The main arterial support to the lower extremity is from the femoral artery which is a direct continuation of the external iliac artery [1]. The femoral artery changes name to the popliteal artery (PA) once it passes through the adductor hiatus into the popliteal fossa. Developmentally, the PA is formed by the fusion of the femoral plexus and the regressing axial plexus. The final form of the PA is found to be superficial to the popliteus muscle and inferior to the medial head of the gastrocnemius muscle. The inferior portion of the PA forms from the anterior tibial (ATA) and posterior tibial (PTA) artery, with the former originating from the popliteal vessels and the latter from popliteal vessels and the primordial femoral artery [2]. The typical branching pattern of the PA is into an ATA and PTA with the fibular artery (FA) branching from the PTA. The PTA and FA stay in the posterior compartment on the leg while the ATA travels forward to supply the anterior compartment of the leg [3].

There have been many reported cases of variations of the PA, ranging from 6.4%–18.2%. Variations of the PA can be classified into three different categories with three subtypes in each category. This classification system was developed by Kim and co-authors in 1989, which adapted the descriptions provided by Lippert and Pabst [2].

Category I describes the typical PA presentation (Type A) (Fig. 1A), with two different variations: a trifurcation of the PTA, ATA, and FA (Type B) (Fig. 1B) or a PTA and a common tibiofibular trunk (CTT) which branches into the ATA and FA (Type C) (Fig. 1C). Type A is seen in 81.8%–93.6% of population, Type B has an incidence of 0%–6% and Type C has been seen in 0.1%–5% of the population [2].

Figure 1. The figure contains a summary of Type I variations of the PA that can be found. (A) The typical presentation, PA with ATA and PTA branches with FA branching from PTA. (B) A trifurcation of the PA, all branches originating from the PA. (C) PA with PTA and CTT, with ATA and FA branching from CTT. PA, popliteal artery; ATA, anterior tibial artery; PTA, posterior tibial artery; FA, fibular artery; CTT, common tibiofibular trunk.

Category II describes a PA who divides superiorly to the popliteal muscle. There are three subtypes of this category: type A describes when ATA comes off the PA superior to or at the level of the patella and travels toward the anterior compartment in front of or behind the popliteus muscle, type B describes a PTA which arises superior to or at the level of the patella and there is a CTT present, type C describes a high FA. The incidence of these types are as follows: type IIA: 1.2%–5%, type IIB: 0.4%–5.9%, and type IIC: 0%–0.2% [2].

Category III describes a situation when one or more of the arteries is hypoplastic or aplastic. There are also three subcategories associated with Category III. The three subcategories are: PT is hypoplastic (type A), ATA/dorsalis pedis is hypoplastic (type B), or both PT and ATA are hypoplastic (type C). The reported percentages of these types are 0%–5.1%, 0%–5%, and 0%–0.8%, respectively [2].

In this case study, a variation in the PA branching will be described and reasons for the importance of understanding of the variations of lower limb arterial supply will be discussed.

During a routine dissection of the right leg in a 92-year-old female cadaver who died of cardiopulmonary respiratory failure, a variation of the lower limb arterial supply was found. To better visualize the variation, the gastrocnemius muscle was reflected laterally by detaching the proximal head of the muscle. In this cadaver, the branches of the PA are the CTT and PTA. Branching from the CTT is the ATA and FA (Fig. 2). This is classified as a type IC variation [2]. This branching pattern is found in 0.1% to 5% of the population [2, 4-8]. Further dissection of the arteries showed that they supply the areas of the leg they are expected to supply even with variation: ATA for the anterior compartment and PTA and FA for the posterior compartment. There were no additional anomalies or pathologies present in the right leg of this cadaver. There was normal patterning of the PA in the left leg of this cadaver.

Figure 2. The image above contains the posterior view of the right leg. The reflected gastrocnemius is pictured. PA is located between the femoral condyles and splits into the PTA and the CTT below the popliteus muscle. Branching from the CTT is the FA and ATA. PA, popliteal artery; PTA, posterior tibial artery; CTT, common tibiofibular trunk; FA, fibular artery; ATA, anterior tibial artery; br., branch; m, muscle; S, superior; L, lateral.

It is important to understand how variation can occur in the PA during development in order to correctly prepare for knee and lower leg vascular procedures. The vascular limb bud for lower extremity typically begins to form at the end of the fourth week of embryonic development originating from the intersegmental arteries arising from the aorta. The vascular pattern that forms stems from the dorsal root of the umbilical artery that gives rise to the sciatic and axial arteries. The distal sciatic artery gives rise to the PA and fibular branch, meanwhile the PA gives rise to the ATA. The PA also combines with the distal femoral artery to form the PTA [2]. A balance between angiogenesis, vasculogenesis and apoptosis is what forms the typical variation of the vasculature in the lower extremity; however, if we see an imbalance of angiogenesis, vasculogenesis, and apoptosis there can be variations seen with the PA and its branching pattern [2].

In this case study, the cadaver has an atypical branching pattern of the PA in the right leg, a type IC PA variation in the right leg. The PA branches into a PTA and a CTT instead of the PTA and ATA branching from the PA. This variation is only present in 0.1%–5% of the population; however, this is even more uncommon since this variation is found unilaterally in this case [2, 4-8]. There is an incidence of 9%–13% of a unilateral PA branching variation among various studies with Type IC, Type IB, and Type IIB being the most common anatomical variations that appear unilaterally [5, 7].

PA anatomical variations are found in 10% of the normal population with many people not knowing they have a variation until it is discovered accidentally by imaging for another health problem [6, 7]. Understanding the anatomy of the lower leg arteries is important for surgeons when creating a surgical plan for a patient. There are many surgical implications when knowing an anatomical variation of the PA is important including: PTA plateau fractures and infrapopliteal balloon angioplasty [5, 9-13].

Posterolateral tibial plateau fractures are caused by a valgus and axial compressive force while the knee is in flexion leading to a shearing force being exerted on the posterolateral tibial plateau by the lateral femoral condyle [10, 11]. The posterolateral repair approach for a tibial plateau fracture provides a biomechanical advantage, however, attention to the variations of the ATA branching from the PA is required [10]. When performing this procedure, the distal dissection is restricted to no more than 5 centimeters below the joint level to avoid the vessels traversing the interosseous membrane [11]. This dissection restriction has been set for normal PA branching patterns; however, this does not account for PA variations where there is abnormal branching of the ATA. For a PA Type IC variation, the PA branches into PTA and CTT with the CTT giving rise to the ATA and FA branches [2]. This variation can alter the location where the ATA pierces the interosseous membrane creating an increased risk for nicking the CTT or ATA when performing the deep structures dissection for this procedure, leading to ischemic necrosis of the muscles of this compartment [10].

Infrapopliteal balloon angioplasty is a treatment option for patients who have been diagnosed with critical limb ischemia due to atherosclerotic disease. For this procedure, the balloon size was selected based on the diameter of an adjacent non-diseased artery. The tibiofibular trunk, with the common branches of PTA and fibular arteries, needed a larger balloon compared to the tibial arteries [12]. In patients with a Type 1C variation, the CTT is no longer medial but a lateral branch of the PA. Surgeons and interventional radiologists should be aware of this variation in order to avoid any difficulties during the procedure [13]. With this knowledge, podiatric, vascular, and orthopedic surgeons can determine the best approach for the procedure at hand and minimize any potential complications both operatively or post-operatively.

In conclusion, this case study describes a rare variation in the branching pattern of the PA discovered during a routine dissection of the right lower limb of a 92-year-old female cadaver. The embryonic development of the arterial supply to the lower limb can account for the variation in branching patterns that exist in the population. Because of the high prevalence of PA variation in the population, it is important to recognize these variations and how they can affect surgical procedures and outcomes.

The authors sincerely thank those who donated their bodies to science so that anatomical research could be performed. Results from such research can potentially increase mankind’s overall knowledge that can then improve patient care.

Conceptualization: CS. Data acquisition: CS, DC. Data analysis or interpretation: CS, RK. Drafting of the manuscript: CS, DC. Critical revision of the manuscript: CS, DC, RK. Approval of the final version of the manuscript: all authors.

No potential conflict of interest relevant to this article was reported.

None.