Extra-articular deformities of the femur and tibia in conjunction with advanced knee osteoarthritis pose unique challenges for the arthroplasty surgeon. Careful preoperative planning is needed to evaluate both the intra-and extra-articular deformities and to determine the best route to total knee arthroplasty. An intra-articular compensatory correction can typically be performed if the extraarticular deformity is distant from the joint or if preoperative templating shows that bony cuts do not interfere with ligamentous attachments. Staged osteotomy followed by arthroplasty is beneficial in severe cases in which bony cuts are excessive or would interfere with softtissue structures and in cases with leg-length discrepancy. Osteotomies can be performed percutaneously and fixed with intramedullary nails, external fixators, or plate and screw constructs. Ligamentous laxity after correction and risk of peroneal nerve injury are increased in extra-articular deformity cases and must be considered during the knee arthroplasty procedure with increased implant constraint and patient counseling, respectively. Computerassisted navigation has an emerging role in total knee arthroplasty in patients with extra-articular deformity. M ore than 700,000 total knee arthroplasties (TKAs) are performed annually in the United States. 1 Although correction of intra-articular pathology is a mainstay of TKA, less has been published on the evaluation and management of extra-articular deformity in the setting of TKA. An extra-articular deformity may be a result of previous trauma or skeletal developmental abnormalities and may increase the risk of knee osteoarthritis. 2 Thus, orthopaedic surgeons should be aware of the diagnosis and treatment algorithms for extraarticular deformity in the setting of TKA. Performing a TKA without addressing underlying extra-articular malalignment may place the patient at risk of ongoing pain and early implant failure. 3 The purpose of this article is to present treatment algorithms for the management of extra-articular deformity in either the femur or tibia and in the coronal, sagittal, or axial plane and to review the radiographic imaging, surgical planning, and multidisciplinary approach necessary to optimize clinical outcomes and minimize arthroplasty failure. Causes of Extra-articular Deformity of the Femur and Tibia and Its Association With Knee Osteoarthritis Causes of extra-articular deformity of the femur and tibia are numerous