Methods: Baseline muscle biopsies: Percutaneous biopsies are taken just before the first intramuscular botulinum toxin injection is given. The doses and the intervals for the botulinum toxin treatment will follow clinical routines. Biopsies 4-6 months, 12 months and 24 months after the first botulinum toxin injection: The exact same procedure as above will be performed, but the biopsies will be taken 2 cm distant, medial or lateral, from previous biopsy sites * Significance:. More knowledge is warranted regarding the actual molecular process in the muscle leading to a contracture, and its relation to the constant communication with the injured central nervous system. This study will give answers that could result in new, early prophylactic treatment of joint movement restrictions and motor impairment in children with CP.