Functional assistive devices to support the impaired shoulder and hand
Claudia Haarman is a PhD student in the research group Biomechanical Engineering. Supervisors are prof.dr.ir. H. van der Kooij and prof.dr. J.S. Rietman from the Faculty of Engineering Technology.
To be able to independently perform daily activities, it is important that humans can use their arms and hands to a sufficient extent. The positioning of the arm and the execution of grasping tasks play an essential role in this. Disability caused by impairments of arm and hand function can lead to activity limitations and participation restrictions. Assistive devices can contribute to reducing the effect of disability. However, these devices must meet users’ expectations regarding effectiveness, reliability, durability, comfort and ease of use to reduce the risk of device abandonment. In this thesis we developed and evaluated three novel assistive devices that support patients with impaired shoulders or hands. During the design process we focused on restoring performance (i.e. on the activity and participation level) rather than restoring capacity (i.e. on the impairment level). Therefore, all device functionality that did not contribute to this goal was omitted from the design.
The shoulder plays an important role in positioning the arm. When the passive structures around the shoulder joint are continuously stretched, pain often occurs that prevents patients to actively engage their arm in daily activities. In Chapter 2, a dynamic shoulder orthosis has been developed with the aim of reducing the stress on the shoulder joint and thereby reducing pain without impeding the retaining range of motion of the shoulder. This orthosis works by statically balancing the arm with two elastic bands. In a clinical study with 10 patients (Chapter 5), the effects of the orthosis on shoulder pain and arm function were investigated after two weeks of use. The results show that the orthosis supports the shoulder and that patients can use the shoulder orthosis well during daily activities.
For an optimal functioning of the balancing principle of the shoulder orthosis, the orthosis must be aligned with the glenohumeral joint. There is currently no easy method to do this. Therefore, in Chapter 3 a new method was developed to determine the center of rotation of the glenohumeral joint using only one camera and two printed markers. Experiments with a test bench have shown that the method is accurate. Experiments with 5 healthy subjects have shown that the method is reproducible.
An orthosis can only be effective if it is worn by the user. It is therefore important to determine the wearing time objectively. Subjective methods such as diaries or questionnaires are often used in the current clinical practice, but these frequently lead to an overestimation of the actual use. In Chapter 4 an algorithm has been developed that provides an objective estimate of the wearing time of orthoses for the upper extremities using miniature temperature loggers. The algorithm was trained and validated with data from 15 healthy subjects who repeatedly put the temperature loggers on and off during a 24h period.
In order to perform grasping tasks, it is important that the hand can be opened far enough to grasp objects, and then sufficient force can be applied to stabilize or lift objects.
Hand opening may be compromised if patients do not have sufficient muscle strength to overcome the effects of contractures or hypertonia of the finger flexors. In these cases it may be necessary to support the hand opening with an assistive device. In Chapter 6, a hand exoskeleton has been developed that supports finger extension of stroke patients. The device is controlled by a cable and can actively stretch the index and middle finger. The feasibility of the exoskeleton has been investigated in a pilot test with four stroke patients. Results show that the exoskeleton was able to improve finger extension of severely affected stroke patients.
Performing grasping tasks is also complicated if patients do not have sufficient muscle strength to grasp and lift objects. In Chapter 7, an active orthosis has been developed to support the hand function of spinal cord injury patients. The developed thumb orthosis is lightweight and supports the lateral grip (key grip) of the hand by means of a miniature linear actuator. A study with three spinal cord injury patients showed that the orthosis improved the grip force which enabled patients to regain basic hand function.
In conclusion, the work presented in this thesis showed the significant steps that were made in improving assistive devices to support shoulder and hand function during daily activities.