Since its introduction, unicompartmental knee arthroplasty has been controversial because of poor early clinical outcomes due to implant design, bony fixation, surgical instrumentation, and technique. Improvements in surgical technique and implant design have resulted in improved results and greater survivorship. The ability to obtain accurate implant placement includes avoiding surgeon decisions leading to potential errors. These errors include alignment in the sagittal, coronal, and axial planes on each prepared condyle as well as the preservation of the joint line and the resulting overall limb alignment as something critical to obtaining a successful outcome.