Background Shoulder dislocation is a common sporting injury. Glenoid deficiency is thought to be a risk factor for recurrent shoulder dislocations. This study was performed to assess the role of CT scan in predicting recurrence following primary traumatic anterior shoulder dislocation.

Methods Prospective data was collected for 39 patients following first time traumatic anterior shoulder dislocation between April 2008 and June 2009 under the care of a specialist shoulder surgeon, including demographic details and CT scan findings to identify structural defects of the glenoid and humeral head in the form of bony bankart lesion, glenoid flattening and Hill sach's lesion. Electronic records from emergency and orthopaedic departments were checked in January 2013 to confirm recurrent shoulder dislocations.

Results The mean age was 26 years (range 15–56). There were 36 males and 3 females. CT scan showed bony bankart lesion in ten patients (26%), glenoid flattening in seven patients (18%) and Hill sach's lesion in thirtythree patients (85%). Patients were divided into groups according to the number of bone defects on CT scan (No bone defect-0, bony bankart lesion-1, glenoid flattening-1 and Hill sach's lesion-1).

Group A (no bone defect) had six patients (15%), Group B (Bone defect) had thirtythree patients (85%); twenty-two patients (56%) had 1 bone defect (Group C), five patients (13%) had 2 bone defects (Group D) and six patients (15%) had 3 bone defects ( Group E).

Group A (no bone defect) had 1 recurrent shoulder dislocation (16%) and Group B (Bone defect) had 16 recurrent shoulder dislocations (48%). Group C (1 bone defect) had 11 recurrent shoulder dislocations (50%), Group D (2 bone defects) had 2 recurrent shoulder dislocations (40%) and Group E (3 bone defects) had 3 recurrent shoulder dislocations (50%).

Discussion/Conclusion We studied the structural defects of glenoid and humeral head on the CT scan following primary shoulder dislocations and risk of recurrence in the presence of bone defects. Hill sach's lesion was the most common finding on the CT scan (85%). Patients with bone defects had a higher rate of recurrent shoulder dislocations (48% vs 16%). We recommend the use of CT scan following primary shoulder dislocations to identify structural defects of humeral head and glenoid before deciding the appropriate treatment to prevent recurrence.