Causes:

Knee pain can be caused by injuries, mechanical issues, various types of arthritis, and other issues.

• Injuries
• Anterior cruciate ligament (ACL)
• ACL damage
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• Meniscus tear
• Meniscus tear
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A knee injury can affect the ligaments, tendons, or fluid-filled sacs (bursae) that surround your knee joint, as well as the bones, cartilage, and ligaments that make up the joint itself. The following are some of the more common knee injuries:

• ACL tear. An ACL injury is a tear in the anterior cruciate ligament (ACL), which connects your shinbone to your thighbone. ACL injuries are prevalent in basketball, soccer, and other sports that require sudden changes in direction.
• Fractures. During falls or car accidents, the bones of the knee, including the kneecap (patella), can be broken. Furthermore, people whose bones have been weakened by osteoporosis can sometimes sustain a knee fracture simply by taking an incorrect step.
• Meniscus tear. The meniscus is tough, rubbery cartilage that sits between your shinbone and thighbone and acts as a shock absorber. It can be torn if you twist your knee suddenly while bearing weight on it.

• Bursitis of the knee. Some knee injuries cause inflammation in the bursae, which are tiny sacs of fluid that cushion the outside of the knee joint and allow tendons and ligaments to glide smoothly over it.

• Tendinitis of the patella. Tendinitis is characterized by irritation and inflammation of one or more tendons, the thick, fibrous tissues that connect muscles to bones. This inflammation can occur when the patellar tendon, which runs from the kneecap (patella) to the shinbone and allows you to kick, run, and jump, is injured. Patellar tendonitis can occur in runners, skiers, cyclists, and those involved in jumping sports and activities.

  Mechanical issues:

Mechanical issues that can cause knee pain include:

• The body is loose. Injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not cause any issues unless the loose body interferes with knee joint movement, in which case the effect is similar to a pencil caught in a door hinge.
• Iliotibial band syndrome This happens when the tough band of tissue that runs from the outside of your hip to the outside of your knee (iliotibial band) becomes so tight that it rubs against the outer portion of your thighbone. Distance runners and cyclists are especially vulnerable to iliotibial band syndrome.
• Kneecap dislocated This happens when the patella (the triangular bone that covers the front of your knee) slips out of place, usually to the outside of your knee. In some cases, the kneecap may remain displaced and the dislocation will be visible.
• Foot or hip pain If you have hip or foot pain, you can alter your walking style to protect your painful joint. However, this altered gait can put more strain on your knee joint, resulting in knee pain.

Arthritis Types

There are over 100 different types of arthritis. The following are the most likely to affect the knee:

• Osteoarthritis. Osteoarthritis, also known as degenerative arthritis, is the most common type of arthritis. It's a wear-and-tear condition that occurs when your knee's cartilage deteriorates with use and age.
• Arthritis rheumatoid. Rheumatoid arthritis, the most severe form of arthritis, is an autoimmune disease that can affect almost any joint in your body, including your knees. Although rheumatoid arthritis is a chronic disease, its severity varies and it can even come and go.
• Gout. When uric acid crystals accumulate in the joint, this type of arthritis develops. Gout most commonly affects the big toe, but it can also affect the knee.
• Pseudogout. Pseudogout, which is frequently confused with gout, is caused by calcium-containing crystals that form in the joint fluid. The most common joint affected by pseudogout is the knee.
• Arthritis is caused by bacteria. Swelling, pain, and redness can occur when your knee joint becomes infected. Septic arthritis is frequently associated with a fever, and there is usually no trauma prior to the onset of pain. Septic arthritis can quickly wreak havoc on the knee cartilage. Consult your doctor right away if you have knee pain and any of the symptoms of septic arthritis.

Risk elements:

A variety of factors can increase your chances of developing knee problems, including:

• Extra weight. Being overweight or obese puts more strain on your knee joints, even during everyday activities like walking or stair climbing. It also increases your risk of osteoarthritis by hastening the breakdown of joint cartilage.
• Muscle inflexibility or weakness Knee injuries can be exacerbated by a lack of strength and flexibility. Muscle strength helps to stabilize and protect your joints, while muscle flexibility allows you to achieve a full range of motion.
• Some sports or occupations. Some sports place more strain on your knees than others. Alpine skiing, with its rigid ski boots and potential for falls, basketball jumps, pivots, and running or jogging all increase your risk of a knee injury. Construction and farming jobs that require repetitive knee stress can also increase your risk.
• Injury in the past. A previous knee injury increases your chances of injuring your knee again.