Medial Distal Tibial Angle: Comparison Between Weightbearing Mortise View and Hindfoot Alignment View

Background: The medial distal tibial angle (MDTA) is used to determine ankle alignment. The mortise view is the standard to measure MDTA, but the hindfoot alignment view (HAV) has become popular. The MDTA may vary between views, influencing the choice of surgery. Methods: The MDTA was compared between the mortise and HAY in 146 ankles. MDTA was correlated to age and sagittal tibial tilt for each view. Differences in MDTA by gender and ethnicity were assessed. Diagnostic agreement (yarns, valgus, normal) between views was calculated. Clinical assessment of alignment was determined and percent agreement between clinical and radiographic alignment was quantified. Results: The MDTA measured from the mortise view and HAV radiographs was 89.0 (range, 81 to 96 degrees; SD = 2.8) degrees and 86.0 (range, 73 to 95 degrees; SD = 3.5) degrees, respectively. The MDTA was comparable for both genders for mortise (p = 0.356) and HAV (p = 0.621). The MDTA was comparable in all ethnic groups for mortise view (p = 0.616) and HAV (p = 0.916). Correlation between the measured MDTA and age was not statistically significant for both the mortise (r = 0.118; p = 0.158) and HAV (r = 0.148; p = 0.074). In only 47.3% of all ankles was the radiographic diagnosis of alignment the same between views. Agreement between clinical and radiographic classifications was 60.3% for the mortise view and 52.8% for the HAV. Conclusion: Substantial disagreement in primary alignment was found between the mortise and HAY as quantified by the MDTA. Agreement between clinical and radiographic alignment was also poor. Clinical Relevance: Advanced imaging such as CT or MRI may better describe ankle alignment.