Two types of perforating vein can be distinguished below
the popliteal fossa:
Perforating veins not related to intramuscular veins:
they directly connect superficial veins with deep intermuscular
veins (anterior or posterior tibial veins, peroneal veins,
and tibioperoneal trunk) (Figure
97);
Perforating veins connected to intrainuscular veins:
they connect superficial
veins with gastrocnemius or soleus veins (Figure 98)and often have multiple branches. connecting superficial,
intermuscular. and intramuscular networks.
There are also transgastrocnemius perforating veins of the
soleus muscle, which connect a superficial vein and veins
of the medial head of the gastrocneniius muscle and the soleus
muscle,
Functionally, direct perforating veins not related to intramuscular
veins constitute a safety valve in the case of positional
obstruction to superficial blood flow in the saphenous networks
(stretching and compression by crossing the legs). The most
important of these perforating veins are Boyd's perforators
and Cockett's perforators. In contrast, in the case of hypertension
in the deep venous network, their short, direct course facilitates
the development of skin lesions at this level.
The main perforating veins connected to intramuscular veins
are the medial gastrocnemius perforating veins. They are usually
multibranched (
Figure 99),
and receive fine collaterals derived from the muscle. By draining
their own muscle territory, they act as an intermediary for
the calf muscle pump to act on the saphenous networks and intersaphenous
arches. According to Gillot, a gastrocnemius perforating vein
is not only a branch of the recipient gastrocnemius vein, but
its initial segment is also an integral part of this gastrocnemius
vein.
When the intramuscular venous network is the site of hypertension
(dilatation or incompetence of gastrocnemius veins, insufficient
muscle pump, obstruction to blood flow), transgastrocnemius
intersaphenous connections can ensure diffusion of reflux to
saphenous trunks, intersaphenous arches, and/or collaterals.
The rich network of medial gastrocnemius perforating veins,
in combination with intersaphenous arches, transforms the middle
segment of the short saphenous vein into a real exchange center
between the long and short saphenous veins and medial gastrocnemius
veins.
The short saphenous vein is also usually suprafascial in this
zone, which explains why, in contrast with the long saphenous
vein, the short saphenous vein can present a greater caliber
than its junction with the deep system. Ultrasound investigation
of the trunk must therefore be just as detailed as that of the
saphenopopliteal junction and proximal reflux. Precise mapping
of intersaphenous arches and gastrocnemius perforating veins
is absolutely essential. The absence of these data can account
for certain failures of isolated saphenopopliteal junction ligation.
Finally, two portions of intramuscular perforating veins can
be distinguished (
Figure 100)

the first, subfascial,
portion is the longer of the two. It has a descending course
until it crosses the fascia, where it describes a concave upwards
curvature;

the second, suprafascial,
portion ascends over a much shorter distance;
These perforating veins possess two or three valves situated
at their origin and in the zone of their transfascial passage.

Further reading
Dortu J., Dortu JA. Les veines perforantes du membre inférieur : physiologie
et physiopathologie. Phlébologie, 1994; 47: 167-75.
Gillot C. Les veines perforantes inférieures de la jambe, de la cheville
et du pied. Phlébologie, 1994; 47: 76-104.
Thomson H. The surgical anatomy of the superficial and perforating veins of
the lower limb. Annals of the Royal College of Surgeons, 1979; 61: 197-205.