Four-dimensional computed tomography can visualise the in vivo glenoid track and quantify dynamic glenohumeral contact mechanics during active motion in subjects with shoulder instability: A preliminary study.

Purpose: The concept of the glenoid track was proposed to evaluate the risk of shoulder dislocation with bipolar lesions, but dynamic in vivo evaluation during active motion has remained limited. The purpose of this pilot study was to evaluate glenohumeral (GH) contact area, contact centroid translation, and in vivo glenoid track visualisation during shoulder external and internal rotation using four-dimensional computed tomography (4DCT). Methods: We obtained 4DCT data from the affected and intact shoulders of seven patients (mean age, 27.4 ± 5.5 years) with anterior shoulder instability and a Hill-Sachs lesion during active cocking motion. The GH contact area (defined as the region with a glenohumeral joint space ≤4 mm) and translation of its centre were calculated from 3D bone models using customised software and compared between affected and intact shoulders at maximal internal rotation (MIR) and maximal external rotation (MER). Results: Affected shoulders showed a significantly smaller mean contact area at MER (429.5 ± 39.7 mm Conclusion: This pilot feasibility study demonstrated that 4DCT can visualise the in vivo glenoid track and quantify dynamic glenohumeral contact mechanics during active motion. In affected shoulders, contact area decreased at MER and the centre of the contact area translated anteriorly during external rotation. Clinical Relevance: Dynamic assessment of the glenoid track using 4DCT enables in vivo visualisation of GH contact mechanics in patients with bipolar lesions. This method can identify anterior translation and reduced contact area during shoulder external rotation, which may provide complementary biomechanical information beyond conventional static assessment. Level of Evidence: Level IV, case series with intra-patient comparison.