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DUPLEX ASSESSMENT OF LOWER LIMB ARTERIAL DISEASE
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border of the calf, until it becomes the dorsalis pedis artery, over the top of the foot.
Posterior tibial artery
1. Withthelegrolledoutwardandthekneeflexed, the origin of the posterior tibial (PT) artery is imaged from a medial position, below the knee, where the tibioperoneal trunk divides into the PT artery and the peroneal artery. The proximal PT artery will gently rise toward the transducer, and the associated paired veins act as useful land- marks. The origin of the peroneal artery is often visible from this plane and will lie posterior to the PT artery origin.
2. The PT artery is then followed along the medial aspect of the calf toward the inner ankle or medial malleolus. The PT artery lies superfi- cial to the peroneal artery when imaged from the medial aspect of the calf.
3. The origin and a short segment of the PT artery can often be visualized from a posterolateral position below the knee, where it will be seen to run deep as it divides from the tibioperoneal trunk.
Peroneal artery
Imaging of the peroneal artery may have to be performed from a number of different positions (Fig. 9.11B). The optimum position varies from patient to patient.
View 1 The peroneal artery can be followed from its origin along the calf using the same medial calf position as that described to image the PT artery. From this position, the peroneal artery will be seen lying deeper than the PT artery against the border of the fibula, surrounded by the larger peroneal veins. Slight anterior or posterior longitudinal tilting of the probe may be needed to follow the artery distally.
View 2 The peroneal artery can usually be fol- lowed distally from its origin using a posterolateral position, below the knee and along the calf.
View 3 The peroneal artery can sometimes be imaged from the anterolateral aspect of the calf, where it will be seen lying deep to the AT artery.
This is the most difficult position from which to obtain images of the peroneal artery.
Assessment of tibial arteries and the
plantar arch prior to bypass surgery
Duplex scanning in combination with continuous wave Doppler recordings can be a useful method of determining which calf artery is supplying most blood to the distal region of the foot prior to distal bypass surgery (McCarthy et al 1999). In this way, it is possible to select a target vessel to position the distal anastomosis. This is important as there needs to be a low-resistance arterial pathway to the foot, distal to a graft, to ensure that the graft remains patent and the foot perfused. The three tibial arter- ies of the calf have connections to the plantar arch, which is located toward the end of the foot. The PT and dorsalis pedis arteries usually contribute most flow to the arch via plantar arteries. The plantar arch supplies blood to the plantar metatarsal arteries and digital arteries of the toes. The patient should be assessed with the leg in a dependent position to maximize blood flow distal to the diseased part of the vessel. Using the duplex scanner, it is possible to assess the patency and quality of each of the tibial arteries to ankle level. A continuous wave Doppler probe is then used to assess the Doppler signals from the plantar arch. The probe position for record- ing flow at the plantar arch is demonstrated in Figure 9.3. Selective digital pressure is then applied over the most suitable tibial artery, as previously demonstrated by duplex scanning of the target vessel, to occlude it at the ankle. A substantial reduction or cessation of flow at the plantar arch during com- pression would suggest that the arch is in continua- tion with the selected tibial artery. This type of assessment can be complex, as there may be more than one patent tibial artery supplying the plantar arch. The peroneal artery can also supply the distal AT artery or dorsalis pedal artery via branches, which in turn may supply the plantar arch.
Commonly encountered problems
There are a number of problems and pitfalls associ- ated with lower limb duplex scanning. Table 9.4 lists some of the more frequently encountered problems.