Lower Signal Intensity of the Anterior Talofibular Ligament is Associated with a Higher Rate of Return to Sport After ATFL Repair for Chronic Lateral Ankle Instability

Background: The treatment strategy for anterior talofibular ligament (ATFL) injury is usually determined by the ATFL remnant condition during surgery. Preoperative magnetic resonance imaging (MRI)–based signal intensity of the ATFL remnant, represented by the signal/noise ratio (SNR) value, can reveal the ATFL remnant condition. Thus far, there is a lack of evidence regarding the relationship between the ATFL remnant condition and functional outcomes. Purpose/Hypothesis: The purpose was to quantitatively evaluate whether the MRI-based ATFL ligament SNR value is related to functional outcomes after ATFL repair for ankles with chronic lateral ankle instability. The hypothesis was that a lower preoperative SNR is related to a better clinical outcome, particularly a higher rate of return to sport. Study Design: Cohort study; Level of evidence, 3. Methods: First, a preliminary study was performed to measure the ATFL SNR in preoperative MRI, the results of which suggested that a preoperative SNR >10.4 was indicative of a poor ATFL condition. Then, a cohort study was retrospectively performed with consecutive patients who underwent open repair of ATFL injuries between January 2009 and August 2014. Accordingly, the patients were divided into 2 groups: high SNR (HSNR; ≥10.4) and low SNR (LSNR; <10.4). Functional outcomes based on the American Orthopaedic Foot and Ankle Society (AOFAS) score, Karlsson Ankle Functional Score (KAFS), and Tegner Activity Scale were then compared between the HSNR group and the LSNR group. Results: Ultimately, 70 patients were available for the final follow-up: 37 in the HSNR group and 33 in the LSNR group. No significant difference was detected between the HSNR group and the LSNR group in terms of the AOFAS score, KAFS, or Tegner Activity Scale ( P > .05 for all) preoperatively. At the final follow-up, the mean ± SD AOFAS score in the LSNR group (92 ± 6) was higher than that in the HSNR group (87 ± 12), although no significant difference was detected postoperatively ( P = .16). The mean KAFS in the LSNR group (94 ± 7) was significantly higher than that in the HSNR group (88 ± 11) postoperatively ( P = .03). At follow-up, the mean Tegner score in the LSNR group (6; range, 3-7) was significantly higher than that in the HSNR group (5; range, 1-8) postoperatively ( P = .03). Patients in the LSNR group had a significantly higher percentage of sports participation than those in the HSNR group (91% vs 65%, P = .02) postoperatively. Conclusion: A lower signal intensity in the ATFL ligament based on preoperative MRI is associated with a better clinical outcome, particularly a higher rate of return to sport.