The knee joint has four main stabilising ligaments. Not all knee ligament injuries require surgery. Injury to the anterior cruciate ligament (ACL), deep within the knee joint, is often the result of sporting activity. Rupture of the ACL may lead to a sense of knee instability which impairs the return to normal function. This is particularly the case if the patient participates in sports which require pivoting motions upon the knee (rugby, football, netball etc.) An ACL reconstruction can be performed using key-hole (arthroscopic) techniques and this is followed by a carefully prescribed course of physiotherapy to restore knee function and allow a return to normal activities.