[ARTICLE] Mechanical Design of a Bioinspired Compliant Robotic Wrist Rehabilitation Equipment – Full Text

Abstract

Early social reintegration of patients with disabilities of the wrist is possible with the help of dedicated rehabilitation equipment. Using such equipment reduces the duration of recovery and reduces significantly rehabilitation costs. Based on these considerations the paper puts forward a novel constructive solution of rehabilitation equipment that ensures the simultaneous passive mobilization of the radiocarpal, metacarpophalangeal, and interphalangeal joints. The novelty of this equipment consists in the bioinspired concept of the hand support based on the Fin-Ray effect and in driving it by means of a pneumatic muscle, an inherently compliant actuator. The paper places an emphasis on the compliant character of the rehabilitation equipment that is responsible for its adaptability to the concrete conditions of patient pain tolerability.

1. Introduction

The hand, with its 27 bones of the palm skeleton and the fingers, qualifies as the most complicated osteoarticular segment of the human body. This most complex articulation includes the 8 carpal bones displayed in two transversal rows forming the wrist, the 5 metacarpal bones, followed by the 14 phalanxes of the fingers. Obviously a bone system of such complexity is more susceptible to trauma that would inhibit the functions of the hand. Gripping, discriminatory sensitivity, expressivity, and conducting professional tasks can be thus hindered or even cancelled.Any partial or total impairment of the hand is a professional and social emergency that calls for therapeutical methods able to accelerate the recovery of the affected joint. Adequate medical treatment of the effects of trauma sustained by joints of the hand is typically followed by immobilization in a gypsum cast. However, extended repose of the joints leads to muscle hypertrophy or even atrophy, to bone demineralization and dysfunctions of the circulatory apparatus. Consequently, in order to prevent the negative effects of immobilization passive kinesiotherapy or excitomotor therapy (the latter in cases of muscle atrophy by denervation) are used [1,2,3]. These techniques are part of the general approach to swift patient rehabilitation and thus favor a high functional recovery rate and early return to work life.Motion-based rehabilitation of the hand depends of the location of the trauma and the type of the already applied (surgical or nonsurgical) treatment. The rehabilitation protocols are aimed mainly at pain control and restoring the functionality of the affected area. Such protocols need to be adapted to patients’ motor state (muscle tone), sensitivity state (proprioception), and last but not least to their psycho–social and occupational state.The functional reeducation program needs to be initiated approximately 3 days after the trauma has been treated. In order to avoid excessive local straining, the use of customized orthoses is recommended, as well as light physical exercises that consist of compression/elevation active and passive mobilization of the fingers [4].Subsequently to this stage continuous passive motion (CPM) is applied. This entails the mechanical mobilization of the affected joint without straining the patient’s muscles. These motions are designed to impede the generation of fibrous tissue and to reduce joint rigidity. CPM is performed by means of specially conceived equipment that is capable of applying customized optimum rehabilitation motions to the joint.The passive mobilization of the hand joints by means of rehabilitation equipment requires controlling the various parameters of the motion, like the amplitude and speed of the motion and duration and frequency of the exercises. Not to be neglected is the magnitude of the applied forces such as to ensure pain-free rehabilitation exercising. CPM rehabilitation equipment need to allow the adjustment of the quantities mentioned above so that rehabilitation exercises can be adapted to the clinical state of the patient.At present the rehabilitation of the hand joints is performed with the help of equipment the majority of that is actuated electrically. Thus the 6000 Hand CPM OrthoAgility^® is used for postfracture recovery, reconstructive surgery on bone, cartilage, tendons, and ligaments, and allows patients to achieve a full composite fist of 270° [5]. Another often-deployed piece of equipment is the Kinetec—8091 Portable Hand CPM designed for rehabilitation after prosthetic replacement of the MCP (MetaCarpoPhalangeal), PIP (Proximal InterPhalangeal) and DIP (Distal InterPhalangeal) joints, and related to rheumatoid/neurological or afterburn stiffness [6].Designed for postoperative rehabilitation, the Kinetec Maestra™ CPM is yet another device that provides a rehabilitation solution for wrist pathology, allowing the achievement of a full composite fist de 255° [7]. The WaveFlex Hand system developed by Remington Medical is a light construction deployable both in hospital and in patients’ homes. It supports the performing of rehabilitation exercises within the limits of hand joint biomechanics [8].Recovery of hand joints is also conducted by means of a system with 3 degree-of-freedom that can be attached on a MIT-MANUS robot. This piece of equipment limits motion to 60°/60° in flexion/extension, 30°/45° in abduction/adduction, and 70°/70° in pronation/supination [9].Besides CPM-based rehabilitation literature also discusses game therapy for poststroke recovery of upper limbs. Thus, motor-training software on tablets or smartphones offer a low-cost, widely-available solution to supplement arm physiotherapy after stroke. Studies involving 127 therapists revealed that the most commonly used device was Nintendo Wii. Gaming was reported to be enjoyable but therapists described barriers, which relate to time, space and cost [10,11,12].This category of game therapy includes also a smart mobile device for the assessment and training of hand functions called GripAble Device [13], which is connected to a tablet by means of a dedicated software application. Its deployment is not based on CPM, as the equipment is driven by the patients themselves, patients who have not suffered total mobility loss.Given the benefits of soft robotics several research teams have developed variants of wearable orthotic devices for the rehabilitation of the hand. Known are for example the Exo-Glove PM—a customizable modularized pneumatic assistive glove [14] or the Harvard Soft Robotic Glove for Neuromuscular Rehabilitation developed by researchers of the Wyss Institute at Harvard University [15]. In both cases the soft actuators are mobilized by compressed air.During rehabilitation exercising motion can often exceed the limits of patient supportability with the consequence of onsetting pain. The system’s response time since the moment of pain onset needs to be as small as possible and thus is an essential characteristic of any rehabilitation equipment. While the electrically actuated systems described above do have such a self-adaptive behavior, this is made possible only be excessive sensorization and complicated control diagrams, all of this leading to cost-intensive rehabilitation equipment.Rethinking their construction makes it possible to reduce the cost of rehabilitation equipment. By eliminating many of the sensors, simplifying control diagrams and most importantly by using adjustable compliance actuators (ACAs) performant equipment can be developed at significantly lesser costs. An example of adjustable compliance actuator is the pneumatic muscle whose inherently compliant behavior is due to air compressibility. Characteristics of pneumatic muscles are safe interaction with human operators and their ability of storing and releasing energy into passive elastic elements [16].Conception of pneumatic muscle actuated rehabilitation equipment for hand joints is still in its incipient stage as to date merely few published patents are known and just a small number of prototypes or functional equipment. One such piece of equipment is the Hand Mentor Pro (manufactured by Motus Nova) actuated by a pneumatic muscle. The Hand Mentor is a stroke rehabilitation device that provides active assistance. It moves the patient like a skilled physical therapist, and is designed for recovering the gripping ability of the hand [17].Another example of rehabilitation equipment is the EXOWRIST, using four pneumatic muscle actuators to undertake the 2-degrees-of-freedom movements performed by the human wrist. It is characterized by adjustable performance to meet the needs of individualized configuration, assisted movement capabilities, high reliability in different treatment environments and conditions for safe human–robot interactions, low development and construction costs, and high portability for autonomous and independent use [18].Starting from the current state of available rehabilitation equipment for the joints of the hand and given the necessity of further developing such light, portable, affordable, and reliable systems benefitting from a compliant behavior this paper pots forward a novel constructive solution able to mobilize simultaneously both wrist and finger joints. The joints of the hand are set into motion by a pneumatic muscle, and the novel concept of the palm support is based on the Fin-Ray effect, bioinspired from the fins of fish.The structure of the paper includes a second section that describes the biomechanics of the hand joints and defines the limits of their motions. These are the input data used for the concept of the novel rehabilitation system. The third section of the paper presents the bioinspired elements that determine the concept of the equipment, as well as its functional principle and construction. The fourth section presents the experimental results and the last section is dedicated to the conclusions of the discussed study.

2. Biomechanics of the Hand Joints

The construction of this type of rehabilitation equipment is based on detailed knowledge of the anatomy of the hand and of the motions its joints are capable of conducting. Further necessary data are the limits to such motions and the generated forces and moments. Figure 1 details the main bones and joints of the hand skeleton [19]:

Figure 1. Bones and joints of the hand.

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[Abstract] Functional range of motion of the hand joints in activities of the International Classification of Functioning, Disability and Health

Abstract

Study Design

Cross-sectional research design.

Introduction

Active range of motion (AROM) is used as indicator of hand function. However, functional range of motion (FROM) data are limited, and fail to represent activities of daily living (ADL).

Purpose of the Study

To estimate dominant hand FROM in flexion, abduction and palmar arching in people under 50 years of age performing ADL.

Methods

AROMs and hand postures in 24 representative ADL of the International Classification of Functioning, Disability and Health (ICF) were recorded in 12 men and 12 women. FROM data were reported by activity and ICF area, and compared with AROMs. The relationship between ROM measures to gender and hand size was analyzed by correlation.

Results

FROM was 5° to 28° less than available AROM depending on the joint and movement performed.

Discussion

Joints do not necessarily move through full AROM while performing ADL which has benefits in retaining function despite loss of motion. This may also suggest that ADL alone are insufficient to retain or restore full AROM.

Conclusions

Therapists should consider FROM requirements and normal AROM when defining hand therapy goals, interventions and evaluating the success of treatment.

Source: Functional range of motion of the hand joints in activities of the International Classification of Functioning, Disability and Health – Journal of Hand Therapy