Test your understanding with 10 random multiple-choice questions from the question bank.
Introduction
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Alright so in this video we’re going to talk specifically about the Lumbar Plexus.
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Ok so the lumbar plexus is a really important and we’ll ad a little clinical correlation
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to it aswell.
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So first we’re gonna go through the topography.
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Just talk a little bit about which nerves feed into the lumbar plexus.
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Then after that we’re gonna make a scheme of the lumbar plexus.
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And to make this as easy as possible to understand and remember, we’re going to draw the general
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outline first.
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Then we’re gonna go ahead and go through each nerve and a little bit of clinical importance
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related to those nerves.
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And at the end, there’ll be a little quiz.
Topography of Lumbar Plexus
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So let’s go ahead and get started with the topography.
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So here we see the spinal cord within the vertebral canal.
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And here we see the spinal nerve leaving the intervertebral foramen, so there’ll be one
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spinal nerve leaving on each side.
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They’re paired.
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To be specific, though, we’re not really talking about the whole spinal nerve, right?
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We’re actually talking about the anterior branch of the spinal nerve.
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Because the anterior branch is what forms all the plexuses that we’re going to talk
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about in this series of videos.
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So, lumbar plexus, formed by the spinal nerves.
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Which branch of the spinal nerves?
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The anterior branch.
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More specifically.
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The lumbar plexus is formed from the anterior branches of spinal nerves L1–L4 and a contributing
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branch from T12.
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The plexus is located within the psoas major, lateral to the lumbar vertebrae
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Let’s now go ahead and simplify this drawing so that we can actually make a scheme out
Scheme of the Lumbar Plexus
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of this.
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Now what I want you to do, is to grab a piece of paper and a pen, and I want you to draw
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this scheme with me.
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Once you do that, I promise you’ll remember this much much easier.
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Aright.
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First off, L1 is going to give off a branch called the Ilioinguinal nerve.
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So the primary nerve that the L1 give off is the Ilioinguinal nerve.
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The nerve above T12 is the subcostal nerve, right?
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It’s not actually a part of the lumbar plexus, but the Subcostal nerve is, it’s a mixed
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nerve.
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It has a sensory and a motor function.
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Sensory for the skin on the lower abdomen and inguinal regions, and motor for the abdominal
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wall muscles.
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Now the subcostal nerve again it’s not a part fot he lumbar plexus, but the reason
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why I mention it here is because it’s going to give off a branch that’s going to go
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with the branch of L1 to form the iliohypogastric nerve.
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We’ll mention all of those in detail in a minute but let’s actually finish off this
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scheme first.
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Now.
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L2 will traverse this way.
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L1 and L2 will both give off branches that go together to form the so called genitofemoral
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nerve.
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L3 will traverse this way, and join L2 in forming the Lateral femoral cutaneous nerve.
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L4 will traverse this way, right?
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Now.
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L3, L2 and L4 will go together in forming the Femoral nerve.
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Then the last one, L4, will join L3, and L2 to from the obturator nerve.
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So that is out scheme, this is the basic outline of our lumbar plexus.
Iliohypogastric Nerve
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Let’s go ahead and focus on each one, starting at the top.
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The Iliohypogastric nerve.
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Let’s do the course first.
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This one is going to traverse laterally from the psoas major, then it’s going to run
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above the iliac crest travelling and terminate in the hypogastric and inguinal regions.
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Let’s divide this one into cutaneous branches and motor branches.
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For the cutaneaous branches, it’s gonna supply two places.
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We got the lateral cutaneous branch, which provides somatosensory innervation of the
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skin on the lateral abdomen, and the anterior cutaneous branch, which innervates the skinaround
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the superficial inguinal ring.
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The muscular branches are provide motor innervation for the internal oblique and it’s going
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to supply the transversus abdominis muscle.
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And as you know from the fysiology of these muscles, the transverse abdominis muscle is
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gonna contract to increase the intraabdominal pressure, to push on the diaphragm to assist
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in the forced expiratory process.
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Whereas the internal oblique is gonna be one of the muscles that’s gonna primarily help
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with flexion of the abdomen, as well as increasing the intraabdominal pressure for the forces
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expiratory process.
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Awesome.
Ilioinguinal Nerve
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Now.
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Next the Ilioinguinal nerve, is actually going to traverse laterally from the psoas major
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and continues below the iliohypogastric nerve, right?
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It follows the iliohypogastric nerve at the beginning.
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Then it travels through the inguinal canal to innervate the skin of the anterior part
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of the scrotum in men and the skin on the anterior part of the labia majora in women.
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So it’s primarily a cutaneous nerve.
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Ok.
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So we did the Ilioinguinal and the Iliohypogastric.
Genitofemoral Nerve
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Now.
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The genitofemoral nerve.
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Now the genitofemoral nerve is actually going to, instead of going on the lateral side of
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the psoas major, like the iliohypogastric and the ilioinguinal nevre, this one is actually
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going to penetrates the psoas major and leaves it on its ventral surface.
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To then give off a Genital branch and a Femoral branch.
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Genitofemoral branch, just split the word.
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Alright the genital branch passes through the inguinal canal to innervates the cremaster
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muscle, as well as sensory innervation of the scrotum and a small area on the medial
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side of the thigh in men.
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While in women, it innervates part of the labia majora and a small area on the medial
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side of the thigh.
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The femoral branch however, passes through the vascular space to innervates the skin
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of the medial side of the thigh.
Lateral Femoral Cutaneous Nerve
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Awesome.
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Next.
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Lateral Cutaneous nerve of the thigh.
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This simple nerve will traverse laterally from the psoas major, then run towards the
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anterior superior iliac spine, travels through the muscular space to reach the lateral thigh.
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It’s called the lateral cutaneous nerve of the thigh, so it will provide somatosensory
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innervation for the lateral thigh.
Femoral Nerve
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Alright.
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Now.
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Femoral Nerve.
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One of the really important nerves.
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The femoral nerve will travel laterally from the psoas major, travels above the iliopsoas,
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then pass medially through the muscular space to reach the anterior thigh.
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Once it reaches the anterior thigh, it’ll end up in the femoral triangle, then splits
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into muscular and cutaneous branches.
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Let’s do the cutaneous supply first.
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So, one of the cutaneous supply branches, is actually called the, anterior femoral cutaneous
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branch.
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And you can obviously tell where this one is going to supply.
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It’s going to supply the anterior and a little bit of the lateral sensations of the
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thigh.
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The other branch is called the Saphenous branch.
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And the saphenous branch is a really cool nerve because it’s a terminal branch.
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Or a terminal somatosensory branch.
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And what it does is that it follows the great saphenous vein, so it runs within the adductor
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canal.
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On it’s way, it gives off the Infrapatellar branch, which provides somatosensory innervation
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of the skin inferior to the patella, and it gives off the Medial cutaneous nerve of leg,
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which provides somatosensory innervation for the skin of the medial part of the leg.
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So what it really does is cover a good portion of the medial side of our thigh and leg.
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Supplies the medial hip joint, medial thigh, medial knee joint, medial calf, and medial
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heel as well.
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So, a lot of different cutaneous sensation come from this branch of the femoral nerve.
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So you can just imagine, if there’s any type of damage to the femoral nerve, the type
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of paraesthesia that you’d experience from that guy.
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Now.
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Motor supply.
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The femoral nerve innervates a whole lot of muscles, that’s why if there’s any herniated
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disks, or some type of situation where there’s a compression of the femoral nerve, it can
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affect the ability to walk, because the motor supply is iliopsoas, for flexion at the hip.
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It also supplies the pectineus, which is also another muscle for flextion at the hip joint.
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It supplies the quadriceps femoris.
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And for those of yo who know that it consists of the vastus medialis, lateralis and intermediate
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which they all cause extension of the knee.
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And it also consists of the rectus femoris which causes flexion of the hip and extension
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of the knee.
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And another muscle that’s gonna be supplied by the muscular branches of the femoral nerve
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is the Sartorius muscle.
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Sartorius can flex the hip, it can flex the knee and it can even do lateral rotation of
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the hip.
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So you can see here, if there’s any damage or irritation of the femoral nerve.
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Let’s go through some common causes here.
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Pelvic fractures can cause damage to the femoral nevre, hip dislocations can cause damage to
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the femoral nerve, herniated disks at around L2, L3 and L4.
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That’s why it’s important to actually know what parts supply the actual nerve.
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Let’s actually just go through what a herniated disk is really quick so you actually get the
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visual idea of this damage, because it’s sadly very common.
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So here you have two vertebral bodies, and then you have a jelly like material between
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these two vertebral bodies, called nucleus pulposus, right?
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So nucleus pulposis is a jelly like structure, and around it there’s a whole lot of fibers
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called anulus fibrosus, consisting of cartilage, fibroud cartilage.
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So the spinal nerve is going to leave through the intervertebral foramen, right?
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Let’s say for any type of situation there’s a compression, or rotation, or any situation
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that causes this nucleus pulposis to bulge out.
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And if it is herniated out from that anulus fibrous connective tissue, it can obviously
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cause compression of these nerves.
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And if it causes compression of these nerves, it can affect the motor supply, causing peripheral
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paresis of these muscles here supplied by the femoral nerve.
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Mainly, the reason for the impaired walking function is due to weaknes of the quadriceps
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muscle.
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If that happens, walking without support and walking upstairs can become difficult.
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It’s almost impossible for the patient to raise their lower limb when lying supine.
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And also standing and squatting can become unstable.
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Other symptoms that may occur is that it may also cause loss or parestesia, so they might
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have pain, numbness, tingling within the medial hip, thigh, knee, leg, anterior and lateral
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thigh.
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A lot of different things can come from damage to the femoral nerve.
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Alright.
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So that’s that one.
Obturator Nerve
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Last one.
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Obturator Nerve.
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This nerve again comes from L2, L3 and L4, then it traverses medially from the psoas
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major and passes through the obturator canal.
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When it passes through the obturator canal, it branches into an anterior branch which
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innervates the gracilis, which helps with hip adduction, knee flexion and internal rotation.
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It supplies the adductor longus and brevis for hip adduction.
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Supplies the pectineus which flexes and adducts the thigh, and the anterior branch also provides
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somatosensory innervation for the medial thigh.
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It’ll also branch out to a posterior branch for the adductor magnus for the adduction
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and medially rotation at the hip joint.
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Now.
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The obturator nerve also has muscular branches for the obturator externus.
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Alright, so that is mainly the big nerves that come from the femoral plexus.
QUIZ
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Now what I’m going to do is give you all a fairly easy quiz.
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I’m going to change all the labels to numbers, and put the names in a table.
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Then I’m going to make all the names disappear, and can you, from the beginning, tell me what
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is the name of number 1?
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What is the name of numer 2?
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What does number 3 supply and what does number 4 supply?
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If you can do that, then you’ve got a good grasp of this topic.
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There you have it my friends, thank you so much for watching another one of my videos.
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See you next time.
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Peace.
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