The Effect of Number of Preoperative Instability Episodes on Distance-to-Dislocation and Risk of Recurrent Instability After Arthroscopic Bankart Repair

Objectives: Recurrent anterior shoulder instability after arthroscopic Bankart repair represents a challenging clinical problem, with rates of recurrence being highly dependent on specific preoperative patient risk factors. Although increased preoperative instability episodes have been previously identified as a risk factor, a threshold for instability episodes that increase risk of injury recurrence is not well established in scientific literature. Furthermore, the impact of preoperative instability episodes on distance-to-dislocation (DTD) is poorly understood. The objective of this study is to establish a threshold value of preoperative instability episodes that predict DTD and injury recurrence after arthroscopic Bankart repair. Methods: This was a retrospective review of consecutive patients with on-track lesions who underwent primary arthroscopic Bankart repair for recurrent anterior glenohumeral instability at a single institution between 2007 and 2019. Patients with missing data on preoperative instability episodes, less than 2 years of follow-up data, and glenoid bone loss >20% were excluded. Measurements of glenoid bone loss and length of Hill-Sachs lesions were performed by two fellowship trained orthopedic surgeons. DTD was calculated by the difference between the medial edge of the glenoid track and the medial edge of the Hill-Sachs lesion. Near track lesions were defined as an on-track lesion with less than 10 mm DTD. Recurrent shoulder instability was defined as recurrent postoperative dislocation and/or subluxation. Receiver operating characteristic (ROC) curves were constructed for preoperative instability episodes to determine critical thresholds that best predict near-track lesions and injury recurrence. The optimal cutoff point was determined using Youden’s index (Sensitivity + Specificity − 1). Results: 155 patients were included for analysis with average age 20.2 ± 5.6 years and follow-up of 6.1 ± 3.1 years. 28 patients (18%) experienced recurrent postoperative instability following ABR. Higher number of preoperative instability episodes was an independent predictor of lower DTD when adjusting for age, sex, contact athlete, hyperlaxity, and number of anchors used in the repair (β = -0.26, 95% CI = -0.48 - -0.04, p = 0.023). ROC curve analysis of preoperative instability episodes showed that a threshold value of 1 preoperative instability episode was the best predictor of both near-track lesions (area under the curve AUC = 0.63) and failure (AUC = 0.72). Increasing values of preoperative instability episodes beyond the threshold value of 1 did not increase the ability to predict failure. Conclusions: Patients with greater than one preoperative instability episode may be predictive of lower DTD and higher postoperative injury recurrence rates. Thus, surgeons should consider patients with multiple preoperative instability episodes as a higher-risk patient, but stratifying patients beyond this threshold may not be necessary.