Collateral ligament injuries of the knee are common, either in isolation or in combination with damage to the meniscus or cruciate ligament or capsule. Collateral ligaments may be damaged by -
- a direct contact blow on the side of the knee while the foot is 'planted' (on the ground). This forces the joint to bend sideways ('varus' or 'valgus' force) and tears the ligament on the opposite side. The illustration above shows a valgus force, and it is the medial collateral ligament (on the inner aspect of the knee) which will be damaged.
- landing badly from a jump so that the knee is forced sideways by the weight of the body.
Collateral ligament injuries are graded as -
Grade I collateral ligament tear
There is tenderness at site of injury but no opening up when stress is applied
Grade II collateral ligament tear
There may be severe discomfort and up to 5mm opening up when stress is applied
Grade III collateral ligament tear
There may be marked pain, instability and swelling, with joint opening up to 10mm when stressed