Dorsal Digital Expansion Of Thumb Joshi, S.S., Joshi, S.D., Aavale S.A., Kishve, P. S. and Jadhav S.D. Rural Medical College,Pravara Institute of Medical Sciences, Loni Abstract: Human hands perform e complicated functions of gripping, pinching, feeling and expressing. All ese activities depend on e coordinated actions of e umb and e fingers. The functional importance and e complexity of movements of umb are well reflected in an extensive representation of umb in e brain. The extensor apparatus of umb displays obvious structural variations in its proximo-distal expanse. There is no unanimity amongst various auors on e anatomy of dorsal digital expansion (DDE) of umb. Some (Schafer et al, 1923; Sinnatamby, 1999) are of e view at ere is no extensor expansion of e umb. Variations are described in e contributions made by various elements which go into e formation of DDE. We have undertaken a detailed study of formation and attachment of DDE of umb in 110 upper limbs (Rt- 55, Lt-55) available in e department. DDE of umb was present in all e limbs examined. It was triangular in shape. The anchoring fibers were well defined in e form of a hood over e dorsal surface of metacarpophalangeal (MP) joint. Medial margin of e expansion was well defined in all e cases; whereas, e lateral margin was variably developed. In 68% of umbs e lateral margin of DDE was contributed by abductor pollicis brevis (APB) out of ese in 60% is margin was well defined. In 98% cases e oblique head of adductor pollicis (AP) contributed fibres to medial margin of DDE. In 62.7% fibres of first palmar interosseous could also be traced to e medial margin. The mechanism of DDE permits for greater variations in extension of various joints of umb en would have been possible in its absence. Key words: Thumb, dorsal digital expansion, extensor pollicis longus, extensor pollicis brevis, adductor pollicis, abductor pollicis brevis Introduction: The dorsal apparatus of e umb is very similar to e arrangement of e fibres of dorsal digital expansion (DDE) of any oer fingers but shows obvious structural variations in its proximo-distal expanse. DDE forms a movable hood like structure over e dorsum of metacarpophalangeal (MP) joints of e fingers. The extensor hood moves distal to e MP joint during flexion and proximally when extended. This mechanism permits greater variation in extension an would be possible if a single extensor tendon was used for each joint. DDE allows for extension of e interphalangeal (IP) joints when MP joints are flexed by e flexors. Going rough e literature we find at ere is no unanimity amongst e various auors about e presence and formation of DDE of umb. Schafer et al (1923) stated at ere is no extensor expansion on e umb. Similar view was expressed by Sinnatamby (1999). The muscles of e umb can be compared to e stays attached to a mobile articulated mast. They are in a state of balance from which movements are carried out by contraction of some and relaxation of oers. This complexity of movements is well reflected in an extensive representation of umb in e brain (Lamb, Hooper and Kuczyski, 1989). The dorsal expansion occasionally adheres to e collateral ligaments and us an important anchorage unites e extensor apparatus to e immobile flexor tunnel. The construction of DDE permits independent extension of e distal phalanx Correspondence to :- Dr. Joshi S.S. Department of Anatomy, Rural Medical College, Pravara Institute of Medical Sciences, Loni 413736. Dist: Ahmednagar (Maharashtra). 135 (DP) by traction applied by e various constituents forming e expansion. Bade et al (1995) while describing e fibrous architecture of dorsal aponeurosis of umb have stated at dorsal connective tissue of umb forms different layers of collagen lamellae as a peritendinous system around e tendons of extensor pollicis longus (EPL) and extensor pollicis brevis (EPB). In eir opinion is is an expression of different topographical zones of stress along e lines of a balanced musculofibrous stabilization of e IP joint of umb. As ere is no unanimity about e presence, mode of formation and contribution of various muscle elements in e formation of DDE of umb, a detailed study was undertaken in 110 upper limbs (Right-55; Left-55) to study e formation and variations of DDE. Variations in e attachment of two long extensors of umb and e contribution made by various small muscles of umb in e formation of DDE were also studied. Material And Meods : For e present study 110 upper limbs (Rt- 55; Lt-55) were dissected over a period of 3 years. The region of dorsum of umb was dissected carefully. The tendons of EPL and EPB were exposed from e wrist up to eir insertion and variations in eir mode of insertion were noted. The dorsal digital expansion over e MP joint was exposed and its shape and anchoring fibers were noted. Medial and lateral margins of e expansion were cleaned and contributions from various short muscles of umb were carefully seen. Observations : DDE was found as a well defined entity, triangular in shape present on e dorsum of proximal phalanx of umb in all e limbs examined
Dorsal Digital Expansion Of Thumb...Joshi, S.S., Joshi, S.D., Aavale S.A., Kishve, P. S. and Jadhav S.D. (fig.1a,b). The base was directed proximally covering e dorsal aspect of MP joint as a hood. Medial margin of expansion was very prominent and well defined. Fig. 1a: Shows a well defined triangular expansion i.e. dorsal digital expansion (DDE) of umb, its base is joined by e tendons of EPB and EPL; at e angles of e base it is laterally joined by APB and medially by AP. Red arrows indicate e lateral and medial borders of DDE. The apex of DDE which is broad is getting attached to dorsal surface of terminal phalanx. Fig. 1b: Same as in 1a but here EPB tendon is very narrow. As seen in Table no. I: in 98 % cases oblique head of adductor pollicis contributed fibres to e medial margin of e expansion (fig.1a,b). Its transverse head also gave fibres to e medial margin of DDE in about 8 % specimens examined. In 62.7 % fibres of first palmar interosseous could also be traced to e medial margin of expansion (fig.2 b). Fig. 2a: The well defined triangular DDE has been pulled backwards. Passing rough e centre of it e tendon of EPL can be easily visualized. Margins of DDE are well defined. Tendon of EPB, which is placed deep to EPL and DDE, is getting inserted on e dorsum of base of PP. A superficial slip from EPB is seen joining e deep surface of DDE (red arrow). Fig. 2b: In is photograph e contribution of first palmar interosseous (FPI) to e medial margin of DDE is seen clearly. Table No. I Showing contribution from various muscles in e formation of DDE of umb (in percent): Muscle Right Left Average Abductor pollicis brevis 63.6 72.8 68.21 Adductor Oblique head pollicis Transverse head 7.2 9.0 8.1 70.9 54.5 62.7 First Palmar interosseous In about 60.8 % (Rt-58.1 %; Lt-63.6 %) e lateral margin of expansion was well defined. Even when it was not well defined, in 68.2 % cases fibres of APB could be traced to e lateral margin (fig.1a,b). In a very small percentage (3.6 %) fibres of FPB joined e lateral margin of expansion. Tendon of EPL could be traced to DP in 98.2 % umbs studied. In 1.8 % it was getting attached to bo proximal phalanx (PP) and DP. In e present series EPB was present in all e hands and in approximately 58 % it was getting attached to PP, whereas in 27.25 % it extended upto DP. In 14.6 % e tendon of EPB was getting attached to bo PP and DP (fig.3) (Table no. II). Fig. 3: The components of DDE viewed from lateral aspect. EPB is seen joining bo e deep surface of DDE and inserting on dorsal surface of base of PP. Contribution from APB to e DDE and e formation of lateral margin is distinctly seen. The insertion of DDE to e terminal phalanx is very broad (white arrow). 136
Dorsal Digital Expansion Of Thumb...Joshi, S.S., Joshi, S.D., Aavale S.A., Kishve, P. S. and Jadhav S.D. Table No. II Showing insertions of extensor tendons of umb (in percent): EPL EPB Right Left Average DP 96.4 100 98.2 PP 3.6 - - DP + PP - 1.8 - DP 30.9 23.6 27.25 PP 54.5 61.8 58.15 DP + PP 14.6 14.6 14.6 Discussion : Human umb plays a crucial role in e functioning of e hand, and us it has a proportionately larger representation in e brain compared to oer fingers. Group of intrinsic and extrinsic muscles bring about e various movements of umb. Due to e presence of a dorsal digital expansion it enjoys greater variation in extension an would have been possible if a single extensor tendon was used. There is no unanimity amongst various workers about e presence of dorsal digital expansion of umb. Some (Schafer et al, 1923; Sinnatamby, 1999) believe at ere is no such entity; whereas, e vast majority have described a dorsal expansion of umb; alough e mode of formation and e contributions made by various muscles varies. The dorsal digital expansion of umb is mainly formed by tendons of EPL and EPB receiving an extension from adductor pollicis on e ulnar side and APB on e radial side. In approximately 98% e tendon of EPL could be traced upto e DP where its attachment was broad. On e left it gave an additional slip to e PP in 1.8% cases, whereas in 3.6% on e right it terminated on e PP. In such cases it was e EPB at reached e DP. Spinner (1984) has described at e tendon of EPL widens over e PP and is inserted over e dorsum of base of DP. Lamb et al (1989) have stated at e EPL extends all e joints of umb and rotates e first metacarpal laterally at e same time. Owing to its oblique course and side to side displacement of about 10mm it can also adduct e umb in e late stages of its action. EPL also assists in extension and abduction of e wrist and in supination. Sometimes e tendon of EPL may be double, and e division may progress proximally. Spinner (1984) while describing e variations of EPL has shown e presence of additional extensor (extensor accessorius); at supernumery extensor from extensor digitorum may reinforce EPL. In some cases a supernumery muscle may divide to join EPL and extensor indices. He furer states at EPL is e most mobile of e digital extensors. It has 50 mm longitudinal excursion and 13 mm mediolateral translation. EPL is usually wider an EPB; however, occasionally ey may be equal in wid or rarely EPB may be slightly wider. Romanes (1978) and Spinner (1984) have described at EPL tendon replaces e dorsal part of capsule of MP joint and forms a triangular expansion by being joined by APB on e lateral side and adductor pollicis on e medial side. The expansion may be joined by tendon of EPB. Schafer et al (1923) while describing e two extensors of umb have stated at e two tendons lie side by side and do not insert into e expansion and at on e sides ey are joined by in membranes connected wi slips from APB, first palmar interosseous and oblique head of adductor pollicis. In e present series in 6 cases (5.4%) e tendon of EPL splitted into ree and in 27 cases (24.5%) it divided into two tendons before inserting into DP. Lamb et al (1989) while discussing EPB have stated at as is tendon approaches e first metacarpal from e radial side, it can bring about abduction at CM joint of umb. It is inserted on e dorsal aspect of base of proximal phalanx and helps to replace e dorsal capsule of MP joint. Its superficial fibres continue distally along e lateral margin of EPL to reach e base of DP. It may be absent in 5% people or may have multiple tendons and at times it may be fused wi abductor pollicis longus (APL). According to Spinner (1984) EPB may not extend beyond e middle of metacarpal as is found in anropoid ape. It sends an expansion to e dorsal apparatus of umb. Hollinshead (1984) quoting Parson and Robinson (1982) states at EPB often shows doubling, eier at e wrist or on e dorsum of umb and in 72% EPB is inserted into PP, in 6.8% entirely on DP and in 21.2% it is inserted on bo e phalanges. In e present series EPB was present in all e cases studied and doubling was found in 17 cases (15.4%). It was found to be attached to e PP in 58.15%, to e DP in 27.5% and to e bo phalanges in 14.6%. Thus, ese findings are at variance from ose reported by above auor. In ose cases where EPB extends upto e DP it may act as extensor of DP when EPL is divided completely. Spinner (1984) has stated at over e dorsum of MP joint e two extensor tendons received e fibres of expansion of abductor and occasionally flexor pollicis brevis (FPB) on e radial side and adductor pollicis (AP) on e ulnar side. These fibres of expansion run directly across e extensors in e proximal part of dorsal apparatus and in a more oblique course towards distal part of umb. He states at some observers find no extension of abductor brevis into e DDE but in his own investigations he has constantly found is extension, and stimulation of 137
Dorsal Digital Expansion Of Thumb...Joshi, S.S., Joshi, S.D., Aavale S.A., Kishve, P. S. and Jadhav S.D. EPB produced abduction of umb combined wi extension of DP and a moderate flexion at MP joint. APB may be likened to e lumbrical muscle in oer digits. In e present series e contribution APB to DDE was seen in 68.21% umbs examined. Lamb et al (1989) have shown e extension of e first palmar interosseous muscle to e DDE of umb. Similarly Schafer et al (1923) had also described at e first palmar interosseous, as a in slip joins e extensor tendons of umb. In e present series in 62.7% cases we could observe a contribution from first palmar interosseous muscle to DDE of umb. Spinner (1987) and Lamb et al (1989) have described at e FPB like APB also joins extensor expansion of umb. In e present series we could observe contribution from FPB to e DDE of umb in 3.6% cases only. It is well documented at Adductor pollicis (AP) is inserted into e tubercle on ulnar side of base of PP, ulnar sesamoid of MP joint and into extensor expansion of umb. Schafer et al (1923) mention at e oblique part of is muscle is connected by membranous slips to extensors of umb. During evolution, e non opposable umb was converted into an opposable umb which was so very essential for power, prehensile and precision work. Alough it has been widely separated from medial four digits it can still be adducted primarily because of AP. It seems at e prominent medial margin of DDE of umb (in e DDE of oer digits e two margins are equal in size), where e fibres are derived from AP, is an expression of a dominant role of is muscle to keep e umb closer to oer digits during various movements of umb including extension. In contrast to e lateral margin e medial margin of DDE was prominent and well defined in all e cases examined and was mainly contributed by oblique head of adductor pollicis. Hunter et al (2002) have stated at e contribution of AP to DDE stabilizes e extensor tendons and transfers extensor forces to e IP joint. Spinner (1984) has shown at faradic stimulation of is muscle produces adduction wi simultaneous extension of e DP. We could not find any mention of separate contributions of e two heads of AP to e DDE as has been studied in present series (Table I). Unlike e division of DDE in oer digits, in e umb it does not divide into ree slips an intermediate and two collateral slips. Hollinshead (1982) has described at e EPL and EPB are more likely to be involved in tendovaginitis. The EPL is more commonly ruptured as a result of colles's fracture and in such cases e extensor indicis tendon can be used to replace is. Fasciotomy distal to e extensor retinaculum during surgery for dequervain's disease may alter e balance of forces of e umb. Rupture of EPB and dorsal fibres of extensor apparatus produce loss of MP joint extension and displacement of EPL may accentuate flexion of MP joint and contributes to hyperextension of e interphalangeal (IP) joint. 138 Rupture of EPL at e level of Lister's tubercle leads to loss of MP joint extension which is e most significant functional loss. Closed rupture of e EPL mimics e mallet tendon injury of e finger. Extension at e IP joint is by intrinsic muscles rough eir contribution to dorsal apparatus of umb. Thus, e construction of dorsal apparatus of umb permits extension of DP by traction applied separately by ree structures: e tendon of EPL; e tendon of EPB, when its insertion reaches e DP; and e enar muscles of umb - APB and AP, on e radial and ulnar side respectively. Conclusion : It's a well known fact e human umb plays an important role in prehension, opposition and in performance of intricate skilled and precision movements of hand. The functional importance and e complexity of movements of umb are well reflected in an extensive representation of umb in e brain (Lamb et al, 1989). Like in oer digits we have found a well defined dorsal digital expansion of umb in all e hands studied. It is triangular in outline wi base directed proximally. The medial margin, which is very well defined, receives e contribution mainly from e oblique head of adductor pollicis (%); alough in approximately 8% e transverse head of is muscle contributes fibres to is. Surprisingly in 62.7% hands ere is a contribution from e first palmar interosseous muscle also a fact not very well recognized by majority of e workers. APB in about 68% contributes fibres to e lateral margin of expansion (which is not as prominent as e medial). In 98% umbs EPL is inserted on e DP, in e remaining it was attached to bo e phalanges. In approximately 27% EPB reached e DP and in 14.6% it was attached to bo e phalanges. Thus, is complexity of muscular arrangements and e formation of DDE of umb can explain e varying ranges of movements at e various joints of umb and in contributing its major share in performance of composite movements of e hand. References : 1. Bade H, Krolak C, Koebke J; Fibrous architecture of dorsal aponeurosis of e umb. Anatomical Record 1995; 243 (4) 524-530. 2. Fahrer M. On e form and function of e abductor pollicis muscle. Aust N Z J surg. 1977 Apr, 47(2) 242-247. rd 3. Hollinshead WH; Anatomy for Surgeons.3 Edn; Vol III. Harper and Row Publishers. Philadelphia, 1982, pp 423-426. 4. Lamb DW,Hooper G and Kuczynski K, The practice of hand surgery In restoration of n d umb. 2 Edn. Blackwell scientific publications, 1989, pp 376-379. 5. Mackin EJ, Callahan AD, Skirven TM, Osterman AL in Hunter, Mackin, Callahan; Rehabilitation of e Hand and Upper Extremity. 5 Edn. Vol I. Mosby, St. Louis, London, Philadelphia 2002, pp 527-533.
Dorsal Digital Expansion Of Thumb...Joshi, S.S., Joshi, S.D., Aavale S.A., Kishve, P. S. and Jadhav S.D. 6. Romanes G J; Cunningham's Textbook of anatomy. 11 Edn. Oxford University Press, Oxford, New York, Tokyo, 1978, pp 325. 7. Schafer E S, Syrrington J, Bryce T H; Quain's Elements of Anatomy in Myology. 11 Edn; Longman's and Green and co. New York, Toronto, 1923, pp 142. 8. Spinner M. Kaplan's functional and surgical rd anatomy of hand in umb. 3 Edn. J.B. Lippincott Company, 1984, pp 124-141. 9. Synnatamby CS; In Last's Anatomy: Regional and Applied. 10 Edn. Churchill Livingstone,Edinburg, London, New York, 1999,pp 74. 139