P suffered an injury to her knee from an auto accident. P sued D and testified that she suffered swelling and pain in the knee after walking, as in shopping, and that as a substitute teacher she was no longer able to participate in physical education activities involving 'physical games' or to play volleyball and tennis. Her doctor testified that P suffered from a torn semi-lunar cartilage in her knee; that 'the probable future of this knee' was 'one of gradual deterioration'; that her injury was 'permanent'; and that it was 'very probable' that she would 'require a surgical procedure' to remove the torn cartilage. He also testified that after such an operation 'the recovery is fairly good' and that 'the outlook for good recovery would be very optimistic.' P's doctor had not prescribed any 'treatment' for P. D's doctor disagreed that P suffered from a torn semilunar cartilage, but that if she did have such an injury, as is 'a very frequent injury seen in athletes,' the torn cartilage should be 'surgically excised,' i.e., 'removed in total,' and that after such an operation 'the patient should recover completely' and be able 'to return to all normal and usual activities.' P did not indicate that she would ever undergo surgery for her condition. P was awarded $7,500, which included an element for her permanent disability. D appealed contending that the court erred in instructing the jury on whether P sustained a permanent injury and P failed to mitigate her damages. Note: D failed to request the instruction he was appealing upon.