Preoperative gravity stress radiograph parameters predicting the need for deltoid ligament repair after lateral malleolar fixation in Weber B ankle fractures

BACKGROUND: Radiographic criteria for deltoid ligament repair in Weber B ankle fractures without a medial malleolar fracture remain unclear. Medial clear space (MCS) on gravity stress radiographs is commonly used to assess medial instability, but the optimal cutoff value and diagnostic accuracy are still debated. METHODS: This retrospective comparative study included 55 patients with Weber B ankle fractures without medial malleolar fractures who underwent operative treatment between 2016 and 2021. All patients underwent preoperative gravity stress radiography and intraoperative fluoroscopic stress testing after completion of fracture stabilization. Patients were classified as unstable (deltoid ligament repair due to persistent medial instability) or stable (no repair). Preoperative radiographic parameters-including MCS, medial clear space angle (MCA), superior clear space (SCS), medial-to-superior clear space ratio, fibular lateral shift distance (FLSD), and MCS-FLSD difference-were measured. Diagnostic performance and optimal cutoff values were evaluated using receiver operating characteristic curves and Youden's index. RESULTS: Sixteen patients were classified as unstable and 39 as stable. On preoperative gravity stress radiographs, the unstable group showed significantly greater MCS (8.3 ± 2.6 vs. 5.9 ± 1.9 mm, p = 0.002) and MCA (16.6 ± 3.8° vs. 6.4 ± 3.1°, p < 0.001) than the stable group. MCA demonstrated high discriminative ability, with an area under the curve of 0.98, whereas MCS showed an area under the curve of 0.81. The optimal cutoff values were 6.0 mm for MCS and 11.5° for MCA. At 1 year postoperatively, clinical outcomes were similar between groups. CONCLUSIONS: MCA demonstrated high discriminative ability on preoperative gravity stress radiographs and may serve as a useful adjunct to MCS for anticipating the need for deltoid ligament repair after completion of fracture stabilization in Weber B ankle fractures.