Popliteal Artery Pseudoaneurysm: An Unusual Complication of Tibial Traction

Pins inserted for external fixators of the tibia have injured the anterior tibial vessels and branches of the peroneal and saphenous nerves. A proximal tibial traction pin, in essence a transfixion pin, can cause similar injuries, particularly with imperfect placement (Figure 5).^3,10

A pseudoaneurysm is a pulsating, encapsulated hematoma that remains in communication with the lumen of a ruptured or injured vessel. The arterial wall itself is torn or ruptured, and the external wall of the aneurysmal sac consists of outer arterial layers, perivascular tissue, blood clot, or a layer of reactive fibrosis. This contrasts with a true aneurysm, in which all 3 arterial layers (intima, media, adventitia) remain confluent but are dilated beyond their normal diameter. Of all pseudo­aneurysms, those caused iatrogenically are the most common and are typically produced by femoral artery catheterization, accounting for 70% to 80% of the incidence.¹¹

Our patient’s injury was most likely caused by an initial error in pin placement before the pin was driven across the tibia. The typical teaching for traction-pin placement involves finding the correct starting point and then using the pin to feel the anterior and posterior surfaces of the bone (described earlier). If the pin slid posteriorly, it may have contacted the artery and caused a small tear that eventually led to the formation of the pseudoaneurysm.

The pseudoaneurysm was not the only complication in the present case. There was also the delay in diagnosis. A standard technique is used to evaluate the lower extremity venous system for DVT. The ultrasonographer starts with the probe as proximal as possible (above the inguinal ligament), ideally proximal to the saphenofemoral junction, and moves distally in 1-cm increments, checking the veins for compressibility, color, and Doppler signal. Unless advised otherwise, the ultrasonographer typically does not examine distal to the knee.^12,13 As this patient’s pseudoaneurysm was distal to the knee, it was not found on initial ultrasound, and her inability to obtain her MRI compounded the delay. The second ultrasound identified the pseudoaneurysm. The ultrasonographer examined more distally, given the contrast between the clinical diagnosis of vascular pathology and the negative Doppler study. Computed tomography angiogram confirmed the diagnosis and guided the vascular surgeons in identifying the lesion as a pseudoaneurysm, allowing it to be coiled rather than bypassed.

Duplex ultrasound is the preferred diagnostic modality for imaging pseudoaneurysms. Although our patient’s scan was performed in timely fashion, it did not image the area of pathology. Instead, this patient with multiple orthopedic injuries was scanned for DVT, the most likely cause of her lower extremity swelling. Had a pseudoaneurysm been suspected, the ultrasonographer would have been instructed to image the entire extremity and not just the area where DVT might be found.

Fortunately, despite the treatment delay, the patient recovered well from both the traumatic injuries sustained in the car crash and the likely iatrogenic pseudoaneurysm. Although traction pins are easily and frequently used, they can have complications, which are often preventable. Starting with pin placement itself, there were several opportunities for improving this patient’s care or, at a minimum, reducing the time spent in diagnosis. If the pin had been noticed sliding posteriorly during insertion, extra attention during follow-up visits could have helped identify the injury sooner. Another difficulty in diagnosis was that of obtaining the appropriate outpatient radiology studies which necessitated repeat ED visits. An additional juncture was between the patient’s multiple ED visits for similar complaints. Obtaining advanced imaging sooner could have helped in diagnosing the pseudoaneurysm earlier.