« An animation of knee anatomy »
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The knee is a complex hinge-type joint and is made up of the following
components:
[1] Bones:
The knee joint is made up of four bones:
The femur [thigh bone] is the largest bone in the body.
The tibia [shin bone] is the larger bone of the lower leg.
The fibula is the smaller bone in the lower leg, sitting on the outer
aspect of the tibia.
The patella [knee cap] is located in front of the femur and
tibia and slides within its own groove on the femur as the knee
moves.
[2] Ligaments:
There are two groups of ligaments and these connect the bones of the
upper and lower leg. They are made up of strong groups of fibres that
help to provide stability to the knee, allow joint movement and prevent
excessive or abnormal motion. The two main groups of ligaments are
called the collateral ligaments, which are at the sides of the knee,
and the cruciate ligaments which cross in the centre of the knee.
Collateral ligaments:
The medial and lateral collateral ligaments [MCL and LCL] lie on the
inner and outer sides of the knee respectively. They help to prevent
sideways motion.
Cruciate ligaments:
The anterior cruciate ligament [ACL] and posterior cruciate ligament
[PCL] lie in the centre of the knee crossing each other (hence cruciate).
The ACL helps to limit rotation and forward motion of the tibia whilst
the PCL located just behind the ACL limits the backward motion of
the tibia.
[3] Muscles and
tendons:
Two major sets of muscles cross the knee joint in order to make it
move:-
The quadriceps [‘quads’] are four muscles in front of
the thigh that act to straighten the knee.
The hamstrings are the muscles in the back of the thigh that work
together to bend the knee.
Tendons are structures that attach muscles to bones. The four quadriceps
form into one tendon called ‘the quadriceps tendon’ which
surrounds the patella and then becomes the patellar tendon as it attaches
to the tibia below the knee.
[4] Cartilage:
There are two types of cartilage within the knee:
Articular cartilage: the end surfaces of each bone
are covered with smooth articular (joint surface) cartilage which
reduces friction between the moving surfaces of the joint and also
helps to spread the loads that are applied to the joint.
Meniscal cartilage, meniscus: Between the femur and
the tibia are two ‘C’ shaped wedges called menisci. These
are situated one on either side of the joint, and act as shock absorbing
cushions between the two main bones, in addition to other functions.
When a meniscus is damaged, it is often referred to as a ‘torn
cartilage’. This can be a confusing term, but when people talk
about a torn cartilage, they usually mean the meniscus and not the
articular cartilage.
