The knee is made stable by several extremely tough cord-like structures – your ligaments. These connect parts of your tibia to your femur. It can be thought that there are two groups of ligaments that provide stability to your knee and prevent excessive movement. One group are in the middle of your knee and are called the cruciate ligaments – the anterior cruciate (ACL) and the posterior cruciate ligaments (PCL). The other group are situated outside the knee – one on the inside of your knee called the medial collateral ligament (MCL) and a ligament on the outside part of your knee called the lateral collateral ligament (LCL). The lateral collateral ligament is in reality one of over 20 structures that stabilise this area of the knee termed the posterolateral corner (PLC). Injury to these ligaments will lead to excessive abnormal movement of the knee and can lead to further damage to cartilage, menisci and increase the rate of development of arthritis.