GAME CHANGERS IN SHOULDER ARTHROSCOPY: SCAPULA VARIATION INSIGHTS

Anatomic variations in the acromion and coracoid affect arthroscopic anatomic glenoid reconstruction (AAGR) for shoulder instability. The acromion is crucial for locating the posterior portal, creating the far-medial (Halifax) portal, and facilitating bone graft placement. However, the posterolateral corner's variability is greater than previously known. In addition, the impact of coracoid size and shape on arthroscopic bone graft fixation remains unexplored. These anatomical variations often lead to difficulties in glenoid reconstruction and graft misplacement. Mixed reality (MR) and 3D-printing offer potential solutions, but current understanding of scapular anatomy is insufficient. This study aimed to assess the variability in acromion and coracoid anatomy using 3D models and MR measurements to support MR-based, patient-specific glenoid reconstruction. CT scans of 100 patients requiring an AAGR were analyzed. Scapula's 3D-CT scans were used to create 3D-models displayed on a commercially available surgical MR system (RSQ-HOLO, RSQ Technologies, Poznan, Poland). Using the headset, we measured glenoid height and width and simulated ideal scope position from the posterior portal using a 0.5cm pointer placed along the glenoid surface. Additionally, we measured the superior-to-inferior and medial-to-lateral distances of acromion and coracoid, along with the angle between glenoid face and the acromion. A second rater repeated these measurements on 48 models to determine interrater reliability of the measurements. The acromion had a mean superior-to-inferior distance of 3.89 mm (SD: 6.09) and a mean medial-to-lateral distance of 8.76 mm (SD: 6.06). The position of the coracoid had less variation, reporting a mean superior-to-inferior distance of 21.18 mm (SD: 5.90) and a mean medial-to-lateral distance of 14.41 mm (SD: 4.63). The posterolateral corner showed significant variation. The angle between the glenoid face and acromion varied widely, with a mean angle of 38.42 degrees (SD:8.1312). The intra-class correlation coefficients (ICC) were high for all measurements, except for the angle between the glenoid and acromion (ICC 0.019), speaking to the variations in the anatomy, making these measurements more difficult. There are significant anatomical variations in the anatomy of the acromion and coracoid, making the standard two cm inferior and two cm medial landmarks rarely the ideal position for the posterior portal. This can affect surgical outcomes. We suggest using computer manipulated 3D-modeling, MR, and 3D printing to enhance individualized surgical plans for glenoid reconstruction.