Pain around the knee after traumatic hip dislocation is often caused by a bone bruise. The force of the impact through the knee may cause tiny fractures. These occur just under the cartilage in the first layer of bone called subchondral bone.
Bone bruises can also occur as a result of falls, sports injuries, or a direct blow to the knee from people or objects. Bruises can be painful (mild to severe) and last from days to months.
MRI shows swelling inside the bone marrow as a sign of a bone bruise. The injury usually heals on its own without treatment. Surgery may be needed if there's a large fracture of any of the bones around the knee.