Adaptation of the Signal Noise Quotient MRI classification for graft ligamentization analysis following ATFL and CFL anatomical reconstruction: Validation of the SNQA.

Background: Chronic ankle instability is the most frequent clinical sign of an antero tibiofibular (ATFL) and/or calcaneo fibular ligament (CFL) tear. One common surgical technique is to use the distal tendon of the gracilis muscle to reconstruct both the ATFL and CFL. In the knee, the hamstring tendons used in anterior cruciate ligament (ACL) reconstruction may go through structural modifications called "ligamentization ". A noninvasive MRI technique has been developed using the Signal/Noise Quotient to compare the signal of the graft following reconstruction to that of the posterior cruciate ligament. To our knowledge no studies have ever evaluated radiographic changes in the graft over time. The main goal of this study was to develop a specific MRI protocol to evaluate graft remodeling following ATFL and CFL reconstruction over time.

Methods: A prospective study of the changes in the MRI signal of the ATFL-CFL graft 3-months postoperatively was performed in 20 patients. The main outcome was a comparison of the graft signal to that of the peroneal fibular tendon and the surrounding noise to determine the Ankle SNQ (SNQA). MRI images were evaluated by two senior radiologists to assess inter-rater reliability and then 2 weeks later for the intra-rater reproducibility.

Results: The intraclass correlation (ICC) showed excellent inter- and intra rater reliability for the ATFL SNQA (0.96 and 0.91, respectively); and for the CFL SNQA, the ICC was 0.97 and 0.99, respectively. Bland-Altman analysis showed very limited bias in the interpretation of SNQA.

Conclusion: This preliminary study confirmed the inter- and intra- rater reliability of a new tool using the SNQA.