These are common injuries. Pain is on the inner(medial) or the outer(lateral) side. Many isolated injuries heal by themselves, specially the MCL injuries. Lateral injuries can occur isolation or in combination with PLC injuries. These are very serious injuries and occur from car accidents and contact sports. These are also often missed on X-rays and seen very well on MRI scans.
Some complex MCL and LCL injuries in association with other ligament injuries need surgical treatment to make the knee stable and functional.