INTRODUCTION: Trochlear dysplasia is one of the most relevant anatomic factors predisposing patients to patellofemoral instability and its recurrence. This study introduces two novel radiographic measurements: the crossing-sign angle and the trochlear dysplasia length.
METHODS: A concordance study was conducted in patients aged 10-40 years with at least one episode of patellofemoral dislocation and radiographic evidence of trochlear dysplasia on a true lateral knee radiograph. Three observers independently measured the crossing-sign angle, the trochlear dysplasia length, and bump height, as well as classified the degree of trochlear dysplasia according to a modified Dejour classification. Inter- and intra-observer reliability for continuous variables were assessed using the intra-class correlation coefficient (ICC), while agreement for the modified Dejour classification was evaluated using Krippendorff's alpha ( α) and weighted kappa (κ). Pearson correlation analysis was performed between the radiographic measurements, and an analysis of variance (ANOVA) test was performed between these and Dejour grades.
RESULTS: The crossing sign angle demonstrated moderate inter-observer reliability (ICC = 0.71) and excellent intra-observer reliability (ICC = 0.96). Trochlear dysplasia length showed moderate inter-observer reliability (ICC = 0.73) and excellent intraobserver reliability (ICC = 0.95). Bump height exhibited good inter-observer reliability (ICC = 0.87) and excellent intra-observer reliability (ICC = 0.97). The modified Dejour classification demonstrated substantial inter-observer agreement (α = 0.62) and perfect intraobserver agreement (κ = 1.00). A strong positive correlation was found between trochlear dysplasia length and bump height (r = 0.73; 95% confidence interval [CI]: 0.52 to 0.85; p < 0.001). Bump height and trochlear dysplasia length increased progressively from Dejour type A to higher grades (B and D, ANOVA p < 0.001).
CONCLUSIONS: The crossing sign angle and trochlear dysplasia length provide a novel quantification of trochlear dysplasia and demonstrate moderate inter- and excellent intra-observer reliability. Bump height and the modified Dejour classification, when using a standardized protocol, also showed high inter- and intra-observer reliability. Bump height and trochlear dysplasia length have a strong positive correlation. The clinical and surgical implications of these new parameters need further investigation in future studies.
LEVEL OF EVIDENCE: II.