A collateral ligament may be injured together with other structures such as the cruciate ligament or the meniscus.
In fact collateral ligament tears are rarely found in isolation.
A high proportion of medial collateral tears are associated with anterior cruciate ligament tears. A MCL tear in conjuction with an ACL tear and a medial meniscus tear is called the 'unhappy triad of O'Donoghue'.
Lateral collateral ligaments may be part of 'postero-lateral' corner insufficiency - which usually involves any or all of the capsule in this region, the popliteus tendon, the arcuate ligament and the cruciates.