Systematic Review of Stress Radiographic Modalities Stability Assessment in Supination External Rotation Ankle Fractures

BACKGROUND: Isolated distal fibular fractures resulting from supination external rotation (SER) injuries without evidence of obvious talar shift on standard radiographs present a diagnostic dilemma for clinicians. The status of the deep deltoid ligament, the main stabilizer of the ankle joint, is assessed by an increase in medial clear space (MCS) on radiographs. Therefore, these injuries can be either stable or unstable. In recent years, considerable clinical and research efforts have been made to determine ankle stability following SER fracture. The purpose of this systematic review was to evaluate and compare the role of different stress radiograph modalities in assessing stability of the ankle with SER fractures with no obvious talar subluxation on standard radiographs. METHODS: The electronic databases MEDLINE, EMBASE, Ovid, Cochrane Central, CINAHL, and Google Scholar were searched from January 2000 to January 2018 to identify literature relating to radiologic assessment of stability of SER ankle fractures. RESULTS: Our literature search revealed 10 peer-reviewed articles that fulfilled inclusion criteria. This yielded a total of 698 patients. The systematic review found 3 broad categories of radiographic investigations in the assessment of ankle joint stability: external rotation (ER) stress radiographs, gravity stress views (GSV), and weightbearing (WB) radiographs. Proponents of WB radiographs have demonstrated how axial load can normalize ankle joint alignment in cases of proven instability. There was a consistently high grade of evidence for using a medial clear space (MCS) value of more than 4 to 5 mm to indicate an unstable ankle following SER fracture. CONCLUSION: In conclusion, the results of this systematic review support an MCS value of less than 4 to 5 mm as a good indicator of stability, regardless of choice of stress imaging modality. These patients can be allowed early weightbearing with expected good functional outcomes. Recent published literature favors WB stress radiographs as a reliable and safe technique for assessing stability in SER ankle fractures. However, it should be kept in mind that this is based on studies with relatively low grades of evidence. LEVEL OF EVIDENCE: Level II, systematic review of variable quality studies.