Summary

Inter-rater reliability of TT-TG distance is good and not highly dependent on slice selection on MRI, while inter-rater reliability of trochlear morphology measures based on axial MRI slices are fair.

Abstract

Introduction

Patellar instability is a frequent cause of knee dysfunction in young active patients. Among other factors, tibial tubercle-trochlear groove (TT-TG) distance and trochlear morphology (trochlear depth and sulcus angle) are felt to contribute to patellar instability and may influence treatment. These measurement are frequently performed on axial MRI images. We hypothesized that inter-rater reliability of measures would be god and that between rater variation is driven primarily by axial slice selection.

Methods

Twenty-six patients with at least one documented episode of patellar instability confirmed by MRI were identified. Six raters (two sports medicine fellowship-trained orthopaedics surgeons and four orthopaedic sports medicine fellows) reviewed axial MRI images from each patient. Each rater measured and recorded the TT-TG distance, trochlear depth, and trochlear sulcus angle for each patient as well as the tibial and femoral slices utilized for the measurement. Each rather then repeated the measurement using pre-selected femoral and tibial slices. Inter-rater reliability was calculated by inter-class correlations (ICCs) for femoral and tibial slice selection as well as for TT-TG distance and trochlear morphology measures with both independently selected and pre-selected axial slices. Statistically significant differences (p < 0.05) in ICC based on slice selection were defined as those values without overlap of their 95% confidence internals.

Results

Inter-rater reliability was noted to be excellent (ICC > 0.80) for both femoral (ICC = 0.88) and tibial (ICC = 0.93) slice selection on MRI. Utilizing independent slice selection, inter-rater reliability was good (0.60 < ICC <0.80) for TT-TG distance (ICC = 0.79) and fair (0.40 < ICC <0.60) for trochlear depth (ICC = 0.57) and sulcus angle (ICC = 0.57). When pre-selected axial slices were used, inter-rater reliability was inter-rater reliability was excellent for TT-TG distance (ICC = 0.85) and sulcus angle (ICC = 0.83) and good for trochlear depth (ICC = 0.68). Only sulcus angle demonstrated a significantly significant (p < 0.05) improvement in inter-rater reliability the use of pre-determined axial slices.

Conclusion

Inter-rater reliability of TT-TG distance is good and not highly dependent on slice selection on MRI. Inter-rater reliability of trochlear morphology measures based on axial MRI slices are fair. Inter-rater variation can be reduced (particularly in the case of sulcus angle) through improved agreement on axial femoral slice selection.