* Cerebral palsy (CP) is a motor disorder caused by an injury to the immature brain. Even though the brain damage does not change, children with CP will have progressively weaker, shorter and stiffer muscles that will lead to contractures, bony deformations, difficulty to walk and impaired manual ability. An acquired brain injury (ABI) later during childhood, such as after a stroke or an injury, will result in similar muscle changes, and will therefore also be included in this study. For simplicity, these participants will in this text be referred to as having CP. * The mechanism for the muscle changes is still unknown. Contractures and the risk for the hips to even dislocate is now treated by tendon lengthening, muscle release and bony surgery. During these surgeries muscle biopsies, tendon biopsies and blood samples will be taken and compared with samples from typically developed (TD) children being operated for fractures, knee injuries, and deformities. The specimens will be explored regarding inflammatory markers, signaling for muscle growth, signaling for connective tissue growth and muscle and tendon pathology. In blood samples, plasma and serum, e.g. pro-inflammatory cytokines and the cytoprotective polypeptide humanin will measured, and will be correlated to the amount humanin found in muscle. With this compound information the mechanism of contracture formation may be found, and hopefully give ideas for treatment that will protect muscle and joint health, including prevention of hip dislocation and general health. * The results will be correlated to the degree of contracture of the joint and the severity of the CP (GMFCS I-V, MACS I-V). * By comparing muscle biopsies from the upper limb with muscle biopsies from the lower limb, muscles that are used in more or less automated gait will be compared to muscles in the upper limb that are used more voluntarily and irregularly. * Muscles that flex a joint, often contracted, will be compared with extensor muscles from the same patient. Fascia, aponeurosis and tendon will also be sampled when easily attainable.