Design considerations for a wearable monitor to measure finger posture

Journal of NeuroEngineering and Rehabilitation Design considerations for a wearable monitor to measure finger posture Lisa K Simone*1 and Derek G Kamper2 0 Sensory Motor Performance Program, Rehabilitation Institute of Chicago , Chicago, IL , USA 1 Kessler Medical Rehabilitation Research and Education Corporation , West Orange, NJ , USA Background: Objective measures of hand function as individuals participate in home and community activities are needed in order to better plan and evaluate rehabilitation treatments. Traditional measures collected in the clinical setting are often not reflective of actual functional performance. Recent advances in technology, however, enable the development of a lightweight, comfortable data collection monitor to measure hand kinematics. Methods: This paper presents the design analysis of a wearable sensor glove with a specific focus on the sensors selected to measure bend. The most important requirement for the glove is easy donning and removal for individuals with significantly reduced range of motion in the hands and fingers. Additional requirements include comfort and durability, cost effectiveness, and measurement repeatability. These requirements eliminate existing measurement gloves from consideration. Glove construction is introduced, and the sensor selection and glove evaluation process are presented. Results: Evaluation of commercial bend sensors shows that although most are not appropriate for repeatable measurements of finger flexion, one has been successfully identified. A case study for sensor glove repeatability using the final glove configuration and sensors does show a high degree of repeatability in both the gripped and flat hand positions (average coefficient of variability = 2.96% and 0.10%, respectively). Conclusion: Measuring functional outcomes in a portable manner can provide a wealth of information important to clinicians for the evaluation and treatment of movement disorders in the hand and fingers. This device is an important step in that direction as both a research and an evaluation method. Finger flexionRange of Motionsensorshome monitoring - Background Rehabilitation research has recently begun to emphasize the use of objective outcome measures to assess the efficacy of rehabilitation treatment or intervention [1]. These goals could be greatly furthered through the development of wearable measurement systems that provide an opportunity to evaluate how the individual participates in home and community activities. Information collected in this manner can provide a more realistic snapshot of activity and function than traditional methods which restrict measurements to the clinical or research site. Data describing actual usage in the home is especially important for the hand as hand movement is so closely tied to performance of functional tasks. In order to understand how individuals truly interact with their environments, we wish to obtain quantitative measures of finger flexion and extension over longer periods of time than traditionally investigated (such as monitoring over a full circadian cycle). Unfortunately, rehabilitation researchers have very few methods available to objectively evaluate hand use and function outside the clinic, especially for individuals with moderate to severe reduction in range of motion in the hand and fingers. Joint range of motion (ROM) is a primary measure in hand rehabilitation, and is traditionally assessed using manual goniometry. Manual methods, however, are limited to static measurements. In addition, they can be adversely affected by common issues such as inter- and intra-operator error and operator experience level [2]. In order to objectively measure hand use outside the clinic, the selected method must be both portable and capable of recording continuous streams of data over time. Automated measurement methods can meet these requirements as well as eliminate most operator-related issues. For example, 24-hour monitoring has proven useful for tracking parameters such as heart rate and blood pressure, and the same concept can be extended to other useful parameters, although currently no wearable devices are available to measure finger posture in a similar manner. Practical medical applications can include providing input for virtual reality therapy, measuring hand function in the planning of rehabilitation therapies, or evaluating the outcome of interventions under more realistic conditions. Sensor gloves have been proposed to provide automatic measurements of finger and joint position during different activities, with the virtual reality industry continuing to drive the market for sensor gloves [3]. For example, Fifth Dimension Technologies (5DT, Irvine, CA) produces a 5-sensor and a 16-sensor version wireless sensor glove which transmits data to a nearby computer. Two joints per finger are captured with these expensive devices (proximal interphalangeal joint (PIP) and metacarpophalangeal joint (MCP)) using fiber optic sensors. The White Hand Group (Mississippi State University) is developing a lower-cost (<$500) flexion data glove using fiber optics that has two sensors per finger. The glove is tethered to a computer and is aimed at VR and gaming applications rather than accurate measurement applications. CyberGlove (Immersion Corporation, San Jose, CA) contains 5 to 22 "patented bend-sensing technology" strain gauges to measure individual joint movements. This glove, however, is very expensive and difficult for stroke survivors to don. The Essential Reality (Mineola, NY) P5 glove also uses bend sensors, Abrams/Gentile flex sensors (wired flexion measurements), and infrared (IR) emitters (line-of-site wireless position and rotation measurements). The flex sensors are attached to each finger by rings between the proximal and distal interphalangeal joints (DIP). While price of this glove is appealing (<$200), the glove is not portable and requires the wearer to keep the top of the glove always facing a fixed antenna IR receiver. The Humanglove (Humanware S.R.L., Pisa, Italy) is a flexible glove with 20 Hall effect sensors to measure bend. The Humanglove was evaluated for feasibility and repeatability in finger range of motion in all joints; work continues to establish the measurement accuracy [2]. Several research gloves have been reported with no clinical results. Karlsson et al. [4] determined finger flexion by measuring the pressure changes in airtight polyvinyl tubes on three fingers. Zurbrgg [5] measured flexion using potentiometers mounted on the back of the hand, although the construction is not durable for long term measurements. Hofmann and Henz [6] used inductive length encoders attached to a cotton glove to measure flexion and gestures in real time. The glove is not easy to put on, and the sensors can move around relative to the joint position. Jurgens et al. [7] proposed an innovative method using electrically conducting ink printed on a flexible p (...truncated)