title: Differentiation between non-neural and neural contributors to ankle joint stiffness in cerebral palsy.
abstract: BACKGROUND
  Spastic paresis in cerebral palsy (CP) is characterized by increased joint stiffness that may be of neural origin, i.e. improper muscle activation caused by e.g. hyperreflexia or non-neural origin, i.e. altered tissue viscoelastic properties (clinically: "spasticity" vs. "contracture"). Differentiation between these components is hard to achieve by common manual tests. We applied an assessment instrument to obtain quantitative measures of neural and non-neural contributions to ankle joint stiffness in CP.
  
  
  METHODS
  Twenty-three adolescents with CP and eleven healthy subjects were seated with their foot fixated to an electrically powered single axis footplate. Passive ramp-and-hold rotations were applied over full ankle range of motion (RoM) at low and high velocities. Subject specific tissue stiffness, viscosity and reflexive torque were estimated from ankle angle, torque and triceps surae EMG activity using a neuromuscular model.
  
  
  RESULTS
  In CP, triceps surae reflexive torque was on average 5.7 times larger (p = .002) and tissue stiffness 2.1 times larger (p = .018) compared to controls. High tissue stiffness was associated with reduced RoM (p < .001). Ratio between neural and non-neural contributors varied substantially within adolescents with CP. Significant associations of SPAT (spasticity test) score with both tissue stiffness and reflexive torque show agreement with clinical phenotype.
  
  
  CONCLUSIONS
  Using an instrumented and model based approach, increased joint stiffness in CP could be mainly attributed to higher reflexive torque compared to control subjects. Ratios between contributors varied substantially within adolescents with CP. Quantitative differentiation of neural and non-neural stiffness contributors in CP allows for assessment of individual patient characteristics and tailoring of therapy.
authors.affiliation: Department of Rehabilitation Medicine, Leiden University Medical Centre, Leiden, The Netherlands. k.l.de_gooijer-van_de_groep@lumc.nl
authors.forename: Karin L
authors.initials: KL
authors.lastname: de Gooijer-van de Groep
authors.forename: Erwin
authors.initials: E
authors.lastname: de Vlugt
authors.forename: Jurriaan H
authors.initials: JH
authors.lastname: de Groot
authors.forename: Hélène C M
authors.initials: HC
authors.lastname: van der Heijden-Maessen
authors.forename: Dennis H M
authors.initials: DH
authors.lastname: Wielheesen
authors.forename: Rietje M S
authors.initials: RM
authors.lastname: van Wijlen-Hempel
authors.forename: J Hans
authors.initials: JH
authors.lastname: Arendzen
authors.forename: Carel G M
authors.initials: CG
authors.lastname: Meskers
mesh_terms: D000293:Adolescent; D000843:Ankle Joint / Q000503:physiopathology*; D002547:Cerebral Palsy / Q000150:complications* / Q000503:physiopathology*; D002648:Child; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009128:Muscle Spasticity / Q000209:etiology* / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000502:physiology; D055815:Young Adult