First-time anterior dislocation of the shoulder is associated with the development of recurrent instability. It is recognised that patients with recurrent instability often have osseous defects. Using 3D computerised tomography (3DCT) it is possible to quantify these defects. Whether these defects are present after the primary dislocation or occur progressively from multiple dislocations is unclear. We correlated the presence of Hill-Sachs lesions and anterior glenoid bone loss with evidence of recurrent dislocation and clinical outcomes.

78 patients were followed up for two years. All underwent a 3DCT within a week of injury. Standardised images of the humeral head and glenoid were produced. Using standardised digital techniques bone loss was measured.

39% of the patients developed further instability. Average Hill-Sachs circumferential length = 15.23%. Average Hill-Sachs surface area = 5.53%. The length and surface area of the Hill-Sachs lesions were significantly associated with further instability. (p=0.019 and p=0.003). Average en face glenoid surface area loss=1.30% with no association to instability (p=0.685). There was poor correlation between the size of the glenoid lesion and the size of the Hill-Sachs lesion.

Results showed that age and increasing size of the Hill-Sachs lesions result in a higher rate of instability. Interestingly glenoid bone loss was relatively low and did not predict recurrent instability. The size of the Hill-Sachs lesion does not have a linear relationship with glenoid bone loss. Further work defining the morphology of the Hill-Sachs lesion and its engagement with a glenoid defect is required.