation of the hand muscles. J. Bone and Joint Surg.,31-B(4): 505-510, 1949.31-B(4)505 1949

Ruder, J. R., and |and |Wood, V. E.: Ulnar nerve-compression at the arch of origin of the adductor pollicis muscle. J. Hand Surg.,18A: 893-895, 1993.18A893 1993

Salgeback, S.: Ulnar tunnel syndrome caused by anomalous muscles. Case report. Scandinavian J. Plast. and Reconstr. Surg.,11: 255-258, 1977.11255 1977 [CrossRef]

Shea, J. D., and |and |McClain, E. J.: Ulnar-nerve compression syndromes at and below the wrist. J. Bone and Joint Surg.,51-A: 1095-1103, Sept. 1969.51-A1095 1969

Starke, W.; Rathay, B.; and |and |Hülsmann, P.: Anatomische Variante als seltene Ursache einer distalen Ulnariskompression. Handchir. Mikrochir. Plast. Chir.,20: 347-348, 1988.20347 1988 [PubMed]

Swanson, A. B.; Biddulph, S. L.; Baughman, F. A., Jr.; and |and |de Groot, G.: Ulnar nerve compression due to an anomalous muscle in the canal of Guyon. Clin. Orthop.,83: 64-69, 1972.8364 1972 [PubMed][CrossRef]

Tountas, C. P., and Bergman, R. A.: Anatomic Variations of the Upper Extremity. New York, Churchill Livingstone, 1993.

Uriburu, I. J. F.; Morchio, F. J.; and |and |Marin, J. C.: Compression syndrome of the deep motor branch of the ulnar nerve (piso-hamate hiatus syndrome). J. Bone and Joint Surg.,58-A: 145-147, Jan. 1976.58-A145 1976

Wartenberg, R.: A sign of ulnar palsy. J. Am. Med. Assn.,112: 1688, 1939.1121688 1939

Zook, E. G.; Kucan, J. O.; and |and |Guy, R. J.: Palmar wrist pain caused by ulnar nerve entrapment in the flexor carpi ulnaris tendon. J. Hand Surg.,13A: 732-735, 1988.13A732 1988

Topics