Changes in lumbar disc angles of Chinese subjects from upright to flexion

Ex vivo computed tomography evaluation of loading position on morphometry of the caudal cervical intervertebral disk spaces of dogs

OBJECTIVE To provide an objective, quantitative morphometric description of the caudal cervical intervertebral disk (IVD) spaces of dogs. SAMPLE Vertebral specimens consisting of C4 through C7 from 5 medium-sized dogs. PROCEDURES CT images were obtained with the specimens positioned in neutral, flexion, extension, and lateral bending positions. Size and shape of the cranial and caudal end plates, angle between the end plates (IVD wedge angle), and craniocaudal distance (IVD width) between end plates for the 4 loading positions were measured and compared for the 3 segments (C4-5, C5-6, and C6-7). RESULTS End plate size and shape, IVD wedge angle, and IVD width were not significantly different among the 3 segments. Caudal cervical end plates were consistently larger than cranial cervical end plates. The IVD wedge angle ranged from -4.8° to 15.2°. Flexion induced a reduction in IVD width in the ventral portion of the IVD, whereas extension induced a decrease in width in the dorsal portion of the IVD. Central IVD width remained unchanged among the loading positions. CONCLUSIONS AND CLINICAL RELEVANCE Unique morphometric and dynamic characteristics of the caudal cervical IVD space of dogs were detected. These findings may help investigators when designing IVD prostheses for dogs with cervical spondylomyelopathy.

Requirements for an artificial intervertebral disc

Intervertebral disc degeneration is an important social and economic problem. Presently available artificial intervertebral discs (AIDs) are insufficient and the main surgical intervention is still spinal fusion. The objective of the present study is to present a list of requirements for the development of an AID which could replace the human lumbar intervertebral disc and restore its function. The list addresses geometry, stiffness, range of motion, strength, facet joint function, center of rotation, fixation, failsafety and implantation technique. Date are obtained from the literature, quantified where possible and checked for consistency. Existing AIDs are evaluated according to the presented list of requirements. Endplate size is a weak point in existing AIDs. These should be large and fit vertebral bodies to prevent migration. Disc height and wedge angle should be restored, unless this would overstretch ligaments. Finally, stiffness and range of motion in all directions should equal those of the healthy disc, except for the axial rotation to relieve the facet joints.

Disproportion of end plates and the lumbar intervertebral disc herniation

BACKGROUND CONTEXT

It is suggested that the shape of the vertebral end plates may play a role in the development of abnormalities in the intervertebral disc. On midsagittal magnetic resonance images of the spine in patients with lumbar intervertebral disc herniation, a notable disproportion frequently exists between the end plates of two vertebrae to which the disc is attached. There is apparently no study in the literature examining possible association of this disproportion with development of disc herniation.

PURPOSE

To determine whether a disproportion between two neighboring vertebral end plates is associated with the presence of disc herniation at the same level.

STUDY DESIGN

Case-control study.

PATIENT SAMPLE

Two hundred fifty patients with primary lumbar disc herniation in the case group and 250 age- and sex-matched normal individuals in the control group.

OUTCOME MEASURES

On midsagittal sections, the difference of anteroposterior diameter of upper and lower end plates neighboring a herniated (in the case group) or normal (in the control group) intervertebral disc was calculated and expressed as "difference of end plates" or "DEP."

METHODS

Subjects with previous spinal surgery, spondylolisthesis, or a significant vertebral deformity were excluded. For the main outcome variable, DEP was calculated at the level with herniated intervertebral disc in the case group, and the mean value was compared with mean DEP at the same level in the controls.

RESULTS

Mean DEP was significantly higher in the case group at both L4-L5 (2.45±0.28 vs. 2.08±0.27 mm, p=.02) and L5-S1 (3.32±0.18 vs. 2.51±0.13 mm, p<.001) levels. Similar differences were only marginally insignificant at L2-L3 (1.96±0.14 mm in the cases vs. 1.33±0.15 mm in the controls, p=.07) and L3-L4 (2.17±0.11 mm in the cases vs. 1.55±0.09 mm in the controls, p=.06) levels, with no significant difference at L1-L2 level (1.81±0.10 mm in the cases vs. 1.28±0.09 mm in the controls, p=.12). Each 1 mm increase of DEP at L4-L5 and L5-S1 levels was associated with 53% and 56% elevation in disc herniation risk at the corresponding levels, respectively.

CONCLUSIONS

Difference of end plate is a significant and probably independent risk factor for lumbar disc herniation.

Estimation of trunk muscle forces using the finite element method and in vivo loads measured by telemeterized internal spinal fixation devices

Direct quantitative measurement of muscle forces is not possible. Forces in the trunk muscles were estimated for standing and flexion of the upper body using three-dimensional, nonlinear finite element models of the lumbar spine with and without an internal spinal fixation device. Muscle forces assumed were two pairs dorsally and one ventrally, each representing several muscles. Muscle forces in the model with internal fixators were varied in discrete steps until the implant loads calculated closely corresponded to those measured in a patient with an instrumented implant. The calculated angles between adjacent lumbar vertebrae were compared with corresponding values measured on X-ray films of a patient as well as with literature values and served as a second criterion for predicting muscle forces. For the model without an implant, the muscle forces of the first model were slightly varied until the lumbar spine shape and the intradiscal pressure were physiological. The abdomen was shown to have a considerable supporting function for flexion.

Geometric measurements of the lumbar spine in Chinese men during trunk flexion

STUDY DESIGN

An analysis of the geometric data of the lumbar spine in Chinese men. Lateral radiographs were obtained of 16 men in the upright position to a trunk flexion of 90 degrees in 30 degrees increments.

OBJECTIVES

To establish reference data concerning the geometry of the lumbar spine for various degrees of trunk flexion.

SUMMARY OF BACKGROUND DATA

In previous studies, the morphometry and alignment of the lumbar spine have been investigated. Reports of systematic analyses of the lumbar spine in trunk flexion have lacked adequate radiographic data. Moreover, few studies have focused on measuring lumbar spine geometric data in Chinese individuals.

METHODS

A total of 67 landmarks on each radiograph were identified. They were marked by investigators and digitized using a HyperSpace digitizing system (V.17: Mira Imaging Inc., Salt Lake City, UT). The geometric configuration of the vertebrae and discs then was derived from the digitized points.

RESULTS

The dimensions of the vertebrae and disc on the lumbar spine obtained in this study were similar to those of previous studies. The motion of the lumbosacral spine had the greatest contribution in trunk flexion, approximately 90% (i.e., rotating at the rate of 9 degrees for each 10 degrees of trunk flexion) when the trunk was flexed from 30 degrees to 60 degrees. After that, the hips were dominant in accomplishing the trunk flexion from 60 degrees to horizontal. This motion patterns may be useful for making clinical diagnoses of lumbar function in Chinese men.

CONCLUSIONS

No obvious interracial differences were found in the geometric data found in this study, which suggests that morphometric data obtained from Caucasian individuals may be applied to Chinese patients for clinical purposes.

Morphology of the lumbar vertebral endplates

STUDY DESIGN

The dimensions and shapes of vertebral body endplates of inferior L4, inferior and superior L5, and superior S1 were analyzed. Computed tomographic scans parallel to each endplate were used to develop a standardized geometric model of the boundaries of each vertebral body.

OBJECTIVES

To provide a detailed analytic and geometric model of the vertebral endplates from the inferior surface of L4 to the superior surface of S1.

SUMMARY OF BACKGROUND DATA

Although measurements of the sagittal and maximum transverse diameters of the vertebral bodies have been well documented, no study offers a complete geometric description of the shape of the endplates. Also, information acquired using the techniques of previous published reports may not provide measurements as accurate as those of the current investigation.

METHODS

Twenty-five men and 21 women were studied. Computed tomographic scans of the endplates were digitized. The data were interpolated, and multivariate regression equations were derived to devise a standardized model. Measurements were taken, and the data were curve fitted to give best-fit equations for the standardized models.

RESULTS

The endplates resembled a cardioid at the inferior L4 level and became more elliptical toward the superior S1 level. The sagittal and transverse diameters of the endplates of inferior L4, superior and inferior L5, and superior S1 are provided and compared with those reported in previous studies.

CONCLUSION

Although the female endplates are smaller than their male counterparts, the overall shapes are similar.

A non-invasive protocol for the determination of lumbosacral vertebral angle

OBJECTIVE: The purpose of this study was to develop a non-invasive method to predict the lumbosacral and vertebral angles. DESIGN: The candidate predicting variables were the externally measured marker angle, pelvic angle, and lumbosacral angle. BACKGROUND: Several investigators used surface rigid markers to represent the angles of lumbosacral vertebrae. Previous studies show a high level of validity for measuring the lumbar curvature during stance and for obtaining the vertebral angle in the lumbar region. However, our review of literature failed to find a data transformation model illustrating the lumbosacral vertebral angle using external measurements as predictors. METHODS: Sixteen healthy male subjects participated in the radiographic and videographic measurements. Data of 12 of the 16 subjects were used for model development, and data of the other four subjects were used for model validation. RESULTS: The results showed significant differences between the directly measured vertebral angle from the X-ray film and the externally measured angles of the surface markers at the L(5) and S(1) levels (P<0.05). Linear regression models for calculating vertebral angles were developed with R(2) values of 0.97, 0.98, 0.91, and 0.92 for the vertebral levels of L(1), L(3), L(5), and S(1) respectively. The validation result showed that there was no significant difference between the calculated and the X-ray data. CONCLUSIONS: The protocol of using the skin-surface rigid markers and the predicting models was justified in the study to provide a simple and valid non-invasive method for the recording of the internal vertebral angle in the sagittal plane. RELEVANCE: Measurements of lumbosacral vertebral angle are important in assessing the stresses acting on the low back in lifting. The results of this study provided a simple and valid non-invasive method by rigid markers for the prediction of internal vertebral angles under various trunk positions.

A non-invasive protocol for the determination of lumbar spine mobility

OBJECTIVE: This article presents a non-invasive protocol for the determination of lumbar spine mobility and compares intersegmental lumbar spinal mobility data from 45 subjects using both radiographic (invasive) and videographic (non-invasive) techniques. DESIGN: Non-linear mathematical models were developed to transfer skin marker coordinates into corresponding vertebral body positions. BACKGROUND: To relate skin surface motion with that of the underlying vertebrae and to enhance the reliability of using the non-invasive technique relied on a model of transformation. METHODS: This set of models was developed by taking the L(4) skinfold, the L(1)-S(1) skin distraction, and the non-linear difference between the lumbar spinal profile and the skin profile into consideration. Based on the digitized and model transformed data, the intersegmental joint angles (ISA) and intersegmental joint mobilities (ISM) were calculated and compared. RESULTS: In this study the non-invasive and invasive coordinate differences ranged from 0.485 to 1.099 cm; the mean ISA differences ranged from 0.29 to 2.08 degrees the mean ISM differences ranged from 0.62 to 1.88 degrees. CONCLUSIONS: With these small differences, the quality of the non-invasive protocol and the application of the transformation model were justified sufficient.

Predictive model of intersegmental mobility of lumbar spine in the sagittal plane from skin markers

This article describes a sagittal motion model that transforms skin marker coordinates into corresponding vertebral body coordinates. Coordinate data were obtained from 45 subjects with radiopaque skin markers over the vertebral spinous processes. Data of 30 subjects were used for model development while data of the other Fifteen subjects were used for model validation. The subjects were subjected to lateral spinal radiographs in positions of neutral, flexion, and extension. The model was developed by taking the non-linear difference between lumbar spinal profile and skin profile, the L(4) skin-fold, and the difference of L(1)-S(1) skin distraction into consideration. Regression analysis shows high coefficients of determination (range, 62.43-99.86%; mean, 86.41%) in comparing the estimated position data with the actual data in all vertebral body positions. Based on the estimated coordinates, both the intersegmental joint angles and intersegmental joint mobilities were calculated. The result of this study using the non-invasive protocol and the transformation matrices demonstrated that the intersegmental sagittal motion of lumbar spine can be obtained with error ranged from 0.05 to 0.56 degrees.