Dr. Niv Marom, a senior surgeon in the sports unit at Meir Medical Center, explains that an injury to the thigh muscles is essentially an injury to the hamstring muscle group, which are the knee flexor muscles. Common injuries include partial or complete ruptures of the connection between the tendon and the muscle, or an injury to the muscle itself. In more serious cases, surgery may be required if the injury is to the tendon or its connection to the bone. However, if