Initial lateral stress radiographs predict instability in fragility fractures of the pelvis type I and II: a...

Stress radiographs are widely used to define instability in lateral-compression type I injuries, but its applicability to fragility fractures of the pelvis (FFP) is unclear. We investigated whether lateral stress radiographs (LSRs) predict failure of non-operative treatment in patients with FFP types I and II. In this prospective observational study, 55 ambulatory patients aged ≥ 60 years with pubic ramus fractures underwent anteroposterior (AP) and inlet LSRs. Displacement was measured on AP LSRs using the femoral head (D_FH) and teardrop (D_TD), and cortical apposition at the superior pubic ramus fracture was assessed on inlet LSRs. Failure of non-operative treatment was defined as inability to ambulate due to persistent or worsening pain at any time during the first week after injury. Receiver operating characteristic analysis evaluated the predictive performance of LSR-derived parameters. Of the 55 patients, seven were classified as FFP type I and 48 as type II. Non-operative treatment failed in 21 patients (38.2%), all with type II fractures. Failure was associated with D_FH ≥10 mm, D_TD ≥10 mm, and a non-appositional displacement pattern on LSRs (all p < 0.001). The displacement pattern on inlet LSRs provided the highest predictive accuracy (area under the curve [AUC] 0.96), followed by D_FH ≥10 mm (AUC 0.81) and D_TD ≥ 10 mm (AUC 0.76). LSRs may help identify instability and predict failure of non-operative treatment in patients with FFP, particularly in those with FFP type II. Assessment of the displacement pattern on inlet LSRs-specifically the presence or absence of cortical apposition under stress-showed the greatest predictive value and may serve as a practical and intuitive indicator to guide early treatment decisions.