Abstract: BACKGROUND: Palmar locking plate fixation is the most commonly used fixation method for distal radius fractures. However, when the fracture line involves the dorsal articular surface, palmar plate fixation carries a higher risk of postoperative displacement of the dorsal bone mass, especially the dorsal sigmoid notch bone mass.
OBJECTIVE: To analyze the fracture line characteristics of distal radius fracture involving the dorsal articular surface, and further investigate the risk factors of postoperative displacement of the dorsal bone mass involving the sigmoid notch, so as to provide evidence for improving the success rate of surgery.
METHODS: Retrospective analysis was performed on patients with distal radius fracture who were admitted to Third Affiliated Hospital of Guangzhou University of Chinese Medicine from January 2021 to September 2022. The number of dorsal fractures of the distal radius of 1, 2, 3 and above was divided into types I, II, and III based on preoperative CT images. The fracture line maps were drawn respectively to analyze the morphological characteristics of the dorsal fracture lines. Patients with dorsal sigmoid notch fracture were followed up for more than 3 months and divided into displaced group and non-displaced group according to whether the dorsal sigmoid notch bone mass displacement occurred after surgery. Age, sex, preoperative and postoperative CT anatomical parameters were compared between the two groups.
RESULTS AND CONCLUSION: (1) 145 patients with type C of AO/OTA involving the dorsal articular surface were analyzed by fracture line map. According to the number of dorsal fractures, there were 25 cases of type I fracture (17.2%), 82 cases of type II fracture (56.6%), and 38 cases of type III fracture (26.2%). Fracture line map showed that the fracture line of type I fracture block mainly involved sigmoid notch; type II mainly involved sigmoid notch and lister tubercle, and type III involved sigmoid notch, lister tubercle, and dorsal radial column. Among the 145 patients, 86.2% (125/145 cases) were involved in sigmoid notch, of which type III was involved as high as 94.7% (36/38 cases); type II was involved as high as 88.0% (72/82 cases), and type I was involved as high as 68% (17/25 cases). (2) 76 cases of type C of AO/OTA involving the dorsal sigmoid notch were included for further study, of which 65 cases were not displaced after operation and 11 cases were displaced. In univariate analysis, there were no statistically significant differences between the two groups in age, sex, injury site, preoperative CT dorsal sigmoid notch bone mass length (d1), ulnar length (d2), dorsal height of dorsal sigmoid notch bone mass (d4), and ulnar edge distance between steel plate and radius (d5) (P > 0.05). The proportion of dorsal sigmoid notch involving the radioulnar joint: [d2/(d2+d3)], the proportion of articular surface of dorsal sigmoid notch (s1/s2), the distance between the ulnar screw tail and the edge of dorsal sigmoid notch (d6), and the number of screw fixation of dorsal sigmoid notch were statistically significant (P < 0.05). (3) Multivariate Logistic regression analysis showed that the number of screw fixation of sigmoid notch was the only risk factor affecting the displacement of sigmoid notch on dorsal ulnar side (P < 0.05). (4) It is indicated that type II is the most common intra-articular fracture of distal radius involving the back of the radius, followed by type III and type I with dorsal sigmoid notch bone mass. However, the dorsal sigmoid notch bone mass is prone to postoperative displacement due to the influence of the inferior radioulnar joint ligament, and the fixation of at least one effective screw during the operation can reduce the risk of displacement and help to improve the treatment effect.

Key words: distal radius fracture, dorsal sigmoid notch bone mass, volar plate, internal fixation, fracture line