# Medical Devices for Tremor Suppression: Current Status and Future Directions
## 4 Wearable Orthoses
### Active Suppression  
In 2005, the Wearable Orthosis for Tremor Assessment and Suppression (WOTAS) exoskeleton was developed as part of the Dynamically Responsive Interventions for Tremor Suppression (DRIFTS) project of the European Commission [89; 90; 91; 92]. WOTAS consists of sensors that measure rotational motions around the joints, electrical direct current (DC) motors that act as actuators to exert force to suppress tremor by converting electrical energy into mechanical energy, and a controller. This device is placed parallel to the upper limb, suppressing tremor in the wrist flexion/extension and pronation/supination and the elbow flexion/extension. In ten patients with tremors, WOTAS demonstrated a 40% tremor suppression [92]. The major drawback of this device is that it is large and bulky, posing social exclusion concerns [91].  
Subsequent active orthoses were developed with similar designs and mechatronics to WOTAS but vary in the types of actuators to reduce the weight and improve the tremor suppression efficacy. The pneumatic actuator, which has a large power-to-weight ratio, was implemented in an orthosis, along with an adaptive tremor estimation algorithm, to suppress tremors in the wrist flexion/extension and adduction/abduction [93; 94; 95]. The results at the testbench using datasets from ten patients with ET or PD tremor showed a 98.1% tremor suppression [95]. The adaptive disturbance rejection controller, utilizing a permanent magnet linear motor (PMLM), demonstrated a 97.6% tremor suppression when examined with five tremulous signals from patients with PD [96]. Compared to the pneumatic actuator, the PMLM is simpler and faster to control and requires only one sensor [96]. The voluntary-driven elbow orthosis, using an electronically communicated (EC) motor, provided a 99.8% tremor suppression in lab simulation using data from a patient with ET [97]. The wearable tremor suppression glove (WTSG), consisting of an actuation box that includes a multi-channel mechatronic splitter (MMS), aims to provide power support from a single input source to multiple output applications [98]. The MMS incorporates a power EC motor and a steering EC motor to suppress tremors in the wrists and hands [98]. The efficacy of this actuation system, however, has not been evaluated.  
Other active orthoses have sought to integrate complex sensor systems to characterize voluntary motions and detect tremors. The myoelectric-controlled upper limb orthosis incorporated an algorithm that recognizes and extracts voluntary movements from surface myoelectric signals [99; 100; 101; 102]. The results from six participants who were healthy or with ET showed a recognition rate of 82% [102]. The newer version of this orthosis adopted a different design that improved flexibility and ease of wear [103; 104]. In a healthy participant with FES-induced muscle contraction, the myoelectric-controlled orthosis reduced oscillations in the elbow flexion/extension by about 50-80% [104]. [PERSON] and colleagues implemented context aware body sensor network (BSN) sensors into an upper limb orthosis to enable the detection of six ADLs [105]. In six healthy participants with simulated tremor movements, the BSN-integrated exoskeleton exhibited a 70% accuracy rate in identifying ADLs and a 77% tremor suppression [105].