Knee jerk responses in infants at high risk for cerebral palsy: an observational EMG study.
Following our clinical observation of tonic responses in response to the knee jerk in infants at very high risk for cerebral palsy (VHR infants), we systematically studied tonic responses, clonus, and reflex irradiation. We questioned (i) whether these responses occurred more often in VHR infants than in typically developing (TD) infants, and (ii) whether they were associated with abnormal general movement quality.



Twenty-four VHR and 26 TD infants were assessed around 3 mo corrected age. Surface electromyograms of leg, trunk, neck, and arm muscles were recorded while eliciting the knee jerk. All assessments were video-recorded.



VHR infants more often than TD infants showed tonic responses in the ipsilateral quadriceps and hamstring (Mann-Whitney U; P = 0.0005 and P = 0.0009), clonus (Chi-square; P = 0.0005) and phasic responses in the contralateral quadriceps and hamstring (Mann-Whitney U; P = 0.002 and P = 0.0003, respectively). Widespread reflex irradiation occurred in VHR and TD infants. Definitely abnormal general movements and stiff movements were associated with tonic responses (Mann-Whitney U; P = 0.0005, P = 0.007, respectively) and clonus (Mann-Whitney U; P = 0.003 and P = 0.0005) in the ipsilateral quadriceps.



Similar to clonus, tonic responses may be regarded as a marker of a loss of supraspinal control. Reflex irradiation primarily is a neurodevelopmental phenomenon of early ontogeny.
Department of Pediatrics, Division of Developmental Neurology, University of Groningen, University Medical Center, Groningen, The Netherlands.|Department of Neurology, Radboud University Medical Center, Nijmegen, The Netherlands.
Elisa G
EG
Hamer
Department of Pediatrics, Division of Developmental Neurology, University of Groningen, University Medical Center, Groningen, The Netherlands.
Linze J
LJ
Dijkstra
Department of Pediatrics, Division of Developmental Neurology, University of Groningen, University Medical Center, Groningen, The Netherlands.
Siebrigje J
SJ
Hooijsma
Department of Neuroscience, University of Groningen, University Medical Center, Groningen, The Netherlands.
Inge
I
Zijdewind
Department of Pediatrics, Division of Developmental Neurology, University of Groningen, University Medical Center, Groningen, The Netherlands.
Mijna
M
Hadders-Algra
D002547:Cerebral Palsy / Q000175:diagnosis / Q000503:physiopathology*; D002657:Child Development; D004576:Electromyography; D005260:Female; D005865:Gestational Age; D000070633:Hamstring Muscles / Q000503:physiopathology; D006801:Humans; D007223:Infant; D007717:Knee / Q000502:physiology*; D008297:Male; D009068:Movement; D009129:Muscle Tonus; D052097:Quadriceps Muscle / Q000503:physiopathology; D016032:Randomized Controlled Trials as Topic; D012018:Reflex; D012306:Risk; D014741:Video Recording