Seat Belt Aorta Mohinder P.S. Randhawa, Jr, MD, James O. Menzoian, MD, Boston, Massachusetts

This review of 11 cases of seat-belt associated blunt abdominal aortic trauma, includes nine cases reported in the literature and two new cases. Lap-type seat belts were the cause of this injury in eight of the 11 patients (73%). Clinical presentation was acute in 73% of the cases, with symptoms of acute arterial insufficiency, or an acute abdomen or neurologic deficits. Chronic manifestations, such as, persistent abdominal pain, claudication, abdominal mass with a bruit and decreased distal pulses, presented as late as nine months after the injury occurred. The mechanism producing the injury is discussed and a classification system for the different types of abdominal aortic injuries is put forth. Circumferential intimal disruption was the most common aortic defect. The majority of these were located distal to the inferior mesenteric artery. Diagnosis involves a high degree of suspicion in a victim wearing a seat belt with neurologic deficits, signs of acute arterial insufficiency, or a pulsatile abdominal mass. The mortality rate was 18% (2/11 patients), and occurred in patients wearing lap belts. Overall outcome depends on prompt recognition followed by appropriate surgical intervention. (Ann Vasc Surg 1990;4:370-377). KEY WORDS: Blunt vascular injury; abdominal aorta; seat belt syndrome; seat belt sign; chance fracture.

Seat belts were initially used in the 1930s by racing car drivers as a fastening device that attached them to their seats and thereby enhanced their ability to feel the movements of the car [1]. They provide an additional sensory input, which along with visual and auditory stimuli, allows better control while driving. This concept was subsequently applied to ordinary traffic, but the notion of safety belts, as a means of protecting a driver in an accident, did not emerge until the 1940s. Since then much research has been done in the areas of safety belts--their efficacy, the appropriate design, alternative safety devices and the injuries produced by safety belts. From the Department of Vascular Surget3', Boston University School of Medicine, Boston, Massachusetts. Reprint requests: James O. Menzoian, MD, Department of Vascular Surgeo', Boston University School of Medicine, 88 East Newton Street, Boston, Massachusetts 02118.

The benefits of seat belts in reducing injuries to accident victims is well known and were described as early as 1961 by Garrett and Braunstein [2]. In North America seat belts did not become standard equipment in automobiles until 1964 [3]. A point of contention that has remained since then has been the benefits of the 3-point lap and diagonal shoulder inertial belt versus the 2-point lap belt. Intraabdominal injuries have been reported to be much more frequent when only the lap type belt is worn [4]. In 1967, Volvo of Sweden looked at 28,780 accidents involving 37,5II front seat passengers [4]. They found that no deaths occurred at speeds less than 60 mph when a 3-point harness was used, whereas fatalities were observed at speeds as low as 12 mph when a 2-point harness was used. It was not until 1973 that 3-point restraints became standard equipment in United States automobiles for front seats. Of note is the fact that lap belts are not considered to be safety belts in Europe. Many types of intraabdominal injuries have been 370

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a s s o c i a t e d w i t h seat b e l t s , A s e a t belt s y n d r o m e [2,4,5] has b e e n d e s c r i b e d , p a r t i c u l a r l y in r e f e r e n c e to specific a b d o m i n a l v i s c e r a l i n j u r i e s p r o d u c e d b y blunt t r a u m a f r o m s a f e t y b e l t s . A l s o d i s c u s s e d a r e a seat belt sign [5] a n d a specific v e r t e b r a l c o l u m n i n j u r y , the C h a n c e f r a c t u r e [6]. O f n o t e is a r a r e a b d o m i n a l a o r t i c i n j u r y that r e s u l t s in e i t h e r a c u t e t h r o m b o s i s o f the i n f r a r e n a l a o r t a , a n e u r y s m a l c h a n g e s , i n t i m a l t e a r w i t h flap f o r m a t i o n , o r d i s t a l e m b o l i z a t i o n [7-15]. Seat belt-associated abdominal aortic injury was first d e s c r i b e d in 1969 b y C a m p b e l l [71. S i n c e t h e n eight m o r e c a s e s h a v e b e e n r e p o r t e d [8-15]. T w o c a s e s , in o u r e x p e r i e n c e , o f a c u t e t r a u m a t i c a b d o m inal a o r t i c o c c l u s i o n f r o m l a p - t y p e seat b e l t s p r o m p t e d this p r e s e n t r e v i e w .

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Patient 1 A 19-year-old white man was a rear seat passenger wearing a lap-type seat belt when his vehicle was involved in an automobile accident. He was initially taken to a community hospital, from which he was transferred by helicopter to University Hospital. On arrival, he was hemodynamically stable, with a blood pressure of 120-150/80 mm Hg and a pulse of 120 per minute. He complained of abdominal and back pain, The examination revealed an ecchymotic area over the lower abdomen, a tender, rigid abdomen with rebound and guarding, weak femoral pulses, loss of sensation below TI0 and muscle paralysis of both lower extremities. X-ray studies of the chest, C-spine and T-spine were within normal limits. Lumbar spine studies revealed an L2-L3 fracture dislocation. At emergency laparotomy, complete transverse transection of the rectus abdominus muscle was noted. There was approximately 300 cc--400 cc of free blood in the peritoneal cavity. The liver, spleen, stomach, and duodenum showed no evidence of injury, The small bowel had two areas with multiple tears, while the serosa and mesentery were torn from a large area of the right colon. The small bowel injuries were repaired by resecting two segments--one about 35 cm in length and the other approximately 6 cm in length. The continuity of the small bowel was reestablished with side-to-side functional anastomoses, using a G I A stapling device. Repair of the right colon was deferred until the retroperitoneum was explored, On exploration of the retroperitoneum, the aorta was found to be contused, with an area of ecchymosis extending just distally from the inferior mesenteric artery to approximately 1 cm above the bifurcation. There was a weak pulse at the level of the injury and an obvious thrill. After proximal and distal control was obtained, a vertical ar~eriotomy was made. This revealed an intraluminal thrombus and complete circumferential disruption of the intima and media with distal dissection and folding of the resultant flap of degloved intima/ media into the lumen of the aorta (Fig. 1). Vascular integrity at the site of injury was maintained by a very tenuous

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Fig. 1. Circumferential fracture of intima and media. Fractured layers formed flap that prolapsed on itself, thereby occluding lumen of aorta.

segment of bruised adventitia (Fig, 2), The injured aortic segment was replaced with a 20 mm Gore-Tex interposition graft. Good distal pulses were noted upon restoration of flow. The retroperitoneum was closed with running 2--0 Vicryl suture, after which a standard right colectomy was done for an ischemic colon and a J-tube for feeding was placed. There were no intraoperative complications. Postoperatively, the patient did well, except for a persistent TI0 paraplegia. He did require an L2-L3 stabilization with Harrington rods and lumbar spine bone fusion. On discharge, he had normal lower extremity perfusion, but no improvement in motor or sensory function,

Patient 2 A 44-year-old black man was wearing a lap seat belt when his automobile was hit from behind by a fire truck. On arrival at Boston City Hospital emergency room, he was hypotensive and he complained of abdominal pain. Examination revealed that he had a diffusely tender, rigid and distending abdomen and absent femoral pulses. Neurological examination was within normal limits and there was no evidence of fractures in his x-ray studies. Once the patient's blood pressure was stabilized by fluid resuscitation, he was promptly taken to the operating room for an exploratory laparotomy.

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ANNALS OF

SEA T B E L T A O R T A

VASCULAR SURGERY

Fig. 2. Operative photograph showing resected edges of intima and media. Area of bruised adventitia can be seen spanning defect.

At exploration, the peritoneal cavity was found to contain a large amount of free blood. Active bleeding was occurring from jejuno-ileal branches of the superior ruesenteric artery in areas where small bowel lacerations were present. The liver, spleen, stomach, duodenum, and colon-rectum showed no evidence of injury. Prior to exploration of the retroperitoneum, the small bowel was resected and the bleeding controlled. Exploration of the retroperitoneum revealed contused and thin-walled abdominal aorta just above the level of the inferior mesenteric artery. There was no pulse distal to the contused area, while the proximal aorta appeared normal and had an excellent pulse. Proximal and distal control was established and the lumbar vessels were clipped. A transverse arteriotomy was made at the level of the injury-approximately 2 cm above the inferior mesenteric artery. This revealed a fresh intraluminal thrombus and a circumferential fracture of the intima with distal dissection which formed a flap that folded upon itself and thereby occluded the lumen of the abdominal aorta (Fig. 1). About 4 cm of damaged aorta was resected and the inferior mesenteric artery was divided and ligated. Vascular integrity of the aorta was reestablished with a 14 mm Dacron interposition graft. The inferior mesenteric artery was not reimptanted as the colon-rectum showed no evidence of ischemia. There were no intraoperative complications and the lower extremities

appeared well perfused upon completion of the procedure. Postoperatively, the patient did well and was subsequently discharged with no residual sequelae.

DISCUSSION In general, nonpenetrating aortic trauma is a rare injury that has been infrequently described in the literature. Historically, aortic injury, presumably due to blunt trauma, was first describe by Vesalius in 1557 and reintroduced into the literature by Rindfleisch in 1893 [16]. The incidence of aortic trauma has been variously reported as comprising 1-9% of all major arterial injuries, the vast majority o f which are from knife and gunshot wounds [17]. Greater than 95% o f blunt aortic trauma involves the thoracic aorta at its points of fixation, such as, the base of the heart, the ligamentum arteriosum and the diaphragmatic hiatus [18]. This type of injury usually results in significant mortality, as 80-90% o f these individuals die instantly secondary to rapid exsanguination. Nonpenetrating abdominal aortic injury, on the

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other hand, is a rare injury, that has been infrequently reported. Strassman [19] reviewed 7000 autopsies and reported 72 cases of aortic trauma-only three of which involved the abdominal aorta (42% of the cases). ParmeJy and associates [20] reviewed 1174 autopsies and noted 296 cases of blunt aortic injury. Only 13 cases or 4.4% involved the abdominal aorta. Blunt abdominal aortic injury tends to have a variable presentation ranging from complete absence or diminution of femoral pulses, to unilateral loss of lower extremity pulses, central or peripheral neurologic deficits, intestinal angina, claudication, distal embolization, aneurysmal changes resulting in a bruit with a pulsatite abdominal mass, aortic stenosis secondary to loss of vasa vasorum, or intimal damage ultimately leading to fibrosis and partial occlusion of the aorta. As may be apparent, there can be a significant time interval in the presentation of these symptoms, particularly if one is not vigilant for such an injury. The first case of a closed abdominal aortic injury described in modern literature is attributable to Ricen in 1941 [21]. He discusses a man who presented with an abdominal aortic aneurysm of 27 years duration, caused by a blow to the midabdomen by a gun butt. A variety of other mechanisms, involving cattle wire, a surfboard, an industrial drying machine, and motor vehicle accidents [17,22], to name a few, have been reported as resulting in this type of aortic injury. By far, the majority of cases are the result of automobile accidents. Recently, Sumpio and Gusberg [17] reviewed all 32 cases reported in the literature on aortic thrombosis and blunt abdominal trauma. They found that 23, or 72% of the cases, involved motor vehicle accidents, six of which were directly attributable to seat belts. On further review of the literature and including our own experience, there are 11 cases in which seat belts resulted in traumatic blunt abdominal aortic injury (Table I).

Mechanism/Etiology

The factors involved in this type of aortic injury can be broadly divided into two categories, major and minor. The major factors include direct force, deceleration injury, and atherosclerosis [1,11,13,17,22]. The minor factors include the development of the person's abdominal musculature and his or her stature [17,22]. Direct force basically implies a crush injury to the aorta as it gets pinched between the seat belt or steering wheel and the noncompJiant lumbar spine. On a more specific basis, one can examine the type of forces generated during a deceleration injury. Aldman, in 1961, looked at the biodynamics of seat belts on impact protection, using anthropometric dummies. In the process of his work he described

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the forces exerted by seat belts on the dummies during sudden deceleration from impact with a barrier. The physics involved in his work are beyond the scope of this paper, but as Dajee [13] described in 1979, the principles of Newton's laws of motion apply. The deceleration force, which can be at least 150 g at an impact velocity of 34 mph [I,13], can be resolved into its two component vectorsma longitudinal and transverse vector in relation to the vertebral column (Fig. 3). The longitudinal component ( " e y e balls up") acts on the dorsal aorta and results in compression of a column of blood already under pressure, and results in back flow and distention of the aortic arch, consequently stretching the dorsal aorta. Longitudinal tension has been suggested as resulting in rupture of the ascending aorta [23]. The transverse vector ( " e y e balls o u t " ) acts perpendicular to the spine at L3-L4. These directional forces along with the compressive force of the seat belt which drives the aorta and abdominal contents caudad into the pelvis, exacerbate the stretching of the dorsal aorta, and thereby result in intimal fracture. An atherosclerotic aorta would increase the likelihood of intimal fracture or embolization of atherosclerotic plaques. In four of ten patients atherosclerosis was found to be significant in the genesis of their aortic injury from blunt trauma [22]. This may be related to the decreased elasticity of a semirigid atheromatous aorta, thereby increasing its susceptibility to disruption, dissection, and embolization. The remaining factors, abdominal musculature and stature may have a minor rote in the extent of abdominal aortic injury. It is to be noted that one can get complete transection of the rectus muscle from seat belt injuries, as occurred in Patient 1. Sites of injury

In the present series, disruption of the aortic intima occurred distal to the origin of the inferior mesenteric artery (IMA) in eight of eleven cases. In an earlier review of 27 cases of blunt abdominal trauma, 12 occurred distal to the IMA, five involved the IMA, and all but two of the remaining cases involved the infrarenal aorta, with the majority being distal to the IMA, particularly when seat belts are involved. The lower thorax may provide some protection to the suprarenal segment of the aorta. Types of injury

Blunt abdominal trauma with aortic injury may present as a " t r i a d " involving the abdominal aorta, the bowel and its mesentery, and the vertebral column. In a review of all reported cases of non penetrating abdominal aortic injuries, associated

40/F

38/F

78/F

28/F

65/M

65/F

54/M

67/M

19/M

45/M

Rybak 1969

Thai t971

Blute 1973

Danto 1976

Hertzer 1977

Dajee 1979

Clyne 1985

Dunlop 1986

Present Case 1

Present Case 2

* IMA = Inferior mesenteric artery

Age/ Sex 24/M

Author Campbell 1969

Driver

Rear passenger

Driver

Driver

Driver

Driver

Rear passenger

Driver

Driver

Front passenger

Location in Vehicle Driver

Lap belt

Lap belt

3-point lap/

3-point lap/ diagonal belt

Lap belt

Unknown

Lap belt

Lap belt

Lap belt

Lap belt

Seat belt Lap belt

Absent

Diminished

Present with absent pedal pulse

RE--reduced LE--absent

Absent

Diminished right lower extremity

Diminished

Absent

Diminished right lower extremity

Absent

Femoral pulses Unknown

Present

Present

Absent

Absent

Present

Absent

Present

Present

Present

Present

Bowel injury Present

Absent

Present

Present

Present

Present

Present

Present

Present

Absent

Present

Neurologic injury Absent

5 months

14 hours

< 6 hours

9 months

Operative delay 7 months

Absent

Present

Present

Absent

< 6 hours

8 hours

18+ hours

< 6 hours

Unknown < 6 hours

Unknown < 6 hours (est)

Present

Present

Present

Present

Lumbar fracture Present

Proxomal to IMA

Distal to IMA

Posterior tibial arteries

Distal to IMA

Distal to IMA

Distal right popliteal

Distal to IMA

Distal to IMA

Distal to IMA

Distal to IMA

Occlusion level Distal to IMA*

TABLE I.--Summary data of eleven cases with seat belt associated blunt abdominal aortic trauma

Aortic graft

Aortic graft

Fasciotomies and embolectomy

Aortoright iliac and left femoral

Embolectomy suture of intima

Embolectomy

Aortic graft

Aortofemoral graft

Aortoiliac graft

Aortoiliac graft

Operation Unknown

Recovered

Neurologic sequelae

Bilateral below-knee amputations

Recovered

Died

Recovered

Recovered

Died

Recovered

Below-knee amputation

Results Recovered

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Seat belt aorta.

This review of 11 cases of seat-belt associated blunt abdominal aortic trauma, includes nine cases reported in the literature and two new cases. Lap-t...
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