EP1.75 The Role of Radiographs In the Diagnosis of Hip Microinstability – a Comparative MultiCenter Study of 802 Patients With Surgically Confirmed Diagnoses

Abstract

Abstract Introduction Hip microinstability has emerged as an important, though underrecognized, source of pain and dysfunction. The aim of this study is to provide ascertain the imaging features to improve the ability to diagnose hip microinstability. Methods Using prospectively obtained data, we analyzed 802 patients that underwent hip arthroscopy from 2023–2025 across 3 international high-volume hip preservation practices. Patients were categorized into two groups: those with and without intraoperative confirmation of hip microinstability. All patients underwent the same pre-operative imaging evaluation. Advanced statistical analyses were performed to analyze the relationships between imaging variables on the odds of MI diagnosis. Analyses were completed in RStudio using a two-sided level of significance of 0.05. Results Of the 802 hips, 240 (30%) were diagnosed with microinstability intraoperatively. Patients had an average age of 34.4 (± 11.4) years (50.5% female). Overall, 36.7% of patients with microinstability had a radiographic feature of hip dysplasia (LCEA <25°, ACEA <25° and/or acetabular index / Tonnis Angle >10°). Those with microinstability had a lower average lateral center edge angle (LCEA) (32.9° ± 7.1° vs 35.1° ± 6.6°, p<0.001) (OR 2.90 [1.39–6.23], p=0.005); lower anterior center edge angle (ACEA) (32.0° vs 35.2°, p<0.001), higher femoral neck shaft angle (132° vs 131°, p=0.031) and higher Tonnis angle (5.3°vs 3.6°, p<0.001) (OR 2.21 [1.34–3.62], p=0.002). The FEAR index was statistically greater in those with microinstability (-11.3° ± 8.4° vs -12.6° ±7.9°, OR 1.03 [1.01 - 1.05], p = 0.003). The alpha angle was higher in those without microinstability (60.3° vs 57.2°, p<0.001). A third (33.5%) of microinstability patients had a cliff sign as compared with 23.3% of non-instability patients (OR 1.93 [1.32–2.82), p<0.001). The Divot sign, posterior wall sign, cross over sign, distal femoral neck sclerosis and fibroosseous inclusion cysts or “pits” were not significantly different between those with and without microinstability. Discussion and Conclusion This is the first multicenter study of surgically confirmed hip microinstability patients to ascertain which specific imaging finding(s) correlate with the diagnosis of hip microinstability. Radiographic features of hip dysplasia, absence of a cam lesion, and the presence of a Cliff sign were all more common in those with hip microinstability. However, while all features of hip dysplasia were more likely present in those diagnosed intra-operatively with hip microinstability, no one specific measurement was a strong differentiator between microinstability and no microinstability. Further, using defined parameters for dysplasia, many with microinstability would be missed. Thus, based on the accuracy and area under the curve data, no radiographic finding, independently, is diagnostic of hip microinstability. Continued research is necessary to help in the clinical diagnosis of hip microinstability.