ACL, LCL, MCL and PCL: the knee ligaments explained

The ACL and PCL cross inside the knee, while the MCL supports the inner side and the LCL supports the outer side. A twist, awkward landing or force to the knee can stretch or tear one or several of them.

ACL means anterior cruciate ligament; it limits the shin bone moving too far forward and helps control rotation. PCL means posterior cruciate ligament; it restrains excessive backward movement of the shin. MCL means medial collateral ligament and resists the knee collapsing inward. LCL means lateral collateral ligament and resists excessive outward opening.

An injured ligament may present with pain, swelling, reduced movement or a sense that the knee gives way. The pattern alone cannot confirm which structure is damaged because cartilage, tendons and bone can produce overlapping symptoms.

Stop pivoting, running and contact activity. Protect the knee, use a wrapped cold pack for comfort, elevate it if swollen and avoid forcing the joint through painful movement. If walking feels unstable, reduce weight through the leg until assessed.

A clinician can examine stability and decide whether imaging is useful. Treatment depends on the ligament involved, the extent of damage, other injured structures and your activity goals. Rehabilitation commonly rebuilds movement, muscle control and confidence; a brace may be used for selected injuries.

Arrange a prompt assessment if the knee repeatedly gives way, swelling develops after injury, you cannot fully straighten it, or pain prevents normal walking. Seek urgent care after major trauma if the knee looks deformed, you cannot bear weight, the foot becomes cold or pale, or numbness or weakness appears below the knee.

Ask which ligament appears injured, whether another structure may also be involved, what movements to avoid, whether you need a brace or walking aid, and which milestones should guide your return to work, driving and sport.