Abstract: BACKGROUND: There is a long surgical learning curve for safe and accurate placement of the acetabular prosthesis in hip replacement surgery. Mixed reality technology can fuse virtual image data models with real patient entities, which can help operations such as virtual surgery and intraoperative navigation, potentially improving the accuracy of acetabular prosthesis placement and shortening the surgical learning curve for less experienced surgeons.
OBJECTIVE: To develop positional data for the accurate placement of acetabular components via HoloLens 2, and conduct surgical operations in combination with an in-vitro 3D-printed pelvic acetabular model, so as to clarify the efficacy of mixed reality technology in both training and intraoperative guidance for hip replacement surgery.  
METHODS: Orthopedic surgeons with extensive experience in joint replacement surgery and those with limited experience in acetabular cup placement were recruited to perform in vitro surgical operations for joint replacement using an in vitro 3D printed pelvic acetabular model under conventional surgical operation and/or guided by HoloLens 2 head-mounted device, respectively. The abduction angle, the anteversion angle, the offset degree of the acetabular prosthesis were measured and recorded to compare the differences in the accuracy of acetabular component placement angles. 
RESULTS AND CONCLUSION: (1) Under manual operation conditions, the experienced surgeon group had an acetabular cup abduction angle of (41.52±3.76)° and an anteversion angle of (21.35±3.63)°; the inexperienced surgeon group had an abduction angle of (44.29±7.62)° and an anteversion angle of (21.55±7.82)°. The differences in placement angles between the two groups were statistically significant (P < 0.05). (2) After using the HoloLens device for assistance, the inexperienced surgeon group had abduction and anteversion angles of (41.10±1.28)° and (20.09±0.53)°, respectively, while the experienced surgeon group had abduction and anteversion angles of (41.08±1.09)° and (20.28±0.65)°, respectively. There was no significant difference between the two groups. (3) This suggests that for total hip replacement, the use of mixed reality technology significantly improves the accuracy of acetabular cup placement compared with manual operation. The application of mixed reality technology provides significant clinical assistance for surgeons in precisely reaming the acetabulum and placing the acetabular cup, and can shorten the learning curve for orthopedic surgeons. 

Key words: ">mixed reality technology, HoloLens 2, hip replacement, acetabular prosthesis, learning curve, surgical navigation