Posterior and combined shoulder instability in a sporting population

Authors: Emma Torrance, Michael Walton, Puneet Monga, Adam Watts and Lennard Funk

Background: Isolated anterior shoulder instability is traditionally believed to account for over 90% of shoulder instability, with posterior and combined shoulder instabilities, believed to be rare, accounting for only 2% to 5% of cases.  Interestingly however, recent studies have highlighted an increased incidence of posterior and combined shoulder instabilities in young, active populations.  In this study, we aim to compare surgically treated shoulder instability, according to the direction of instability, in sporting and non-sporting populations. 

Methods: Patients diagnosed with shoulder instability were retrospectively reviewed over a three-year period. Data was extracted from intraoperative reports from all 442 patients, under the care of four senior shoulder surgeons.  The total cohort had a mean age of 25.91±9.48 and consisted of 89.6% males.  All patients underwent and examination under anaesthesia, arthroscopic assessment of the glenoid capsulolabral structures and subsequent repair.

Results: Isolated anterior shoulder instability occurred in 52.9% (n=234) of all shoulder instabilities, with posterior and combined instability accounting for 16.3% (n=72) and 30.8% respectively (n=136).  Of all 442 patients with shoulder instability, 74.9% of patients were categorised as sporting (n=331) and had a mean age of 24.91±5.69.  The non-sporting population were older with a mean age of 35.40±11.94 at the time of surgery.  In the non-sporting population 68.5% (n=76) of patients had isolated anterior instability with 12.6% (n=14) posterior and 18.9% (n=21) combined. This is in contrast to the sports group where isolated anterior stabilisation only accounted for 47.7% (n=158) of all sporting instabilities, posterior 17.5% (n=58) and combined 34.7% (n=115).  Rugby players had the greatest incidence of shoulder instability within the sporting cohort accounting for 231 cases of which 47.2% anterior, 12.6% posterior and 40.3% combined.  

Conclusion: Posterior and combined shoulder instabilities are far more prevalent in young, sporting populations than previously reported. Careful assessment for posterior instability clinically and arthroscopically is mandatory in all instability cases especially in the sporting population.