Genu varum (bowlegs) is a condition in which the knees stay wide apart when a person stands with the feet and ankles together. It is consindered normal in children under 18 months. (From MedlinePlus)
Genu valgum (knock-knees) is a common lower leg abnormality that is usually seen in the toddler, preschool and early school age child. In genu valgum, the lower extremities turn inward, causing the appearance of the knees to be touching while the ankles remain apart. (From Nationwide Children's Hospital)
Two wedge-shaped pieces of cartilage act as "shock absorbers" between your thighbone and shinbone. These are called meniscus. They are tough and rubbery to help cushion the joint and keep it stable.
Meniscal tears are among the most common knee injuries. Athletes, particularly those who play contact sports, are at risk for meniscal tears. However, anyone at any age can tear a meniscus. When people talk about torn cartilage in the knee, they are usually referring to a torn meniscus. (From the American Academy of Orthopaedic Surgeons)
Osgood-Schlatter disease (also known as "Jumper's Knee") is an overuse injury that occurs in the knee area of growing adolescents. It is caused by inflammation of the tendon below the kneecap (patellar tendon) where it attaches to the shinbone (tibia). (From the American Academy of Orthopaedic Surgeons)
Patellar tracking disorder means that the kneecap (patella) shifts out of place as the leg bends or straightens. In most cases, the kneecap shifts too far toward the outside of the leg. In a few people, it shifts toward the inside. (From St Francis Health)
Injured ligaments are considered "sprains" and are graded on a severity scale.
Grade 1 Sprains. The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.
Grade 2 Sprains. A Grade 2 Sprain stretches the ligament to the point where it becomes loose. This is often referred to as a partial tear of the ligament.
Grade 3 Sprains. This type of sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces, and the knee joint is unstable.
It is possible to injure two or more ligaments at the same time. (From the American Academy of Orthopaedic Surgeons)