The coronal alignment of femoral prostheses is one determinant that affects knee kinematics and patient satisfaction after total knee arthroplasty (TKA) [[1], [2], [3]]. Various computer-navigated and robotics-assisted systems have been developed to improve the precision of bone resection during TKA [4]. Previous cost-effectiveness analyses, however, questioned these computer-assisted systems because TKA using these systems is much more expensive than the conventional procedure [5]. The introduction of less expensive systems could reduce financial burdens on health care budgets [6].

Portable navigation systems have attracted attention because they work without any large and expensive computer consoles [7]. The KneeAlign 2 accelerometer-based navigation system (OrthAlign, Aliso Viejo, CA) is a validated portable navigation system that consists of a disposable display console and reusable reference sensor [7]. Several randomized controlled trials (RCTs) showed that the accelerometer-based navigation system was more precise than the conventional manual technique and as precise as large console imageless navigation systems [[7], [8], [9], [10]]. The augmented reality (AR)-assisted navigation system is a newly developed portable navigation system [11,12]. AR technology can project the femoral mechanical axis and the coronal and sagittal angles of femoral cutting guide on real world through a smartphone display. Although one retrospective comparative study showed that the AR-assisted navigation system had better precision than the conventional manual procedure [12], there is a paucity of clinical data regarding the effectiveness of the AR-assisted navigation system.

The purpose of this study was to compare the precision between TKA using AR-assisted navigation and that using an accelerometer-based navigation system. The null hypothesis was that the success rate of femoral prosthesis alignment for the AR-assisted navigation system would be poorer than that of the accelerometer-based navigation system within a noninferiority margin.