Need for mechanically and ergonomically enhanced tremor-suppression orthoses for the upper limb: a systematic review

Abstract

Introduction Tremor is the most common movement disorder, affecting 5.6% of the population with Parkinson’s disease or essential tremor over the age of 65. Conventionally, tremor diseases like Parkinson’s are treated with medication. An alternative non-invasive symptom treatment is the mechanical suppression of the oscillation movement. The purpose of this review is to identify the weaknesses of past wearable tremor-suppression orthoses for the upper limb and identify the need for further research and developments. Method A systematic literature search was conducted by performing a keyword combination search of the title, abstract and keyword sections in the four databases Web of Science, MedLine, Scopus, and ProQuest. Initially, the retrieved articles were selected by title and abstract using selection criteria. The same criteria were then applied to the full publication text. After the selection process, relevant information on the retrieved orthoses was isolated, sorted and analysed systematically. Results Forty-six papers, representing 21 orthoses, were identified and analysed according to the mechanical and ergonomic properties. The identified orthoses can be divided into 5 concepts and 16 functional prototypes, then subdivided further based upon their use of passive, semi-active, or active suppression mechanisms. Most of the orthoses concentrate on the wrist and elbow flexion and extension. They mainly rely on rigid structures and actuators while having tremor-suppression efficacies for tremorous subjects from 30 to 98% using power spectral density or other methods. Conclusion The comparison of tremor-suppression orthoses considered and mapped their various mechanical and ergonomic properties, including the degrees of freedom, weight, suppression characteristics, and efficacies. This review shows that most of the orthoses are bulky and heavy, with a non-adapted human-machine interface which can cause rejection by the user. The main challenge of the design of an effective, minimally intrusive and portable tremor-suppressing orthosis is the integration of compact, powerful, lightweight, and non-cumbersome suppression mechanisms. None of the existing prototypes combine all the desired characteristics. Future research should focus on novel suppression orthoses and mechanisms with compact dimensions and light weight in order to be less cumbersome while giving a good tremor-suppression performance.

Tremor Control Devices for Essential Tremor: A Systematic Literature Review

“…19,25,32 The design of the tremor suppression part of an upper limb orthosis, the actuator, needs to include a sensing mechanism able to provide position, velocity, and acceleration information to the control and feedback system with minimum delay. These sensors need to extract information following a hierarchical integration scheme: first, to detect user’s intention to perform a certain voluntary movement; second, to evaluate tremor characteristics with an estimation of its amplitude, frequency, and phase; and third, to determine how tremor affects each joint and which muscles contribute to joint tremor.…”

Design of a lightweight passive orthosis for tremor suppression

“…These orthoses can be classified by the type of tremor suppression mechanism employed: passive = energy dissipation and/or absorption, semi-active = active controller adjusted energy dissipation and/or absorption, and active = force inducing. The most prevalent approach is an active orthosis [19]. However, none of the presented systems reached the market, because the solutions presented showed drawbacks, such as too much weight and restrictions in degrees of freedom (leading to patient rejection in some cases) [20].…”

“…However, none of the presented systems reached the market, because the solutions presented showed drawbacks, such as too much weight and restrictions in degrees of freedom (leading to patient rejection in some cases) [20]. Low patient acceptance can be explained by bad wearability [19]. The majority of existing suppressing orthoses are bulky and have rigid structures, to which a wearer is burdened with an additional weight of 20% on the arm, not considering the energy source and control unit of the active and semi-active orthoses, leading to muscle fatigue [21].…”

“…Furthermore, the patient's unknown voluntary motion intention complicates control in active orthoses, compared to traditional stabilisation or tracking control. It can, therefore, be hypothesised that a tremor suppression orthosis with better wearability and lower weight will be better accepted by the wearers, while having a similar tremor absorption efficacy of 67% [19]. Passive and even semi-active mechanisms are often lighter and less cumbersome compared to force-inducing mechanisms.…”

“…An individual adaptation of the device to a user's anthropometry ensures an optimised fit. The mass should be as lightweight as possible and the size as small as possible [19]. Apart from a high level of comfort, a lightweight design will also prevent muscle fatigue, which is of special importance for tremor patients because of their advanced age and the associated degenerative loss of skeletal muscle mass [19].…”