Poster 215. Influence of Chronicity, Number, and Type of Anterior Shoulder Instability Events on Hill-Sachs Lesion Size: A Morphometric Analysis of 255 Patients

Abstract

Objective: Previous literature has demonstrated that larger Hill-Sachs lesion (HSL) size is an important predictor of recurrent anterior shoulder instability after arthroscopic Bankart repair (ABR), and may necessitate augmentation procedures such as remplissage to reduce rates of recurrent instability. However, it remains unclear what pre-operative factors influence HSL size at time of imaging. Therefore, the purpose of this study was to evaluate factors associated with HSL size at time of imaging, including the chronicity, number, and type of prior anterior shoulder instability events. The hypothesis was that chronic instability, multiple prior instability events, and experiencing glenohumeral dislocation versus subluxation would result in larger HSL size. Methods: A retrospective review was conducted on all patients undergoing arthroscopic Bankart repair (ABR) with or without remplissage for anterior shoulder instability between 2007-2023. Exclusion criteria included age <14 years, revision surgery, glenoid bone loss >20%, unknown date of instability, missing or unavailable magnetic resonance imaging (MRI), and lack of HSL. Patients were characterized based on chronicity of anterior shoulder instability (acute <=6 months versus chronic >6 months), experiencing one versus multiple prior anterior shoulder instability events, and experiencing glenohumeral subluxation (no manual reduction required) versus dislocation (manual reduction required). HSL medial-lateral width and cranio-caudal length were measured on axial and sagittal MRI respectively. HSL area (recorded in mm2) was calculated as HSL width times HSL length. Percent glenoid bone loss and distance-to-dislocation (DTD) of the HSL were additionally measured as previously described. Univariate analysis was performed between chronicity groups, number of instability event groups, and dislocators versus subluxators using chi-square, Student t-tests, and Mann-Whitney U tests as appropriate. Significance was set to p<0.050. Results: After applying exclusion criteria, 255 patients (age: 22±8 years; 24% female) were included, of which 153 patients had acute instability and 102 patients had chronic instability. There was no association between acute versus chronic instability and HSL width (11.6 vs 12.4 mm; p>0.050), HSL length (16.4 vs 16.7 mm; p>0.050), and HSL area (201.6 vs 215.7 mm2; p>0.050), however DTD was significantly smaller in chronic instability patients (8.9 vs 10.5 mm; p=0.021) (Table 1). While number of prior anterior shoulder instability events was not associated with HSL size, patients who experienced dislocation versus subluxation were found to have larger HSL length (16.7 vs 13.4 mm; p<0.001), and area (201.9 vs 150.7 mm2; p=0.012) (Table 1). Within-group analysis identified a smaller DTD in chronic versus acute dislocators (9.1 vs 10.9 mm; p=0.043), as well as a smaller DTD (9.0 vs 13.5 mm; p=0.005) and larger HSL width (12.3 vs 8.8 mm; p=0.009) in chronic versus acute subluxators. Conclusions: HSL size was not associated with chronicity or number of anterior shoulder instability events, however was found to be larger in patients who experienced glenohumeral dislocation versus subluxation. These findings suggest that HSL size may be influenced more by nature and degree of initial anterior shoulder instability event than the chronicity of anterior shoulder instability events.