The legs are supplied with arterial blood via the aorta which bifurcates at
the level of the umbilicus into the left and right common iliac arteries (CIA)
which themselves divide into the internal iliac arteries that supply the muscles
of the buttock and the pelvic organs and the external iliac arteries (EIA) that
run around the pelvic brim to enter the top of the leg.
The common femoral artery (CFA) enters the thigh just posterior to the inguinal
ligament near its mid point and at this point the artery is easily palpable
by compression against the underlying bones. The CFA bifurcates in the upper
thigh into two unequal branches. The smaller branch is the profunda femoris
artery (PFA) which passes posteriorly and supplies the muscles of the thigh;
the larger branch is the superficial femoral artery (SFA) which supplies the
calf and foot by spiralling more superficially around the medial side of the
thigh to pierce the adductor muscles above the knee. From here it continues
as close to the posterior surface of the femur as the popliteal artery where
it can be palpated just above the knee joint with the knee slightly flexed and
The popliteal artery crosses the knee joint deep between the femoral condyles
and divides posterior to the tibia in the upper calf to form the three distal
arteries: the anterior tibial (AT), the posterior tibial (PT) and the peroneal.
The AT passes between the tibia and fibula and runs deep in the anterior compartment
to emerge on the dorsum of the foot as the dorsalis pedis (DP) artery where
it is easily palpable just lateral to the extensor hallucis longus tendon. The
posterior tibial artery runs deep in the posterior compartment of the calf,
entering the foot posterior to the medial malleolus where it is easily palpable
half way between the medial malleolus and the calcaneus.
During lower limb exercise the blood flow in the femoral vessels may increase
many fold and the normal arteries are able to carry this increase flow with
ease. Occlusive arterial disease can affect any and many sites in the leg and
very often affects the SFA where it pierces the adductor muscles. An arterial
stenosis causes the flow of blood to become disordered and less efficient and,
if severe enough, a single arterial stenosis can restrict the blood flow during
exercise causing relative ischaemia of the muscles which is felt as pain.
The cross-sectional area of the normal SFA must be reduced by more than 70%
before these symptoms are produced. A further reduction in area has relatively
little effect because of the compensatory effect of small collateral arteries
that link the profunda femoris with the popliteal artery. However, if occlusive
disease develops at more than one site in the iliac, femoral and distal vessels,
the effects become additive. If this happens the severity of the symptoms will
increase and the distance that a patient can walk before symptoms develop will
decrease. Eventually the compensatory physiological reserve is exhausted such
that pain is present even at rest (critical ischaemia) and at this point there
is a high risk of ulceration, infection, gangrene and limb loss.
The cardinal early symptom of occlusive arterial disease is muscle pain that
develops during exercise and that is relieved by rest (intermittent claudication).
The speed of onset and severity of the pain is related to the degree of exercise
and is reproducible from day to day.
The site of the pain gives clues as to the site of the arterial disease:
- Isolated SFA and popliteal disease cause calf muscle claudication
- External iliac, common femoral and profunda femoris disease cause thigh
and calf claudication