Structures of the Leg (Nursing)

by Darren Salmi, MD, MS

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    00:02 So this brings us to the leg which again, you're probably used to seeing arm and leg, but we know arm is only a part of the upper limbs.

    00:10 Similarly, leg is only a part of the lower limb, just the part between the knee and the foot.

    00:17 And again, there should be some similarities coming to mind when we talked about the forearm because this is the lower limb equivalent of the forearm.

    00:25 So instead of one bone, we have two, one's a bit smaller than the other.

    00:30 The small one laterally is the fibula.

    00:34 It has a head and a neck.

    00:37 And at the distal end, there's a bump or malleolus.

    00:41 And because it's the lateral bone, it's called the lateral malleolus.

    00:45 And when you reach down towards your ankle, and you feel those two bumps on either side, that's what you're feeling the lateral malleolus of the fibula.

    00:53 The larger bone more immediately is the tibia.

    00:58 And it has a long anterior crest, you can usually palpate or more likely run into something hard in the dark and hit your shin.

    01:06 And that anterior crest is pretty vulnerable, because there's not a lot of muscles directly over it.

    01:12 And that's why when you hit your shin bone, that's where you tend to hit it.

    01:17 And it's bumped at the distal end is called the medial malleolus.

    01:21 So when you feel that bump on either side of your ankle, they're actually on two different bones, the lateral malleolus on the fibula, and the medial malleolus on the tibia.

    01:32 And there are these interosseous borders very similar to what happened in the radius and the ulna.

    01:38 If we look at the proximal end of that tibia, we see there's a lateral condyle and a medial condyle.

    01:47 And of little space in between between the two would be called intercondylar, so little on intercondylar eminence there.

    01:55 Very similar, again, to the joints of the upper limb.

    02:00 So we'll put those bones back together as they like to be.

    02:04 And we see we have a superior tibiofibular joint and an inferior tibiofibular joint.

    02:11 Again, all of this is very, very similar if you've already seen the form.

    02:17 Generally speaking, the movements are a little confusing when we talk about the movements down at the ankle, and the muscles that we're going to talk about what they do don't really fit our typical descriptions with flexion and extension.

    02:32 So the situation here is a little different.

    02:35 And you're just gonna have to bear with the fact that these terms really only exist down here.

    02:40 So what I'm saying is when the foot is moved, such that the toes lift up, that's something called dorsiflexion.

    02:49 And that's something that we're going to see called the deep fibular nerve comes into play, but the opposite is also called flexion, unfortunately, so moving the other ways, something called plantar flexion.

    03:02 So pointing the toes up is dorsiflexion, pointing them down, is plantar flexion.

    03:07 It's kind of funny because we're like wait flexion and flexion.

    03:10 But we throw in these descriptors, dorsi versus plantar to help us understand.

    03:15 Unfortunately, that's just how they're named in this area.

    03:19 That said, when we're talking about the anterior compartment of the leg muscles, generally they're going to be the toe razors or dorsiflexors.

    03:29 And there's going to be a nerve we're going to see called the deep fibular nerve that takes care of things here.

    03:35 So we have the tibialis anterior, great name.

    03:40 We just said the tibia is here and we're talking about the anterior compartment.

    03:44 We have extensor digitorum longus.

    03:48 Right now, you're probably thinking that sounds very similar.

    03:50 So why don't we just call dorsiflexion extension if we're calling these muscles extensors? Well, we just we just don't unfortunately, I'm sorry.

    04:00 But it tells you a little bit about what's going on.

    04:03 Digitorum in this sense, not four fingers, but for toes.

    04:08 We also have extensor hallucis longus and fibularis tertius.

    04:13 Fibularis over on the fibular side.

    04:16 But extensor hallucis longus, hallicus a new one.

    04:19 Hallucis is our word for big toe just like we had pollicis for thumb and lot of similarities here.

    04:28 If we swing around to the lateral compartment, these do another unique movement here at a different ankle joint called the subtalar joint we'll see.

    04:37 And that's where we move the outside of the foot up something called eversion.

    04:42 And we're going to see there's a nerve called the superficial fibular nerve that takes care of things here.

    04:48 So here we have the fibularis brevis.

    04:52 And we can see that it's going down into the foot to carry out that eversion action and a fibularis longus which also is going down into the foot to carry out those actions.

    05:02 And fibularis is a great name because we said the fibula is the lateral bone and we're in the lateral compartment.

    05:10 If we go to the posterior compartment, we're going to see that there are some superficial and deep layering to the muscles here.

    05:17 But they're generally going to be the opposite of the anterior compartment, as is usually the case.

    05:21 So they're going to do plantar flexion or basically point the toes downward.

    05:26 And they're going to be innervated by something called the tibial nerve.

    05:31 The first thing we're going to see something called the gastrocnemius.

    05:35 Gastrocnemius, it's going to have two heads, a medial head and a lateral head.

    05:42 And we can see that it has this really thick tendon called the calcaneal tendon, because that's the bone in the foot it's attaching to.

    05:49 But more commonly referred to as the Achilles tendon, because you've probably heard of the Achilles tendon and the story of Achilles and being dipped by the heel, and that was the vulnerable part.

    06:00 Well, here we see it's a really thick tendon.

    06:03 And it's attached to these muscles that you probably have heard before called as calf muscles.

    06:09 And the first one we're seeing is the gastrocnemius, really strong, thick tendon, a lot of stress is put on it.

    06:15 That's why it's so big and thick.

    06:19 But if we remove it, we see a flat muscle called the soleus.

    06:24 Almost like if you've seen, like Dover sole, the flat fish, it's kind of like a sole, like a very thin flat muscle.

    06:33 And unlike the gastrocnemius, which also crosses the knee, and therefore has an action of a little bit of knee flexion, the soleus acts purely as a plantar flexor.

    06:47 And actually, that's why if you've kind of noticed some soreness in your calves, when you go up hills, for example.

    06:53 If you have your knees bent, the gastrocnemius because it's crossing the knee joint can't actually do plantar flexion.

    07:01 So if your knees are kind of bent, such as like, if you're going up a steep hill, it's actually all your soleus.

    07:07 So that calf soreness is actually deeper, and it's not your gastrocnemius, it's your soleus.

    07:14 We also have this tiny muscle with a really long tendon called the plantaris.

    07:20 And that is sort of the equivalent of our palmaris longus in the sense that we don't really need it.

    07:25 But if we needed a long tendon for a surgery to replace something more useful elsewhere, we can take that out and not really have any consequences.

    07:36 Now we'll go into the deep compartment.

    07:39 And that's where we're going to find that little unlocking muscle of the knee called the popliteus.

    07:44 And the tibialis posterior, which again, we can see that tendon going all the way down into the foot.

    07:51 We also have the flexor hallucis longus.

    07:54 Again, hallucis, meaning our toe or big toe.

    08:00 And we can see that going all the way down to the big toe as well.

    08:03 Flexor digitorum longus, And again, this is all equivalent to the stuff that we saw in the forearm, going down to the digits.

    08:12 In this case, the toes, all very similar to the stuff we saw already in the hand.

    08:20 So now let's look at the arterial supply of the leg.

    08:25 We already said the femoral artery has to go behind the knee so that it doesn't get so compressed, and when it goes behind the knee, it changes named to the popliteal artery.

    08:35 Then we're going to have these branches such as the anterior tibial artery, as the name implies, it's going to go take care of the anterior compartment.

    08:43 We're gonna have the posterior tibial artery taking care of the posterior compartment.

    08:47 And a fibular artery.

    08:49 Again, fibular, the fibula is on the lateral side, that's going to take care of our lateral compartment.

    08:56 Now let's take a look at the nerves of the leg.

    08:59 That big prominent nerve we saw on the posterior thigh called the sciatic nerve is eventually going to branch into a posterior tibial nerve and take care of the muscles of the posterior compartment.

    09:11 And then a common fibular nerve that is going to branch again, into a deep fibular nerve going over to the anterior compartment, and a superficial fibular nerve taking care of the lateral compartment.

    About the Lecture

    The lecture Structures of the Leg (Nursing) by Darren Salmi, MD, MS is from the course Anatomy of the Musculoskeletal System (Nursing).

    Included Quiz Questions

    1. Lateral malleolus
    2. Anterior crest
    3. Head
    4. Neck
    5. Medial condyle
    1. Anterior crest
    2. Lateral condyle
    3. Medial malleolus
    4. Lateral malleolus
    5. Neck
    1. Tibialis anterior
    2. Extensor digitorum longus
    3. Extensor hallucis longus
    4. Tibialis posterior
    5. Extensor digitorum anterior
    1. Fibular artery
    2. Posterior tibial artery
    3. Iliac artery
    4. Anterior tibial artery
    5. Popliteal artery

    Author of lecture Structures of the Leg (Nursing)

     Darren Salmi, MD, MS

    Darren Salmi, MD, MS

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