An increased McKibbin Index is associated with anterosuperior labral hypertrophy in the context of non-dysplastic hips.

Abstract

This study aims to investigate the relationship between anterosuperior labral hypertrophy and other morphological parameters in hips with radiographically sufficient lateral coverage. Our hypothesis is that anterior undercoverage or combined high values of femoral torsion and acetabulaer version, represented as an increased McKibbin Index, would be associated with localized anterior labral hypertrophy. This was a retrospective case-control study at a single institution. A consecutive cohort was screened between January 2014 and September 2024 that received either magnetic resonance imaging (MRI) or MR-arthrography of the hip. Only hips with normal lateral centre edge angle values (between 25° and 40°) were included. Previously described radiographic parameters were evaluated: femoral torsion, acetabular version, Tönnis angle, anterior wall index (AWI), posterior wall index (PWI), McKibbin Index and labral height-to-length ratio on axial planes as a measure of anterior labral hypertrophy. Statistical analysis included <i>χ</i> ² test, Fisher's exact test, Pearson and partial Pearson correlation analysis, as well as univariate and multiple regression analysis. A total of 132 patients were included in the study, of whom 51 (39%) exhibited anterosuperior labral hypertrophy (labral height-to-length ratio of less than 1:2). The McKibbin Index demonstrated a significant negative correlation with the labral height-to-length ratio on the axial plane (<i>r</i> = -0.182, <i>p</i> = 0.018), indicating greater labral hypertrophy with increased combined femoral and acetabular anteversion. Femoral torsion showed a similar association (<i>r</i> = -0.167, <i>p</i> = 0.028). Using the multiple regression analysis, the McKibbin Index remained significant in variable exclusion testing (<i>p</i> = 0.037), supporting its relevance to labral morphology. Our findings highlight the correlation of the increased McKibbin index with anterosuperior labral hypertrophy and suggest relevant implications of the global rotational alignment, including both the acetabular version and femoral torsion on joint and labral biomechanics. Level IV.