If osteoarthritis affects only one compartment of the knee (most commonly the medial compartment), a unicompartmental knee replacement is considered the gold standard treatment. The question then arises: how do we determine if a patient is suitable for a unicompartmental knee replacement? Determining a patient's suitability is straightforward. Diagnosis and suitability for a unicompartmental knee replacement can be determined through patient history, physical examination, and simple standing radiographs. In some cases, an MRI scan may be requested to confirm suitability and determine the type of prosthesis.