The Hill-Sachs Lesion: Volumetric modeling using Three-Dimensional Computed Tomography Reconstructions

OBJECTIVES: The purposes of our study were to identify the volume and relative location of Hill-Sachs lesions, measure the amount of glenoid bone loss in patients who have existing Hill-Sachs lesions, and finally draw any correlations that exist between increased glenoid bone loss and increased Hill-Sachs volume. METHODS: A total of 217 consecutive three-dimensional (3D) Computed Tomography (CT) scans were reviewed for the presence and measurement of Hill-Sachs volume and location. Hill-Sachs volume was measured by measuring the size of the Hill-Sachs defect in sequential CT images and a 3D model was created to measure the volume of the defect using Osirix (Osirix Imaging Software, Osirix-viewer.com). The Hill-Sachs lesion was then quantified in terms of both location and size. Further, older classification systems were applied to the data to draw comparison. Location of the lesion was measured by utilizing anterior and posterior margins of the lesion in relation to the biceps groove to give a clock face location. The height, depth and length of each lesion were also recorded in its greatest dimension. In addition a 3D model of the individual Hill-Sachs lesion was generated to observe the rough shape of the bony defect. RESULTS: The Hill-Sachs lesion was identified in 60% of patients, N=130. The mean volume of the Hill-Sachs lesions was 1.22 cm3, with a range of 0.13 cm3 to 5.3 cm3. The three dimensional shape of the Hill-Sachs lesion was consistently an orange slice. Using prism measurements the average volume was 3.19 cm3 with a range of 0.33 cm3 to 9.76 cm3. Average arc of the circle of each lesion measured at the axial mid point (10 mm below the top of the humeral head) was 68.9° with a range of 9.49° to 165.88°. The average depth of the lesion was 6.7 mm with a range of 2.8 mm to 11.1 mm. CONCLUSION: This study identified a unique yet important way to measure the absolute size of the Hill-Sachs lesion in the shoulder. This method is positively correlated with previous measurement systems, but utilizes novel methods to fully measure the unique shape of Hill-Sachs lesions. Using absolute measures not only increases accuracy, but 3D modeling also shows the nature of the defect and location in order to consider operative repair of the lesion. However, the Hill-Sachs lesion only describes one side of the problem, with this data side by side comparison with glenoid bone loss is needed to fully understand the nature of shoulder instability that is a bipolar problem.