A calf thick, a calf thin, the following common causes: First, lumbar disc herniation and other lumbar diseases will compress the sciatic nerve, so that the sciatic nerve innervation area, such as the loss of innervation of the calf, so that muscle wasting atrophy occurs, the calf muscle will become thin. Patients will also be accompanied by lumbar spine pain and lumbar spine activity limitation, MRI can clearly show the lumbar spine lesions. Second, fractures in the lower extremities, such as femur fractures, knee fractures, and tibiofibular fractures, require short-term braking, so the muscles cannot contract and stretch properly. If the patient’s rehabilitation is not in place, it will make the muscle atrophy more serious. Third, osteoarthritis of the knee joint or necrosis of the femoral head can lead to persistent pain in the leg, and the patient is afraid to bear weight normally, thus leading to calf muscle atrophy.