Preoperative analysis of the Hill-Sachs lesion in anterior shoulder instability: how to predict engagement of the lesion.

BACKGROUND: It has been reported that engagement of the Hill-Sachs lesion affects postoperative recurrence of anterior shoulder instability. However, no method has been recognized as an effective preoperative means to predict engagement of the Hill-Sachs lesion.
PURPOSE: This study was undertaken to assess the diagnostic validity of computed tomography (CT) with 3-dimensional (3D) reconstruction to judge engagement of the Hill-Sachs lesion preoperatively. STUDY
DESIGN: Cohort study (diagnosis); Level of evidence, 2.
METHODS: One hundred four consecutive patients (107 shoulders) who underwent arthroscopic Bankart repair for traumatic anterior shoulder instability were enrolled for this study. Preoperatively, CT with 3D reconstruction was performed on all patients to evaluate the size (width and depth measured on axial and coronal images), orientation (Hill-Sachs angle), and location (bicipital and vertical angles) of the Hill-Sachs lesion. Dynamic arthroscopic examination was made to confirm engagement of the Hill-Sachs lesion. Then the correlation between the results and measurements on CT images was statistically analyzed.
RESULTS: In cases of engaging lesions, the mean width was 52% (range, 27%-66%) and the mean depth was 14% (range, 8%-20%) of the humeral head diameter on axial images. The corresponding measurements on coronal images were 42% (range, 16%-67%) and 13% (range, 5%-24%), respectively. In cases of nonengaging lesions, the corresponding measurements were 40% (range, 0%-71%) and 10% (range, 0%-21%) on axial images and 31% (range, 0%-62%) and 11% (range, 0%-46%) on coronal images. The size of engaging Hill-Sachs lesions was significantly larger than that of nonengaging lesions on both axial and coronal images (P = .001, < .001, .012, .007). The Hill-Sachs angle was 25.6° ± 7.4° in engaging lesions, which was significantly larger than 13.8° ± 6.2° in nonengaging lesions (P < .001). The bicipital and vertical angles did not demonstrate significant correlation with engagement of the Hill-Sachs lesion (P = .850, .584).
CONCLUSION: On CT with 3D reconstruction images, the engaging Hill-Sachs lesions were larger in size and more horizontally oriented to the humeral shaft than nonengaging lesions. The authors concluded that preoperative prediction of the engagement of the Hill-Sachs lesion, based on these findings, would be useful in planning additional procedures to treat a significant bone defect on the humeral head.