The validity and reliability of modelled neural and tissue properties of the ankle muscles in children with cerebral palsy.
Spastic cerebral palsy (CP) is characterized by increased joint resistance, caused by a mix of increased tissue stiffness, as well as involuntary reflex and background muscle activity. These properties can be quantified using a neuromechanical model of the musculoskeletal complex and instrumented assessment. The construct validity of the neuromechanical parameters was examined (i.e. the internal model validity, effect of knee angle, speed and age, sensitivity to patients versus controls, spasticity severity and treatment), together with the repeatability. We included 38 children with CP and 35 controls. A motor driven footplate applied two slow (15°/s) and two fast (100°/s) rotations around the ankle joint, at two different knee angles. Ankle angle, torque and EMG of the gastrocnemius (GA), soleus (SO) and tibialis anterior (TA) muscle were used to optimize a nonlinear neuromuscular model. Outcome measures were tissue stiffness, reflex and background activity for GA, SO and TA. The internal model validity showed medium to high parameter confidence and good model fits. All parameter could discriminate between patients with CP and controls according to CP pathology. Other measures of external model validity (effect of test position, speed and age) showed behaviour along the lines of current knowledge of physiology. GA/SO background activity was sensitive to spasticity severity, but reflex activity was not. Preliminary data indicated that reflex activity was reduced after spasticity treatment. The between-trial and -day repeatability was moderate to good. The large variance between patients in the ratio of stiffness and neural resistance indicates that the method could potentially contribute to patient-specific treatment selection.
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands. Electronic address: l.sloot@vumc.nl.
Lizeth H
LH
Sloot
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
Marjolein M
MM
van der Krogt
Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, The Netherlands.
Karin L
KL
de Gooijer-van de Groep
Faculty of Mechanical Engineering, Delft University of Technology, Delft, The Netherlands.
Stijn
S
van Eesbeek
Department of Rehabilitation Medicine, Leiden University Medical Center, Leiden, The Netherlands.
Jurriaan
J
de Groot
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
Annemieke I
AI
Buizer
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
Carel
C
Meskers
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
Jules G
JG
Becher
Faculty of Mechanical Engineering, Delft University of Technology, Delft, The Netherlands.
Erwin
E
de Vlugt
Department of Rehabilitation Medicine, MOVE Research Institute Amsterdam, VU University Medical Center, Amsterdam, The Netherlands.
Jaap
J
Harlaar
D000843:Ankle Joint / Q000294:innervation / Q000503:physiopathology*; D002547:Cerebral Palsy / Q000503:physiopathology*; D002648:Child; D004576:Electromyography / Q000009:adverse effects; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009128:Muscle Spasticity / Q000503:physiopathology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology / Q000503:physiopathology*; D009469:Neuromuscular Junction / Q000502:physiology; D016059:Range of Motion, Articular / Q000502:physiology*; D012016:Reference Values; D012021:Reflex, Abnormal / Q000502:physiology; D015203:Reproducibility of Results
Biomechanics; Cerebral palsy; Muscle spasticity; Muscle stiffness; Rehabilitation