Introduction

In humans, pseudoaneurysms are common vascular abnormalities that are also known as false aneurysms, which result from a defect in the arterial wall. Blood leaks through the disrupted wall into the surrounding tissues, which leads to a persistent communication between the originating artery and the adjacent cavity.¹ In contrast, true aneurysms are dilations of the arterial wall in which all three wall layers (the tunica intima, tunica media, and tunica adventitia) remain intact.² Pseudoaneurysms have a variety of causes, such as inflammation, trauma, and iatrogenic causes such as surgery, percutaneous biopsy, drainage, and vascular catheterization. Pseudoaneurysms may occur in any damaged vessel, including the carotid, extremity, and visceral arteries.¹ They are also a common occurrence after orthopedic procedures. Damage occurs due to partial division and erosion of the pulsating arterial wall, often as a result of the projection of metallic screws or hardware. In humans, this complication has been reported after fixation of femoral, tibial, and radial fractures and total knee arthroplasty.^3–8

There is a paucity of information regarding pseudoaneurysms in dogs, which suggests that they are rare in this context. To our knowledge, arterial pseudoaneurysms have only been scarcely reported in dogs, including pseudoaneurysms of the aorta and cranial mesenteric artery.^9,10 Thus, we report two cases of a rare complication of cranial tibial artery (CTA) pseudoaneurysm following routine canine orthopedic procedures. One case involved a pseudoaneurysm associated with the placement of tibial pins that presented 25 days after external skeletal fixator implantation. The other case involved a pseudoaneurysm associated with osteotomy or tibial screw placement that presented 30 days after tibial plateau leveling osteotomy (TPLO).

Case Reports

Informed consent was obtained from the pet owners. All patients were clinically managed according to contemporary standards of care.

Case 1

A 5 yr old male Gascon-Saintongeois weighing 30 kg presented 25 days after repair of a left-side common calcaneal tendon rupture, which had occurred during a hunting expedition. Surgical repair involved debridement and apposition of the ends of tendons with a three-loop pulley suture, as well as temporary immobilization of the tarsus with a transarticular external skeletal fixator (TESF) (Figures 1A, B). External support was provided for an intended period of 4 wk after surgery. Radiographic evaluation was performed immediately after TESF placement and showed satisfactory implant positioning. A light-weight bandage was applied around only the TESF frame to reduce the risk of self-injury from the sharp pins. The dog made an uneventful recovery and was discharged on postoperative day 3. Regular bandage changes were scheduled with the referring veterinarian every 7 to 10 days until frame removal.

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The dog was readmitted 25 days after surgery following acute-onset lethargy, dysorexia, and non–weight-bearing lameness on the operating limb. On presentation, the dog was lethargic with pallor of the mucous membranes and tachycardia at 130 beats per minute. Physical examination demonstrated severe swelling and pain over the entire left tibia. The area was warm, and the skin was discolored with ecchymoses. A poorly defined pulsatile bulge measuring approximately 3 cm in diameter was palpated around the lateral aspect of the most proximal pin of the TESF. Furthermore, there was major active bleeding from this most proximal pin tract, which was initially managed using large gauze sponges stretched between pins of the TESF (Figures 1C, D). The temperature of the lower extremity was grossly normal, and the dog had normal distal sensation. The packed cell volume (PCV) at presentation was 0.27 L/L (reference range 0.37–0.61 L/L), which subsequently decreased to 0.22 L/L over the initial 12 hr of hospitalization. The results of serum biochemistry analyses were unremarkable. The prothrombin level and activated partial thromboplastin time were both within their normal ranges. Radiographic examination revealed marked periosteal reactions on tibial diaphysis centered around the two most proximal pins suggesting a surgical site infection. No implant loosening was observed (Figures 1E, F).

Ultrasonography was performed by a board-certified radiologist and revealed a well-defined hypoechoic cavity that was adjacent to the CTA and measured 3.5 cm × 1.9 cm. A hyperechoic mass suspected to be a hematoma was abutting this hypoechoic cavity. Color Doppler ultrasonography demonstrated a swirling pattern of the arterial blood within this cavity with a typical “yin-yang sign” that was consistent with pseudoaneurysm (Figure 2A). The pseudoaneurysm was in proximity to the lateral aspect of the most proximal pin of the TESF. We hypothesized that this pin could be a potential cause of the pseudoaneurysm formation. To better characterize this vascular anomaly, computed tomography angiography was performed using a 64-slice multidetector scanner. The images were acquired in soft tissue windows, and the angiograms were acquired with repeated scans that were obtained 30 to 90 s after the administration of 2 mL/kg of iohexol (300 mg/mL) at a rate of 2 mL/s into the left cephalic vein. This confirmed the presence of a well-defined oval structure (3.45 cm × 1.9 cm), which was filled with contrast material and was adjacent to the two most proximal pins with perilesional hematoma (12 × 6.5 × 3.6 cm). No active contrast extravasation was observed (Figure 2B).

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On the day after, an open surgical ligation of the supplying vessel (CTA) was performed by a board-certified surgeon (J-G.G.). A 3 cm–long incision proximal to the palpable pulsatile bulge over the fibular head was performed. The CTA supplying the pseudoaneurysm was exposed and was double ligated using simple ligatures with 2/0 polydioxanone^a. No pulsatile sensation was felt intraoperatively after CTA ligation. Hematoma evacuation was then performed using a second surgical incision distal to the first one on the lateral aspect of the crus with no associated active bleeding. Clots were submitted for aerobic and anaerobic bacterial culture. During hematoma evacuation, the most proximal pin of the TESF was visualized adjacent to the pseudoaneurysm. Given the concern for potential infection and the immobilization of the tarsus already carried out for 25 days (external support initially desired for 4 wk), the decision was taken to remove the entire TESF. The surgical site was closed over a closed-suction drain owing to the large size of the hematoma that was evacuated and the high suspicion of surgical site infection. No intraoperative complications occurred.

The dog had an uneventful recovery. Morphine^b (0.2 mg/kg, IV, q 4 hr) was administered for 24 hr, and meloxicam^c (0.1 mg/kg, per os [PO], q 24 hr) was administered for 7 days. Three days after surgery, the surgical site appeared normal except for mild skin ecchymoses, and the closed-suction drain was removed. Four days postoperatively, the dog was discharged from the hospital and was fully weight-bearing on the operated limb with a normograde stance. A strain of Staphylococcus pseudintermedius with sensitivity to cefalexin was isolated from bacterial culture. Oral cefalexin^d (15 mg/kg, PO, q 12 hr) was administered for 2 wk. The dog’s postoperative course was unremarkable. At the 6 mo follow-up, the dog had no further lameness, and physical examination did not reveal abnormalities.

Discussion

This report describes the clinical and imaging features of CTA pseudoaneurysm in two dogs that underwent routine tibial orthopedic procedures. The clinical features identified were lethargy, pallor of the mucous membranes, non–weight-bearing lameness, bleeding from the surgical site with hematoma, pain, and a palpable, poorly delineated, pulsatile bulge. In color Doppler ultrasonography, both dogs showed imaging features of a hypoechoic cavity adjacent to the CTA containing a swirling blood flow connected to the vascular lumen. Similar to humans, this complication was presumed to be a delayed sequela of the initial surgical trauma and was recognized between 25 and 30 days following the initial orthopedic surgery. The symptoms displayed by our two patients were consistent with a rupture of the pseudoaneurysm. This is why the pseudoaneurysm was likely appreciated by the owners and prompted re-presentation. If not for those findings, the pseudoaneurysm may have gone unnoticed much longer.^3–6,11 For orthopedic surgeons, it is important to recognize clinical signs of a potential tibial arterial pseudoaneurysm, as early surgical intervention may prevent loss of limb or life.

In humans, the popliteal artery is the most frequent region for pseudoaneurysm in the lower extremities because it is not supported by muscular tissue that shields it from dilatation and bending, unlike superficial and deep femoral arteries.¹² In contrast, pseudoaneurysms of the anterior tibial artery (a branch of the popliteal artery) are exceedingly rare.¹² Pseudoaneurysms of this artery after internal fixation of proximal tibial fractures have been reported to be caused primarily by overpenetration of drill bits or screws. Inamdar et al. described a case of pseudoaneurysm of the anterior tibial artery when placing the proximal interlocking bolt of an intramedullary tibia nail.⁵ Another report described this complication after minimally invasive plate osteosynthesis for proximal tibial fracture fixation.⁴ In the present cases, the involved artery was the CTA, which has not been previously reported in dogs to our knowledge. As in humans, the CTA in dogs is the major branch of the popliteal artery that emerges at the distal part of the popliteal muscle.

Moles and colleagues described the anatomy of the CTA, which was suspected to be the source of severe hemorrhage during TPLO procedures.¹³ The CTA runs caudal to the stifle between the tibial condyles, deep to the popliteus muscle and just medial to the popliteal sesamoid, and then deviates laterally between the tibia and fibula as it courses further distally.¹³ At about the proximal third of the tibia, at which TPLO is commonly performed, the artery runs deep to the extensor digitorum longus muscle ∼4 mm apart from the caudolateral margin of the tibia. Another recent study on dogs using computed tomography angiography revealed a median distance between the caudal tibial cortex and CTA of ∼2.24 mm (1.53–3.63 mm).¹⁴ Such anatomical characteristics make the CTA relatively fixed, reduce its mobility, and potentially make it more prone to injury during surgery.

In case 1, the most likely cause of the pseudoaneurysm was injury to the CTA with placement of the most proximal percutaneous pin during the surgery. Safe anatomical corridors in the canine tibia have been evaluated and should be considered by the orthopedic surgeon to avoid iatrogenic damages to neurovascular structures. Angles measurements in cross sections of the canine crus show that at the level of the proximal diaphysis (distal to the tibial tuberosity), at which the most proximal pin of the TESF was inserted, pin insertion is safe within a 105° arc, from the midpoint of the cranial tibial muscle crosses the sagittal midline toward the medial side. Interestingly, the tibial safe corridor showed its lowest extent in diaphysis at this level.¹⁵ Pin insertion in the proximal tibia should be carried out from the medial aspect as caudally as possible (in order to drive the pin through the widest bone diameter and achieve a better purchase) and transfixation should be ideally avoided because of the presence of the cranial tibial vessels, peroneal nerve, and extensor muscles on the lateral aspect of the tibia.¹⁵ In case 2, it was not obvious whether the CTA injury was caused by osteotomy (vascular laceration by the oscillating saw blade) or overpenetration of the drill bit, depth gauge, or proximal screws located on the head of the plate. After evaluating the 3D reconstructions in the study by Cieciora and colleagues, the positioning of the TPLO might influence the incidence of vascular damage. Based on the 3D reconstructions, a higher-positioned osteotomy might increase the risk of lacerating the CTA.¹⁶ No overpenetration of the screws was identified in the postoperative radiographic evaluation, but given the triangular shape of the proximal tibia in the cross-section, one can have a false impression of screw length. Thus, radiography may be misleading.

In both cases, injury to the CTA wall may have caused an acute local hemorrhage that remained unnoticed during the initial surgical procedure. In humans, a recommendation is to avoid overpenetration of the drill bit after drilling the far cortex. A short drill bit should be used, and the length of the drill outside the sleeve should not be more than the approximate diameter of the bone.¹⁷ Interestingly, predrilling during placement of an external skeletal fixator has also been reported as a risk factor for pseudoaneurysms in humans.⁴ In case 1, no predrilling was used.

Diagnosis of pseudoaneurysm was established based on ultrasound examination in the present cases and was confirmed in computed tomography angiography in one dog. In humans, ultrasonography is a useful, cost-effective method and is usually the first choice in diagnosis of femoral and tibial pseudoaneurysms. A prospective study demonstrated that color Doppler ultrasonography has high sensitivity (94%) and specificity (97%) for the diagnosis of peripheral pseudoaneurysms.¹⁸ Two-dimensional B-mode (brightness mode) image shows an anechoic or hypoechoic cavity adjacent to the damaged artery. However, it is not always easy to demonstrate the communication between the originating artery and the sac with B-mode ultrasonography. Color Doppler ultrasonography supports the diagnosis by demonstrating arterial blood flow within the sac adjacent to the damaged artery. In this context, this blood flow is known to have a characteristic “yin-yang sign.” Turbulent blood flow is represented by an interchangeable color appearance (either red or blue) when using color Doppler.^19,20 The present cases showed saccular outpouching of the vessel, and we considered the swirling appearance of the blood flow to correspond to the “yin-yang sign.” Computed tomography angiography was only performed in case 1 and allows detailed anatomical evaluation of the pseudoaneurysm’s anatomical borders and association with adjacent structures, which is more informative for preoperative planning. In addition, an arterial phase was useful for assessing any direct communication with adjacent arteries to exclude an arteriovenous fistula.²⁰

To avoid consequences of rupture or rapid enlargement resulting in pressure on the surrounding tissues with life-threatening complications, surgery should be undertaken as soon as feasible as the diagnosis is confirmed and the patient is hemodynamically stable. In humans, several techniques for the treatment of pseudoaneurysms have been reported, including excision of the aneurysmal sac and lateral wall repair, obliterative or reconstructive endoaneurysmorrhaphy, limited arterial resection, end-to-end anastomosis, pseudoaneurysm resection with graft placement, and ligation of the artery supplying the pseudoaneurysm.^21–24 Interventional radiological treatment methods such as ultrasound-guided compression, percutaneous thrombin injection, and endovascular approaches have become the preferred methods in the treatment of pseudoaneurysms and have lower morbidity and mortality rates compared with surgical options.^1,20 In the present cases, surgical occlusion of the CTA was successful using a proximocaudolateral approach and was preferred over surgical excision of the pseudoaneurysm because surgical occlusion of the CTA was deemed to be a less technically demanding procedure. Interestingly, Moles and colleagues reported that the distal popliteal artery and the proximal CTA could also be reliably accessed just proximal to the medial femoral condyle in the popliteal fossa by separating the cranial and caudal bellies of sartorius muscle and dissecting between vastus medialis and semimembranosus muscles. The authors suggested that this approach was rapid and facilitated by a small extent of the surgical incision that would be routinely used in TPLO procedures.¹³

Conclusion

Acute vascular injuries during surgery that result in delayed vascular malformations, such as pseudoaneurysms, are potentially serious complications that can arise secondary to orthopedic procedures performed at the level of the proximal tibia. Improved knowledge of the CTA vasculature may help prevent inadvertent damage during surgery. Increased risk for injury may occur when performing high tibial osteotomies or when overpenetration of a drill bit, depth gauge, or implant occurs, which pose risk for vascular structures on the contralateral side of the bone. Because the vascular structures are distant from the operative field and the clinical presentation is often delayed, it is possible to overlook significant vascular injury during surgery. This makes it imperative for surgeons to recognize the presentation of these delayed vascular malformations to avoid limb or life-threatening long-term morbidity.