Knee replacement surgery is recommended for arthritis or injury on the knee that prevents it from moving freely. The knee comprises of three compartments namely the medial compartment (inside portion of the knee), the lateral compartment (outside) and the patellofemoral compartment (in front portion of the knee). When the cartilage wears off and the bone rubs against the bone, it causes severe pain on the knee. This puts a great strain on the mobility and can prevent you from performing your daily activities. Now this option is sought out when knee pain shows no improvement or the knee develop deformity.