## 4 Discussion
Because of trauma and surgical joint invasion, the levels of pain-related neuropeptides, such as substance \(P\) and bioactive mediators, increase [42]. Patients with DRF are likely to experience pain during the acute phase because of this mechanism. Vibration at a frequency of 80 Hz suppressed the activation of calcitonin gene-related peptide-positive neurons, which are involved in pain associated with joint fixation [43]. In patients with DRF, vibratory stimulation improves brain activity in the primary motor cortex and somatosensory area, improves wrist joint RoM, and alleviates pain and anxiety [10]; subjective pain is diminished by actual exercise [44]. In other words, it was speculated that vibratory stimulation of the tendon, without somatic movement, resulted in brain activity similar to that when exercise is performed [45]; hence, a pain reduction effect was achieved. The results of this study suggest that the intensity of pain decreased during the period after DRF when patients were prohibited from moving by applying an external stimulus to the injured area, which promoted subsequent joint movement and improved RoM. Future studies should report on improvements in pain and anxiety. This study has some limitations. First, because this study was conducted as a preliminary experiment to examine the feasibility of Ghost, patients were not randomly selected. Patient randomization and blinding or placebo interventions should be performed to demonstrate the dominance of Ghost. Whether this inference analysis fits the actual measurement should be analyzed by adding more cases in the future. Because of the small sample size, more patients in the control group than the Ghost group had a severe fracture (75% vs. 50%, respectively), although the severity was comparable in both groups in the resampled data. There was no difference in RoM after conventional treatment was started (7 days postoperatively), but the pre-intervention fracture severity of the control group was more than that of the Ghost group (Table 2, AO classification). Consequently, it can be assumed that RoM recovery after the intervention was worse in the control group than in the Ghost group. In future studies, the effect of Ghost should be verified after controlling for fracture severity using the AO classification. Secondly, all the study participants were women. Epidemiological studies show that DRF commonly occurs in older women [46; 47]. Future studies must include young men and those with sports injuries. Third, Ghost is still under development and the device used in this study was a prototype; therefore, the quality of the visual stimuli and procedure may have influenced the results. Researchers who were familiar with Ghost required approximately 10 min to operate the device. However, Japanese insurance covers interventions for outpatients with musculoskeletal issues for only 20 min per session. Therefore, to expand the applicability of Ghost, the procedure must be simplified to allow therapists to use the device within a short time without errors. Fourth, this study merely reported the arc of motion of flexion-extension of the wrist joint. Forearm supination involves the proximal and distal radioulnar joints, which consist of the radius and ulna, and trauma from DRF affects the radius [48]. Moreover, DRF is frequently associated with ligament lesions [49]. Pronosupination after DRF helps the recovery of bones and soft tissues that comprise the wrist joint. Forearm supination is used for toilet activities and changing clothes [2]. The forearm is also in the supination position during meals [50]. Therefore, forearm pronosupination is indispensable for the activities of daily living. Because other arcs of motion were not analyzed during this study, the treatment effects on them should be verified through future studies. Fifth, a previous study obtained data regarding brain activity during visual stimuli; however, it included healthy young adults [51]. We did not have the brain imaging data of patients with DRF during this study.