Instrumented three dimensional gait analysis (3DGA) permits to record spatial, temporal, kinetics, kinematics and electromyographic (EMG) parameters in order to understand gait impairment in children and teenagers with cerebral palsy (CP). Nowadays, single-event multilevel surgery in subjects with CP cannot be performed without 3DGA. However, interpretation of multiple and interdependent data remains complex for the clinician. To address this issue, gait statistical index have been developed to give a single measure of the quality of the gait pattern. Among actual index, the Gait Profile Score (GPS), developed by Baker et al (2009), measure the deviation of kinematics parameters from a controlled dataset. The GPS can be divided in nine Gait Variable Score (GVS), corresponding to major lower limb joints: the MAP (Movement Analysis Profile). Many studies have reported the interest of the GPS to analysis gait of subjects with CP: good inter-session reliability, predictor of postoperative kinematic improvement, minimal clinical threshold calculated at 1.6°, significant relationship with clinical data (joint contractures), and sensibility to change after a single-event multilevel surgery.

Inclusion Criteria:

• Etiology of cerebral palsy
• Unilateral, bilateral, triplegic or quadriplegic forms of cerebral palsy.
• 6 to 18 years old
• GMFCS (Gross Motor Function Classification System) I to III
• Instrumented gait analysis of the laboratory of St-Etienne
• Absence of botulinum toxin injection or serial casting in the three months after a first instrumented gait analysis.

Exclusion Criteria:

• Etiology others than cerebral palsy as defined classically (ex: ischemic infarcts in a child older than two years).
• Previous surgery in lower-limb.

Children and adolescents with cerebral palsy treated at the Saint-Etienne University Hospital will be included.