摘要:

A technique was developed for measuring the distribution of stress within loaded cadaveric intervertebral discs. A strain-gauged membrane mounted on the side of a 1.3-mm diameter needle was pulled through the disc at constant speed. The orientation of the membrane was changed by rotating the needle, so that profiles of vertical and horizontal components of compressive stress could be obtained. The measurements were reproducible and did not perturb the tissue to any significant extent. Stress profiles varied considerably between discs and were highly dependent on the severity of degenerative changes. They also showed that the mechanical behavior of individual disc tissues was dependent not only on their location, but also on the loading and loading history of the disc. The new insight into internal disc mechanics revealed by stress profilometry may lead to a greater understanding of the mechanisms of disc function and failure.

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The lumbosacral joint is frequently indicated as a source of low-back pain, a cause of which may be abnormal patterns of vertebral motions. The goal of this study was to describe the influence of injury on the coupled motions of the L5-S1 joint in a human cadaveric model. Nine whole lumbosacral spine specimens were studied under the application of flexion, extension, left/right axial torque and right/left lateral bending pure moments. Injuries to the posterior ligaments, intervertebral disc, and articular facets at L5-S1 were produced, and the motion at L5-S1 was determined after each sequential injury. No significant coupled rotations were observed under flexion or extension moments. Under axial torque, lateral rotation at L5-S1 occurred to the same side as the applied torque and increased significantly only after injury to the intervertebral disc. Also coupled to axial torque was flexion rotation in the intact specimen, which became extension rotation after facetectomy. Under lateral bending moments, coupled axial rotation was to the opposite side of the applied moment and increased significantly only after removal of the facets of L5. Based on these results, it was concluded that intervertebral disc most resisted the coupled motion of lateral rotation under the application of axial torque, whereas the articular facets most resisted the coupled axial rotation under the application of lateral bending at the lumbosacral joint. Also, the facets were the structures that produced the flexion rotation of L5 on S1 under axial torque loading.

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

This study describes a technique to measurein vivoloads and the resultant load-contact locations in the facet joint of the canine lumbar spine. The technique is a modification of a previously describedin vitromethod that used calibrated surface strains of the lateral aspect of the right L3 cranial articular process. In the present study, strains were measured during variousin vivostatic and dynamic activities 3 days after strain gage implantation. Thein vivorecording technique and its errors, which depend on the location of the applied facet loads, is described. The results of applying the technique to five dogs gave the following results. Relative resultant contact load locations on the facet tended to be in the central and caudal portion of the facet in extension activities, central and cranial in standing, and cranial and ventral in flexion or right-turning activities. Right-lurning contact locations were ventral and cranial to left-turning locations. Resultant load locations at peak loading during walking were in the central region of the facet, whereas resultant load locations at minimum loading during walking were relatively craniad. This resultant load-contact location during a walk gait cycle typically migrated in an arc with a displacement of 4 mm from minimum to maximum loading. Static tests resulted in a range of facet loads of 0 N in flexion and lying to 185 N for two-legged standing erect, and stand resulted in facet loads of 26 ± 15 N (mean ± standard deviation [SD]). Dynamic tests resulted in peak facet loads ranging from 55 N while walking erect to 170 N for climbing up stairs. Maximum walk facet loads were 107 ± 27 N. The technique is applicable toin vivostudies of a canine facet joint osteoarthritis model and may be useful for establishing an understanding of the biomechanics of low-back pain.

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

To improve our understanding of the dynamic characteristics of the human lumbar spine, both experimental and finite-element methods are required. The experimental methods included measurement of the axial steady state response, resonant frequencies, and damping of seven lumbar motion segments under an upper-body mass of 40 kg. The influence of the presence of posterior elements and different magnitudes of compression preload on the response was also studied. To supplement the measurements, linear and nonlinear, axisymmetric, and threedimensional finite-element models of a L2-L3 disc-vertebra unit were developed to predict the free and forcedvibration responses. The step and harmonic loadings in the axial direction were considered for the forced-vibration analysis. The effect of the presence of the body mass and compression preloads were also examined.The results of experimental and finite-element studies were in good agreement with each other. They indicated that the system resonant frequencies are reduced considerably with the addition of a body mass of 40 kg and increase significantly (P< .005) as the compression preload increases. The compliance at both low and resonant frequencies decreases with increasing compression preload. Under preloads of not more than 680 N, removal of the facet joints tends to decrease slightly the segmental resonant frequencies irrespective of the magnitude of compression preload (P< .1). The finite-element model studies show quasistatic response under harmonic loads with periods much larger than the fundamental period of the segment and under step loads with slow rising times. Under a step load without the body mass, the nucleus pressure varies with both location and time and reaches a maximum of about 2.5 times that under equivalent static load. The addition of a 40-kg mass, in this case, renders a single degree-of-freedom response, with the pressure remaining nearly constant with location inside the nucleus. The stresses and strains throughout the segment in this case increase approximately twofold in comparison with equivalent static values. Partial or complete removal of the disc nucleus considerably decreases the resonant frequency and increases the corresponding segmental response amplitude (ie, compliance). The results indicate that the most vulnerable element under axial vibration loads is the cancellous bone adjacent to the nucleus space. Fatigue fracture of bone as a cumulative trauma and the subsequent loss of nucleus content likely initiates or accelerate the segmental degenerative processes. The annulus fibers do not appear to be vulnerable to rupture when the segment is subjected to pure

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

A retrospective study was conducted on 262 patients with minor idiopathic scoliosis, having supine angles of less than 30° and rib humps of less than 30 mm at the first examination. The initial radiographic measurement of the Cobb supine angle and rib hump height, recorded during a bending test performed on subjects in a sitting position, was correlated with the rate of scoliosis progression. Scoliosis progression was estimated graphically from an angle diagram established by monitoring untreated patients for 7 months to several years, depending on the rate of progression before treatment. More than 95% of the patients with initial supine angles of more than 17° or rib humps greater than 11 mm suffered from progressive scoliosis. The importance of the size of the supine angle, rib-hump height, scoliotic pattern, and state of maturation for the progression rate are analyzed. Knowledge of these parameters can be used to make individual prognoses for approximately 95% of these subjects.

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The height development during childhood and puberty was analyzed in 54 girls with adolescent idiopathic scoliosis by the use of the Infancy Childhood Puberty growth model, which is based on healthy Swedish children. This model adjusts adolescent reference values for height for individual age at pubertal maturation. The scoliotic girls had an above-average height 2 years before the onset of the pubertal growth spurt. However, because they displayed an early pubertal maturation as well as a low pubertal gain in height, their values were only slightly higher than the reference mean values at maturity. The results indicate an increased growth hormone activity in childhood in girls with adolescent idiopathic scoliosis.

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

摘要:

The changes in the sagittal alignment of the lumbar spine were investigated in 28 patients with adolescent idiopathic scoliosis undergoing long posterior spinal fusion to L4 or L5 with contoured Luque rods and segmental sublaminar wiring. The lumbar lordosis over the instrumented levels was preserved, and there was no compensatory hyperlordosis of vertebral segments distal to the fusion. In situations where long posterior spinal fusions are indicated, instrumentation with contoured Luque rods and segmental sublaminar wiring can preserve the normal sagittal alignment of the lumbosacral spine.

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID

ISSN:0362-2436    

出版商:OVID    

年代:1992

数据来源: OVID