Rheumatoid arthritis or synovitis, osteoporosis, osteomalacia and so on are the main causes of ankle pain for no reason. 1. Rheumatoid arthritis or synovitis: Rheumatoid arthritis or synovitis can cause ankle pain for no reason, mostly with a history of rheumatoid arthritis, you can go to orthopedics or rheumatology, and blood tests can make a clear diagnosis. 2. Osteoporosis: Osteoporosis can cause a decrease in bone density, resulting in generalized bone disease. Unexplained pain in the ankles often occurs in the osteoporosis population, and osteoporosis will cause back pain, sudden pain in the ankles, deformation of the spine, and bone fracture when the disease strikes. 3. Osteomalacia: Osteomalacia belongs to the degenerative lesions of bone and joint, and its pathology is the pain caused by edema, adhesion, and aseptic inflammation at the site of hyperplasia and compression of nerve root. If osteophyte disease is present in the ankle it can involve the ankle joints, resulting in unexplained ankle pain, often accompanied by persistent pain that worsens with activity. In addition, other conditions can also lead to ankle pain for no reason, you should go to the hospital for examination in time, after clarifying the cause of the disease, under the guidance of the doctor for appropriate treatment.