Hello all it is your good friend Dr Alsup and I am very excited
to discuss with you the muscles of the anterior compartment of the leg.
So the learning objective is full of many of our typical players here, we will be naming the
muscles talking about actions innervation and of course any clinical considerations.
Okay so while we call this the anterior compartment of the leg it is actually
oriented and the muscles are at least oriented anterolaterally. And very close to the aptly named
lateral compartments a fibularis longus is a portion of the lateral compartment as well as
fibularis brevis. So you can see that, you can truly see and feel the tibia for much of the anterior
medial portion of the leg and then the muscles of the anterior compartment are located in this
general region here so anteriolaterally. There are four muscles in this compartment but we are
only having you identify two of them which happen to be the more superficial and easier to locate.
The tibialis anterior is going to be the most medial within this compartment as well as the
most superficial. The extensor digitorum longus which I'm just going to put an E
right here is going to be right next to the TA or tibialis anterior and when I say
just next to it's just lateral to the tibialis anterior and these are the two main muscles you
can see from a more superficial view. The EDL similar to what we had in the forearm
will have four long tendons that will extend to digits 2-5 and you can see
that coming you can see the extensor digitorum longus belly here and you can see it extending to
the tendons. Deeper in this compartment will also be the extensor hallucis longus
which is which will be similar to the extensor digitorum longus but specifically heading to
the first digit or the big toe. Additionally there will be a small fibularis tertius muscle
that kind of looks like a little slip of muscle associated with the extensor digitorum longus
not a particularly powerful muscle or even a very high yield muscle so we won't have you
identify that one either but I did want you to at least have heard these names before.
These muscles in the anterior compartment will affect joints in the ankle as well as the foot
with the primary action in which all muscles in this compartment play some role being dorsiflexion
of the ankle joint or the talocrural joint. I always think of dorsiflexion is really digging
in your heels into the ground and then starting to point the toes up or elevating the forefoot.
While again all of these muscles will play a role in dorsiflexion it's the tibialis anterior or TA
that has the most mechanical advantage and making
it the strongest or primary mover in terms of dorsiflexion.
Tibialis anterior will also cross the subtalar and transverse tarsal joints
to attach to the medial border of the foot which makes this muscle capable of inverting
the foot, working with the tibialis posterior muscle which is located in the posterior leg.
So I always think of inversion as moving the sole of the foot or the plantar surface
more medially whereas the opposite motion eversion is moving the sole of the foot more laterally.
There is a greater range so try to do inversion and eversion on your own foot and you'll find
that the greater range of motion is going to be an inversion rather than eversion.
An easy way to remember which muscles do what is that tibialis muscles will
invert whereas fibularis muscles, so if it has tibialis in the name
such as tibialis anterior it will invert the foot, or if it has fibularis in the name of the muscle
it will evert the foot. And yes we just discussed that fibularis tertius is in this compartment and
yes it will play a slight role in eversion but it is relatively weak so we didn't put it here
with this compartment it will be a much bigger deal eversion will be a much bigger deal in the
lateral compartment. Lastly we had all of those long tendons from the extensor digitorum longus
and hallucis longus and these will cause extension of the digits or straightening from a flexed position.
The muscles of the anterior compartment are innervated by the deep fibular or deep peroneal
nerve which is one of the two terminal branches of the common fibular or peroneal nerve.
Damage or a lesion to the deep fibular nerve may lead to a complete inability to dorsiflex
the ankle, as in the toes as in the foot kind of has this appearance of being too long, the toes
do not clear the ground during the swing phase of walking if you cannot dorsiflex your ankle.
And this could be due to just a direct injury to the deep fibular peroneal or it could be due to
an injury to the common fibular peroneal as well. That common fibular wraps around
the neck of the fibula in a fairly subcutaneous position leaving it vulnerable to direct trauma
so an injury to the common fibular peroneal would affect the deep fibular as well as the
superofibular which innervate the anterior and lateral compartments respectively.
Lastly let's discuss a few additional clinical considerations in this area.
We discussed compartment syndrome back in our first session of MSK by which increased volume
in a compartment caused by all kinds of different things it could be infection it could be a
hematoma just a variety of issues could cause this, that is not able to move out of that compartment
due to a relatively unyielding deep fascia and that can lead to increased compartmental pressure,
this is compartment syndrome. And the anterior compartment of the leg is typically named as the
most common compartment for which this occurs so this is a common thing that I hope you understand
the connection between the two. Additionally this compartment is commonly considered with shin
splints or sometimes called tibialis anterior strain. Shin splints typically present as pain
and or edema in the area of the distal two-thirds of the anterior leg which is often caused by
repetitive microtrauma to the tibialis anterior so little micro tears associated with the muscle
or even minor tears of the periosteum or that connective tissue that's surrounding the
neighboring tibia. So when you think shin splints I want you to think anterior compartment of the leg.
Excellent thank you for joining me on this journey of the muscles of the
anterior compartment of the leg. Please take time to review and reach out with
any questions. Thank you for your time and attention and have a great rest of your day