The additional value of weight-bearing and gravity stress ankle radiographs in determining stability of isolated type B ankle fractures.

Abstract

The aim of this study is to investigate whether weight-bearing and gravity stress radiographs have additional value in predicting concomitant deep deltoid ligamentous (DDL) injury in case of isolated Weber type B fibular fractures. This may help to make the clinically relevant distinction between unstable fractures and fractures that can be treated conservatively. In this prospective cohort study, 90 patients with an isolated type B ankle fracture, without a medial or posterior fracture, and a medial clear space (MCS) < 6mm on the regular mortise (RM) view were included. In all patients, an additional gravity stress (GS) view and an MRI scan were performed. Furthermore, in 51 patients, an additional weight-bearing (WB) radiograph was performed. The MCS and superior clear space (SCS) measurements of these radiographs were compared with MRI findings to measure sensitivity and specificity in excluding deep deltoid ligament (DDL) rupture. The mean MCS on the RM view was 3.32mm (1.73-5.93) compared to 4.75mm (2.33-10.40) on the GS view and 3.18mm (1.93-6.9) on the WB radiograph. MRI showed a high-grade or complete deltoid ligament tear in 25 (28%) patients. Using an MCS cut-off value of ≥ SCS + 2mm, the RM view showed 0% sensitivity and 97% specificity in diagnosing a DDL rupture. Both the GS view (with MCS ≥ SCS + 3mm as cut-off value) and the WB radiograph (with cut-off value MCS ≥ SCS + 2mm) showed 6% sensitivity and 100% specificity. The gravity stress and weight-bearing radiograph can accurately exclude DDL injury. They might have extra value in addition to the conventional mortise view in assessing the stability of isolated type B ankle fractures. This helps in deciding whether patients should be selected for operative or safe conservative treatment.