Purpose

The purpose of this study was to determine the inter- and intra-rater reliability of the symmetry, classification, and underlying pathoanatomy associated with the J-sign using video recordings of knees in subjects with recurrent lateral patellofemoral instability.

Methods

In this blinded, inter-rater reliability study, 30 patellofemoral joint experts independently assessed 30 video recordings of the knees of patients with recurrent lateral patellofemoral instability performing the J-sign test. Raters documented J-sign symmetry, and graded it according to the quadrant and Donell classifications. Raters indicated the most significant underlying pathoanatomy, and presence of sagittal plane mal-tracking. Intra-rater reliability was assessed by a test-retest with four raters repeating the assessments 2-weeks apart. Mean pairwise simple and/or weighted Cohen’s kappa were performed to measure inter- and intra-rater reliability, as well as calculation of percent agreement.

Results

J-sign symmetry demonstrated fair inter-rater reliability (k=0.26), while intra-rater reliability was moderate (k=0.48). Inter-rater reliability for the quadrant and Donell classifications indicated moderate agreement, k=0.51 and k=0.49 respectively; while intra-rater reliability was k=0.79 and k=0.72, indicating substantial agreement. Inter-rater reliability of the foremost underlying pathoanatomy produced only slight agreement (k=0.20), however intra-rater reliability was substantial (k=0.68). Sagittal plane mal-tracking demonstrated slight inter-rater (k=0.23) but substantial intra-rater agreement (k=0.64).

Conclusions

The symmetry, classification, and underlying pathoanatomy of the J-sign demonstrated fair to moderate inter-rater reliability, and moderate to substantial intra-rater reliability among expert reviewers using video recordings of recurrent lateral patellofemoral instability patients. These findings suggest individual raters have a consistent standard for assessing the J-sign, but that these standards are not reliable between assessors.

Level of Evidence: III

Key Words: J-sign, patellar instability; patellofemoral instability; patellar dislocation; patellar tracking;