Ulnar styloid fractures are commonly associated with DRF. The rate of ulnar styloid fracture in our study was 58%. Our results were consistent with previous reports that ulnar styloid fractures are usually present in 50% to 65% of the DRF [17, 19, 21, 25, 31]. The incidence of the TFCC tear complicated to the DRF was reported to vary widely from 9% to 84% [32–36]. Lindau et al.  reported that 43 of the 51 patients (84%) were detected by arthroscopy to have complete or partial TFCC tears at the time of fracture. Richards et al.  showed that 35% of intra-articular fractures and 53% of extra-articular fractures in 118 patients had TFCC tears identified by arthroscopy. In contrast, Spence et al.  found that only two of 21 patients (9%) with the DRFs were identified by wrist MRI to have TFCC tear. He suggested that the TFCC tear was infrequently associated with the DRF and the incidence of TFCC tear might be overestimated by arthroscopy. He explained that since most DRFs occur in the elderly; age-related degenerative changes may contribute to the high rate of the TFCC tear detected by arthroscopy. Spence et al.’s suggestion was supported by the study of Wright et al. , who examined 62 cadaver wrists to determine the incidence of pathologic changes in asymptomatic elderly wrists, and found that TFCC tear was present in 53% of the cadaver wrists. In the present study, we performed a press-test at the final follow-up visit, which creates an axial ulnar load and has high sensitivity for detecting a tear of TFCC , to detect the incidence of the TFCC tear. We found that only five of 106 patents (4.7%) showed a positive sign. Our incidence of the TFCC tear was similarly low to that found by Spence et al., and our results indicated that the symptomatic TFCC tear may be infrequently complicated to the elderly with unstable DRF.
Concerns about DRUJ instability in ulnar styloid fractures derive from the fact that the TFCC inserts to the base of the ulnar styloid and plays the essential soft-tissue stabilizer of the DRUJ [29, 38]. Until now, the relationship between ulnar styloid fractures and TFCC tear is still not established. Richards et al.  reported that no statistical correlation between ulnar styloid fractures and TFCC injuries could be found in the elderly with a mean age of 54 years. Similar to Richards et al.’s finding, our study showed that the incidence of the symptomatic TFCC tear in the patients with a mean age of 51 years detected by the press-test was 4.5% in the non-fracture group, 5% in the tip-fracture group and 4.8% in the base-fracture group. There was no significant difference (p=0.997) in the incidence of the TFCC tear among the three groups in our study.
May et al.  reviewed retrospectively 166 patients with DRFs and found that all DRFs complicated by DRUJ instability were accompanied by an ulnar styloid fracture. However, Lindau et al.  tried to detect the relationship between the ulnar styloid fracture and the DRUJ instability, and found that DRUJ instability was not correlated to the initial ulnar styloid fracture (p=0.53) or the ulnar styloid nonunion (p=0.32). During our data collection, only three patients were found intraoperatively to have DRUJ instability, and the occurrence of DRUJ instability in the patients with unstable DRFs was only 2.8%. Our results indicated that the unstable DRF might be infrequently complicated with DRUJ instability. These findings were also in line with some previous studies [20, 35, 36]. In particular, Sammer et al.  reported that the incidence of DRUJ instability complicated to DRF was only 2%; while Lindau et al.  reported that no DRUJ instability was found in 50 young adults with intra-articular DRFs.
Anatomic and biomechanical studies have demonstrated that, besides the TFCC, the distal interosseous membrane, the extensor carpi ulnaris, the pronator quadratus and the congruence between the sigmoid notch of the distal radius and the ulnar head all contribute to the DRUJ stability [29, 38]. These studies explained why DRUJ instability complicated to DRF rarely occurred. Clearly, some ulnar styloid fractures do result in DRUJ instability, and we believe that treating the ulnar styloid fracture with open reduction and internal fixation is generally supported. The question we attempted to answer in the present study was if the DRUJ is stable, what effect an ulnar styloid fracture may have on the outcome of the DRF. In our study of the patients whose unstable DRF had been treated with closed reduction and external fixation, we were unable to detect any significant difference in the radiological findings, the range of wrist motion, the grip strength, the PRWE-HK scores, and the wrist pain scores among the three patient groups at the external fixator removal time, three months postoperatively and the final follow-up visit. Our results suggest that an untreated ulnar styloid fracture does not affect the wrist outcomes of the patient with unstable DRF, provided that the patient’s DRUJ is stable.
Ulnar-sided wrist pains were sometimes complained by the patients with unstable DRF. In our study, six of the 106 patients (5.7%) complained of persistent ulnar-sided wrist pain during daily activities at the final follow-up visit, with no significant difference in the incidence of the ulnar-sided wrist pain obtained among the three patient groups. Our findings were in agreement with the study reported by Zenke et al. , where the incidence of the ulnar-sided wrist pain complicated to DRF treated by volar plating was 16% at three months, 8.5% at six months, and 5.1% at twelve months postoperatively. In our study, among the six patients mentioned above, two showed distal radius shortening and a positive sign in the provocative-test; one showed malunion of the DRF and positive signs in the stress-test, provocative-test and press-test (Figure 2); and one presented crepitus during forearm rotation. Our results indicated that ulnar-sided wrist pain can be caused by ulnar styloid impaction, distal radius shortening, malunion of the distal radius, incongruity of the distal radio-ulnar joint, the injury of TFCC, or a combination of these causes.
Two limitations can be noted of our research. We relied mainly on the press-test and the stress-test to evaluate the incidence of TFCC tear and DRUJ instability. The two detecting methods are somewhat subjective, by being dependent on the researchers’ judgment. Another weakness is that there was no control group in which the ulnar styloid fracture was surgically treated. However, we believe convincing evidence has been presented in this paper to demonstrate that an untreated ulnar styloid fracture does not affect the wrist outcomes of a patient with unstable DRF treated with external fixation, if the patient’s DRUJ is stable.