Posterior Translation of the Humeral Head after Arthroscopic Bankart Repair: A Quantitative Analysis of Preoperative and Postoperative Axial MRI.

BACKGROUND: Anterior shoulder instability leads to anterior humeral head translation on static axial imaging. While arthroscopic Bankart repair restores stability, its quantitative impact on static humeral head translation remains unclear. This study aimed to compare static anteroposterior translation of the humeral head on axial magnetic resonance imaging (MRI) before and after arthroscopic Bankart repair and identify independent factors influencing these translations and their magnitude of change.

METHODS: This retrospective study included consecutive patients who underwent arthroscopic Bankart repair for anterior shoulder instability between June 2023 and July 2025. Humeral head anteroposterior translation (HHAT; positive values indicate a more posterior position) was assessed on T1-weighted axial MRI using a posterior-referenced ellipse method to account for anterior glenoid bone loss. The impact of demographic and baseline clinical characteristics, positional variables during MRI acquisition, and preoperative glenohumeral morphology on preoperative and postoperative HHAT, as well as the magnitude of change (Δ HHAT), was evaluated.

RESULTS: Fifty patients were evaluated. Intra- and interobserver reliability for HHAT measurements was good. The HHAT significantly increased from 0.59 ± 1.24 mm preoperatively to 1.50 ± 1.02 mm postoperatively (mean change, 0.91 mm; P < .001). In multivariable analysis, preoperative HHAT was a significant independent factor associated with postoperative outcomes; it showed a positive correlation with postoperative HHAT (P = .032) but an inverse correlation with Δ HHAT (P < .001). Additionally, the time from initial dislocation to surgery was a significant independent factor positively associated with the preoperative HHAT (P = .043).

CONCLUSIONS: Arthroscopic Bankart repair results in a statistically significant reduction in anterior humeral head translation in anterior shoulder instability. Preoperative humeral head translation, linked to the chronicity of the instability, correlated positively with postoperative humeral head translation, yet inversely with the magnitude of this shift.

LEVEL OF EVIDENCE: Level IV, Case Series, Treatment Study.