What are the different types of knee injuries?
The knee is one of the most commonly injured parts of the body. Sports, falls, and motor-vehicle accidents account for the vast majority of injuries to the knee.
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, articular 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 and/or aging.
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 and nerves about the knee. This requires emergency treatment or surgery.
The kneecap (patella) can dislocate to the side of the knee. 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), splinting, and physical therapy.
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.