A sprain is an injury to a ligament, the strong bands of tissue that connect a bone to another at a joint. The severity of a sprain can be classified by the amount of tissue tearing, impact on joint stability, pain and swelling.
The knee joint relies on ligaments (ACL, PCL, MCL, LCL) and surrounding muscles for stability, so they are easily injured. Any direct contact to the knee or rapid direction change while moving can injure a knee ligament.
Runners’ knee, also known as patellofemoral pain syndrome, is often described as pain located beneath or around the kneecap. Running can cause irritation where the kneecap rests on the thigh bone (femur) and the pain is aggravated by squatting and using stairs. Stiffness in the knee after prolonged sitting is also a symptom of this injury.
Osteoarthritis, also known as degenerative joint disease, is the most common type of arthritis. Osteoarthritis is more likely to develop as people age. The changes in osteoarthritis usually occur slowly over many years. Inflammation and injury to the joint cause a breaking down of cartilage tissues, resulting in pain, swelling, and deformity of the joint.