Quantifying Lower Limb Joint Position Sense Using a Robotic Exoskeleton: A Pilot Study Antoinette Domingo, Eric Marriott, Remco Benthem de Grave, Tania Lam School of Human Kinetics International Collaboration on Repair Discoveries University of British Columbia Vancouver, BC, Canada Abstract— Clinicians and scientists often focus on tracking the recovery of motor skills after spinal cord injury (SCI), but less attention is paid to the recovery of sensory skills. Measures of sensory function are imperative for evaluating the efficacy of treatments and therapies. Proprioception is one sensory modality that provides information about static position and movement sense. Because of its critical contribution to motor control, proprioception should be measured during the course of recovery after neurological injury. Current clinical methods to test proprioception are limited to crude, manual tests of movement and position sense. The purpose of this study was to develop a quantitative assessment tool to measure joint position sense in the legs. We used the Lokomat, a robotic exoskeleton, and custom software to assess joint position sense in the hip and knee in 9 able-bodied (AB) subjects and 1 person with incomplete SCI. We used two different test paradigms. Both required the subject to move the leg to a target angle, but the presentation of the target was either a remembered or visual target angle. We found that AB subjects had more accurate position sense in the remembered task than in the visual task, and that they tended to have greater accuracy at the hip than at the knee. Position sense of the subject with SCI was comparable to those of the AB subjects. We show that using the Lokomat to assess joint position sense may be an effective clinical measurement tool. Keywords-proprioception, assessment, rehabilitation, gait I. INTRODUCTION In clinical settings, much effort has been placed into finding ways of restoring and tracking the recovery of voluntary motor function after spinal cord injury [1]. However, there is far less emphasis on doing the same for sensory function. Because motor function can be highly influenced by sensory information, it may be beneficial to improve sensory function in order to maximize overall motor recovery. Therefore, precise clinical assessments of sensory function are necessary to evaluate the effectiveness of treatments [2, 3]. Proprioception (static position sense and kinesthesia, or movement sense) is a sensory modality that is important for maintaining posture, locomotion [4], and motor learning [5], yet a reliable and precise method to measure proprioception in the lower limbs, especially one that could be used for neurological populations, is lacking. There currently is no “gold standard” for clinical measurement of joint position sense in the lower limbs. Assessments of proprioception used by clinicians are not quantitative and lack sensitivity [6]. For example, one clinical measure of joint position sense involves the clinician grossly moving a limb and asking the patient to simply indicate the direction that the limb was moved [7]. Another measure involves imitating a presented movement but quantification of the response is usually only estimated. More precise and sensitive methods to measure proprioception in clinical populations need to be developed and validated. Several groups have developed methods to quantitatively measure proprioception in the upper extremities of able-bodied subjects for the purposes of basic research [8-12]. In addition, tools have been developed to quantitatively measure joint position sense in the upper extremity in persons with stroke [13-15] and hemiplegic cerebral palsy [16]. Wright and colleagues investigated how axial kinesthesia affected posture and locomotion in patients with Parkinson’s disease [17]. There are a small number of studies that quantitatively measure kinesthesia in the leg [18-22], and none of these studies involve neurological populations. The purpose of our study was to develop a quantitative assessment tool of lower limb joint position sense using the Lokomat (Hocoma AG, Volketswil, Switzerland). Previously, the Lokomat has been used to assess voluntary muscle force and spasticity in the lower limbs [23, 24]. We used 2 different assessments to track lower limb proprioception at the hip and knee joint in able-bodied subjects and in 1 subject with incomplete SCI. Subjects had to move their hip or knee joint to a target angle when they were presented with either a remembered target (the subject’s joint was moved to the target angle and memorized, then moved away to a distractor position) or a visual target (a stick figure diagram configured into the target angle was displayed to the subject). The visual task eliminates the memory component of the remembered task, but subjects will be required to make a transformation of visual information into proprioceptive information. Testing these different paradigms will give a clearer picture of proprioceptive ability and help determine the ideal way to measure position sense in future studies. II. METHODS A. Subjects Nine able-bodied subjects (3 males, 6 females; age (mean ± SD) = 26.4 ± 2.9 years, leg length (mean ± SD) = 86.5 ± 6.5 This work was supported by the Canadian Institutes for Health Research (CIHR). TL was supported by a CIHR New Investigator Award. 2011 IEEE International Conference on Rehabilitation Robotics Rehab Week Zurich, ETH Zurich Science City, Switzerland, June 29 - July 1, 2011 978-1-4244-9861-1/11/$26.00 ©2011 IEEE 791