Background data: An accurate description of the biomechanical behavior of the spine is crucial for the understanding of degenerative spine disorders and spinal deformities as well as for the development of new treatment strategies. Nowadays, surgeons have limited data on the segmental spinal mobility of their patients and no information concerning their biomechanical stiffness. This is not only a major problem to select the appropriate treatment strategy, but also to standardize the procedure between surgeons and to propose guidelines and recommendations concerning the appropriate treatments. In addition, new strategies, such as artificial discs, interspinous process spacers, non-fusion techniques and target-oriented conservative approaches aim at preserving spine function. However, little is known about the complex functional behavior and stiffness of the normal and degenerated spinal segment under physiological loading conditions, because the existing studies focused solely on the spinal kinematics without considering mechanical loads. Objective: The aim of this project is to determine the mechanical properties of the spine based on pre-operative tests. The main challenge will be to develop an appropriate measurement technique able to provide the surgeons with an observer independent and reproducible three-dimensional assessment of the spine flexibility suitable for daily clinical use. Previous results: During the past years, the applicants developed a method for in-vivo measurements of the segmental spine stiffness in complex pediatric deformities. This information, acquired intra-operatively, requires significant efforts from the OR staff, additional operation time, which is not suitable for use in the clinical routine, but provides gold standard direct biomechanical data. Methods: The method will be based on standing elevation of the patient. Advanced image processing techniques will be used to extract the 3D position and orientation of the patients? vertebras from planar pre-operative images. Numerical tools will be used to model spine biomechanical behavior and identify the local stiffness characteristics. The segmental spine flexibility obtained will be compared to the intra-operative stiffness measurements obtained on the same patients with the previously developed method. Therefore, developments conducted in this project will primarily focus on the stiffness assessment for pediatric deformities and will be secondarily applied to degenerative spine pathologies. Significance: The first outcome of the project is a standardized test setup for the clinician to assess spinal flexibility in an accurate and reproducible manner. Such an approach is mandatory to compare surgical techniques across surgeons working at different institutions. Furthermore, with the increasing database of patients being measured, precise guidelines could be defined for each surgical treatment. The method will also serve stiffness-adapted implants or surgical strategies and could be used to work out non-surgical approaches, standards and ?safe zones? for daily clinical use. Additionally, this information is mandatory for the development of planning solutions that consider patient-specific biomechanical information. Such tools will become increasingly important in the future due to the ever-increasing complexity of the surgical instrumentation and procedures.