<s>[INST] My brotherinlaw is having severe pain in the calves of both legs. He has been having this problem for years and he recently had knee replacement on both sides. That seems to be OK. Muscle pain in the calf is the problem. He said it feels like cramping. When hestretches the muscle of the calf it seems to help. [/INST] Hi, You did not mention the age of your brother-in-law and for what reason, he underwent knee replacement. Assuming that he was suffering from osteoarthritis these could be the causes of his calf pain.1. The most common one in osteoarthritis patients is virus deformity i.e. legs starts bending inwards, if that was the reason, he will be relieved with calf muscle pain now as he underwent the replacement surgery in which deformity is also corrected.2. Calcium and vitamins deficiencies are also one of the cause, so start taking supplements.3. Sodium potassium imbalance is also a cause for calf muscle pain, so take oral rely Chat Doctor. 4. Wrongly designed footwear is also a cause of calf muscle pain.5. Chronic venous malformations in calf muscles like varicose veins, or venous incompetence can be a cause so to rule out getting a color Doppler done. Hope I have answered your query. Let me know if I can assist you further.   </s>