Summary

The rate of progression to glenohumeral arthritis after arthroscopic posterior stabilization surgery was 12% in a young and high demand population.

Abstract

Introduction

Shoulder instability is a common cause of shoulder pain and dysfunction, particularly in young and active individuals. While anterior instability remains the most common type, recent literature shows that posterior instability occurs more frequently than previously thought. As opposed to its anterior counterpart, posterior instability most often presents with pain, particularly in active individuals involved in dynamic posterior loading of the shoulder resulting in repetitive microtrauma of the posterior capsulolabral structures. While arthroscopic stabilization for posterior glenohumeral instability has shown excellent success preventing recurrent instability and allowing return to sport, eventual progression to glenohumeral arthritis remains a concern in these patients. However, the rate of and risk factors for arthritis post-surgery in young and high demand populations have not been described in the literature and may be important in guiding decision making when treating the young patient with posterior shoulder instability. The purpose of this study was to evaluate the rate of progression to glenohumeral arthritis and identify potential risk factors after arthroscopic posterior stabilization in a young and high demand population.

Methods

This study included 110 active duty servicemembers identified in the Military Heath System (MHS) with posterior shoulder instability who underwent primary arthroscopic surgical stabilization and had postoperative imaging or medical records available over a twelve-year period between January 2004 and September 2016. All procedures were performed at a single institution. Patients were excluded if they had previously undergone a stabilization procedure on the shoulder of interest, if no pre-operative imaging was available, or if operative information regarding the number of anchors used was unavailable. Presence of arthritis (yes/no) was defined over follow-up using radiographic parameters as described by Samilson and Prieto identifying patients with at least ‘mild arthritis.” Glenohumeral bone loss was reported as a continuous variable using the perfect circle technique. Kaplan-Meier survival curves were estimated for development of arthritis and compared by patient characteristics using log-rank tests. Cox proportional hazard models were used to calculate Hazard Ratios (HR) with 95% confidence intervals (95% CI) associated with patient characteristics as predictors of the development of glenohumeral (GH) arthritis. The proportional hazards assumption was evaluated for each predictor using Schoenfeld residual-based tests.

Results

Among the 110 patients with posterior shoulder instability requiring surgical fixation, 12.7% (14/110) developed glenohumeral arthritis. The mean age of all patients was 23.9 years (SD 6.7). The Kaplan-Meier estimate of 10-year survival free of GH arthritis was 0.87 (0.79, 0.95). The median follow-up time was 8.1 years (IQR 5.8). Kaplan-Meier curves did not show statistical differences in time to arthritis among patient groups stratified by age (HR (per 10 year increase) 1.45 (95% CI 0.76, 2.74), index surgery anchor number (HR 1.21 (95% CI 0.75, 1.93), or glenoid bone loss (HR 0.87 (95% CI 0.74, 1.03).

Conclusion

No previous study has reported the incidence and risk factors for glenohumeral arthritis after arthroscopic surgical stabilization for posterior shoulder instability. The progression to glenohumeral arthritis after posterior stabilization surgery occurred in 12.7% of a young and high demand patient population over median follow-up of 8.1 years. No patient characteristics were found statistically associated with risk of GH arthritis; however statistical power was limited by the low incidence of GH arthritis in our cohort. The near significant confidence interval for glenoid bone loss and the potentially clinically relevant effect size for higher risk with increasing age warrant further evaluation in larger cohorts which may help guide clinical decision making and chronicity of treatment.