Technologies such as augmented reality (AR) have facilitated the creation of immersive user interfaces for handling 3D medical data during surgery. To date, computer-assisted orthopaedic surgery (CAOS) relies on touchscreen displays to deliver a 2D user interface for handling medical data. In contrast, the use of AR headsets allows 3D projection of medical data directly onto patient anatomy, removing the need for any mental coordinate transformation, and enabling a surgeon to maintain focus on the operating site. In this study, a new AR-centric workflow was created and closely integrated with a commercially available CAOS system, enabling a HoloLens 2 headset to receive and render medical data during key stages of the procedure – patient registration and cutting. The AR workflow co-registered the CAOS system’s optical tracker with the AR headset, thus rendering patient-specific holograms in-situ, directly onto patient anatomy, during the patient-registration and cutting phases of simulated patellofemoral arthroplasty (PFA). A pre-clinical study recruited six non-clinical subjects to investigate the impact of using AR on mental workload when compared to standard CAOS display methods. The system’s usability was probed through an investigation of mental workload using Task Load Index (TLX) surveys, which found no significant increases in mental workload associated with the use of AR in this study. Overall, this study reports successful initial deployment of AR in a pre-clinical setting for CAOS, in a non-expert group, with no significant impairments to mental workload, presenting the potential to continue exploring more intuitive visual guidance options for future surgical applications.