The knee is a complex structure and one of the most stressed joints in the body. It is the largest joint, vital for movement, and vulnerable to injury.
The knee is the most commonly injured joint by adolescent athletes with an estimated 2.5 million sports-related injuries annually.
Many knee injuries can be successfully treated with simple measures, such as bracing and strengthening exercises. Other injuries may require surgery to correct.
Although not all knee injuries can be prevented, education on knee anatomy, how injuries happen, and how best to care for them when they do, can help prevent potential complications or long-term disability from common knee injuries.
Contents of this article:
You will also see introductions at the end of some sections to any recent developments that have been covered by MNT's news stories. Also look out for links to information about related conditions.
Here are some key points about knee injuries. More detail and supporting information is in the main article.
- An estimated 6,664,324 knee injuries were presented to emergency departments from 1999 through 2008, equaling 2.29 knee injuries per 1,000 individuals.
- Those 15 to 24 years of age had the highest injury rate.
- Participation in sports and recreational activities are risk factors for knee injury.
- Stairs, ramps, landings, and floors are most associated with knee injuries sustained outside of sports.
- As life expectancy increases, the incidence of knee injuries among older adults can also be expected to increase.
- Knee injuries account for 60% of high school sports-related surgeries, and occur among both sexes and across all age groups.
- The point at which two or more bones are connected is called a joint.
- The cruciate ligaments are named such as they form a cross in the middle of the knee.
- Female athletes participating in basketball and soccer are two to eight times more likely to suffer an anterior cruciate ligament (ACL) injury compared to male athletes.
- Athletes who have suffered an ACL injury are at increased risk of developing arthritis later on in life.
- A direct blow to the knee is a serious injury and requires immediate medical attention.
- A history of locking episodes suggests a tear in the meniscus.
The knee is a hinge joint that is responsible for weight bearing and movement. It consists of bones, meniscus, ligaments, and tendons.
The knee is a complex pivotal hinge joint that connects the bones in the upper and lower leg, comprised of muscle, ligaments, tendons, and the meeting of four bones.
The femur (thigh bone), tibia (leg bone), and patella (knee cap), make up the bones of the knee.
Meniscus is sometimes called cartilage, and the knee has two; the medial (inner) and lateral (outer). These crescent-shaped discs act as a cushion, or "shock absorber" so that the bones of the knee can move through their range of motion without rubbing against each other.
Ligaments act like strong ropes to connect bones to other bones. The knee has four; ACL (anterior cruciate ligament), MCL (medial collateral ligament), PCL (posterior cruciate ligament), and LCL (lateral collateral ligament).
These tough bands of tissue connect muscles to bone and provide stability to the joint.
Although they are not technically part of the knee joint, the equally important hamstrings and quadriceps are the muscles that strengthen the leg and help flex the knee.
Common knee injuries
Knees are most often injured during sports activities, exercising, or as a result of a fall. Pain and swelling, difficulty with weight bearing, and instability are the most common symptoms experienced with a knee injury.
In athletes, the most common acute injuries are ACL and MCL sprains. A sprain is the stretching or tearing of a ligament.
Sprains and strains
Sprains and strains are injuries to the ligaments. The ACL and MCL are the ligaments most often injured.
These injuries usually happen in sports such as soccer, football, and basketball where the knee might experience a sudden twisting motion, a rapid change in direction, or an incorrect landing from a jump.
Often a pop or a snap is heard followed by swelling. Symptoms also include tenderness along the joint line and pain with walking.
A meniscal tear generally happens during sports where the knee twists, pivots, or an individual is tackled.
Even normal wear from aging can weaken the meniscus, causing it to tear with a simple awkward turn during normal day to day activities. Symptoms of a tear are usually pain, stiffness, swelling, locking, and decreased range of motion.
A fracture is most often caused by trauma, such as falls, motor vehicle accidents, and sports-related contact. The most common bone broken around the knee is the patella.
The most common overuse injury is "runner's knee," a loose term that refers to several disorders, including patellofemoral pain syndrome (PFPS). These painful conditions are common among athletes such as runners and cyclists.
Pain is experienced behind or around the kneecap, and can travel to the thigh or shin. The pain worsens with activity and is relieved by rest.
On the next page we look at the treatments and rehabilitation for knee injuries and how knee injuries can be prevented.