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Transthecal digital nerve block
TRANSTHECAL
DIGITAL NERVE BLOCK
An anatomical appraisal N. S. SARHADI and J. SHAW-DUNN
From the Department of Anatomy, University of Glasgow, Glasgow, UK Injection studies using methylene blue and latex were used in 60 digits from 40 cadavers to study how anaesthetic fluid injected into the flexor tendon sheath might spread around the proximal part of the finger. The injected solution escaped from the flexor tendon sheath around the vincular vessels which are present near the base and head of the proximal phalanx. Outside the digital canal, the dye flowed smoothly through the perivascular loose areolar tissue and spread alongside the main digital vessels and nerves and their palmar and dorsal branches. Journal of Hand Surgery (British and European Volume, 1998) 23B: 4." 490-493 Chiu (1990) observed that after the injection of steroid and lignocaine into the flexor tendon sheath during the treatment of a trigger finger, the entire finger became numb. In anatomical investigations he showed that after injection of methylene blue into the flexor tendon sheath there was "complete staining of the entire flexor tendon sheath and centrifugal diffusion of the blue dye circumscribing the entire circumference of the proximal phalanx". There was also staining of all the palmar and dorsal digital nerves. This type of digital block has since been reported to have a rapid onset of action and require only a small volume of anaesthetic solution (Chin, 1990; Morrison, 1993; Morros et al, 1993; Ramamurthy and Hickey, 1993). However, Chevaleraud et al (1993) did not find anaesthesia of the dorsum of the finger in all cases. Some authors consider the transthecal method to be as effective as a traditional digital nerve block (Hill et al, 1995) and others have found it gives results comparable to the newer single injection subcutaneous digital blocks both in experimental and clinical situations, (Low et al, 1997 a; b). Intrathecal anaesthesia appears to be safe and effective without causing any long term damage to the tendon sheath. In our clinical cases, on injection of 3 ml of local anaesthetic solution into the flexor tendon sheath at the level of the distal palmar crease as described by Chiu (1990), it was observed that a swelling appeared first on the sides and then on the dorsum of the finger at the metacarpophalangeal and proximal interphalangeal joint levels. Even when a small volume of 0.5 to 1 ml had been injected, a thrill was felt and a patch of skin became pale and shiny, with flattening of fine skin Creases, increased tissue turgidity and numbness to needle prick. On further injection the effect spread over a wider area. However, there was a zone of normal looking skin and subcutaneous tissue between the affected areas over the metacarpophalangeal joint and around the proximal interphalangeal joint. These observations suggested that local anaesthetic injected into the flexor tendon sheath appears at specific points on the sides and the dorsum of the finger i.e. at the metacarpophalangeal or proximal interphalangeal level. This prompted us to investigate the anatomical basis of the transthecal digital nerve block.
MATERIAL AND METHODS Methylene blue injections
Experiment 1 Here, 3 ml of 5% methylene blue dye solution was injected into the proximal part of the flexor tendon sheath in five cadaver digits, through a percutaneous puncture at the level of the distal palmar crease. This reproduced the local injection in the clinical setting described by Chiu (1990). Injection was stopped when blotches of the dye or a swelling were seen at the sides of the finger at the proximal interphalangeal or metacarpophalangeal joint. These signs showed that sufficient dye had been injected to demonstrate the path of diffusion; further injection is apt to lead to indiscriminate staining and flooding of the tissues. The dorsum of each finger and the thumb were then exposed through a midline incision and the skin flaps retracted laterally to investigate the areas of staining. The skin was excised from the palmar aspect of the distal phalanx, to confirm that the dye injection had reached the distal flexor tendon sheath, and to see if there was a generalized flooding of the dye in the subcutaneous tissue.
Experiment 2 In 20 digits from 20 cadavers, a much smaller volume (1 ml) of methylene blue dye was injected at the level of the proximal digital crease. Four of each digit (thumb, index, etc.) were used and both neurovascular bundles were then exposed through midlateral incisions to see if there was injected dye around the nerves. The dorsum of the digits was exposed by raising the skin flaps, and the dye tracks in the fibrofatty tissue followed to identify where the dye had escaped from the flexor tendon sheath. In five digits, from thumb to little finger but in different cadaveric hands, the volume of the injected solution was further reduced to 0.5 ml, and given at the level of the proximal digital crease. Windows were created on the palmar surface of the proximal, middle and the distal phalanges to examine the subcutaneous tissues. The fingers were then explored by midline dorsal and palmar incisions. 490
TRANSTHECALDIGITALNERVEBLOCK
Experiment 3 Here, 3 ml of 5% methylene blue solution was injected into the flexor tendon sheath by a percutaneous puncture at the level of the DIP crease in ten digits. The needle was advanced through the tough tendon tissue and the injection given behind the tendon, inside the sheath. The fingers were explored through midline incisions on the dorsum and the skin flaps retracted laterally. Skin was excised from the palmar aspect of the fingers at the proximal phalanx to examine the neurovascular bundles. The palms were explored at the level of the distal palmar crease to confirm if the dye was present in the flexor tendon sheath.
Latex solution injections Methylene blue dye in aqueous solution spreads in the tissues during dissection. Further experiments were carried out, using latex mixed with yellow dye. Latex has a thicker consistency and sets in the tissues through which it flows. The hands used for these experiments had the blood vessels injected earlier with latex and Indian ink. The flexor tendon sheath o f each digit was injected with 1 to 3 ml of the latex at the level of the proximal digital crease in 20 digits. The end point was the visualization of the yellow pigment on the dorsum of the finger. The specimens were left for 2 weeks, to allow the latex to solidify. The digits were explored through dorsal midline incisions to visualize the regions of the proximal interphalangeal joints and the metacarpophalangeal joints. Windows were created by excising the palmar skin over each phalanx and the palm to see any generalized staining of the fat or spillage into the palm proximally. The interior of the flexor tendon sheath was examined. The tracks of solidified latex were followed from within the tendon sheath outwards. The neurovascular bundles were exposed via a midlateral incision and then the flexor tendon sheaths were explored by excising the skin and subcutaneous tissue from the palmar side. The route taken by the latex from the tendon sheath to the neurovascular bundle was noted.
491 middle or the ring finger did not produce deep staining in the proximal palm. This reflects the different lengths of the synovial sheath and indicates that the fluid does not escape from the proximal end of the synovial sheath (Fig 1).
Experiment 2 On injection of a small volume (0.5 ml) of the dye into the flexor tendon sheath the staining was seen to appear on the dorsum of the digit at the base of the proximal phalanx, and around the proximal interphalangeal joint. The dye could easily be seen tracking alongside the vessels. There was no generalized flooding but only linear staining of the subcutaneous fatty tissue. The nerves were not stained by the dye solution. Deeper staining was present at the base of the proximal phalanx or in the region of the middle phalanx. On exerting gentle pressure on the tendon sheath ballooning of the dye containing channels could be appreciated. After transthecal injection of 1 ml of methylene blue, exploration showed a pool of dye around the neurovascular bundles but the fat on the palmar aspect did not show generalized staining. The pooling of the dye was seen in the tissue space enclosed by Cleland's ligament and Grayson's ligament, right up to the tip of the finger.
Latex solution injections Dissection confirmed the impression given by the methylene blue injections. Set latex was present on the dorsum
RESULTS
Methylene blue injections Experiments 1 and 3 In the digits where 3 ml of solution had been injected, irrespective of the site of puncture of the flexor tendon sheath, there were blotchy dye stains on the dorsum of the proximal part of the finger at the sides of the proximal interphalangeal joint and the metacarpophalangeal joint. There was also staining of both the neurovascular bundles and the flexor tendon sheath. Injections into the thumb base and the little finger produced dye stains at the level of the wrist. However, injections into the index,
Fig 1 2 ml methylene blue injection given at the level of the distal interphalangeal joint in the index finger. The palmar skin has been excisedto show the synovial sheath. There is dye around the main neurovascularbundles 'V' and in the tendon synovial sheaths (arrow). There is no escape of methylene blue dye proximallyinto the palm.
492
T H E J O U R N A L OF H A N D SURGERY VOL. 23B No. 4 AUGUST 1998
of the proximal interphalangeal joint and it had a greater concentration around the vessels and nerve of the neurovascular bundle. There was no generalized pooling of latex in the subcutaneous tissue. DISCUSSION The injected dye solution seemed to escape from the flexor tendon sheath through the perivascular tissue of the vincular vessels and their parent vessels and to spread along the neurovascular bundles (Figs 2, 3). There was no generalized sieve-like diffusion from the length of the flexor tendon sheath. There was no escape of the injected solution proximally into the palm. However, once the fluid reached the perivascular loose areolar tissue, it spread along the main digital nerves and their branches. Our findings are consistent with the observation of Chiu (1990) that there is a "centrifugal circumferential" spread o f the anaesthetic agent at the level of the base of the proximal phalanx. The dye was found around the proximal interphalangeal joint and the metacarpophalangeal joint area. However, its mechanism is not a simple diffusion through the sheath as concluded by Chiu (1990) nor simply the effect of local pooling of the anaesthetic agent around the main digital vessels and nerves as inferred by Morros et al (1993). It seems that the volume injected and the pressure applied by the previous investigators produced generalized staining and flooding of the dye solution. We injected much smaller volumes of the tracer dye to delineate the path of flow, and used latex injections to avoid smudging during dissections. As in our clinical practice no external pressure was exerted over the flexor tendon sheath.
If the distribution of the anaesthetic solution in the digit is determined by the extent of the digital synovial sheath, then the level of injection should be immaterial as the fluid will very quickly fill the whole sheath. This was demonstrated in our experiments using methylene blue solution injected at different levels. The present study shows that the injected solution seems to escape from the tendon sheath alongside the vincular vessels. It then flows through the perivascular loose areolar tissue alongside the neurovascular bundles and their branches (Figs 2, 3). The injected dye solution appeared first in the region of the base of the proximal phalanx and the proximal interphalangeal joint. This distribution could also be explained on the basis of the blood supply of the flexor tendons in the finger (Edwards, 1946; Leddy, 1993; Ochiai et al 1979; Zbrodowski and Gajisin, 1991). There was an early appearance of the dye, mainly in the regions where larger feeding vessels to the flexor tendon are present, namely the base of the proximal phalanx and the proximal interphalangeal region. As the dye escapes along the course of the vincular vessels, it obtains access to the loose areolar tissue around the parent vessels and the accompanying nerves. If local anaesthetic injected into the flexor tendon sheath follows the pattern of distribution of the injected dye, it will be distributed near the main nerves and their
Dist. trans dig. artery Inter. tran
dig. artery
PIPJ -
Prox. tran dig. artery
VBS
.=cted d Branc to VU
MCPJ Common
dig. artery
cular ;sels
Fig 2 Suggested path of flow of the injected fluid from the flexor tendon sheath to reach the nerves, shown in a cross section of the finger. T = tendon. B = phalangeal bone. The fluid flows smoothly through the loose areolar tissue in the perivascular space, shown as lines.
Fig. 3 The flowof the injectedfluidfrom the tendon sheath. The main vincular vessels and the transverse digital vessels alongside which the fluid escapes from the flexor tendon sheath are situated mainlyin the proximalpart of the finger. MCPJ= metacarpophalangealjoint; PIPJ=proximal interphalangealjoint; VBS=vinculumbrevesuperficialis;VLS=vinculum longum superficialis;FDS=flexordigitorumsuperficialis;FDP= flexor digitorum profundus; VLP=vinculum longum profundi; VBP=vincnlum breve profundi. Reproducedwith kind permission of WB Saunders, Philadelphia, from Leddy(1993).
TRANSTHECAL DIGITAL NERVE BLOCK
branches. This may explain why transthecal digital anaesthetic block has a rapid onset of action as first noticed during the treatment of trigger finger by Chiu (1990). The close proximity of the anaesthetic agent to the main nerves and their smaller branches may explain why only a small volume of the anaesthetic agent is required. After the injection, very little fluid remains inside the sheath because most of it comes to lie in the tissues surrounding the main vessels and their branches which run alongside the digital nerves and their branches. Our anatomical study demonstrates that a solution injected into the flexor tendon sheath of the digits, escapes from the tendon sheath in the region of the vincular vessels. There is a smooth flow of the fluid through the loose areolar perivascular tissue as it passes along side the main digital vessels and their branches to the proximal part and the dorsum of the digit. Acknowledgements The authors wish to thank Mr C. Bainbridge, consultant hand and plastic surgeon, Derbyshire Royal Infirmary for demonstrating the technique of digital block; Mr Anthony Patton and Mr G Reford from the Department of Anatomy for their help; Bill Paterson, Jean MacDonald and the staff at Medical Illustrations, Glasgow Royal Infirmary for the photographs and the illustrations and Mr D. S. Soutar for his support and comments.
References Chevaleraud E, Ragot JM, Brunelle E, Dumontier C, Brunelli F (1993). Anesth6sie locale digitale par la gaine des fl~chisseurs. Local anaesthesia
493 of the finger using the flexor tendon sheath. Annales Fran~aises d'Anesthesie et de R6animation, 12: 237-240. Chiu DT (1990). Transthecal digital block: flexor tendon sheath used for anesthetic infusion. Journal of Hand Surgery, 15A: 471M73. Edwards DAW (1946). The blood supply and lymphatic drainage of tendons. Journal of Anatomy, 80: 147-152. Hill RG, Patterson JW, Parker JC, Bauer J, Wright E, Heller MB (1995). Comparison of transthecal digital block and traditional digital block for anesthesia of the finger. Annals of Emergency Medicine, 25:604 607. Leddy JR Flexor tendons-acute injuries. In: Green DP (Ed) Operative hand surgery, ,3rd edn. New York, Churchill Livingstone, 1993, Vol. 2: 1824-1826. Low CK, Vartany A, Engstrom JW, Poncelet A, Diao E (1997a). Comparison of transthecal and subcutaneous single-injection digital block techniques. Journal of Hand Surgery, 22A: 901-905. Low CK, Wong HP, Low YP (1997b). Comparison between single injection transthecal and subcutaneous digital blocks. Journal of Hand Surgery, 22B: 582-584. Morrison WG (1993). Transthecal digital block. Archives of Emergency Medicine, 10: 35-38. Morros C, Perez D, Raurell A, Rodriguez JE (1993). Digital anaesthesia through the flexor tendon sheath at the palmar level. International Orthopaedics, 17: 273-274. Ochiai N, Matsui T, Miyaji N, Merklin RJ, Hunter JM (1979). Vascular anatomy of flexor tendons. I. Vincular system and blood supply of the profundus tendon in the digital sheath, Journal of Hand Surgery, 4:321 330. Ramamurthy S, Hickey R. Anesthesia. In: Green DP (Ed) Operative hand surgery, 3rd edn. New York, Churchill Livingstone, 1993, Vol. 1: 41. Zbrodowski A, Gajisin S (1991). Tendineal arteries of the flexor tendons in the human hand. Clinical Anatomy, 4: 348-356.
Received: 10 December 1997 Accepted after revision:23 March 1998 Mr N. S. Sarhadi, c/o Dr J. Sbaw-Dunn, Department of Anatomy,The Universityof Glasgow, GlasgowG12 8QQ, UK. © 1998The British Societyfor Surgery of the Hand
DIGITAL NERVE BLOCK
An anatomical appraisal N. S. SARHADI and J. SHAW-DUNN
From the Department of Anatomy, University of Glasgow, Glasgow, UK Injection studies using methylene blue and latex were used in 60 digits from 40 cadavers to study how anaesthetic fluid injected into the flexor tendon sheath might spread around the proximal part of the finger. The injected solution escaped from the flexor tendon sheath around the vincular vessels which are present near the base and head of the proximal phalanx. Outside the digital canal, the dye flowed smoothly through the perivascular loose areolar tissue and spread alongside the main digital vessels and nerves and their palmar and dorsal branches. Journal of Hand Surgery (British and European Volume, 1998) 23B: 4." 490-493 Chiu (1990) observed that after the injection of steroid and lignocaine into the flexor tendon sheath during the treatment of a trigger finger, the entire finger became numb. In anatomical investigations he showed that after injection of methylene blue into the flexor tendon sheath there was "complete staining of the entire flexor tendon sheath and centrifugal diffusion of the blue dye circumscribing the entire circumference of the proximal phalanx". There was also staining of all the palmar and dorsal digital nerves. This type of digital block has since been reported to have a rapid onset of action and require only a small volume of anaesthetic solution (Chin, 1990; Morrison, 1993; Morros et al, 1993; Ramamurthy and Hickey, 1993). However, Chevaleraud et al (1993) did not find anaesthesia of the dorsum of the finger in all cases. Some authors consider the transthecal method to be as effective as a traditional digital nerve block (Hill et al, 1995) and others have found it gives results comparable to the newer single injection subcutaneous digital blocks both in experimental and clinical situations, (Low et al, 1997 a; b). Intrathecal anaesthesia appears to be safe and effective without causing any long term damage to the tendon sheath. In our clinical cases, on injection of 3 ml of local anaesthetic solution into the flexor tendon sheath at the level of the distal palmar crease as described by Chiu (1990), it was observed that a swelling appeared first on the sides and then on the dorsum of the finger at the metacarpophalangeal and proximal interphalangeal joint levels. Even when a small volume of 0.5 to 1 ml had been injected, a thrill was felt and a patch of skin became pale and shiny, with flattening of fine skin Creases, increased tissue turgidity and numbness to needle prick. On further injection the effect spread over a wider area. However, there was a zone of normal looking skin and subcutaneous tissue between the affected areas over the metacarpophalangeal joint and around the proximal interphalangeal joint. These observations suggested that local anaesthetic injected into the flexor tendon sheath appears at specific points on the sides and the dorsum of the finger i.e. at the metacarpophalangeal or proximal interphalangeal level. This prompted us to investigate the anatomical basis of the transthecal digital nerve block.
MATERIAL AND METHODS Methylene blue injections
Experiment 1 Here, 3 ml of 5% methylene blue dye solution was injected into the proximal part of the flexor tendon sheath in five cadaver digits, through a percutaneous puncture at the level of the distal palmar crease. This reproduced the local injection in the clinical setting described by Chiu (1990). Injection was stopped when blotches of the dye or a swelling were seen at the sides of the finger at the proximal interphalangeal or metacarpophalangeal joint. These signs showed that sufficient dye had been injected to demonstrate the path of diffusion; further injection is apt to lead to indiscriminate staining and flooding of the tissues. The dorsum of each finger and the thumb were then exposed through a midline incision and the skin flaps retracted laterally to investigate the areas of staining. The skin was excised from the palmar aspect of the distal phalanx, to confirm that the dye injection had reached the distal flexor tendon sheath, and to see if there was a generalized flooding of the dye in the subcutaneous tissue.
Experiment 2 In 20 digits from 20 cadavers, a much smaller volume (1 ml) of methylene blue dye was injected at the level of the proximal digital crease. Four of each digit (thumb, index, etc.) were used and both neurovascular bundles were then exposed through midlateral incisions to see if there was injected dye around the nerves. The dorsum of the digits was exposed by raising the skin flaps, and the dye tracks in the fibrofatty tissue followed to identify where the dye had escaped from the flexor tendon sheath. In five digits, from thumb to little finger but in different cadaveric hands, the volume of the injected solution was further reduced to 0.5 ml, and given at the level of the proximal digital crease. Windows were created on the palmar surface of the proximal, middle and the distal phalanges to examine the subcutaneous tissues. The fingers were then explored by midline dorsal and palmar incisions. 490
TRANSTHECALDIGITALNERVEBLOCK
Experiment 3 Here, 3 ml of 5% methylene blue solution was injected into the flexor tendon sheath by a percutaneous puncture at the level of the DIP crease in ten digits. The needle was advanced through the tough tendon tissue and the injection given behind the tendon, inside the sheath. The fingers were explored through midline incisions on the dorsum and the skin flaps retracted laterally. Skin was excised from the palmar aspect of the fingers at the proximal phalanx to examine the neurovascular bundles. The palms were explored at the level of the distal palmar crease to confirm if the dye was present in the flexor tendon sheath.
Latex solution injections Methylene blue dye in aqueous solution spreads in the tissues during dissection. Further experiments were carried out, using latex mixed with yellow dye. Latex has a thicker consistency and sets in the tissues through which it flows. The hands used for these experiments had the blood vessels injected earlier with latex and Indian ink. The flexor tendon sheath o f each digit was injected with 1 to 3 ml of the latex at the level of the proximal digital crease in 20 digits. The end point was the visualization of the yellow pigment on the dorsum of the finger. The specimens were left for 2 weeks, to allow the latex to solidify. The digits were explored through dorsal midline incisions to visualize the regions of the proximal interphalangeal joints and the metacarpophalangeal joints. Windows were created by excising the palmar skin over each phalanx and the palm to see any generalized staining of the fat or spillage into the palm proximally. The interior of the flexor tendon sheath was examined. The tracks of solidified latex were followed from within the tendon sheath outwards. The neurovascular bundles were exposed via a midlateral incision and then the flexor tendon sheaths were explored by excising the skin and subcutaneous tissue from the palmar side. The route taken by the latex from the tendon sheath to the neurovascular bundle was noted.
491 middle or the ring finger did not produce deep staining in the proximal palm. This reflects the different lengths of the synovial sheath and indicates that the fluid does not escape from the proximal end of the synovial sheath (Fig 1).
Experiment 2 On injection of a small volume (0.5 ml) of the dye into the flexor tendon sheath the staining was seen to appear on the dorsum of the digit at the base of the proximal phalanx, and around the proximal interphalangeal joint. The dye could easily be seen tracking alongside the vessels. There was no generalized flooding but only linear staining of the subcutaneous fatty tissue. The nerves were not stained by the dye solution. Deeper staining was present at the base of the proximal phalanx or in the region of the middle phalanx. On exerting gentle pressure on the tendon sheath ballooning of the dye containing channels could be appreciated. After transthecal injection of 1 ml of methylene blue, exploration showed a pool of dye around the neurovascular bundles but the fat on the palmar aspect did not show generalized staining. The pooling of the dye was seen in the tissue space enclosed by Cleland's ligament and Grayson's ligament, right up to the tip of the finger.
Latex solution injections Dissection confirmed the impression given by the methylene blue injections. Set latex was present on the dorsum
RESULTS
Methylene blue injections Experiments 1 and 3 In the digits where 3 ml of solution had been injected, irrespective of the site of puncture of the flexor tendon sheath, there were blotchy dye stains on the dorsum of the proximal part of the finger at the sides of the proximal interphalangeal joint and the metacarpophalangeal joint. There was also staining of both the neurovascular bundles and the flexor tendon sheath. Injections into the thumb base and the little finger produced dye stains at the level of the wrist. However, injections into the index,
Fig 1 2 ml methylene blue injection given at the level of the distal interphalangeal joint in the index finger. The palmar skin has been excisedto show the synovial sheath. There is dye around the main neurovascularbundles 'V' and in the tendon synovial sheaths (arrow). There is no escape of methylene blue dye proximallyinto the palm.
492
T H E J O U R N A L OF H A N D SURGERY VOL. 23B No. 4 AUGUST 1998
of the proximal interphalangeal joint and it had a greater concentration around the vessels and nerve of the neurovascular bundle. There was no generalized pooling of latex in the subcutaneous tissue. DISCUSSION The injected dye solution seemed to escape from the flexor tendon sheath through the perivascular tissue of the vincular vessels and their parent vessels and to spread along the neurovascular bundles (Figs 2, 3). There was no generalized sieve-like diffusion from the length of the flexor tendon sheath. There was no escape of the injected solution proximally into the palm. However, once the fluid reached the perivascular loose areolar tissue, it spread along the main digital nerves and their branches. Our findings are consistent with the observation of Chiu (1990) that there is a "centrifugal circumferential" spread o f the anaesthetic agent at the level of the base of the proximal phalanx. The dye was found around the proximal interphalangeal joint and the metacarpophalangeal joint area. However, its mechanism is not a simple diffusion through the sheath as concluded by Chiu (1990) nor simply the effect of local pooling of the anaesthetic agent around the main digital vessels and nerves as inferred by Morros et al (1993). It seems that the volume injected and the pressure applied by the previous investigators produced generalized staining and flooding of the dye solution. We injected much smaller volumes of the tracer dye to delineate the path of flow, and used latex injections to avoid smudging during dissections. As in our clinical practice no external pressure was exerted over the flexor tendon sheath.
If the distribution of the anaesthetic solution in the digit is determined by the extent of the digital synovial sheath, then the level of injection should be immaterial as the fluid will very quickly fill the whole sheath. This was demonstrated in our experiments using methylene blue solution injected at different levels. The present study shows that the injected solution seems to escape from the tendon sheath alongside the vincular vessels. It then flows through the perivascular loose areolar tissue alongside the neurovascular bundles and their branches (Figs 2, 3). The injected dye solution appeared first in the region of the base of the proximal phalanx and the proximal interphalangeal joint. This distribution could also be explained on the basis of the blood supply of the flexor tendons in the finger (Edwards, 1946; Leddy, 1993; Ochiai et al 1979; Zbrodowski and Gajisin, 1991). There was an early appearance of the dye, mainly in the regions where larger feeding vessels to the flexor tendon are present, namely the base of the proximal phalanx and the proximal interphalangeal region. As the dye escapes along the course of the vincular vessels, it obtains access to the loose areolar tissue around the parent vessels and the accompanying nerves. If local anaesthetic injected into the flexor tendon sheath follows the pattern of distribution of the injected dye, it will be distributed near the main nerves and their
Dist. trans dig. artery Inter. tran
dig. artery
PIPJ -
Prox. tran dig. artery
VBS
.=cted d Branc to VU
MCPJ Common
dig. artery
cular ;sels
Fig 2 Suggested path of flow of the injected fluid from the flexor tendon sheath to reach the nerves, shown in a cross section of the finger. T = tendon. B = phalangeal bone. The fluid flows smoothly through the loose areolar tissue in the perivascular space, shown as lines.
Fig. 3 The flowof the injectedfluidfrom the tendon sheath. The main vincular vessels and the transverse digital vessels alongside which the fluid escapes from the flexor tendon sheath are situated mainlyin the proximalpart of the finger. MCPJ= metacarpophalangealjoint; PIPJ=proximal interphalangealjoint; VBS=vinculumbrevesuperficialis;VLS=vinculum longum superficialis;FDS=flexordigitorumsuperficialis;FDP= flexor digitorum profundus; VLP=vinculum longum profundi; VBP=vincnlum breve profundi. Reproducedwith kind permission of WB Saunders, Philadelphia, from Leddy(1993).
TRANSTHECAL DIGITAL NERVE BLOCK
branches. This may explain why transthecal digital anaesthetic block has a rapid onset of action as first noticed during the treatment of trigger finger by Chiu (1990). The close proximity of the anaesthetic agent to the main nerves and their smaller branches may explain why only a small volume of the anaesthetic agent is required. After the injection, very little fluid remains inside the sheath because most of it comes to lie in the tissues surrounding the main vessels and their branches which run alongside the digital nerves and their branches. Our anatomical study demonstrates that a solution injected into the flexor tendon sheath of the digits, escapes from the tendon sheath in the region of the vincular vessels. There is a smooth flow of the fluid through the loose areolar perivascular tissue as it passes along side the main digital vessels and their branches to the proximal part and the dorsum of the digit. Acknowledgements The authors wish to thank Mr C. Bainbridge, consultant hand and plastic surgeon, Derbyshire Royal Infirmary for demonstrating the technique of digital block; Mr Anthony Patton and Mr G Reford from the Department of Anatomy for their help; Bill Paterson, Jean MacDonald and the staff at Medical Illustrations, Glasgow Royal Infirmary for the photographs and the illustrations and Mr D. S. Soutar for his support and comments.
References Chevaleraud E, Ragot JM, Brunelle E, Dumontier C, Brunelli F (1993). Anesth6sie locale digitale par la gaine des fl~chisseurs. Local anaesthesia
493 of the finger using the flexor tendon sheath. Annales Fran~aises d'Anesthesie et de R6animation, 12: 237-240. Chiu DT (1990). Transthecal digital block: flexor tendon sheath used for anesthetic infusion. Journal of Hand Surgery, 15A: 471M73. Edwards DAW (1946). The blood supply and lymphatic drainage of tendons. Journal of Anatomy, 80: 147-152. Hill RG, Patterson JW, Parker JC, Bauer J, Wright E, Heller MB (1995). Comparison of transthecal digital block and traditional digital block for anesthesia of the finger. Annals of Emergency Medicine, 25:604 607. Leddy JR Flexor tendons-acute injuries. In: Green DP (Ed) Operative hand surgery, ,3rd edn. New York, Churchill Livingstone, 1993, Vol. 2: 1824-1826. Low CK, Vartany A, Engstrom JW, Poncelet A, Diao E (1997a). Comparison of transthecal and subcutaneous single-injection digital block techniques. Journal of Hand Surgery, 22A: 901-905. Low CK, Wong HP, Low YP (1997b). Comparison between single injection transthecal and subcutaneous digital blocks. Journal of Hand Surgery, 22B: 582-584. Morrison WG (1993). Transthecal digital block. Archives of Emergency Medicine, 10: 35-38. Morros C, Perez D, Raurell A, Rodriguez JE (1993). Digital anaesthesia through the flexor tendon sheath at the palmar level. International Orthopaedics, 17: 273-274. Ochiai N, Matsui T, Miyaji N, Merklin RJ, Hunter JM (1979). Vascular anatomy of flexor tendons. I. Vincular system and blood supply of the profundus tendon in the digital sheath, Journal of Hand Surgery, 4:321 330. Ramamurthy S, Hickey R. Anesthesia. In: Green DP (Ed) Operative hand surgery, 3rd edn. New York, Churchill Livingstone, 1993, Vol. 1: 41. Zbrodowski A, Gajisin S (1991). Tendineal arteries of the flexor tendons in the human hand. Clinical Anatomy, 4: 348-356.
Received: 10 December 1997 Accepted after revision:23 March 1998 Mr N. S. Sarhadi, c/o Dr J. Sbaw-Dunn, Department of Anatomy,The Universityof Glasgow, GlasgowG12 8QQ, UK. © 1998The British Societyfor Surgery of the Hand