The Effects of Carpal Tunnel Syndrome on the Kinematics of Reach-to-Pinch Function

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1 The Effects of Carpal Tunnel Syndrome on the Kinematics of Reach-to-Pinch Function Raviraj Nataraj, Peter J. Evans, MD, PhD, William H. Seitz, MD, Zong-Ming Li. Cleveland Clinic, Cleveland, OH, USA. Disclosures: R. Nataraj: None. P.J. Evans: None. W.H. Seitz: None. Z. Li: None. Introduction: Reach to grasp is fundamental to activities of daily living involving sensorimotor coordination across both the central and peripheral nervous systems. Individuals with carpal tunnel syndrome (CTS) suffer from hand dysfunction due to compression of the median nerve. With CTS, the thumb and index finger are focally afflicted by pain, tingling, and sensorimotor deficit of the thenar and first lumbrical muscles. This diminished processing across sensory inputs and motor outputs can produce disorganization at the cortical level (Gay, Parratte et al. 2007). While CTS is noted as a peripheral neuropathy, it can also produce central-level changes as shown by altered muscle-based representations at the primary sensory cortex (Napadow, Kettner et al. 2006). In this study, we examined the effects of CTS on movement range and variability of reach-to-pinch function, which involves transport of the hand occurring in concert with precision grasp of smaller objects by the thumb and index finger (Domalain, Vigouroux et al. 2008). It was hypothesized that individuals with CTS would exhibit a decrease in range and an increase in variability of the grasping digits, which are local to the peripheral neuropathy, and in global transport of the entire reaching hand compared to able-bodied controls (ABL). Variability was used to indicate lack of movement efficiency and was defined as the trial-to-trial standard deviation about the mean trajectory over the reach-to-pinch movement cycle. Methods: Fourteen female subjects (seven CTS aged 48.0 ± 10.4 years, seven ABL aged 47.5 ± 7.7 years) participated in this study. All participants were right-hand dominant. CTS subjects were diagnosed according to standard clinical guidelines (Keith, Masear et al. 2009). ABL subjects did not previously report a history of disease, injury, or complications involving the hand or wrist. All participants had normal or corrected-to-normal vision and signed informed consent approved by the local Institutional Review Board. A minimal set of retro-reflective markers (Nataraj and Li 2013) were affixed to the surface of the right hand of each subject (Figure 1, LEFT). Anatomically-aligned coordinate systems were determined for marker-clusters (Shen, Mondello et al. 2012). The 3D position of each marker was tracked at 100Hz using motion capture (Vicon Motion Systems and Peak Performance, Inc.). {Shen, 2012 (in press) #1153}A custom platform-rig (Figure 1, RIGHT) was constructed to perform the reachto-pinch experiments with no visual feedback of the reaching hand. Each subject was seated in front of the left alley to clearly gaze the mirror reflection of a real marker, but unable to view their reaching right hand in the right alley. It was necessary to control for vision in this protocol since visual feedback can compensate for impaired proprioception while performing reaching tasks (Ghez, Gordon et al. 1995). Subjects treated the reflection as a virtual target to be contacted with their grasping digits. Subjects were instructed to reach and pinch the perceived target with the thumb and index finger as accurately and consistently as possible across trials. Subjects paced their movement according to a metronome such that the reach-to-pinch cycle was ~1 second. A total of 30 reach-to-pinch trials were executed for each subject with minimal time elapsing between trials according to experimenter discretion. Wrist marker position (WR) was utilized to calculate transport of the proximal hand relative to the global coordinate system (C.S.) affixed to the platform-rig. Coordinate systems affixed to the nail marker-clusters were utilized to define the position and orientation of the distal segments of the thumb and index finger relative to the local hand coordinate system. A Wilcoxon rank-sum test was performed on subject range values. A standard t-test was used to determine significant (p<0.05) differences for variability about the mean trajectory across the movement cycle for the two groups (ABL, CTS). Results: All position and distance data were normalized according to subject hand size (palm width). The CTS group demonstrated smaller (p<0.05) range of motion in mean trajectory for both inter-nail distance (IND) and wrist-transport distance (WT) compared to ABL (0.72 to 0.49 for IND; 3.0 to 2.3 for WT). The variability about this mean trajectory was significantly greater (p<0.001) for IND (Figure 2). The local position variability of the distal segments of both digits was significantly greater (p<0.05) for all cases except in the proximal-distal component (Z h ) for the index finger (Table 1). While variability for total WT was not significantly different across groups (Figure 2), the anterior-posterior (X p ) and medial-lateral (Y p ) components were significantly greater for CTS than ABL (Table 1). Discussion: The results of this pilot study suggest that CTS decreases movement range and increases variability both at the local and global levels across the reach-to-pinch cycle. Given median nerve compression, increased local variability of the digits was expectantly demonstrated, likely due in part to sensorimotor motor dysfunction of the adjacent thenar and lumbrical musculature. However, significant increase in variability for two of three components for wrist transport suggest global effects of CTS on movement function may also be evident. This may be due to cortical maladaptations of the cortex due to chronic CTS or possibly online disruption of peripheral-central sensorimotor integration due to the afflicted sensation.

2 Significance: This study suggests that CTS can have local and global effects on movement functions. These effects may comprehensively encompass peripheral- and central-level sensorimotor dysfunction of the hand, which should be considered for the evaluation, treatment and rehabilitation of CTS. Acknowledgments: NIH R01AR References: Domalain, M., L. Vigouroux, et al. (2008). "Effect of object width on precision grip force and finger posture." Ergonomics 51(9): Gay, A., S. Parratte, et al. (2007). "Proprioceptive feedback enhancement induced by vibratory stimulation in complex regional pain syndrome type I: an open comparative pilot study in 11 patients." Joint, bone, spine : revue du rhumatisme 74(5): Ghez, C., J. Gordon, et al. (1995). "Impairments of reaching movements in patients without proprioception. II. Effects of visual information on accuracy." Journal of neurophysiology 73(1): Keith, M. W., V. Masear, et al. (2009). "Diagnosis of carpal tunnel syndrome." The Journal of the American Academy of Orthopaedic Surgeons 17(6): Napadow, V., N. Kettner, et al. (2006). "Somatosensory cortical plasticity in carpal tunnel syndrome--a cross-sectional fmri evaluation." NeuroImage 31(2): Nataraj, R. and Z. M. Li (2013). "Robust identification of three-dimensional thumb and index finger kinematics with a minimal set of markers." Journal of biomechanical engineering 135(9): Shen, Z. L., T. A. Mondello, et al. (2012). "A digit alignment device for kinematic analysis of the thumb and index finger." Gait & posture 36(3):

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4 ORS 2014 Annual Meeting Poster No: 1921

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