MR arthrographic examination of the association with glenohumeral instability of posterior labroligamentous insertion types and posterior labrum anatomical variants

OBJECTIVES: The objective of this study is to evaluate the relationship between posterior labroligamentous morphological variants and abnormal position of the humeral head in the glenoid cavity using MR arthrography (MRA). Additionally, the study seeks to investigate whether these variations act as biomechanical risk factors for subclinical instability. METHODS: The study's sample population comprised 190 patients who did not exhibit posterior labral tears or clinical instability. The posterior labrum morphology and capsulolabral insertion types were assessed using MRA, and the posterior subluxation index (PSI) of the humeral head in the glenoid cavity was quantitatively measured. A statistical analysis was conducted to examine the associations between capsulolabral variations and posterior humeral head positioning. RESULTS: The prevalence of labral hypoplasia was observed to be 29% among the patient population, while aplasia was identified in 2% of cases. Sublabral clefts were identified in 52% of cases. A statistically significant increase in posterior displacement of the humeral head was observed in cases of labral hypoplasia and sublabral clefts, particularly in cases of deep clefts (p < 0.001). Posterior capsular insertion type was also identified as an independent predictor of the posterior subluxation index (PSI). CONCLUSIONS: Posterior labral variations, specifically hypoplasia and deep sublabral clefts, have been observed to be associated with increased posterior humeral head translation, even in the absence of clinical instability. These structures may serve as biomechanical risk factors contributing to subclinical posterior shoulder instability. LEVEL OF EVIDENCE: Level IV; Case Series Using Large Database. CLINICAL TRIAL NUMBER: Protocol code: E-10840098-202.3.02-2631, date of approval: 21/04/2025.