The sigmoid notch of the radius is rarely studied because of its hidden position. In the current study, the sigmoid notch was clearly displayed by use of the 3D reconstruction technique with data transferred from postoperative CT test, and corresponding details help to predict postoperative rotation function and pain score during activity. The results showed that patients with gaps or steps on sigmoid notch not only limit forearm pronation rotation as well as supination rotation, but also cause apparent wrist pain during forearm rotation movement.
Three-dimensional reconstruction technology has been rapidly developed in the medical field, and has become feasible and accessible for wild application in orthopedic surgery[9–11]. It is extremely helpful for preoperative evaluation and planning as well as for intraoperative navigation, but few studies used this technique to predict the outcomes of DRUJ after surgical treatment of DRFs. After the CT images are transformed into 3D images, the occlusion of other bones can be well solved. The ulna and carpal bones are easily removed, and thus surface of sigmoid notch can be clearly displayed, which make following measurement, classification and further analysis become feasible [12].
Free forearm rotation relies on a normal structure of proximal radioulnar joint as well as distal radioulnar joint. DRUJ comprises the distal radius, ulna, and triangular fibrocartilage complex. Malunited DRFs was frequently found to cause forearm rotational restriction, for example, previous studies have revealed that a dorsal angulated deformity of more than 30° causes pronation restriction and a volar angulated deformity of more than 20° causes supination restriction [13, 14]. Radial shortening of 10 mm also causes rotational restriction [15]. However, the association of contact area with forearm rotation is rarely investigated. The sigmoid notch not only serves as an anchor for the TFCC that plays an important role in DRUJ stability, but also provide a smooth articular surface for rotation movement. When the fracture line or displaced fragment of distal radius involving the sigmoid notch, the tension of the TFCC may be changed, which would produce a rotation dysfunction of the forearm [5, 16]. Besides, the gaps or steps could cause articular incongruity of the DRUJ and limited forearm rotation. This could explain our final result that both the pronation and supination rotation was restricted in patients with fractured sigmoid notch in comparison with those without.
Postoperative pain is common in DRFs patients even after surgical treatment[17]. Irregular articular surface has been demonstrated to be the main reason to increase the risk of traumatic osteoarthritis and to cause unsatisfactory function recovery [18–20], and if it is associated with postoperative pain remains unclear. To clarify this confusion, we made a comparison, and the results showed that patients with gaps or steps on sigmoid notch have significant more severe pain during forearm rotation at the one-year follow-up. We supposed that postoperative pain symptoms begin much earlier before osteoarthritis develops. This information allows doctors to have a clearer understanding of the prognosis of fracture, and to better communicate with patients.
This study has several limitations. First of all, this is a retrospective study. The study design and potential for bias are the typical restrictions of our study. Secondly, the exact degree of reduction by surgery which left minimized rotation dysfunction has not been established. Thirdly, limited by the accuracy of CT test, the current technology is unable to differentiate tiny fracture fragments, especially in patients with severely comminuted fractures. Finally, the follow-up time is relatively short, which is only one year. Wrist degenerative changes or osteoarthritis may occur in long-term follow-up, and should be recorded in further studies.