Functional spinal unit
Encyclopedia
A functional spinal unit (FSU) is the smallest physiological motion unit of the spine
to exhibit biomechanical
characteristics similar to those of the entire spine.
A FSU consists of two adjacent vertebrae, the intervertebral disc
and all adjoining ligaments between them and excludes other connecting tissues such as muscles. The three-joint complex that results is sometimes referred to as the 'articular triad'. Another term for the FSU is spinal motion segment.
In vitro
studies of isolated or multiple FSU's are often used to measure biomechanical
properties of the spine. The typical load-displacement behavior of a cadaveric FSU specimen is nonlinear. Within the total range of passive motion of any FSU, the typical load-displacement curve consists of 2 regions or 'zones' that exhibit very different biomechanical behavior. In the vicinity of the resting neutral position of the FSU, this load-displacement behavior is highly flexible. This is the region known as the 'neutral zone', which may be defined as the motion region of the joint where the passive osteoligamentous stability
mechanisms exert little or no influence. During passive physiological movement of the FSU, motion occurs in this region against minimal internal resistance. It is a region in which a small load causes a relatively large displacement.The 'elastic zone' is the remaining region of FSU motion that continues from the end of the neutral zone to the point of maximum resistance (provided by the passive osteoligamentous stability mechanism), thus limiting the range of motion.
Spinal cord
The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system...
to exhibit biomechanical
Biomechanics
Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells. Perhaps one of the best definitions was provided by Herbert Hatze in 1974: "Biomechanics is the study of the structure and function of biological systems by means of...
characteristics similar to those of the entire spine.
A FSU consists of two adjacent vertebrae, the intervertebral disc
Intervertebral disc
Intervertebral discs lie between adjacent vertebrae in the spine. Each disc forms a cartilaginous joint to allow slight movement of the vertebrae, and acts as a ligament to hold the vertebrae together.-Structure:...
and all adjoining ligaments between them and excludes other connecting tissues such as muscles. The three-joint complex that results is sometimes referred to as the 'articular triad'. Another term for the FSU is spinal motion segment.
In vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...
studies of isolated or multiple FSU's are often used to measure biomechanical
Biomechanics
Biomechanics is the application of mechanical principles to biological systems, such as humans, animals, plants, organs, and cells. Perhaps one of the best definitions was provided by Herbert Hatze in 1974: "Biomechanics is the study of the structure and function of biological systems by means of...
properties of the spine. The typical load-displacement behavior of a cadaveric FSU specimen is nonlinear. Within the total range of passive motion of any FSU, the typical load-displacement curve consists of 2 regions or 'zones' that exhibit very different biomechanical behavior. In the vicinity of the resting neutral position of the FSU, this load-displacement behavior is highly flexible. This is the region known as the 'neutral zone', which may be defined as the motion region of the joint where the passive osteoligamentous stability
Joint stability
Joint stability refers to the resistance offered by various musculoskeletal tissues that surround a skeletal joint. Several subsystems ensure the stability of a joint. These are the passive, active and neural subsystems. The opposite of stability is instability...
mechanisms exert little or no influence. During passive physiological movement of the FSU, motion occurs in this region against minimal internal resistance. It is a region in which a small load causes a relatively large displacement.The 'elastic zone' is the remaining region of FSU motion that continues from the end of the neutral zone to the point of maximum resistance (provided by the passive osteoligamentous stability mechanism), thus limiting the range of motion.