The first serious suspicion is meniscal damage to the knee or osteoarthritis of the knee. The most important thing at this point is to have an MRI of the knee to determine exactly what kind of damage is involved. If it is clear that the knee is a meniscal injury, the first step is to decide whether to treat it conservatively or surgically, depending on the extent of the meniscal injury. Conservative treatment involves avoiding walking on the lower extremities, microwave physiotherapy, giving blood-boosting drugs, and even intra-articular injections. If the knee is rattling due to osteoarthritis, it should be treated with anti-osteophyte therapy, or even surgery if the osteophytes are particularly severe.