Manohar M. Panjabi

Combining orthopedic surgery with biomechanical engineering, this reference and teaching text reviews and analyzes the clinical and scientific data on the mechanics of the human spine. This edition adds new material on vibration (i.e. road driving) and its effect on the spine; anatomy and kinematics

The neutral zone is a region of intervertebral motion around the neutral posture where little resistance is offered by the passive spinal column. Several studies--in vitro cadaveric, in vivo animal, and mathematical simulations--have shown that the neutral zone is a parameter that correlates well with other parameters indicative of instability of the spinal system. It has been found to increase with injury, and possibly with degeneration, to decrease with muscle force increase across the spanned level, and also to decrease with instrumented spinal fixation. In most of these studies, the change in the neutral zone was found to be more sensitive than the change in the corresponding range of motion. The neutral zone appears to be a clinically important measure of spinal stability function. It may increase with injury to the spinal column or with weakness of the muscles, which in turn may result in spinal instability or a low-back problem. It may decrease, and may be brought within the physiological limits, by osteophyte formation, surgical fixation/fusion, and muscle strengthening. The spinal stabilizing system adjusts so that the neutral zone remains within certain physiological thresholds to avoid clinical instability.

The lumbar region is a frequent site of spinal disorders, including low-back pain, and of spinal trauma. Clinical studies have established that abnormal intervertebral motions occur in some patients who have low-back pain. A knowledge of normal spinal movements, with all of the inherent complexities, is needed as a baseline. The present study documents the complete three-dimensional elastic physical properties of each lumbar intervertebral level from the level between the first and second lumbar vertebrae through the level between the fifth lumbar and first sacral vertebrae. Nine whole fresh-frozen human cadaveric lumbar-spine specimens were used. Pure moments of flexion-extension, bilateral axial torque, and bilateral lateral bending were applied, and three-dimensional intervertebral motions were determined with use of stereophotogrammetry. The motions were presented in the form of a set of six load-displacement curves, quantitating intervertebral rotations and translations. The curves were found to be non-linear, and the motions were coupled. The ranges of motion were found to compare favorably with reported values from in vivo studies.

Knowledge of the normal movements of whole lumbar spine and lumbosacral joint is important for evaluating clinical pathologic conditions that may potentially produce unstable situations in these regions. At present there are few studies that report systemic three-dimensional movement analysis of these regions. The purpose of this in vitro study was to quantitatively determine three-dimensional movements of the whole lumbar spine and lumbosacral joint. Ten fresh human cadaveric spine specimens including from L1 to sacrum (six specimens) and ilium (four specimens) were studied. Pure moments of a maximum of 10 N-m were applied incrementally. Parameters of neutral zone, elastic zone, and range of motion for rotations as well as for translations were measured. Neutral zones for flexion-extension, right/left axial torque, and right-left lateral bending were, respectively: 1.6 degrees, 0.9 degrees, and 1.4 degrees (L1-2); 1.0 degrees, 0.8 degrees, and 2.0 degrees (L2-3); 1.4 degrees, 0.7 degrees, and 1.4 degrees (L3-4); 1.8 degrees, 0.4 degrees, and 1.6 degrees (L4-5); 3.0 degrees, 0.4 degrees, and 1.8 degrees (L5-S1). Ranges of motion for flexion, extension, axial torque (one side), and lateral bending (one side) were, respectively: 5.8 degrees, 4.3 degrees, 2.3 degrees, and 4.9 degrees (L1-2); 6.5 degrees, 4.3 degrees, 2.6 degrees, and 7.0 degrees (L2-3); 7.5 degrees, 3.7 degrees, 2.6 degrees, and 5.7 degrees (L3-4); 8.9 degrees, 5.8 degrees, 2.2 degrees, and 5.7 degrees (L4-5); 10.0 degrees, 7.8 degrees, 1.4 degrees, and 5.5 degrees (L5-S1). Neutral zone values were small except for flexion at L5-S1.(ABSTRACT TRUNCATED AT 250 WORDS)