Summary. Anatomy of the knee joint is one of the most complicated when compared to other joints in the human body. Due to high demands and strong forces acting on the knee joint, it is also one of the most injured joints. Every structure in the joint can be damaged and some of the damages demand earlier treatment. Except intraarticular fractures, stress fractures of the proximal tibia, as a result of lower extremity malalignment, need earlier treatment to prevent the dislocation of the fragments. Damage to the articular cartilage needs earlier treatment due to its tendency to involve wider area of the joint. Meniscus rupture is not an indication for earlier treatment, except a »bucket handle« rupture due to its potential to block the movements of the knee joint. Collateral ligament injury needs early treatment to prevent chronic laxity of the joint. Anterior cruciate ligament early recon- struction in top athletes results in their complete rehabilitation and return to the previous level performance. Total knee replace-ments may result in a number of complications, some of which need prompt treatment. Septic arthritis is a condition that requires prompt treatment, without any hesitation. Failure of earlier or prompt treatment of the conditions of the knee men- tioned in this chapter may result in permanent damage to the knee joint.