Can you tell me the story from the Satcharitra about the doctor's nephew from Malegaon who had a bone-cyst?

Certainly. Chapter 34 of the Shri Sai Satcharitra recounts the story of a degree-holding doctor from Malegaon, in the Nashik district, whose nephew was afflicted with a severe bone-cyst, also known as Hadyavarn. Despite the doctor himself being a physician and enlisting the help of his expert physician and surgeon friends, no remedy could cure the boy. They tried all native and foreign treatments, and even surgery, but all efforts were exhausted and felt helpless as the young boy suffered greatly. This difficult and extraordinary malady showed no signs of improvement with conventional medicine.