An improved stiffness matrix model of the functional spinal unit for application to an improved understanding of pathological changes.

The stiffness matrix is a useful way to describe the mechanical behaviour of the functional spinal unit, which is defined as the superior and inferior vertebrae, capsules and ligaments. This usefulness is extended by means of the concept of the "balance point". The balance point is the load application point where the coupling coefficients of the stiffness matrix are minimized. Theoretical considerations are used to demonstrate that the stiffness matrix varies with load point location and thus a single stiffness matrix does not fully characterize the motion segment as well as to derive the stiffness matrix at any one specified point from the stiffness matrix at some other specified point. Special characteristics of the stiffness matrix obtained by loading through the "balance point" were shown. Some possible advantages derived from mechanical testing using the "balance point" concept are discussed. This study validates an improved stiffness matrix model that enhances the understanding of pathological changes by setting the gold standard of the behaviour of a normal functional spinal unit.

Feasibility of magnetic resonance imaging (MRI) in obtaining nucleus pulposus (NP) water content with changing postures.

Opportunities to evaluate spinal loading in vivo are limited and a large majority of studies on the mechanical functions of the spine have been in vitro cadaveric studies and/or models based on many assumptions that are difficult to validate. The purpose of this study was to investigate the feasibility of magnetic resonance imaging (MRI) in obtaining nucleus pulposus (NP) water content measurements with changing postures. MRI studies were conducted on 25 healthy males with no history of low back pain (age 20-38). The L1 to S1 intradiscal levels were imaged in supine, sitting and standing postures using an upright 0.6 Tesla magnet, where a set of H2O: D2O7 phantoms were mounted on the back of the subjects. A calibration curve, provided from these phantoms, was applied to the absolute proton density image, yielding a pixel-by-pixel map of the water content of the NP. The NP at all levels showed a highly significant water loss (p<0.001) in sitting and standing postures compared with the supine posture. A trend towards higher levels of water was observed at all levels in the standing posture relative to sitting postures, however statistically significant differences were found only at L4-L5 and L5-S1 levels. This study demonstrates that variations in water content of the NP in different postures are in agreement with those determined from published invasive disc pressure measurements. The result of study demonstrates the feasibility of using MRI to determine the water content of the NP with changing postures and to use these data to evaluate spinal loading in these postures. This measurement method of water content by quantitative MR imaging could become a powerful tool for both clinical and ergonomic applications. The proposed methodology does not require invasive pressure measurement techniques.

Reality about migration of the nucleus pulposus within the intervertebral disc with changing postures.

BACKGROUND: Previous studies reported that, in non-degenerate discs, the nucleus pulposus migrates posteriorly during flexion and anteriorly during extension within the intervertebral disc. However, in these studies the differences between anterior and posterior distances have been regarded as an indicator of nucleus pulposus migration. This study investigated the reality of migration of the nucleus pulposus within the intervertebral disc with changing postures. METHOD: Magnetic resonance images were obtained of the lumbar spines of 25 asymptomatic volunteers in sitting, standing and supine postures. The anterior and posterior height of the intervertebral disc, the anterior -posterior length of the intervertebral disc and nucleus pulposus, and the positions of the anterior and posterior margins of the nucleus were measured from mid-line sagittal images. FINDINGS: Changing postures altered the anterior and posterior height of the disc and three types of morphological changes, including changes in the anterior -posterior lengths of the intervertebral disc and nucleus pulposus, together with the position of the nucleus in the disc were found. The length of the intervertebral disc and nucleus pulposus changed under the variations in spinal loading caused by posture. INTERPRETATION: The results of this study indicated that the apparent nucleus pulposus migration within intervertebral disc is actually deformation of the nucleus pulposus length which depends on posture and the magnitude of the load. In other words, adopting different postures deforms the nucleus pulposus and therefore, changes the position of the nucleus pulposus but there is no apparent nucleus pulposus migration within the intervertebral disc.

In-vitro kinematic testing of porcine cervical spine: a rotational manipulation model.

Although spinal manipulation is widely used in the management of neck and pain, its exact mechanisms and biomechancial effects are not clear. A porcine model was used to study the relative movements of intervertebral joints under spinal rotation maneuvers with different input angular displacements and thrust velocities. Ten porcine spines (C2/4) were fixed and mounted in a material testing machine. Rotational maneuvers with different input angular displacements (0.8, 1.5, 2 and 3 degrees) and thrust velocities (0.1 - 200 degrees/s) were applied to C2 with C4 fixed. Angular displacement induced at the adjacent level was measured and expressed as percentage of the applied angular displacement. For all the tested conditions, angular deformation at the adjacent level could not be avoided when an angular thrust was applied to the target level. The percentage of the angular displacement induced at the adjacent level was found to be dependent on both the input angular displacement and thrust velocity. If rapid thurst of manipulation is used to direct the input energy and motion at the target level with minimal interference at the adjacent levels, the applied angular displacement should not be too large and the thrust velocity should be within a medium velocity range.

Effects of static compression with different loading magnitudes and durations on the intervertebral disc: an in vivo rat-tail study.

STUDY DESIGN: An in vivo rat-tail model was used to study the effects of static compression with different loading magnitudes and durations on the intervertebral disc. OBJECTIVE: To investigate the effects of static compression with different loading magnitudes and durations on the intervertebral disc over a period of time. SUMMARY OF BACKGROUND DATA: A disc degeneration model is essential for studying therapeutic effects on degenerated disc. Static compression can induce degenerative-like changes in the intervertebral disc. However, the consequences of the simulation model over a period of resting have not been clearly documented, which may have confounding effects on the experimental outcome. METHODS: Thirty-five rats were used. Static compressions with different loads (11 or 17 N) and durations (1 hour daily or continuous) were applied to the rat-tail caudal 8-9 disc for 2 weeks, and followed with 3 weeks of rest. The disc height was quantified in vivo on days 4, 18, and 39. The rats were killed and the discs were harvested for morphologic examination on day 39 after the disc height measurement. RESULTS: Significant decrease in disc height was observed after continuous static compression for both 11 and 17 N, and continued during the resting period. The morphologic evaluation of the continuous compressed disc showed a decreased nuclear size, reduced number of nuclear cells, and irregular nuclear shape with inward bulging of disorganized annular collagen lamellas. Daily compression of 1 hour was found to induce a transient increase in disc height, but restored after the 3-week resting period. Favorable morphologic changes, including vacuolated nuclear cells and oval nuclear shape with well-organized annular collagen lamellas, were seen in the rat disc specimens with daily compression of 1 hour. CONCLUSION: Disc degenerative-like changes without recovery were demonstrated in the rat caudal disc after continuous compression. The changes in disc height and disc morphology were found to be dependent on the duration of load application and may have clinical implication.

Postural changes of the dural sac in the lumbar spines of asymptomatic individuals using positional stand-up magnetic resonance imaging.

STUDY DESIGN: Positional magnetic resonance imaging (MRI) study of control subjects. OBJECTIVES: To determine dimensional changes in the lumbar dural sac as a function of posture, and to establish changes between the supine, erect and seated positions. SUMMARY OF BACKGROUND DATA: Studies using computerized tomography and MRI were done to determine the mechanical effects on the lumbar spinal canal in the different positions. There has been no consecutive study, however, in which normal individuals were investigated for positional changes of the dural sac, including true standing position. METHODS: Thirty-two male asymptomatic volunteers were recruited. The examination was performed using a new MRI system. All subjects were examined with sagittal T2 and axial T1-weighted spin-echo images. The subjects were studied in the supine, standing, and sitting positions. The measurements were made using OSIRIS software (Digital Imaging Unit University Hospital of Geneva, Geneva, Switzerland). On axial images, dural sac cross-sectional area and anteroposterior (AP) dural sac diameter were measured at the level of the L3/4, L4/5, and L5/S1 discs. On midsagittal images, AP dural sac diameter and the upper-endplate angles of L1 and S1 were measured. RESULTS: We found a disc degeneration or disc protrusion in 41% (12/29) of the subjects, but there was no obvious compression of the dural sac. Depending on the postures, the mean dural sac cross-sectional area and AP dural sac diameter changed. At all levels, mean dural sac cross-sectional area in the supine position was significantly smaller than in other postures. The dural area decreased most at the L5/S1 level due to positional change from standing to supine. The largest dural area at the L5/S1 level was in sitting extended. AP dural sac diameter on axial and midsagittal images showed a similar tendency. CONCLUSIONS: A significant posture-dependent difference of the dural sac cross-sectional area at the level of intervertebral disc in asymptomatic volunteers has been demonstrated. When the posture changed from supine to standing position, lumbar dural sac volume expanded by the increased pressure of cerebrospinal fluid, and the dural sac cross-sectional area increased. The smallest values were found in the supine position.

The length of the cervical cord: effects of postural changes in healthy volunteers using positional magnetic resonance imaging.

STUDY DESIGN: The length of the cervical cord in healthy volunteers was measured in the supine and erect position using positional magnetic resonance imaging (MRI). OBJECTIVE: To assess the relationship between the length of the cervical cord and cervical posture in healthy volunteers. SUMMARY OF BACKGROUND DATA: A number of detailed descriptions of the normal morphologic features of the cervical cord have been published. However, to our knowledge, there is no report to compare the relationship between the length of the cervical cord and cervical posture in healthy volunteers using positional MRI. METHODS: This study was performed on 20 healthy volunteers using positional MRI. The subjects were studied in the supine and erect positions. The recumbent series consisted of 3 positions: neutral, flexion, and extension. The erect series consisted of 3 positions: neutral, flexion, and extension. On the midsagittal image, the length of the cervical cord from C1 to C7 was measured at the anterior, middle, and posterior line. The angle of the lower-endplate of C2 and C7 was measured. The results were compared with each series. RESULTS: In the recumbent and erect series, the mean length of the cervical cord in flexion was longer than in neutral and extension at the anterior, middle, and posterior line. There were significant differences between the length of the cervical cord in flexion, neutral, and extension. The mean length of the cervical cord in extension was shorter than in neutral and flexion at the anterior, middle, and posterior line. There were significant differences between length of the cervical cord in extension, neutral, and flexion. CONCLUSIONS: We found posture-dependent differences of the length of the cervical cord in the recumbent and erect series. These results may be important when assessing the dynamic factor in cervical spondylotic myelopathy.

Biomechanical aspects of the cervical cord: effects of postural changes in healthy volunteers using positional magnetic resonance imaging.

STUDY DESIGN: The area in cross-sectional view of the cervical cord (ACSCC) at each disc levels was measured in supine and erect positions using positional magnetic resonance imaging (pMRI). OBJECTIVES: To assess the relationship between ACSCC and cervical posture in healthy volunteers using pMRI. SUMMARY OF BACKGROUND DATA: There have been few detailed descriptions of the normal morphologic features of the cervical cord. However, there is no report to compare the relationship between ACSCC and cervical posture in healthy volunteers. METHODS: The study was performed on 20 healthy volunteers. The subjects were studied with pMRI in the supine and erect positions. The recumbent series and the erect series consist of 3 positions each: neutral, flexion and extension. On axial images, ACSCC was measured at the C2/3, C3/4, C4/5, C5/6, and C6/7 disc levels. On midsagittal image, the angle of the lower-endplate of C2 and C7 was measured. The results were compared between each series. RESULTS: In the recumbent and erect series, ACSCC was larger in extension than in neutral and flexion at all levels. There were significant differences between ACSCC in extension, neutral and flexion. ACSCC was smaller in flexion than in neutral and extension at all levels. There were significant differences between ACSCC in flexion, neutral and extension. CONCLUSIONS: We found posture-dependent differences of ACSCC in the recumbent and erect series. These results may be valuable for identifying a dynamic factor in patients with cervical spondylotic myelopathy.

Giovanni Alfonso Borelli--the father of biomechanics.

Giovanni Alfonso Borelli is often described as the father of biomechanics. He was born in Naples in 1608. His De Motu Animalium, published in 1680, extended to biology the rigorous analytical methods developed by Galileo in the field of mechanics. Borelli calculated the forces required for equilibrium in various joints of the human body well before Newton published The Laws of Motion Borelli was the first to understand that the levers of the musculoskeletal system magnify motion rather than force, so that muscles must produce much larger forces than those resisting the motion. Borelli died in Rome on December 31, 1679, but his impressive body of original work helped inspire a great number of future scientists, microscopists, and inventors. The highest honor bestowed by the American Society of Biomechanics is the Giovanni Borelli Award.

Sagittal plane moment arms of the female lumbar region rectus abdominis in an upright neutral torso posture.

BACKGROUND: Prior imaging studies of torso muscle moment arms for use as inputs into biomechanical models have been derived from subjects lying supine. Recent research suggests moment arms of the rectus abdominis are larger when standing versus lying supine. METHODS: Axial MRI images, through and parallel to the intervertebral discs were obtained from five females in a standing upright neutral posture. Digitizing software was utilized to quantify the distance in the sagittal plane between the centroids of the intervertebral disc and the rectus abdominis muscle, and converted to the transverse plane to allow comparisons with studies with subjects in a supine posture. FINDINGS: The mean sagittal plane moment arms in the transverse plane were 9.7, 9.1, 8.5, 8.5 and 9.8 cm at the L(1)/L(2), L(2)/L(3), L(3)/L(4), L(4)/L(5) and L(5)/S(1) intervertebral levels, respectively. Compared with a study on females of a similar age group, the moment arms from this study were larger at each level, increasing from 7.3% larger at L(1)/L(2) to 43.7% larger at L(5)/S(1). INTERPRETATION: Accurate anatomical geometrical representation in biomechanical models is necessary for valid estimates of internal loading. Sagittal plane rectus abdominis moment arms were larger from the upright neutral torso posture in this study compared to studies with subjects lying supine. This suggests the torso internal moment generating capability would be represented differently in biomechanical models that use data from studies where subjects were upright, which is more reflective of the postures biomechanical models are utilized for, than when using anatomical geometry derived from supine postures.

Bernardino Ramazzini: the father of occupational medicine.

Bernardino Ramazzini was born on October 4, 1633, in the small town of Capri located in the duchy of Modula, Italy. He is credited with establishing the field of occupational medicine during his lifetime. His major contributions came after 1682, when Duke Francesco II of Modena assigned him to establish a medical department at the University of Modena. He was installed in the title of professor "Medicinae Theoricae." In 1700, Ramazzini was appointed chair of practical medicine in Padua, Republic of Venice, the premier medical faculty in Italy. In 1700, he wrote the seminal book on occupational diseases and industrial hygiene, De Morbis Artificum Diatriba (Diseases of Workers). Although Ramazzini is perhaps most well known for his work on exposure to toxic materials, he wrote extensively about diseases of the musculoskeletal system. In particular, he warned of the problems of inactivity and poor postures inherent in some jobs.

Spine height and disc height changes as the effect of hyperextension using stadiometry and MRI.

STUDY DESIGN: In vivo biomechanical design using stadiometry and MRI to measure the height change due to (hyper)extension. SUMMARY OF BACKGROUND DATA: Spine height is decreased under loads such as lifting, whole body vibration and sitting. Extension including increased lumbar lordosis reduces the load on the spine. METHODS: The aim was to assess the effects of a supine hyperextended posture as a means of restoring the intervertebral disc height after loading and allowing rehydration of the discs. Ten healthy male subjects were tested. A hyperextension intervention was achieved by the means of an inflatable cushion placed under the lumbar spine. The spine height was measured using a stadiometer and MRI was used to assess disc height changes. RESULTS: The spine height gain after 10 minutes of a supine hyperextended posture differed significantly between individuals but everybody gained height. MRI images of the lumbar spine were used to measure the disc height. All but one subjects gained height during the hyperextension. Images of the spine during hyperextended posture showed increased lumbar curve and an increased anterior height of each disc compared with the dimensions of the disc with the spine in neutral posture. CONCLUSIONS: All subjects lost height during sitting. Both methods demonstrated a recovery of height due to hyperextension. Hyperextension could be considered as a prophylaxis against the height loss in occupational loading.

Spine ergonomics.

Occupational low back pain (LBP) is an immense burden for both industry and medicine. Ergonomic and personal risk factors result in LBP, but psychosocial factors can influence LBP disability. Epidemiologic studies clearly indicate the role of mechanical loads on the etiology of occupational LBP. Occupational exposures such as lifting, particularly in awkward postures; heavy lifting; or repetitive lifting are related to LBP. Fixed postures and prolonged seating are also risk factors. LBP is found in both sedentary occupations and in drivers as well as those involved in manual materials handling. Any prolonged posture will lead to static loading of the soft tissues and cause discomfort. Standing and sitting have specific advantages and disadvantages for mobility, exertion of force, energy consumption, circulatory demands, coordination, and motion control. The seated posture leads to inactivity causing an accumulation of metabolites, accelerating disk degeneration and leading to disk herniation. Driver's postures can also lead to musculoskeletal problems. Workers in a driving environment are often subjected to postural stress leading to back, neck, and upper extremity pain. This exacerbates the problems due to the vibration. Prevention is by far the treatment of choice. Improved muscle function can be preventative. Poor coordination and motor control systems are as important as endurance and strength. Fixed postures should be avoided. Seats offering good lumbar support should be used in the office. A suspension seat should be used in vehicles whenever possible. Heavy and awkward lifting should be avoided and lifting aids should be made available. Workers should report LBP as early as possible and seek medical advice if they think occupational exposure is harming them. The combined effects of the medical community, labor, and management are required to cause some impact on this problem.

Ski Binding Biomechanics.

In brief The binding is the most important factor for causing or preventing skiing injuries. Its function is to hold the ski during normal maneuvers but release it when injury-producing loads are encountered. Binding-related injuries are usually due to improper design, installation, adjustment, and maintenance. Advanced skiers who want to avoid inadvertent release can use two-mode release bindings, but beginners should use multimode bindings. Before skiing, skiers should make sure their bindings release in all directions without causing pain. Equipment should be up to date and functionally tested by a qualified shop mechanic.