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posterolateral to the SFA and supplies blood to the thigh. It also acts as an important collateral path- way in the presence of an SFA occlusion. The pro- funda femoris artery usually gives off the medial and lateral circumflex arteries just beyond its ori- gin. The SFA follows a medial course down the thigh, becoming the popliteal artery at the level of the adductor canal above the knee. The SFA gives off relatively few major branches, although the descending genicular artery can act as an important collateral pathway. The popliteal artery then runs behind the knee, or popliteal fossa, and bifurcates below the knee into the anterior tibial (AT) artery and tibioperoneal trunk. The popliteal artery has a number of genicular and sural branches supplying blood to the knee joint and gastrocnemius and soleus muscles. The proximal AT artery runs in an anterolateral direction through the interosseous mem- brane to the anterolateral aspect of the upper calf. It then continues to run to the lower calf, becoming the dorsalis pedis artery over the dorsum of the foot. The tibioperoneal trunk can vary in length and bifur- cates into the posterior tibial (PT) and peroneal arteries (Fig. 9.1B). The PT artery follows a medial course along the calf and runs behind the medial malleolus (or ankle bone) in its distal segment. The peroneal artery lies deeper than the PT artery against the border of the fibula and runs toward the lateral malleolus (outer aspect of the ankle) in its distal seg- ment. It is important to note that the peroneal artery is often spared in the presence of tibial artery disease. This is why its identification can be useful if a distal bypass procedure is being considered.
The distal area of the foot is mainly supplied by the dorsalis pedis artery and the medial and lateral plantar arteries, which are terminal branches of the PT artery. The dorsalis pedis and plantar arteries anastomose to form the plantar arch, which supplies the arteries to the toes.
Collateral pathways and anatomical
variations
If an arterial segment is severely diseased or occluded, there are often alternative pathways that are able to carry blood flow around the diseased segment, referred to as collateral vessels. In this situation, reverse flow is observed in major branches of arteries just distal to an area of severe disease, where they
occluded (O) and reverse flow (blue) is demonstrated in the internal iliac artery, as it supplies flow to the external iliac artery (red).
DUPLEX ASSESSMENT OF LOWER LIMB ARTERIAL DISEASE
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O
Figure 9.2 An example of collateral flow. The CIA is
help to resupply blood flow to the main vessel. One such example is flow reversal observed in the internal iliac artery, supplying blood to the external iliac artery in the presence of a CIA occlusion (Fig. 9.2). It should be noted that it is actually very difficult to follow collateral vessels for any length using the duplex scanner, especially in the pelvis. This is not really a problem, as it is the length and severity of the disease in the main vessels that the sonographer is attempting to document. However, the quality of the collateral circulation is very impor- tant, and this can be determined by assessing the patient clinically and measuring the ankle–brachial pressure index (ABPI). Common collateral pathways are summarized in Table 9.1.
There are a number of anatomical variations in the lower limb arterial system that may be occa- sionally encountered during routine examinations. The most common variations are listed in Table 9.2.
ANKLE–BRACHIAL PRESSURE MEASUREMENTS AND EXERCISE TESTING
In the vascular laboratory the measurement of the ABPI using continuous wave Doppler is one of the simplest and commonest ways of detecting and grading arterial disease. The test normally takes 10–15 min and is performed as follows. The patient should be fully rested and lying supine to remove the effect of hydrostatic pressure. A blood pressure cuff is then placed around the ankle. A high-frequency