Current standard techniques used for anterior cruciate ligament reconstruction are unable to restore normal knee biomechanics. One explanation for this is that ongoing anterolateral rotatory instability is due to damage to anterolateral knee structures that current surgical techniques fail to address. Focus had previously moved away from the periphery of the knee towards intra-articular reconstruction, however in the past rotational instability was addressed with a lateral extra- articular tenodesis, and these were widely used techniques in the 1970s and 80s before falling out of favour. A detailed review of this surgery, including the Lemaire, Macintosh and Ellison procedures has been performed in this thesis, as well as a review of the pre existing anatomical knowledge of the anterolateral knee structures. Due to gaps in knowledge identified, an attempt to further define anterolateral knee anatomy has been made. 40 fresh frozen cadaveric knees have been dissected. A consistent structure termed the anterolateral ligament (ALL) was identified in 33 (83%) of the specimens. The ALL passed antero- distally from a femoral attachment point posterior and proximal to the lateral femoral epicondyle. It passed superficial to the lateral collateral ligament, to an attachment point midway between Gerdy’s tubercle and the fibula head. We sought to further determine the biomechanical role of the structure using length change experiments. The ALL was isometric from 0° to 60° degrees of flexion, and then slackened when the knee was flexed to 90°. Two independent musculoskeletal radiologists reviewed MRI appearances of the ALL and findings were consistent with our anatomical observations. The

ALL may be involved in resisting the pivot shift and inserts at the site of the Segond fracture. Since the experiment numerous anatomical, biomechanical and radiological investigations have been published on the ALL and these are reviewed in detail.