Posterior instability of the shoulder joint accounts for approximately 10% of surgically treated shoulder instabilities and is being seen with increasing frequency. Posterior shoulder instability (PSI) can result from numerous causes. In general, a traumatic cause can be distinguished from an atraumatic cause with various acknowledged trauma mechanisms having been described in the literature. However, in clinical outcome studies, the definition of traumatic PSI is often vague and not necessarily linked to the acknowledged mechanisms described in the literature.
Arthroscopic capsulolabral anchor stabilization is the current surgical gold standard for patients with PSI who do not have bone loss and in whom nonoperative treatment has failed. Most studies reporting outcomes of arthroscopic capsulolabral repair have presented results of patient populations with mixed causes of PSI or focused on patients with either traumatic or atraumatic onset. Apart from one study that found inferior outcomes for adolescent patients with atraumatic PSI, little is known about functional outcomes and return to sport after arthroscopic capsulolabral repair for traumatic and atraumatic PSI.16
In the past, some authors have described an association between atraumatic PSI and excessively increased glenoid retroversion (GR). Furthermore, patients with traumatic PSI were shown to have significantly more GR than patients with anterior shoulder instability. In addition, increased GR was recently identified as the most significant risk factor for PSI in young athletes. However, it remains unclear if the degree of GR differs between patients with traumatic onset of PSI and patients with atraumatic onset of PSI.
Therefore, the aim of this study was to compare GR and functional outcomes between patients with traumatic onset of PSI and patients with atraumatic onset of PSI. It was hypothesized that there would be more GR and that functional outcome scores would be significantly lower in patients with PSI that had an atraumatic onset.