Dean O. Smith, Naoya Tajima, Chikayoshi Oura, and Kiyotaka Toshimori
DIGITAL ARTERY TORTUOSITY AND ELASTICITY:
Downloaded by: Universite Laval. Copyrighted material.
A BIOMECHANICAL STUDY ABSTRACT The gross structure of the digital artery distal to the proximal interphalangeal joint is significantly different from its proximal portion. Previous research in this laboratory has revealed that over half of all fingers exhibit marked tortuosity of this artery in juxtaposition to the distal interphalangeal joint. Any structure with a large amount of bending will have the properties of a spring. An understanding of these properties may help in creating tension-free anastomoses during finger tip replantation. The elastic strength and energy storage capacities of the distal digital artery were measured in 26 cadaver arteries.
Replantation of finger amputations is one of the most commonly performed reconstructive microsurgical procedures.1 Attention to anatomic detail is important in order to achieve any degree of success in surgery. In a study of the gross anatomy of the digital artery, it was discovered that there is often bending of this vessel near the distal interphalangeal joint. 23 The purpose of this study was to see if these bends have any of the characteristics of a spring, and if so, to quantify the intrinsic tensile strength of the digital artery in this region.
MATERIAL AND METHODS Fingers were taken at random from Japanese cadaver specimens after completion of the gross anatomy course at the Miyazaki Medical College. A total of 67 digits had their digital arteries dissected free along their entire course, from the proximal interphalangeal joint distally. Of these 134 radial and ulnar arteries, 69 (51.5 percent) had deflections in their course measuring at least 270 degrees. This is one type in the recently devised classification of arterial tortuosity of Smith,3 an example of which can be seen in Figure 1. Fifteen of
these tortuous arteries along with six non-tortuous control arteries were subjected to tensile stretch of 2 and 5 mm. The technique used for recording linear tension in microsurgical systems has been previously reported,4 but can be summarized as follows. In a standard electronic balance scale, a vernier caliper is suspended over the weighing pan assembly. A clip is attached to the vernier caliper, and a second counter weight of known mass (which also has a clip incorporated into it) is placed on the weighing pan. A 2.2-cm segment of digital artery is then connected to the caliper suspended over the counter weight and simultaneously clamped to the balance weight on the scale's weighing pan. Gripped at 2 cm length, the artery hanging above the scale causes no reduction in the counter weight on the pan, as it is at zero tension. When the carriage of the vernier caliper is moved up 2 mm, it lifts up on the much heavier counter weight, thus stretching the artery and resulting in a decreased weight measured on the scale. Weight in grams for this laboratory's scale is accurate to .01 mg and distance stretched to a tolerance of 0.1 mm for the vernier caliper. Because grams of weight are measured against the gravitational constant of the earth, weights can be readily changed to energy units simply by multiplying
Departments of Orthopedic Surgery and Anatomy, Miyazaki Medical College, Miyazaki, Japan Reprint requests-. Dr. Smith, 808 East Wakefield, Sikeston, MO 63801 Accepted for publication October 15, 1990 Copyright © 1991 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
105
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 7, NUMBER 2
APRIL 1991
distribution for small samples shows that they are not statistically significant.6 For these specimens, the adventitia comprises 25.9 percent and 33.9 percent of the vessels' total weight. Figure 2 is a graph of the individual measurements for each artery, showing the stress in dynes for 2 and 5 mm of linear tension or stretch. Because of the tremendous variation in compliance of these vessels, the results are plotted on a log scale. Table 2 shows a comparison of arteries with 270° tortuosity stretched 2 and 5 mm versus control vessels that are straight. It is evident that if an artery is tortuous, the distance it can stretch before pulling up on the counter weight is greater. Highly tortuous arteries, io£
(+) With Adventitia (-)Without Straight •
io
4
•
Adventitia Artery
Tortuous Artery
:l \ ""
2 by the conversion factor 981 cm/sec2, which gives en- dynes/mm stress • • ergy units in dynes.5 The decrease in gram weight is the amount of energy in dynes stored in the artery after stretching it 2 or 5 mm. Shortening the vessel back, to : • io 3 the original length returns all of the energy or weight to the balance. Measurements were made at 2 and 5 mm of linear tension for straight and tortuous arteries, with the straight arteries serving as the control. Both sets of vessels then had a meticulous adventectomy performed under 10x microscopic visualization and were io 2 subjected to a second tensile test to quantify the 2mm 5 mm energy storage capacity of the vascular conduit without Figure 2. A plot of the data from Tables 2 and 3, this structure.
17 •
RESULTS Table 1 lists the artery weight of 2.2-cm segments from the coiled and control group arteries. Although these averages differ, analysis according to the Student-t
showing the effects on arterial compliance when subjected to a linear tensile force translation of 2 and 5 mm. Note how an artery stretched 5 mm but devoid of adventitia | minus column ( - ) at 5 mm] has approximately the same tension as an artery stretched 2 mm which has its adventitia intact |plus column ( + )at2 mm). It can also be seen that tortuous arteries have lower tension/unit area when stressed than straight vessels [black dots versus open triangles], as stretching them results in the linear translation force being stored in the bends of the artery.
Table 1. Artery Measurements Artery + Adventitia Artery Weight
106
Weight in grams Standard deviation
Adventitia Weight
Tortuous n = 15
Straight n = 6
Tortuous n = 15
Straight n = 6
Tortuous n = 15
Straight n = 6
.01643 .00711
.01355 .00620
.01216 .00492
.00901 .00559
.00426 .00285
.00459 .00381
Downloaded by: Universite Laval. Copyrighted material.
Figure 1. An example of Smith's 270° tortuosity. Note three successive bends of at least 90° within a 2-cm segment. This degree of tortuosity is known to be common in the distal digital artery at the distal interphalangeal joint level. Mobilizing an artery of this class even 1 or 2 mm when performing a digital replant, will subject the anastomosis to a slight but significant amount of tension. Although one cannot pull a straight artery without encountering turgid resistance, this class of vessel can unwittingly be mobilized by the microsurgeon unaware of the unique anatomy in this region (8x magnification, coils located at DIP joint line).
DIGITAL ARTERY/SMITH, TAJIMA, OURA, TOSHIMORI
Table 2.
Stress in Tortuous versus Straight Arteries
Wit A Adventitia Distance stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
Tortuous
Straight
2 15 1,894 3,209
2 6 7,097 7,786 2.302 95%
Tortuous
Straight
5 5 15 4 13,314 38,826 12,717 16,626 2.268 95%
After Adventectomy
1,937 1,562 2.511 95%
when tensioned, behave as if one were pulling on one end of a pile of spaghetti. Thus, the force of stress on a coiled artery is measured as being less than of a straight one. The tensile energy necessary to stretch a certain distance is stored in the bends of the artery. Or it may be said that the coiled artery has a greater compliance. The differences are all highly significant. Table 3 then compares the same data from a different perspective, that of whether the artery has its adventitia or not. If the adventitia is removed, an artery that is straight like a rope becomes compliant like the coiled vessels. It then acquires a greater compliance or ability to deform in a linear dimension. Another way of looking at it is, if you stretch an artery 5 mm but have previously removed its adventitia, it reacts to the tension of being stretched only about 2 mm. These differences are significant but only at low levels.
DISCUSSION When the digital arteries adjacent to the distal interphalangeal joint are examined, it is found that in
Table 3.
2 6
2 15 714 518
5 15 6,217 6,670
5 4 19,119 9,617 3.150 99%
this location there is a high degree of tortuosity present. The kinking or bending of the artery in this domain is unique and makes this structure physiologically different than at more proximal levels in the finger. The strain measurements from this study confirm this unique property which has important clinical significance for the operating microsurgeon. When performing vascular inosculation, it is important that there be no tension at the repair site. Obviously, no microsurgeon will pull two artery ends together and purposely suture them under tension. For a straight, uncoiled artery, tugging on its stump presents to the surgeon as turgid resistance. Usually, at this point of the procedure, the bony skeleton is shortened or an interposition graft is placed. But what if the artery has several coils or kinks either proximal or distal to the injury site in the neurovascular bundle that the surgeon cannot see? If one tugs the two ends together in this instance, resistance may not be felt. However, Table 2 shows that for a coiled artery, there is always a low-level resistive tension on an order of magnitude smaller than the stiffness of a straight vessel: 1,894 dynes versus 7,097 dynes (t = 2.302, 95
Downloaded by: Universite Laval. Copyrighted material.
Distance stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
Stress Strengths in Arteries with and without Adventitia
Tortuous Arteries
With
Without
Distance Stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
2 15 1,894 3,209
2 15 714 518
5 5 15 15 13,314 6,217 12,717 6,670 1.914 90%
2 6 1,937 1,562
5 5 4 4 38,826 19,119 16,626 9,617 2.052 90%
1.487 80%
With
V/ithout
Non-tortuous Arteries Distance stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
2 6 7,097 7,586 .632
107
percent confidence limit). Although a surgeon will rarely try to mobilize a small artery of 0.5 cm, experience in this laboratory shows that while manipulating vessel ends in our approximate vascular clamps, the cut ends are often gently pulled 1 or 2 mm In animal experimental models, simply cutting an artery or nerve causes it to retract ever so slightly. A supposedly tension-free anastomosis is often not free of all tensile stress. The coiled nature of the digital artery near the distal joint is no doubt an adaptive mechanism that provides protection against the limits of tension exerted in flexion and extension of the vessel, acting much like a protective spring.3 However, this gentle force, if the vessel is mobilized even a small distance, will produce some degree of tension at the repair site. In the Results section, it was noted that the readily removable adventitia which ensheathes an artery comprises about 30 percent of the total vessel weight. For its weight, this structure exerts a disproportionate force on the overall stiffness of the vessel. Removal of the adventitia reduces the force it takes to stretch the artery either 2 or 5 mm from 2lA to 2 times (from 1894 dynes to 714 dynes at 2 mm, 13,313 dynes to 6217 dynes at 5 mm). This is a 200 percent reduction in tensile resistance from removing only 30 percent of the structure's mass. It is the biological equivalent of turning a straight stiff artery into a coiled supple vessel. The adventitia, as is well known, is a tough, resistive coating that makes the artery less compliant, bendable, and supple. Its main properties are to provide protection, as well as conduction of visceral sympathetic and parasympathetic stimuli.7 With joint excursion, the arteries are subjected to uniaxial tension and compression. This biologic system is properly described physically as an anisotropic system. Anisotropic materials differ from isotropic ones in some important ways that are germane to the operating microsurgeon. On occasion, while performing a free flap, spasm is encountered in either the donor or recipient artery. When one performs an adventitial excision for apparent vascular spasm in an attempt to increase flow through this iatrogenic arterial laceration, it is commonly thought that the salubrious effects of this action stem from the opening of the luminal cross-section diameter in the area that has been manipulated. However, anisotropic systems, when subjected to changes in stress, by definition, must change in shape.8 What happens during adventectomy? Does the vessel lumen
108
APRIL 1991
open? Locally, at least, this appears so. However, is this the ameliorating effect of the intervention? What seems obvious may not be the answer. Adventectomy greatly reduces the tensile strength of the artery, as shown in Table 3; this change in tension locally presents as a ballooning of the vessel. We assume that the opening of the lumen corrects the problem. But, with an increase in diameter, there is also a change in the length of the vessel segment where the adventitia has been excised, as anisotropic systems tend to change in all dimensions simultaneously. A change in length in one portion of a vessel will result in a change in tension along the overall length of the conduit, similar to putting a shock absorbing spring in the system. It is entirely possible that the beneficial effects of segmental adventectomy for "apparent spasm," in an artery that is being used as a feeding vessel for a free flap (either upstream or downstream from the anastomosis), may be due to a reduction in linear tension that results in closure of microscopic gaps at the vascular repair site some distance from the area of adventitial excision. The physical structure of the digital artery distally in the finger is unique. The coiled nature of many of these vessels gives them minute strain forces that may be important in their surgical repair. Manipulation of the vessel adventitia has profound effects on vascular shape and tensile strength that must be better understood before the surgeon can work with these structures in an informed way.
REFERENCES 1.
Urbaniack JR, Roth IH, Nunley |A, et al.-. The results of replantation after amputation of a single finger. I Bone Joint Surg 67A:611, 1985 2 Strauch B, de Moura W: Arterial system of the fingers. ) Hand Surg 15A148, 1990 3. Smith DO, Kimura C, Oura C, Toshimori K: Artery anatomy and tortuosity in the distal finger. ) Hand Surg: 1991, in press 4 Smith DO, Tajima N: A new method for measuring stress and strain in microscopic anatomical systems. I Am Assoc Osteopath Spec 11:3, 1990 5. Fryshman B: Problem Solving in Physical Science. Reading, MA: Addison-Wesley, 1970, p 11 6. Freund )E: Modern Statistics, 2nd ed. Tokyo: Prentice-Hall, Maruzen Asian Edition, 1960 7. Bruce DFM, Atlas of Arterial Histology. St. Louis: Warren H Green, 1974
8.
Paul IP, Barbenel JC: Stress and strain, in Ray C (ed): Medical Engineering. Chicago: Year Book Medical Publishers, 1974
Downloaded by: Universite Laval. Copyrighted material.
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 7, NUMBER 2
DIGITAL ARTERY TORTUOSITY AND ELASTICITY:
Downloaded by: Universite Laval. Copyrighted material.
A BIOMECHANICAL STUDY ABSTRACT The gross structure of the digital artery distal to the proximal interphalangeal joint is significantly different from its proximal portion. Previous research in this laboratory has revealed that over half of all fingers exhibit marked tortuosity of this artery in juxtaposition to the distal interphalangeal joint. Any structure with a large amount of bending will have the properties of a spring. An understanding of these properties may help in creating tension-free anastomoses during finger tip replantation. The elastic strength and energy storage capacities of the distal digital artery were measured in 26 cadaver arteries.
Replantation of finger amputations is one of the most commonly performed reconstructive microsurgical procedures.1 Attention to anatomic detail is important in order to achieve any degree of success in surgery. In a study of the gross anatomy of the digital artery, it was discovered that there is often bending of this vessel near the distal interphalangeal joint. 23 The purpose of this study was to see if these bends have any of the characteristics of a spring, and if so, to quantify the intrinsic tensile strength of the digital artery in this region.
MATERIAL AND METHODS Fingers were taken at random from Japanese cadaver specimens after completion of the gross anatomy course at the Miyazaki Medical College. A total of 67 digits had their digital arteries dissected free along their entire course, from the proximal interphalangeal joint distally. Of these 134 radial and ulnar arteries, 69 (51.5 percent) had deflections in their course measuring at least 270 degrees. This is one type in the recently devised classification of arterial tortuosity of Smith,3 an example of which can be seen in Figure 1. Fifteen of
these tortuous arteries along with six non-tortuous control arteries were subjected to tensile stretch of 2 and 5 mm. The technique used for recording linear tension in microsurgical systems has been previously reported,4 but can be summarized as follows. In a standard electronic balance scale, a vernier caliper is suspended over the weighing pan assembly. A clip is attached to the vernier caliper, and a second counter weight of known mass (which also has a clip incorporated into it) is placed on the weighing pan. A 2.2-cm segment of digital artery is then connected to the caliper suspended over the counter weight and simultaneously clamped to the balance weight on the scale's weighing pan. Gripped at 2 cm length, the artery hanging above the scale causes no reduction in the counter weight on the pan, as it is at zero tension. When the carriage of the vernier caliper is moved up 2 mm, it lifts up on the much heavier counter weight, thus stretching the artery and resulting in a decreased weight measured on the scale. Weight in grams for this laboratory's scale is accurate to .01 mg and distance stretched to a tolerance of 0.1 mm for the vernier caliper. Because grams of weight are measured against the gravitational constant of the earth, weights can be readily changed to energy units simply by multiplying
Departments of Orthopedic Surgery and Anatomy, Miyazaki Medical College, Miyazaki, Japan Reprint requests-. Dr. Smith, 808 East Wakefield, Sikeston, MO 63801 Accepted for publication October 15, 1990 Copyright © 1991 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.
105
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 7, NUMBER 2
APRIL 1991
distribution for small samples shows that they are not statistically significant.6 For these specimens, the adventitia comprises 25.9 percent and 33.9 percent of the vessels' total weight. Figure 2 is a graph of the individual measurements for each artery, showing the stress in dynes for 2 and 5 mm of linear tension or stretch. Because of the tremendous variation in compliance of these vessels, the results are plotted on a log scale. Table 2 shows a comparison of arteries with 270° tortuosity stretched 2 and 5 mm versus control vessels that are straight. It is evident that if an artery is tortuous, the distance it can stretch before pulling up on the counter weight is greater. Highly tortuous arteries, io£
(+) With Adventitia (-)Without Straight •
io
4
•
Adventitia Artery
Tortuous Artery
:l \ ""
2 by the conversion factor 981 cm/sec2, which gives en- dynes/mm stress • • ergy units in dynes.5 The decrease in gram weight is the amount of energy in dynes stored in the artery after stretching it 2 or 5 mm. Shortening the vessel back, to : • io 3 the original length returns all of the energy or weight to the balance. Measurements were made at 2 and 5 mm of linear tension for straight and tortuous arteries, with the straight arteries serving as the control. Both sets of vessels then had a meticulous adventectomy performed under 10x microscopic visualization and were io 2 subjected to a second tensile test to quantify the 2mm 5 mm energy storage capacity of the vascular conduit without Figure 2. A plot of the data from Tables 2 and 3, this structure.
17 •
RESULTS Table 1 lists the artery weight of 2.2-cm segments from the coiled and control group arteries. Although these averages differ, analysis according to the Student-t
showing the effects on arterial compliance when subjected to a linear tensile force translation of 2 and 5 mm. Note how an artery stretched 5 mm but devoid of adventitia | minus column ( - ) at 5 mm] has approximately the same tension as an artery stretched 2 mm which has its adventitia intact |plus column ( + )at2 mm). It can also be seen that tortuous arteries have lower tension/unit area when stressed than straight vessels [black dots versus open triangles], as stretching them results in the linear translation force being stored in the bends of the artery.
Table 1. Artery Measurements Artery + Adventitia Artery Weight
106
Weight in grams Standard deviation
Adventitia Weight
Tortuous n = 15
Straight n = 6
Tortuous n = 15
Straight n = 6
Tortuous n = 15
Straight n = 6
.01643 .00711
.01355 .00620
.01216 .00492
.00901 .00559
.00426 .00285
.00459 .00381
Downloaded by: Universite Laval. Copyrighted material.
Figure 1. An example of Smith's 270° tortuosity. Note three successive bends of at least 90° within a 2-cm segment. This degree of tortuosity is known to be common in the distal digital artery at the distal interphalangeal joint level. Mobilizing an artery of this class even 1 or 2 mm when performing a digital replant, will subject the anastomosis to a slight but significant amount of tension. Although one cannot pull a straight artery without encountering turgid resistance, this class of vessel can unwittingly be mobilized by the microsurgeon unaware of the unique anatomy in this region (8x magnification, coils located at DIP joint line).
DIGITAL ARTERY/SMITH, TAJIMA, OURA, TOSHIMORI
Table 2.
Stress in Tortuous versus Straight Arteries
Wit A Adventitia Distance stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
Tortuous
Straight
2 15 1,894 3,209
2 6 7,097 7,786 2.302 95%
Tortuous
Straight
5 5 15 4 13,314 38,826 12,717 16,626 2.268 95%
After Adventectomy
1,937 1,562 2.511 95%
when tensioned, behave as if one were pulling on one end of a pile of spaghetti. Thus, the force of stress on a coiled artery is measured as being less than of a straight one. The tensile energy necessary to stretch a certain distance is stored in the bends of the artery. Or it may be said that the coiled artery has a greater compliance. The differences are all highly significant. Table 3 then compares the same data from a different perspective, that of whether the artery has its adventitia or not. If the adventitia is removed, an artery that is straight like a rope becomes compliant like the coiled vessels. It then acquires a greater compliance or ability to deform in a linear dimension. Another way of looking at it is, if you stretch an artery 5 mm but have previously removed its adventitia, it reacts to the tension of being stretched only about 2 mm. These differences are significant but only at low levels.
DISCUSSION When the digital arteries adjacent to the distal interphalangeal joint are examined, it is found that in
Table 3.
2 6
2 15 714 518
5 15 6,217 6,670
5 4 19,119 9,617 3.150 99%
this location there is a high degree of tortuosity present. The kinking or bending of the artery in this domain is unique and makes this structure physiologically different than at more proximal levels in the finger. The strain measurements from this study confirm this unique property which has important clinical significance for the operating microsurgeon. When performing vascular inosculation, it is important that there be no tension at the repair site. Obviously, no microsurgeon will pull two artery ends together and purposely suture them under tension. For a straight, uncoiled artery, tugging on its stump presents to the surgeon as turgid resistance. Usually, at this point of the procedure, the bony skeleton is shortened or an interposition graft is placed. But what if the artery has several coils or kinks either proximal or distal to the injury site in the neurovascular bundle that the surgeon cannot see? If one tugs the two ends together in this instance, resistance may not be felt. However, Table 2 shows that for a coiled artery, there is always a low-level resistive tension on an order of magnitude smaller than the stiffness of a straight vessel: 1,894 dynes versus 7,097 dynes (t = 2.302, 95
Downloaded by: Universite Laval. Copyrighted material.
Distance stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
Stress Strengths in Arteries with and without Adventitia
Tortuous Arteries
With
Without
Distance Stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
2 15 1,894 3,209
2 15 714 518
5 5 15 15 13,314 6,217 12,717 6,670 1.914 90%
2 6 1,937 1,562
5 5 4 4 38,826 19,119 16,626 9,617 2.052 90%
1.487 80%
With
V/ithout
Non-tortuous Arteries Distance stretched in mm Number of specimens Stress in dynes/mm2 Standard deviation dynes/mm2 t = value Degree of significance
2 6 7,097 7,586 .632
107
percent confidence limit). Although a surgeon will rarely try to mobilize a small artery of 0.5 cm, experience in this laboratory shows that while manipulating vessel ends in our approximate vascular clamps, the cut ends are often gently pulled 1 or 2 mm In animal experimental models, simply cutting an artery or nerve causes it to retract ever so slightly. A supposedly tension-free anastomosis is often not free of all tensile stress. The coiled nature of the digital artery near the distal joint is no doubt an adaptive mechanism that provides protection against the limits of tension exerted in flexion and extension of the vessel, acting much like a protective spring.3 However, this gentle force, if the vessel is mobilized even a small distance, will produce some degree of tension at the repair site. In the Results section, it was noted that the readily removable adventitia which ensheathes an artery comprises about 30 percent of the total vessel weight. For its weight, this structure exerts a disproportionate force on the overall stiffness of the vessel. Removal of the adventitia reduces the force it takes to stretch the artery either 2 or 5 mm from 2lA to 2 times (from 1894 dynes to 714 dynes at 2 mm, 13,313 dynes to 6217 dynes at 5 mm). This is a 200 percent reduction in tensile resistance from removing only 30 percent of the structure's mass. It is the biological equivalent of turning a straight stiff artery into a coiled supple vessel. The adventitia, as is well known, is a tough, resistive coating that makes the artery less compliant, bendable, and supple. Its main properties are to provide protection, as well as conduction of visceral sympathetic and parasympathetic stimuli.7 With joint excursion, the arteries are subjected to uniaxial tension and compression. This biologic system is properly described physically as an anisotropic system. Anisotropic materials differ from isotropic ones in some important ways that are germane to the operating microsurgeon. On occasion, while performing a free flap, spasm is encountered in either the donor or recipient artery. When one performs an adventitial excision for apparent vascular spasm in an attempt to increase flow through this iatrogenic arterial laceration, it is commonly thought that the salubrious effects of this action stem from the opening of the luminal cross-section diameter in the area that has been manipulated. However, anisotropic systems, when subjected to changes in stress, by definition, must change in shape.8 What happens during adventectomy? Does the vessel lumen
108
APRIL 1991
open? Locally, at least, this appears so. However, is this the ameliorating effect of the intervention? What seems obvious may not be the answer. Adventectomy greatly reduces the tensile strength of the artery, as shown in Table 3; this change in tension locally presents as a ballooning of the vessel. We assume that the opening of the lumen corrects the problem. But, with an increase in diameter, there is also a change in the length of the vessel segment where the adventitia has been excised, as anisotropic systems tend to change in all dimensions simultaneously. A change in length in one portion of a vessel will result in a change in tension along the overall length of the conduit, similar to putting a shock absorbing spring in the system. It is entirely possible that the beneficial effects of segmental adventectomy for "apparent spasm," in an artery that is being used as a feeding vessel for a free flap (either upstream or downstream from the anastomosis), may be due to a reduction in linear tension that results in closure of microscopic gaps at the vascular repair site some distance from the area of adventitial excision. The physical structure of the digital artery distally in the finger is unique. The coiled nature of many of these vessels gives them minute strain forces that may be important in their surgical repair. Manipulation of the vessel adventitia has profound effects on vascular shape and tensile strength that must be better understood before the surgeon can work with these structures in an informed way.
REFERENCES 1.
Urbaniack JR, Roth IH, Nunley |A, et al.-. The results of replantation after amputation of a single finger. I Bone Joint Surg 67A:611, 1985 2 Strauch B, de Moura W: Arterial system of the fingers. ) Hand Surg 15A148, 1990 3. Smith DO, Kimura C, Oura C, Toshimori K: Artery anatomy and tortuosity in the distal finger. ) Hand Surg: 1991, in press 4 Smith DO, Tajima N: A new method for measuring stress and strain in microscopic anatomical systems. I Am Assoc Osteopath Spec 11:3, 1990 5. Fryshman B: Problem Solving in Physical Science. Reading, MA: Addison-Wesley, 1970, p 11 6. Freund )E: Modern Statistics, 2nd ed. Tokyo: Prentice-Hall, Maruzen Asian Edition, 1960 7. Bruce DFM, Atlas of Arterial Histology. St. Louis: Warren H Green, 1974
8.
Paul IP, Barbenel JC: Stress and strain, in Ray C (ed): Medical Engineering. Chicago: Year Book Medical Publishers, 1974
Downloaded by: Universite Laval. Copyrighted material.
JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 7, NUMBER 2
