If we now move on to the posterior compartment
of the leg, we can see we have both superficial
and deep layers that I mentioned. Let’s
deal with the superficial layers first.
On here, we can see most superficially closest
to the skin, we have gastrocnemius. And this
has two heads. There’s a lateral head to
gastrocnemius we can see running over here.
This is a lateral head of gastrocnemius, and
here we can see the medial head of gastrocnemius.
So here, we have the posterior view of a right
leg. We have the lateral head of gastrocnemius
here, and we have the medial head here. Deep
to gastrocnemius, we find we have soleus,
and this is a large muscle, a very fleshy muscle
that is sitting directly deep to gastrocnemius.
So gastrocnemius, the lateral head, comes
from the lateral condyle of the femur while
the medial head comes from the medial condyle
of the femur. Soleus, this comes from the
posterior surface of the fibula, and also
as we mentioned in the osteology lecture,
it comes from the soleal line of the tibia. Both
of these muscles pass through the posterior
aspect of the calcaneus via the calcaneal
tendon. They’re supplied by the tibial nerve.
So these muscles in the posterior compartment
are supplied by the tibial nerve, one of those
divisions that are coming away from the sciatic
nerve. Gastrocnemius and soleus are both involved
in plantarflexion of the ankle, so enabling you
to stand on tiptoes. And because gastrocnemius
crosses the knee joints, then it can actually
flex the knee as well. One other muscle that
I haven’t mentioned is plantaris. Plantaris
is running alongside the medial aspect of
the lateral head, and this gives rise to a
very thin and long tendon that runs between
gastrocnemius and soleus. So we can see plantaris.
It’s coming from the inferior aspect of
the lateral supracondylar ridge of the femur,
and its long tendon passes between the soleus
muscle and the gastrocnemius muscle. It has a long
tendon that then blends with the calcaneal
tendon inserting on to the calcaneus. It’s
in the posterior compartment. So it’s also
supplied by the tibial nerve, and it is a
weak plantarflexor of the ankle. If we look
at more deep layers, then there are three
muscles here that I want to talk about, first
of all. We have popliteus, flexor digitorum
longus, and flexor hallucis longus.
So we can see these if we look into the deep compartments.
We have popliteus here. We have flexor digitorum longus.
We have flexor hallucis longus. And we also
have this muscle here, which is tibialis
posterior, and I’ll come to that in a moment.
So popliteus, we can see coming from these
lateral aspects of the leg. It’s coming from
the lateral surface of the femoral condyle.
We can see it’s passing across to the tibia.
We then have long muscles that give rise to
tendons that pass into the foot, flexor digitorum
longus and flexor hallucis longus. So we can
see popliteus coming from the lateral aspects
of the lateral condyle of the femur. It also
comes from the lateral meniscus, and it passes
to the posterior tibia above the soleal line
which we mentioned before. Flexor digitorum
longus, this is coming from the posterior
surface of the tibia below the soleal line,
and this passes to the distal phalanges of
digits 2 to 5. Flexor hallucis longus, this
is coming from the lower two-thirds of the
posterior fibula, and also their interosseous
membrane. It passes to the distal phalanx
of the great toe. All of these muscles, as
they’re in the posterior compartment, are
supplied by the tibial nerve. Popliteus, this
is going to be a weak knee flexor.
It’s also involved in unlocking the knee by lateral
rotation of the femur on a stable tibia.
So when you’re in standing position and the
femoral condyle is tightly articulating with
the tibial plateau, then popliteus is important
in unlocking the knee enabling flexion to occur.
Flexor digitorum longus flexes the digits
2 to 5, and it also helps to plantarflex
the ankle. Flexor hallucis longus flexes the
great toe and is also a weak plantarflexor.
Now let’s turn to the deep layer within
the posterior compartment. There are four
muscles here I would like to talk about. We
have popliteus; we have tibialis posterior,
flexor digitorum longus, and flexor digitorum
hallucis. And we can see that we have this
muscle here, popliteus, important in unlocking
the knee from its fully extended position.
Then we have tibialis posterior, and then
flexor digitorum longus, and flexor hallucis
longus then they’re going to pass tendons
into the foot. So if we look at popliteus,
it comes from the lateral aspects of the
lateral condyle of the femur, and also the
lateral meniscus. It passes to the posterior tibia
above the soleal line. And this muscle is
important. It’s innervated via the tibial
nerve, and it’s a weak knee flexor as it
does technically across the knee joint. But
its prime responsibility is to unlock the
knee bilaterally rotating the femur when the
femur and the tibia are stable. So when the
knee is fully extended, it can unlock the
knee allowing flexion to occur. Flexor digitorum
longus and flexor hallucis longus, as we can
see, pass long tendons into the foot, into
the sole of the foot. And these two muscles
flexor digitorum longus, comes from the posterior
surface of the tibia below the soleal line,
and it passes to the distal phalanges of digits
2 to 5. Flexor hallucis longus, this passes
from the lower two-thirds of the posterior
fibula and interosseous membrane specifically
to the distal phalanx of the great toe.
These three muscles are associated with flexing
the digits 2 to 5 if you’ll flex the digitorum
longus, and the great toe if you’ll flex
the hallucis longus, as their names
would suggest. FDL, flexor digitorum longus, is
also a plantarflexor of the ankle, and flexor
hallucis longus is also a plantarflexor but
somewhat weaker. Tibialis posterior is coming
from the posterior tibia below the soleal
line. It also comes from the posterior surface
of the fibula and the interosseous membrane.
It passes to the tuberosity of the navicular
bone. This muscle is important in plantarflexing
the ankle, and also, inverting the foot.
So tibialis anterior and tibialis posterior work
together with foot inversion. All of these
muscles are supplied by the tibial nerve,
just like the gastrocnemius, the soleus, and
the plantaris muscle were supplied by the
tibial nerve, so these deeper muscles within
the posterior compartment are also supplied
by the tibial nerve. So if we look at the