The Signal Intensity of Preoperative Magnetic Resonance Imaging Has Predictive Value for Determining the Arthroscopic Reparability of the Anterior Talofibular Ligament

SLR - November 2021 - Ramez S. Sakkab

Reference: Ahn J, Choi JG, Jeong BO. The Signal Intensity of Preoperative Magnetic Resonance Imaging Has Predictive Value for Determining the Arthroscopic Reparability of the Anterior Talofibular Ligament. Knee Surg Sports Traumatol Arthrosc. 2021 May;29(5):1535-1543. doi: 10.1007/s00167-020-06208-w. Epub 2020 Aug 8. PMID: 32770383.

Level of Evidence: IV

Scientific Literature Review

Reviewed By: Ramez S. Sakkab, DPM
Residency Program: Scripps Mercy Hospital – San Diego, CA

Podiatric Relevance: A common pathology seen in foot and ankle practice is chronic ankle instability (CAI). Failure of conservative measures often leads to surgical intervention via lateral ankle stabilization. There is increasing debate regarding optimal procedures, particularly in open versus arthroscopic “all-inside” repair of the anterior talofibular ligament (ATFL). One factor in deciding between these two procedures (i.e., modified Broström procedures) is the reparability of the ATFL, as there may be difficulty in arthroscopic repair with poor or absent ATFL remnants. Correlation between magnetic resonance imaging (MRI) of the ATFL and intraoperative reparability is currently unclear. This study compares the ATFL signal on MRI to intraoperative ATFL reparability through a purely arthroscopic approach. This potentially helps foot and ankle surgeons choose between arthroscopic or traditional approaches in ATFL repair.

Methods: The study is a retrospective review of 55 patients between 2018 and 2019 at Kyung Hee University Hospital with a 3.0 T-MRI scanner. Patients were included if their MRI examination was within 60 days of subsequent arthroscopy. Signal of ATFL was quantified via comparison to background, described as signal to noise ratio (SNR). MRI was reviewed by two orthopedic surgeons who were blinded to the patient's history (including arthroscopic findings) and outcome. This was compared to the arthroscopic assessment via traction force to determine ligament tension as: taut, mild laxity, or laxity. ATFL quality was assessed as excellent (intact without tear), moderate (abnormal but reparable), or poor (irreparable). Intraclass correlation was done for agreement on MRI and arthroscopic findings. ATFL SNR was then correlated to its tension and quality.

Results: The SNR was significantly different according to the presence of an ATFL tear in arthroscopy (P = 0.001). The SNR was also significantly different according to the ATFL tension (P=0.001), as well as according to the ATFL quality (P=0.001). High SNR  predicted poor ATFL quality at an odds ratio (OR) of 1.136 (95 percent CI 1.034–1.248). Cutoff points for ATFL being poor quality based on SNR was 32.3 (sensitivity 76.9 percent, specificity 92.0 percent).

Conclusions: Previous studies have noted the signal intensity of the ATFL on MRI, i.e., SNR, as a factor associated with ATFL condition (Li et al., 2019), without comparison to intraoperative reparability. The present study reports that an increased SNR is significantly correlated to reduced quality and tension of the ATFL. Sensitivity and specificity were relatively high for cutoff SNR of 32.3 indicating a poor quality ATFL. One interpretation being that a SNR >32.3 will lead to difficult arthroscopic repair, requiring some augmentation. This lends diagnostic value to ATFL signal on MRI as a predictor of reparability. However, poor ATFL tissue quality has been reported as an indicator of poor clinical outcome of CAI regardless of open or arthroscopic procedure type (Dierckman et al., 2015), raising reservations of the application of these findings to any one technique.