Summary

The morphologic glenoid change at 6 to 12 months in Type I of the SSE classification has the potential for positive glenoid morphology change, similarly to those without the SSE group. The SSE influences the progression of glenoid erosion in both Type II and III.

Abstract

Background

The one questionable factor in progressive anterior glenoid erosion after arthroscopic Bankart repair (ABR) or arthroscopic bony Bankart repair (ABBR) is the stress shielding effect (SSE). The SSE is often a precipitating factor that contributes to the cause of decreasing glenoid diameter width due to resorption of the anterior glenoid rim. The progressive glenoid erosion from SSE might be one factor contributing to the increased rate of recurrence of shoulder instability.

Purpose

The SSE is studied and followed up in terms of pattern classification and severity, which can predict the progressive glenoid morphology change prognosis, including the chance of recurrence of shoulder instability after ABR or ABBR.

Methods

A total of 202 shoulders performed the ABR and ABBR between January 2018 and April 2023 in a retrospective cohort study design. At 12 months of follow-up, there were 89 shoulders that were classified in the without SSE group and 113 shoulders that were classified in the SSE group (figure 1). There are three different types of specific characteristic differences in the slope and contour of the SSE at the anterior glenoid rim that determine the severity of the condition. The group without SSE is compared with the SSE group at 6 and 12 months postoperatively by 3D CT scan glenoid reconstruction (figure 2). In terms of the comparative outcomes study, the percentage of glenoid defect change between 6 and 12 months, the distribution and incidence of SSE, and the rate of recurrence of shoulder instability.

Results

The SSE group is found in 113/202 shoulders (55.94%), and Type II is the most common finding in the SSE group (47.79%, 54/113). The mean difference in percentage glenoid defect change between 6 and 12 months is not significant between the groups without SSE and the Type I group (1.24 ± 0.84, P = 0.87). However, the mean difference of percentage glenoid defect change between 6 and 12 months is significant between without SSE VS Type II, without SSE VS Type III, and Type II VS Type III (-3.35 ± 0.78 (P < 0.0001), -8.09 ± 1.20 (P < 0.0001), and -4.74 ± 1.25 (P = 0.001), respectively). The recurrence rate of instability in between groups is not related to that between the groups without SSE and SSE (6.74% (6/89) and 4.42% (5/113), respectively (P = 0.52)) (figure 3).

Conclusion

In terms of morphologic glenoid change at 6 to 12 months, Type I of the SSE classification has the potential for positive glenoid morphology change, similarly to those without the SSE group. The SSE influences the progression of glenoid erosion in both Type II and III. Although, the SSE group and those without SSE are not related to the increasing rate of shoulder instability, further follow-up study is necessary to draw a definitive conclusion.