Functional spinal unit
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2008-05-28T15:36:17Z
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A '''functional spinal unit''' (FSU) is the smallest physiological motion unit of the [[Spinal cord|spine]] to exhibit [[biomechanics|biomechanical]] characteristics similar to those of the entire spine.<ref>{{cite book | author = White AA, Panjabi MM. | year = 1990 | title = Clinical biomechanics of the spine. Philadelphia, [[J. B. Lippincott Company]].}}</ref>
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 [[biomechanics|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 [[joint stability|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.<ref>{{cite journal | author = Panjabi MM. | title = The stabilizing system of the spine. Part II. Neutral zone and instability hypothesis. | journal = J Spinal Disord | volume = 5 | issue = 4 | pages = 390–7 | year = 1992}}</ref>
==References==
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[[Category:Physiology]]