Lower Extremity Vascular Trauma

Level of Injury

The lower extremity is the most frequent site of arterial injury in both civilian and military trauma. The femoral arteries in general and the superficial femoral artery (SFA) specifically have the highest consistently reported rates of injury, with the remainder divided between the popliteal and tibial arteries. The distribution of tibial artery injuries is not consistently reported in the literature and injuries to the anterior tibial, posterior tibial, and peroneal arteries are variably consolidated or reported individually, making it difficult to compare injury location data across studies. In general, however, the reported combined rate of overall tibial artery injury is similar to that of combined femoral injuries. Multiple arterial injuries in a single lower extremity are likely to have resulted from a devastating degree of traumatic energy transfer—either trans-extremity penetrating trauma or near or complete traumatic amputations from high impact blunt and shear forces. Such patterns of vascular injury are reported most commonly at the tibial level and are present in 6% to 20% of cases. Concomitant injury to multiple lower extremity artery levels is reported in civilian trauma patients in 10% to 20% of cases. This finding is more common with more complex injury patterns, such as those produced by severe blunt trauma and crush injuries. Multiple injuries at the same arterial level or within the same artery (for example, multiple tibial artery injuries or concomitant above- and below-knee popliteal injury) are not specifically reported in the literature but presumably occur more frequently than injury at multiple levels.

Mechanism of Injury

Most reports of lower extremity vascular injuries have about equal proportions of blunt and penetrating injuries. In civilian trauma, blunt arterial injuries are more frequently seen at or below the knee in the popliteal and tibial segments than above the knee in the femoral segment. Common superficial and deep femoral arterial injuries are more likely to be caused by penetrating mechanisms. Blunt mechanisms in civilian trauma produce higher rates of fracture and significant soft tissue and nerve injuries than penetrating ones. Correspondingly, these injuries tend to be associated with greater limb injury severity and have poorer limb outcomes. In modern military trauma, recent reports of lower extremity vascular injury consist of almost three-quarters of injuries produced via explosions. These injuries are particularly devastating, resulting in extensive tissue destruction and rates of limb salvage correspondingly lower than those seen in civilian lower extremity vascular trauma. In limbs sustaining combat-related below-knee explosive trauma with fracture and arterial injury, the delayed amputation rate following initial limb salvage has been reported at almost 80%.

Table 22.1 presents selected civilian and military arterial injury data since 2000.

Arterial Pathology

The nature of the injury to a lower extremity artery has implications for the workup and treatment that will be discussed later in the chapter. Arterial occlusion is reported in up to a third of cases, while transection is seen in 25% to 45% of lower extremities. Other arterial injury types explicitly reported in the civilian literature include: laceration (partial transection), intimal injury, and pseudoaneurysm. The reported pathologies represent the majority of the variety of traumatic injuries that can affect the arteries of the lower extremity. There are two basic categories of these pathologies: occlusive and disruptive. These pathologic categories align with clinical presentations that will be discussed later in this chapter.

Occlusive injuries can disrupt flow completely or partially and are the result of thrombosis, intimal dissection, mural hematoma, or entrapment/kinking. Thrombosis of an injured artery is caused by intimal damage that precipitates platelet activation and initiation of the clotting mechanisms. Focal dissection and mural hematoma result in direct luminal diameter compromise and can also serve as a nidus for thrombosis. Lower extremity arterial entrapment within, or kinking of a vessel around, a fracture can also cause an occlusive injury. Depending on the degree of vessel wall trauma in the area of the bony injury, the occlusion may resolve with surgical freeing of the entrapped artery or fracture reduction without the necessity for vascular reconstruction. This highlights the importance of early reduction of displaced fractures and reassessment of the vascular status of the limb prior to committing to an operative plan. Regardless of the underlying pathology, complete or partial occlusive lower extremity arterial injuries present with varying degrees of clinical ischemia distal to the arterial injury.

Complete and partial arterial transections, punctures, and pseudoaneurysms comprise the pathologies producing disruptive arterial injuries. These pathologies all involve varying degrees of direct luminal disruption resulting in the potential for blood to escape the vessel. Arterial wall disruption usually results from direct trauma to the vessel whether by a projectile, blade, or fragment of bone. Iatrogenic femoral artery injuries such as those resulting from percutaneous access typically result in disruptive injuries that may be initially occult. These injuries manifest as pseudoaneurysms or arteriovenous fistulas and can be a challenge to diagnose and treat. Bleeding from named arterial disruptive injuries can be significant, and even life-threatening. These injuries present clinically with signs of hemorrhage and usually demand prompt identification and hemorrhage control. Traumatic arteriovenous fistula may also be present if a major artery and vein sustain disruptive injuries in proximity to each other. Though not explicitly reported, it stands to reason that occlusive arterial injuries to the lower extremities are more likely to result from blunt mechanisms, whereas transections (both partial and complete) are more likely to arise from penetrating trauma. The degree of traumatic tissue disruption and the degree of limb ischemia seem to predict limb loss regardless of mechanism. Due to the complex nature of occlusive injuries and the varying degree of thrombosis that can be involved, reconstruction of these injuries can be challenging.

Military lower extremity injuries usually result from high-energy explosions and deserve special mention due to their unique nature. Explosions produce extensive damage to multiple limb tissues due to primary (blast overpressure), secondary (fragment), and tertiary (blunt) blast trauma. The high-energy and complex nature of the military explosion mechanism of injury can produce any of the arterial pathologies listed previously alone or in combination. Complex segmental arterial destruction, sometimes at multiple levels, is a common finding ( Fig. 22.1 ).

Mortality

In the injured patient, hemorrhage causes of about one-third of deaths. Deaths resulting from hemorrhaging isolated lower extremity vascular injuries, however, are very uncommon, even in the presence of a named arterial or venous injury. Because of this, mortality is infrequently reported as an outcome in clinical series of vascular injuries to the lower extremity and specific risk factors are not defined. The recent, military inspired adoption of tourniquets as primary hemostatic measures in the civilian prehospital arena may serve to diminish mortality associated with vascular injuries to the leg further. In isolated leg vascular injuries, as the level of vascular injury becomes more proximal, the mortality rate increases, ranging from around 1% with tibial injuries to almost 8% at the common femoral level. Because hemorrhage is the likely cause of mortality from a vascular injury to the lower extremity, it stands to reason that disruptive injuries (primarily resulting from penetrating mechanisms) produce most of these fatalities.