After you injure a knee, you might hobble to your doctor’s
office or a hospital’s emergency department for treatment.
Often, the degree of pain or the inability to walk causes you to
seek emergency care.
Injury to the knee can damage any number of structures. Until the
doctor makes a diagnosis, these are the possible knee injuries you
Although there are many ways to injure your knee, discussion here will
address a general approach to knee injuries and then focus on injuries
of the knee ligaments and cartilage.
- Bone: Injuries result in fractures (breaks) and dislocations.
- Cartilage (support tissue for the joints): Injuries result in tears
in or degeneration of cartilage and arthritis.
- Ligaments (connections of bone to bone): Injuries result in sprains.
- Tendons (connections of muscle to bone): Injuries result in strains,
ruptures, or inflammation.
- Bursa (fluid-filled sacs for cushion during joint motion): Injuries
result in infection or inflammation.
- Actual space within the joint: Injuries result in infection or
Four bones come together to form the knee joint to allow motion—
the femur, tibia, fibula, and patella. This extremely high-functioning
joint acts as a hinge to allow forward and backward motion.
But a knee also must be able to provide some side-to-side motion
while still maintaining its form as a hinge. To allow this motion, many
ligaments, tendons, cartilage structures, and bursa join the 4 knee bones
The 2 main bones of the joint are the thighbone (femur) and the
shinbone (tibia). The other bones, the kneecap (patella) and the fibula,
which runs down the outside of the calf, play more of a supportive role
to the knee.
Four ligaments then connect the femur and tibia:
- Two pieces of cartilage make up a disklike pillow in the joint space
between the femur and the tibia to cushion the bones where they meet.
This is called the meniscus.
- Lateral meniscus - The outside portion of the cushion
- Medial meniscus - The inside portion of the cushion
- Anterior cruciate ligament (ACL): Located in the middle of the joint,
this ligament prevents the tibia from sliding forward on the femur.
- Posterior cruciate ligament (PCL): Also located in the middle of the
joint, this ligament prevents the tibia from sliding backward on the
- Lateral collateral ligament (LCL): This ligament, located on the outside of the knee, prevents the knee from buckling to your outside.
- Medial collateral ligament (MCL): This inside ligament prevents the knee
from buckling inward.
Tendons around your knee that provide support fall into 2 main groups:
Several bursae lie on the inside, outside, and in front of your knee and
provide smooth movement of the joint. The largest is the pre-patellar,
or supra-patellar, bursa, which lies almost on top of the kneecap.
- Quadriceps tendon: The tendon of the muscles that make up your thigh
comes over the front of the knee. This tendon surrounds the patella and
provides stability from the front. It terminates—as the patellar
tendon—at a knoblike structure on the upper end of your tibia,
called the tibial tubercle.
- Hamstring tendons: The tendons of the hamstring muscles split in back of
the femur and go both inside and outside of the tibia to provide support
The joint space of the knee is filled with a fluid called synovial fluid
to provide smooth movement.