Computational biomechanics of capsulolabral stress and elongation in Hill–Sachs bone defect: a finite element method aimed at patient-specific prediction of glenohumeral instability

Hill–Sachs is a compression fracture of the posterolateral humeral head that occurs in up to 93% of patients with recurrent anterior glenohumeral instability. Although previous research has primarily focused on the osseous defect, joint stability depends on a complex interaction between the soft tissue biomechanics (bone, cartilage, labrum, capsule, and ligaments). The mechanical interaction between the Hill–Sachs defect and joint soft tissues remains insufficiently characterized. This study used finite-element method analysis to evaluate the biomechanical response of the capsulolabral complex to humeral head defects of different sizes in the abduction and external rotation position. A patient-specific computational model of the glenohumeral joint was reconstructed from computed tomography; based on data from a female volunteer. Five defect sizes were simulated: 0% (healthy for reference), 6%, 9%, 31%, and 44% of the humeral head. Stress distributions in the labrum and elongation of the articular capsule were analyzed using ANSYS Workbench®. The model represents the changes present in the corresponding bone and cartilage. Therefore, the reported outcomes are limited to the biomechanical parameters of stress and elongation of the soft tissues derived from the numerical simulation. The healthy model served as the baseline for comparison. In the labrum, models with bone defects showed lower stress values than the healthy model, indicating reduced functional disruption of the suction-cup effect. Regional analysis revealed localized compression in the superior labrum, suggesting tissue pinching, and areas close to zero stress indicated a loss of uniform distribution. For the articular capsule, elongation remained stable up to a 31% bone defect; beyond this threshold, elongation increased, which was interpreted as capsular laxity. The values presented correspond to a trend seen exclusively in the numerical simulation. This study establishes a foundation for patient-specific simulations to predict the risk of instability and guide surgical decision-making. From Bankart repair to remplissage or bone augmentation procedures, this approach supports a more personalized method for managing shoulder instability.