Blunt Popliteal Artery Injuries

Physical Examination

A careful vascular examination is the key to the diagnosis of a popliteal artery injury. Unlike some patients with a popliteal artery injury caused by penetrating trauma who have an entirely normal vascular examination, patients with popliteal injuries secondary to blunt forces rarely do. In our experience, blunt popliteal artery injuries were associated with either an absent (94%) or diminished (4%) distal pulse.

In a related series of 115 patients with knee dislocations, angiographically documented popliteal artery injuries affected 27 (23%) patients. An abnormal pedal pulse identified popliteal artery injuries with a sensitivity of 85% and specificity of 93%. All injuries that required intervention were associated with a diminished pulse. Dennis reported an identical experience in 37 patients with knee dislocations. All patients who required a popliteal repair had absent pedal pulses. More recently, Abou-Sayed and Berger confirmed the sensitivity of physical examination in 52 patients. Twenty-three patients, who had normal pulse examinations, did not undergo angiography and required no vascular intervention. Angiography was performed in 13 patients with normal pulse examinations (at the discretion of the attending surgeon), and no clinically significant lesions were identified that required intervention.

A complete vascular examination should include an ankle-to-brachial index (ABI). In a study of 100 consecutive injured limbs, Lynch and Johanson showed that arterial injuries that required intervention were discovered in 14 cases, and an ABI less than 0.90 predicted the injury with 87% sensitivity and 97% specificity. A study at our own institution validated Lynch’s findings, although we found an ABI threshold of less than 1.0 more precise in predicting the presence of an arterial injury. Thus, ABI has become a routine part of the vascular assessment of the injured extremity, and ABI less than 0.9 to 1.0 warrants further investigation for the presence of an arterial injury, even when the pulse examination is reported to be normal.

Because of the close proximity of major nerves to the popliteal vessels, a thorough neurologic examination is critical. In the popliteal area, the close proximity of major nerves has led to an incidence of associated nerve injuries between 8% and 58%. Nerve injuries result in severe long-term neurologic deficits in up to 20% of patients and are a key determinant in subsequent limb function.

Imaging

Plain radiographs are part of a standard diagnostic evaluation for a trauma patient. In patients with blunt trauma, fractures or dislocations in key anatomic areas, such as a posterior knee dislocation, can alert the surgeon to the possibility of a vascular injury. In patients who come to the hospital with obvious deformities, bony injuries are easily appreciated. However, even the most minor-appearing injured extremity can harbor an occult bony disruption. Christian identified unrecognized arterial injuries in 50% of patients who come to the hospital with severe tibial fractures. Therefore, a series of plain radiographs to ensure the absence of a fracture is obligatory in the evaluation of lower extremity trauma.

Digital angiography is being replaced by computed tomography angiography (CTA) in the diagnosis of vascular extremity trauma. When compared to digital angiography for trauma patients, CTA has the distinct advantage of being equivalent in accuracy, more time efficient, less invasive, and less expensive. Current CT scanning is also readily available and provides simultaneous imaging of the head, neck, chest and abdomen as well as surrounding extremity structures and adjacent anatomy in a single examination.

Soto and colleagues performed one of the early comparisons between CTA and digital angiography for evaluation of suspected vascular injuries. In this study, all extremity trauma patients referred for digital angiography underwent CTA. Two independent observers documented sensitivity and specificity levels greater than 90% for diagnosis of vascular injuries, with an interobserver agreement of 0.9 (kappa coefficient).

In selected circumstances, digital angiographic confirmation of the popliteal artery injury is helpful in planning the arterial repair. A digital angiogram can provide a more precise localization of the injury, a better visualization of occlusion length and which infrapopliteal vessels are involved, and a more accurate assessment of distal thrombus and the presence of a second, more distal injury.

When evaluating either CTA or digital angiographic images, the surgeon must not be trapped into misdiagnosing a short segmental narrowing of the artery as “spasm” and assume that the lesion will spontaneously resolve. Such lesions usually represent intramural hemorrhage or other forms of vessel wall injury that can progress to total occlusion. Vasospasm can occur but is usually seen as a long, smooth narrowing of an otherwise patent vessel, or there may be multiple areas of beading in a vessel with smooth, intact intima. These findings suggesting external compression may also be seen in patients with increased compartment pressures and should alert the surgeon that the compartment pressures must be assessed.