What is ADHD? ADHD (attention deficit-hyperactivity disorder) affects both adults and school-aged children. Symptoms include restlessness, difficulty paying attention, and hyperactivity. The causes of ADHD are unknown, however factors such as diet, environment and genetics may contribute to symptoms.
The knee muscles control how the knee joint and patella move. There are two main groups of muscles, the quadriceps and the hamstrings, as well as a small muscle behind the knee (popliteus).
What can pain behind the knee be a symptom of? Swelling from knee injuries and ailments produces lump-like appearances on both sides of the knee. For example, the bursa, a sac of fluid that protects and cushions the joints, can become irritated and enlarged, explains WebMD.