Description

This video covers the full anatomy of the knee joint, followed by a breakdown of common injuries like ACL tear, meniscus tear, osteoarthritis, and bursitis.

Bones of the Knee Joint

Femur (femur): Forms the upper part of the knee joint.
Tibia (tibia): Bears weight and forms the lower part of the joint.
Patella (patella): Protects the anterior surface and improves leverage of the quadriceps.

Articulations

Femorotibial joint: Between femoral condyles and tibial plateau.
Femoropatellar joint: Between femur and posterior patella.

Menisci of the Knee

Medial meniscus (meniscus medialis): C-shaped; less mobile; firmly attached to tibia.
Lateral meniscus (meniscus lateralis): Nearly circular; more mobile.

Intra-articular Ligaments

Meniscotibial ligaments (ligg. meniscotibialia)
Transverse ligament of the knee (ligamentum transversum genus)
Anterior meniscofemoral ligament (Humphrey) (ligamentum meniscofemorale anterius)
Posterior meniscofemoral ligament (Wrisberg) (ligamentum meniscofemorale posterius)
Anterior cruciate ligament (ACL) (ligamentum cruciatum anterius): Prevents anterior tibial displacement.
Posterior cruciate ligament (PCL) (ligamentum cruciatum posterius): Prevents posterior tibial displacement.

Joint Capsule

Synovial membrane (membrana synovialis): Produces synovial fluid for lubrication.
Fibrous membrane (membrana fibrosa): Outer supportive layer.

Extracapsular Ligaments & Retinacula

Medial patellar retinaculum: Fibrous expansion supporting the patella.
Lateral patellar retinaculum: Stabilizes the patella laterally.
Medial patellofemoral ligament: Anchors patella to medial femur.
Lateral patellofemoral ligament: Anchors patella to lateral femur.
Patellar ligament (ligamentum patellae): Connects patella to tibial tuberosity.
Oblique popliteal ligament (ligamentum popliteum obliquum): Reinforces posterior capsule.
Arcuate popliteal ligament (ligamentum popliteum arcuatum): Posterolateral reinforcement.
Tibial collateral ligament (ligamentum collaterale tibiale): Resists valgus stress.
Fibular collateral ligament (ligamentum collaterale fibulare): Resists varus stress.
Anterolateral ligament

Fat Pads: Infrapatellar fat pad (corpus adiposum infrapatellare): Cushions anterior joint space.

Bursae Around the Knee

Subcutaneous prepatellar bursa (bursa prepatellaris subcutanea): Over patella; prone to swelling.
Subcutaneous infrapatellar bursa (bursa infrapatellaris subcutanea
Deep infrapatellar bursa (bursa infrapatellaris profunda)
Suprapatellar bursa (bursa suprapatellaris)
Anserine bursa (bursa anserina)
Subtendinous bursa of gastrocnemius (bursa subtendinea m. gastrocnemii)
Semimembranosus bursa (bursa m. semimembranosi)

Movements of the Knee

Flexion (flexio): Bending the knee backward.
Extension (extensio): Straightening the leg forward.
Internal rotation (rotatio interna)
External rotation (rotatio externa)

Common Knee Joint Conditions

Osteoarthritis

Progressive degeneration of articular cartilage leading to joint space narrowing and osteophyte formation.
Common in older adults, especially women, and those with obesity or previous injuries.
Symptoms: joint pain, morning stiffness under 30 mins, crepitus, swelling, reduced range of motion.

Meniscus Tear

Common in athletes, often due to twisting injuries with a fixed foot.
Peripheral tears (in outer vascular zone) may heal conservatively.
Symptoms: localized joint pain, delayed swelling, stiffness, difficulty squatting.

ACL Tear

Often occurs with pivoting, sudden stops, or awkward landings.
Common in female athletes.
Symptoms: audible pop, rapid swelling, instability, limited motion.

Prepatellar Bursitis

Inflammation of the bursa in front of the patella.
Caused by repeated kneeling, direct trauma, or infection.
Symptoms: anterior swelling, pain with pressure or movement, redness, possible fever.

Sources

Kozlowski, T. (2017). Memorix Anatomy, 2nd ed.
Standring, S. (2020). Gray’s Anatomy, 42nd edition
White TD, Folkens PA. (2005). The Human Bone Manual
Tubbs RS, Shoja MM, Loukas M. (2016). Bergman’s Encyclopedia of Human Anatomic Variation
Moore, K.L., Dalley, A.F., Agur, A.M.R. Clinically Oriented Anatomy
Kenhub.com

Tools Used: Complete Anatomy (3D4Medical), PowerPoint, Canva, Camtasia

Transcript

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The knee joint is the largest and one of the
most complex joints in the body. It carries

0:00:04.720,0:00:10.400
our entire weight and that’s exactly why
it’s so prone to problems, meniscal tears,

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ligament injuries, patellar dislocations, and of
course, wear and tear like osteoarthritis show

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up in clinics all the time. But to understand why
these things happen, we need to go inside the knee

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joint—look at how it’s built from the inside out.
So in this video, we’re going to break down the

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full anatomy of the knee joint: the menisci,
its capsule, the ligaments, the patella,

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the bursae and how it all comes together in
movement. And as always, I’ll highlight some

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of the most common issues that can damage the
knee joint, because once you understand the

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structure, you’ll understand the injuries.
What’s up everyone, my name is Taim. I’m a

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medical doctor, and I make animated medical
lectures to make different topics in medicine

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visually easier to understand. If you’d like a PDF
version or a quiz of this presentation, you can

0:00:51.760,0:00:55.200
find it on my website, along with organized
video lectures to help with your studies.

0:00:55.200,0:00:57.600
Alright, let’s get started.
If you’ve been watching my

0:00:57.600,0:01:01.120
previous videos you know that I have this
thing to really understand something I need

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to remove everything and add structures one
by one. So what are the bones we can see now?

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it’s the femur, the tibia, and the
patella. These are the three bones that

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come together to form the knee joint.
The bone down here is the fibula,

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and while the fibula is right next to the
tibia here, notice how it just grabs onto

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the tibia and doesn’t actually participate in the
joint itself, it’s not part of the articulation.

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So, what are the actual articulating
surfaces of the knee joint?

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Well, there are two main ones. The
first is the femorotibial joint,

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which is between the distal end of the femur
and the proximal end of the tibia. The second

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is the femoropatellar joint, which is between
the femur and the back surface of the patella.

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So to visualize this, here we see the two curved
condylar surfaces of the femur articulating with

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the relatively flat articular surfaces of the
tibia. And if we switch to a superior view,

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we can see those tibial surfaces
more clearly. Makes sense so far?

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Now here in the middle, this anterior side of
the femur is the area that is facing the patella,

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that’s the femoropatellar joint.
Just to see this more clearly,

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here’s the femorotibial articulation, and here’s
the femoropatellar articulation. These surfaces

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you’re looking at now, are what we call true,
direct articulating surfaces of the knee joint.

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You know the knee joint takes on a lot of weight
and twisting and everything, and to support

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all of this, our amazing body has extra layers of
protection between these articulating surfaces.

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And the first I wanna highlight sitting in between
these joints are structures known as the menisci.

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They sit on top of the tibia
and help deepen the articulating

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surface while also acting as shock absorbers.
To understand them better, let’s just remove

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the femur and look at them from this direction,
we’ll see this. Now we can clearly see the shape

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and size of the medial and lateral menisci. The
medial one is more C-shaped and firmly attached

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to the tibial plateau, while the lateral
one is more circular and a bit more mobile.

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In addition to the menisci, the knee joint
also has some ligaments within the joint

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that help stabilize it during movement. These
ligaments are the meniscotibial ligaments,

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also called coronary ligaments. These help
anchor the menisci to the tibial plateau.

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Then we’ve got the transverse ligament
of the knee, which connects the anterior

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horns of both menisci and helps them
move in union during knee motion.

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On the backside we can see this small ligament
called the anterior meniscofemoral ligament,

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also called the ligament of Humphrey. And here’s
its counterpart, the posterior meniscofemoral

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ligament, also called the ligament of Wrisberg.
Both of these extend from the lateral meniscus

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to the medial femoral condyle.
And here are the other joints,

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relative to the knee itself.
Now in addition to all of those,

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there are two incredibly important ligaments
that form an “X” shape inside the joint

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capsule, these are the cruciate ligaments.
We have the anterior cruciate ligament (ACL)

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and the posterior cruciate ligament (PCL).
The PCL originates from the posterior

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intercondylar area of the tibia and
ascends anteriorly to attach to the

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medial femoral condyle. It prevents
posterior displacement of the tibia.

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The ACL originates from the anterior
intercondylar area of the tibia and runs

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posteriorly to attach to the lateral
femoral condyle. It prevents anterior

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displacement of the tibia relative to the femur.
They’re called “cruciate” because of this crossing

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pattern, they literally form a cross or “crux.”
Clinically, the ACL is by far the most commonly

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injured ligament in the knee, especially
in athletes. I’ll show you why a little

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later in this video, but now, you see all
of those ligaments we just talk about?

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Those are all commonly referred to as
intracapsular ligaments of the knee joint,

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because they all lie relatively within the knee
capsule. And this capsule consists of two parts,

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there’s the synovial membrane, which lines
the inner surface of the joint capsule and

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produces synovial fluid. This fluid lubricates
the joint and helps reduce friction during

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movement. Here we can see the membrane
from both an anterior and posterior view.

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Lying just on top of the synovial membrane is
the fibrous layer of the articular capsule, which

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gives the joint its outer strength and stability.
And sitting on top of this fibrous capsule are

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ligaments that support the knee in
all directions. As you can see here,

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we’ve got the medial and lateral patellar
retinacula. The term “retinaculum” refers to

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a fibrous band that helps hold structures
like tendons or the patella in place.

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Just above those, we also see the medial
and lateral patellofemoral ligaments,

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which help stabilize the patella.
In addition to those ligaments,

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we can also see this yellow structure in the
center. This is called the infrapatellar fat pad,

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which cushions the front of the joint
and fills the space beneath the patella.

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Sitting directly on top of that
fat pad is the patellar ligament.

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This ligament connects the apex of the patella
to the tibial tuberosity, and it’s essentially

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a continuation of the quadriceps tendon.
Moving to the back side of the knee,

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we see the oblique popliteal ligament
and the arcuate popliteal ligament,

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which reinforce the posterior capsule.
Now if we rotate the joint this way,

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we get a view of the medial side. And rotating it
this way, we see the lateral side. On the medial

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side here we can see the tibial collateral
ligament. And on the lateral side we can

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see fibular collateral ligament. You’ll
also notice another structure here called

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the anterolateral ligament of the knee, and is
thought to contribute to rotational stability.

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So those are the main ligaments of the knee.
You know, the knee is so well protected. In

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addition to all this, it also has extra
cushioning structures called bursae.

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Bursae are small sacs filled with synovial fluid
that act like pillows – they reduce friction and

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prevent tissues from rubbing against each other.
There are several bursae around the knee, but some

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of the important ones are the subcutaneous
prepatellar bursa, deep infrapatellar bursa,

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subcutaneous infrapatellar bursa, anserine
bursa, and the suprapatellar bursa. And if we

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look from the back side of the knee, we can also
see the subtendinous bursa of the gastrocnemius,

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as well as the semimembranosus bursa.
So if you now stand up and kick your leg

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backwards, that movement is called knee flexion.
And if you bring your leg forward as much as you

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can, that’s knee extension, or even hyperextension
if it goes beyond the normal range. Turn your feet

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outwards, that’s external rotation of the knee.
And inwards is internal rotation. Makes sense?

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The knee joint is incredibly well protected,
but sometimes problems still occur,

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things that cause the joint to swell up, hurt,
or become unstable. And now that you’ve seen all

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the internal and external structures of the
knee, I wanna walk you through some of the

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most common conditions that affect this joint.
So you remember the cartilage we saw earlier,

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right? One of the most common problems that
can affect this cartilage is something called

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osteoarthritis. In a healthy joint, this
cartilage provides a smooth, protective

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layer that cushions the bones and maintains
proper joint space as you move. But over time,

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with repeated use, flexing, extending, bearing
weight, that cartilage gradually starts to wear

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down. And this is where osteoarthritis begins.
In grade one, we start to see minor damage to the

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cartilage, maybe a bit of softening or roughness.
By grade two, the damage becomes more noticeable,

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and small bone spurs may start forming around
the joint edges. In grade three, these spurs get

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larger, and the cartilage is significantly
eroded. And by grade four, there’s barely

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any cartilage left. The bones are now rubbing
directly against each other, which causes pain,

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inflammation, and seriously limits movement.
So who typically develops osteoarthritis of

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the knee? It’s usually older adults, especially
women after menopause, likely due to hormonal

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changes that affect cartilage repair. Obesity
is a big one too, because more weight means

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more pressure on the joint with every step.
Repeated stress on the knee from certain jobs,

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or prior injuries and surgeries, can also make
the joint more vulnerable. Genetics play a role,

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and muscle weakness, particularly
in the quadriceps, can reduce the

0:09:19.040,0:09:25.440
joint’s stability and increase wear over time.
So how does osteoarthritis feel? People often

0:09:25.440,0:09:31.040
describe pain during activities like walking or
climbing stairs, stiffness after periods of rest,

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usually less than thirty minutes, swelling,
you can hear a crackling or grinding sensation

0:09:36.080,0:09:41.440
called crepitus, and also reduced range of
motion. As the disease gets worse, the joint

0:09:41.440,0:09:47.840
might look enlarged or deformed, and symptoms
tend to flare up more in cold or damp weather.

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A meniscus tear is another common knee problem
and can occur as a result of twisting or turning

0:09:53.440,0:09:58.240
quickly. There are many different ways this
can tear up. One type of tear that can happen

0:09:58.240,0:10:02.880
is called a peripheral tear, which occurs
along the outer edge of the meniscus. This

0:10:02.880,0:10:08.000
may cause pain and swelling of the knee joint as
you move. That outer zone has a good blood supply,

0:10:08.000,0:10:11.840
so these kinds of tears have a better
chance of healing if managed properly.

0:10:11.840,0:10:16.320
So who gets this injury? It happens
mostly as a result of twisting injury,

0:10:16.320,0:10:21.760
often with the foot planted. Especially in sudden
pivoting or directional changes that’s why this

0:10:21.760,0:10:26.960
happens a lot in sports. We often see it in
people who squat deeply, or just from general

0:10:26.960,0:10:32.880
wear and tear as we get older, particularly after
forty. Weak leg muscles and previous surgeries can

0:10:32.880,0:10:38.560
also increase the risk. So what does the patient
actually feel? Typically, localized pain on either

0:10:38.560,0:10:43.600
the inner or outer side of the knee, swelling
occurs a few hours later, and stiffness that

0:10:43.600,0:10:50.240
limits movement, especially pain during squatting.
Another common issue we have to mention is ACL

0:10:50.240,0:10:56.000
tear. ACL tear is a damage of the anterior
cruciate ligament, which is one of the most

0:10:56.000,0:11:02.160
important stabilizing structures in the knee, and
when it tears, the knee becomes very unstable. The

0:11:02.160,0:11:07.680
most common mechanism is when the upper leg overly
rotates as the leg is fixated on the ground,

0:11:07.680,0:11:13.360
or when the upper leg is pushed backwards or
sideways while the lower leg is fixed. A torn

0:11:13.360,0:11:19.840
ACL doesn’t heal well on its own and usually
requires surgery. So who gets an ACL tear?

0:11:19.840,0:11:25.360
These injuries often happen when someone suddenly
stops and pivots like in basketball or soccer. It

0:11:25.360,0:11:30.480
can also occur when someone lands wrong after a
jump. The typical patient is often an athlete,

0:11:30.480,0:11:35.840
and females have a higher risk, partly because
of differences in anatomy and hormones. Weak

0:11:35.840,0:11:41.120
hamstrings relative to the quadriceps also
increase the risk. When it tears, people

0:11:41.120,0:11:46.720
often describe hearing a loud “pop,” followed by
immediate swelling and a sense of instability.

0:11:46.720,0:11:51.600
They can’t move the knee fully anymore, and
they severely lose their range of motion.

0:11:51.600,0:11:57.360
Lastly, let’s talk about prepatellar bursitis.
Earlier we looked at the bursae, those little

0:11:57.360,0:12:02.880
fluid-filled sacs that cushion the joint. The
prepatellar bursa sits just in front of the

0:12:02.880,0:12:08.320
patella, and when it gets inflamed, the whole area
swells up and becomes painful. This is sometimes

0:12:08.320,0:12:14.000
called housemaid’s knee. So who are most likely
to get prepatellar bursitis? It often happens

0:12:14.000,0:12:18.800
in people who kneel a lot, like plumbers and
carpet layers, anyone putting repeated pressure

0:12:18.800,0:12:23.840
on the front of the knee. But it can also be
caused by a direct blow, or in some cases,

0:12:23.840,0:12:29.440
an infection. Obesity, and people with diabetes
are more vulnerable. The symptoms are pretty easy

0:12:29.440,0:12:34.800
to spot, there’s swelling right over the kneecap,
pain with kneeling or pressure, and in cases where

0:12:34.800,0:12:40.080
it’s infected, the area might feel warm, look
red, and the person might even have a fever.

0:12:40.080,0:12:44.560
Movement becomes painful because the swelling
limits how far you can bend the joint.

0:12:44.560,0:12:49.440
So that’s everything I wanted to go through on the
knee joint. I really hope it all made sense. In

0:12:49.440,0:12:54.320
the next video in the lower limb skeletal series,
we’re going to talk about the tibia and fibula—how

0:12:54.320,0:12:58.880
they’re shaped, what joints hold them together,
and what muscles attach here. Click the next video

0:12:58.880,0:13:02.560
to continue learning and I’ll see you there.
If you want a handmade PDF version of this

0:13:02.560,0:13:06.400
lecture, take a quiz to test your knowledge,
or access an organized list of all my videos,

0:13:06.400,0:13:09.360
you can find everything on my website.
Thanks for watching! See you in the next one.