## 1 Introduction  
According to the newest Japanese national guidelines for Distal radius fractures (DRF), which were published in 2017, the annual incidence of DRF in adults (20 years and older) ranges from 10.9 to 14 per 10,000 population and women are 3.2 times more likely to be affected than men. The incidence increases with age, and people aged 70 years or older are approximately two times more likely to be affected than young people irrespective of sex. The same trends have been observed internationally [1]. The main complication of DRF is restriction of range of motion (RoM). Full RoM of the wrist joint and forearm is required for activities of daily living (ADL) involving the upper extremities [2]. Prolonged restriction of using the injured wrist causes joint contracture, which adversely impacts the performance of ADLs [3]. Restricting the use of the injured side is recommended until bone repair is observed [4]. However, during this period, somatosensory inactivity is induced [5], which may cause hesitation and anxiety and reduce wrist joint RoM [6]. This adverse event occurs not only among patients undergoing immobilization for fracture, but also among their healthy counterparts [5, 7]. Decreased limb use can cause changes in the cortical representation of the unused muscles [8]. These changes represent a disuse-dependent type of neuroplasticity [9]. Therapists play an important role in ensuring recovery and guiding the improvement of RoM in DRF patients, especially in older women.  
One of the currently available interventions for improving the ROM of patients with DRF is somatosensory treatment involving vibratory stimuli [10]. The application of low-frequency vibration to the peripheral nerves may contribute to alleviating pain, resulting in improvement of RoM [11]. Vibration seems to provoke the interaction of the activation of receptors and the adjustment of afferent signals that are possibly acting via the sensorimotor system [12; 13]. Another intervention for effectively improving RoM is visual stimulation via a head-mounted display, which activates the hypothalamus and prefrontal cortex [14]. Interventions aimed at improving pain and motor dysfunction are termed movement representation techniques (MRT) [15]. Treatment with MRT involves observing or imagining an intact and painless movement. Sensory stimulation and active movements can be performed simultaneously. The purpose of MRT is to promote painless movements in painful limbs [15]. In recent years, the effectiveness of MRT in patients with DRF has been studied [16]. MRT have been found to improve RoM in patients with knee osteoarthritis [17; 18]. Interventions involving combined sensory stimuli, such as somatosensory and visual stimuli, have been reported to more effectively alleviate pain than interventions involving a single sensory stimulus [14]. Virtual training with vibration and visualization during the acute phase of DRF may suppress disuse-dependent plasticity and contribute to subsequent RoM recovery.  
Given the interest in improving RoM among patients with DRF, we developed a prototype device that provides a combination of vibratory and visual stimuli that could be used during the early postoperative joint fixation period (patent no. 6425355) [19]. This device consists of a head-mounted display for observing movements of intact hands and a vibrator that stimulates the wrist extensor tendons. We examined its feasibility for clinical use in a preliminary study involving a small sample. We also identified issues that can be addressed in future studies.  
This study addressed the following research questions:  
1. Is the new device applicable to patients with restriction of the wrist joint RoM?
2. Does therapy with the new device improve RoM?