Summary

This study showed that there are different patterns of subcritical bipolar bone lesions in anterior shoulder instability, that can be divided into 4 groups, with a significantly different prevalence. Those are significant predictors of failure after surgery. Moreover, surgeons should be aware that additional procedures may be considered depending on a specific pattern of lesion.

Abstract

Introduction

Glenoid bone defects (GBD) over 20% and off-track Hill-Sachs lesions are often considered predictor of failure after arthroscopic bankart repair (ABR). However, recent literature called into questions the predictive value of those parameters, indicating 13.5% of GBD and a Distance to dislocation (DTD) lower than 8 mm as subcritical thresholds. However, they have never been considered together to determine different patterns of subcritical bipolar bone lesions (SBBD). The aim of the present study was to analyze the prevalence of different patterns of SBBD and determine their predictive value for the recurrence rate and PROMs after ABR.

Methods

A retrospective study was conducted. Patients affected by recurrent anterior gleno-humeral instability with an on-track bipolar lesion who underwent ABR alone with a minimum of 24 months follow-up were included. Three-dimensional computer-based reconstruction of the Hill-Sachs and GBD were performed to obtain DTD and percentage of GBD measured using the best-fit circle method. Patients were divided into groups according to varying combinations of DTD and GBD: type 1 (-/-), where both measures were less than subcritical (GBD < 13.5% and DTD > 8mm): type 2 (-/+), where GBD was less than subcritical (GBD < 13.5%) and DTD < 8mm: type 3 (+/-), where GBD was > 13.5% and DTD was less than subcritical (> 8mm); and type 4 (+/+), where both measures where subcritical (GBD > 13.5% and DTD < 8mm).
The primary outcome was the analysis of the prevalence of different patterns of SBBD. Secondary outcomes were the predictive value of the different patterns of SBBD for the recurrence rate and PROMs measured with the ASES score, the WOSI Index and the Tegner Activity Scale. Significance was set at p<0.05.

Results

The study included 274 patients with a median age of 26 years old (IQR: 9.6). Patterns of SBBD were distributed as follows: type 1 in 108 cases (39.4%); type 2 in 94 cases (34.3%); type 3 in 25 cases (9.1%); and type 4 in 47 cases (17.2%) (p<0.0001). From the entire study population, 143 patients were randomly selected for follow-up evaluation, with a recurrence rate of 10.5%. Comparison between groups for recurrence rate showed a significant difference between them. Particularly, type 2 and 4 showed the greatest recurrence rates (11.5% and 26.1% respectively). Comparison between groups for PROMs showed no significant differences. Univariate logistic regression analyses demonstrated that the SBBD pattern was independently associated with the recurrence of instability, together with age and type of sport. On multivariate analysis, the same variables were confirmed to be significant predictors of failure.

Discussion And Conclusion

This study showed that there are different patterns of SBBD, that can be divided into 4 groups, with a significantly different prevalence among patients with anterior shoulder instability with an on-track bipolar lesion. Those patterns are significant predictors of failure after ABR. Moreover, surgeons should be aware that additional procedures may be considered depending on a specific pattern of SBBD.