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Flexor digitorum superficialis tendon in the fingers of the human hand
Flexor Digitorum Super[ieialis Tendon in the Fingers oi the Human Hand--K. Kuczynski
FLEXOR DIGITORUM SUPERFICIALIS TENDON IN THE FINGERS OF THE HUMAN HAND
MARVIN M. SHREWSBURY, San Jose, California and K. KUCZYNSKI, Edinburgh With slight variation, the arrangement of the fibre bundles of the flexor digitorum superficialis tendon in the fingers is described in the same way in early anatomical works (Weitbrecht, 1742; Camper, 1760; Albinus, 1774; Knox, 1831, 1853; Henle, 1871) and more recently (MacKenzie, 1918; Jones, 1942; Martin, 1958; Arnold, 1968; Gardner, 1969; Lampe, 1969; Grant, 1971; Cunningham, 1972). Particular attention has been focussed upon two features, spiralling and decussation of the fibres. The pattern is given in the standard texts much as it was observed by Weitbrecht (1742) and later, more precisely described, by Camper (1760) whose name the decussation bears. In his drawing Leonardo da Vinci showed the superficialis tendon embracing the deep tendon and he was greatly interested in the penetration of one tendon by the other because of the mechanical principles involved. The early views of the arrangement of fibres in the superficialis tendon was that it was the same in all fingers of the human hand (Albinus, 1774). Current publications also indicate no variations in the arrangement of these fibres from finger to finger or from hand to hand. A similar fibre design in this tendon is reported in the fingers of other primates (Raven, 1950; Kaplan, 1965) and in its homologue, the flexor digitorum brevis in the human foot (Jones, 1944; Grant, 1971). Most sources indicate that the arrangement of the bundles in this tendon is in general understood, but not its functional significance. Two functional aspects are advanced which are in keeping with the structural characteristics of the tendon. Some authors claim that the spiralling of the superficialis tendon makes a tunnel for the deep tendon so that it is not gripped when the superficial muscle contracts, ensuring a freedom from interference with the movement of the deep tendon (Hollinshead, 1958; Grant, 1971). The action of a sling, a retention band, an efficient pulley for the deep tendon is also attributed to the superficialis tendon arrangement (Weitbrecht, 1742). The functional significance given to the chiasma tendinum is less obvious. One suggestion is that the thin, plate-like chiasma posterior to the deep tendon in the region of the proximal interphalangeal joint, allows the deep tendon to cross the joint at about the same distance from the axis of flexion as the superficial tendon. This feature accounts partly for the fact that the total excursion produced by each of the tendons is almost equal in spite of the disparity in the number of joints they cross (Stack, 1963). Our present study is an attempt to investigate in more detail the pattern of fibres in the flexor digitorum superficialis tendons and its functional significance, particularly variations from finger to finger and from hand to hand, and comparison of detailed measurements. MATERIAL AND METHODS Twenty-three hands from fifteen male cadavers were dissected. The first three hands were used for preliminary studies in order to establish the procedure and scope of the observations to be recorded. The index, middle, ring and little fingers of all the remaining hands were separately examined and measurements taken and recorded for the flexor digitorum superfieialis tendon. The Hand--Vol. 6
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Flexor Digitorum Superficialis Tendon in the Fingers of the Human Hand--K. Kuczynski TABLE 1 MEASUREMENTS FOR THE FLEXOR DIGITORUM SUPERFICIALIS TENDON IN T H E F I N G E R S OF T H E H U M A N H A N D Description of Measurement
Finger Index mm
Middle mm
A. At 0 ° (neutral) extension of PIP joint with all finger joints extended: A1. Finger length . . . . . . . . . 97 (85-105)* A2. FDST'~ width at proximal edge of PFSA (+):~ 5 (4-7) A3. F D P T width at proximal edge of P F S A ( q - ) 5 (3.5-7) A4. FDSB width just proximal to its splitting (q-) 8.5 (7-10) A5. RSB width ............ (-b-) 4 (3-5) A6. USB width ... (-[-) 4 (3.5-5) 17. a. Distance separaiing 1~S]3 an~t'[SSB at distal edge of PFSA . . . . . . (q-) 3 (2-4) b. Distance separating RSB anci'iJSB at distal edge of PFSA . . . . . . . . . (--) 2 (1.5-3.5) A8. Distance from distal edge of PFSA to: a. proximal edge o f DFSA ...... (-t-) 23 (19-28) b. middle of PIP joint . . . . . . . . . (nt-) 15 (11.5-20) c. palmar separation of RSB and USB ( - - ) 11 (4.5-24) Ag. Chiasma Tendinum (CT): a. Distance from proximal point of CT (PCT) to: (1) distal point of CT (DCT) ... (--) 10.5 (7.5 14) (2) distal edge of PFSA ... (--) 3 (1-6) (3) palmar separation of I~'SB and USB ... (--) 13 (4.5-22) b. Distance from'"distal'"point"'of CT (DCT) to: (1) middle of PIP joint ... (--) 3.5 (2-7) (2) proximal edge of DFS,~" ... (--) 11 (6-14) c, UxB width ............ (--) 2.5 (1.5-4) d. RxB width ... ......... (--) 2 (1-3) A10. U T T width at PIP joint . . . . . . . . . (--) 3 (2.5-4) A l l . R T T width at PIP joint . . . . . . (--) 3.5 (3-5) B. At 90 ° flexion of PIP joint with a'li other joints extended: B1. Distance separating U T T and R T T at distal edge of PFSA . . . . . . (q-) 5 (4-6.5) After longitundinal incision o f ' C T ... ( + ) 5 (3-6) B2. Distance separating U T T and R T T at distal edge of PFSA . . . . . . (--) 3 (2-5) After longitudinal incision of CT ... (--) 2 (1-5) B3. Distance ("bowing") from volar plate surface of PIP joint to U T T and R T T (--) 2.5 (2-3) After longitudinal incision of CT ... (--) 3 (2-3.5) B4. Distance of distal point of CT (DCT) to: a. distal edge of PFSA . . . . . . . . . (--) 3.5 (1.5-10) b. middle of PIP joint . . . . . . . . . (--) 6 (2.5-10.5) B5. FDST excursion . . . . . . . . . . . . (-1-) 14 (12-15.5) After longitudinal incision of CT ... (-~) 14 (11.5-16) B6. F D P T excursion after flexion of all IP joints ............... 20 (15-23.5)
Ring mm
Little mm
109 (100-115) 102 (90-110) 6.5 (5-8.5) 5.5 (4-8) 6 (4.5-7) 5 (4-7) 9 (7.5-11) 8 (6.5-10) 4.5 (3.5-5.5) 4 (2.5-5) 4.5 (3.5-5.5) 4 (3.5-5)
84 (72-95) 3 (2-5.5)(16)§ 4.5 (3-5) 5.5 (4-7.5) 3 (2.5-4) 3 (2-4)
3.5 (2.5-4)
3 (2-4)
2 (1-4)
2.5 (1.5-3.5)
2 (1-3)
2 (1-3)
25 (23-28) 16 (13.5-19.5) 14.5 (7-28.5)
24 (22-27) 15.5 (13.5-19) 11 (5.5-24)
19 (14.5-21.5) 11 (7.5-15) 5.5 (1.5-9.5)
10 (8-14) 3 (1-5.5)
8 (6-12) 3.5 (1-6.5)
5 (2-6.5) 5 (2.5-9.5)
17 (12.5-30.5))
14.5 (7-26.5)
3.5 (2-5.5) 12 (8.5-15.5) 2.5 (1.5-3.5) 2.5 (1-4) 3 (2-4) 3.5 (3-4.5)
4.5 (3-8.5) 13 (10-17.5) 2 (1.5-3) 2 (1.5-3) 3 (2-4.5) 2.5 (2-4)
8.5 (3.5-17) 4 (1.5-6) 8.5 (5-16) 1.5 (1-2) (14) 2 (1-3) (16) 2.5 (1.5-3.5) 2 (1.5-2.5)
6 (4.5-7) 6 (4.5-7)
5 (4-6) 5 (3.5-6)
4 (3-5) 4 (3-5)
3 (1.5-4) 3 (1.5-5)
2.5 (2-4) 2 (1-2.5)
2.5 (1-3.5) 2 (1.5-3)
3 (2-4) 3 (2-3.5)
3 (2-3.5) 3 (2-3.5)
2 (2-4) 2 (1.5-3.5)
2.5 (1.5-5.5) 5.5 (3-10.5) 14 (11.5-17.5) 14 (12.5-17.5)
2.5 (1.5-5) 5.5 (2.5-10) 14 (12.5-15.5) 14 (13-16)
3.5 (2-10) (5 (2.5-9) 11 (7.5-13.5) 11.5 (8-13.5)
17 (14.5-20.5)
19 (15.5-22)
15 (10.5-18.5)
* Average values with ranges in parentheses, determined for twenty fingers. Measurements of less than 1 m m were estimated to the nearest 0.5 m m for all calculations. ? Letter abbreviations were used for brevity in description of measurements. They correspond to the terms and definitions seen in Fig. 1 _$ A plus ( + ) following the description of measurement for each finger indicates the measurement was recorded in the oresence of the FDPT, whereas those with a minus (--) represent measurements taken in the absence of that tendon. § Number in parenthesis indicates the n u m b e r of fingers in which the FDST was present in the little fingers. 122
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Thirteen hands were left and seven were right. Since there was little difference between the mean values for individual fingers of the right and left hands, the values from both were averaged for each finger. Measurements were made with calipers and a millimetre ruler. Some detailed measurements were carried out with the aid of a dissecting microscope (10X--20X), estimations being made for values less than 1 mm. and rounded off to the nearest 0.5 ram. The length of each finger was measured from the finger tip to the dorsal plane of the knuckle with the metacarpophalangeal joint flexed to 90 ° and the interphalangeal joints fully extended. The measurements of the components of the superficialis tendon were divided into two groups according to the position of the finger: (1) with extension (0 ° as neutral) of all finger joints (A in Table 1) and (2) with 90 ° of flexion at proximal interphalangeal joint while the remaining joints were in full extension (B in Table 1). Some observations of the tendon's structure were made both in the presence ( + ) and absence ( - - ) of the flexor digitorum profundus tendon. These measurements were designated ( ± ) after the description of the measurement for each finger in Table 1. For most of these observations the annular parts of the flexor sheath over the proximal and middle phalanges were left intact, while the slack cruciate part of the sheath between the two annular parts were excised. In some (B1, B2, B3, B5 in Table 1), the chiasma tendinum was sectioned longitudinally to determine the possible effect on the excursion of the superficialis tendon, the separation of its two released tendinous limbs, and the distance of these limbs from the middle of the volar plate surface of the proximal interphalangeal joint while the finger was in position B. A dissecting pin was placed in the middle of the proximal interphalangeal joint cavity to determine all measurements relating to the distances from this joint to the chiasma tendinum and to the proximal and distal flexor sheaths. As our measurements included a portion of the tendon which has not yet been precisely described, it was necessary to coin appropriate terms for these components of the tendon (Fig. 1). In five middle fingers the superficialis tendon was carefully excised and spread out on a transilluminated plastic lid. It was stabilised with dissecting pins and then carefully studied by shredding the intratendinous fibres. In all toes from four different cadaver feet, the flexor digitorum brevis tendon was dissected and examined for the pattern of its fibrous arrangement. No measurements were made, but the observations were recorded for comparison with the fingers. RESULTS
Average measurements of the flexor digitorum superficialis tendon (FDST) and its components in all fingers of twenty human hands are presented in Table 1 with the ranges in parentheses. When appropriate, observations and measure~ ments were made and recorded for the tendon of the flexor digitorum profundus tendon (FDPT). Each measurement in Table 1 is lettered and numbered so that reference can be made to it in the text. T h e Flexor T e n d o n s and their Sheaths. The finger length (A1) was greatest for the middle finger, with the ring, index and little fingers having progressively decreasing values. A similar distribution is noted with regard to: (1) the width of the flexor tendons in .the region of the base of the proximal phalanx (A2, A3), (2) the width of the superficialis band within the proximal annular sheath (A4), (3) the distance (A8a) separating the proximal and distal annular flexor sheaths and (4) the distance from the distal edge of the proximal sheath to the The Hand~Vol. 6
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Flexor Digitorum Superficialis Tendon in the Fingers of the Human H a n d - - K . Kuczynski
Chiasma Tendinum Points
Scissur Bands
Flexor Digit, Superficialis
Flexor Digit, Superficialis
Fig. 1 C O M P O N E N T S OF THE F L E X O R D I G I T O R U M S U p E R F I C I A L I S T E N D O N Flexor Digitorum Superficialis Tendon (FDST)=single oval tendon trunk proximal to its flattening into its band (FDSB). FDST is located at the region of the metacarpophalangeal joint and base of the proximal phalanx. Measured in full extension of the finger at the proximal edge of the proximal anular flexor sheath (PFSA). Flexor Digitorum Superficialis Band (FDSB)=undivided flattened tendon trunk, distal to FDST, which splits into halves. Located usually about middle of the proximal phalanx. Measured after longitudinal incision of the proximal annular flexor sheath (PFSA). Ulnar and Radial Scissura Bands (USB and RSB)---distal to the palmar split of the FDSB and proximal to separation of its fibres into two parts: uncrossed which remains ipsilateral and crossed which enters into formation of the chiasma tendinum. Located and spiralling around sides of the flexor digitorum profundus tendon (FDPT). Measured at the distal part of the PFSA after its longitudinal section. Chiasma Tendinum (CT)=a midline decussation of the outer fibre bundles of the ulnar and radial scissura bands, uniting distally with the uncrossed inner fibres of the USB and RSB to form the terminal tendons of insertion. Located in fully extended finger between the distal edge of the PFSA and the PIP joint. It forms a thin fibrous plate posterior to the FDPT, which was partially resected to permit measurements of the chiasma to be taken. Proximal Point of the Chiasma Tendinum (PCT)=midline intersection point of the proximal fibres of the crossed bands from USB and RSB. Ulnar and Radial Crossed Bands (UxB and RxB)=the fibre bundles which are derived from the outer parts of the USB and RSB and which decussate to form the chiasma. These bands become contralateral distally and unite with the uncrossed fibre bundles from the inner parts of the scissura bands. Distal Point of the Chiasma Tendinum (DCT)=midline intersection point of the distal fibres of the crossed bands from the USB and RSB. Ulnar and Radial Uncrossed Bands (U-xB and R-xB)=the fibre bundles which are derived from the inner parts of the USB and RSB. These bands are ipsilateral and unite distally with the RxB and UxB. Ulnar and Radial Terminal Tendons (UTT and R T T ) = t w o tendons limbs formed distall~ by the union of RxB with U - x B and UxB with R-xB. Located: from about PIP joint proximally to their insertion into the middle phalanx. Measured at PIP joint at the base of the middle phalanx.
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middle of the proximal interphalangeal joint (A8b). The distal edge of the proximal flexor sheath in all fingers was about 20% further away from the proximal interphalangeal joint than the proximal edge of the distal sheath. Clearly, the variations in the finger length are reflected in the width of the flexor tendons and the distance between their pulleys across the proximal interphalangeal joint. Tendon Excursions. Measurements for excursions of the tendons are recorded with the finger flexed to 90 ° at the proximal interphalangeal joint and the rest of the joints extended (B5, B6). The values for the excursion of both tendons in the index, middle and ring fingers varied only little from each other. The values for the excursion of the tendons of the little finger lie in the same range but are smaller than in the other fingers. Dividing the chiasma cleanly in the median plane did not alter the range of motion of the superficialis tendon in any finger (B5). The excursion of the deep flexor tendon was increased by 3-5 ram. over the values recorded for the superficial tendon in all fingers when the interphalangeal joints were flexed (B6). In order to carry out measurements on the two flexor tendons in the region of the proximal interphalangeal joint, the cruciate part of the fibrous flexor sheath covering the flexor tendons was excised between the proximal and distal flexor sheaths. Before excision, the cruciate part was examined for degree of slackness with the proximal interphalangeal joint extended. In this position it was possible to move its central part about 2 ram. away from the tendons in a palmar direction. On hyperextension of the joint the cruciate sheath is made taut, acting as a tie-beam across the proximal interphalangeal joint and checking hyperextension forces. We found that the cruciate part of the sheath is more superficial and is a separate structure in its attachments from the annular part. The arrangement of the fibres, their density and the function are different as suggested by Henle (1871). Observations made during surgical procedures confirm that the two parts of the sheath are not continuous. The cruciate part may be thought to be continuous with the pretendinous fibres of the palmar aponeurosis while the annular rigid flexor pulleys are a deeper continuation of the fibres from the palmar aspect of the metacarpophalangeal joint and the deep transverse ligament of the palm (Grant, 1971). Bowing Distance. With the proximal interph.alangeal joint flexed to 90 °, the measurements of distance from the palmar surface of the volar plate to the dorsal surface of the two flexor tendons (the "bowing" distance), appeared to be constant, although it was difficult to obtain accurate measurements (B3). Longitudinal section of the chiasma tendinum only slightly changed these measurements (B3). It would seem that the "bowing" distance across the proximal interphalangeal joint in different fingers is generally constant in spite of the difference in finger lengths (A1) as a result of the proportional changes in the distance between the two margins of the proximal and distal flexor pulleys (A8a). The excursion of a tendon is thought to be a function of the degree of the angular movement of the joint and of the distance of the tendon from the axis of the joint, this last distance being related to the distance between the rigid edges of the two annular sheaths across the flexing joint (Landsmeer, 1955), and the diameter of the tendon. Our measurements support this concept since with the different lengths, e.g. in the little finger, there are proportional changes in (1) the excursion of the tendons during flexion (B5), (2) the "bowing" distance of the tendons at the level of the joint (B3), and (3) the distance separating the two margins of the annular flexor sheaths at the proximal interphalangeal joint (A8a). The Hand--Vol. 6
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Flexor Digitorum Superficialis Tendon ill the Fingers o/ the Human Hand--K. Kuczyns~:i
Bands and Tendons of the Flexor Digitorum Superficialis Ulnar and Radial Scissura Bands. The beginning of the split of the flexor digitorum superficialis band occurred usually within the proximal annular flexor sheath, but the point of the commencement of that separation varied considerably (A8c). In a number of instances, the split occurred at the region of the metacarpophalangeal joint before the superficial band entered the proximal fibrous sheath. In an earlier study the split in this tendon was observed to occur at the level of the metacarpophalangeal joint, the tendon being broad and flat at the joint but becoming crescentic with its concavity towards the proximal phalanx (Henle, 1871). We observed this cupping of the tendon but it occurred rather within the proximal sheath. Measurements of width and observations made during the fibre shredding show that the tendon divides equally into ulnar and radial bands (A5, A6). The distance separating the ulnar and radial bands at the distal margin of the proximal sheath was greater in the index and middle fingers than in the ring and little fingers (A7a). This is a reflection of the greater anterioposterior flattening of the profundus tendon in the index and middle fingers. In this region the profundus tendon is broader on its dorsal aspect and narrower on its palmar surface (Martin, 1958). With the profundus removed and the proximal interphalangeal joint in full extension, the two scissura bands came closer together in all the fingers and the difference between the various fingers disappeared (A7b). These observations suggest that there is some "gripping" of the sides of the deep tendon which is held between the two scissura bands in the region of the distal part of the proximal sheath. This hugging effect is reflected in a lateral compression of the profundus tendon which becomes more oval as it passes onto the palmar surface of the chiasma tendinum and then between the terminal tendons of the superficialis. Measurements of the oval cross-section of the deep tendon for about 4 ram. of its length in the region of the chiasma tendinum and the terminal tendons of the superficialis showed that the width of the tendon in all fingers was about 1 ram. greater than its anterioposterior thickness. Ulnar and Radial T e r m i n a l T e n d o n s ( U T T , R T T ) . In the index and middle fingers the radial terminal tendon is wider than the ulnar terminal tendon (A10, All). In the ring and little fingers this difference is reversed. A cross-section of both these terminal tendons just distal to the proximal interphalangeal joint shows their configuration to be triangular with one angle palmar and one on each side dorsally. The length of the insertion of the ulnar and radial terminal tendons in all the fingers is practically the same (8 mm.). The site of the insertion is in the region of the proximal part of the lateral crests of the middle phalanx and is of interest because of its geometrical pattern. The shape of this insertion is like a triangle (Fig. 3) with the right angle proximal towards the midline of the phalanx, while the hypotenuse runs from the proximal and outer part of the crest to its distal and inner part. If both radial and ulnar insertions were to become confluent in the midline of the middle phalanx, they would form an isosceles triangle with the apex in the middle pointing distally and with the base parallel to the proximal surface of the phalanx and transverse axis of the joint. A dissection of the insertion of the profundus tendon into the distal phalanx shows that it has a similar triangular shape, as shown by Wilkinson (I953). On the bony surface of the palmar crests not occupied by the insertion of the superficialis tendon there are attachments of the collateral ligaments of the proximal interphalangeal joint and of the proximal part of the distal fibrous sheath. 126
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Flexor Digitorum Superficialis Tendon in the Fingers o/ the Human Hand--K. Kuczynski Distal
ertion ~ngle
RT"
U x
ial e RS ~B
)ST Proximal
Fig. 2 Untwisted scissura bands. Fig. 3 Components of the FDS with related synovial tissue; insertion triangle shown.
Chiasma Tendinum (CT) With the Fingers Extended at all joints. The length of the chiasma from its proximal point to its distal point varied with the size of the superficialis tendon and with the finger length, being least in the little finger (A9a (1)). The proximal point of the chiasma was always distal to the distal edge of the proximal fibrous sheath (A9a (2)). This means that with the proximal interphalangeal joint extended the chiasma was dorsal to the broad part of the profundus tendon and distal to its proximal pulley. Since the distal point of the chiasma was always found to be proximal to the proximal interphalangeal joint (A9b (1)), the chiasma in all the fingers with the joint extended lies posterior to the profundus tendon between the distal edge of the proximal flexor sheath and the proximal interphalangeal joint. The width of the fibre bundles (ulnar crossed band, radial crossed band) which crossed to form the chiasma were not equal in all the fingers (A9c, A9d). The width of both bands was approximately the same in the middle and ring fingers, but the values for the middle finger were greater than those of the ring finger. In the index finger the ulnar crossed band was consistently greater than its radial counterpart, while the reverse was present in the little finger. In four of the twenty hands dissected there was no evidence of any chiasma tendinum in the little finger (Agcd) or of the superficial tendon itself (A2); however, the radial and ulnar uncrossed bands, the flexor digitorum superficialis The Hand--Vol. 6
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band and the radial and ulnar scissura bands were present. These latter bands were attached or seemed to arise from the surrounding synovial tissue or from the underside of the proximal flexor sheath. In two of the little fingers in which the superficial tendon and its distal components were present, the chiasma tendinum had only a radial crossed band the ulnar crossed band being absent (A9c). In the chiasma tendinum of the little fingers, the radial crossed bands were wider and more frequently present than those of its ulnar counterpart (A9c, Agd).
There is a noticeable similarity in the fibre bundle pattern found in the little finger and that of the 2nd, 3rd, and 4th flexor digitorum brevis tendons in the foot. That is, there is usually only a single crossed band in the chiasma tendinum of these toes which corresponds to the radial dominance of the crossed bands seen in the little finger. W i t h the Fingers F l e x e d to 90 ° at t h e P r o x i m a l Interphalangeal Joint. When the chiasma was sectioned longitudinally with the profundus tendon present, no changes were observed in: (1) the distance separating the two terminal tendons (B1), (2) the distance from the tendons to the surface of the palmar plate of the proximal interphalangeal joint ("bowing" distance) (B3) or (3) in the excursion of the superficial tendon (B5). In the absence of the profundus tendon the section of the chiasma resulted in a smaller distance separating the two terminal tendons than when the chiasma was left intact (B2). When the superficial tendon moved proximally on flexion, the fibres of the chiasma came to lie at the distal edge of the proximal pulley. Usually half of the length of the chiasma is inside the flexor sheath, the distal half being out of it and beyond its distal edge (B4a). Also, the distance from distal point of the chiasma to the proximal interphalangeal joint (B4b) is almost doubled when compared with the extended position of the finger (A9b (1)). Dissection of the fibre bundles of the flexor digitorum superficialis. When the radial and ulnar scissura bands are separated distally from the superficial bands and untwisted in such a way that their inner surfaces face forwards, they present a midline X, the chiasma, which has on its sides the scissura bands, uncrossed bands, and distally the terminal tendons. The appearance is now like two I pillars on either side of the X = IXI (Fig. 2). This preparation allows the arrangement of the fibre bundles to be seen from their insertion to their origin within the scissura bands. These fibre bundles which insert more proximally and near the side of the middle phalanx on its palmar crest can be traced to the bundles at the outer side of the untwisted scissura band while those which are inserted more distally and centrally on the contralateral palmar crest cross in the chiasma and can be traced to the inner side of the untwisted scissura band. In other words, the scissura bands behave as two contrary helices twisting round the sides of the deep tendon (Fig. 3). Teasing out of the fibres of the chiasma to trace their origin, termination and relationship to each other demonstrates that sometimes the pattern of the fibre crossing is in the form of a lacing of the bundles. The fibres from the crossed band may split off and remain ipsilateral while the fibres usually destined to be ipsilateral may contribute to the crossed band of chiasma. DISCUSSION The precise location of the fibre bundles of a tendon at its insertion and the specific path they take within the tendon relative to each other may have considerable functional significance. The unique relationship, the similarity of the 128
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Flexor Digitorum Superficialis Tendo,n in the Fingers O[ the Human Hand--K. Kuczynski
intratendinous fibre structure, and the pattern of insertion of the two flexor tendons in the fingers suggest such a significance. The anatomical features of these tendons have been known for years and recently investigated in detail in the flexor digitorum profundus tendon (Wilson, 1973). However, the functional and applied significance of these features is poorly understood. Our measurements indicate that differences in the finger length are reflected in the size of the two flexor tendons and in the different distance between the segments of the annular fibrous flexor sheath. The lengths of the fingers recorded here are in agreement with the primate pattern (Napier, 1962), although the index finger is not infrequently found to be slightly longer than the ring finger (Jones, 1942). The width of the tendons for the middle and ring fingers is greater than in the index and little fingers in man and other primates (Raven, 1950). The superficial tendon to the little finger, when present, was usually smaller and narrower than the corresponding deep flexor tendon. The width of the superficialis tendon at the base of the proximal phalanx was greater than that of the profundus; this was due to the broadening of the superficial tendon just prior to formation of its bands within the proximal annular flexor sheath. The profundus tendon is oval in cross-section at the base of the proximal phalanx after passing through the split of the superficialis tendon. This has been observed previously in the superficialis (Henle, 1871; Martin, 1958). The similarity of shape and insertion of both tendons means that the profundus tendon mirrors the structure of the superficialis but at a more distal position within the finger. The excursion of both tendons to flex the proximal interphalangeal joint to 90 ° was constant for each finger in a number of hands, though the excursion in the little finger was noticeably smaller. The values for the excursion of the two flexors in the radial three fingers were only 2 mm. less than those recorded earlier (Stack, 1963), a fact resulting from our use of a more limited range of flexion (00-90 °) at the proximal interphalangeal joint. It was possible also that limitations were imposed by the method of preservation of the cadaveric material. The excursion of the deep tendon when the interphalangeal joints were both flexed resulted in expected increases similar to the values previously recorded (Stack, 1963). However, there was a tendency for the index finger to be slightly favoured in its total excursion when compared with the profundus of the ring and middle fingers. The constancy of excursion of the flexor tendons was to be expected with varying finger lengths for the separation of the pulleys over which they act varied similarly. This distance separating the pulleys has been shown to determine the "bowing" of the tendons across a joint which was a factor in the shortening necessary for any particular change in joint angle (Landsmeer, 1954). In the little finger the superficial tendon was absent in about 20% of the hands studied and in the remaining hands it was less developed in proportion to the finger length than its counterpart in the radial three fingers. This was in agreement with other observations (Long, 1968). The deep tendon retained its size relative to the finger length. Where the superficial tendon was missing in the little finger, the more distal components of the tendon were present even including the split to accommodate the deep tendon. The size of these distal bands was proportional to the finger length. The width and the insertion pattern of the terminal tendons again reflected the finger size. EMG readings suggested that the superficial muscle was involved in activities to sustain increasing loads'o~ the proximal interphalangeal joint (Backhouse, 1968; Long, 1968). It was used when power was needed for long periods, when the hook grip was required and precision was minimal, and when the grip did not The Hand--Vol. 6
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Flexor Digitorum Superficialis Tendon in the Fingers o/ the Human H a n d - - K . K . c z y n s k i
require a finger tip hold (Napier, 1956). In these circumstances the most active muscle was the flexor superflcialis (Backhouse, 1968). There was a remarkable similarity between the pattern of the tendon bundles of the flexor digitorum brevis in the 2nd-4th toes and that in the little finger. The 5th toe showed no evidence of the tendon or its bands. This may reflect the loss of gripping function in the foot (Morton, 1966). A similar suggestion may be made with regard to the absence of the superficialis in the thumb and the little finger, the thumb taking no part in the hook grip and the little finger contributing to it only in a limited way. The palmar splitting of the superficial band into its two scissura bands occurred with great variation within the proximal flexor sheath, in some instances even occurring proximal to it. This splitting of the tendon over the lateral sides of the deep flexor tendon has been given significance as retention bands for the deep tendon, improving its leverage (Kaplan, 1965) or keeping the deep tendon from overstretching its proximal fibrous flexor sheath (Weitbrecht, 1742; Jones, 1942). In view of our observations that the splitting of the tendon within the finger is such a variable condition, its underdevelopment within the little finger, and the observation that the tendon sometimes fails to split (Bryce, 1923), its function as a retention band in the presence of a very strong annular flexo~ sheath is difficult to prove. Our measurements suggested that the radial and ulnar scissura bands at the distal margin of the proximal pulley appeared to "hug" the deep tendon passing over their inner surfaces. The removal of the deep tendon in the extended finger resulted in a closer approximation of the bands in the absence of any increased tension in the superficialis muscle other than the visco-elastic forces produced by extending the finger. The same effect was noticed in the distance separating the radial and ulnar terminal tendons at the distal edge of the proximal pulley when the joint was flexed by a pull on the superficialis tendon in the absence of the deep tendon. While longitudinal section of the chiasma tendinum of the superficial tendon did not change the distance between terminal tendons in the presence of the profundus tendon, the absence of the deep tendon resulted in their approximation. It is possible that the chiasma does have some effect on the pressure exerted by the superficialis bands on the lateral sides of the deep tendon but this requires further investigation. Our findings, however, for the variations in the splitting of the superficial tendon and for the possible pressure exerted by the two split bands of this tendon over the sides of the deep perforating tendon would support the earlier observation for the occurrence of nodular thickenings on the surface of the long flexor tendons being found at different locations along these tendons in triggering of the finger; and, that such nodules formed on the profundus tendon may result from a tight bifurcation of the superficialis tendon "rucking" the surface intratendinous fibres of the deep tendon as it glides through the tunnel of the superficial bands (Helal, 1970). We can offer no convincing comment on the function of the chiasma tendinum fibre bands during sustained flexion of the proximal interphalangeal joint, though its position is consistently dorsal to the deep tendon at the dis,~al edge of the proximal flexor sheath. In extension, the chiasma lays flat against the distal part of the proximal phalanx and against the palmar plate of the proximal interphalangeal joint, being attached by a vinculum breve to the palmar plate and synovial tissue. A study by one of the authors (Kuczynski, 1968) has shown that after removal of both flexor tendons of the finger, some of the capsular fibres and the cruciate part of the flexor sheath prevented hyperextension of the proximal interphalangeal joint. The 130
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palmar plate appeared to be tensed only in extreme hyperextension, while the collateral ligaments of the joint were not responsible for preventing hyperextension. It has been shown also that excision of the superficialis tendon when inserting a tendon graft t o replace the divided flexor digitorum profundus tendon may lead to a loss of the finger strength and balance and to a hyperextension deformity at the proximal interphalangeal joint (White, 1960; Jaffe, 1967). It seemed that the activity of the flexor superficialis muscle was a first line of defence against a hyperextension deformity at the proximal interphalangeal joint, stabilising it well before these other factors could come into play. The terminal tendons of the superficial tendon were triangular in cross section with one angle directed to the side and palmarly, forming between them a bed for lhe passage of the deep flexor tendon. They were formed by the union of uncrossed fibres and crossed ones from the chiasma tendinum. Since the scissura bands were always found equal in size, differences in the size of the radial and ulnar terminal tendons depend on the number of crossed bundles passing to each terminal tendon. In the index finger the radial was larger than the ulnar terminal tendon because the crossed band in the chiasma was contributing more fibres from the opposite scissura band to the radial terminal tendon than the crossed fibres from the radial scissura band to the ulnar terminal tendon. The terminal tendons on each side of the middle and ring fingers were of approximately the same size and so were their crossed bands. In the little finger, however, the values for the ulnar terminal tendon were greater than for the radial not only because the radial crossed bands of the chiasma were larger but also because they were more often present than their ulnar counterpart. In some little fingers there was no chiasma. Although the difference in size of the crossed bands in the chiasma and thus of the terminal tendons, is small, this difference takes on a greater significance when it is realised that the parallel collagen fibres which constitute these bands are capable of transmitting tensile forces which can reach from 15 to 30 kgs/mmY It is not unreasonable to expect then, that small differences in the size of the two crossed bands and the terminal tendons should reflect a difference in distribution of the forces which are applied at the small proximal interphalangeal joint. If the tendon size reflects the tension developed across the joint, the force? developed are likely to be similar in both terminal tendons in the middle and ring fingers, with the radial greater in the index and the ulnar greater in the little finger. The study of coronal deviation (abduction-adduction) at the proximal interphalangeal joint during flexion (Holcomb, 1958) shows that the index undergoes an ulnar deviation, while the little finger shows marked deviation in the radial direction. A study of the interphalangeal joint during flexion-extension movements (MacConaill, 1953) shows that a conjunct rotation occurs at the joint. This is dependent on the shape of the articular surfaces and the arrangement of the articular ligaments. Figure 4 shows the asymmetry of the condyles of the head of the proximal phalanx which could account for the deviation and conjunct rotation which occurs during flexion at the proximal interphalangeal joint (MacConaill, 1953; Kuczynski, 1968). The condylar surfaces being asymmetrical in both sagittal and coronal planes results in a mechanical effect which is related to the different forces applied to each condyle of a particular proximal interphalangeal joint. This aspect requires further detailed mechanical analysis. In the index finger the greater size of the radial terminal tendon would reflect a greater moment of force generated on the radial than on the ulnar side of the The Hand--Vol. 6
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Flexor Digitorum Superficialis Tendon in the Fingers o[ the Human Hand--K. Kuezynski
Fig. 4 Asymmetry of the condyles of the head of the proximal phalanx. joint. This asymmetrical force may act in unison with the first dorsal interosseous muscle in counteracting the tendency of the interosseous muscles to produce ulnar deviation of the fingers (Backhouse, 1968; Kuczynski, 1972). These observations suggest that the use of a "slip" of the superficial tendon for reconstruction of a pulley system for the deep flexor m a y create an imbalance of forces in the remaining slip of the tendon unless its crossed fibres of the chiasma can be preserved. This attempt to preserve the chiasma may prove to be difficult in practice, thus some other means of constructing a pulley for the deep flexor tendon would appear more judicious than the use of a good intact terminal tendon and its proximal scissura band. ACKNOWLEDGEMENTS
We are grateful to Professor G. J. Romanes and to Dr. R. K. Johnson for their interest and advice in the preparation of this study and to Karen Kvenvold for the line drawings. REFERENCES
ALB1NUS, BERNARD S. (1734) Historia Musculorum Hominis. Le'dae Batavorum. 479, 639. ARNOLD, MAURICE (1968) Reconstructive Anatomy. A Method for the Study of Human Structure. Philadelphia, W. B. Saunders. 383, 385. BACKHOUSE, K. M. (1968) The Mechanics of Normal Digital Control In The Hand An:l An Analysis of the Ulnar Drift of Rheumatoid Arthritis. Annals of the Royal College of Surgeons of England. 43: 154-173. BRYCE. T. H. (1923) Quain's Elements of Anatomy. New York, Longmans, Green & Co. 4: No. 2. 133. CAMPER, P. (1769) Demonstrationum Antomico-Pathologicarum; liber primus. Amstelaedami. 4, 19. CUNNINGHAM, D. J. (1972) Textbook of Anatomy. Ed. by G. J. Romanes. llth Edition. London, Oxford University Press. 319. GRANT, J. C. B., and BASMAJIAN, J. V. (1971) Method of Anatomy by regions, descriptive and deductive. 8th Edition. Baltimore, Williams and Wilkins Co. 142. HELAL, B. (1970) Distal Profundus Entrapment in Rheumatoid Disease. The Hand. 2: 48-51. HENLE, F. G. J. (1871) Handbuch der Systematischen Anatomie des Menschen. 2nd Edition. Braunschweig. 1: Muskellehre. 236. 132
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Flexor Digitorum Superficialis Tendon in the' Fingers o[ the Human Hand--K. Kuczynski HOLCOMB, G. R., IRVING, T. E., and SMITH, R. D. (1958) Coronal Deviation And Tilt In the Proximal Interphalangeal Joints of Man. American Journal of Physical Anthropology. 16: 429-440. HOLLINSHEAD, W. H. (1958) Anatomy for Surgeons: Back and Limbs. Philadelphia, W. B. Saunders. Vol. 3. 522. HUESTON, J. T., and WILSON, W. F. (1972) The Aetiology of Trigger Finger. Explained on the Basis of Intratendinous Architecture. The Hand. 4: 257-260. JAFFE, S., and WECKESSER, E. (1967) Profundus Tendon Grafting with the Sublimis Intact. An End-Result Study of Thirty Patients. Journal of Bone and Joint Surgery. 49A: 1298-1308. JONES, F. W. (1942) The Principles of Anatomy as seen in the Hand. 2nd Edition. London, Bailli6re Tindall and Cox. 233, 295. JONES, F. W. (1944) The Foot. London, Bailli6re Tindall and Cox. 183. KAPLAN, E. B. (1950) Embryological Development of The Tendinous Apparatus of the Fingers. Relation To Function. Journal of Bone and Joint Surgery. 32A: 820-826. KAPLAN, E. B. (1965) Functional and Surgical Anatomy of the Hand. 2nd Edition. Philadelphia, J. B. Lippincott Company. 62. KNOX, ROBERT (1831) Cloquet's Anatomy. 2nd Edition. Privately printed. 319. KNOX, ROBERT (1853) Renshaw's Manual of Human Anatomy. Private printed. 193. KUCZYNSKI, K. (1968) The Proximal Interphalangeal Joint. Anatomy and Causes of Stiffness in the Fingers. Journal of Bone and Joint Surgery. 50B: 656-663. KUCZYNSKI, K. (1972) The Variations in the Insertion of the First Dorsal Interosseous Muscle and their Significance in Rheumatoid Arthritis. The Hand. 4: 37. LAMPE, E. W. (1969) Surgical Anatomy of the Hand. Clinical Symposia. New Jersey Ciba Pharmaceutical Products Inc. 75. LANDSMEER, J. M. F. (1954) Studies in the Anatomy of Articulation. I. The equilibrium of the "Intercalated" bone. Acta Morphologica Neerlando-Scandinavia. 3: 278-303. LANDSMEER, J. M. F. (1955) Anatomical And Functional Investigations On The Articulation Of The Human Fingers. Acta Anatomica. 25: Supplement 24, 5-69. LONG, CHARLES (1968) Intrinsic-Extrinsic Muscle Control of the Fingers. Electromyographic Studies. Journal of Bone and Joint Surgery. 50A: 973-984. MacCONAILL, M. A. (1953) The Movements Of Bones And Joints. 5. The Significance of Shape. Journal of BOne and Joint Surgery. 35B: 290-297. MACKENZIE, W. C. (1918) Action of Muscles including muscle rest and muscle re-education. Privately printed. 87. MARTIN. B. F. (1958) The Tendons of Flexor Digitorum Profundus. Journal of Anatomy. 92: 602-608. MORTON, D. J. (1935) The Human Foot. Its Evolution, Physiology and Functional Disorders. New York, Columbia University Press. 80. NAPIER, J. R. (1956) The Prehensile Movements Of The Human Hand. Journal of Bone and Joint Surgery. 38B: 902-913. NAPIER, J. R. (1962) The Evolution of the Hand. Scientific American. 207: 56-62. RAVEN, H. C. (1950) Anatomy of the Gorilla. Ed. by William Gregory. New York, Columbia University Press. 44, 67. STACK, H. G. (1963) A Study of Muscle Function in the Fingers. Annals of the Royal College of Surgeons of England. 33: 307-322. WEITBRECHT, JOSIAS (1969) Syndesmology. A Description of the Ligaments of the Human Body. Trans. by E. B. Kaplan. Philadelphia, W. B. Saunders Co. 37, 142. WHITE, WILLIAM L. (1960) Restoration of Function and Balance of the Wrist and Hand by Tendon Transfers. Surgical Clinics of North America. 40: No. 2. 427-459. WILKINSON, J. L. (1953) The Insertions Of The Flexors Pollicis Longus Et Digitorum Profundus. Journal of Anatomy. 87: 75-88. WILSON, W. F., and HUESTON, J. T. (1973) The Intratendinous Architecture of the Tendons of the Flexor Digitorum Profundus and Flexor Pollicis Longus. The Hand. 5: 33-38.
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FLEXOR DIGITORUM SUPERFICIALIS TENDON IN THE FINGERS OF THE HUMAN HAND
MARVIN M. SHREWSBURY, San Jose, California and K. KUCZYNSKI, Edinburgh With slight variation, the arrangement of the fibre bundles of the flexor digitorum superficialis tendon in the fingers is described in the same way in early anatomical works (Weitbrecht, 1742; Camper, 1760; Albinus, 1774; Knox, 1831, 1853; Henle, 1871) and more recently (MacKenzie, 1918; Jones, 1942; Martin, 1958; Arnold, 1968; Gardner, 1969; Lampe, 1969; Grant, 1971; Cunningham, 1972). Particular attention has been focussed upon two features, spiralling and decussation of the fibres. The pattern is given in the standard texts much as it was observed by Weitbrecht (1742) and later, more precisely described, by Camper (1760) whose name the decussation bears. In his drawing Leonardo da Vinci showed the superficialis tendon embracing the deep tendon and he was greatly interested in the penetration of one tendon by the other because of the mechanical principles involved. The early views of the arrangement of fibres in the superficialis tendon was that it was the same in all fingers of the human hand (Albinus, 1774). Current publications also indicate no variations in the arrangement of these fibres from finger to finger or from hand to hand. A similar fibre design in this tendon is reported in the fingers of other primates (Raven, 1950; Kaplan, 1965) and in its homologue, the flexor digitorum brevis in the human foot (Jones, 1944; Grant, 1971). Most sources indicate that the arrangement of the bundles in this tendon is in general understood, but not its functional significance. Two functional aspects are advanced which are in keeping with the structural characteristics of the tendon. Some authors claim that the spiralling of the superficialis tendon makes a tunnel for the deep tendon so that it is not gripped when the superficial muscle contracts, ensuring a freedom from interference with the movement of the deep tendon (Hollinshead, 1958; Grant, 1971). The action of a sling, a retention band, an efficient pulley for the deep tendon is also attributed to the superficialis tendon arrangement (Weitbrecht, 1742). The functional significance given to the chiasma tendinum is less obvious. One suggestion is that the thin, plate-like chiasma posterior to the deep tendon in the region of the proximal interphalangeal joint, allows the deep tendon to cross the joint at about the same distance from the axis of flexion as the superficial tendon. This feature accounts partly for the fact that the total excursion produced by each of the tendons is almost equal in spite of the disparity in the number of joints they cross (Stack, 1963). Our present study is an attempt to investigate in more detail the pattern of fibres in the flexor digitorum superficialis tendons and its functional significance, particularly variations from finger to finger and from hand to hand, and comparison of detailed measurements. MATERIAL AND METHODS Twenty-three hands from fifteen male cadavers were dissected. The first three hands were used for preliminary studies in order to establish the procedure and scope of the observations to be recorded. The index, middle, ring and little fingers of all the remaining hands were separately examined and measurements taken and recorded for the flexor digitorum superfieialis tendon. The Hand--Vol. 6
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Flexor Digitorum Superficialis Tendon in the Fingers of the Human Hand--K. Kuczynski TABLE 1 MEASUREMENTS FOR THE FLEXOR DIGITORUM SUPERFICIALIS TENDON IN T H E F I N G E R S OF T H E H U M A N H A N D Description of Measurement
Finger Index mm
Middle mm
A. At 0 ° (neutral) extension of PIP joint with all finger joints extended: A1. Finger length . . . . . . . . . 97 (85-105)* A2. FDST'~ width at proximal edge of PFSA (+):~ 5 (4-7) A3. F D P T width at proximal edge of P F S A ( q - ) 5 (3.5-7) A4. FDSB width just proximal to its splitting (q-) 8.5 (7-10) A5. RSB width ............ (-b-) 4 (3-5) A6. USB width ... (-[-) 4 (3.5-5) 17. a. Distance separaiing 1~S]3 an~t'[SSB at distal edge of PFSA . . . . . . (q-) 3 (2-4) b. Distance separating RSB anci'iJSB at distal edge of PFSA . . . . . . . . . (--) 2 (1.5-3.5) A8. Distance from distal edge of PFSA to: a. proximal edge o f DFSA ...... (-t-) 23 (19-28) b. middle of PIP joint . . . . . . . . . (nt-) 15 (11.5-20) c. palmar separation of RSB and USB ( - - ) 11 (4.5-24) Ag. Chiasma Tendinum (CT): a. Distance from proximal point of CT (PCT) to: (1) distal point of CT (DCT) ... (--) 10.5 (7.5 14) (2) distal edge of PFSA ... (--) 3 (1-6) (3) palmar separation of I~'SB and USB ... (--) 13 (4.5-22) b. Distance from'"distal'"point"'of CT (DCT) to: (1) middle of PIP joint ... (--) 3.5 (2-7) (2) proximal edge of DFS,~" ... (--) 11 (6-14) c, UxB width ............ (--) 2.5 (1.5-4) d. RxB width ... ......... (--) 2 (1-3) A10. U T T width at PIP joint . . . . . . . . . (--) 3 (2.5-4) A l l . R T T width at PIP joint . . . . . . (--) 3.5 (3-5) B. At 90 ° flexion of PIP joint with a'li other joints extended: B1. Distance separating U T T and R T T at distal edge of PFSA . . . . . . (q-) 5 (4-6.5) After longitundinal incision o f ' C T ... ( + ) 5 (3-6) B2. Distance separating U T T and R T T at distal edge of PFSA . . . . . . (--) 3 (2-5) After longitudinal incision of CT ... (--) 2 (1-5) B3. Distance ("bowing") from volar plate surface of PIP joint to U T T and R T T (--) 2.5 (2-3) After longitudinal incision of CT ... (--) 3 (2-3.5) B4. Distance of distal point of CT (DCT) to: a. distal edge of PFSA . . . . . . . . . (--) 3.5 (1.5-10) b. middle of PIP joint . . . . . . . . . (--) 6 (2.5-10.5) B5. FDST excursion . . . . . . . . . . . . (-1-) 14 (12-15.5) After longitudinal incision of CT ... (-~) 14 (11.5-16) B6. F D P T excursion after flexion of all IP joints ............... 20 (15-23.5)
Ring mm
Little mm
109 (100-115) 102 (90-110) 6.5 (5-8.5) 5.5 (4-8) 6 (4.5-7) 5 (4-7) 9 (7.5-11) 8 (6.5-10) 4.5 (3.5-5.5) 4 (2.5-5) 4.5 (3.5-5.5) 4 (3.5-5)
84 (72-95) 3 (2-5.5)(16)§ 4.5 (3-5) 5.5 (4-7.5) 3 (2.5-4) 3 (2-4)
3.5 (2.5-4)
3 (2-4)
2 (1-4)
2.5 (1.5-3.5)
2 (1-3)
2 (1-3)
25 (23-28) 16 (13.5-19.5) 14.5 (7-28.5)
24 (22-27) 15.5 (13.5-19) 11 (5.5-24)
19 (14.5-21.5) 11 (7.5-15) 5.5 (1.5-9.5)
10 (8-14) 3 (1-5.5)
8 (6-12) 3.5 (1-6.5)
5 (2-6.5) 5 (2.5-9.5)
17 (12.5-30.5))
14.5 (7-26.5)
3.5 (2-5.5) 12 (8.5-15.5) 2.5 (1.5-3.5) 2.5 (1-4) 3 (2-4) 3.5 (3-4.5)
4.5 (3-8.5) 13 (10-17.5) 2 (1.5-3) 2 (1.5-3) 3 (2-4.5) 2.5 (2-4)
8.5 (3.5-17) 4 (1.5-6) 8.5 (5-16) 1.5 (1-2) (14) 2 (1-3) (16) 2.5 (1.5-3.5) 2 (1.5-2.5)
6 (4.5-7) 6 (4.5-7)
5 (4-6) 5 (3.5-6)
4 (3-5) 4 (3-5)
3 (1.5-4) 3 (1.5-5)
2.5 (2-4) 2 (1-2.5)
2.5 (1-3.5) 2 (1.5-3)
3 (2-4) 3 (2-3.5)
3 (2-3.5) 3 (2-3.5)
2 (2-4) 2 (1.5-3.5)
2.5 (1.5-5.5) 5.5 (3-10.5) 14 (11.5-17.5) 14 (12.5-17.5)
2.5 (1.5-5) 5.5 (2.5-10) 14 (12.5-15.5) 14 (13-16)
3.5 (2-10) (5 (2.5-9) 11 (7.5-13.5) 11.5 (8-13.5)
17 (14.5-20.5)
19 (15.5-22)
15 (10.5-18.5)
* Average values with ranges in parentheses, determined for twenty fingers. Measurements of less than 1 m m were estimated to the nearest 0.5 m m for all calculations. ? Letter abbreviations were used for brevity in description of measurements. They correspond to the terms and definitions seen in Fig. 1 _$ A plus ( + ) following the description of measurement for each finger indicates the measurement was recorded in the oresence of the FDPT, whereas those with a minus (--) represent measurements taken in the absence of that tendon. § Number in parenthesis indicates the n u m b e r of fingers in which the FDST was present in the little fingers. 122
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Thirteen hands were left and seven were right. Since there was little difference between the mean values for individual fingers of the right and left hands, the values from both were averaged for each finger. Measurements were made with calipers and a millimetre ruler. Some detailed measurements were carried out with the aid of a dissecting microscope (10X--20X), estimations being made for values less than 1 mm. and rounded off to the nearest 0.5 ram. The length of each finger was measured from the finger tip to the dorsal plane of the knuckle with the metacarpophalangeal joint flexed to 90 ° and the interphalangeal joints fully extended. The measurements of the components of the superficialis tendon were divided into two groups according to the position of the finger: (1) with extension (0 ° as neutral) of all finger joints (A in Table 1) and (2) with 90 ° of flexion at proximal interphalangeal joint while the remaining joints were in full extension (B in Table 1). Some observations of the tendon's structure were made both in the presence ( + ) and absence ( - - ) of the flexor digitorum profundus tendon. These measurements were designated ( ± ) after the description of the measurement for each finger in Table 1. For most of these observations the annular parts of the flexor sheath over the proximal and middle phalanges were left intact, while the slack cruciate part of the sheath between the two annular parts were excised. In some (B1, B2, B3, B5 in Table 1), the chiasma tendinum was sectioned longitudinally to determine the possible effect on the excursion of the superficialis tendon, the separation of its two released tendinous limbs, and the distance of these limbs from the middle of the volar plate surface of the proximal interphalangeal joint while the finger was in position B. A dissecting pin was placed in the middle of the proximal interphalangeal joint cavity to determine all measurements relating to the distances from this joint to the chiasma tendinum and to the proximal and distal flexor sheaths. As our measurements included a portion of the tendon which has not yet been precisely described, it was necessary to coin appropriate terms for these components of the tendon (Fig. 1). In five middle fingers the superficialis tendon was carefully excised and spread out on a transilluminated plastic lid. It was stabilised with dissecting pins and then carefully studied by shredding the intratendinous fibres. In all toes from four different cadaver feet, the flexor digitorum brevis tendon was dissected and examined for the pattern of its fibrous arrangement. No measurements were made, but the observations were recorded for comparison with the fingers. RESULTS
Average measurements of the flexor digitorum superficialis tendon (FDST) and its components in all fingers of twenty human hands are presented in Table 1 with the ranges in parentheses. When appropriate, observations and measure~ ments were made and recorded for the tendon of the flexor digitorum profundus tendon (FDPT). Each measurement in Table 1 is lettered and numbered so that reference can be made to it in the text. T h e Flexor T e n d o n s and their Sheaths. The finger length (A1) was greatest for the middle finger, with the ring, index and little fingers having progressively decreasing values. A similar distribution is noted with regard to: (1) the width of the flexor tendons in .the region of the base of the proximal phalanx (A2, A3), (2) the width of the superficialis band within the proximal annular sheath (A4), (3) the distance (A8a) separating the proximal and distal annular flexor sheaths and (4) the distance from the distal edge of the proximal sheath to the The Hand~Vol. 6
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Chiasma Tendinum Points
Scissur Bands
Flexor Digit, Superficialis
Flexor Digit, Superficialis
Fig. 1 C O M P O N E N T S OF THE F L E X O R D I G I T O R U M S U p E R F I C I A L I S T E N D O N Flexor Digitorum Superficialis Tendon (FDST)=single oval tendon trunk proximal to its flattening into its band (FDSB). FDST is located at the region of the metacarpophalangeal joint and base of the proximal phalanx. Measured in full extension of the finger at the proximal edge of the proximal anular flexor sheath (PFSA). Flexor Digitorum Superficialis Band (FDSB)=undivided flattened tendon trunk, distal to FDST, which splits into halves. Located usually about middle of the proximal phalanx. Measured after longitudinal incision of the proximal annular flexor sheath (PFSA). Ulnar and Radial Scissura Bands (USB and RSB)---distal to the palmar split of the FDSB and proximal to separation of its fibres into two parts: uncrossed which remains ipsilateral and crossed which enters into formation of the chiasma tendinum. Located and spiralling around sides of the flexor digitorum profundus tendon (FDPT). Measured at the distal part of the PFSA after its longitudinal section. Chiasma Tendinum (CT)=a midline decussation of the outer fibre bundles of the ulnar and radial scissura bands, uniting distally with the uncrossed inner fibres of the USB and RSB to form the terminal tendons of insertion. Located in fully extended finger between the distal edge of the PFSA and the PIP joint. It forms a thin fibrous plate posterior to the FDPT, which was partially resected to permit measurements of the chiasma to be taken. Proximal Point of the Chiasma Tendinum (PCT)=midline intersection point of the proximal fibres of the crossed bands from USB and RSB. Ulnar and Radial Crossed Bands (UxB and RxB)=the fibre bundles which are derived from the outer parts of the USB and RSB and which decussate to form the chiasma. These bands become contralateral distally and unite with the uncrossed fibre bundles from the inner parts of the scissura bands. Distal Point of the Chiasma Tendinum (DCT)=midline intersection point of the distal fibres of the crossed bands from the USB and RSB. Ulnar and Radial Uncrossed Bands (U-xB and R-xB)=the fibre bundles which are derived from the inner parts of the USB and RSB. These bands are ipsilateral and unite distally with the RxB and UxB. Ulnar and Radial Terminal Tendons (UTT and R T T ) = t w o tendons limbs formed distall~ by the union of RxB with U - x B and UxB with R-xB. Located: from about PIP joint proximally to their insertion into the middle phalanx. Measured at PIP joint at the base of the middle phalanx.
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middle of the proximal interphalangeal joint (A8b). The distal edge of the proximal flexor sheath in all fingers was about 20% further away from the proximal interphalangeal joint than the proximal edge of the distal sheath. Clearly, the variations in the finger length are reflected in the width of the flexor tendons and the distance between their pulleys across the proximal interphalangeal joint. Tendon Excursions. Measurements for excursions of the tendons are recorded with the finger flexed to 90 ° at the proximal interphalangeal joint and the rest of the joints extended (B5, B6). The values for the excursion of both tendons in the index, middle and ring fingers varied only little from each other. The values for the excursion of the tendons of the little finger lie in the same range but are smaller than in the other fingers. Dividing the chiasma cleanly in the median plane did not alter the range of motion of the superficialis tendon in any finger (B5). The excursion of the deep flexor tendon was increased by 3-5 ram. over the values recorded for the superficial tendon in all fingers when the interphalangeal joints were flexed (B6). In order to carry out measurements on the two flexor tendons in the region of the proximal interphalangeal joint, the cruciate part of the fibrous flexor sheath covering the flexor tendons was excised between the proximal and distal flexor sheaths. Before excision, the cruciate part was examined for degree of slackness with the proximal interphalangeal joint extended. In this position it was possible to move its central part about 2 ram. away from the tendons in a palmar direction. On hyperextension of the joint the cruciate sheath is made taut, acting as a tie-beam across the proximal interphalangeal joint and checking hyperextension forces. We found that the cruciate part of the sheath is more superficial and is a separate structure in its attachments from the annular part. The arrangement of the fibres, their density and the function are different as suggested by Henle (1871). Observations made during surgical procedures confirm that the two parts of the sheath are not continuous. The cruciate part may be thought to be continuous with the pretendinous fibres of the palmar aponeurosis while the annular rigid flexor pulleys are a deeper continuation of the fibres from the palmar aspect of the metacarpophalangeal joint and the deep transverse ligament of the palm (Grant, 1971). Bowing Distance. With the proximal interph.alangeal joint flexed to 90 °, the measurements of distance from the palmar surface of the volar plate to the dorsal surface of the two flexor tendons (the "bowing" distance), appeared to be constant, although it was difficult to obtain accurate measurements (B3). Longitudinal section of the chiasma tendinum only slightly changed these measurements (B3). It would seem that the "bowing" distance across the proximal interphalangeal joint in different fingers is generally constant in spite of the difference in finger lengths (A1) as a result of the proportional changes in the distance between the two margins of the proximal and distal flexor pulleys (A8a). The excursion of a tendon is thought to be a function of the degree of the angular movement of the joint and of the distance of the tendon from the axis of the joint, this last distance being related to the distance between the rigid edges of the two annular sheaths across the flexing joint (Landsmeer, 1955), and the diameter of the tendon. Our measurements support this concept since with the different lengths, e.g. in the little finger, there are proportional changes in (1) the excursion of the tendons during flexion (B5), (2) the "bowing" distance of the tendons at the level of the joint (B3), and (3) the distance separating the two margins of the annular flexor sheaths at the proximal interphalangeal joint (A8a). The Hand--Vol. 6
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Bands and Tendons of the Flexor Digitorum Superficialis Ulnar and Radial Scissura Bands. The beginning of the split of the flexor digitorum superficialis band occurred usually within the proximal annular flexor sheath, but the point of the commencement of that separation varied considerably (A8c). In a number of instances, the split occurred at the region of the metacarpophalangeal joint before the superficial band entered the proximal fibrous sheath. In an earlier study the split in this tendon was observed to occur at the level of the metacarpophalangeal joint, the tendon being broad and flat at the joint but becoming crescentic with its concavity towards the proximal phalanx (Henle, 1871). We observed this cupping of the tendon but it occurred rather within the proximal sheath. Measurements of width and observations made during the fibre shredding show that the tendon divides equally into ulnar and radial bands (A5, A6). The distance separating the ulnar and radial bands at the distal margin of the proximal sheath was greater in the index and middle fingers than in the ring and little fingers (A7a). This is a reflection of the greater anterioposterior flattening of the profundus tendon in the index and middle fingers. In this region the profundus tendon is broader on its dorsal aspect and narrower on its palmar surface (Martin, 1958). With the profundus removed and the proximal interphalangeal joint in full extension, the two scissura bands came closer together in all the fingers and the difference between the various fingers disappeared (A7b). These observations suggest that there is some "gripping" of the sides of the deep tendon which is held between the two scissura bands in the region of the distal part of the proximal sheath. This hugging effect is reflected in a lateral compression of the profundus tendon which becomes more oval as it passes onto the palmar surface of the chiasma tendinum and then between the terminal tendons of the superficialis. Measurements of the oval cross-section of the deep tendon for about 4 ram. of its length in the region of the chiasma tendinum and the terminal tendons of the superficialis showed that the width of the tendon in all fingers was about 1 ram. greater than its anterioposterior thickness. Ulnar and Radial T e r m i n a l T e n d o n s ( U T T , R T T ) . In the index and middle fingers the radial terminal tendon is wider than the ulnar terminal tendon (A10, All). In the ring and little fingers this difference is reversed. A cross-section of both these terminal tendons just distal to the proximal interphalangeal joint shows their configuration to be triangular with one angle palmar and one on each side dorsally. The length of the insertion of the ulnar and radial terminal tendons in all the fingers is practically the same (8 mm.). The site of the insertion is in the region of the proximal part of the lateral crests of the middle phalanx and is of interest because of its geometrical pattern. The shape of this insertion is like a triangle (Fig. 3) with the right angle proximal towards the midline of the phalanx, while the hypotenuse runs from the proximal and outer part of the crest to its distal and inner part. If both radial and ulnar insertions were to become confluent in the midline of the middle phalanx, they would form an isosceles triangle with the apex in the middle pointing distally and with the base parallel to the proximal surface of the phalanx and transverse axis of the joint. A dissection of the insertion of the profundus tendon into the distal phalanx shows that it has a similar triangular shape, as shown by Wilkinson (I953). On the bony surface of the palmar crests not occupied by the insertion of the superficialis tendon there are attachments of the collateral ligaments of the proximal interphalangeal joint and of the proximal part of the distal fibrous sheath. 126
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ertion ~ngle
RT"
U x
ial e RS ~B
)ST Proximal
Fig. 2 Untwisted scissura bands. Fig. 3 Components of the FDS with related synovial tissue; insertion triangle shown.
Chiasma Tendinum (CT) With the Fingers Extended at all joints. The length of the chiasma from its proximal point to its distal point varied with the size of the superficialis tendon and with the finger length, being least in the little finger (A9a (1)). The proximal point of the chiasma was always distal to the distal edge of the proximal fibrous sheath (A9a (2)). This means that with the proximal interphalangeal joint extended the chiasma was dorsal to the broad part of the profundus tendon and distal to its proximal pulley. Since the distal point of the chiasma was always found to be proximal to the proximal interphalangeal joint (A9b (1)), the chiasma in all the fingers with the joint extended lies posterior to the profundus tendon between the distal edge of the proximal flexor sheath and the proximal interphalangeal joint. The width of the fibre bundles (ulnar crossed band, radial crossed band) which crossed to form the chiasma were not equal in all the fingers (A9c, A9d). The width of both bands was approximately the same in the middle and ring fingers, but the values for the middle finger were greater than those of the ring finger. In the index finger the ulnar crossed band was consistently greater than its radial counterpart, while the reverse was present in the little finger. In four of the twenty hands dissected there was no evidence of any chiasma tendinum in the little finger (Agcd) or of the superficial tendon itself (A2); however, the radial and ulnar uncrossed bands, the flexor digitorum superficialis The Hand--Vol. 6
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band and the radial and ulnar scissura bands were present. These latter bands were attached or seemed to arise from the surrounding synovial tissue or from the underside of the proximal flexor sheath. In two of the little fingers in which the superficial tendon and its distal components were present, the chiasma tendinum had only a radial crossed band the ulnar crossed band being absent (A9c). In the chiasma tendinum of the little fingers, the radial crossed bands were wider and more frequently present than those of its ulnar counterpart (A9c, Agd).
There is a noticeable similarity in the fibre bundle pattern found in the little finger and that of the 2nd, 3rd, and 4th flexor digitorum brevis tendons in the foot. That is, there is usually only a single crossed band in the chiasma tendinum of these toes which corresponds to the radial dominance of the crossed bands seen in the little finger. W i t h the Fingers F l e x e d to 90 ° at t h e P r o x i m a l Interphalangeal Joint. When the chiasma was sectioned longitudinally with the profundus tendon present, no changes were observed in: (1) the distance separating the two terminal tendons (B1), (2) the distance from the tendons to the surface of the palmar plate of the proximal interphalangeal joint ("bowing" distance) (B3) or (3) in the excursion of the superficial tendon (B5). In the absence of the profundus tendon the section of the chiasma resulted in a smaller distance separating the two terminal tendons than when the chiasma was left intact (B2). When the superficial tendon moved proximally on flexion, the fibres of the chiasma came to lie at the distal edge of the proximal pulley. Usually half of the length of the chiasma is inside the flexor sheath, the distal half being out of it and beyond its distal edge (B4a). Also, the distance from distal point of the chiasma to the proximal interphalangeal joint (B4b) is almost doubled when compared with the extended position of the finger (A9b (1)). Dissection of the fibre bundles of the flexor digitorum superficialis. When the radial and ulnar scissura bands are separated distally from the superficial bands and untwisted in such a way that their inner surfaces face forwards, they present a midline X, the chiasma, which has on its sides the scissura bands, uncrossed bands, and distally the terminal tendons. The appearance is now like two I pillars on either side of the X = IXI (Fig. 2). This preparation allows the arrangement of the fibre bundles to be seen from their insertion to their origin within the scissura bands. These fibre bundles which insert more proximally and near the side of the middle phalanx on its palmar crest can be traced to the bundles at the outer side of the untwisted scissura band while those which are inserted more distally and centrally on the contralateral palmar crest cross in the chiasma and can be traced to the inner side of the untwisted scissura band. In other words, the scissura bands behave as two contrary helices twisting round the sides of the deep tendon (Fig. 3). Teasing out of the fibres of the chiasma to trace their origin, termination and relationship to each other demonstrates that sometimes the pattern of the fibre crossing is in the form of a lacing of the bundles. The fibres from the crossed band may split off and remain ipsilateral while the fibres usually destined to be ipsilateral may contribute to the crossed band of chiasma. DISCUSSION The precise location of the fibre bundles of a tendon at its insertion and the specific path they take within the tendon relative to each other may have considerable functional significance. The unique relationship, the similarity of the 128
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intratendinous fibre structure, and the pattern of insertion of the two flexor tendons in the fingers suggest such a significance. The anatomical features of these tendons have been known for years and recently investigated in detail in the flexor digitorum profundus tendon (Wilson, 1973). However, the functional and applied significance of these features is poorly understood. Our measurements indicate that differences in the finger length are reflected in the size of the two flexor tendons and in the different distance between the segments of the annular fibrous flexor sheath. The lengths of the fingers recorded here are in agreement with the primate pattern (Napier, 1962), although the index finger is not infrequently found to be slightly longer than the ring finger (Jones, 1942). The width of the tendons for the middle and ring fingers is greater than in the index and little fingers in man and other primates (Raven, 1950). The superficial tendon to the little finger, when present, was usually smaller and narrower than the corresponding deep flexor tendon. The width of the superficialis tendon at the base of the proximal phalanx was greater than that of the profundus; this was due to the broadening of the superficial tendon just prior to formation of its bands within the proximal annular flexor sheath. The profundus tendon is oval in cross-section at the base of the proximal phalanx after passing through the split of the superficialis tendon. This has been observed previously in the superficialis (Henle, 1871; Martin, 1958). The similarity of shape and insertion of both tendons means that the profundus tendon mirrors the structure of the superficialis but at a more distal position within the finger. The excursion of both tendons to flex the proximal interphalangeal joint to 90 ° was constant for each finger in a number of hands, though the excursion in the little finger was noticeably smaller. The values for the excursion of the two flexors in the radial three fingers were only 2 mm. less than those recorded earlier (Stack, 1963), a fact resulting from our use of a more limited range of flexion (00-90 °) at the proximal interphalangeal joint. It was possible also that limitations were imposed by the method of preservation of the cadaveric material. The excursion of the deep tendon when the interphalangeal joints were both flexed resulted in expected increases similar to the values previously recorded (Stack, 1963). However, there was a tendency for the index finger to be slightly favoured in its total excursion when compared with the profundus of the ring and middle fingers. The constancy of excursion of the flexor tendons was to be expected with varying finger lengths for the separation of the pulleys over which they act varied similarly. This distance separating the pulleys has been shown to determine the "bowing" of the tendons across a joint which was a factor in the shortening necessary for any particular change in joint angle (Landsmeer, 1954). In the little finger the superficial tendon was absent in about 20% of the hands studied and in the remaining hands it was less developed in proportion to the finger length than its counterpart in the radial three fingers. This was in agreement with other observations (Long, 1968). The deep tendon retained its size relative to the finger length. Where the superficial tendon was missing in the little finger, the more distal components of the tendon were present even including the split to accommodate the deep tendon. The size of these distal bands was proportional to the finger length. The width and the insertion pattern of the terminal tendons again reflected the finger size. EMG readings suggested that the superficial muscle was involved in activities to sustain increasing loads'o~ the proximal interphalangeal joint (Backhouse, 1968; Long, 1968). It was used when power was needed for long periods, when the hook grip was required and precision was minimal, and when the grip did not The Hand--Vol. 6
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require a finger tip hold (Napier, 1956). In these circumstances the most active muscle was the flexor superflcialis (Backhouse, 1968). There was a remarkable similarity between the pattern of the tendon bundles of the flexor digitorum brevis in the 2nd-4th toes and that in the little finger. The 5th toe showed no evidence of the tendon or its bands. This may reflect the loss of gripping function in the foot (Morton, 1966). A similar suggestion may be made with regard to the absence of the superficialis in the thumb and the little finger, the thumb taking no part in the hook grip and the little finger contributing to it only in a limited way. The palmar splitting of the superficial band into its two scissura bands occurred with great variation within the proximal flexor sheath, in some instances even occurring proximal to it. This splitting of the tendon over the lateral sides of the deep flexor tendon has been given significance as retention bands for the deep tendon, improving its leverage (Kaplan, 1965) or keeping the deep tendon from overstretching its proximal fibrous flexor sheath (Weitbrecht, 1742; Jones, 1942). In view of our observations that the splitting of the tendon within the finger is such a variable condition, its underdevelopment within the little finger, and the observation that the tendon sometimes fails to split (Bryce, 1923), its function as a retention band in the presence of a very strong annular flexo~ sheath is difficult to prove. Our measurements suggested that the radial and ulnar scissura bands at the distal margin of the proximal pulley appeared to "hug" the deep tendon passing over their inner surfaces. The removal of the deep tendon in the extended finger resulted in a closer approximation of the bands in the absence of any increased tension in the superficialis muscle other than the visco-elastic forces produced by extending the finger. The same effect was noticed in the distance separating the radial and ulnar terminal tendons at the distal edge of the proximal pulley when the joint was flexed by a pull on the superficialis tendon in the absence of the deep tendon. While longitudinal section of the chiasma tendinum of the superficial tendon did not change the distance between terminal tendons in the presence of the profundus tendon, the absence of the deep tendon resulted in their approximation. It is possible that the chiasma does have some effect on the pressure exerted by the superficialis bands on the lateral sides of the deep tendon but this requires further investigation. Our findings, however, for the variations in the splitting of the superficial tendon and for the possible pressure exerted by the two split bands of this tendon over the sides of the deep perforating tendon would support the earlier observation for the occurrence of nodular thickenings on the surface of the long flexor tendons being found at different locations along these tendons in triggering of the finger; and, that such nodules formed on the profundus tendon may result from a tight bifurcation of the superficialis tendon "rucking" the surface intratendinous fibres of the deep tendon as it glides through the tunnel of the superficial bands (Helal, 1970). We can offer no convincing comment on the function of the chiasma tendinum fibre bands during sustained flexion of the proximal interphalangeal joint, though its position is consistently dorsal to the deep tendon at the dis,~al edge of the proximal flexor sheath. In extension, the chiasma lays flat against the distal part of the proximal phalanx and against the palmar plate of the proximal interphalangeal joint, being attached by a vinculum breve to the palmar plate and synovial tissue. A study by one of the authors (Kuczynski, 1968) has shown that after removal of both flexor tendons of the finger, some of the capsular fibres and the cruciate part of the flexor sheath prevented hyperextension of the proximal interphalangeal joint. The 130
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palmar plate appeared to be tensed only in extreme hyperextension, while the collateral ligaments of the joint were not responsible for preventing hyperextension. It has been shown also that excision of the superficialis tendon when inserting a tendon graft t o replace the divided flexor digitorum profundus tendon may lead to a loss of the finger strength and balance and to a hyperextension deformity at the proximal interphalangeal joint (White, 1960; Jaffe, 1967). It seemed that the activity of the flexor superficialis muscle was a first line of defence against a hyperextension deformity at the proximal interphalangeal joint, stabilising it well before these other factors could come into play. The terminal tendons of the superficial tendon were triangular in cross section with one angle directed to the side and palmarly, forming between them a bed for lhe passage of the deep flexor tendon. They were formed by the union of uncrossed fibres and crossed ones from the chiasma tendinum. Since the scissura bands were always found equal in size, differences in the size of the radial and ulnar terminal tendons depend on the number of crossed bundles passing to each terminal tendon. In the index finger the radial was larger than the ulnar terminal tendon because the crossed band in the chiasma was contributing more fibres from the opposite scissura band to the radial terminal tendon than the crossed fibres from the radial scissura band to the ulnar terminal tendon. The terminal tendons on each side of the middle and ring fingers were of approximately the same size and so were their crossed bands. In the little finger, however, the values for the ulnar terminal tendon were greater than for the radial not only because the radial crossed bands of the chiasma were larger but also because they were more often present than their ulnar counterpart. In some little fingers there was no chiasma. Although the difference in size of the crossed bands in the chiasma and thus of the terminal tendons, is small, this difference takes on a greater significance when it is realised that the parallel collagen fibres which constitute these bands are capable of transmitting tensile forces which can reach from 15 to 30 kgs/mmY It is not unreasonable to expect then, that small differences in the size of the two crossed bands and the terminal tendons should reflect a difference in distribution of the forces which are applied at the small proximal interphalangeal joint. If the tendon size reflects the tension developed across the joint, the force? developed are likely to be similar in both terminal tendons in the middle and ring fingers, with the radial greater in the index and the ulnar greater in the little finger. The study of coronal deviation (abduction-adduction) at the proximal interphalangeal joint during flexion (Holcomb, 1958) shows that the index undergoes an ulnar deviation, while the little finger shows marked deviation in the radial direction. A study of the interphalangeal joint during flexion-extension movements (MacConaill, 1953) shows that a conjunct rotation occurs at the joint. This is dependent on the shape of the articular surfaces and the arrangement of the articular ligaments. Figure 4 shows the asymmetry of the condyles of the head of the proximal phalanx which could account for the deviation and conjunct rotation which occurs during flexion at the proximal interphalangeal joint (MacConaill, 1953; Kuczynski, 1968). The condylar surfaces being asymmetrical in both sagittal and coronal planes results in a mechanical effect which is related to the different forces applied to each condyle of a particular proximal interphalangeal joint. This aspect requires further detailed mechanical analysis. In the index finger the greater size of the radial terminal tendon would reflect a greater moment of force generated on the radial than on the ulnar side of the The Hand--Vol. 6
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Fig. 4 Asymmetry of the condyles of the head of the proximal phalanx. joint. This asymmetrical force may act in unison with the first dorsal interosseous muscle in counteracting the tendency of the interosseous muscles to produce ulnar deviation of the fingers (Backhouse, 1968; Kuczynski, 1972). These observations suggest that the use of a "slip" of the superficial tendon for reconstruction of a pulley system for the deep flexor m a y create an imbalance of forces in the remaining slip of the tendon unless its crossed fibres of the chiasma can be preserved. This attempt to preserve the chiasma may prove to be difficult in practice, thus some other means of constructing a pulley for the deep flexor tendon would appear more judicious than the use of a good intact terminal tendon and its proximal scissura band. ACKNOWLEDGEMENTS
We are grateful to Professor G. J. Romanes and to Dr. R. K. Johnson for their interest and advice in the preparation of this study and to Karen Kvenvold for the line drawings. REFERENCES
ALB1NUS, BERNARD S. (1734) Historia Musculorum Hominis. Le'dae Batavorum. 479, 639. ARNOLD, MAURICE (1968) Reconstructive Anatomy. A Method for the Study of Human Structure. Philadelphia, W. B. Saunders. 383, 385. BACKHOUSE, K. M. (1968) The Mechanics of Normal Digital Control In The Hand An:l An Analysis of the Ulnar Drift of Rheumatoid Arthritis. Annals of the Royal College of Surgeons of England. 43: 154-173. BRYCE. T. H. (1923) Quain's Elements of Anatomy. New York, Longmans, Green & Co. 4: No. 2. 133. CAMPER, P. (1769) Demonstrationum Antomico-Pathologicarum; liber primus. Amstelaedami. 4, 19. CUNNINGHAM, D. J. (1972) Textbook of Anatomy. Ed. by G. J. Romanes. llth Edition. London, Oxford University Press. 319. GRANT, J. C. B., and BASMAJIAN, J. V. (1971) Method of Anatomy by regions, descriptive and deductive. 8th Edition. Baltimore, Williams and Wilkins Co. 142. HELAL, B. (1970) Distal Profundus Entrapment in Rheumatoid Disease. The Hand. 2: 48-51. HENLE, F. G. J. (1871) Handbuch der Systematischen Anatomie des Menschen. 2nd Edition. Braunschweig. 1: Muskellehre. 236. 132
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Flexor Digitorum Superficialis Tendon in the' Fingers o[ the Human Hand--K. Kuczynski HOLCOMB, G. R., IRVING, T. E., and SMITH, R. D. (1958) Coronal Deviation And Tilt In the Proximal Interphalangeal Joints of Man. American Journal of Physical Anthropology. 16: 429-440. HOLLINSHEAD, W. H. (1958) Anatomy for Surgeons: Back and Limbs. Philadelphia, W. B. Saunders. Vol. 3. 522. HUESTON, J. T., and WILSON, W. F. (1972) The Aetiology of Trigger Finger. Explained on the Basis of Intratendinous Architecture. The Hand. 4: 257-260. JAFFE, S., and WECKESSER, E. (1967) Profundus Tendon Grafting with the Sublimis Intact. An End-Result Study of Thirty Patients. Journal of Bone and Joint Surgery. 49A: 1298-1308. JONES, F. W. (1942) The Principles of Anatomy as seen in the Hand. 2nd Edition. London, Bailli6re Tindall and Cox. 233, 295. JONES, F. W. (1944) The Foot. London, Bailli6re Tindall and Cox. 183. KAPLAN, E. B. (1950) Embryological Development of The Tendinous Apparatus of the Fingers. Relation To Function. Journal of Bone and Joint Surgery. 32A: 820-826. KAPLAN, E. B. (1965) Functional and Surgical Anatomy of the Hand. 2nd Edition. Philadelphia, J. B. Lippincott Company. 62. KNOX, ROBERT (1831) Cloquet's Anatomy. 2nd Edition. Privately printed. 319. KNOX, ROBERT (1853) Renshaw's Manual of Human Anatomy. Private printed. 193. KUCZYNSKI, K. (1968) The Proximal Interphalangeal Joint. Anatomy and Causes of Stiffness in the Fingers. Journal of Bone and Joint Surgery. 50B: 656-663. KUCZYNSKI, K. (1972) The Variations in the Insertion of the First Dorsal Interosseous Muscle and their Significance in Rheumatoid Arthritis. The Hand. 4: 37. LAMPE, E. W. (1969) Surgical Anatomy of the Hand. Clinical Symposia. New Jersey Ciba Pharmaceutical Products Inc. 75. LANDSMEER, J. M. F. (1954) Studies in the Anatomy of Articulation. I. The equilibrium of the "Intercalated" bone. Acta Morphologica Neerlando-Scandinavia. 3: 278-303. LANDSMEER, J. M. F. (1955) Anatomical And Functional Investigations On The Articulation Of The Human Fingers. Acta Anatomica. 25: Supplement 24, 5-69. LONG, CHARLES (1968) Intrinsic-Extrinsic Muscle Control of the Fingers. Electromyographic Studies. Journal of Bone and Joint Surgery. 50A: 973-984. MacCONAILL, M. A. (1953) The Movements Of Bones And Joints. 5. The Significance of Shape. Journal of BOne and Joint Surgery. 35B: 290-297. MACKENZIE, W. C. (1918) Action of Muscles including muscle rest and muscle re-education. Privately printed. 87. MARTIN. B. F. (1958) The Tendons of Flexor Digitorum Profundus. Journal of Anatomy. 92: 602-608. MORTON, D. J. (1935) The Human Foot. Its Evolution, Physiology and Functional Disorders. New York, Columbia University Press. 80. NAPIER, J. R. (1956) The Prehensile Movements Of The Human Hand. Journal of Bone and Joint Surgery. 38B: 902-913. NAPIER, J. R. (1962) The Evolution of the Hand. Scientific American. 207: 56-62. RAVEN, H. C. (1950) Anatomy of the Gorilla. Ed. by William Gregory. New York, Columbia University Press. 44, 67. STACK, H. G. (1963) A Study of Muscle Function in the Fingers. Annals of the Royal College of Surgeons of England. 33: 307-322. WEITBRECHT, JOSIAS (1969) Syndesmology. A Description of the Ligaments of the Human Body. Trans. by E. B. Kaplan. Philadelphia, W. B. Saunders Co. 37, 142. WHITE, WILLIAM L. (1960) Restoration of Function and Balance of the Wrist and Hand by Tendon Transfers. Surgical Clinics of North America. 40: No. 2. 427-459. WILKINSON, J. L. (1953) The Insertions Of The Flexors Pollicis Longus Et Digitorum Profundus. Journal of Anatomy. 87: 75-88. WILSON, W. F., and HUESTON, J. T. (1973) The Intratendinous Architecture of the Tendons of the Flexor Digitorum Profundus and Flexor Pollicis Longus. The Hand. 5: 33-38.
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