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Anatomy of the extensor pollicis brevis muscle
ANATOMY
OF THE
EXTENSOR G.
POLLICIS
BREVIS
MUSCLE
A. BRUNELLI and G. R. BRUNELLI
From the Orthopaedic Clinic of the University of Brescia, Italy
52 hands have been dissected to check the anatomy and function of the extensor pollicis brevis. Various abnormalities were found: absence of the E.P.B. (two), insertion on the distal phalanx (four), absence of bony insertion on the base of the first phalanx and insertion on the extensor hood (36). In ten cases (in addition to the two with absence of E.P.B.), no furactionwas elicited by pulling the tendon which inserted upon the extensor hood. Journal of Hand Surgery (British Volume, 1992) 17B: 267-269
During anatomical research aimed at checking the anatomy of the abductor pollicis longus, we were able to observe various anomalies of the extensor pollicis brevis too. We therefore decided to study the real anatomy of this muscle. Dawson and Barton had already done similar research in 1986 on 16 arms in eight cadavers, concluding that “the extensor pollicis brevis shows anatomical variation to the extent that deviation from the standard anatomical description is the rule rather than the exception.” Classically, the E.P.B. originates from the dorsal aspect of the radius (distal to the insertion of the A.P.L.) and from the inter-osseous membrane, inserting distally onto the base of the first phalanx of the thumb (Bairati, 1975; Balboni et al., 1983; Kendall and Kendal, 1974; Testut and Latarjet, 1949). Its action is described as extension of the M.P. joint, with participation in abduction of the thumb and the carpus (Bonola et al., 1981; Cailliet, 1978; Kapandji, 1978; Kaplan, 1966; Lamb and Kuczynski, 1981; Landsmeer, 1976; Leao, 1958; Nigst et al., 1988; Stein, 1951; Tubiana et al., 1984). Its innervation is said to be through the radial nerve (from C6, C7 and CS), though in fact this is not constant and not even common. In our anatomical study we found various differences from the so-called “normal” anatomy.
h
Fig. 1
Material and method Our research was carried out on 52 hands of cadavers. The muscle was dissected from its origin down to its distal insertion, paying meticulous attention in isolating its fibrous terminations and their attachment. Results Several anomalies or anatomical variations were found. In two cases (3.75%) the E.P.B. muscle was absent (Table 1). In one of these, a “ligament” going from the radial styloid to the extensor hood at the M.P. joint was found to replace the musculo-tendinous unit. The tendon was almost always very thin, so that we were able to consider only ten tendons (19.2%) as “normal” (i.e. wider than 2 mm.). In five cases (9.7x), the E.P.B. ran in a separate compartment of the first osteofibrotic canal over the radius, being divided from the A.P.L. by a fibrous septum. The E.P.B. muscle was always single, unlike theA.P.L. which was always multiple. Surprisingly, and in disagreement with the descriptions in the anatomy texts, the great majority of the E.P.B. tendons (36 = 69.2%) did not have any bony attachment to the base of the first metacarpal. Instead, the tendon
b
So-called “normal” anatomy of the extensor pollicis brevis. At: transverse part of the adductor pollicis muscle. Ao: oblique portion of the same muscle. h= hood of the extensors of the thumb, formed by the adductor pollicis muscle (two bellies) and abductor pollicis brevis. E.P.B. : Extensor pollicis brevis muscle with its bony insertion. E.P.L. : extensor pollicis longus. A.P.L. : abductor pollicis longus. b= bony insertion. 267
THE JOURNAL
268
OF HAND SURGERY
VOL. 17B No. 3 JUNE
1992
ended like a fan inserting into the hood of the extensors of the thumb at the M.P. joint; only ten cases (19.2%) had bony attachment to the base of the first metacarpal and even these had fibres terminating on the extensor hood (Table 2). In four cases (7.5x), the tendon which should have been the E.P.B. and occupied the first dorsal compartment of the wrist did not insert on the base of the proximal phalanx but went on to attach to the base of the distal phalanx, thus acting like an accessory extensor pollicis longus. Pulling the tendon of the E.P.B. proximally in the 39 cases out of the 49 (75%) in which the tendon was present produced extension of the M.P. joint to a different extent. In ten cases (19.2x), pulling the tendon of the E.P.B. proximally did not produce any movement of either the M.P. or the I.P. joint (Table 3). In these ten cases the
Table l-Presence and size of E.P.B. Absent Ligament (absent) Very thin (1 mm.) Thin (l-2 mm.) Normal (?) 22 mm.
1 1 20 20 10
Total
52
Table 2-Insertion 10 36 4 2
Base of the proximal phalanx Extensor hood Base of the middle phalanx Absent
Table 3-Fonction 2
Absent muscle Extension of the M.P. joint Strong Weak Extension of the I.P. joint No function
11 25 4 10
Fig. 2
Different distal insertions of the extensor pollicis brevis. (a) Onto the extensor hood (69.2x), (b) onto the proximal phalanx
(19.2x), (c) onto the distal phalanx (7.5x), (d) absent, (e) ligament.
Table 4-Comparison of the finding of Dawson and Barton (1986) and ours as to the insertion of E.P.B. Partly to theprox. phalanx andpartly to hood
Wholly toprox. phalanx (%)
Wholly to extensor hood
To the distal phalanx (%)
Absent (%)
(%I
(%)
Dawson and Barton (16 hands) Brunelli and Brunelli (52 hands) *Substituted by a slip of A.P.L
56.2
25
18.7
_
6.2*
19.2
_
69.2
7.5
3.75
ANATOMY
OF THE EXTENSOR
POLLICIS
BREVIS
MUSCLE
269
insertion of the E.P.B. on the extensor hood seemed to be too proximal. Dawson and Barton (1986) found a great number of anatomical variations, but they were different from our findings (see Table 4), demonstrating the wide range of abnormalities and the need of further anatomical research. However, we agree with Dawson and Barton that there are many significant differences of the extensor pollicis brevis between the two sides of the same subjects. Conclusion
Our series of dissections, even if it needs wider confirmation as regards the percentage of abnormalities, shows a great variety in the E.P.B. unit. Few (19.2%) are “normal” according to the anatomy books. The so-called “normal” bony attachment is very rare while the attachment on the extensor hood seems to be the true normal. This must be taken into consideration, especially when planning reconstructive surgery. One should be aware that E.P.B. may be absent, may be too thin for the expected new functions and may be attached to the extensor hood instead of the bone. References BAIRATI, A. Trattato di Anafomia IV : 680.
BALBONI, G. C., BASTIANINI, A., BRIZZI, E., COMPARINI, L., FILOGAMO, G., GIORDANO-LANZA, G., GROSSI, C. E., MANZOLI, F. A., MARINOZZI, G., MOTTA, P., ORLANDINI, G. E., PASSAPONTI, A., REALE, E., RUGGERI, A., SANTORO, A.. ZACCHEO, D. Anatomia Umana. Milan, Ermes, 1983: 334. BONOLA, A., CAROLI, A. and CELLI, L. La Mano. Padua, Piccin, 1981: 160, 183.262. CAILLIET, R. La Main. Paris, Masson, 1978: 110. DAWSON, S. and BARTON, N. J. (1988). Anatomical variations of the extensor pollicis brevis. Journal of Hand Surgery, 1 IB: 3: 378-381. KAPANDJI, A. Physiologic Articulaire. Paris, Maloine, 1978: Tome 1: 171. KAPLAN, E. B. Surgical Approaches to the Neck, Cervical Spine and Upper Extremity. Philadelphia, W. B. Saunders, 1966. KAPLAN, E. B. Functional and Surgical Anatomy of the Hand, 2nd edn. Philadelphia, J. B. Lippincott, 1984: 131. KENDALL, F. P. and KENDAL, E. McC. Les Muscles, 3rd edn. Paris, Maloine, 1974: 39. LAMB, D. W. and KUCZYNSKI, K. The Practice of Hand Surgery. Oxford, Blackwell, 1981. LANDSMEER, J. M. F. Atlas of Anatomy of the Hand. Edinburgh, Churchill Livingstone, 1976: 129. LEAO, L. (1958). De Quervain’s Disease. A Clinical and Anatomical Study. Journal of Bone and Joint Surgery, 40A: 5: 1063-1070. NIGST, H., BUCK-GRAMCKO, D., MILLESI, H. and LISTER, G. D. Hand Surgery. Stuttgart, Thieme, 1988: Vol. 1: 39. STEIN, A. M. (1951). Variations of the tendons of insertion of the abductor pollicis longus and the extensor pollicis brevis. Anatomical Record, 110: 4955. TESTUT, L. and LATARJET, A. Traite d’Attatomie Humaine. Paris, G. Doin, 1949: 201. TUBIANA, R., THOMINE, J. M. and MACKIN, E. Examination of the Hand and Upper Limb. Philadelphia, Saunders, 1984: 381.
Accepted: 4 July 1991 Umana. Turin, Minerva
Medica,
1975: Vol.
Professor 0
G. Bmnelli,
1992 The British
Via Campiana
Society for Surgery
77, Cellatica, of the Hand
Brescia,
25060 Italy.
OF THE
EXTENSOR G.
POLLICIS
BREVIS
MUSCLE
A. BRUNELLI and G. R. BRUNELLI
From the Orthopaedic Clinic of the University of Brescia, Italy
52 hands have been dissected to check the anatomy and function of the extensor pollicis brevis. Various abnormalities were found: absence of the E.P.B. (two), insertion on the distal phalanx (four), absence of bony insertion on the base of the first phalanx and insertion on the extensor hood (36). In ten cases (in addition to the two with absence of E.P.B.), no furactionwas elicited by pulling the tendon which inserted upon the extensor hood. Journal of Hand Surgery (British Volume, 1992) 17B: 267-269
During anatomical research aimed at checking the anatomy of the abductor pollicis longus, we were able to observe various anomalies of the extensor pollicis brevis too. We therefore decided to study the real anatomy of this muscle. Dawson and Barton had already done similar research in 1986 on 16 arms in eight cadavers, concluding that “the extensor pollicis brevis shows anatomical variation to the extent that deviation from the standard anatomical description is the rule rather than the exception.” Classically, the E.P.B. originates from the dorsal aspect of the radius (distal to the insertion of the A.P.L.) and from the inter-osseous membrane, inserting distally onto the base of the first phalanx of the thumb (Bairati, 1975; Balboni et al., 1983; Kendall and Kendal, 1974; Testut and Latarjet, 1949). Its action is described as extension of the M.P. joint, with participation in abduction of the thumb and the carpus (Bonola et al., 1981; Cailliet, 1978; Kapandji, 1978; Kaplan, 1966; Lamb and Kuczynski, 1981; Landsmeer, 1976; Leao, 1958; Nigst et al., 1988; Stein, 1951; Tubiana et al., 1984). Its innervation is said to be through the radial nerve (from C6, C7 and CS), though in fact this is not constant and not even common. In our anatomical study we found various differences from the so-called “normal” anatomy.
h
Fig. 1
Material and method Our research was carried out on 52 hands of cadavers. The muscle was dissected from its origin down to its distal insertion, paying meticulous attention in isolating its fibrous terminations and their attachment. Results Several anomalies or anatomical variations were found. In two cases (3.75%) the E.P.B. muscle was absent (Table 1). In one of these, a “ligament” going from the radial styloid to the extensor hood at the M.P. joint was found to replace the musculo-tendinous unit. The tendon was almost always very thin, so that we were able to consider only ten tendons (19.2%) as “normal” (i.e. wider than 2 mm.). In five cases (9.7x), the E.P.B. ran in a separate compartment of the first osteofibrotic canal over the radius, being divided from the A.P.L. by a fibrous septum. The E.P.B. muscle was always single, unlike theA.P.L. which was always multiple. Surprisingly, and in disagreement with the descriptions in the anatomy texts, the great majority of the E.P.B. tendons (36 = 69.2%) did not have any bony attachment to the base of the first metacarpal. Instead, the tendon
b
So-called “normal” anatomy of the extensor pollicis brevis. At: transverse part of the adductor pollicis muscle. Ao: oblique portion of the same muscle. h= hood of the extensors of the thumb, formed by the adductor pollicis muscle (two bellies) and abductor pollicis brevis. E.P.B. : Extensor pollicis brevis muscle with its bony insertion. E.P.L. : extensor pollicis longus. A.P.L. : abductor pollicis longus. b= bony insertion. 267
THE JOURNAL
268
OF HAND SURGERY
VOL. 17B No. 3 JUNE
1992
ended like a fan inserting into the hood of the extensors of the thumb at the M.P. joint; only ten cases (19.2%) had bony attachment to the base of the first metacarpal and even these had fibres terminating on the extensor hood (Table 2). In four cases (7.5x), the tendon which should have been the E.P.B. and occupied the first dorsal compartment of the wrist did not insert on the base of the proximal phalanx but went on to attach to the base of the distal phalanx, thus acting like an accessory extensor pollicis longus. Pulling the tendon of the E.P.B. proximally in the 39 cases out of the 49 (75%) in which the tendon was present produced extension of the M.P. joint to a different extent. In ten cases (19.2x), pulling the tendon of the E.P.B. proximally did not produce any movement of either the M.P. or the I.P. joint (Table 3). In these ten cases the
Table l-Presence and size of E.P.B. Absent Ligament (absent) Very thin (1 mm.) Thin (l-2 mm.) Normal (?) 22 mm.
1 1 20 20 10
Total
52
Table 2-Insertion 10 36 4 2
Base of the proximal phalanx Extensor hood Base of the middle phalanx Absent
Table 3-Fonction 2
Absent muscle Extension of the M.P. joint Strong Weak Extension of the I.P. joint No function
11 25 4 10
Fig. 2
Different distal insertions of the extensor pollicis brevis. (a) Onto the extensor hood (69.2x), (b) onto the proximal phalanx
(19.2x), (c) onto the distal phalanx (7.5x), (d) absent, (e) ligament.
Table 4-Comparison of the finding of Dawson and Barton (1986) and ours as to the insertion of E.P.B. Partly to theprox. phalanx andpartly to hood
Wholly toprox. phalanx (%)
Wholly to extensor hood
To the distal phalanx (%)
Absent (%)
(%I
(%)
Dawson and Barton (16 hands) Brunelli and Brunelli (52 hands) *Substituted by a slip of A.P.L
56.2
25
18.7
_
6.2*
19.2
_
69.2
7.5
3.75
ANATOMY
OF THE EXTENSOR
POLLICIS
BREVIS
MUSCLE
269
insertion of the E.P.B. on the extensor hood seemed to be too proximal. Dawson and Barton (1986) found a great number of anatomical variations, but they were different from our findings (see Table 4), demonstrating the wide range of abnormalities and the need of further anatomical research. However, we agree with Dawson and Barton that there are many significant differences of the extensor pollicis brevis between the two sides of the same subjects. Conclusion
Our series of dissections, even if it needs wider confirmation as regards the percentage of abnormalities, shows a great variety in the E.P.B. unit. Few (19.2%) are “normal” according to the anatomy books. The so-called “normal” bony attachment is very rare while the attachment on the extensor hood seems to be the true normal. This must be taken into consideration, especially when planning reconstructive surgery. One should be aware that E.P.B. may be absent, may be too thin for the expected new functions and may be attached to the extensor hood instead of the bone. References BAIRATI, A. Trattato di Anafomia IV : 680.
BALBONI, G. C., BASTIANINI, A., BRIZZI, E., COMPARINI, L., FILOGAMO, G., GIORDANO-LANZA, G., GROSSI, C. E., MANZOLI, F. A., MARINOZZI, G., MOTTA, P., ORLANDINI, G. E., PASSAPONTI, A., REALE, E., RUGGERI, A., SANTORO, A.. ZACCHEO, D. Anatomia Umana. Milan, Ermes, 1983: 334. BONOLA, A., CAROLI, A. and CELLI, L. La Mano. Padua, Piccin, 1981: 160, 183.262. CAILLIET, R. La Main. Paris, Masson, 1978: 110. DAWSON, S. and BARTON, N. J. (1988). Anatomical variations of the extensor pollicis brevis. Journal of Hand Surgery, 1 IB: 3: 378-381. KAPANDJI, A. Physiologic Articulaire. Paris, Maloine, 1978: Tome 1: 171. KAPLAN, E. B. Surgical Approaches to the Neck, Cervical Spine and Upper Extremity. Philadelphia, W. B. Saunders, 1966. KAPLAN, E. B. Functional and Surgical Anatomy of the Hand, 2nd edn. Philadelphia, J. B. Lippincott, 1984: 131. KENDALL, F. P. and KENDAL, E. McC. Les Muscles, 3rd edn. Paris, Maloine, 1974: 39. LAMB, D. W. and KUCZYNSKI, K. The Practice of Hand Surgery. Oxford, Blackwell, 1981. LANDSMEER, J. M. F. Atlas of Anatomy of the Hand. Edinburgh, Churchill Livingstone, 1976: 129. LEAO, L. (1958). De Quervain’s Disease. A Clinical and Anatomical Study. Journal of Bone and Joint Surgery, 40A: 5: 1063-1070. NIGST, H., BUCK-GRAMCKO, D., MILLESI, H. and LISTER, G. D. Hand Surgery. Stuttgart, Thieme, 1988: Vol. 1: 39. STEIN, A. M. (1951). Variations of the tendons of insertion of the abductor pollicis longus and the extensor pollicis brevis. Anatomical Record, 110: 4955. TESTUT, L. and LATARJET, A. Traite d’Attatomie Humaine. Paris, G. Doin, 1949: 201. TUBIANA, R., THOMINE, J. M. and MACKIN, E. Examination of the Hand and Upper Limb. Philadelphia, Saunders, 1984: 381.
Accepted: 4 July 1991 Umana. Turin, Minerva
Medica,
1975: Vol.
Professor 0
G. Bmnelli,
1992 The British
Via Campiana
Society for Surgery
77, Cellatica, of the Hand
Brescia,
25060 Italy.