Evaluation of severe radial translation of distal radius fractures which is a potential cause of distal radioulnar joint instability

Purpose: This study aimed to (1) introduce a simple and reproducible method to assess severe radial translation of distal radius fractures (DRF) which is a potential cause of distal radioulnar joint (DRUJ) instability, and (2) to construct a treatment-oriented classification. Materials and methods: From 2018 to 2023, stress test (ballottement test) was performed to detect DRUJ instability associated with DRF after treatment with locking plate fixation. Potential radiographic predictors of DRUJ instability focus on radial translation were accessed. The severity of radial translation was described by a readily and easily technique as ‘point- baseline’ method. According to this method, radial translation was categorized into three grades: no translation (the marking points not moved), moderate translation (the marking points moved, but were located on the ulnar side of the baseline), and severe translation (the marking points moved and reached the baseline position, or even completely moved to the radial side of the baseline). All these fractures were divided into two groups, namely Group A (cases with no translation or moderate translation) and Group B (cases with severe translation). Relationships between DRUJ instability and the radiographic parameter of radial translation were analyzed. To investigate the causes of DRUJ instability, all of the cases with DRUJ instability were further divided into two subgroups: subgroup A (cases with DRUJ instability in Group A) and subgroup B (cases with DRUJ instability in Group B). Practices to address DRUJ instability at the time of DRF fixation were explored. Results: There were 226 patients enrolled in this study. According to ‘point- baseline’ method, there were 174 wrists in Group A and 52 wrists in Group B. There were 34 cases (19.54%) diagnosed as having DRUJ instability intraoperatively via manual stress testing in Group A, while 36 cases (69.23%) in Group B. There was significant difference in the incidence of DRUJ instability between the two groups (p < 0.0001). Of the 70 cases with DRUJ instability, 18 cases regained stability by ulnar styloid fracture fixation, 12 cases by dorsal ulnar corner fragment (sigmoid notch fracture) fixation, and 40 cases by arthroscopy-assisted triangular fibrocartilage complex (TFCC) repair. To investigate the causes of DRUJ instability, there were 34 wrists in subgroup A, while 36 wrists in subgroup B. There were no significant differences between the two subgroups regarding the causes of DRUJ instability including ulnar styloid process fracture, dorsal ulnar corner fragment (sigmoid notch fracture), and traumatic TFCC injury. Conclusions: This study helped establish a ‘point- baseline’ method which can be readily and easily used to identify the severity of radial translation, which was a significant predictor of DRUJ instability. On the other hand, whether or not severe radial translation, treatment of DRUJ instability by the three major ways: (1) the ulnar styloid fracture fixation; (2) the dorsal ulnar corner fragment fixation; and (3) traumatic TFCC injuries repairing.