Neuromechanical Redundancy for Gait Compensation in Transtibial Amputees Kinsey Herrin, B.S. Advisor: Young-Hui Chang, Ph.D. 1
Transtibial Amputees Limb length Ankle Normal joint mobility Direct muscular control Local proprioception [Perry, 1992] Joint kinematics Introduction Injured rats shown to return to preinjured limb level goal kinematic trajectories [Bauman and Chang, 2010] Understanding of recovery after injury [Bauman and Chang, 2010] 2
Introduction Human locomotion: highly redundant [Srinivasan and Ruina, 2006, Latash, Scholz, Schoner, 2002] Lower limbs have three major joints Leg length and orientation are limb level GOALS Kinematic motor redundancy: multiple joint configurations for a desired GOAL - Amputees: How do you coordinate if you are missing one of those joints? 3
Introduction Quantify motor redundancy by analysis of variance [Scholz, Reisman, Schoner, 2001] Deviations at one joint counteracted by other joints allows decreased variance at the limb level [Chang,et al., 2009, Heiderscheit, 2000, Yen, 2009, Auyang, 2009] Importance: vs. [Barrett, Noordegraaf, Morrison, 2008] 4
Purpose Understand differences in healthy and amputee gait Understand how the nervous system of an amputee coordinates joint kinematics to compensate Better gait rehab strategies 5
Spoiler Alert!: Conclusions Sound limb Sound limb is affected by amputation Remaining joints and limb level goals work to maintain similarity Return to pre-amputation kinematics may not be as important as symmetry Focus rehab to prevent overuse injuries Amputees use redundancy to stabilize limb level goals 6
Hypotheses 1. Mean prosthetic side limb level goals will be preserved to able-bodied state. 2. Within prosthetic side, joints act to preserve invariant leg orientation and leg length. 7
Methods 5 unilateral traumatic, transtibial amputees 7 able-bodied control subjects Three 30 second walking trials at 1.2 m/s Kinematic data collected from a six-camera motion analysis system (120 Hz, VICON) QuickTime and a H.264 decompressor are needed to see this picture. Courtesy of Karen Liu GT Computer Graphics Lab 8
120 115 R 2 Metrics 105 Variance 115 110 110 105 105 100 100 95 95 90 90 85 R 2 = 0.3968 R 2 = Ankle Angle ( ) 85 80 80 80 85 90 95 100 105 110 115 80 85 90 95 100 105 Prosthetic Ankle 110 115 120 Control Ankle R 2 : an approximator for determining similarity of 2 trajectories - R 2 > 0.5 means trajectories are similar - R 2 < 0.5 means trajectories are different [Chang, 2009] Variance: Measure of the average variability from step to step 85 0 ---------------------------------------------------> 100 % Gait Cycle 9
R 2 =0.985 10
R 2 =0.45 11
R 2 =0.98 12
R 2 =0.25 13
R 2 =0.997 14
R 2 =0.74 15
Amputee Joint Kinematics R 2 =0.39 R 2 =0.98 R 2 =0.94 16
Variance of Joints and LO Total Variance Per Joint 0.16 p=0.03 LO Variance 0.14 * p=0.01 * p=0.01 * 0.12 Variance 0.1 0.08 0.06 0.04 0.02 0 Prosthetic (excludes Ankle) Sound Control 17
Leg Length Variance 0.0035 LL Variance 0.003 0.0025 Variance 0.002 0.0015 0.001 0.0005 0 Prosthetic (excludes Ankle) Sound Control 18
Discussion of Major Findings Hypothesis 1 partially accepted: Preservation of LO and LL in amputees LO preserved [Bauman and Chang, 2010] LL not preserved 19
Discussion Leg Length: Different region of the task space Symmetry LO LL Sound limb affected Joints Asymmetry can lead to other health problems [Tura, 2010, Sanderson and Martin, 1997] 20
Discussion Hypothesis 2 accepted: Redundancy used to stabilize limb level goals Similar limb level variances (LO and LL) Achieving same level of performance [Auyang, 2009, Yen,2009] Amputees coordinate only 2 joints to stabilize invariant leg orientation and leg length Injured cats coordinate joints [Chang, 2009] 21
Limitations & Future Work Limitations: No single, standardized prosthesis Future Work: Congenital amputees Transfemoral amputees Kinetic analysis 22
Take Home Message Symmetry in gait more important than return to pre-amputated gait Amputees use redundancy 23
References Latash, Scholz, Schoner (2002). "Motor control strategies revealed in the structure of motor variability." Exercise and Sports Science Reviews 30(1). Bauman and Chang (2010). Conservation of Limb Function after Peripheral Nerve Injury in Rat Locomotion ASB Abstract. Perry, J. (1992). Gait Analysis Normal and Pathological Function. Thorofare, SLACK Incorporated. Barret, R., Noordegraaf, M.V., Morrison, S. (2008). "Gender differences in the variability of lower extremity kinematics during treadmill locomotion." Journal of Motor Behavior 40(1): 62-70. Sanderson, D.J., and Martin, P.E. (1997). "Lower extremity kinematic and kinetic adaptations in unilateral below-knee amputees during walking." Gait and Posture 6: 126-136. Scholz, Reisman, Schoner, 2001 Exp Brain Research 141:485-500 Effects of varying task constraints on solutions to joint coordination in a sit-to-stand task Scholz, Reisman, Schoner (2001). "Effects of varying task constraints on solutions to joint coordination in sitto-stand task." Experimental Brain Research 141: 485-500. Scholz, et al. (2002). "Understanding finger coordination through analysis of the structure of force variability." Biol Cybern 86: 29-39. Srinivasan, R. A. M. (2006). "Computer optimization of a minimal biped model discovers walking and running." Nature 439(7072): 72-75. Chang, Y., et al. (2009). "Whole limb kinematics are preferentially conserved over individual joint kinematics after peripheral nerve injury." J. Exp. Biology 212(3511-3521). Heiderscheit, B. C. (2000). " Movement variability as a clinical measure for locomotion." J. of Applied Biomechanics 16: 419-427. Yen, J. (2009). "Joint-level kinetic redundancy is exploited to control limb-level forces during human hopping." Experimental Brain Research 196: 439-451. Auyang, A.G. (2009). "Neuromechanical stabilization of leg length and orientation through interjoint compensation during human hopping." Experimental Brain Research 192: 253-264. Breakey, J. (1976). "Gait of unilateral below-knee amputees." Orthotics and Prosthetics 30(3): 17-24. Isakov, E., et al (2000). "Trans-tibial amputee gait: Time-distance parameters and EMG activiy." Prosthetics and Orthotics International 24(3): 216-220. Tura, A., et al. (2010). "Gait symmetry and regularity in transfemoral amputees assessed by trunk accelerations." Journal of NeuroEngineering and Rehabilitation 7(4). 24
Special Thanks Young Hui Chang, Advisor Comparative Neuromechanics Lab Members: Arick Auyang Jasper Yen Megan Toney Jay Bauman Megan Krause Susie Cha Rob Kistenberg My subjects 25
Questions? 26
Additional Slides 27
Variance Per Joint: Amputees and Able-Bodied v=1.2 m/s 0.003 0.0025 Prosthesis Sound Control Left 0.002 0.0015 0.001 0.0005 0 Ankle Knee Hip LO Joint and LO 28
0.8 Stance and Swing Times, v=1.2 m/s 0.7 0.6 0.5 time (s) 0.4 stance t swing t 0.3 0.2 0.1 0 Control R Control L Amp Px Amp Sd 29
Amputee Stride Length, v=1.2 m/s 1.6 1.4 1.2 1 0.8 Px Sd 0.6 0.4 0.2 0 1 2 3 4 5 subject 30
Symmetry in Amputee Gait: Leg Length 31
R 2 values Prosthetic vs Control Sound vs Control Prosthetic vs Sound 1 Range of Similarity 0.5 0 Ankle Knee Hip Leg Leg Joint or Task Goal Orientation Length 0 1 2 3 4 5 6 32
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Comparison of Prosthetic and Sound Kinematics of Amputee Symmetry 34
Discussion Overall trajectory shapes of the ankle, knee and hip were similar, but differences seen (p<0.05) at various points in the gait cycle between: Prosthetic/sound and control ankles Prosthetic and sound ankles Prosthetic/sound and control knees Prosthetic and sound knees No differences were found at any point of the gait cycle for the hip joint Ankle and knee joints on both the prosthetic and sound sides may be responsible for compensation after amputation 35
Methods/Data Analysis Limb level goals Leg Orientation (LO): angle of vector defined by anterior superior iliac spine (ASIS) and toe markers Leg Length (LL): length of the vector defined by ASIS and toe markers Auyang, AG, et al. Experimental Brain Research. 192: 253-264, 2009. 36