In Vivo Flexibility Characteristics of Cervical Spine in Young Healthy Subjects during Sagittal and Coronal Neck Movements

INTRODUCTION An unstable spine is clinically defined as the state of excessive spinal motion beyond the normal physiological limits. Muscles play an important role to provide the spinal movement and to maintain the spinal stability by increasing the bending stiffness at the same time. The issues of spinal stability controlled by the active muscular system are complicated since the numbers of muscles surrounding the spinal segments are larger than the degrees of freedom of the musculoskeletal system. Flexibility testing of in vitro studies has shown the feasibility to investigate the effects of muscle recruitments on the mechanical stability of the spine [1]. However, the “load-displacement” property of the spine would not reveal the active roles of the muscles in controlling the spinal stability under different environments. The purpose of this study is to estimate the in vivo flexibility characteristics of the human cervical spine to quantify the spinal stability during neck movements.