After reading the following case study who would your verdict be for, the plaint

After reading the following case study who would your verdict be for, the plaintiff or the defendant? Using your knowledge of what is required to prove negligence explain your verdict. 
“The plaintiff, age sixty-nine, was undergoing treatment of osteoarthritis with pain from the lower back and derangement of his left knee. The plaintiff claimed that in June 2003 a physical therapist stretched and injured the left knee by improperly manipulating the knee. The knee was iced and leg-press exercises were prescribed, but the plaintiff claimed that the exercises aggravated his injury. Three days later the plaintiff went to a physician. He later underwent an MRI scan which revealed tears of the posterior horns of the left knee’s lateral and medial menisci. The plaintiff underwent about two and one-half months of additional physical therapy at the center. 
The plaintiff alleged negligence in the treatment of the knee. 
The defendant claimed that there was no negligence and that the MRI scan showed long-standing degenerative injuries which pre-existed the treatment.”