I recently bailed off a moped and tried to land on my feet and now the lateral portion of my knee is in pain, do you think i will need to have a joint replacement?

It depends.: You may just have a knee contusion, but a high energy landing like that can cause a lateral tibia plateau fracture or lateral meniscus tear. These may not lead to a joint replacement, but they can require other types of surgeries. If its been a few weeks and you're still symptoamtic, you should probably have the knee evaluated by a trained professional and get a set of x-rays and possbily an mri.

Yes: Mcl tears rarely need surgery.