Summary
The results indicate that the palpation method or digital imaging analysis of J-sign grading improves the reliability of J-sign assessment in patellar instability and should be used to communicate findings between and among physicians and studies.
Abstract
Background
In recent years, clinical assessment of the J-sign has become increasingly important for decision making in patients with patellar instability, yet observer reliability remains uncertain. The aim of this study was to investigate whether palpation, in addition to plain visual assessment, and the use of merged digital imaging analysis improved the previously reported low interrater reliability of J-sign assessment.
Material And Methods
J-sign grading was prospectively assessed by two experienced raters in 50 consecutive patients (male/female 19/31; aged 25.1 ± 10 y) with recurrent lateral patellar instability according to the quadrant method of Zhang et al. Assessment was performed independently by (1) plain visual evaluation, (2) plain visual evaluation and palpation of the medial and lateral patellar facets with the thumb and index finger during active knee joint motion, and by using a newly developed digital photo application device that merged two pictures—obtained at 90° of knee joint flexion and in full extension—from which the software calculated the relative difference in both patellar positions. In addition, anatomic risk factors for patellar instability, including patellar height, trochlear dysplasia, the TT-TG/TT-PCL distance, and varus/valgus deformity, were evaluated. Cohen’s kappa was used to calculate interrater reliability, and Spearman rank correlation was used to investigate the correlation between the degree of the J-sign and the incidence of instability-associated anatomic risk factors.
Results
The interrater reliability was 0.39 ± 0.11 (0.18–0.6) (p < 0.001), 0.89 ± 0.05 (0.8–0.98) (p < 0.001), and 0.85 ± 0.05 (0.74–0.95) (p = 0.001) for plain visual assessment, visual assessment plus palpation, and digital imaging analysis, respectively. In addition, a significant correlation between the number of anatomical risk factors and the severity of the J-sign was found for both raters when the palpation method was used (r=0.34 (p=0.015) and r=0.30 (p=0.032)).
Conclusion
Plain visual evaluation of the J-sign showed only fair agreement, similar to the findings of previous studies. In contrast, both the palpation method and the digital imaging analysis yielded almost perfect interrater agreement. The results indicate that the palpation method or digital imaging analysis of J-sign grading improves the reliability of J-sign assessment in patellar instability and should be used to communicate findings between and among physicians and studies.