The Diagnostic Role of the Pronator Quadratus Sign in Paediatric Wrist Fractures: A Retrospective Study

Background/Objectives: Wrist fractures are common paediatric injuries, yet some remain radiographically occult. The Pronator Quadratus Sign (PQS), defined by displacement or alteration of the fat stripe overlying the pronator quadratus muscle (PQm), remains a debated radiologic diagnostic marker. This study evaluated whether PQS can serve as a diagnostic adjunct for wrist fractures and whether specific PQS morphological types are associated with different fracture patterns. Methods: This retrospective study included paediatric patients presenting with wrist trauma. Radiographs were categorized into three groups: no fracture, torus fracture, and other non-displaced distal radius fractures. PQS morphology was classified using a six-tier system. Quantitative assessment included measurement of the anterior distance from the distal radius to the external border of the pronator quadratus muscle (X) and radial width (R), expressed as the X/R ratio to standardize comparisons. Results: A total of 247 patients were included. The X/R ratio differed significantly among groups (p < 0.001), with higher values observed in patients with fractures. ROC analysis demonstrated good discrimination performance between no fracture and non-displaced distal radius fractures (AUC = 0.80), but limited performance for torus fractures (AUC = 0.62). Although PQS morphology alone was not a reliable indicator of fracture presence, the distribution of PQS types—representing distinct patterns of pronator quadratus fat stripe appearance and displacement—differed significantly across fracture groups (p < 0.001). Conclusions: Quantitative PQS assessment using the X/R ratio is associated with improved discrimination for non-displaced distal radius fractures, while PQS morphology alone shows limited diagnostic utility. Further prospective studies incorporating magnetic resonance imaging are warranted to clarify its role in occult fracture detection.