Traumatic shoulder dislocation among adolescents: Hill-Sachs lesion volume and recurrent instability

Background: Accurate assessment of Hill-Sachs lesions (HSLs) and their relationship to the glenoid track is essential to optimizing management following traumatic shoulder dislocation. The purpose of this study was to measure the size of HSLs by a novel method with magnetic resonance (MR) arthrography and to investigate the relationship between lesion size and instability history in adolescents (below 19 y of age) with a history of traumatic dislocation. Methods: All shoulder MR arthrograms queried to identify HSLs over a 4-year period were retrospectively reviewed and independently evaluated by 2 blinded musculoskeletal radiologists. HSLs were evaluated on axial T1-weighted fat-saturated images. For each consecutive image slice in which the HSL was identified, a freehand region of interest was constructed along the compression fracture cavity. Region of interest sum was multiplied by image slice thickness (and gap between slices if present) to generate a total HSL volume (mm³). Subject chart review was then performed to acquire demographic data, including shoulder dislocation history. Results: A total of 30 patients met inclusion criteria and included 22 boys (mean age, 16.3 y) and 8 girls (mean age, 16.4 y). Four patients had a history of 1 traumatic dislocation, 12 had a history of 2, and 14 had a history of ≥3. The average size of the HSL for all patients was 3.8mm³ (range, 0.52 to 11mm³). There was no significant difference in HSL volume between the 21 skeletally immature (3.7mm³) and 9 skeletally mature (4.2mm³) patients (P=0.67). Patients with a history of 1, 2, or 3+ dislocations had an average HSL volume of 1.3, 3.7, and 4.7mm³, respectively. The measurement method revealed excellent interreader reliability (P=0.00). There was a statistically significant difference between dislocation history group mean HSL volumes (P=0.019), as well as a statistically significant difference between the number of dislocations and lesion volume (P=0.011). Conclusions: HSLs can be effectively measured in adolescent patients using MR arthrography and patients with larger HSLs have more recurrent instability episodes, potentially meriting greater and earlier attention to the defect. Level of Evidence: Prognostic/diagnostic study level IV.