Incidence of posterior shoulder instability and trends in surgical reconstruction: a 22-year population-based study

Background: The incidence of posterior shoulder instability (PSI) in the general population is not well defined. This study aimed to define the population-based incidence of PSI and describe trends in incidence and surgery rates. Methods: The study population included 143 patients (16 females, 127 males) diagnosed with new-onset PSI between January 1, 1994, and December 31, 2015. Medical records were reviewed to extract patient data. Age- and sex-specific incidence rates were calculated and adjusted to the 2010 United States population. Poisson regression was performed to examine trends by timeline, sex, and age. Results: Age- and sex- adjusted annual incidence of PSI was 4.64 per 100,000 person-years, and posterior dislocation was 1.30 per 100,000 person-years. Peak PSI incidence for males and females was at 14 to 19 years (31.82 and 5.23 per 100,000 person-years). PSI incidence was higher in males than females (8.86 vs. 1.07 per 100,000 person-years, P <.001). The 5-year cumulative risk of surgery for patients with PSI was 53.1% between 1996 and 2002, 59.9% between 2003 and 2008, and 87.5% between 2009 and 2015. Patients with PSI between 2009 and 2015 had a significantly increased rate of surgery (hazard ratio, 2.2; 95% confidence interval, 1.4-3.6; P =.001) compared with those between 1996 and 2002. Conclusion: The age- and sex- adjusted incidence of PSI in the general population was 4.64 per 100,000 person-years. There is a significantly greater incidence of PSI in males than females, with both sexes peaking at 14 to 19 years and incidence rates remaining elevated throughout the third and fourth decades of life. The incidence of PSI remained stable over time; however, the rate of surgical intervention increased significantly, from 53.1% of patients between 1996 and 2002 to 87.5% of patients between 2009 and 2015.