Review of radiological and clinical interpretation of anterior group shoulder dislocations and testing of a novel radiological measurement to distinguish between subcoracoid and subglenoid subtypes

The lack of formal diagnostic criteria for anterior shoulder dislocation subtype classification has led to confusion in the literature and the clinical setting. Accurately distinguishing between type 1 (subcoracoid) and type 2 (subglenoid) subtypes is important for reduction technique choice and likelihood of success in reduction technique. We aimed to examine how emergency and radiology clinicians describe anterior group shoulder dislocations and to assess whether radiological measurements were able to accurately distinguish between subcoracoid and subglenoid subtypes. Retrospective review of imaging and clinical notes of two years of anterior group shoulder dislocation cases presenting to a tertiary emergency department (ED). In 101 eligible cases a consensus anterior shoulder dislocation subtype diagnosis was made by two expert reviewers. The descriptions of anterior group dislocations used by emergency and radiology clinicians in these cases were analysed. Imaging was reviewed to determine whether landmark radiological measurements could accurately distinguish between type 1 (SC) and type 2 (SG) dislocation subtypes. There were 86 (84.31%) type 1, 15 (14.71%) type 2, no type 3 or 4 subtypes, and one (0.98%) case with an unclear diagnosis. There were different themes noted in terminology used by the ED and radiology groups. The emergency clinicians used broad terms, employing the term ‘anterior’ most frequently (48.5%), with ‘dislocation’ (26.7%) second. The radiology clinicians used the term ‘antero-inferior’ or variants most frequently (63.4%), with ‘anterior’ (32.7%) second. Terminology that matched the consensus subtype diagnosis was made by emergency clinicians in 47.5%, and radiology clinicians in 32.7% of cases (p=.0312). A landmark radiological measurement, IGIANV, was accurate for subtype differentiation in 96% of cases, with a sensitivity 98.8%, (95% CI: [0.937 to 0.998]) and a specificity of 80%, (95% CI [0.548 to 0.93]). In this retrospective sample the type 1 subtype was most common consistent with previous literature. Emergency department and radiology clinicians diagnosed dislocation of the shoulder but did not consistently identify or distinguish between anterior dislocation subtypes. The clinical relevance for incorrect subtype diagnosis is that reduction techniques may be misapplied, potentially affecting success rates and discomfort to patients. The novel IGIANV measurement was accurate for subtype differentiation and a radiological guideline is proposed to assist emergency and radiology clinicians in correctly diagnosing anterior group shoulder dislocation subtypes. Further research on a larger sample is required to validate the guideline. Ethics approval was sought and gained from the St Vincent’s Hospital, Melbourne Human Research Ethics Committee reference number QA 24,002 registered 12th February 2024. All methods were performed in accordance with the relevant guidelines and regulations (Declaration of Helsinki). The study adheres to the CONSORT guidelines.