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What are the different types of knee injuries?
The knee is one of the most common parts of the body to be injured. Sports,
falls, and motor vehicle accidents account for the vast majority of injuries to
The different types of injuries to the knee are defined by the affected
anatomy of the knee and the mechanism by which it's injured.
Knee sprains are injuries to the ligaments that hold the knee together. There
are multiple ligaments that stabilize the knee and keep it in alignment. The
anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL)
stabilize the knee in movement from front to back and cross each other in the
middle of the knee joint. The medial collateral ligament (MCL) and lateral
collateral ligament (LCL) stabilize the knee so that the bones do not slide from
side to side.
Ligament sprains are graded by the amount of stretching or tearing of the
ligament fibers and how much instability it causes as follows:
Grade 1 knee sprain: The ligament is stretched and painful, but
fibers are not torn and no instability is present.
Grade 2 knee sprain: The ligament
fibers are torn partially, mild instability may be evident.
Grade 3 knee
sprain: The ligament fibers are completely torn and the knee is unstable.
Knee strains occur when tendons or muscles surrounding the knee are
stretched, usually due to hyperflexion or hyperextension of the knee. These
strains can lead to
pain outside of the knee joint but can cause dysfunction of
the normal range of motion of the knee. The patellar tendon stretches from the
lower kneecap to the front of the tibia bone at the front of the leg.
Knee bursitis occurs when a fluid-filled pouch (called a bursa) in the knee
is irritated, inflamed, or infected. Bursas are fluid-filled sacs located around
joints that act as shock absorbers that minimize the friction between various
tissues, such as the muscles and tendons around the joints. In the knee, there
are two main bursas, one above the kneecap (patella), and one below the knee
joint near the front of the tibia bone.
Tears of the meniscus can occur from damage to the inside of the knee. The
medial and lateral menisci (plural of meniscus) are semi-round pieces of
cartilage that act as shock absorbers and smooth cushions for the thighbone
(femur). These menisci can be injured acutely or can become dysfunctional
gradually due to overuse.
Knee joint dislocation can occur due to high-impact, large-force injuries to
the knee (sports, motor vehicle accidents). This is a rare injury but causes
severe damage to all the anatomical components of the knee and can include
damage to the blood vessels. This requires emergency treatment or surgery.
The kneecap (patella) can dislocate to the side of the knee. The patella
dislocation can be very painful but is generally not life-threatening and can
be treated by popping it back into place (reduction of the patella) and
Knee fractures occur from direct blows to the bones. Patella, or kneecap,
fractures occur when a person falls directly down onto the knees and the kneecap
cracks due to the force. Collapse of the top of the tibia bone in the knee
(tibia plateau fracture) can occur from sudden compression injury to the knee,
especially in people with osteoporosis. Other fractures of the long bones
(fibula, tibia, and femur) are rare with isolated injures to the knee.
Other overuse injuries of the knee include patellofemoral pain syndrome
(often referred to as "runner's knee") and weakness and degeneration of the
cartilage under the kneecap (chondromalacia patella). These injuries are due to
an accumulation of repetitive damage to the knee structures. This may be cause
by either congenital problems or improper mechanics of the knee movement.