There are two different patterns of posterior glenoid deficiency. For traumatic posterior shoulder instability a triangular (“delta”) bony defect has been described in contrast to a rounded posterior glenoid deficiency (“lazy J”), which is mainly found in atraumatic posterior instability. It is essential that the graft be voluminous (up to 3 cm long). A tricortical bone graft is harvested from the ipsilateral anterior iliac crest. The mean glenoid retroversion measured in the MRI scans according to the method described by Friedman et al. is 10.5°.