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The hypothenar adductor muscle: An anomalous intrinsic muscle compressing the ulnar nerve
The Hypothenar Adductor Muscle: An Anomalous Intrinsic Muscle Compressing the Ulnar Nerve Joseph M. Failla, MD, Detroit, MI
Two cases of ulnar nerve compression by a transverse muscle, deep to the palmaris brevis muscle and inserting into the hypothenar fascia, were treated surgically. One patient had purely deep motor branch palsy, and the other had motor and sensory changes.
osseous and adductor pollicis muscles, with visible increase in muscle bulk, although not to normal size, and elimination of Froment's sign. The patient noted normal hand function.
Case Reports
A 72-year-old man noted paresthesias in the ring and little fingers, muscle wasting, and hand weakness that began 2 months after 1 intensive week of golf school. On examination there was generalized interosseous and abductor digiti quinti muscle wasting, with grade 4 strength (Fig. 2). The Tinel test over Guyon's canal gave paresthesias to the tips of the ring and little fingers. The Allen test result was normal. Nerve conduction testing showed no response for the ulnar sensory component at the affected wrist, with a normal value contralaterally. Electromyography showed fibrillations in the first dorsal interosseous and abductor digiti quinti muscles. Release of Guyon's canal revealed a transverse muscle compressing the ulnar nerve proximal to motor and sensory branching (Fig. 2). The muscle spanned from the periosteum at the ulnar aspect of the base of the hook of hamate to the proximal and deepest hypothenar muscle fascia. The fascia over the anomalous muscle was very thick and contributed to the compression. Paresthesias were immediately relieved by release of the muscle, and interosseous muscle strength gradually improved but was less than in the opposite hand.
Case 1
An 18-year-old man, who played handball regularly, noted hand weakness and visible muscle wasting for several months. On examination, the first dorsal interosseous and adductor pollicis muscles showed wasting and weakness. Froment's sign was positive. Sensation was normal, and the Allen test result was normal. Electromyography showed fibrillations in the first dorsal interosseous and adductor pollicis. Release of the ulnar nerve showed a thick, transversely oriented muscle, deep to the ulnar neurovascular bundle, compressing only the motor branch of the ulnar nerve (Fig. IA). The muscle spanned from the ulnar aspect of the distal portion of the transverse carpal ligament to the hypothenar fascia. After the muscle was cut, the motor branch of the ulnar nerve ran radially beneath the ulnar flexor tendons, free of compression (Fig. IB). By 18 months after surgery, full strength had returned to the first dorsal inter-
From the Department of Orthopaedic Surgery, Henry Ford Hospital, Detroit, MI. Received for publication Feb. 28, 1995; accepted in revised form July 18, 1995. 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. Reprint requests: Joseph M. Failla, MD, Department of Orthopaedic Surgery, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202.
366
The Journal of Hand Surgery
Case 2
Discussion In both cases, an anomalous muscle in the depths of Guyon's canal compressed the ulnar nerve (Fig. 3). In one, the muscle was distal and compressed only the motor branch of the ulnar nerve; in the other, the entire nerve was compressed proximally.
The Journal of Hand Surgery/Vol. 21A No. 3 May 1996
367
Figure 2. A transverse anomalous muscle (between small white arrows) compressing the ulnar nerve deep to Guyon's canal. The ulnar nerve (long black arrows) is pulled anteriorly by vessel loops proximally (left) and distally (right). P, proximal; D, distal; R, radial; U, ulnar.
abductor digiti quinti type muscle, 4 the palmaris brevis profundus, 5 and the intrinsic muscles described above. Symptoms can be purely motor or motor and sensory. Although median nerve compression by anomalous muscles can occur, this was due to aberrant lumbricals in one case. 6 In contrast to the m a n y Figure 1. (A) Anomalous transverse muscle (between small white arrows) distal to Guyon's canal compressing the motor branch of the ulnar nerve (between black arrows). The rake is radial and the smooth retractor is ulnar. P, proximal; D, distal; R, radial; U, ulnar. (B) After release of the muscle, the motor branch of the ulnar nerve (between arrows) courses toward the adductor pollicis, dorsal to the ulnar flexor profundus tendons (f).
Both patients had a history of chronic mechanical pressure on the ulnar palm, by a handball in one case and by a golf club grip in the other; the differential diagnosis therefore included ulnar artery thrombosis, but the ulnar artery was seen to be normal. Other entities in the differential diagnosis were a ganglion in G u y o n ' s canal and hook of hamate nonunion, which also were not present. Proximal compression of the ulnar nerve at the elbow or cervical spine level was also considered and eliminated. Anomalous muscles compressing the ulnar nerve can be extrinsic; such muscles include an accessory palmaris longus, 1 an accessory flexor digiti quinti, 2 and an accessory abductor digiti quinti, 3 all originating in the forearm. They can be intrinsic, such as an
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.
Figure 3. Diagram of the origin and insertion of the anomalous muscles (1) in case 1 and (2) in case 2, and their relationship to the ulnar nerve (u), the motor branch of the ulnar nerve (m), and the hypothenar muscles (H). h, hook of hamate; p, pisiform; tcl, transverse carpal ligament; T, thenar muscles; f, flexor digitorum profundus of little finger.
368
Failla/Hypothenar Adductor Muscle
possible anomalous hypothenar muscles that cause ulnar nerve compression, anomalous thenar muscles are rare, have an extrinsic component, and have not been associated with median nerve compression. 7 This is consistent with the clinical observation by Verdan 8 that thenar muscles vary in terms of innervation, while the hypothenar muscles vary greatly in form, with the only constant portion being the opponens digiti quinti. Anomalous muscles can be either duplicated or modified versions of normal muscles. Examples are the reversed palmaris longus 9 and duplicated extrinsic finger extensors, l~They can also be considered to be expressions of muscles present in animals lower on the evolutionary scale. An example is the intrinsic superficial digital flexor muscle found in salamanders, the human foot, and in one human hand. 11 The function of the two muscles reported is a matter of speculation, but both appear to be more related to the hypothenar muscles than to the palmaris brevis, since they are deeper and inserted on the hypothenar fascia. The small size of both muscles implies minimal functional impact. However, in the first case, the plane of the muscle was at the same depth as the adductor pollicis, and it was positioned anatomically to cause adduction of the hypothenar mass. In the second case, the muscle was similar in depth to the palmaris brevis profundus, but it was attached ulnarly to the hypothenar fascia, rather than the pisiform, and thus was also positioned to adduct the hypothenar mass. Both muscles are very different in origin and insertion from the palmaris brevis, which originates much more superficially from the palmar aponeurosis and flexor retinaculum subcutaneously, and inserts on dermis of the hypothenar palm. '2 Because of the location of these muscles, they likely function to adduct the
ulnar aspect of the palm by pulling the hypothenar musculature in a radial direction. For these reasons, the two muscles presented were named the hypothenar adductor muscle.
References 1. Regan PJ, Feldberg L, Bailey BN. Accessory palmaris longus causing ulnar nerve compression at the wrist. J Hand Surg 1991;16A:736-738. 2. Swanson AB, Biddulph SL, Baughman FA, DeGroot G. Ulnar nerve compression due to an anomalous muscle in the canal of Guyon. Clin Orthop 1972;83:64-69. 3. Jeffrey AK. Compression of the deep palmar branch of the ulnar nerve by an anomalous muscle. J Bone Joint Surg 1971 ;53B :718-723. 4. Uriburu IJF, Morchio FJ, Marin JC. Compression of the deep motor branch of the ulnar nerve (piso-hamate hiatus syndrome). J Bone Joint Surg 1976;58A:145-147. 5. Tonkin MA, Lister GD. The palmaris brevis profundus: an anomalous muscle associated with ulnar nerve compression at the wrist. J Hand Surg 1985;10A:862-864. 6. Asai M, Wong ACW, Matsunaga T, Akahoshi Y. Carpal tunnel syndrome caused by aberrant lumbrical muscles associated with cystic degeneration of the tenosynovium. J Hand Surg I986;11A:218-221. 7. Legan J, Shepler TR. Congenital hypertrophy of the thenar eminence with accessory head of the abductor pollicis brevis in the forearm. J Hand Surg 1992;17A:884-886. 8. Verdan C. Les anomalies musculo-tendineuses et leur signification en chirurgie de la main. Rev Chit Orthop 1981; 67:221-230. 9. Van Demark R. Tumor of the wrist of anomalous muscle origin. J Bone Joint Surg 1955;37A:1284-5. 10. Cusenz BJ, Hallock GG. Multiple anomalous tendons of the fourth dorsal compartment. J Hand Surg 1986;11A: 263-264. 11. Wesser DR, Calostypis F, Hoffman S. The evolutionary significance of an aberrant flexor superficialis muscle in the human palm. J Bone Joint Surg 1969;51A:396-398 12. Gray H. Gray's anatomy. Philadelphia: Running Press, 1901:406.
Two cases of ulnar nerve compression by a transverse muscle, deep to the palmaris brevis muscle and inserting into the hypothenar fascia, were treated surgically. One patient had purely deep motor branch palsy, and the other had motor and sensory changes.
osseous and adductor pollicis muscles, with visible increase in muscle bulk, although not to normal size, and elimination of Froment's sign. The patient noted normal hand function.
Case Reports
A 72-year-old man noted paresthesias in the ring and little fingers, muscle wasting, and hand weakness that began 2 months after 1 intensive week of golf school. On examination there was generalized interosseous and abductor digiti quinti muscle wasting, with grade 4 strength (Fig. 2). The Tinel test over Guyon's canal gave paresthesias to the tips of the ring and little fingers. The Allen test result was normal. Nerve conduction testing showed no response for the ulnar sensory component at the affected wrist, with a normal value contralaterally. Electromyography showed fibrillations in the first dorsal interosseous and abductor digiti quinti muscles. Release of Guyon's canal revealed a transverse muscle compressing the ulnar nerve proximal to motor and sensory branching (Fig. 2). The muscle spanned from the periosteum at the ulnar aspect of the base of the hook of hamate to the proximal and deepest hypothenar muscle fascia. The fascia over the anomalous muscle was very thick and contributed to the compression. Paresthesias were immediately relieved by release of the muscle, and interosseous muscle strength gradually improved but was less than in the opposite hand.
Case 1
An 18-year-old man, who played handball regularly, noted hand weakness and visible muscle wasting for several months. On examination, the first dorsal interosseous and adductor pollicis muscles showed wasting and weakness. Froment's sign was positive. Sensation was normal, and the Allen test result was normal. Electromyography showed fibrillations in the first dorsal interosseous and adductor pollicis. Release of the ulnar nerve showed a thick, transversely oriented muscle, deep to the ulnar neurovascular bundle, compressing only the motor branch of the ulnar nerve (Fig. IA). The muscle spanned from the ulnar aspect of the distal portion of the transverse carpal ligament to the hypothenar fascia. After the muscle was cut, the motor branch of the ulnar nerve ran radially beneath the ulnar flexor tendons, free of compression (Fig. IB). By 18 months after surgery, full strength had returned to the first dorsal inter-
From the Department of Orthopaedic Surgery, Henry Ford Hospital, Detroit, MI. Received for publication Feb. 28, 1995; accepted in revised form July 18, 1995. 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. Reprint requests: Joseph M. Failla, MD, Department of Orthopaedic Surgery, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202.
366
The Journal of Hand Surgery
Case 2
Discussion In both cases, an anomalous muscle in the depths of Guyon's canal compressed the ulnar nerve (Fig. 3). In one, the muscle was distal and compressed only the motor branch of the ulnar nerve; in the other, the entire nerve was compressed proximally.
The Journal of Hand Surgery/Vol. 21A No. 3 May 1996
367
Figure 2. A transverse anomalous muscle (between small white arrows) compressing the ulnar nerve deep to Guyon's canal. The ulnar nerve (long black arrows) is pulled anteriorly by vessel loops proximally (left) and distally (right). P, proximal; D, distal; R, radial; U, ulnar.
abductor digiti quinti type muscle, 4 the palmaris brevis profundus, 5 and the intrinsic muscles described above. Symptoms can be purely motor or motor and sensory. Although median nerve compression by anomalous muscles can occur, this was due to aberrant lumbricals in one case. 6 In contrast to the m a n y Figure 1. (A) Anomalous transverse muscle (between small white arrows) distal to Guyon's canal compressing the motor branch of the ulnar nerve (between black arrows). The rake is radial and the smooth retractor is ulnar. P, proximal; D, distal; R, radial; U, ulnar. (B) After release of the muscle, the motor branch of the ulnar nerve (between arrows) courses toward the adductor pollicis, dorsal to the ulnar flexor profundus tendons (f).
Both patients had a history of chronic mechanical pressure on the ulnar palm, by a handball in one case and by a golf club grip in the other; the differential diagnosis therefore included ulnar artery thrombosis, but the ulnar artery was seen to be normal. Other entities in the differential diagnosis were a ganglion in G u y o n ' s canal and hook of hamate nonunion, which also were not present. Proximal compression of the ulnar nerve at the elbow or cervical spine level was also considered and eliminated. Anomalous muscles compressing the ulnar nerve can be extrinsic; such muscles include an accessory palmaris longus, 1 an accessory flexor digiti quinti, 2 and an accessory abductor digiti quinti, 3 all originating in the forearm. They can be intrinsic, such as an
~
: tcl
~
.
Figure 3. Diagram of the origin and insertion of the anomalous muscles (1) in case 1 and (2) in case 2, and their relationship to the ulnar nerve (u), the motor branch of the ulnar nerve (m), and the hypothenar muscles (H). h, hook of hamate; p, pisiform; tcl, transverse carpal ligament; T, thenar muscles; f, flexor digitorum profundus of little finger.
368
Failla/Hypothenar Adductor Muscle
possible anomalous hypothenar muscles that cause ulnar nerve compression, anomalous thenar muscles are rare, have an extrinsic component, and have not been associated with median nerve compression. 7 This is consistent with the clinical observation by Verdan 8 that thenar muscles vary in terms of innervation, while the hypothenar muscles vary greatly in form, with the only constant portion being the opponens digiti quinti. Anomalous muscles can be either duplicated or modified versions of normal muscles. Examples are the reversed palmaris longus 9 and duplicated extrinsic finger extensors, l~They can also be considered to be expressions of muscles present in animals lower on the evolutionary scale. An example is the intrinsic superficial digital flexor muscle found in salamanders, the human foot, and in one human hand. 11 The function of the two muscles reported is a matter of speculation, but both appear to be more related to the hypothenar muscles than to the palmaris brevis, since they are deeper and inserted on the hypothenar fascia. The small size of both muscles implies minimal functional impact. However, in the first case, the plane of the muscle was at the same depth as the adductor pollicis, and it was positioned anatomically to cause adduction of the hypothenar mass. In the second case, the muscle was similar in depth to the palmaris brevis profundus, but it was attached ulnarly to the hypothenar fascia, rather than the pisiform, and thus was also positioned to adduct the hypothenar mass. Both muscles are very different in origin and insertion from the palmaris brevis, which originates much more superficially from the palmar aponeurosis and flexor retinaculum subcutaneously, and inserts on dermis of the hypothenar palm. '2 Because of the location of these muscles, they likely function to adduct the
ulnar aspect of the palm by pulling the hypothenar musculature in a radial direction. For these reasons, the two muscles presented were named the hypothenar adductor muscle.
References 1. Regan PJ, Feldberg L, Bailey BN. Accessory palmaris longus causing ulnar nerve compression at the wrist. J Hand Surg 1991;16A:736-738. 2. Swanson AB, Biddulph SL, Baughman FA, DeGroot G. Ulnar nerve compression due to an anomalous muscle in the canal of Guyon. Clin Orthop 1972;83:64-69. 3. Jeffrey AK. Compression of the deep palmar branch of the ulnar nerve by an anomalous muscle. J Bone Joint Surg 1971 ;53B :718-723. 4. Uriburu IJF, Morchio FJ, Marin JC. Compression of the deep motor branch of the ulnar nerve (piso-hamate hiatus syndrome). J Bone Joint Surg 1976;58A:145-147. 5. Tonkin MA, Lister GD. The palmaris brevis profundus: an anomalous muscle associated with ulnar nerve compression at the wrist. J Hand Surg 1985;10A:862-864. 6. Asai M, Wong ACW, Matsunaga T, Akahoshi Y. Carpal tunnel syndrome caused by aberrant lumbrical muscles associated with cystic degeneration of the tenosynovium. J Hand Surg I986;11A:218-221. 7. Legan J, Shepler TR. Congenital hypertrophy of the thenar eminence with accessory head of the abductor pollicis brevis in the forearm. J Hand Surg 1992;17A:884-886. 8. Verdan C. Les anomalies musculo-tendineuses et leur signification en chirurgie de la main. Rev Chit Orthop 1981; 67:221-230. 9. Van Demark R. Tumor of the wrist of anomalous muscle origin. J Bone Joint Surg 1955;37A:1284-5. 10. Cusenz BJ, Hallock GG. Multiple anomalous tendons of the fourth dorsal compartment. J Hand Surg 1986;11A: 263-264. 11. Wesser DR, Calostypis F, Hoffman S. The evolutionary significance of an aberrant flexor superficialis muscle in the human palm. J Bone Joint Surg 1969;51A:396-398 12. Gray H. Gray's anatomy. Philadelphia: Running Press, 1901:406.