The position of the femoral fovea can indicate hip instability and highly correlates with lesions of the ligamentum teres: an observational study

The aim of this study was to assess the reliability of Delta angle (DA) as a parameter of microinstability compared to established radiographic instability parameters. It was assessed whether the morphology of the Ligamentum teres (LT) was affected by DA, established instability parameters. Further, the correlation between clinical status and microinstability parameters was assessed. Data was retrospectively analysed from a single centre database for hip preservations surgery. All patients underwent a comprehensive and standardized radiographic and clinical assessments. Sixty patients, with a mean age of 29.7 years (Standard Deviation [SD] 8.02),, with 63 hips (40 right [63.5%] and 23 left [36.5%]) were included. Inter-observer reliability using the intraclass correlation coefficient (ICC) method, Pearson Correlation Coefficient, and further Analysis of Variance (ANOVA) and Multivariate Analysis of Variance (MANOVA) with post hoc Bonferroni correction were performed. Inter-observer reliability assessed by ICC showed excellent reliability for all radiographic parameters. DA, as well as the Femoro-Epiphyseal Acetabular Roof (FEAR) index and (Gothic Arch Angle) GAA, showed strong correlation with Lateral Centre Edge Angle (LCEA) values. LT tears were highly linked to the presence of hip instability, showing significant differences in each model when analysing DA as well as the FEAR index and GAA (p < .001), MANOVA of microinstability parameters combined with clinical tests showed significant correlation (p < .001) with the Hyperextension-External Rotation (HEER) test. Other functional tests did not show significant correlation. The DA can be reliably measured and can serve as a valuable supportive parameter in the assessment of hip microinstability. Radiographic instability parameters showed significant correlation with LT tears, suggesting they may function as useful additional markers for this specific lesion. Additionally, a positive HEER test was associated with the presence of microinstability parameters and may therefore be included in the clinical evaluation of these patients.