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The anatomy of the incision for carpal tunnel decompression
The Anatomy of the Incision for Carpal Tunnel Decompression E. E. Denman T H E A N A T O M Y OF T H E INCISION FOR C A R P A L T U N N E L DECOMPRESSION E. E. D E N M A N , Swindon
SUMMARY The coarse fibrous pattern o f the roots o f the palmar aponeurosis and o f the flexor retinaculum, comprising the r o o f o f the carpal tunnel, is described, to define the structures incised in the operation to relieve carpal tunnel compression syndrome.
INTRODUCTION Division of the flexor retinaculum for the relief of carpal tunnel syndrome is one of the most c o m m o n and rewarding minor procedures in orthopaedic practice. The skin incision usually advocated is a longitudinal one. Engber and Gmeiner (1980) emphasize the need for the incision to be placed between the palmar cutaneous branches of the median and ulnar nerves. As the skin incision is deepened fibres of the proximal part of the palmar aponeurosis are encountered first, and deep to these the flexor retinaculum presents as a thick band. Muscle fibres are often seen in or to the radial side o f the proximal part of the wound and in or to the ulnar side of the distal part of the wound. The detailed a n a t o m y of the fibrous structures through which this incision passes has received scant attention. Description o f the palmar aponeurosis in anatomical and surgical literature has largely been confined to its metacarpal, rather than its carpal part. In the past surgical interest in the anatomy of the flexor retinaculum has concentrated on its related deep structures, a n d its penetration by nerve branches, namely the thenar m o t o r branch o f the median nerve (Papathanassiou, 1968), the the palmar branch of the median nerve (Taleisnik, 1973), and a variant m o t o r branch of the ulnar nerve (Lassa, 1975). The flexor retinaculum is dismissed in most standard works as a strong fibrous sheet between its well known bony attachments completing the carpal tunnel. In order to better appreciate the fibrous structures through which the standard incision for the relief of carpal tunnel syndrome passes, dissections of this region in cadaveric hands were carried out under magnification. This paper describes the findings of this study.
ANATOMICAL STUDY Twelve formalin-preserved cadaveric hands were dissected under magnification and photographs taken to illustrate various points. A single deep frozen cadaveric specimen was sectioned transversely at half-centimetre intervals and examined under E. E. Denman, F.R.C.S., Princess Margaret Hospital, Swindon, Wiltshire. 9 1981 British Society for Surgery of the Hand 0072-968X-81-00030017 $02.00 The Hand--Folume 13
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m a g n i f i c a t i o n . I n a n o t h e r specimen an incision was m a d e to decompress the carpal t u n n e l , a n d the course o f the incision was related to the fibrous structures described.
THE PROXIMAL ROOTS OF THE PALMAR APONEUROSIS The apex o f the p a l m a r a p o n e u r o s i s , lying a n t e r i o r to the flexor r e t i n a c u l u m , gives rise distally to the l o n g i t u d i n a l system o f fibres o f the a p o n e u r o s i s . It can be regarded as being f o r m e d by a n u m b e r o f roots, The palmaris root. T h e m a i n c o n t r i b u t i o n to the p a l m a r a p o n e u r o s i s , f r o m the t e n d o n o f the p a l m a r i s longus, can be called the p a l m a r i s r o o t . As this t e n d o n a p p r o a c h e s the flexor r e t i n a c u l u m it is superficial to the deep fascia o f the Iower forearm, s u r r o u n d e d b y f i b r o - f a t t y connective tissue. Dissection o f this tissue d e m o n s t r a t e s f i b r o u s b a n d s which, in relation t o the t e n d o n , take either a centrifugal or a centripetal course. C e n t r i f u g a l fibres pass distally f r o m the t e n d o n in all directions, a n d especially radially into the f i b r o - f a t t y s u b c u t a n e o u s tissue at
Fig. 1. A photograph of a X10 magnification dissection of a right hand in the anatomical position to show the transition zone between the palmaris longus tendon and the apex of the palmar aponeurosis - - the palmaris root of the aponeurosis. A needle is raising a fibrous band which is passing from the subcutaneous tissue of about the region of the distal skin crease of the wrist to the apponenrosis. Fig. 2. A photograph of a X3 magnification of a transverse section of a hand, at the level of the distal part of the flexor retinaculum, to show the area of interlacement of fibres at the site of attachment of the apex of the palmar aponeurosis to the retinaculum. This area is called the carina in the text, and is labelled C in the diagram. F, flexor retinaculum. A, palmar aponeurosis. 18
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the base o f the t h e n a r e m i n e n c e a n d the p r o x i m a l fascia o f the a b d u c t o r pollicis brevis. C e n t r i p e t a l fibres arise f r o m the s u r r o u n d i n g tissue a n d pass distally, into t h e t e n d o n , c o n t r i b u t i n g to its s u b s t a n c e (Fig. 1). The p a l m a r i s longus t e n d o n is superficial to the p r o x i m a l p a r t o f t h e flexor r e t i n a c u l u m , being s e p a r a t e d f r o m it b y its s u r r o u n d i n g connective tissue. T h e t e n d o n is often quite n a r r o w at this level, a n d in passing distally e x p a n d s t r a n s v e r s e l y to f o r m the superficial p a r t o f the p r o x i m a l p a r t o f the l o n g i t u d i n a l f i b r o u s system o f the p a l m a r a p o n e u r o s i s . T h i s system o f fibres becomes a t t a c h e d to t h e distal p a r t o f the anterior surface o f t h e flexor r e t i n a c u l u m , slightly to the r a d i a l side o f the midline, b y the d e e p e r o r i g i n o f t h e other r o o t s o f the a p o n e u r o s i s , n a m e l y t h e u l n a r a n d r a d i a l r o o t s . This region o f interlacement between the d i s t a l p a r t o f t h e r e t i n a c u l u m a n d the p a l m a r i s longus a n d p a l m a r a p o n e u r o s i s , when viewed in section or f r o m the p a l m a r surface is reminiscent o f the keel o f an u p t u r n e d b o a t , a n d could t h e r e f o r e p e r h a p s be usefully referred to as the carina o f t h e r e t i n a c u l u m (Fig. 2).
Fig. 3. The same hand as in Fig. 1. To the left of the figure the longitudinal bands of the palmar aponeurosis are seen. To the right, running transversely are fasciculi of the palmaris brevis, forming aponeurotic bands, which run through the carina of the retinaculum. Some aponeurotic bands pass distally contributing to the palmar aponeurosis. Between the fasciculi of the palmaris brevis can be seen some fa~ in the pisoretinacular space or space of Guyon. Fig. 4. Aphotograph of a X3 magnification dissection of a right hand in the anatomical position. VC, longitudinal fibres of the volar carpal ligament. PA, pisoaponeurotic fibres, raised by the point of the probe. The hiatus of the pisoretinacular space or space of Guyon lies at the tip of the probe, and the trigone of the retinaculum is outlined below it, between the descending groups of fibres. The Hand-- Volume 13
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The ulnar roots
Fibre bundles can be followed into the ulnar side of the apex of the palmar aponeurosis from several sources. The most prominent and superficial fibres that enter the palmar aponeurosis from the ulnar side come from aponeurotic bands of the palmaris brevis. The radial attachment o f the muscular fasciculi of the palmaris brevis consists of a trabecular arrangement o f aponeurotic bands. Proximally these bands pass into the anterior surface of the flexor retinaculum deep to the tendon of the palmaris longus. More distally they pass into the carina of the retinaculum. In the carina some fibre bands appear to pass radially through it to merge with the anterior aspect of the flexor retinaculum and the fascia over the origin of the abductor pollicis brevis. Other bands are seen to extend proximally, giving the impression that they have arisen from longitudinal bundles of the palmar aponeurosis. Yet others pass distally contributing bands to the palmar aponeurosis (Fig. 3). Some fibres that enter the aponeurosis deeply, from the ulnar side, most proximally, may come from the volar carpal ligament (Denman, 1979). This ligament may form a prominent longitudinally running band on the anterior surface of the retinaculum, and some fibres of his band can sometimes be traced into the palmar aponeurosis. In Fig. 4 the longitudinal band of fibres of the volar carpal ligament has been sectioned to show its independence from the deeper fibres and is labelled VC. In this specimen it was the most radial fibres of the longitudinal band that could be traced into the aponeurosis. A few fibres of the volar carpal ligament may possibly pass longitudinally on the deep aspect of the retinaculum to reach the palmar aponeurosis. Those fibres that enter the palmar aponeurosis deeply, from the ulnar side, at an intermediate level, come from the pisiform bone, and are a superficial group of the strong fan o f fibres which sweeps radially and distally from this bone into the flexor retinaculum. This is the group o f fibres described by Landsmeer (1976). A contribution to the palmar aponeurosis by these fibres is shown in Fig. 4 and is labelled PA. Those fibres that enter the aponeurosis deeply, from the ulnar side at a more distal level, come from the hook of the hamate, and from the fascia over the origin of the opponens digiti minimi. They can be seen in Fig. 5, labelled HA. Fahrer (1980), noted that when the palmaris longus is congenitally absent, in five dissections, the "flexor carpi ulnaris completely takes over as the longitudinal tensor of the palmar aponeurosis", referring to fibres arising from the pisiform. No case in this present series was encountered totally without a palmaris longus, but in one a very narrow palmaris longus tendon arose from the antebrachial fascia in the distal forearm, giving but a feeble root to the aponeurosis. It would seem that without a palmaris root the ulnar roots are more important. 20
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Fig. 5. A photograph of a X6 magnification of the same hand to show the hamuloaponeurotic fibres, labelled HA. The position of the hook of the h a m a t e is labelled H. The fasciculi of the opponens digiti minimi are passing downwards and to the right. The proximal hiatus of the pisohamate canal, leading from the pisoretinacular space to the deep palmar space is seen in the top right corner of the figure. Fig. 6. A similar view of the same hand, this time towards the thenar eminence; The longitudinal fibres of the palmar aponeurosis are seen to the right of the figure. The subcutaneous aponeurotic bands which have been described in the text as the proximal radial root of the palmar aponeurosis have been divided and pressed to the right of the figure. This reveals the course of the palmar branch of the median nerve.
The radial roots
The subcutaneous tissue at the base of the thenar eminence, to the ulnar and distal side o f the tubercle o f the scaphoid, and towards the proximal end of the thenar crease, contains fibrous trabeculae, similar to those of the subcorial fibrous tissue layer of the hypothenar region. These trabeculae of fibrous tissue are continuous deeply with the deep fascia which covers the origin of the proximal part of the abductor pollicis brevis, and which is quite thick. Centrifugal fibres of the palmaris longus tendon merge with this subcutaneous fibrous system, and the abductor fascia. This can be confirmed clinically on contraction o f the palmaris longus. Through this area passes the palmar cutaneous branch or branches of the median nerve. Two more or less distinct groups of fibres pass to the palmar aponeurosis from the radial side. There is a superficial proximal contribution from the abductor fascia and subcutaneous fibrous system just described, and is illustrated in Fig. 6. There is The Hand-- Volume 13
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Fig. 7. A photograph of a X3 dissection of a right hand in the anatomical position. The tendon of the palmaris !ongus has been lifted to the ulnar side to show what has been described in the text as the distal radial root of the palmar aponeurosis, and marked R. Some thenar muscle fibres are seen through a window of fascia. Fig. 8 A photograph of a X3 dissection of a right hand. The flexor retinaculum has been sectioned longitudinally, as it might be in a carpal tunnel decompression operation. The sagittal face of the ulnar half of the retinaculum occupies the centre of the figure, the distal edge to the fight, and the proximal to the left. The origin of hypothenar musculature can be seen passing upwards and to the right of the figure. The median nerve lies in the lower part of the figure, overlying flexor tendons. 1, 2, and 3, refer to the laminae described in the text. Lamina 1 is thickened distally by the carina. also a m u c h stronger c o n t r i b u t i o n to the deep aspect o f the p a l m a r a p o n e u r o s i s , m o r e distally, f r o m the thick fascia which overlies the p r o x i m a l part o f the a b d u c t o r pollicis brevis n e a r a n d o n the ridge o f the t r a p e z i u m . These fibres are s h o w n in Fig. 7. The volar roots Just as b o t h centrifugal a n d centripetal fibres c a n be described in relation to the t e n d o n o f the p a l m a r i s l o n g u s , it is possible to discern similarly a r r a n g e d , b u t finer, fibres in r e l a t i o n to the diverging l o n g i t u d i n a l b u n d l e s o f the p r o x i m a l p a r t or apex o f the p a l m a r a p o n e u r o s i s . T h e y seem to arise in rather ill defined sagittal septae which pass f r o m between the p r o m i n e n t l o n g i t u d i n a l b u n d l e s o f the p a l m a r a p o n e u r o s i s to the dermis, e n c l o s i n g l o b u l a e o f relatively soft fat. T h e centripetal fibres can be regarded as a small volar root c o n t r i b u t i o n to the p a l m a r a p 6 n e u r o s i s . THE FLEXOR RETINACULUM T h e m a i n part o f the flexor r e t i n a c u l u m consists o f a mass o f fibrous b a n d s r u n n i n g in d i f f e r e n t directions, at first difficult to disentangle into a c o m p r e h e n s i b l e p a t t e r n . A characteristic feature is the weaving o f b a n d s across each other, b u n d l e s 22
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o f fibres passing in one direction breaking up to pass both superficially and deeply to fibres passing in another. For descriptive purposes, four inseparable layers can be distinguished. The superficial layer, or Lamina 1, could be thought of as that seen from the palmar surface. It has several characteristic features, but predominantly its fibres run obliquely downwards. It extends from the proximal to the distal limits of the retinaculum. Lamina 4, can be described as that seen from the dorsal or deep surface. Its fibres are predominantly transverse. It forms the smooth and glistening anterior wall o f the carpal tunnel, extending from the proximal to the distal limits of the retinaculum. The intermediate substance o f the retinaculum between the volar and dorsal aspects can tentatively be divided into a superficial Lamina 2, deep tO Lamina 1, and a deep Lamina 3. Lamina 2 is confined to about the distal two thirds of the retinaculum and its fibres are predominantly transverse. Lamina 3 is confined to about the distal third o f the retinaculum, and its fibres are more oblique. The retinaculum thus increases in thickness proximodistally, (Fig. 8), the thickness of the distal part being exaggerated, slightly to the radial side o f the midline, by the interlacement of the roots o f the palmar aponeurosis, here called the carina o f the retinaculum.
Lamina 1
When the superficial tissues are carefully dissected off the retinaculum the fibre systems displayed can be described under several headings (Fig. 9).
The pisoradial fibres Proximally the fibres which form the greater part of the superficial aspect of the retinaculum arise from the pisiform, and for the purposes of description can be divided into four diverging rays. The most proximal ray of fibres runs transversely to the radial side in the proximal border of the retinaculum. These fibres form the deep crus of the hiatus of the pisoretinacular space (or space of Guyon), and the proximal border of what may be described as the ulnar trigone of the retinaculum (Denman, 1979). This ray of fibres could also be described as thepisocrural ray. They mingle with fibres from the volar carpal ligament which have formed the superficial crus of the hiatus, and with fibres which pass ulnarwards and distally from the scaphoid. They are continuous proximally with the deep fascia o f the forearm. Fibres from the pisiform which run distally to the pisocrural fibres pass obliquely distally and to the radial side. They give rise to fasciculi o f the abductor pollicis brevis, and more deeply to the opponens pollicis, intermingling with the superficial transversely running fibres to the Same muscles, which have arisen from the region of the hook of the hamate. This ray of fibres which passes from the pisiform and gives rise to the thenar muscles could be called the p&othenar ray. The fibres to the thenar muscles from the hamate are to be described as the hamulothenar fibres. The fibres of the pisothenar ray pass deep to the carina of the retinaculum, interlacing with the deep radial root of the palmar aponeurosis, and the transversely running fibres of insertion of palmaris brevis. The Hand-- Volume 13
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Fig. 9. A photograph of a X3 dissection of the right hand in the anatomical position. The soft tissues, and palmafis longus and the apex of the palmar aponeurosis have been removed. P, site of the pisiform. H, site of the tip of the hook of the hamate. T, site of the ridge of the trapezium. S, site of the tubercle of the scaphoid. PC, pisocrural fibres. PT, pisothenar fibres. PA, pisoaponeurotic fibres. PH, pisohamate fibres. SU, scaphoulnar fibres. VC, volar carpal fibres. SHT, superficial hamulothenar fibres. Fig. 10. A photograph of a X9 dissection of a fight hand in the anatomical position, to show the weave between the pisoradial fibres (PR) and the hamulothenar fibres (HT), towards the ulnar and distal quadrant of the flexor retinaculum.
The third ray, distal to the pisothenar fibres, passes distally to the ulnar side of the palmaris longus tendon, before merging into the carina of the retinaculum, and passing into the palmar aponeurosis. This band of fibres has been encountered as an ulnar root of the aponeurosis. It could be referred to as the
pisoaponeurotic ray. Finally, fibres from the pisiform pass directly to the hook of the hamate, and are pai-t of the pisohamate ligament. Some of these fibres extend into the deep fascia of the abductor digiti minimi. They form the deep part of the proximal hiatus of the pisohamate tunnel, the deep ulnar nerve and vessels running over it.
The scaphoulnar fibres Fibres from the tubercle of the scaphoid, in the same plane above with the transversely running fibres of the deep fascia, and below with the pisothenar fibres, pass distally and to the ulnar side. They pass deep to the vertically running volar carpal fibres, into the ulnar trigone, and then on, deep to the pisohamate ligament, some of the fibres appearing to merge with the pisometacarpal ligament, and others with the hook of the hamate. These fibres may explain the observations of Young and Harrison (1947) that the 24
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pisotriquetral attachment of the retinaculum can be completely severed without opening the carpal tunnel. The palmar branch of the median nerve passes through a small hiatus between these fibres near their origin, to the ulnar side of the flexor carpi radialis, and near where the deep fascia becomes continuous with the retinaculum. The nerve often divides into its two main terminal branches before piercing the retinaculum. Some of the proximal fibres form a thin roof, which distally becomes much thicker, of the entrance to the sheath for the tendon of the flexor carpi radialis. The proximal fibres of insertion o f palmaris brevis pass behind the palmaris longus tendon, merging radially with the scaphoulnar fibres, and with the proximal, transversely running fibres of the volar carpal ligament. The volar carpal f i b r e s
The deeper longitudinal fibres of the volar carpal ligament weave among the bundles of the pisothenar ray. d
The superficial h a m u l o t h e n a r f i b r e s
From the hook o f the hamate a mass of fibres passes transversely to the radial side. The superficial o f these fibres pass deep to the piso-aponeurotic ray, but weave between the fibres of the pisothenar ray (Fig. 10). They reach to the radial side of the retinaculum, where they seem to give rise predominantly to fibres of the opponens pollicis. These fibres also receive fibres derived from the palmaris brevis, which have passed through the carina. Lamina 2
The fibre patterns of Laminae 2 and 3 were more difficult to make out, but the following plan seemed to emerge. Lamina 2 is made up of fibreS~which pass slightly obliquely downwards and to the radial side from the pisiform bone, deep to those pisoradial fibres already described and seen from the volar surface, to intermingle with a deep mass of fibres which pass transversely to the radial side from the hamate. This weaving pattern extended deeply, through the thickness of Lamina 2, and the deeper the pattern was followed the more tightly fitting and completely transverse did the fibres seem to become. They appear to give rise to muscle fasciculi o f the opponens pol~icis and to some of the superficial head o f the flexor pollicis brevis. Lamina 3
From fibres of this layer arise some o f the muscular fasciculi of the superficial head o f the flexor pollicis brevis and the opponens digiti minimi. The fibres from which the superficial head o f the flexor pollicis brevis seems to originate come from the region o f the hook o f the hamate, deep to those o f Lamina 2. They proceed radially and a little distally, lying for the most part superficially to, but showing some obvious interweaving with, the deeper fibres, which in turn pass in the opposite direction distally from the region of the ridge of the trapezium to the ulnar side, giving rise to some muscle fibres of the opponens digiti minimi. Deeply and distally the interweaving bands are quite coarse. The Hand-- Volume 13
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Fig. 11. A photograph of a X 6 dissection of the same hand, to show the dorsal aspect of the flexor retinaculum, Lamina 4 as described in the text. The longitudinal fibres described are shown. Fig. 12. Another, similar view of the dorsum o f a flexor retinaculum. The longitudinal fibres appear much more prominently than usual, passing distally from the superior crus o f the hiatus o f the pisoretinaeular space.
Lamina 4
This aspect of the retinaculum is smooth and shiny, and in direct contact with the median nerve. Most of the fibres are transversely running, or slightly oblique, but a few thin strands of longitudinally running fibres, more or less centrally placed, were observed (Figs. 11 and 12). Their course was difficult to follow. Some appeared to arise proximally f r o m towards the radial side, but some seemed to come from deep fibres of the volar carpal ligament. Some, distally, could be traced as a small contribution to the deep aspect of the palmar aponeurosis. At the ulnar and radial margins the deep transversely running fibres seemed to pass smoothly into the covering of the side walls and dorsal aspect of the carpal tunnel. In dissecting the distal course of the tendon of the flexor carpi radialis, on the radial side of the carpal tunnel, the impression was gained that the fibres that could be regarded as constituting Lamina 4 are those that sweep round deep to the tendon, helping to form the medial wall of the sheath within which it runs. The fibres of Laminae 1, 2 and 3 appear to be anterior, or superficial to this sheath, which itself lies posterior to the slightly overhanging tubercle of the scaphoid and ridge of the trapezium. The canal containing the tendon of flexor carpi radialis moves posteriorly as it passes distally sandwiched between the fibrous radial wall of the carpal tunnel, and the scaphoid above and the groove between the trapezium and trapezoid below. 26
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SURGICAL INCISION It is well recognised that the flexor retinaculum should be divided more to the ulnar side than to the radial, because of the danger of section of the palmar cutaneous branch of the median nerve, and of the occasional origin of the motor thenar branch from the ulnar side of the median nerve. It would also seem sensible to place the incision towards the ulnar side of the retinaculum to avoid the interlacement of the roots of the palmar aponeurosis, where the retinaculum is at its thickest. Obviously, however, if the incision is placed too far to the ulnar side, branches of the patmar branch o f the ulnar nerve may be damaged. A useful marker for the upper limit of the incision has been found to be a point at the junction of the radial third with the ulnar two-thirds of a line joining the tubercle of the scaphoid to the pisiform, just distal to the distal wrist crease and to the ulnar side of the palmaris root of the palmar aponeurosis. It usually lies just proximal to the proximal end of the mid-palmar vertical crease when this is present. The incision is then directed distally for 3 cms in a slightly curved direction, convex to the ulnar side, between the mid-palmar and thenar creases, or to the ulnar side of the latter when the mid-palmar crease is absent. The incision passes to the ulnar side of the palmaris root, and the carina of the retinaculum. It cuts the proximal ends of some of the fibres of the aponeurosis which go to form the pretendinous band to the little finger. It passes through the fibres forming the ulnar roots of the palmar aponeurosis which comprise, superficially, aponeurotic bands of the palmaris brevis, and, more deeply, fibres from the volar carpal ligament, from the pisiform, f r o m the-hook of the hamate, and from the fascia of the opponens digiti minimi. Deep to all these fibres, in the first, most superficial lamina of the flexor retinaculum the incision passes through the pisocrural and pisothenar rays of the pisoradial group of fibres and sometimes the proximal fibres of the abductor pollicis brevis, and through the scaphoulnar and hamulothenar fibres. As the incision passes through the second lamina the main thickness of the retinaculum is encountered. Passing through the third lamina the incision is likely to pass through fibres of origin of the opponens digiti minimi. The fibres of the thin lamina four are the deepest to be divided, when the incised edges of the retinaculum spring apart. ACKNOWLEDGEMENTS I wish to record my thanks to Professor C. G. Phillips of the Department of H u m a n Anatomy, University of Oxford, for his courtesy in allowing the dissection of the material in his department. I would also like to thank Mr. B. Archer and Mr. R. F. Gerrish, Heads of their respective Photography Departments, at the A n a t o m y School, Oxford, and Princess Margaret Hospital, Swindon, for their valuable assistance.
REFERENCES
DENMAN, E. E. (1979) The Volar Carpal Ligament. The Hand, 11: 22-27. ENGBER, W. D. and GMEINER, J. G. (1980) Palmar cutaneous branch of the ulnar nerve. The Journal of Hand Surgery, 5: 26-29. FAHRER, M. (1980) The Prgximal End of the Palmar Aponeurosis. The Hand, 12: 33-38. The Hand--Volume l3
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LANDSMEER, J. M. F. Atlas of Anatomy of the Hand. Edinburgh and London, and New York. Churchill Livingstone. (1976). LASSA, R. and SHREWSBURY, M. M. (1975) A Variation in the Path of the Deep Motor Branch of the Ulnar Nerve at the Wrist. The Journal of Bone and Joint Surgery, 57A: 990-991. PAPATHANASSIOU, B. T. (1968) A Variant of the Motor Branch of the Median Nerve in the Hand. The Journal of Bone and Joint Surgery, 50B: 156-157. TALEISNIK, J. (1973) The Palmar Cutaneous Branch of the Median Nerve and the Approach to the Carpal Tunnel. An Anatomical Study. The Journal of Bone and Joint Surgery, 55A: 1212-1217. YOUNG, A. and HARRISON, R. J. (1947) The anatomy of the retinacula of the wrist joint. The Journal of Anatomy, 81: 397.
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SUMMARY The coarse fibrous pattern o f the roots o f the palmar aponeurosis and o f the flexor retinaculum, comprising the r o o f o f the carpal tunnel, is described, to define the structures incised in the operation to relieve carpal tunnel compression syndrome.
INTRODUCTION Division of the flexor retinaculum for the relief of carpal tunnel syndrome is one of the most c o m m o n and rewarding minor procedures in orthopaedic practice. The skin incision usually advocated is a longitudinal one. Engber and Gmeiner (1980) emphasize the need for the incision to be placed between the palmar cutaneous branches of the median and ulnar nerves. As the skin incision is deepened fibres of the proximal part of the palmar aponeurosis are encountered first, and deep to these the flexor retinaculum presents as a thick band. Muscle fibres are often seen in or to the radial side o f the proximal part of the wound and in or to the ulnar side of the distal part of the wound. The detailed a n a t o m y of the fibrous structures through which this incision passes has received scant attention. Description o f the palmar aponeurosis in anatomical and surgical literature has largely been confined to its metacarpal, rather than its carpal part. In the past surgical interest in the anatomy of the flexor retinaculum has concentrated on its related deep structures, a n d its penetration by nerve branches, namely the thenar m o t o r branch o f the median nerve (Papathanassiou, 1968), the the palmar branch of the median nerve (Taleisnik, 1973), and a variant m o t o r branch of the ulnar nerve (Lassa, 1975). The flexor retinaculum is dismissed in most standard works as a strong fibrous sheet between its well known bony attachments completing the carpal tunnel. In order to better appreciate the fibrous structures through which the standard incision for the relief of carpal tunnel syndrome passes, dissections of this region in cadaveric hands were carried out under magnification. This paper describes the findings of this study.
ANATOMICAL STUDY Twelve formalin-preserved cadaveric hands were dissected under magnification and photographs taken to illustrate various points. A single deep frozen cadaveric specimen was sectioned transversely at half-centimetre intervals and examined under E. E. Denman, F.R.C.S., Princess Margaret Hospital, Swindon, Wiltshire. 9 1981 British Society for Surgery of the Hand 0072-968X-81-00030017 $02.00 The Hand--Folume 13
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m a g n i f i c a t i o n . I n a n o t h e r specimen an incision was m a d e to decompress the carpal t u n n e l , a n d the course o f the incision was related to the fibrous structures described.
THE PROXIMAL ROOTS OF THE PALMAR APONEUROSIS The apex o f the p a l m a r a p o n e u r o s i s , lying a n t e r i o r to the flexor r e t i n a c u l u m , gives rise distally to the l o n g i t u d i n a l system o f fibres o f the a p o n e u r o s i s . It can be regarded as being f o r m e d by a n u m b e r o f roots, The palmaris root. T h e m a i n c o n t r i b u t i o n to the p a l m a r a p o n e u r o s i s , f r o m the t e n d o n o f the p a l m a r i s longus, can be called the p a l m a r i s r o o t . As this t e n d o n a p p r o a c h e s the flexor r e t i n a c u l u m it is superficial to the deep fascia o f the Iower forearm, s u r r o u n d e d b y f i b r o - f a t t y connective tissue. Dissection o f this tissue d e m o n s t r a t e s f i b r o u s b a n d s which, in relation t o the t e n d o n , take either a centrifugal or a centripetal course. C e n t r i f u g a l fibres pass distally f r o m the t e n d o n in all directions, a n d especially radially into the f i b r o - f a t t y s u b c u t a n e o u s tissue at
Fig. 1. A photograph of a X10 magnification dissection of a right hand in the anatomical position to show the transition zone between the palmaris longus tendon and the apex of the palmar aponeurosis - - the palmaris root of the aponeurosis. A needle is raising a fibrous band which is passing from the subcutaneous tissue of about the region of the distal skin crease of the wrist to the apponenrosis. Fig. 2. A photograph of a X3 magnification of a transverse section of a hand, at the level of the distal part of the flexor retinaculum, to show the area of interlacement of fibres at the site of attachment of the apex of the palmar aponeurosis to the retinaculum. This area is called the carina in the text, and is labelled C in the diagram. F, flexor retinaculum. A, palmar aponeurosis. 18
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the base o f the t h e n a r e m i n e n c e a n d the p r o x i m a l fascia o f the a b d u c t o r pollicis brevis. C e n t r i p e t a l fibres arise f r o m the s u r r o u n d i n g tissue a n d pass distally, into t h e t e n d o n , c o n t r i b u t i n g to its s u b s t a n c e (Fig. 1). The p a l m a r i s longus t e n d o n is superficial to the p r o x i m a l p a r t o f t h e flexor r e t i n a c u l u m , being s e p a r a t e d f r o m it b y its s u r r o u n d i n g connective tissue. T h e t e n d o n is often quite n a r r o w at this level, a n d in passing distally e x p a n d s t r a n s v e r s e l y to f o r m the superficial p a r t o f the p r o x i m a l p a r t o f the l o n g i t u d i n a l f i b r o u s system o f the p a l m a r a p o n e u r o s i s . T h i s system o f fibres becomes a t t a c h e d to t h e distal p a r t o f the anterior surface o f t h e flexor r e t i n a c u l u m , slightly to the r a d i a l side o f the midline, b y the d e e p e r o r i g i n o f t h e other r o o t s o f the a p o n e u r o s i s , n a m e l y t h e u l n a r a n d r a d i a l r o o t s . This region o f interlacement between the d i s t a l p a r t o f t h e r e t i n a c u l u m a n d the p a l m a r i s longus a n d p a l m a r a p o n e u r o s i s , when viewed in section or f r o m the p a l m a r surface is reminiscent o f the keel o f an u p t u r n e d b o a t , a n d could t h e r e f o r e p e r h a p s be usefully referred to as the carina o f t h e r e t i n a c u l u m (Fig. 2).
Fig. 3. The same hand as in Fig. 1. To the left of the figure the longitudinal bands of the palmar aponeurosis are seen. To the right, running transversely are fasciculi of the palmaris brevis, forming aponeurotic bands, which run through the carina of the retinaculum. Some aponeurotic bands pass distally contributing to the palmar aponeurosis. Between the fasciculi of the palmaris brevis can be seen some fa~ in the pisoretinacular space or space of Guyon. Fig. 4. Aphotograph of a X3 magnification dissection of a right hand in the anatomical position. VC, longitudinal fibres of the volar carpal ligament. PA, pisoaponeurotic fibres, raised by the point of the probe. The hiatus of the pisoretinacular space or space of Guyon lies at the tip of the probe, and the trigone of the retinaculum is outlined below it, between the descending groups of fibres. The Hand-- Volume 13
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The ulnar roots
Fibre bundles can be followed into the ulnar side of the apex of the palmar aponeurosis from several sources. The most prominent and superficial fibres that enter the palmar aponeurosis from the ulnar side come from aponeurotic bands of the palmaris brevis. The radial attachment o f the muscular fasciculi of the palmaris brevis consists of a trabecular arrangement o f aponeurotic bands. Proximally these bands pass into the anterior surface of the flexor retinaculum deep to the tendon of the palmaris longus. More distally they pass into the carina of the retinaculum. In the carina some fibre bands appear to pass radially through it to merge with the anterior aspect of the flexor retinaculum and the fascia over the origin of the abductor pollicis brevis. Other bands are seen to extend proximally, giving the impression that they have arisen from longitudinal bundles of the palmar aponeurosis. Yet others pass distally contributing bands to the palmar aponeurosis (Fig. 3). Some fibres that enter the aponeurosis deeply, from the ulnar side, most proximally, may come from the volar carpal ligament (Denman, 1979). This ligament may form a prominent longitudinally running band on the anterior surface of the retinaculum, and some fibres of his band can sometimes be traced into the palmar aponeurosis. In Fig. 4 the longitudinal band of fibres of the volar carpal ligament has been sectioned to show its independence from the deeper fibres and is labelled VC. In this specimen it was the most radial fibres of the longitudinal band that could be traced into the aponeurosis. A few fibres of the volar carpal ligament may possibly pass longitudinally on the deep aspect of the retinaculum to reach the palmar aponeurosis. Those fibres that enter the palmar aponeurosis deeply, from the ulnar side, at an intermediate level, come from the pisiform bone, and are a superficial group of the strong fan o f fibres which sweeps radially and distally from this bone into the flexor retinaculum. This is the group o f fibres described by Landsmeer (1976). A contribution to the palmar aponeurosis by these fibres is shown in Fig. 4 and is labelled PA. Those fibres that enter the aponeurosis deeply, from the ulnar side at a more distal level, come from the hook of the hamate, and from the fascia over the origin of the opponens digiti minimi. They can be seen in Fig. 5, labelled HA. Fahrer (1980), noted that when the palmaris longus is congenitally absent, in five dissections, the "flexor carpi ulnaris completely takes over as the longitudinal tensor of the palmar aponeurosis", referring to fibres arising from the pisiform. No case in this present series was encountered totally without a palmaris longus, but in one a very narrow palmaris longus tendon arose from the antebrachial fascia in the distal forearm, giving but a feeble root to the aponeurosis. It would seem that without a palmaris root the ulnar roots are more important. 20
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Fig. 5. A photograph of a X6 magnification of the same hand to show the hamuloaponeurotic fibres, labelled HA. The position of the hook of the h a m a t e is labelled H. The fasciculi of the opponens digiti minimi are passing downwards and to the right. The proximal hiatus of the pisohamate canal, leading from the pisoretinacular space to the deep palmar space is seen in the top right corner of the figure. Fig. 6. A similar view of the same hand, this time towards the thenar eminence; The longitudinal fibres of the palmar aponeurosis are seen to the right of the figure. The subcutaneous aponeurotic bands which have been described in the text as the proximal radial root of the palmar aponeurosis have been divided and pressed to the right of the figure. This reveals the course of the palmar branch of the median nerve.
The radial roots
The subcutaneous tissue at the base of the thenar eminence, to the ulnar and distal side o f the tubercle o f the scaphoid, and towards the proximal end of the thenar crease, contains fibrous trabeculae, similar to those of the subcorial fibrous tissue layer of the hypothenar region. These trabeculae of fibrous tissue are continuous deeply with the deep fascia which covers the origin of the proximal part of the abductor pollicis brevis, and which is quite thick. Centrifugal fibres of the palmaris longus tendon merge with this subcutaneous fibrous system, and the abductor fascia. This can be confirmed clinically on contraction o f the palmaris longus. Through this area passes the palmar cutaneous branch or branches of the median nerve. Two more or less distinct groups of fibres pass to the palmar aponeurosis from the radial side. There is a superficial proximal contribution from the abductor fascia and subcutaneous fibrous system just described, and is illustrated in Fig. 6. There is The Hand-- Volume 13
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Fig. 7. A photograph of a X3 dissection of a right hand in the anatomical position. The tendon of the palmaris !ongus has been lifted to the ulnar side to show what has been described in the text as the distal radial root of the palmar aponeurosis, and marked R. Some thenar muscle fibres are seen through a window of fascia. Fig. 8 A photograph of a X3 dissection of a right hand. The flexor retinaculum has been sectioned longitudinally, as it might be in a carpal tunnel decompression operation. The sagittal face of the ulnar half of the retinaculum occupies the centre of the figure, the distal edge to the fight, and the proximal to the left. The origin of hypothenar musculature can be seen passing upwards and to the right of the figure. The median nerve lies in the lower part of the figure, overlying flexor tendons. 1, 2, and 3, refer to the laminae described in the text. Lamina 1 is thickened distally by the carina. also a m u c h stronger c o n t r i b u t i o n to the deep aspect o f the p a l m a r a p o n e u r o s i s , m o r e distally, f r o m the thick fascia which overlies the p r o x i m a l part o f the a b d u c t o r pollicis brevis n e a r a n d o n the ridge o f the t r a p e z i u m . These fibres are s h o w n in Fig. 7. The volar roots Just as b o t h centrifugal a n d centripetal fibres c a n be described in relation to the t e n d o n o f the p a l m a r i s l o n g u s , it is possible to discern similarly a r r a n g e d , b u t finer, fibres in r e l a t i o n to the diverging l o n g i t u d i n a l b u n d l e s o f the p r o x i m a l p a r t or apex o f the p a l m a r a p o n e u r o s i s . T h e y seem to arise in rather ill defined sagittal septae which pass f r o m between the p r o m i n e n t l o n g i t u d i n a l b u n d l e s o f the p a l m a r a p o n e u r o s i s to the dermis, e n c l o s i n g l o b u l a e o f relatively soft fat. T h e centripetal fibres can be regarded as a small volar root c o n t r i b u t i o n to the p a l m a r a p 6 n e u r o s i s . THE FLEXOR RETINACULUM T h e m a i n part o f the flexor r e t i n a c u l u m consists o f a mass o f fibrous b a n d s r u n n i n g in d i f f e r e n t directions, at first difficult to disentangle into a c o m p r e h e n s i b l e p a t t e r n . A characteristic feature is the weaving o f b a n d s across each other, b u n d l e s 22
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o f fibres passing in one direction breaking up to pass both superficially and deeply to fibres passing in another. For descriptive purposes, four inseparable layers can be distinguished. The superficial layer, or Lamina 1, could be thought of as that seen from the palmar surface. It has several characteristic features, but predominantly its fibres run obliquely downwards. It extends from the proximal to the distal limits of the retinaculum. Lamina 4, can be described as that seen from the dorsal or deep surface. Its fibres are predominantly transverse. It forms the smooth and glistening anterior wall o f the carpal tunnel, extending from the proximal to the distal limits of the retinaculum. The intermediate substance o f the retinaculum between the volar and dorsal aspects can tentatively be divided into a superficial Lamina 2, deep tO Lamina 1, and a deep Lamina 3. Lamina 2 is confined to about the distal two thirds of the retinaculum and its fibres are predominantly transverse. Lamina 3 is confined to about the distal third o f the retinaculum, and its fibres are more oblique. The retinaculum thus increases in thickness proximodistally, (Fig. 8), the thickness of the distal part being exaggerated, slightly to the radial side o f the midline, by the interlacement of the roots o f the palmar aponeurosis, here called the carina o f the retinaculum.
Lamina 1
When the superficial tissues are carefully dissected off the retinaculum the fibre systems displayed can be described under several headings (Fig. 9).
The pisoradial fibres Proximally the fibres which form the greater part of the superficial aspect of the retinaculum arise from the pisiform, and for the purposes of description can be divided into four diverging rays. The most proximal ray of fibres runs transversely to the radial side in the proximal border of the retinaculum. These fibres form the deep crus of the hiatus of the pisoretinacular space (or space of Guyon), and the proximal border of what may be described as the ulnar trigone of the retinaculum (Denman, 1979). This ray of fibres could also be described as thepisocrural ray. They mingle with fibres from the volar carpal ligament which have formed the superficial crus of the hiatus, and with fibres which pass ulnarwards and distally from the scaphoid. They are continuous proximally with the deep fascia o f the forearm. Fibres from the pisiform which run distally to the pisocrural fibres pass obliquely distally and to the radial side. They give rise to fasciculi o f the abductor pollicis brevis, and more deeply to the opponens pollicis, intermingling with the superficial transversely running fibres to the Same muscles, which have arisen from the region of the hook of the hamate. This ray of fibres which passes from the pisiform and gives rise to the thenar muscles could be called the p&othenar ray. The fibres to the thenar muscles from the hamate are to be described as the hamulothenar fibres. The fibres of the pisothenar ray pass deep to the carina of the retinaculum, interlacing with the deep radial root of the palmar aponeurosis, and the transversely running fibres of insertion of palmaris brevis. The Hand-- Volume 13
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Fig. 9. A photograph of a X3 dissection of the right hand in the anatomical position. The soft tissues, and palmafis longus and the apex of the palmar aponeurosis have been removed. P, site of the pisiform. H, site of the tip of the hook of the hamate. T, site of the ridge of the trapezium. S, site of the tubercle of the scaphoid. PC, pisocrural fibres. PT, pisothenar fibres. PA, pisoaponeurotic fibres. PH, pisohamate fibres. SU, scaphoulnar fibres. VC, volar carpal fibres. SHT, superficial hamulothenar fibres. Fig. 10. A photograph of a X9 dissection of a fight hand in the anatomical position, to show the weave between the pisoradial fibres (PR) and the hamulothenar fibres (HT), towards the ulnar and distal quadrant of the flexor retinaculum.
The third ray, distal to the pisothenar fibres, passes distally to the ulnar side of the palmaris longus tendon, before merging into the carina of the retinaculum, and passing into the palmar aponeurosis. This band of fibres has been encountered as an ulnar root of the aponeurosis. It could be referred to as the
pisoaponeurotic ray. Finally, fibres from the pisiform pass directly to the hook of the hamate, and are pai-t of the pisohamate ligament. Some of these fibres extend into the deep fascia of the abductor digiti minimi. They form the deep part of the proximal hiatus of the pisohamate tunnel, the deep ulnar nerve and vessels running over it.
The scaphoulnar fibres Fibres from the tubercle of the scaphoid, in the same plane above with the transversely running fibres of the deep fascia, and below with the pisothenar fibres, pass distally and to the ulnar side. They pass deep to the vertically running volar carpal fibres, into the ulnar trigone, and then on, deep to the pisohamate ligament, some of the fibres appearing to merge with the pisometacarpal ligament, and others with the hook of the hamate. These fibres may explain the observations of Young and Harrison (1947) that the 24
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pisotriquetral attachment of the retinaculum can be completely severed without opening the carpal tunnel. The palmar branch of the median nerve passes through a small hiatus between these fibres near their origin, to the ulnar side of the flexor carpi radialis, and near where the deep fascia becomes continuous with the retinaculum. The nerve often divides into its two main terminal branches before piercing the retinaculum. Some of the proximal fibres form a thin roof, which distally becomes much thicker, of the entrance to the sheath for the tendon of the flexor carpi radialis. The proximal fibres of insertion o f palmaris brevis pass behind the palmaris longus tendon, merging radially with the scaphoulnar fibres, and with the proximal, transversely running fibres of the volar carpal ligament. The volar carpal f i b r e s
The deeper longitudinal fibres of the volar carpal ligament weave among the bundles of the pisothenar ray. d
The superficial h a m u l o t h e n a r f i b r e s
From the hook o f the hamate a mass of fibres passes transversely to the radial side. The superficial o f these fibres pass deep to the piso-aponeurotic ray, but weave between the fibres of the pisothenar ray (Fig. 10). They reach to the radial side of the retinaculum, where they seem to give rise predominantly to fibres of the opponens pollicis. These fibres also receive fibres derived from the palmaris brevis, which have passed through the carina. Lamina 2
The fibre patterns of Laminae 2 and 3 were more difficult to make out, but the following plan seemed to emerge. Lamina 2 is made up of fibreS~which pass slightly obliquely downwards and to the radial side from the pisiform bone, deep to those pisoradial fibres already described and seen from the volar surface, to intermingle with a deep mass of fibres which pass transversely to the radial side from the hamate. This weaving pattern extended deeply, through the thickness of Lamina 2, and the deeper the pattern was followed the more tightly fitting and completely transverse did the fibres seem to become. They appear to give rise to muscle fasciculi o f the opponens pol~icis and to some of the superficial head o f the flexor pollicis brevis. Lamina 3
From fibres of this layer arise some o f the muscular fasciculi of the superficial head o f the flexor pollicis brevis and the opponens digiti minimi. The fibres from which the superficial head o f the flexor pollicis brevis seems to originate come from the region o f the hook o f the hamate, deep to those o f Lamina 2. They proceed radially and a little distally, lying for the most part superficially to, but showing some obvious interweaving with, the deeper fibres, which in turn pass in the opposite direction distally from the region of the ridge of the trapezium to the ulnar side, giving rise to some muscle fibres of the opponens digiti minimi. Deeply and distally the interweaving bands are quite coarse. The Hand-- Volume 13
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Fig. 11. A photograph of a X 6 dissection of the same hand, to show the dorsal aspect of the flexor retinaculum, Lamina 4 as described in the text. The longitudinal fibres described are shown. Fig. 12. Another, similar view of the dorsum o f a flexor retinaculum. The longitudinal fibres appear much more prominently than usual, passing distally from the superior crus o f the hiatus o f the pisoretinaeular space.
Lamina 4
This aspect of the retinaculum is smooth and shiny, and in direct contact with the median nerve. Most of the fibres are transversely running, or slightly oblique, but a few thin strands of longitudinally running fibres, more or less centrally placed, were observed (Figs. 11 and 12). Their course was difficult to follow. Some appeared to arise proximally f r o m towards the radial side, but some seemed to come from deep fibres of the volar carpal ligament. Some, distally, could be traced as a small contribution to the deep aspect of the palmar aponeurosis. At the ulnar and radial margins the deep transversely running fibres seemed to pass smoothly into the covering of the side walls and dorsal aspect of the carpal tunnel. In dissecting the distal course of the tendon of the flexor carpi radialis, on the radial side of the carpal tunnel, the impression was gained that the fibres that could be regarded as constituting Lamina 4 are those that sweep round deep to the tendon, helping to form the medial wall of the sheath within which it runs. The fibres of Laminae 1, 2 and 3 appear to be anterior, or superficial to this sheath, which itself lies posterior to the slightly overhanging tubercle of the scaphoid and ridge of the trapezium. The canal containing the tendon of flexor carpi radialis moves posteriorly as it passes distally sandwiched between the fibrous radial wall of the carpal tunnel, and the scaphoid above and the groove between the trapezium and trapezoid below. 26
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SURGICAL INCISION It is well recognised that the flexor retinaculum should be divided more to the ulnar side than to the radial, because of the danger of section of the palmar cutaneous branch of the median nerve, and of the occasional origin of the motor thenar branch from the ulnar side of the median nerve. It would also seem sensible to place the incision towards the ulnar side of the retinaculum to avoid the interlacement of the roots of the palmar aponeurosis, where the retinaculum is at its thickest. Obviously, however, if the incision is placed too far to the ulnar side, branches of the patmar branch o f the ulnar nerve may be damaged. A useful marker for the upper limit of the incision has been found to be a point at the junction of the radial third with the ulnar two-thirds of a line joining the tubercle of the scaphoid to the pisiform, just distal to the distal wrist crease and to the ulnar side of the palmaris root of the palmar aponeurosis. It usually lies just proximal to the proximal end of the mid-palmar vertical crease when this is present. The incision is then directed distally for 3 cms in a slightly curved direction, convex to the ulnar side, between the mid-palmar and thenar creases, or to the ulnar side of the latter when the mid-palmar crease is absent. The incision passes to the ulnar side of the palmaris root, and the carina of the retinaculum. It cuts the proximal ends of some of the fibres of the aponeurosis which go to form the pretendinous band to the little finger. It passes through the fibres forming the ulnar roots of the palmar aponeurosis which comprise, superficially, aponeurotic bands of the palmaris brevis, and, more deeply, fibres from the volar carpal ligament, from the pisiform, f r o m the-hook of the hamate, and from the fascia of the opponens digiti minimi. Deep to all these fibres, in the first, most superficial lamina of the flexor retinaculum the incision passes through the pisocrural and pisothenar rays of the pisoradial group of fibres and sometimes the proximal fibres of the abductor pollicis brevis, and through the scaphoulnar and hamulothenar fibres. As the incision passes through the second lamina the main thickness of the retinaculum is encountered. Passing through the third lamina the incision is likely to pass through fibres of origin of the opponens digiti minimi. The fibres of the thin lamina four are the deepest to be divided, when the incised edges of the retinaculum spring apart. ACKNOWLEDGEMENTS I wish to record my thanks to Professor C. G. Phillips of the Department of H u m a n Anatomy, University of Oxford, for his courtesy in allowing the dissection of the material in his department. I would also like to thank Mr. B. Archer and Mr. R. F. Gerrish, Heads of their respective Photography Departments, at the A n a t o m y School, Oxford, and Princess Margaret Hospital, Swindon, for their valuable assistance.
REFERENCES
DENMAN, E. E. (1979) The Volar Carpal Ligament. The Hand, 11: 22-27. ENGBER, W. D. and GMEINER, J. G. (1980) Palmar cutaneous branch of the ulnar nerve. The Journal of Hand Surgery, 5: 26-29. FAHRER, M. (1980) The Prgximal End of the Palmar Aponeurosis. The Hand, 12: 33-38. The Hand--Volume l3
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LANDSMEER, J. M. F. Atlas of Anatomy of the Hand. Edinburgh and London, and New York. Churchill Livingstone. (1976). LASSA, R. and SHREWSBURY, M. M. (1975) A Variation in the Path of the Deep Motor Branch of the Ulnar Nerve at the Wrist. The Journal of Bone and Joint Surgery, 57A: 990-991. PAPATHANASSIOU, B. T. (1968) A Variant of the Motor Branch of the Median Nerve in the Hand. The Journal of Bone and Joint Surgery, 50B: 156-157. TALEISNIK, J. (1973) The Palmar Cutaneous Branch of the Median Nerve and the Approach to the Carpal Tunnel. An Anatomical Study. The Journal of Bone and Joint Surgery, 55A: 1212-1217. YOUNG, A. and HARRISON, R. J. (1947) The anatomy of the retinacula of the wrist joint. The Journal of Anatomy, 81: 397.
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