The main purpose of this study is the evaluation of the efficacy of zoledronic acid on bone density in children with osteoporosis caused by multiple disabilities.

Secondary purposes are:

1. Description of child population with osteoporosis in the context of motor impairment in Lorraine region
2. Description of osteoporosis stage (level of bone mineralization and clinical consequences) in children with multiple disabilities
3. Description of current osteoporosis preventive care
4. Description of risk factors associated to bone status (drugs)
5. Evaluation of zoledronic acid treatment on fracture numbers
6. Evaluation of zoledronic acid on phosphocalcic profile
7. Description of side effects of zoledronic acid in this indication
8. Description of treatment effects in the sub-population of children with Rett syndrome.

Inclusion Criteria:

• Non refusal of parents of participation of their child to the study
• Patients followed for multiple disabilities
• Osteoporosis: lumbar osteodensitometry z-score <-2.5 SD associated or not to pathologic fracture

Exclusion Criteria:

• Bone pathology due to other genetic reasons (rickets, osteogenesis imperfecta)
• Absence of multiple disabilities

All children followed for osteoporosis associated to multiple disabilities, treated with zoledronic acid, followed at pediatric department of Nancy hospital, between 01/01/2012 and 11/01/2016.