Surgical Radiolog,c Anatomy
Surg Radiol Anat (1992) i4 : 325-329
Journal of Clinical Anatomy
© Springer-Verlag I992
The thenar muscles New findings
S Van Sint Jan and M Rooze Laboratory of Functional Anatomy, University of Brussels, CP 619, Route de Lennik, 808, B-1070 Brussels, Belgium
Summary. Examination of the thenar muscles in 30 anatomical preparations of the hand have shown that the abductor pollicis brevis, the opponens pollicis, and the adductor pollicis muscles are made up of several muscle bellies. The number and insertions of these bellies are varied. Both heads of flexor pollicis brevis do not originate from any particular muscle belly. The superficial head of this m u s c l e always inserted into the head of the thumb metacarpal, either completely, or, some of the fibres of the dorsal aponeurosis of the thumb were attached to the base of the proximal phalanx. F u r t h e r m o r e the a n a t o m y of the abductor pollicis brevis muscle was related to the presence of a tendinous slip from abductor potlicis longus. These variations could have an influence on proprioception in the thumb ray.
Offprint requests" : S Van Sint Jan
La m u s c u l a t u r e t h 6 n a r i e n n e : apports nouveaux R6sum~. Certaines particularit6s anatomiques concernant les muscles th6nariens sont raises en 6vidence dans ce travail suite ~ l'observation de trente prdparations anatomiques de mains. Le court abducteur du pouce, l'opposant du pouce et Fadducteur du pouce sont composds de fascicules. Le nombre et les insertions de ces fascicules sont tr6s variables. Les deux chefs du court fl6chisseur du pouce ne semblent pas pr6senter de fasciculation particuli6re. L'insertion distale du chef superficiel de ce muscle se fair part i e l t e m e n t mais de m a n i b r e tr6s constante sur la t~te du p r e m i e r mdtacarpien. Des fibres de l'apon& vrose d'extension du pouce vont s'ins6rer sur la base de la deuxi6me phalange. De plus l'aspect du court abducteur du pouce ddpend fortemerit de la pr6sence de l'expansion du long abducteur du pouce. Les variations observ6es pourraient avoir une incidence sur la qualit6 de la proprioception de la premibre colonne digitale de la main.
Key words : Anatomy - - Muscle -- Thenar eminence -- Thumb
The description of the muscle bellies within the thenar eminence has only appeared recently. Kuhlmann and Gu6rin-Surville [3] first used the term "fascicular arrangement". Prior to this several authors concluded that the sub-divisions within the thenar muscles were important in the control of thumb movement [5, 7]. T h e v a r i o u s m u s c l e bellies however were not described. More recently Simard and Roberge [8] d e s c r i b e d the m u s c l e bellies of abductor pollicis brevis (APB). The present study assesses the variation in the i n s e r t i o n s o f the thenar muscles. A biomechanical study is planned in the future.
Material and method Thirty anatomical preparations of hands were dissected and observed under a microscope. Twenty hands were taken from cadavers (embalming performed by a modification
326 of Dankmeyer' s method, see appendix), the other ten were from fresh post-mortem specimens. All were Caucasian and over 60 years old. The muscle bellies of the APB were described using the classification of Simard and Roberge [8].
Van Sint Jan et al : The thenar muscles:new findings ved (20.0%). This would give a characteristic appearance of APB (Fig. 3a) where the muscles seemed shifted medially compared to a more typical APB. The APB muscle bellies inserted into the base of the proximal phalanx and the dorsal aponeurosis of the thumb.
Results Dorsal aponeurosis Abductor pollicis brevis m. The APB was often composed of six muscle bellies, divided into three groups; medial, central and lateral (Fig. 1). Each APB muscle belly had a separate nellie supply (Fig. 2). The medial group had three superimposed muscle bellies inserted proximally into the flexor retinaculure. V1 was the most superficial and received tendinous fibres from the palmaris longus muscle. V1 partially or totally covered the other muscle bellies of the medial group, the V2 and V2',V2 being the deepest one. If palmaris longus did not insert fibres into the APB, then V1 was not p r e s e n t (26.7% of the cases). Sometimes V2 and V2' formed single muscle mass (33.3% of the cases). The central group comprised one muscle belly, V2". This was inserted proximally into the sheath of the flexor carpi radialis muscle, sometimes onto the scaphoid bone (16.7%), the flexor retinalculum (16.7%), or the tendinous slip of the abductor pollicis longus muscle (3.3%). The lateral group comprised two muscle bellies, V3, the m o s t superficial and lateral which partially or totally covered V3'. These mainly inserted into the tubercle of the scaphoid and to a lesser extent the tubercle of the trapezium. The presence of the lateral group seemed to be connected to the presence of a tendinous slip between abductor pollicis longus and abductor pollicis brevis. If this slip was absent V3 and V3' were not obser-
In 25% of the cases, the most distal fibres of the lateral side of the thenar dorsal aponeurosis formed an angle to b e c o m e parallel to the extensor pollicis longus tendon. These fibres relayed along the lateral side of the extensor tendon and inserted into the distal phalanx of the thumb. Because of their characteristic length they are called the "long lateral fibres" of the thenar aponeurosis (such fibres also exist on the medial side of the aponeurosis, see below and Fig. 4). Opponens poUicis m. The opponens pollicis muscle most fYequently comprised two muscle bellies (86.7%), the most superficial (OS) was more slender than the deep one (OD). Because of its more extensive insertion, OD often emerged proximal to, or distally under the OS (Fig. 3b and 3c). Both muscle bellies always inserted into the flexor retinaculum. Sometimes they had attachments to the trapezium (OS 16.7% and OD 70.0%). Distally OS was inserted to the base and diaphysis of the thumb metacarpal bone (66.7%), but extended onto the trapezio-metacarpal (T-M) joint capsule in 20.0% of cases (33.3% of cases for the OD). In 13.3% of cases the OD and OS formed one muscle belly. The oppohens pollicis muscle was always fully developed in comparison with the other thenar muscles, where muscle bellies were often missing.
Adductor pollicis m. Eight bellies of adductor polticis muscle (ADP) were noted though the insertion and relative positions were variable and will be reported in another publication. Two important observations can be reported here: Firstly, the transverse head of the ADP muscle was reduced in size in 26.7% of the cases. There was a small thin or even atrophied single muscle belly. Secondly, the dorsal aponeurosis of the ADP often inserted distally into the base of the distal phalanx (Fig. 4) in a similar way to that of the APB. These "long medial fibres" of the thenar aponeurosis were noted in 73.9% of the cases. Flexor pollicis brevis m. Both heads of flexor pollicis brevis muscle (FPB) did not have a subdivision. The origins of these muscles are as previously described. However, the superficial head of the FPB frequently inserted into the head of the t h u m b m e t a c a r p a l b o n e (96.7%), as well as to the lateral sesamoid, and was continuous with the p r o x i m a l phalanx. The deep head also inserted into the lateral sesamoid and was continuous with the phalanx but more distally. Rarely there was a secondary insertion into the medial sesamoid (6.7%). Discussion Variation and proprioception This study shows that the thenar muscles have many anatomical variations that may be secondary to the various skills that can be noted clinically. Further research is required on the long fibres of the thenar dorsal aponeurosis, both medially and laterally, and on the tendinous slips, especially to determine whether they
Van Sint Jan et al : The thenar muscles: new findings
327
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Figs. 1, 2a-d 1 The fascicles of the abductor pollicis brevis muscle (palmar view, fight hand) 1 first phalanx of the thumb 2 index metacarpal bone 3 palmaris longus m. 4 flexor carpi radialis m. 5 abductor pollicis longus m. 6 V1 7 V2 8 V2' 9 V2" 10 V3 11 V3'. 2 Nerve supply of the fascicles of the abductor pollicis brevis muscle (fight hand, palmar view), a diagram of figure 2b. b fascicle V2' (marked with *) in normal position, e diagram of figure 2d. d fascicle V2' (marked with *) resected 1 hypothenar eminence 2 thumb 3 wrist 4 flexor pollicis brevis m. 5 opponens pollicis m. 6 digital branches of the median nerve 7 thenar branch of the median nerve 8 motor branch for the V2 fascicle 9 motor branch running through the deep layer to give 11, 12, 13 (left picture) 10 V2' nerve supply I t V1 nerve supply 12 V2" nerve supply 13 branch for both the V3 and V3' fascicles (merged in this case) 1 Les fascicuIes du muscle court abductenr ( vue palmaire, main droite ) l premi6re phalange du pouce 2 deuxi~me m6tacarpien 3 m. long palmaire 4 m. fidchisseur radial du carpe 5 m. long abducteur du pouce 6 V1 7V2 8 V2' 9 V2" I0 V3 11 V3'. 2 Innervation des fascicules du muscle court abducteur du pouce (vue palmaire, main droite), a Schdma de la figure 2b. b fascicule V2' (marqu6 par *) laiss6 en place, c sh6ma de la figure 2d. d fascicule V2' (marqu6 par *) r6clin6 vers le haut 1 6minence hypoth6nar 2 pouce 3 poignet 4 m, court ft6chisseur du pouce 5 m. opposant du pouce, 6 branches interdigitales du neff m6dian 7 branche thdnarienne du neff m6dian 8 branche motrice pour le fascicule V2 9 branche perforant la couche profonde pour donner les branches marqu6es 11, 12, 13 snr l'image de gauche 10 innervation de V2' 11 innervation de V1 12 innervation de V2" i3 branche destin6e ~ l'innervation de V3 et V3' (fusionn6s darts ce cas)
h a v e a propriocepfive role. T h e y link the p a l m a r m u s c u l a r s t r u c t u r e s (the thenar eminence, palmaris longus, a n d a b d u c t o r pollicis longus) to b o t h the dorsal a p o n e u r o s i s a n d the distal p h a l a n x o f the t h u m b . F a h r e r [2] has
d e s c r i b e d t h e d i g a s t r i c m u s c l e form e d b y a b d u c t o r pollicis l o n g u s a n d palmaris longus, with the APB. T h e s e structures are distally e x t e n d e d b y the t w o types o f previously m e n t i o n e d l o n g fibres o f the dorsal apo-
neurosis. F u r t h e r w o r k is n e e d e d to find out the functional significance a n d c o n s e q u e n c e o f these variations e.g. the p r e s e n c e o f a residual o f a n A D P transverse head, or the a b s e n c e o f the m u s c l e s b e l l i e s o f the lateral
328
Van Sint Jan et al : The thenar muscles: new findings
Fig. 3a-e Palmar appearance of the thenar eminence (right hand), a m . abductor pollicis brevis untouched, b m , abductor pollicis brevis resectexl, e diagram of figure 3b 1 flexor retinaculum 2 palmaris longus m. 3 flexor carpi radialis m, 4 abductor pollicis longus m. 5 marker stuck in the metacalpo-phalangeal joint 6 trapezio-metacarpal joint 7 abductor pollicis brevis m. 8 superficial belly of the opponens pollicis muscle 9 deep belly of the opponens pollicis muscle 10 superficial head of the flexor pollicis brevis muscle ( - - - - - - ) limit between 8 and 10, In this case, the APB muscle has no lateral fascicular group (V3, V3'). So it seems medially displaced Vue pahnaire de I'6minence th6nar (main droite), a muscle court abducteur en place, b muscle court abducteur r6clin6, e schema de la figure 3b I retinaculum des fl6chisseurs 2 m. long palmaire 3 m. fl6chisseur radial du carpe 4 m. long abducteur du pouce 5 repbre gliss6 dans l'interligne mdtacarpo-phalangien 6 interligne trap6zo-m6tacarpien 7 m. court abducteur du pouce 8 ventre superficiel du m. opposant 9 ventre profond du m. opposant 10 ventre superficiel du m. court fldchisseur ( - - - - - - ) limite entre 8 et 10. Dans le cas present6 ce muscle ne poss6dait pas de groupe fasciculaire latdral (V3,V3'), Ce muscle semblait ainsi avoir une position plus m6diale
group of the APB muscle, and their effect on the grips. It may be that such muscles function is affected by a lack of part of their muscle belly, and that this may have been due to the age of the population studied. Unfortunately, the records of the studied specimens were too incomplete to find out whether there was any correlation between reduced transverse head bulk and underlying degenerative pathology.
The FPB muscular origin The two o r i g i n a l s of the FPB muscle should be functionally separated because, firstly, they have a very different spatial orientation, and secondly, the superficial head inserts into the metacarpal. This makes the superficial head function very close to both the opponens pollicis and APB muscle. However the deep head of the FPB is similar
to the ADP muscle by its predicted action of closing the first webspace. The association of a superficial head of the FPB with the opponens muscle is not a new finding [4, 5, 6]. It also fits in with the classically described double nerve supply of FBP [1]. Acknowledgement, Special thanks to L Duson and J-L Sterckx for their technical help
Van Sint Jan et al : The thenar muscles: new findings
329
Fig. 4 2['he long fibers of the dorsal aponeurosis (medial view, left hand) t transverse fibers 2 oblique fibers 3 long fibers 4 extensor potlicis longns muscle tendon Les "fibres longues" de l'apon6vmse d'extension du pouce( vue mddiale, main gauche ) i fibres transverses 2 fibres obliques 3 fibres longues 4 tendon du muscle long extenseur du ponce
References 3. i~ Backhouse KM (t980) Inuervation du bras et de la main. In: Tubiana R (ed) Traitd de chirurgie de ta main (tome I). Masson, Paris, p 309 2. Fahrer M (1975) Considdrations sur les insertions d'origines des muscles lombri-
4.
caux; les systbmes digastriques de la main. Ann Chir 11 : 979-82 Kuhlmann JN, Gudrin-Survilte H (1985) Agencement fasciculaire des muscles intrinsbques du pouce. Bull Assoc Anat 207 : 29-4t Long C, Conrad PW, Hall EA, Furler SL (1970) Intrinsic-extrinsic muscle control of the hand in power grip and precision
handling. J Bone Joint Surg [Aml 52 : 853-67 5. McFarlane RM (t 962) Observations on the functional anatomy of the intrinse muscles of the thumb. J Bone Joint Surg [Am] d4 : 1073-88 6. Napier JR (1952) The attachments and function of the Abductor Pollicis Brevis. J Anat 86 : 335-41 7. Rouvi6re H (1970) Anatomie humaine descriptive et topographique. Masson, Paris 8. Simard Th, Roberge J (1988) Human abductor potlicis brevis divisions and the nerve hila. Anat Rec 222 : 426-36 9. Wood Jones F (1946) Principles of anatomy as seen in the hand. Bailli~re, Tindall and Cox, London
Received December 19, 1991 / Accepted in finaI form August 20, 1992
Annex Embalming solution (Dankmeyer's m e t h o d m o d i f i e d ) : f o r 1 liter H 2 0 : 50 m l a l c o h o l (95°), 50 ml F o r m o l (40°), 10 g P h e n o l , 20 g g l y c e r i n , 50 g C h l o r a l H y d r a t e , 12.5 g N a S O 4, 12.5 g M g S O 4 , 25 g K N O 3
Surg Radiol Anat (1992) i4 : 325-329
Journal of Clinical Anatomy
© Springer-Verlag I992
The thenar muscles New findings
S Van Sint Jan and M Rooze Laboratory of Functional Anatomy, University of Brussels, CP 619, Route de Lennik, 808, B-1070 Brussels, Belgium
Summary. Examination of the thenar muscles in 30 anatomical preparations of the hand have shown that the abductor pollicis brevis, the opponens pollicis, and the adductor pollicis muscles are made up of several muscle bellies. The number and insertions of these bellies are varied. Both heads of flexor pollicis brevis do not originate from any particular muscle belly. The superficial head of this m u s c l e always inserted into the head of the thumb metacarpal, either completely, or, some of the fibres of the dorsal aponeurosis of the thumb were attached to the base of the proximal phalanx. F u r t h e r m o r e the a n a t o m y of the abductor pollicis brevis muscle was related to the presence of a tendinous slip from abductor potlicis longus. These variations could have an influence on proprioception in the thumb ray.
Offprint requests" : S Van Sint Jan
La m u s c u l a t u r e t h 6 n a r i e n n e : apports nouveaux R6sum~. Certaines particularit6s anatomiques concernant les muscles th6nariens sont raises en 6vidence dans ce travail suite ~ l'observation de trente prdparations anatomiques de mains. Le court abducteur du pouce, l'opposant du pouce et Fadducteur du pouce sont composds de fascicules. Le nombre et les insertions de ces fascicules sont tr6s variables. Les deux chefs du court fl6chisseur du pouce ne semblent pas pr6senter de fasciculation particuli6re. L'insertion distale du chef superficiel de ce muscle se fair part i e l t e m e n t mais de m a n i b r e tr6s constante sur la t~te du p r e m i e r mdtacarpien. Des fibres de l'apon& vrose d'extension du pouce vont s'ins6rer sur la base de la deuxi6me phalange. De plus l'aspect du court abducteur du pouce ddpend fortemerit de la pr6sence de l'expansion du long abducteur du pouce. Les variations observ6es pourraient avoir une incidence sur la qualit6 de la proprioception de la premibre colonne digitale de la main.
Key words : Anatomy - - Muscle -- Thenar eminence -- Thumb
The description of the muscle bellies within the thenar eminence has only appeared recently. Kuhlmann and Gu6rin-Surville [3] first used the term "fascicular arrangement". Prior to this several authors concluded that the sub-divisions within the thenar muscles were important in the control of thumb movement [5, 7]. T h e v a r i o u s m u s c l e bellies however were not described. More recently Simard and Roberge [8] d e s c r i b e d the m u s c l e bellies of abductor pollicis brevis (APB). The present study assesses the variation in the i n s e r t i o n s o f the thenar muscles. A biomechanical study is planned in the future.
Material and method Thirty anatomical preparations of hands were dissected and observed under a microscope. Twenty hands were taken from cadavers (embalming performed by a modification
326 of Dankmeyer' s method, see appendix), the other ten were from fresh post-mortem specimens. All were Caucasian and over 60 years old. The muscle bellies of the APB were described using the classification of Simard and Roberge [8].
Van Sint Jan et al : The thenar muscles:new findings ved (20.0%). This would give a characteristic appearance of APB (Fig. 3a) where the muscles seemed shifted medially compared to a more typical APB. The APB muscle bellies inserted into the base of the proximal phalanx and the dorsal aponeurosis of the thumb.
Results Dorsal aponeurosis Abductor pollicis brevis m. The APB was often composed of six muscle bellies, divided into three groups; medial, central and lateral (Fig. 1). Each APB muscle belly had a separate nellie supply (Fig. 2). The medial group had three superimposed muscle bellies inserted proximally into the flexor retinaculure. V1 was the most superficial and received tendinous fibres from the palmaris longus muscle. V1 partially or totally covered the other muscle bellies of the medial group, the V2 and V2',V2 being the deepest one. If palmaris longus did not insert fibres into the APB, then V1 was not p r e s e n t (26.7% of the cases). Sometimes V2 and V2' formed single muscle mass (33.3% of the cases). The central group comprised one muscle belly, V2". This was inserted proximally into the sheath of the flexor carpi radialis muscle, sometimes onto the scaphoid bone (16.7%), the flexor retinalculum (16.7%), or the tendinous slip of the abductor pollicis longus muscle (3.3%). The lateral group comprised two muscle bellies, V3, the m o s t superficial and lateral which partially or totally covered V3'. These mainly inserted into the tubercle of the scaphoid and to a lesser extent the tubercle of the trapezium. The presence of the lateral group seemed to be connected to the presence of a tendinous slip between abductor pollicis longus and abductor pollicis brevis. If this slip was absent V3 and V3' were not obser-
In 25% of the cases, the most distal fibres of the lateral side of the thenar dorsal aponeurosis formed an angle to b e c o m e parallel to the extensor pollicis longus tendon. These fibres relayed along the lateral side of the extensor tendon and inserted into the distal phalanx of the thumb. Because of their characteristic length they are called the "long lateral fibres" of the thenar aponeurosis (such fibres also exist on the medial side of the aponeurosis, see below and Fig. 4). Opponens poUicis m. The opponens pollicis muscle most fYequently comprised two muscle bellies (86.7%), the most superficial (OS) was more slender than the deep one (OD). Because of its more extensive insertion, OD often emerged proximal to, or distally under the OS (Fig. 3b and 3c). Both muscle bellies always inserted into the flexor retinaculum. Sometimes they had attachments to the trapezium (OS 16.7% and OD 70.0%). Distally OS was inserted to the base and diaphysis of the thumb metacarpal bone (66.7%), but extended onto the trapezio-metacarpal (T-M) joint capsule in 20.0% of cases (33.3% of cases for the OD). In 13.3% of cases the OD and OS formed one muscle belly. The oppohens pollicis muscle was always fully developed in comparison with the other thenar muscles, where muscle bellies were often missing.
Adductor pollicis m. Eight bellies of adductor polticis muscle (ADP) were noted though the insertion and relative positions were variable and will be reported in another publication. Two important observations can be reported here: Firstly, the transverse head of the ADP muscle was reduced in size in 26.7% of the cases. There was a small thin or even atrophied single muscle belly. Secondly, the dorsal aponeurosis of the ADP often inserted distally into the base of the distal phalanx (Fig. 4) in a similar way to that of the APB. These "long medial fibres" of the thenar aponeurosis were noted in 73.9% of the cases. Flexor pollicis brevis m. Both heads of flexor pollicis brevis muscle (FPB) did not have a subdivision. The origins of these muscles are as previously described. However, the superficial head of the FPB frequently inserted into the head of the t h u m b m e t a c a r p a l b o n e (96.7%), as well as to the lateral sesamoid, and was continuous with the p r o x i m a l phalanx. The deep head also inserted into the lateral sesamoid and was continuous with the phalanx but more distally. Rarely there was a secondary insertion into the medial sesamoid (6.7%). Discussion Variation and proprioception This study shows that the thenar muscles have many anatomical variations that may be secondary to the various skills that can be noted clinically. Further research is required on the long fibres of the thenar dorsal aponeurosis, both medially and laterally, and on the tendinous slips, especially to determine whether they
Van Sint Jan et al : The thenar muscles: new findings
327
2
6
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'
7""J
i
Figs. 1, 2a-d 1 The fascicles of the abductor pollicis brevis muscle (palmar view, fight hand) 1 first phalanx of the thumb 2 index metacarpal bone 3 palmaris longus m. 4 flexor carpi radialis m. 5 abductor pollicis longus m. 6 V1 7 V2 8 V2' 9 V2" 10 V3 11 V3'. 2 Nerve supply of the fascicles of the abductor pollicis brevis muscle (fight hand, palmar view), a diagram of figure 2b. b fascicle V2' (marked with *) in normal position, e diagram of figure 2d. d fascicle V2' (marked with *) resected 1 hypothenar eminence 2 thumb 3 wrist 4 flexor pollicis brevis m. 5 opponens pollicis m. 6 digital branches of the median nerve 7 thenar branch of the median nerve 8 motor branch for the V2 fascicle 9 motor branch running through the deep layer to give 11, 12, 13 (left picture) 10 V2' nerve supply I t V1 nerve supply 12 V2" nerve supply 13 branch for both the V3 and V3' fascicles (merged in this case) 1 Les fascicuIes du muscle court abductenr ( vue palmaire, main droite ) l premi6re phalange du pouce 2 deuxi~me m6tacarpien 3 m. long palmaire 4 m. fidchisseur radial du carpe 5 m. long abducteur du pouce 6 V1 7V2 8 V2' 9 V2" I0 V3 11 V3'. 2 Innervation des fascicules du muscle court abducteur du pouce (vue palmaire, main droite), a Schdma de la figure 2b. b fascicule V2' (marqu6 par *) laiss6 en place, c sh6ma de la figure 2d. d fascicule V2' (marqu6 par *) r6clin6 vers le haut 1 6minence hypoth6nar 2 pouce 3 poignet 4 m, court ft6chisseur du pouce 5 m. opposant du pouce, 6 branches interdigitales du neff m6dian 7 branche thdnarienne du neff m6dian 8 branche motrice pour le fascicule V2 9 branche perforant la couche profonde pour donner les branches marqu6es 11, 12, 13 snr l'image de gauche 10 innervation de V2' 11 innervation de V1 12 innervation de V2" i3 branche destin6e ~ l'innervation de V3 et V3' (fusionn6s darts ce cas)
h a v e a propriocepfive role. T h e y link the p a l m a r m u s c u l a r s t r u c t u r e s (the thenar eminence, palmaris longus, a n d a b d u c t o r pollicis longus) to b o t h the dorsal a p o n e u r o s i s a n d the distal p h a l a n x o f the t h u m b . F a h r e r [2] has
d e s c r i b e d t h e d i g a s t r i c m u s c l e form e d b y a b d u c t o r pollicis l o n g u s a n d palmaris longus, with the APB. T h e s e structures are distally e x t e n d e d b y the t w o types o f previously m e n t i o n e d l o n g fibres o f the dorsal apo-
neurosis. F u r t h e r w o r k is n e e d e d to find out the functional significance a n d c o n s e q u e n c e o f these variations e.g. the p r e s e n c e o f a residual o f a n A D P transverse head, or the a b s e n c e o f the m u s c l e s b e l l i e s o f the lateral
328
Van Sint Jan et al : The thenar muscles: new findings
Fig. 3a-e Palmar appearance of the thenar eminence (right hand), a m . abductor pollicis brevis untouched, b m , abductor pollicis brevis resectexl, e diagram of figure 3b 1 flexor retinaculum 2 palmaris longus m. 3 flexor carpi radialis m, 4 abductor pollicis longus m. 5 marker stuck in the metacalpo-phalangeal joint 6 trapezio-metacarpal joint 7 abductor pollicis brevis m. 8 superficial belly of the opponens pollicis muscle 9 deep belly of the opponens pollicis muscle 10 superficial head of the flexor pollicis brevis muscle ( - - - - - - ) limit between 8 and 10, In this case, the APB muscle has no lateral fascicular group (V3, V3'). So it seems medially displaced Vue pahnaire de I'6minence th6nar (main droite), a muscle court abducteur en place, b muscle court abducteur r6clin6, e schema de la figure 3b I retinaculum des fl6chisseurs 2 m. long palmaire 3 m. fl6chisseur radial du carpe 4 m. long abducteur du pouce 5 repbre gliss6 dans l'interligne mdtacarpo-phalangien 6 interligne trap6zo-m6tacarpien 7 m. court abducteur du pouce 8 ventre superficiel du m. opposant 9 ventre profond du m. opposant 10 ventre superficiel du m. court fldchisseur ( - - - - - - ) limite entre 8 et 10. Dans le cas present6 ce muscle ne poss6dait pas de groupe fasciculaire latdral (V3,V3'), Ce muscle semblait ainsi avoir une position plus m6diale
group of the APB muscle, and their effect on the grips. It may be that such muscles function is affected by a lack of part of their muscle belly, and that this may have been due to the age of the population studied. Unfortunately, the records of the studied specimens were too incomplete to find out whether there was any correlation between reduced transverse head bulk and underlying degenerative pathology.
The FPB muscular origin The two o r i g i n a l s of the FPB muscle should be functionally separated because, firstly, they have a very different spatial orientation, and secondly, the superficial head inserts into the metacarpal. This makes the superficial head function very close to both the opponens pollicis and APB muscle. However the deep head of the FPB is similar
to the ADP muscle by its predicted action of closing the first webspace. The association of a superficial head of the FPB with the opponens muscle is not a new finding [4, 5, 6]. It also fits in with the classically described double nerve supply of FBP [1]. Acknowledgement, Special thanks to L Duson and J-L Sterckx for their technical help
Van Sint Jan et al : The thenar muscles: new findings
329
Fig. 4 2['he long fibers of the dorsal aponeurosis (medial view, left hand) t transverse fibers 2 oblique fibers 3 long fibers 4 extensor potlicis longns muscle tendon Les "fibres longues" de l'apon6vmse d'extension du pouce( vue mddiale, main gauche ) i fibres transverses 2 fibres obliques 3 fibres longues 4 tendon du muscle long extenseur du ponce
References 3. i~ Backhouse KM (t980) Inuervation du bras et de la main. In: Tubiana R (ed) Traitd de chirurgie de ta main (tome I). Masson, Paris, p 309 2. Fahrer M (1975) Considdrations sur les insertions d'origines des muscles lombri-
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caux; les systbmes digastriques de la main. Ann Chir 11 : 979-82 Kuhlmann JN, Gudrin-Survilte H (1985) Agencement fasciculaire des muscles intrinsbques du pouce. Bull Assoc Anat 207 : 29-4t Long C, Conrad PW, Hall EA, Furler SL (1970) Intrinsic-extrinsic muscle control of the hand in power grip and precision
handling. J Bone Joint Surg [Aml 52 : 853-67 5. McFarlane RM (t 962) Observations on the functional anatomy of the intrinse muscles of the thumb. J Bone Joint Surg [Am] d4 : 1073-88 6. Napier JR (1952) The attachments and function of the Abductor Pollicis Brevis. J Anat 86 : 335-41 7. Rouvi6re H (1970) Anatomie humaine descriptive et topographique. Masson, Paris 8. Simard Th, Roberge J (1988) Human abductor potlicis brevis divisions and the nerve hila. Anat Rec 222 : 426-36 9. Wood Jones F (1946) Principles of anatomy as seen in the hand. Bailli~re, Tindall and Cox, London
Received December 19, 1991 / Accepted in finaI form August 20, 1992
Annex Embalming solution (Dankmeyer's m e t h o d m o d i f i e d ) : f o r 1 liter H 2 0 : 50 m l a l c o h o l (95°), 50 ml F o r m o l (40°), 10 g P h e n o l , 20 g g l y c e r i n , 50 g C h l o r a l H y d r a t e , 12.5 g N a S O 4, 12.5 g M g S O 4 , 25 g K N O 3
