Semiautomatic Weight Bearing Computed Tomography Area Analysis of the Distal Tibiofibular Syndesmotic Incisura in Subtle Chronic Syndesmotic Instability
Authors: Ahrenholz Samuel , Mansur Nacime Salomao Barbachan , Carvalho Kepler A.M. , Tazegul Tutku , VandeLune Christian , Godoy-Santos Alexandre Leme , Fayed Aly M. , Ehret Amanda , Lalevee Matthieu , de Cesar Netto Cesar 
Published: December 2023

Category: Ankle; Sports Introduction/Purpose: Syndesmotic injuries and residual chronic subtle distal tibiofibular syndesmotic instability (DTFSI) are relatively common injuries, especially in athletes prone to suffering high ankle sprains. The diagnosis of subtle DTFSI remains challenging, with a high prevalence of false-negative results using conventional non-invasive clinical-radiographical diagnostic tools. The current gold standard for diagnosis, arthroscopy, is a surgical operation, which is invasive and, therefore, not ideal. Weightbearing Computed-Tomography (WBCT) has emerged as a possible dynamic non-invasive alternative diagnostic option, with proven high diagnostic accuracy for syndesmotic incisura area measurements in major DTFSI. Our study aimed to assess the capability of semiautomatic weight-bearing computed tomography (WBCT) syndesmotic incisura area in diagnosing subtle chronic syndesmotic instability. Methods: In this diagnostic case-control study, patients with suspected unilateral chronic subtle DTFSI underwent bilateral standing weight-bearing CT (WBCT) before surgical treatment. All patients had gold-standard arthroscopic assessment for DTFSI, introducing a 3mm diameter arthroscopic sphere into the syndesmotic incisura for diagnosis. Bilateral syndesmotic incisura areas were measured 10mm proximally to the apex of the distal tibia articular dome using a semiautomatic measurement algorithm. Two tangent lines marked the anterior and posterior borders of the syndesmotic incisura to the anterior and posterior edges of the distal tibia and fibula. Once borders were marked, the incisura area was automatically calculated by the software based on a Hounsfield units (HU) contrast algorithm. A HU threshold of 200HU was utilized. Measurements were done independently by two fellowship-trained readers. Comparisons between injured and control ankles were made using Student T-test or Wilcoxon, according to normality. Measurements' reliability was assessed with the Intraclass Correlation Coefficient (ICC). Results: From an initial sample of 32 patients, 20 patients (12 female) with arthroscopically confirmed DTFSI (11 right sides) with a mean age of 31.7 years (range 18 to 55 years) and a mean BMI of 30.35kg/m² (SD +/-8.29 kg/m²) were included in the study. All patients had a history of an old ankle sprain 6 to 182 months before the assessment, and athletic lesions were reported in 53% of the population. ICCs were above 0.98 for both intra and interobserver reliability. The average syndesmotic area was 96.91mm2 (SD +/-27.9mm2) in injured ankles compared to 84.61mm2 (SD +/-26.9 mm2) in uninjured ankles. The difference between injured and non-injured tibiofibular areas was 12.31mm2 (95%CI: 9.04-15.58mm2), which was shown statistically significant (p < 0.001; effect size: 1.43). Conclusion: In this case-control study, we assessed the accuracy of semiautomatic WBCT syndesmotic incisura area measurements in diagnosing subtle chronic DTFSI. We found an increased syndesmotic area in injured ankles that reached statistical significance. Due to the minimal differences between injured and uninjured contralateral ankles, larger cohorts would likely solidify this study's findings further. The use of external rotation stress, volumetric assessment, distance, and coverage maps could increase the diagnostic accuracy in DTFSI. However, automatic area measurements have a higher overall reproducibility and applicability in the clinical setting, which could help providers make therapeutic decisions.