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Measurement of neuromechanical ankle parameters in cerebral palsy
Abstracts / Gait & Posture 42S (2015) S1–S90
The time-to-boundary function to assess upright stance in static and dynamic condition C. D’ Anna 1,∗ , F. Patanè 2,3 , M. Schmid 1 , P. Cappa 2,3 , E. Castelli 3 , S. Gazzellini 3 , S. Conforto 1 , M. Petrarca 3 1 Biolab3, Department of Engineering, University Roma TRE, Rome, Italy 2 Department of Mechanical and Aerospace Engineering, “Sapienza” University of Rome, Rome, Italy 3 Pediatric Neuro-Rehabilitation Division, Children’s Hospital “Bambino Gesù” IRCCS, Rome, Italy
Main topics: Movement analysis in clinical practice Introduction and aim: Parameters extracted from CoP data have been used in several studies to describe, interpret and assess the postural control in both static and dynamic conditions. Among these the Time-to-Boundary function (TtB) was introduced in the framework of postural stability by moving a concept defined in the theory of the time-to-collision to visual perception and calculated in upright stance trials. This variable takes position, velocity, and acceleration of the CoP trajectory into account, to estimate the temporal margin to the stability boundaries [1]. No study up to now has studied the TtB function in dynamic posture, so that the aim of this study is to evaluate the difference of the temporal limits of stability in static and dynamic balance, considering eyes-open and eyes-closed visual conditions. Patients/materials and methods: Experiments were conducted in seven volunteers healthy children (age range 9–14 yrs, height 1.5 ± 0.11 m, weight 46.7 ± 9.8 kg). Subjects stood on the RotoBit [2] force plate with heels 2 cm apart, externally rotated at around 30◦ , and were asked to maintain an upright posture with eyes-open (EO) and eyes-closed (EC), in static (stat) and dynamic (dyn) conditions. In dynamic conditions, the RotoBit plate was free to tilt with an angular range of about ±10◦ for roll and pitch. Each condition was repeated three times and each repetitions lasted 30 s. The CoP coordinates were stored for further offline processing. This included mean value removal and digital low-pass filtering (cutoff frequency of 10 Hz). They were used to extract the TtB function and the median value over time was calculated for each repetition. Descriptive statistic and 2-way Anova test with repeated measures (with vision condition (EO/EC) and force plate movement condition (stat/dyn) as factors) were calculated. Results: The statistical analysis shows significant difference (p < 0.05) in EC dyn/EC stat and EO dyn/EC dyn comparisons. No significant difference is shown for EO stat/EO dyn and EO stat/EC stat comparisons. The analysis of numerical result shows that the TtB value in dynamic condition decreases respect to the static condition
Fig. 1. Mean ± standard deviation of TtB function. The significant difference (*p < 0.05) is shown for all comparisons.
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when participants had their eyes closed. In the comparison EO dyn/EC dyn, the TtB value increase when participants stood in upright stance with eyes open. All results are shown in Fig. 1. Discussion and conclusions: The preliminary results show that the temporal margin of stability decrease when the participants performed a postural trial in dynamic condition respect to the static condition. The TtB parameter can be useful to assess different postural control strategies used in the two motor tasks. This behaviour is promising to asses and monitor feature rehabilitation protocols based on dynamic task. References [1] Schmid M, Conforto S. Stability limits in the assessment of postural control through the Time-to-Boundary function. In: Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th annual international conference of the IEEE. IEEE; 2007. [2] Patanè F, Cappa P. A 3-DOF parallel robot with spherical motion for the rehabilitation and evaluation of balance performance. IEEE Trans Neural Syst Rehabil Eng 2011;19(2):157–66.
http://dx.doi.org/10.1016/j.gaitpost.2015.03.037 Measurement of neuromechanical ankle parameters in cerebral palsy L.H. Sloot 1,∗ , M.M. van der Krogt 1 , E. de Vlugt 2 , J. Harlaar 1 1
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands 2 Department of Biomedical Engineering, Delft University of Technology, Delft, The Netherlands Main topics: Analysis of clinical movement data, Musculoskeletal modelling Introduction and aim: Spastic Cerebral Palsy (CP) is characterized by increased joint stiffness, caused by a mix of increased stretch reflex activity and muscle tone, as well as altered visco-elastic tissue properties. Since treatment depends on the specific cause, objective quantification of the ankle neuromechanical parameters would contribute to patient specific treatment. Previous assessment was limited to the triceps surae muscle group and the distinction between reflex activity and tissue visco-elasticity [1,2]. To gain more muscle specific information, the instrumented assessment (IA) combined with system identification was extended to include baseline muscle tone and to differentiate between the three major lower leg muscles. We evaluated the ability of the extended IA to discriminate between children with spastic CP and controls. Patients/materials and methods: 21 children with spastic CP (11.1 ± 3.3 yr, GMFCS 1-3) and 34 control children (10.2 ± 2.7 yr) were included. Their most affected foot was fixated to a motor driven footplate that rotated around the ankle joint. Two passive slow (5◦ /s) and fast (100◦ grad/s) ramp-and-hold rotations were applied in the sagittal plane over the full range of ankle motion (ROM), at two different knee angles (20◦ and 70◦ ) to discriminate between the triceps muscles. Ankle angle and EMG of the gastrocnemius (GAS), soleus (SOL) and tibialis anterior (TIB) muscles were used to optimize a nonlinear neuromuscular model to match the measured ankle torque. Tissue stiffness and viscosity were based on the slow trials and taken at the highest plantar (40◦ ) and dorsiflexion (5◦ ) angle reached by all subjects. Root-mean-squares of baseline muscle tone and reflex torque were taken from the fast trials. Non-parametric tests with Bonferroni correction were performed to assess the difference between CP and controls. Results: In CP, there was a trend of 1,62 times increased stiffness in the SOL (p = 0.02; Fig. 1A) and viscosity was 4.0 and 2.8 times
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Abstracts / Gait & Posture 42S (2015) S1–S90
Fig. 1. median values and 25/75 percentiles for stiffness (A), reflex (B) and tonus (C) for CP patients and controls (C).
larger for the SOL and TIB (p < 0.001; p = 0.03). The reflex torque was enlarged in CP by 5.2 and 3.8 times in the GAS and SOL respectively (both p < 0.001), but not in TA (Fig. 1B). Baseline muscle tone was 2.4 and 1.9 times increased in the GAS and SOL (p = 0.007; p < 0.001; Fig. 1C). Variances were generally larger for CP and ratios between stiffness and reflex torque differed considerably between patients. Discussion and conclusions: The IA was able to discriminate between CP patients and controls. In CP, reflex torque and muscle tone were found to be increased in the triceps muscles, which are often treated for spasticity. Stiffness only showed an increase for SOL, although a difference also emerged for GAS when choosing a higher dorsiflexion angle, at the expense of decreasing the group of subject. The large variances and ratio differences in CP indicate that instrumented assessments could allow for subject specific therapy selection. References [1] de Gooijer-van de Groep et al.; 2013. [2] de Vlugt et al.; 2010.
http://dx.doi.org/10.1016/j.gaitpost.2015.03.038 The level of co-activation during maximal and submaximal dynamometry testing in adolescents with spastic cerebral palsy M.M. Eken 1,2,∗ , A.J. Dallmeijer 1 , C.A.M. Doorenbosch 1,3 , H. Dekkers 2 , J.G. Becher 1 , H. Houdijk 2,4 1
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, the Netherlands 2 Heliomare Rehabilitation, Research and Development, Wijk aan Zee, the Netherlands 3 Academy of Human Kinetic Technology, University of Applied Sciences, the Hague, the Netherlands 4 MOVE Research Institute Amsterdam, Faculty of Human Movement Science, VU University, Amsterdam, the Netherlands Main topics: Analysis of clinical movement data, Rehabilitation Introduction and aim: Muscle weakness is a common motor impairment in individuals with spastic cerebral palsy (CP). Dynamometry is widely used among individuals with CP to quantify this impairment. However, increased muscle co-activation might reduce the validity of dynamometer strength measurements in these individuals. Therefore, the aim of this study is to investigate the degree of muscle co-activation during maximal and submaximal dynamometer tests in adolescents with CP in comparison to TD adolescents. Patients/materials and methods: Surface electromyography (EMG) recordings were made of quadriceps (m.rectus femoris (RF), m.vastus medialis (VM), m.vastus lateralis (VL) and hamstrings (m.biceps femoris (BF), m.semitendinosus (ST)) of 16 adolescents with CP (age: 13–19 y; GMFCS level I/II) and 14 TD
Fig. 1. Boxplots of CAI of agonist-antagonist pair RF/BF separately for the isotonic and isometric tests; *p < .05.
peers (age: 12–19 y) during maximal voluntary isometric knee extension and flexion contractions (MVCs) and series of submaximal isotonic knee extension contractions at three different loads (mean %MVC lowest load: 65%; medium load: 75%; highest load: 85%). After rectifying and low pass filtering (5 Hz), EMG amplitude (amp) was normalized to the amplitude found during the MVC. Co-activation index (CAI) was calculated as: 1 − (|ampagonist | − |ampantagonist |)/(|ampagonist | + |ampantagonist |) [1] and averaged over the extension contraction. CAI was averaged over three contractions for both maximal and submaximal contractions. Differences in CAI between CP and TD were analysed using a Mann–Whitney U-test. To test the influence of load on CAI, a Friedman’s ANOVA was used separately for both groups (p < .05). Results: Higher CAI levels were observed during maximal contractions in adolescents with CP compared to TD adolescents in all agonist-antagonist pairs (mean RF/BF CP: .486, TD: .344; RF/ST CP: .401, TD: .210; VM/BF CP: .479, TD: .272; VM/ST CP: .415, TD: .221; VL/BF CP: .445, TD: .282; VL/ST: CP: .396, TD: .225). No differences in CAI were observed between the groups during submaximal contractions at different loads (Fig. 1, example of RF/BF). Discussion and conclusions: During isometric MVCs, adolescents with CP showed higher CAI levels than TD adolescents, while there were no differences in CAI during submaximal isotonic contractions. The results suggest that dynamometer measurements with maximal contractions are more influenced by co-activation than submaximal contractions in adolescents with CP. Submaximal muscle testing may therefore be preferred when assessing muscle strength in individuals with CP. Reference [1] Doorenbosch CAM, Harlaar J. Clin Biomech 2003;18:142–9.
http://dx.doi.org/10.1016/j.gaitpost.2015.03.039
The time-to-boundary function to assess upright stance in static and dynamic condition C. D’ Anna 1,∗ , F. Patanè 2,3 , M. Schmid 1 , P. Cappa 2,3 , E. Castelli 3 , S. Gazzellini 3 , S. Conforto 1 , M. Petrarca 3 1 Biolab3, Department of Engineering, University Roma TRE, Rome, Italy 2 Department of Mechanical and Aerospace Engineering, “Sapienza” University of Rome, Rome, Italy 3 Pediatric Neuro-Rehabilitation Division, Children’s Hospital “Bambino Gesù” IRCCS, Rome, Italy
Main topics: Movement analysis in clinical practice Introduction and aim: Parameters extracted from CoP data have been used in several studies to describe, interpret and assess the postural control in both static and dynamic conditions. Among these the Time-to-Boundary function (TtB) was introduced in the framework of postural stability by moving a concept defined in the theory of the time-to-collision to visual perception and calculated in upright stance trials. This variable takes position, velocity, and acceleration of the CoP trajectory into account, to estimate the temporal margin to the stability boundaries [1]. No study up to now has studied the TtB function in dynamic posture, so that the aim of this study is to evaluate the difference of the temporal limits of stability in static and dynamic balance, considering eyes-open and eyes-closed visual conditions. Patients/materials and methods: Experiments were conducted in seven volunteers healthy children (age range 9–14 yrs, height 1.5 ± 0.11 m, weight 46.7 ± 9.8 kg). Subjects stood on the RotoBit [2] force plate with heels 2 cm apart, externally rotated at around 30◦ , and were asked to maintain an upright posture with eyes-open (EO) and eyes-closed (EC), in static (stat) and dynamic (dyn) conditions. In dynamic conditions, the RotoBit plate was free to tilt with an angular range of about ±10◦ for roll and pitch. Each condition was repeated three times and each repetitions lasted 30 s. The CoP coordinates were stored for further offline processing. This included mean value removal and digital low-pass filtering (cutoff frequency of 10 Hz). They were used to extract the TtB function and the median value over time was calculated for each repetition. Descriptive statistic and 2-way Anova test with repeated measures (with vision condition (EO/EC) and force plate movement condition (stat/dyn) as factors) were calculated. Results: The statistical analysis shows significant difference (p < 0.05) in EC dyn/EC stat and EO dyn/EC dyn comparisons. No significant difference is shown for EO stat/EO dyn and EO stat/EC stat comparisons. The analysis of numerical result shows that the TtB value in dynamic condition decreases respect to the static condition
Fig. 1. Mean ± standard deviation of TtB function. The significant difference (*p < 0.05) is shown for all comparisons.
S15
when participants had their eyes closed. In the comparison EO dyn/EC dyn, the TtB value increase when participants stood in upright stance with eyes open. All results are shown in Fig. 1. Discussion and conclusions: The preliminary results show that the temporal margin of stability decrease when the participants performed a postural trial in dynamic condition respect to the static condition. The TtB parameter can be useful to assess different postural control strategies used in the two motor tasks. This behaviour is promising to asses and monitor feature rehabilitation protocols based on dynamic task. References [1] Schmid M, Conforto S. Stability limits in the assessment of postural control through the Time-to-Boundary function. In: Engineering in Medicine and Biology Society, 2007. EMBS 2007. 29th annual international conference of the IEEE. IEEE; 2007. [2] Patanè F, Cappa P. A 3-DOF parallel robot with spherical motion for the rehabilitation and evaluation of balance performance. IEEE Trans Neural Syst Rehabil Eng 2011;19(2):157–66.
http://dx.doi.org/10.1016/j.gaitpost.2015.03.037 Measurement of neuromechanical ankle parameters in cerebral palsy L.H. Sloot 1,∗ , M.M. van der Krogt 1 , E. de Vlugt 2 , J. Harlaar 1 1
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands 2 Department of Biomedical Engineering, Delft University of Technology, Delft, The Netherlands Main topics: Analysis of clinical movement data, Musculoskeletal modelling Introduction and aim: Spastic Cerebral Palsy (CP) is characterized by increased joint stiffness, caused by a mix of increased stretch reflex activity and muscle tone, as well as altered visco-elastic tissue properties. Since treatment depends on the specific cause, objective quantification of the ankle neuromechanical parameters would contribute to patient specific treatment. Previous assessment was limited to the triceps surae muscle group and the distinction between reflex activity and tissue visco-elasticity [1,2]. To gain more muscle specific information, the instrumented assessment (IA) combined with system identification was extended to include baseline muscle tone and to differentiate between the three major lower leg muscles. We evaluated the ability of the extended IA to discriminate between children with spastic CP and controls. Patients/materials and methods: 21 children with spastic CP (11.1 ± 3.3 yr, GMFCS 1-3) and 34 control children (10.2 ± 2.7 yr) were included. Their most affected foot was fixated to a motor driven footplate that rotated around the ankle joint. Two passive slow (5◦ /s) and fast (100◦ grad/s) ramp-and-hold rotations were applied in the sagittal plane over the full range of ankle motion (ROM), at two different knee angles (20◦ and 70◦ ) to discriminate between the triceps muscles. Ankle angle and EMG of the gastrocnemius (GAS), soleus (SOL) and tibialis anterior (TIB) muscles were used to optimize a nonlinear neuromuscular model to match the measured ankle torque. Tissue stiffness and viscosity were based on the slow trials and taken at the highest plantar (40◦ ) and dorsiflexion (5◦ ) angle reached by all subjects. Root-mean-squares of baseline muscle tone and reflex torque were taken from the fast trials. Non-parametric tests with Bonferroni correction were performed to assess the difference between CP and controls. Results: In CP, there was a trend of 1,62 times increased stiffness in the SOL (p = 0.02; Fig. 1A) and viscosity was 4.0 and 2.8 times
S16
Abstracts / Gait & Posture 42S (2015) S1–S90
Fig. 1. median values and 25/75 percentiles for stiffness (A), reflex (B) and tonus (C) for CP patients and controls (C).
larger for the SOL and TIB (p < 0.001; p = 0.03). The reflex torque was enlarged in CP by 5.2 and 3.8 times in the GAS and SOL respectively (both p < 0.001), but not in TA (Fig. 1B). Baseline muscle tone was 2.4 and 1.9 times increased in the GAS and SOL (p = 0.007; p < 0.001; Fig. 1C). Variances were generally larger for CP and ratios between stiffness and reflex torque differed considerably between patients. Discussion and conclusions: The IA was able to discriminate between CP patients and controls. In CP, reflex torque and muscle tone were found to be increased in the triceps muscles, which are often treated for spasticity. Stiffness only showed an increase for SOL, although a difference also emerged for GAS when choosing a higher dorsiflexion angle, at the expense of decreasing the group of subject. The large variances and ratio differences in CP indicate that instrumented assessments could allow for subject specific therapy selection. References [1] de Gooijer-van de Groep et al.; 2013. [2] de Vlugt et al.; 2010.
http://dx.doi.org/10.1016/j.gaitpost.2015.03.038 The level of co-activation during maximal and submaximal dynamometry testing in adolescents with spastic cerebral palsy M.M. Eken 1,2,∗ , A.J. Dallmeijer 1 , C.A.M. Doorenbosch 1,3 , H. Dekkers 2 , J.G. Becher 1 , H. Houdijk 2,4 1
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, the Netherlands 2 Heliomare Rehabilitation, Research and Development, Wijk aan Zee, the Netherlands 3 Academy of Human Kinetic Technology, University of Applied Sciences, the Hague, the Netherlands 4 MOVE Research Institute Amsterdam, Faculty of Human Movement Science, VU University, Amsterdam, the Netherlands Main topics: Analysis of clinical movement data, Rehabilitation Introduction and aim: Muscle weakness is a common motor impairment in individuals with spastic cerebral palsy (CP). Dynamometry is widely used among individuals with CP to quantify this impairment. However, increased muscle co-activation might reduce the validity of dynamometer strength measurements in these individuals. Therefore, the aim of this study is to investigate the degree of muscle co-activation during maximal and submaximal dynamometer tests in adolescents with CP in comparison to TD adolescents. Patients/materials and methods: Surface electromyography (EMG) recordings were made of quadriceps (m.rectus femoris (RF), m.vastus medialis (VM), m.vastus lateralis (VL) and hamstrings (m.biceps femoris (BF), m.semitendinosus (ST)) of 16 adolescents with CP (age: 13–19 y; GMFCS level I/II) and 14 TD
Fig. 1. Boxplots of CAI of agonist-antagonist pair RF/BF separately for the isotonic and isometric tests; *p < .05.
peers (age: 12–19 y) during maximal voluntary isometric knee extension and flexion contractions (MVCs) and series of submaximal isotonic knee extension contractions at three different loads (mean %MVC lowest load: 65%; medium load: 75%; highest load: 85%). After rectifying and low pass filtering (5 Hz), EMG amplitude (amp) was normalized to the amplitude found during the MVC. Co-activation index (CAI) was calculated as: 1 − (|ampagonist | − |ampantagonist |)/(|ampagonist | + |ampantagonist |) [1] and averaged over the extension contraction. CAI was averaged over three contractions for both maximal and submaximal contractions. Differences in CAI between CP and TD were analysed using a Mann–Whitney U-test. To test the influence of load on CAI, a Friedman’s ANOVA was used separately for both groups (p < .05). Results: Higher CAI levels were observed during maximal contractions in adolescents with CP compared to TD adolescents in all agonist-antagonist pairs (mean RF/BF CP: .486, TD: .344; RF/ST CP: .401, TD: .210; VM/BF CP: .479, TD: .272; VM/ST CP: .415, TD: .221; VL/BF CP: .445, TD: .282; VL/ST: CP: .396, TD: .225). No differences in CAI were observed between the groups during submaximal contractions at different loads (Fig. 1, example of RF/BF). Discussion and conclusions: During isometric MVCs, adolescents with CP showed higher CAI levels than TD adolescents, while there were no differences in CAI during submaximal isotonic contractions. The results suggest that dynamometer measurements with maximal contractions are more influenced by co-activation than submaximal contractions in adolescents with CP. Submaximal muscle testing may therefore be preferred when assessing muscle strength in individuals with CP. Reference [1] Doorenbosch CAM, Harlaar J. Clin Biomech 2003;18:142–9.
http://dx.doi.org/10.1016/j.gaitpost.2015.03.039