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Penetrating thermal vascular injury in a child: A case report
Penetrating thermal vascular A case report
injury in a child:
James W. McNeil, M D , * William O. T h o m a s III, M D , A r n o l d L u t e r m a n , M D , and Gregory S. McGee, M D , Mobile, Ala. Penetrating vascular trauma in children is most commonly seen in wartime settings or more recently as a result of attempts at invasive imaging. Treatment of these patients can be more complicated than treatment of trauma in adults and must include maintenance of
symmetric limb growth, compensatory growth of the vascular graft and its anastomoses, and the need for very long-term graft patency. This report describes the care of a 5-year-old child who was impaled by a hot metal pipe and sustained a penetrating thermal injury to the distal external iliac artery and vein. Issues such as conduit choice, extraanatomic reconstruction, anastomotic suture technique, and soft tissue coverage are reviewed in the report. (J VASC SURG 1993;18:1060-3.) ~
Penetrating vascular trauma involving pediatric patients occurs much less often than in adults, and its management is less precisely defined. Much o f the information regarding treatment o f pediatric vascular injuries is based on experience with complications o f arterial catheterization. 1,2 In retrospective series from active trauma centers, gunshot wounds and lacerations comprise the majority ofnoniatrogenic cases o f vascular trauma. 3,4 Reports o f pediatric vascular injuries caused by a direct thermal insult are even less common, with m o s t o f the literature describing management o f vascular injuries after electrical burns, s,6 Our patient presented a unique problem in the inanagement o f vascular trauma. We were unable to find a similar case report in the English-language medical literature. CASE R E P O R T
A previously healthy 5-year-old girl was transferred to our facility with a pulseless right lower extremity after sustaining a penetrating injury. She had been playing near a trash fire when an explosion occurred, presumably from combustion of a sealed aerosol can. A 25 cm long segment of 1/2-inch diameter metal pipe was ejected white-hot from From the Divisions of Plastic and ReconstructiveSurgery (Dr. Thomas), Burns and Trauma (Dr. Luterman), and Peripheral VasoalarSurgery(Dr. McGee),Departmentof GcneralSurgery, University of South Alabama Medical School,Mobile. Reprint requests: Gregory S. McGee, MD, 2451 Fillingim St., Mobile, AL 36617. ~Dr. McNeil is currently a senior general surgical resident, University of South Alabama Medical Center. Copyright © 1993 by The Society for Vascular Surgery and International Societyfor CardiovascularSurgery,North American Chapter. 0741-5214/93/$1.00 + .10 24]4]44850 1060
the fire by the explosion and was impaled in the girls' fight groin. On arrival to our institution she was apprehensive but hemodynamically stable. Physical examination revealed a metal pipe firmly embedded in her right groin at the level of the inguinal ligament with a large surrounding fullthickness burn (Fig. 1). The angle of entry suggested pelvic penetration, which was confirmed by roentgenography (Fig. 2), The right lower extremity was cool and ptilseless, but sensation and motor fimction in her foot were grossly intact. Abdominal and anorectal examination were unremarkable and the hematocfit was normal. AntibiOtics were administered, and the patient was taken immediately to the operating room within 90 minutes of injury. The pipe, her abdomen, and both lower extremities were included in the aseptic field. The abdomen was explored through a lower midline incision, the right colon was mobilized, and control of the right common iliac artery and vein was achieved. No hemoperitoneum nor pelvic hematoma was found. The pipe had pierced the inguinal ligament tracking posteriorly and cephalad and had transected and cauterized her external iliac vein. The external iliac artery was severely charred and occluded over a 3 cm segment. Heat from the pipe had effected hemostasis and prevented exsanguination. The pipe also produced an extensive soft tissue thermal injury as it penetrated to the obturator foramen, although the right colon, ureter, and bladder were free of injury. Heparin sulfate (1500 units/24 hr) was then administered, and the external iliac vein was oversewn with 7-0 polypropylene suture.
A second incision was then made over the right groin, and control of the distal common femoral artery and vein was achieved. The proximal portion of both these vessels and femoral nerve had been cauterized by the hot metal pipe. The pipe was removed, and the common femoral vein was ligated. A longitudinal common femoral artefiotomy was performed, and the thermal injury was noted to extend
McNeil et al.
JOURNAL OF VASCULAR SURGERY Volume 18, Number 6
1061
Fig. 1. This photograph depicts metallic pipe exiting patient at medial and cephalad aspect of inguinal ligament.
Fig. 2. This radiograph demonstrates pipe's pelvic penetration. down to just above the femoral bifurcation. This white and dessicated portion of the common femoral artery was excluded, and the grossly normal distal common femoral artery was prepared for an anastomosis. A No. 2 Fogarty
catheter was gently passed distally into the superficial and deep femoral arteries, a small amount of thrombus was extracted, and heparinized saline solution was injected. The contralateral hypogastric artery was mobilized and
JOURNAL OF VASCULAR SURGERY
1062 McNeil et al.
harvested beyond the second distal branch in an attempt m gain adequate conduit length. Both the obturator foramen and the femorofemoral routes were unavailable because of the location and extent of the thermal injury, and an autogenous axillofemoral graft would have required piecing together several conduits with variable longitudinal growth potentials. The route chosen for the hypogastric conduit coursed laterally and caudad under the pelvic wall peritoneum, anteriorly over the lateral inguinal ligament, and medially down to the distal common femoral artery. This route maintained coverage of the conduit by viable, unburned soft tissue. The proximal anastomosis to the external ifiac artery was accomplished with interrupted 7-0 polypropylene suture. The distal hypogastric conduit was of smaller caliber and was sewn to the distal common femoral artery with interrupted 8-0 polypropylene suture. Flow was restored and seemed to be inadequate even after topical papaverine had been applied. The distal anastomosis was opened, and the distal conduit caliber was determined to be too small. Accordingly, the contralateral greater saphenous vein at the groin was harvested, and the hypogastric artery conduit was transected at the first distal branch site. A segment of reversed saphenous vein was then sewn end-to-end to the hypogastric conduit and distally to the common femoral artery with interrupted 8-0 polypropylene suture. Adequate flow to the foot was achieved. No attempt was made to reconstruct the venous injury. The groin wound was debrided, and a long pedicle of greater omenturn was mobilized into the groin to cover the distal anastomosis. Soft tissue was reapproximated at the distal extent of the wound, and the debrided area was packed with sulfadiazine silver-covered sterile gauze. An elastic wrap was then applied circumferentially to the right lower extremity. The patient had a peaked monophasic Doppler signal in her foot immediately after completion of the anastomosis and had a palpable pedal pulse within 12 hours after operation. Her leg was kept elevated and wrapped in elastic compression, and she had only trace edema during her hospital stay. Her hospital course included further operative debridement of necrotic tissue, the creation of a rectus femoris muscular rotation flap to fill the soft tissue defect and skin grafting. At discharge she had peaked biphasic Doppler wave forms in her right dorsalis pedis artery and an ankle/brachial index of 0.85. She had moderate right lower-extremity weakness as a result of femoral nerve thermal injury. At 6-month follow-up she was ambulating without assistance although with a limp. She had equal pulses in her feet and her wounds had healed well. Follow-up examinations at 6-month intervals with segmental pressures and wave forms are planned.
DISCUSSION Reconstruction of vascular injuries in pediatric patients requires consideration of several technical and physiologic variables not often encountered in
December 1993
the adult population. Small vessel caliber was once a severely limiting factor in pediatric vascular reconstruction. With availability of magnification and microvascular suture techniques, this problem is now much less daunting. Vessel spasm is a common occurrence in pediatric vascular reconstruction and is perhaps best managed by gentle dilation and papaverine injection. The need for pediatric vascular anastomoses to "grow" with the patient has been met by the more frequent use of long, spatulated anastomoses with interrupted suture technique. 7,8 Also, at least theoretically, use of an absorbable suture may prevent the development of anastomotic stricture after vascular reconstruction in the pediatric patient. 9 The type of conduit appropriate for pediatric arterial reconstruction depends on the size of the injured vessel, the patient's age, and the urgency to restore circulation. The use of prosthetic vascular grafts in children would only be indicated for larger vessels and older children, when urgent revascularization or the severity of the injury precludes harvesting an autogenous conduit. The need for patency of 50 years or greater, the extremely small caliber of younger children's vessels, the contaminated field, and the inability of prosthetic grafts to grow with the native vessel all but preclude their use as peripheral vascular conduits in pediatric patients. Saphenous vein conduits for pediatric arterial reconstruction have the theoretic advantages of a matched vessel size, an endothelialized luminal surface, and the potential to grow with the native vessel. However, vein conduits have occasionally been shown to undergo aneurysmal dilation when arterialized for protracted periods, requiring replacement with arterial autografts. 1°~2 An arterial autograft, specifically the hypogastric artery, seems to be a more suitable conduit for vascular reconstruction in the pediatric patient and has been used successfully in pediatric renal revascularization. ~3,a~ It has all the advantages of vein conduits, but it has not been shown to undergo aneurysmal dilation. Its disadvantages include its relatively limited length and the need for a suprainguinal incision for harvest. A major vascular injury directly caused by heat damage is distinctly unusual. Wang et al. 5'6 described coagulafive necrosis in arterial walls after electrical burns. Successful management of such injuries required generous debridement and autogenous reconstruction. Early recognition and reconstruction of pediatric vascular injuries are important in the prevention of limb loss and growth discrepancy, the latter a
JOURNALOF VASCULARSURGERY Volume 18, Number 6
well-described complication of uncorrected pediatric arterial injury. The results of late revascularization in an effort to relieve limb length discrepancies have been inconsistant, ls,16 The coordinated, multidisciplinary approach to the care of this patient has become the standard of care for severe burns and trauma in pediatric patients. With early recognition and autogenous reconstruction of vascular injuries in pediatric patients, successful return to a childhood of activity and growth can be expected.
McNeil et al.
7. 8. 9. 10. 11. 12.
REFERENCES
1. Mansfield PB, Gazzania AB, Litwin SB. Management of arterial injuries related to cardiac catheterization in children and young adults. Circulation 1970;42:501-7. 2. Klein MD, Coran AG, Whitehouse WM, Stanley JC, Wesley IR, Lebowitz EA. Management of iatrogenic arterial injuries in infants and children. J Ped Surg 1982;17:933-9. 3. Shaker IJ, White JJ, Singer RD, Golladay ES, Hailer JA. Special problems of vascular injuries in children. J Trauma 1976;16:863-6. 4. Evans WE, King DR, Hayes JP. Arterial trauma in children: diagnosis and management. Ann Vasc Surg 1988;2:268-70. 5. Wang XW, Zoh W. Arterial injuries in electrically burned upper limbs and effects of early reconstruction of blood circulation to the wrist. Burns Incl Therm Inj 1982;8:379-86. 6, Wang XW, Zoh WH. Vascular injuries in electrical burns-
13. 14.
15. 16.
1063
the pathologic basis for mechanism of injury. Burns Incl Therm Inj 1983;9:335-8. Whitehouse WM, Coran AG, Stanley JC, Kuhns LK, Weintraub WH, Fry WJ. Pediatric vascular trauma. Arch Surg 1976;111:1269-75. Meagher DP, Defore WW, Mattox KL, Harberg FJ. Vascular trauma in infants and children. J Trauma 1979;19:532-6. Myers JL, Waldhausen JA, Pae WE, Abt AB, Prophet GA, Pierce WS. Vascular anastomoses in growing vessels: The use of absorbable sutures. Ann Thorac Surg 1982;34:529-37. Yao JST, McCarthy WJ. Aneurysmal dilatation of cephalic vein bypass graft. Contemp Surg 1987;30:69-75. Peer RM, Upson JF. Aneurysmal dilatation in saphenous vein bypass grafts. J Cardiovasc Surg (Torino) 1990;31:668-71. Dean RH, Wilson JP, Burko H, et al. Saphenous vein aortorenal bypass grafts: serial arteriographic study. Ann Surg 1974;180:469-78. Stanley IC. Renal vascular disease and renovascular hypertension in children. Urol Clin North Am 1984;11:451-63. Dean RH. Operative management of renovascular hypertension. In: Bergan JJ, Yao JST, eds. Surgery of the aorta and its body branches. 1st ed. New York: Grune and Stratton, 1979:377-408. Bloom JD, Mozersky DJ, BuckleyCJ, Hagood CO. Defective limb growth as a complication of catheterization of the femoral artery. Surg Gynecol Obstet 1974;138:524-6. Bassett FH, Lincoln CR, King TD, Canent RV. Inequality in the size of the lower extremity following cardiac catheterization. South Med J 1968;61:1013-7.
Submitted Oct. 20, 1992; accepted Dec. 10, 1992.
injury in a child:
James W. McNeil, M D , * William O. T h o m a s III, M D , A r n o l d L u t e r m a n , M D , and Gregory S. McGee, M D , Mobile, Ala. Penetrating vascular trauma in children is most commonly seen in wartime settings or more recently as a result of attempts at invasive imaging. Treatment of these patients can be more complicated than treatment of trauma in adults and must include maintenance of
symmetric limb growth, compensatory growth of the vascular graft and its anastomoses, and the need for very long-term graft patency. This report describes the care of a 5-year-old child who was impaled by a hot metal pipe and sustained a penetrating thermal injury to the distal external iliac artery and vein. Issues such as conduit choice, extraanatomic reconstruction, anastomotic suture technique, and soft tissue coverage are reviewed in the report. (J VASC SURG 1993;18:1060-3.) ~
Penetrating vascular trauma involving pediatric patients occurs much less often than in adults, and its management is less precisely defined. Much o f the information regarding treatment o f pediatric vascular injuries is based on experience with complications o f arterial catheterization. 1,2 In retrospective series from active trauma centers, gunshot wounds and lacerations comprise the majority ofnoniatrogenic cases o f vascular trauma. 3,4 Reports o f pediatric vascular injuries caused by a direct thermal insult are even less common, with m o s t o f the literature describing management o f vascular injuries after electrical burns, s,6 Our patient presented a unique problem in the inanagement o f vascular trauma. We were unable to find a similar case report in the English-language medical literature. CASE R E P O R T
A previously healthy 5-year-old girl was transferred to our facility with a pulseless right lower extremity after sustaining a penetrating injury. She had been playing near a trash fire when an explosion occurred, presumably from combustion of a sealed aerosol can. A 25 cm long segment of 1/2-inch diameter metal pipe was ejected white-hot from From the Divisions of Plastic and ReconstructiveSurgery (Dr. Thomas), Burns and Trauma (Dr. Luterman), and Peripheral VasoalarSurgery(Dr. McGee),Departmentof GcneralSurgery, University of South Alabama Medical School,Mobile. Reprint requests: Gregory S. McGee, MD, 2451 Fillingim St., Mobile, AL 36617. ~Dr. McNeil is currently a senior general surgical resident, University of South Alabama Medical Center. Copyright © 1993 by The Society for Vascular Surgery and International Societyfor CardiovascularSurgery,North American Chapter. 0741-5214/93/$1.00 + .10 24]4]44850 1060
the fire by the explosion and was impaled in the girls' fight groin. On arrival to our institution she was apprehensive but hemodynamically stable. Physical examination revealed a metal pipe firmly embedded in her right groin at the level of the inguinal ligament with a large surrounding fullthickness burn (Fig. 1). The angle of entry suggested pelvic penetration, which was confirmed by roentgenography (Fig. 2), The right lower extremity was cool and ptilseless, but sensation and motor fimction in her foot were grossly intact. Abdominal and anorectal examination were unremarkable and the hematocfit was normal. AntibiOtics were administered, and the patient was taken immediately to the operating room within 90 minutes of injury. The pipe, her abdomen, and both lower extremities were included in the aseptic field. The abdomen was explored through a lower midline incision, the right colon was mobilized, and control of the right common iliac artery and vein was achieved. No hemoperitoneum nor pelvic hematoma was found. The pipe had pierced the inguinal ligament tracking posteriorly and cephalad and had transected and cauterized her external iliac vein. The external iliac artery was severely charred and occluded over a 3 cm segment. Heat from the pipe had effected hemostasis and prevented exsanguination. The pipe also produced an extensive soft tissue thermal injury as it penetrated to the obturator foramen, although the right colon, ureter, and bladder were free of injury. Heparin sulfate (1500 units/24 hr) was then administered, and the external iliac vein was oversewn with 7-0 polypropylene suture.
A second incision was then made over the right groin, and control of the distal common femoral artery and vein was achieved. The proximal portion of both these vessels and femoral nerve had been cauterized by the hot metal pipe. The pipe was removed, and the common femoral vein was ligated. A longitudinal common femoral artefiotomy was performed, and the thermal injury was noted to extend
McNeil et al.
JOURNAL OF VASCULAR SURGERY Volume 18, Number 6
1061
Fig. 1. This photograph depicts metallic pipe exiting patient at medial and cephalad aspect of inguinal ligament.
Fig. 2. This radiograph demonstrates pipe's pelvic penetration. down to just above the femoral bifurcation. This white and dessicated portion of the common femoral artery was excluded, and the grossly normal distal common femoral artery was prepared for an anastomosis. A No. 2 Fogarty
catheter was gently passed distally into the superficial and deep femoral arteries, a small amount of thrombus was extracted, and heparinized saline solution was injected. The contralateral hypogastric artery was mobilized and
JOURNAL OF VASCULAR SURGERY
1062 McNeil et al.
harvested beyond the second distal branch in an attempt m gain adequate conduit length. Both the obturator foramen and the femorofemoral routes were unavailable because of the location and extent of the thermal injury, and an autogenous axillofemoral graft would have required piecing together several conduits with variable longitudinal growth potentials. The route chosen for the hypogastric conduit coursed laterally and caudad under the pelvic wall peritoneum, anteriorly over the lateral inguinal ligament, and medially down to the distal common femoral artery. This route maintained coverage of the conduit by viable, unburned soft tissue. The proximal anastomosis to the external ifiac artery was accomplished with interrupted 7-0 polypropylene suture. The distal hypogastric conduit was of smaller caliber and was sewn to the distal common femoral artery with interrupted 8-0 polypropylene suture. Flow was restored and seemed to be inadequate even after topical papaverine had been applied. The distal anastomosis was opened, and the distal conduit caliber was determined to be too small. Accordingly, the contralateral greater saphenous vein at the groin was harvested, and the hypogastric artery conduit was transected at the first distal branch site. A segment of reversed saphenous vein was then sewn end-to-end to the hypogastric conduit and distally to the common femoral artery with interrupted 8-0 polypropylene suture. Adequate flow to the foot was achieved. No attempt was made to reconstruct the venous injury. The groin wound was debrided, and a long pedicle of greater omenturn was mobilized into the groin to cover the distal anastomosis. Soft tissue was reapproximated at the distal extent of the wound, and the debrided area was packed with sulfadiazine silver-covered sterile gauze. An elastic wrap was then applied circumferentially to the right lower extremity. The patient had a peaked monophasic Doppler signal in her foot immediately after completion of the anastomosis and had a palpable pedal pulse within 12 hours after operation. Her leg was kept elevated and wrapped in elastic compression, and she had only trace edema during her hospital stay. Her hospital course included further operative debridement of necrotic tissue, the creation of a rectus femoris muscular rotation flap to fill the soft tissue defect and skin grafting. At discharge she had peaked biphasic Doppler wave forms in her right dorsalis pedis artery and an ankle/brachial index of 0.85. She had moderate right lower-extremity weakness as a result of femoral nerve thermal injury. At 6-month follow-up she was ambulating without assistance although with a limp. She had equal pulses in her feet and her wounds had healed well. Follow-up examinations at 6-month intervals with segmental pressures and wave forms are planned.
DISCUSSION Reconstruction of vascular injuries in pediatric patients requires consideration of several technical and physiologic variables not often encountered in
December 1993
the adult population. Small vessel caliber was once a severely limiting factor in pediatric vascular reconstruction. With availability of magnification and microvascular suture techniques, this problem is now much less daunting. Vessel spasm is a common occurrence in pediatric vascular reconstruction and is perhaps best managed by gentle dilation and papaverine injection. The need for pediatric vascular anastomoses to "grow" with the patient has been met by the more frequent use of long, spatulated anastomoses with interrupted suture technique. 7,8 Also, at least theoretically, use of an absorbable suture may prevent the development of anastomotic stricture after vascular reconstruction in the pediatric patient. 9 The type of conduit appropriate for pediatric arterial reconstruction depends on the size of the injured vessel, the patient's age, and the urgency to restore circulation. The use of prosthetic vascular grafts in children would only be indicated for larger vessels and older children, when urgent revascularization or the severity of the injury precludes harvesting an autogenous conduit. The need for patency of 50 years or greater, the extremely small caliber of younger children's vessels, the contaminated field, and the inability of prosthetic grafts to grow with the native vessel all but preclude their use as peripheral vascular conduits in pediatric patients. Saphenous vein conduits for pediatric arterial reconstruction have the theoretic advantages of a matched vessel size, an endothelialized luminal surface, and the potential to grow with the native vessel. However, vein conduits have occasionally been shown to undergo aneurysmal dilation when arterialized for protracted periods, requiring replacement with arterial autografts. 1°~2 An arterial autograft, specifically the hypogastric artery, seems to be a more suitable conduit for vascular reconstruction in the pediatric patient and has been used successfully in pediatric renal revascularization. ~3,a~ It has all the advantages of vein conduits, but it has not been shown to undergo aneurysmal dilation. Its disadvantages include its relatively limited length and the need for a suprainguinal incision for harvest. A major vascular injury directly caused by heat damage is distinctly unusual. Wang et al. 5'6 described coagulafive necrosis in arterial walls after electrical burns. Successful management of such injuries required generous debridement and autogenous reconstruction. Early recognition and reconstruction of pediatric vascular injuries are important in the prevention of limb loss and growth discrepancy, the latter a
JOURNALOF VASCULARSURGERY Volume 18, Number 6
well-described complication of uncorrected pediatric arterial injury. The results of late revascularization in an effort to relieve limb length discrepancies have been inconsistant, ls,16 The coordinated, multidisciplinary approach to the care of this patient has become the standard of care for severe burns and trauma in pediatric patients. With early recognition and autogenous reconstruction of vascular injuries in pediatric patients, successful return to a childhood of activity and growth can be expected.
McNeil et al.
7. 8. 9. 10. 11. 12.
REFERENCES
1. Mansfield PB, Gazzania AB, Litwin SB. Management of arterial injuries related to cardiac catheterization in children and young adults. Circulation 1970;42:501-7. 2. Klein MD, Coran AG, Whitehouse WM, Stanley JC, Wesley IR, Lebowitz EA. Management of iatrogenic arterial injuries in infants and children. J Ped Surg 1982;17:933-9. 3. Shaker IJ, White JJ, Singer RD, Golladay ES, Hailer JA. Special problems of vascular injuries in children. J Trauma 1976;16:863-6. 4. Evans WE, King DR, Hayes JP. Arterial trauma in children: diagnosis and management. Ann Vasc Surg 1988;2:268-70. 5. Wang XW, Zoh W. Arterial injuries in electrically burned upper limbs and effects of early reconstruction of blood circulation to the wrist. Burns Incl Therm Inj 1982;8:379-86. 6, Wang XW, Zoh WH. Vascular injuries in electrical burns-
13. 14.
15. 16.
1063
the pathologic basis for mechanism of injury. Burns Incl Therm Inj 1983;9:335-8. Whitehouse WM, Coran AG, Stanley JC, Kuhns LK, Weintraub WH, Fry WJ. Pediatric vascular trauma. Arch Surg 1976;111:1269-75. Meagher DP, Defore WW, Mattox KL, Harberg FJ. Vascular trauma in infants and children. J Trauma 1979;19:532-6. Myers JL, Waldhausen JA, Pae WE, Abt AB, Prophet GA, Pierce WS. Vascular anastomoses in growing vessels: The use of absorbable sutures. Ann Thorac Surg 1982;34:529-37. Yao JST, McCarthy WJ. Aneurysmal dilatation of cephalic vein bypass graft. Contemp Surg 1987;30:69-75. Peer RM, Upson JF. Aneurysmal dilatation in saphenous vein bypass grafts. J Cardiovasc Surg (Torino) 1990;31:668-71. Dean RH, Wilson JP, Burko H, et al. Saphenous vein aortorenal bypass grafts: serial arteriographic study. Ann Surg 1974;180:469-78. Stanley IC. Renal vascular disease and renovascular hypertension in children. Urol Clin North Am 1984;11:451-63. Dean RH. Operative management of renovascular hypertension. In: Bergan JJ, Yao JST, eds. Surgery of the aorta and its body branches. 1st ed. New York: Grune and Stratton, 1979:377-408. Bloom JD, Mozersky DJ, BuckleyCJ, Hagood CO. Defective limb growth as a complication of catheterization of the femoral artery. Surg Gynecol Obstet 1974;138:524-6. Bassett FH, Lincoln CR, King TD, Canent RV. Inequality in the size of the lower extremity following cardiac catheterization. South Med J 1968;61:1013-7.
Submitted Oct. 20, 1992; accepted Dec. 10, 1992.