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Common Anomalous Muscles Encountered During Upper Extremity Surgery
IN BRIEF
Common Anomalous Muscles Encountered During Upper Extremity Surgery Daniel A. Seigerman, MD, Jonas L. Matzon, MD
A
infrequently encountered in the upper extremity, but when present, they are unavoidable obstacles during surgery. Knowledge of their existence is of paramount importance to provide accurate diagnosis, safe surgical exposure, and successful intervention. Although numerous anomalies exist, our focus is on 3 important anomalies: the anconeus epitrochlearis (AE), the extensor digitorum brevis manus (EDBM), and Gantzer’s muscle (GM). We believe that knowledge of these encountered anomalies can help avoid confusion and complication during surgery of the upper extremity.
with greater than 50% loss at the negative peak area. Similarly, Cheriyan et al5 reported that ulnar nerve velocity drop of more than 3.00 m/s per cm suggested the presence of AE. Definitive treatment of AE-associated cubital tunnel syndrome involves ulnar nerve decompression with or without transposition, by AE division and/or excision.1,6e8 Although AE excision has historically been recommended, it is unknown whether simple AE division would yield similar outcomes as demonstrated in Figures 1 and 2. An understanding of this relatively common anomaly is critical to perform ulnar nerve surgery safely.
ANCONEUS EPITROCHLEARIS Once thought to be an anomalous extension of the medial head of the triceps, the AE is an anomalous muscle at the elbow that extends from the medial aspect of the olecranon to the medial epicondyle. Its incidence is highly variable, but reports have indicated its presence in up to 28% of patients.1e3 The muscle lies superficial and posterior to the ulnar nerve; as such, it can compress the nerve, leading to cubital tunnel syndrome. Because the muscle is difficult to palpate and advanced imaging is infrequently warranted in cubital tunnel syndrome, this anomaly is often difficult to identify until surgical exposure. However, nerve conduction velocity studies may be helpful in trying to recognize patients with AE-associated cubital tunnel syndrome. Byun et al4 found that AE patients are more likely to have a motor conduction block
EXTENSOR DIGITORUM BREVIS MANUS Initially described in 1734, the EDBM has a variable incidence of 1% to 9% of the population.9 In a recent meta-analysis, Yammine10 determined a true cadaveric prevalence of 2.3% with bilateral occurrence in 26.3%. The muscle is located on the dorsal aspect of the hand in the fourth dorsal compartment, is closely linked with the extensor indicis proprius (EIP), and is most prominent with wrist flexion and finger extension (Fig. 3). It originates from the dorsal wrist capsule (dorsal radiocarpal ligament), the distal end of the radius, and the dorsal metacarpal surface.10,11 Ogura et al11 described a classification system for the muscle’s variable distal insertions. In type I, the distal EDBM insertion is onto the dorsal aponeurosis of the index finger (IF) when the EIP is absent. In type II, the EDBM and EIP both insert onto the IF dorsal aponeurosis, with 3 subtypes. Type IIa involves a nonfunctional EIP and EDBM becoming confluent and inserting onto the IF dorsal aponeurosis; type IIb involves the distal aspect of the EDBM joining the EIP; and type IIc involves the EDBM attaching to the ulnar aspect of the EIP tendon. Finally, in type III, the EDBM inserts onto the middle finger dorsal aponeurosis.11 Given the few number of cases reported, the EDBM is most often symptomless.10 However, it can occasionally be painful and confused for a mass. To
NOMALOUS MUSCLES ARE
From the Rothman Institute, Division of Hand Surgery, Thomas Jefferson University, Philadelphia, PA. Received for publication February 4, 2015; accepted in revised form March 25, 2015. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Jonas L. Matzon, MD, Rothman Institute, 327 Greentree Road, Sewell, NJ 08080; e-mail: [email protected]. 0363-5023/15/---0001$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2015.03.028
Ó 2015 ASSH
r
Published by Elsevier, Inc. All rights reserved.
r
1
2
COMMON ANOMALOUS MUSCLES
FIGURE 1: Surgical photograph of the medial aspect of the elbow during ulnar nerve decompression surgery in which an AE was identified.
FIGURE 2: The muscle shown in Figure 1 was transected to expose and decompress the ulnar nerve at the cubital tunnel.
make the diagnosis more challenging, the EDBM has been reported to coexist with both ganglion cysts and metacarpal bosses.11e13 Symptomatic patients will typically present with a painful mass on the dorsum of the hand that is exacerbated by finger extension. To minimize concern regarding malignancy, it is imperative to make an accurate diagnosis. Imaging modalities such as ultrasound and magnetic resonance imaging can be diagnostic. However, both the ordering physician and the radiologist must have a high index of suspicion for this anomaly, to avoid confusion when interpreting such studies. After appropriate diagnosis and failure of conservative treatment, surgery can be considered in persistently symptomatic patients. Options include EDBM ablation or extensor retinaculum release with decompression of the hypertrophic EDBM.14 In type I and IIa variants, complete EDBM excision could result in loss of independent IF extension owing to the absent EIP.
FIGURE 3: Surgical photograph of an EDBM during a dorsal approach to the hand. (Courtesy of Joseph Dwyer, MD.)
GANTZER’S MUSCLE A common anomaly in the proximal forearm is the presence of an accessory head of the flexor pollicis longus, named the GM. This anomalous muscle has an incidence varying from 33% to 89%, depending on race and region.15 In a cadaveric study by Al-Qattan,16 85% of specimens had the muscle originate from the medial epicondyle of the humerus, whereas the remaining 15% of specimens had a dual origin from the medial epicondyle and the coronoid process. In all specimens, the muscle inserted onto the ulnar aspect of the flexor pollicis longus. This anomaly is interesting because it lies close to the median and anterior interosseous nerves (AIN) and is considered a possible site of compression. Although its relationship to the AIN and median nerve has been a source of clinical debate, Dellon17 J Hand Surg Am.
found GM deep to the AIN in all cadaveric specimens examined. However, Al-Qattan16 determined that the median nerve can be affected by GM when the nerve passes deep to the deep head of the pronator teres and when the pronator teres is absent. In these scenarios, patients may present with findings of AIN syndrome, including an inability to flex the thumb interphalangeal joint and the IF distal interphalangeal joint, pronator quadratus weakness, and ill-defined forearm pain. There is limited evidence comparing operative and nonsurgical treatment in patients with AIN syndrome; nevertheless, most of these patients will spontaneously improve within 12 months. If no improvement occurs during this period or there is evidence of an anatomic obstruction, decompression of the AIN is recommended.18 r
Vol. -, - 2015
COMMON ANOMALOUS MUSCLES
CLINICAL IMPORTANCE OF ANOMALOUS MUSCLES Perhaps even more important than the nuances of the surgical technique is an understanding of upper extremity anatomy. Although most surgeons have an excellent command of typical anatomy, anomalous anatomy can cause great difficulty and trepidation during surgery. Knowledge of relatively common anomalies can help prevent such challenges. Moreover, when encountering an anomaly, the approach of defining known anatomy outside the zone of uncertainty and methodically working toward this region can help avoid complications.
6. Sucher E, Herness D. Cubital canal syndrome due to subanconeus muscle. J Hand Surg Br. 1986;11(3):460e462. 7. Gessini L, Jandolo B, Pietrangeli A, Occhipinti E. Ulnar nerve entrapment at the elbow by persistent epitrochleoanconeus muscle: case report. J Neurosurg. 1981;55(5):830e831. 8. O’Hara JJ, Stone JH. Ulnar nerve compression at the elbow caused by a prominent medial head of the triceps and an anconeus epitrochlearis muscle. J Hand Surg Br. 1996;21(1):133e135. 9. Dunn AW, Evarts CM. The extensor digitorum brevis manus muscle: a case report. Clin Orthop Relat Res. 1963;28:210e212. 10. Yammine K. The prevalence of extensor digitorum brevis manus and its variants in humans: a systematic review and meta-analysis. Surg Radiol Anat. 2015;37(1):3e9. 11. Ogura T, Inoue H, Tanabe G. Anatomic and clinical studies of the extensor digitorum brevis manus. J Hand Surg Am. 1987;12(1): 100e107. 12. Dostal GH, Lister GD, Hutchinson D, Mogan JV, Davis PH. Extensor digitorum brevis manus associated with a dorsal wrist ganglion: a review of five cases. J Hand Surg Am. 1995;20(1):35e37. 13. Capo JT, Shamian B, Li Y. Extensor digitorum brevis manus muscle in association with a metacarpal boss. J Plast Surg Hand Surg. 2014;48(2):152e154. 14. Ross JA, Troy CA. The clinical significance of the extensor digitorum brevis manus. J Bone Joint Surg Br. 1969;51(3):473e478. 15. Pai MM, Nayak SR, Krishnamurthy A, et al. The accessory heads of flexor pollicis longus and flexor digitorum profundus: incidence and morphology. Clin Anat. 2008;21(3):252e258. 16. Al-Qattan MM. Gantzer’s muscle: an anatomical study of the accessory head of the flexor pollicis longus muscle. J Hand Surg Br. 1996;21(2):269e270. 17. Dellon AL. Musculotendinous variations about the medial humeral epicondyle. J Hand Surg Br. 1986;11(2):175e181. 18. Rodner CM, Tinsley BA, O’Malley MP. Pronator syndrome and anterior interosseous nerve syndrome. J Am Acad Orthop Surg. 2013;21(5):268e275.
REFERENCES 1. Masear VR, Hill JJ, Cohen SM. Ulnar compression neuropathy secondary to the anconeus epitrochlearis muscle. J Hand Surg Am. 1988;13(5):720e724. 2. Dahners LE, Wood FM. Anconeus epitrochlearis, a rare cause of cubital tunnel syndrome: a case report. J Hand Surg Am. 1984;9(4): 579e580. 3. O’Driscoll SW, Horii E, Carmichael SW, Morrey BF. The cubital tunnel and ulnar neuropathy. J Bone Joint Surg Br. 1991;73(4):613e617. 4. Byun SD, Kim CH, Jeon IH. Ulnar neuropathy caused by an anconeus epitrochlearis: clinical and electrophysiological findings. J Hand Surg Eur Vol. 2011;36(7):607e608. 5. Cheriyan T, Neuhaus V, Mudgal CS. Velocity drop in anconeus epitrochlearis-associated cubital tunnel syndrome. Am J Orthop. 2014;43(5):227e229.
J Hand Surg Am.
3
r
Vol. -, - 2015
Common Anomalous Muscles Encountered During Upper Extremity Surgery Daniel A. Seigerman, MD, Jonas L. Matzon, MD
A
infrequently encountered in the upper extremity, but when present, they are unavoidable obstacles during surgery. Knowledge of their existence is of paramount importance to provide accurate diagnosis, safe surgical exposure, and successful intervention. Although numerous anomalies exist, our focus is on 3 important anomalies: the anconeus epitrochlearis (AE), the extensor digitorum brevis manus (EDBM), and Gantzer’s muscle (GM). We believe that knowledge of these encountered anomalies can help avoid confusion and complication during surgery of the upper extremity.
with greater than 50% loss at the negative peak area. Similarly, Cheriyan et al5 reported that ulnar nerve velocity drop of more than 3.00 m/s per cm suggested the presence of AE. Definitive treatment of AE-associated cubital tunnel syndrome involves ulnar nerve decompression with or without transposition, by AE division and/or excision.1,6e8 Although AE excision has historically been recommended, it is unknown whether simple AE division would yield similar outcomes as demonstrated in Figures 1 and 2. An understanding of this relatively common anomaly is critical to perform ulnar nerve surgery safely.
ANCONEUS EPITROCHLEARIS Once thought to be an anomalous extension of the medial head of the triceps, the AE is an anomalous muscle at the elbow that extends from the medial aspect of the olecranon to the medial epicondyle. Its incidence is highly variable, but reports have indicated its presence in up to 28% of patients.1e3 The muscle lies superficial and posterior to the ulnar nerve; as such, it can compress the nerve, leading to cubital tunnel syndrome. Because the muscle is difficult to palpate and advanced imaging is infrequently warranted in cubital tunnel syndrome, this anomaly is often difficult to identify until surgical exposure. However, nerve conduction velocity studies may be helpful in trying to recognize patients with AE-associated cubital tunnel syndrome. Byun et al4 found that AE patients are more likely to have a motor conduction block
EXTENSOR DIGITORUM BREVIS MANUS Initially described in 1734, the EDBM has a variable incidence of 1% to 9% of the population.9 In a recent meta-analysis, Yammine10 determined a true cadaveric prevalence of 2.3% with bilateral occurrence in 26.3%. The muscle is located on the dorsal aspect of the hand in the fourth dorsal compartment, is closely linked with the extensor indicis proprius (EIP), and is most prominent with wrist flexion and finger extension (Fig. 3). It originates from the dorsal wrist capsule (dorsal radiocarpal ligament), the distal end of the radius, and the dorsal metacarpal surface.10,11 Ogura et al11 described a classification system for the muscle’s variable distal insertions. In type I, the distal EDBM insertion is onto the dorsal aponeurosis of the index finger (IF) when the EIP is absent. In type II, the EDBM and EIP both insert onto the IF dorsal aponeurosis, with 3 subtypes. Type IIa involves a nonfunctional EIP and EDBM becoming confluent and inserting onto the IF dorsal aponeurosis; type IIb involves the distal aspect of the EDBM joining the EIP; and type IIc involves the EDBM attaching to the ulnar aspect of the EIP tendon. Finally, in type III, the EDBM inserts onto the middle finger dorsal aponeurosis.11 Given the few number of cases reported, the EDBM is most often symptomless.10 However, it can occasionally be painful and confused for a mass. To
NOMALOUS MUSCLES ARE
From the Rothman Institute, Division of Hand Surgery, Thomas Jefferson University, Philadelphia, PA. Received for publication February 4, 2015; accepted in revised form March 25, 2015. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Jonas L. Matzon, MD, Rothman Institute, 327 Greentree Road, Sewell, NJ 08080; e-mail: [email protected]. 0363-5023/15/---0001$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2015.03.028
Ó 2015 ASSH
r
Published by Elsevier, Inc. All rights reserved.
r
1
2
COMMON ANOMALOUS MUSCLES
FIGURE 1: Surgical photograph of the medial aspect of the elbow during ulnar nerve decompression surgery in which an AE was identified.
FIGURE 2: The muscle shown in Figure 1 was transected to expose and decompress the ulnar nerve at the cubital tunnel.
make the diagnosis more challenging, the EDBM has been reported to coexist with both ganglion cysts and metacarpal bosses.11e13 Symptomatic patients will typically present with a painful mass on the dorsum of the hand that is exacerbated by finger extension. To minimize concern regarding malignancy, it is imperative to make an accurate diagnosis. Imaging modalities such as ultrasound and magnetic resonance imaging can be diagnostic. However, both the ordering physician and the radiologist must have a high index of suspicion for this anomaly, to avoid confusion when interpreting such studies. After appropriate diagnosis and failure of conservative treatment, surgery can be considered in persistently symptomatic patients. Options include EDBM ablation or extensor retinaculum release with decompression of the hypertrophic EDBM.14 In type I and IIa variants, complete EDBM excision could result in loss of independent IF extension owing to the absent EIP.
FIGURE 3: Surgical photograph of an EDBM during a dorsal approach to the hand. (Courtesy of Joseph Dwyer, MD.)
GANTZER’S MUSCLE A common anomaly in the proximal forearm is the presence of an accessory head of the flexor pollicis longus, named the GM. This anomalous muscle has an incidence varying from 33% to 89%, depending on race and region.15 In a cadaveric study by Al-Qattan,16 85% of specimens had the muscle originate from the medial epicondyle of the humerus, whereas the remaining 15% of specimens had a dual origin from the medial epicondyle and the coronoid process. In all specimens, the muscle inserted onto the ulnar aspect of the flexor pollicis longus. This anomaly is interesting because it lies close to the median and anterior interosseous nerves (AIN) and is considered a possible site of compression. Although its relationship to the AIN and median nerve has been a source of clinical debate, Dellon17 J Hand Surg Am.
found GM deep to the AIN in all cadaveric specimens examined. However, Al-Qattan16 determined that the median nerve can be affected by GM when the nerve passes deep to the deep head of the pronator teres and when the pronator teres is absent. In these scenarios, patients may present with findings of AIN syndrome, including an inability to flex the thumb interphalangeal joint and the IF distal interphalangeal joint, pronator quadratus weakness, and ill-defined forearm pain. There is limited evidence comparing operative and nonsurgical treatment in patients with AIN syndrome; nevertheless, most of these patients will spontaneously improve within 12 months. If no improvement occurs during this period or there is evidence of an anatomic obstruction, decompression of the AIN is recommended.18 r
Vol. -, - 2015
COMMON ANOMALOUS MUSCLES
CLINICAL IMPORTANCE OF ANOMALOUS MUSCLES Perhaps even more important than the nuances of the surgical technique is an understanding of upper extremity anatomy. Although most surgeons have an excellent command of typical anatomy, anomalous anatomy can cause great difficulty and trepidation during surgery. Knowledge of relatively common anomalies can help prevent such challenges. Moreover, when encountering an anomaly, the approach of defining known anatomy outside the zone of uncertainty and methodically working toward this region can help avoid complications.
6. Sucher E, Herness D. Cubital canal syndrome due to subanconeus muscle. J Hand Surg Br. 1986;11(3):460e462. 7. Gessini L, Jandolo B, Pietrangeli A, Occhipinti E. Ulnar nerve entrapment at the elbow by persistent epitrochleoanconeus muscle: case report. J Neurosurg. 1981;55(5):830e831. 8. O’Hara JJ, Stone JH. Ulnar nerve compression at the elbow caused by a prominent medial head of the triceps and an anconeus epitrochlearis muscle. J Hand Surg Br. 1996;21(1):133e135. 9. Dunn AW, Evarts CM. The extensor digitorum brevis manus muscle: a case report. Clin Orthop Relat Res. 1963;28:210e212. 10. Yammine K. The prevalence of extensor digitorum brevis manus and its variants in humans: a systematic review and meta-analysis. Surg Radiol Anat. 2015;37(1):3e9. 11. Ogura T, Inoue H, Tanabe G. Anatomic and clinical studies of the extensor digitorum brevis manus. J Hand Surg Am. 1987;12(1): 100e107. 12. Dostal GH, Lister GD, Hutchinson D, Mogan JV, Davis PH. Extensor digitorum brevis manus associated with a dorsal wrist ganglion: a review of five cases. J Hand Surg Am. 1995;20(1):35e37. 13. Capo JT, Shamian B, Li Y. Extensor digitorum brevis manus muscle in association with a metacarpal boss. J Plast Surg Hand Surg. 2014;48(2):152e154. 14. Ross JA, Troy CA. The clinical significance of the extensor digitorum brevis manus. J Bone Joint Surg Br. 1969;51(3):473e478. 15. Pai MM, Nayak SR, Krishnamurthy A, et al. The accessory heads of flexor pollicis longus and flexor digitorum profundus: incidence and morphology. Clin Anat. 2008;21(3):252e258. 16. Al-Qattan MM. Gantzer’s muscle: an anatomical study of the accessory head of the flexor pollicis longus muscle. J Hand Surg Br. 1996;21(2):269e270. 17. Dellon AL. Musculotendinous variations about the medial humeral epicondyle. J Hand Surg Br. 1986;11(2):175e181. 18. Rodner CM, Tinsley BA, O’Malley MP. Pronator syndrome and anterior interosseous nerve syndrome. J Am Acad Orthop Surg. 2013;21(5):268e275.
REFERENCES 1. Masear VR, Hill JJ, Cohen SM. Ulnar compression neuropathy secondary to the anconeus epitrochlearis muscle. J Hand Surg Am. 1988;13(5):720e724. 2. Dahners LE, Wood FM. Anconeus epitrochlearis, a rare cause of cubital tunnel syndrome: a case report. J Hand Surg Am. 1984;9(4): 579e580. 3. O’Driscoll SW, Horii E, Carmichael SW, Morrey BF. The cubital tunnel and ulnar neuropathy. J Bone Joint Surg Br. 1991;73(4):613e617. 4. Byun SD, Kim CH, Jeon IH. Ulnar neuropathy caused by an anconeus epitrochlearis: clinical and electrophysiological findings. J Hand Surg Eur Vol. 2011;36(7):607e608. 5. Cheriyan T, Neuhaus V, Mudgal CS. Velocity drop in anconeus epitrochlearis-associated cubital tunnel syndrome. Am J Orthop. 2014;43(5):227e229.
J Hand Surg Am.
3
r
Vol. -, - 2015