An Algorithmic Approach to the Diagnosis and Staging of Scapholunate Instability in Distal Radius Fractures Using 7 Fluoroscopic Parameters Shows High Reliability and Accuracy

PURPOSE: To determine the reliability and diagnostic accuracy of fluoroscopic parameters for diagnosis and staging of scapholunate (SL) instability in distal radius fractures. METHODS: Between May 2021 and March 2024, intraoperative fluoroscopic assessments were performed after fixation of unstable distal radius fractures. Imaging included anteroposterior, clenched-fist anteroposterior-ulnar deviation, true lateral, and modified scaphoid shift views. Wrist arthroscopy served as the reference standard, with staging according to Geissler (GI-GIV) and European Wrist Arthroscopy Society (EI-EV) classifications. Fluoroscopic parameters-SL gap, SL-ulnar deviation gap, SL translation, scaphoradius (SR) translation, SL angle, delta-SL angle, and delta-SR angle-were analyzed for intra- and interobserver reliability and diagnostic accuracy. RESULTS: Eighty-eight wrists (38 men, 50 women) were included. Fluoroscopic parameters differed significantly across SL instability stages. A staging algorithm was developed using parameters with high intra- and interobserver reliability (intraclass correlation coefficient > 0.89) and good diagnostic accuracy (area under the receiver-operating characteristic [AUC], 0.71-1.00). The SL angle differentiated G0-II, GIII, and GIV instability, with cutoff values of 60° (AUC 0.74) and 74° (AUC 0.97). An SL angle < 60° or delta-SL angle ≤ 4°, combined with delta-SR angle > 11° (AUC 0.71), indicated non-SL instability (G0/E0), whereas delta-SR angle ≤ 11° indicated GI-II/EI-II instability. A delta-SL angle > 4° differentiated EIIIA from G0-II/E0-II (AUC 0.82) and EIIIB-C (AUC 0.88). Delta-SR angle ≤ 5° differentiated EIIIB-C from EIIIA (AUC 1.00). SL-ulnar deviation gap ≥ 2.9 mm, SL translation ≥ 1.8 mm, or SR translation ≥ 2.5 mm differentiated EIIIC from EIIIB (AUC 0.89-1.00). Advanced instability (GIV/EIV/V) was indicated by SL gap ≥ 2.5 mm, SL-ulnar deviation gap ≥ 3.2 mm, or SL translation ≥ 2.4 mm (AUC 0.86-0.95). CONCLUSIONS: Fluoroscopic parameters identified in this study show high reliability and good diagnostic accuracy for diagnosis and staging of SL instability in distal radius fractures. LEVEL OF EVIDENCE: Level II, diagnostic study of consecutive patients.