Unperceived First-Time Anterior Shoulder Subluxation: The Role of MRI in Detection and Characterization of Pathoanatomy

Abstract

Background: First-time anterior shoulder subluxation is typically diagnosed based on subjective instability or positive physical examination findings. However, some patients present without any perceived instability yet demonstrate definitive magnetic resonance imaging (MRI) findings such as Bankart or Hill-Sachs (HS) lesions. Purpose: To study the pathoanatomy of unrecognized subluxation with first-time dislocation and typical subluxation. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study investigated patients diagnosed with first-time shoulder instability who underwent MRI at an army hospital between September 2023 and March 2025. Only patients with no previous history of dislocation, subluxation, or surgery were included. Patients were categorized as having dislocation, typical subluxation, or unrecognized subluxation based on clinical history and examination. Unrecognized subluxation was defined as the absence of perceived instability and negative physical examination findings despite MRI-confirmed Bankart-equivalent lesions. Radiologic assessments included glenoid bone loss and HS lesion characteristics (interval, width, depth, and distance to dislocation [DTD]). The time interval from trauma to MRI acquisition was recorded for all patients, as it may reflect the time to clinical recognition. Results: Of the 75 male soldiers with first-time shoulder instability and MRI-confirmed Bankart lesions, 18 had dislocations, 30 had typical subluxations, and 27 had unrecognized subluxations. Glenoid bone loss was minimal in all groups (mean, <5%) and did not differ significantly among the 3 groups (P = .806). The dislocation group had significantly greater HS interval, width, depth, and lower DTD than the other groups (all P < .001), while no significant differences were found between typical and unrecognized subluxation. MRI was obtained significantly later in the unrecognized subluxation group (median, 35 days), followed by the typical subluxation (19.5 days) and dislocation groups (1 day) (P < .001). Conclusion: Anterior shoulder instability is not always recognized by patients, and initial physical examination may be limited in the acute setting. MRI findings of unrecognized first-time subluxations were similar to those of typical subluxations and showed less severe HS morphology than in dislocations. Clinicians should maintain a high index of suspicion in young patients presenting with traumatic shoulder pain, even in the absence of perceived instability.