Mixed reality guidance improves humeral head cut accuracy

The humeral head osteotomy is a critical step in both anatomic and reverse shoulder arthroplasty because it determines humeral component alignment, including neck-shaft angle (NSA), retroversion, and component height. Inaccurate osteotomy may adversely affect implant positioning, soft tissue tensioning, joint biomechanics, and long-term clinical outcomes. Mixed reality (MR) technology has demonstrated potential to improve intraoperative visualization and surgical accuracy in shoulder arthroplasty; however, its role in improving humeral head osteotomy accuracy remains largely unexplored. The purpose of this study was to determine whether MR guidance improves the accuracy of humeral head osteotomy compared with freehand and extramedullary guide (EG) techniques.

Forty-five identical 3-dimensional printed arthritic proximal humerus models were created and mounted in standardized orientation. Nine orthopedic surgery residents were stratified by postgraduate year and randomly assigned within each stratum to one of 3 groups performing humeral head osteotomies using one of 3 techniques: freehand, EG, or MR holographic guidance using a Microsoft HoloLens 2. Each participant performed 5 osteotomies targeting a 135° NSA and 30° of retroversion. Following osteotomy, specimens were digitized using 3-dimensional scanning and compared with a predefined reference osteotomy plane using iterative closest point analysis in Blender software. Primary outcomes included absolute deviation from planned NSA, retroversion, and cut height.

Forty-two osteotomies were included in the final analysis, including 15 MR-assisted osteotomies, 15 freehand osteotomies, and 12 EG osteotomies. MR-assisted osteotomy demonstrated significantly lower absolute NSA deviation compared with both freehand and EG techniques. Mean absolute NSA deviation was 5.6° ± 5.2° in the MR group, compared with 10.4° ± 6.3° in the freehand group and 10.4° ± 5.2° in the EG group (P = .013). MR guidance also demonstrated significantly lower absolute cut height deviation (4.2 ± 2.0 mm) compared with freehand (7.8 ± 3.0 mm) and EG techniques (7.1 ± 3.5 mm) (P = .008). No significant differences in retroversion deviation were identified between groups (P = .70).

MR holographic guidance improved the accuracy and reproducibility of humeral head osteotomy, particularly with respect to NSA and cut height, compared with freehand and EG techniques. These improvements were achieved using passive holographic guidance without formal navigation, optical tracking, or hologram registration, suggesting that 3-dimensional visualization alone may improve osteotomy reproducibility during shoulder arthroplasty. Further investigation is warranted in cadaveric and clinical settings.