Changes in posterior disc bulging and intervertebral foraminal size associated with flexion-extension movement: a comparison between L4-5 and L5-S1 levels in normal subjects

Differences in MRI measurements of lateral recesses and foramina in degenerative lumbar segments in upright versus decubitus symptomatic patients

OBJECTIVE

To evaluate differences in measurements of the lateral recesses and foramina in degenerative lumbar segments on MR images in symptomatic patients obtained with the patient standing versus lying down and to analyze the relationship between possible differences and patients' symptoms.

MATERIAL AND METHODS

We studied 207 disc levels in 175 patients aged between 17 and 75 years (median: 47 years) with low back pain. All patients underwent MRI in the decubitus position with their legs extended, followed by MRI in the standing position. We calculated the difference in the measurements of the lateral recesses (in mm) and in the foramina (area in mm2 and smallest diameter in mm) obtained in the two positions. To eliminate the effects of possible errors in measurement, we selected cases in which the difference between the measurements obtained in the two positions was ≥10%; we used Student's t-tests for paired samples to analyze the entire group and subgroups of patients according to age, sex, grade of disc degeneration, and postural predominance of symptoms.

RESULTS

Overall, the measurements of the spaces were lower when patients were standing. For the lateral recesses, we observed differences ≥10% in 68 (33%) right recesses and in 65 (31.5%) left recesses; when patients were standing, decreases were much more common than increases (26% vs. 7%, respectively, on the right side and 24% vs. 7.5%, respectively, on the left side; p < 0.005). For the foramina, decreases in both the area and in the smallest diameter were also more common than increases when patients were standing: on the right side, areas decreased in 23% and increased in 4%, and smallest diameters decreased in 20% and increased 6%; on the left side, areas decreased in 24% and increased in 4%, and smallest diameters decreased in 17% and increased in 8% (p < 0.005). Considering the group of patients in whom the postural predominance of symptoms was known, we found significant differences in patients whose symptoms occurred predominantly or exclusively when standing, but not in the small group of patients whose symptoms occurred predominantly while lying. We found no differences between sexes in the changes in measurements of the recesses or foramina with standing. The differences between the measurements obtained in different positions were significant in patients aged >40 years, but not in younger groups of patients. Differences in relation to the grade of disc degeneration were significant only in intermediate grades (groups 3-6 in the Griffith classification system).

CONCLUSION

MRI obtained with patients standing can show decreases in the lateral recesses and foramina related to the predominance of symptoms while standing, especially in patients aged >40 years with Griffith disc degeneration grade 3-6, thus providing additional information in the study of patients who have low back pain when standing in whom the findings on conventional studies are inconclusive or discrepant with their symptoms. Further studies are necessary to help better define the value of upright MRI studies for degenerative lumbar disease.

Differences in MRI measurements of lateral recesses and foramina in degenerative lumbar segments in upright versus decubitus symptomatic patients

OBJECTIVE

To evaluate differences in measurements of the lateral recesses and foramina in degenerative lumbar segments on MR images in symptomatic patients obtained with the patient standing versus lying down and to analyze the relationship between possible differences and patients' symptoms.

MATERIAL AND METHODS

We studied 207 disc levels in 175 patients aged between 17 and 75 years (median: 47 years) with low back pain. All patients underwent MRI in the decubitus position with their legs extended, followed by MRI in the standing position. We calculated the difference in the measurements of the lateral recesses (in mm) and in the foramina (area in mm2 and smallest diameter in mm) obtained in the two positions. To eliminate the effects of possible errors in measurement, we selected cases in which the difference between the measurements obtained in the two positions was ≥10%; we used Student's t-tests for paired samples to analyze the entire group and subgroups of patients according to age, sex, grade of disc degeneration, and postural predominance of symptoms.

RESULTS

Overall, the measurements of the spaces were lower when patients were standing. For the lateral recesses, we observed differences ≥10% in 68 (33%) right recesses and in 65 (31.5%) left recesses; when patients were standing, decreases were much more common than increases (26% vs. 7%, respectively, on the right side and 24% vs. 7.5%, respectively, on the left side; p<0.005). For the foramina, decreases in both the area and in the smallest diameter were also more common than increases when patients were standing: on the right side, areas decreased in 23% and increased in 4%, and smallest diameters decreased in 20% and increased 6%; on the left side, areas decreased in 24% and increased in 4%, and smallest diameters decreased in 17% and increased in 8% (p<0.005). Considering the group of patients in whom the postural predominance of symptoms was known, we found significant differences in patients whose symptoms occurred predominantly or exclusively when standing, but not in the small group of patients whose symptoms occurred predominantly while lying. We found no differences between sexes in the changes in measurements of the recesses or foramina with standing. The differences between the measurements obtained in different positions were significant in patients aged>40 years, but not in younger groups of patients. Differences in relation to the grade of disc degeneration were significant only in intermediate grades (groups 3-6 in the Griffith classification system).

CONCLUSION

MRI obtained with patients standing can show decreases in the lateral recesses and foramina related to the predominance of symptoms while standing, especially in patients aged>40 years with Griffith disc degeneration grade 3 to 6, thus providing additional information in the study of patients who have low back pain when standing in whom the findings on conventional studies are inconclusive or discrepant with their symptoms. Further studies are necessary to help better define the value of upright MRI studies for degenerative lumbar disease.

In vivo 3D tomography of the lumbar spine using a twin robotic X-ray system: quantitative and qualitative evaluation of the lumbar neural foramina in supine and upright position

OBJECTIVES

Supine lumbar spine examinations underestimate body weight effects on neuroforaminal size. Therefore, our purpose was to evaluate size changes of the lumbar neuroforamina using supine and upright 3D tomography and to initially assess image quality compared with computed tomography (CT).

METHODS

The lumbar spines were prospectively scanned in 48 patients in upright (3D tomographic twin robotic X-ray) and supine (30 with 3D tomography, 18 with CT) position. Cross-sectional area (CSA), cranio-caudal (CC), and ventro-dorsal (VD) diameters of foramina were measured by two readers and additionally graded in relation to the intervertebral disc height. Visibility of bone/soft tissue structures and image quality were assessed independently on a 5-point Likert scale for the 18 patients scanned with both modalities. Descriptive statistics, Wilcoxon's signed-rank test (p < 0.05), and interreader reliability were calculated.

RESULTS

Neuroforaminal size significantly decreased at all levels for both readers from the supine (normal intervertebral disc height; CSA 1.25 ± 0.32 cm²; CC 1.84 ± 0.24 cm²; VD 0.88 ± 0.16 cm²) to upright position (CSA 1.12 ± 0.34 cm²; CC 1.78 ± 0.24 cm²; VD 0.83 ± 0.16 cm²; each p < 0.001). Decrease in intervertebral disc height correlated with decrease in foraminal size (supine: CSA 0.88 ± 0.34 cm²; CC 1.39 ± 0.33 cm²; VD 0.87 ± 0.26 cm²; upright: CSA 0.83 ± 0.37 cm², p = 0.010; CC 1.32 ± 0.33 cm², p = 0.015; VD 0.80 ± 0.21 cm², p = 0.021). Interreader reliability for area was fair to excellent (0.51-0.89) with a wide range for cranio-caudal (0.32-0.74) and ventro-dorsal (0.03-0.70) distances. Image quality was superior for CT compared with that for 3D tomography (p < 0.001; κ, CT = 0.66-0.92/3D tomography = 0.51-1.00).

CONCLUSIONS

The size of the lumbar foramina is smaller in the upright weight-bearing position compared with that in the supine position. Image quality, especially nerve root delineation, is inferior using 3D tomography compared to CT.

KEY POINTS

• Weight-bearing examination demonstrates a decrease of the neuroforaminal size. • Patients with higher decrease in intervertebral disc showed a narrower foraminal size. • Image quality is superior with CT compared to 3D tomographic twin robotic X-ray at the lumbar spine.

Occlusion of the lumbar spine canal during high-rate axial compression

BACKGROUND CONTEXT

While burst fracture is a well-known cause of spinal canal occlusion with dynamic, axial spinal compression, it is unclear how such loading mechanisms might cause occlusion without fracture.

PURPOSE

To determine how spinal canal occlusion during dynamic compression of the lumbar spine is differentially caused by fracture or mechanisms without fracture and to examine the influence of spinal level on occlusion.

STUDY DESIGN

A cadaveric biomechanical study.

METHODS

Twenty sets of three-vertebrae specimens from all spinal levels between T12 and S1 were subjected to dynamic compression using a hydraulic loading apparatus up to a peak velocity between 0.1 and 0.9 m/s. The presence of canal occlusion was measured optically with a high-speed camera. This was repeated with incremental increases of 4% compressive strain until a vertebral fracture was detected using acoustic emission measurements and computed tomographic imaging.

RESULTS

For axial compression without fracture, the peak occlusion (O_max) was 29.9±10.0%, which was deduced to be the result of posterior bulging of the intervertebral disc into the spinal canal. O_max correlated significantly with lumbar spinal level (p<.001), the compressive displacement (p<.001) and the cross-sectional area of the vertebra (p=.031).

CONCLUSIONS

Spinal canal occlusion observed without vertebral fracture involves intervertebral disc bulging. The lower lumbar spine tended to be more severely occluded than more proximal levels.

CLINICAL SIGNIFICANCE

Clinically, intermittent canal occlusion from disc bulging during dynamic compression may not show any radiographic features. The lower lumbar spine should be a focus of injury prevention intervention in cases of high-rate axial compression.

Dimensional Changes of Lumbar Intervertebral Foramen in Direct Anterior Approach-Specific Hyperextension Supine Position

Objective

To investigate the changes in the lumbar intervertebral foramen (LIVF) dimensions from neutral supine to direct anterior approach (DAA)‐specific hyperextension supine position through a standardized three‐dimensional (3D) reconstruction computerized tomography (CT) method.

Methods

A total of 35 healthy volunteers (18 men and 17 women) were included in this retrospective study. The mean age of enrolled subjects was 28.9 ± 5.0 years. In September 2018, all the individuals underwent a 3D CT scan of the lumbar spine in neutral and 30° hyperextension supine positions, which mimicked the patient’s position in DAA total hip arthroplasty (THA). The dimensions of the LIVF, including foraminal area, height, and width, were measured on 3D reconstructed CT models at all lumbar foraminal levels. Foraminal area was defined as the area bounded by the adjacent superior and inferior vertebral pedicles, the posterosuperior boundary of the inferior vertebral body, the surface of the intervertebral disc posteriorly, the posteroinferior boundary of the superior vertebral body, and the surface of the ligamentum flavum anteriorly. Foraminal height was defined as the longest distance between the border of the superior and the inferior pedicle. Foraminal width was defined as the shortest distance between the posteroinferior edge of the superior vertebrae and the opposing boundary. Subgroup analysis and multiple linear regression were used to evaluate the relationship between percentage changes of the LIVF dimensions and side, sex, and age.

Results

The LIVF dimensions varied significantly between the two positions at all levels (P < 0.05). From neutral to hyperextension supine position, the foraminal area reduced by 20.1% at lumbar 1–2 (L_1–2), 22.6% at L_2–3, 19.9% at L_3–4, 18.1% at L_4–5, and 12.0% at lumbar 5–sacral 1 (L₅–S₁) level, respectively; the foraminal height reduced by 9.5% at L_1–2, 10.5% at L_2–3, 9.5% at L_3–4, 9.6% at L_4–5, and 6.1% at L₅–S₁ level, respectively; the foraminal width reduced by 12.8% at L_1–2, 14.5% at L_2–3, 13.0% at L_3–4, 10.4% at L_4–5, and 8.4% at L₅–S₁ level, respectively. The changes in LIVF dimensions were biggest at L_2–3 level and smallest at L₅–S₁ level. Subgroup analysis showed that there were no significant differences in the percentage changes of LIVF dimensions between the sexes and sides (P > 0.05). Multiple linear analysis showed that the percentage changes of LIVF dimensions were not related to side, sex, and age (P > 0.05).

Conclusion

The dimensions of the LIVF showed significant decrease at all levels in the DAA‐specific hyperextension supine position compared with the neutral supine position, and the percentage changes of LIVF dimensions were not influenced by side, sex, and age.

Exploring the regional disc bulge response of the cervical porcine intervertebral disc under varying loads and posture

Nerve compression due to intervertebral disc (IVD) bulging is a known mechanism for low back pain and typically occurs in the posterior region of the disc. Most in vitro studies are limited in the ability to quantify the magnitude of bulging on the posterior aspect of the disc due to the boney structures that occlude a direct line-of-sight in the intact functional spinal units (FSUs). This study examined anterior and posterior annulus fibrosus (AF) bulges in reduced (posterior elements removed) cervical porcine specimens across four loading conditions and two postures. Surface scans from the anterior and posterior aspect of the IVD were recorded in both neutral and flexed postures using a 3D laser scanner to characterize changes in AF bulge. A significant negative correlation was observed for peak AF bulge on the anterior and posterior side of the disc in a flexed posture (Pearson's r = -0.448; p = 0.002; r² = 0.2003). The results from this investigation support that there may be a connection between the magnitude of AF bulge on the posterior side and estimations computed using the anterior side.

The acute response of the nucleus pulposus of the cervical intervertebral disc to three supine postures in an asymptomatic population

BACKGROUND

The dynamic disc model refers to the ability of a spinal disc's position to be manipulated by body postures and movements. Research on lumbar discs has indicated movement of the anterior and posterior disc that correlates with posture of the spine. The aim of this study was to assess whether, despite its structural differences, the cervical disc responds to flexed and extended postures in a similar fashion to the lumbar disc.

METHOD

A repeated measures study. Twenty five asymptomatic participants (age: 33.7 ± 9.1 years) volunteered. Scans were performed in supine using an Esaote 0.2T magnetic resonance imaging scanner. Participants lay with their cervical spine initially placed in neutral, followed by flexion and finally extension. The position of the posterior disc nucleus pulposus at C5-6 and C6-7 was measured against a vertical line connecting the posterior vertebral bodies above and below each disc.

RESULTS

Changes in cervical spine position were associated with significant changes in posterior disc nucleus pulposus position at both C5-6 and C6-7 (p < 0.01 for both). Post hoc testing showed a significant difference in posterior disc nucleus pulposus position at C5-6 between flexion and extension (p = 0.02). There was similarly a significant change at C6-7 between neutral and flexion (p = 0.001), and between flexion and extension (p = 0.02).

CONCLUSIONS

These results indicate that the cervical posterior nucleus pulposus is affected by spinal loading, consistent with the concept of the dynamic disc model.

Anterior Lumbar Interbody Fusion May Provide Superior Decompression of the Foraminal Space Compared with Direct Foraminotomy: Biomechanical Cadaveric Study

OBJECTIVE

The objective of this cadaveric biomechanical study was to compare the area of the foraminal space during motion in the intact condition, after direct decompression via foraminotomy, and after indirect decompression via anterior lumbar interbody spacer insertion.

METHODS

Eight (8) L5-S1 cadaver specimens were used for testing. Each specimen was tested in the intact state, after posterior foraminotomy, and after standalone anterior lumbar interbody fusion (ALIF). Each specimen was 3-dimensional imaged under neutral loading, flexion, and extension. The 3-dimensional images were analyzed for changes in the foraminal area under each loading scenario. A repeat-measures design was used. Outcome measures from testing included the frequency in which an increase in cross-sectional area was observed, as well as the percent increase of the foraminal area for each surgical group and loading direction.

RESULTS

Direct foraminotomy and ALIF maintained the foraminal space during initial distraction under no loading with areas 99.7% and 96.5% of the native foraminal area, respectively (P = 0.955 and P = 0.455). Direct foraminotomy increased the foraminal area significantly during flexion to 112.2% of the area before motion (P = 0.008) while ALIF did not. Direct foraminotomy significantly decreased the foraminal area during extension to 89.2% of the area before motion (P = 0.006). ALIF, however, maintained its initial distraction during extension with 98.2% of the area before motion (P = 0.808).

CONCLUSIONS

ALIF maintains the foraminal area in extension while direct posterior foraminotomy does not.

Finite element analysis of the influence of three-joint spinal complex on the change of the intervertebral disc bulge and height

This study evaluated the changes of height and bulging occurring in individual layers of the annulus fibrosus of the intervertebral disc for 3 load scenarios (axial compression, flexion, and extension). The numerical model of a single motion segment of the thoracic spine was analysed for 2 different configurations, ie, for the model of a physiological segment and a segment with the posterior column removed. In the physiological segment, all annulus fibrosus layers decrease in height regardless of the applied load, bulging outside the intervertebral disc. Removal of the posterior column increases mobility and disrupts the load transfer system, with the lamellae bulging into the intervertebral disc.

Effects of Cervical Extension on Deformation of Intervertebral Disk and Migration of Nucleus Pulposus

BACKGROUND

We theorized that active cervical extension should influence the position of the nucleus pulposus (NP) within the intervertebral disk (IVD) in the sagittal plane. Although several studies on the lumbar IVD have been conducted, there are no quantitative data for in vivo positional changes of the NP in the cervical IVD.

OBJECTIVE

To evaluate the influence and mechanism of cervical extension on the deformation and migration of IVD and NP in the sagittal plane and understand underlying mechanisms of the extension maneuver.

DESIGN

Asymptomatic subjects underwent magnetic resonance imaging while supine with their cervical spines in neutral and extended positions.

SETTING

Academic medical center.

PARTICIPANTS

Ten young, healthy male participants (age range 19-30 years; mean 22.4 ± 1.64 years).

METHODS

T2-weighted sagittal images from C3-C4 to C6-C7 of subjects in both neutral and extension positions were analyzed.

MAIN OUTCOME MEASUREMENTS

Deformation of IVD and positional change of NP were quantified and compared between neutral and extension positions. Intersegmental angles between vertebrae, horizontal positions of anterior and posterior IVD and NP margins, IVD outer and inner heights, and sagittal morphology of NP were quantified and compared between the neutral and extension positions. Correlations between the measured parameters and segmental extension angle were also investigated.

RESULTS

Anterior and posterior IVD margins moved posteriorly with respect to the vertebral body in extension. Both NP margins remained unchanged relative to the vertebral body but moved anteriorly with respect to the IVD. IVD outer and inner heights in the anterior region increased in extension, and morphological changes of the NP were less noticeable when compared with its relative migration within the IVD. Most of the intradiskal changes were linearly correlated with the segmental extension angle.

CONCLUSIONS

Cervical extension induces anterior migration of the NP away from the posterior disk margin and may have a clinical effect on diskogenic neck pain resulting from internal disk disruption.

LEVEL OF EVIDENCE

Not applicable.

In vivo dynamic changes of dimensions in the lumbar intervertebral foramen

BACKGROUND CONTEXT

Previous studies have reported position-dependent changes of the lumbar intervertebral foramen (LIVF) dimensions at different static flexion-extension postures. However, the changes of the LIVF dimensions during dynamic body motion have not been reported.

PURPOSE

The objective of this study was to investigate the in vivo dimensions of the LIVF during a dynamic weight-lifting activity.

STUDY DESIGN/SETTING

This was a retrospective study.

METHODS

Ten asymptomatic subjects were recruited for this study. Three-dimensional (3D) vertebral models of the lumbar segments from L2 to S1 were constructed for each subject using magnetic resonance images. The lumbar spine was then imaged using a dual fluoroscopic imaging system as the subject performed a dynamic weight-lifting activity from an upper body position of 45° to a maximal extension position. The in vivo positions of the vertebrae along the motion path were reproduced using the 3D vertebral models and the fluoroscopic images. The minimal area, height, and width of each LIVF during the dynamic body motion were analyzed.

RESULTS

The LIVF area and width monotonically decreased with lumbar extension at all levels except L5-S1 (p<.05). On average, the LIVF area decreased by 7.4±6.7%, 10.8±7.7%, and 10.0±8.0% at the L2-L3, L3-L4, and L4-L5 levels, respectively, from the flexion to the upright standing position, and by 6.4±5.0%, 7.7±7.4%, and 5.1±5.1%, respectively, from the upright standing to the extension position. The LIVF height remained relatively constant at all segments during the dynamic activity. The foramen area, height, and width of the L5-S1 remained relatively constant throughout the activity.

CONCLUSIONS

Human lumbar foramen dimensions show segment-dependent characteristics during the dynamic weight-lifting activity.

In vivo morphological features of human lumbar discs

Recent biomechanics studies have revealed distinct kinematic behavior of different lumbar segments. The mechanisms behind these segment-specific biomechanical features are unknown. This study investigated the in vivo geometric characteristics of human lumbar intervertebral discs. Magnetic resonance images of the lumbar spine of 41 young Chinese individuals were acquired. Disc geometry in the sagittal plane was measured for each subject, including the dimensions of the discs, nucleus pulposus (NP), and annulus fibrosus (AF). Segmental lordosis was also measured using the Cobb method.In general, the disc length increased from upper to lower lumbar levels, except that the L4/5 and L5/S1 discs had similar lengths. The L4/5 NP had a height of 8.6±1.3 mm, which was significantly higher than all other levels (P<0.05). The L5/S1 NP had a length of 21.6±3.1 mm, which was significantly longer than all other levels (P<0.05). At L4/5, the NP occupied 64.0% of the disc length, which was significantly less than the NP of the L5/S1 segment (72.4%) (P<0.05). The anterior AF occupied 20.5% of the L4/5 disc length, which was significantly greater than that of the posterior AF (15.6%) (P<0.05). At the L5/S1 segment, the anterior and posterior AFs were similar in length (14.1% and 13.6% of the disc, respectively). The height to length (H/L) ratio of the L4/5 NP was 0.45±0.06, which was significantly greater than all other segments (P<0.05). There was no correlation between the NP H/L ratio and lordosis. Although the lengths of the lower lumbar discs were similar, the geometry of the AF and NP showed segment-dependent properties. These data may provide insight into the understanding of segment-specific biomechanics in the lower lumbar spine. The data could also provide baseline knowledge for the development of segment-specific surgical treatments of lumbar diseases.

Correlation of vertebral strength topography with 3-dimensional computed tomographic structure

STUDY DESIGN

Biomechanical and radiographical study.

OBJECTIVE

To test the hypothesis that stiffness and strength at discrete sites of human lumbar vertebrae depend on the 3-dimentional structure and density of the vertebral-body bone elements, and can be evaluated using models based on vertebral bone characteristics obtained from quantitative computed tomogrphy.

SUMMARY OF BACKGROUND DATA

We have not found published methods that allow in vivo evaluation of bone mechanical properties at discrete sites of vertebral body applicable for clinical use.We hypothesize that human lumbar vertebral strength topography depends on the local 3-dimensional structural features of the bone structure, and that the stiffness and strength can be evaluated at discrete sites using models based on data obtained from quantitative computed tomographic (CT) images.

METHODS

Forty-eight vertebrae (8 L1, 8 L2, 8 L3, 10 L4, and 14 L5) from 14 cadaveric subjects (9 men and 5 women; age, 43-99 yr) were studied. Stiffness (modulus of elasticity) and strength (maximum load and maximum tolerable pressure) were defined by an indentation test at 11 discrete sites on the cranial and caudal surfaces of each vertebral endplate. Before the indentation test radiography, dual-energy x-ray absorptiometry, micro-CT, and conventional-CT (con-CT) of the vertebrae were performed. Micro-CT characteristics of cortical and cancellous bones of 18 vertebrae were measured at each region of interest defined by a 3-dimensional coordinate system. The most informative indices regarding endplate strength were selected by correlation analysis. Predictive models of local stiffness and strength were created using selected indices obtained by micro-CT and con-CT (40 vertebrae) images.

RESULTS

Local stiffness and strength of the tested specimens were highly variable. Endplate thickness and density in combination with adjacent trabecular bone density, existence of endplate defects, and subject's age were good predictors of local stiffness and strength, applicable for con-CT. Polynomial multiple regression of these characteristics provides the best correlation with stiffness (r2 = 0.82; P < 0.001) and strength (r2 = 0.74).

CONCLUSION

Stiffness and strength at discrete sites of human lumbar vertebrae depend on the superficial vertebral bone structure and density and can be evaluated using models based on quantitative analysis of micro-CT and con-CT images.

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.

Biomechanics of a novel minimally invasive lumbar interspinous spacer: effects on kinematics, facet loads, and foramen height

OBJECTIVE

To study the alteration to normal biomechanics after insertion of a lumbar interspinous spacer (ISS) in vitro by nondestructive cadaveric flexibility testing.

METHODS

Seven human cadaveric specimens were studied before and after ISS placement at L1-L2. Angular range of motion, lax zone, stiff zone, sagittal instantaneous axis of rotation (IAR), foraminal height, and facet loads were compared between conditions. Flexion, extension, lateral bending, and axial rotation were induced using pure moments (7.5 Nm maximum) while recording motion optoelectronically. The IAR was measured during loading with a 400 N compressive follower. Foraminal height changes were calculated using rigid body methods. Facet loads were assessed from surface strain and neural network analysis.

RESULTS

After ISS insertion, range of motion and stiff zone during extension were significantly reduced (P < .01). Foraminal height was significantly reduced from flexion to extension in both normal and ISS-implanted conditions; there was significantly less reduction in foraminal height during extension with the ISS in place. The ISS reduced the mean facet load by 30% during flexion (P < .02) and 69% during extension (P < .015). The IAR after ISS implantation was less than 1 mm from the normal position (P > .18).

CONCLUSION

The primary biomechanical effect of the ISS was reduced extension with associated reduced facet loads and smaller decrease in foraminal height. The ISS had little effect on sagittal IAR or on motion or facet loads in other directions.

Changes in the lumbar spine of athletes from supine to the true-standing position in magnetic resonance imaging

STUDY DESIGN

Case-control observational study.

OBJECTIVE

Determination of dimensional changes in the lumbar spines of athletes between supine and stand-up position in MRI, concerning the lordosis, spinal canal cross-sectional area (SCCA), dural sac cross-sectional area (DSCA), sagittal dural sac diameter (SDSD), the lateral recess and the neural foramina.

SUMMARY OF BACKGROUND DATA

The development of positional MRI allows the examination of spine segments under a true weight-bearing situation.

METHODS

About 35 athletes (20m/15f, Ø: 28a) were examined using a 0.25 T open MRI-Scanner (G-Scan, ESAOTE, Italy). In all cases, axial and sagittal SE-T1 + SSE-T2 images were recorded in supine and true standing position. All measurements were performed using MEDIMAGE software (Vepro AG, Germany). The blinded measurements were performed 3 times by 2 independent examiners. Sagittal images were used to determine the lordosis and the narrowing of the left/right foramen at all levels between L1/2 and L5/S1. Axial images were used to determine the SDSD, the SCCA and the DSCA at L3/4, L4/5, L5/S1, and narrowing of the left/right recessus lateralis of L4, L5 and S1.

RESULTS

The lordosis showed a significant increase of 6.3 degrees (14%) from supine to true standing position (P < 0.001). The SDSD is significantly smaller in true standing position, than in supine position at the level of L3/4 and L4/5 (P < 0.001). Narrowing of the foramen occurred in true standing position in 13.4% at L4/L5 and in 26.7% at level L5/S1. No significant differences were observed at the recessus lateralis, the SCCA and the DSCA.

CONCLUSION

The measurement method in supine and true standing position is excellent for depicting the anatomical regions relevant for spinal canal stenosis in healthy individuals. Measuring the lumbar lordosis angle in both positions is an important requirement for interpreting the relevant anatomical regions. Of particular importance here is the DSCA and the SDSD.

Upright positional MRI of the lumbar spine

Supine magnetic resonance imaging (MRI) is routinely used in the assessment of low back pain and radiculopathy. However, imaging findings often correlate poorly with clinical findings. This is partly related to the positional dependence of spinal stenosis, which reflects dynamic changes in soft-tissue structures (ligaments, disc, dural sac, epidural fat, and nerve roots). Upright MRI in the flexed, extended, rotated, standing, and bending positions, allows patients to reproduce the positions that bring about their symptoms and may uncover MRI findings that were not visible with routine supine imaging. Assessment of the degree of spinal stability in the degenerate and postoperative lumbar spine is also possible. The aim of this review was to present the current literature concerning both the normal and symptomatic spine as imaged using upright MRI and to illustrate the above findings using clinical examples.

A new laser scanning technique for imaging intervertebral disc displacement and its application to modeling nucleotomy

BACKGROUND

Nucleotomy is a standard procedure for treating disc prolapse. It can reduce intervertebral disc height, flattening and displacing the disc, which could lead to a painful narrowing of the foramina due to nerve root compression. The purpose of this study was to investigate the disc displacement of a complete spinal segment with and without nucleotomy. We hypothesized that a nucleotomy under a certain load combination might amplify disc displacement.

METHODS

A laser scanner was developed for recording three-dimensional disc displacement of six loaded L4-5 specimens for three conditions: intact, disc with vertebral bodies and subsequent nucleotomy. Specimens were exposed to pure moments of 7.5 N m in the three principal anatomical directions. Disc displacement was obtained at maximal deflection. A finite element model was validated and subsequently utilized to determine disc displacement. The task of the finite element model was to provide supplemental data for the posterolateral region, which could not be measured from intact specimens.

FINDINGS

Disc displacement measurements of intact specimens were limited to the anterior part of discs, whereas the finite element model was able to provide the missing data of the dorsal disc region. The simulation of load combinations showed that the highest disc displacement was 1.9 mm at the lateral or posterolateral region. The nucleotomy increased the disc displacement up to 2.1mm, whereas the displacement zenith migrated posterolaterally.

INTERPRETATION

These results could be a possible explanation for disadvantages of nucleotomy as a treatment. With the methodology presented here, we would be able to assess the performance of nucleus implants by determining the disc displacement map. This could also give us appropriate information of the annular deformation, which is needed for the development of motion preserving implants.

Creep associated changes in intervertebral disc bulging obtained with a laser scanning device

BACKGROUND

Lumbar disc bulging has been determined with different methods in the past. Reported methods of bulging assessment were limited to a direct physical contact, were two-dimensional and were time-consuming. Assessing the three-dimensional contour of a biological object under load would imply that the tissue would creep and therefore changes its contour. For that purpose, we were interested how fast the contour has to be assessed and how creeping would counteract on the intradiscal pressure and disc height.

METHODS

For that purpose, a laser based three-dimensional contour scanner was developed. This scanner was especially designed to be mounted in a spine tester. For 15 min a static compression of 500 N was applied to seven human lumbar segments having all ligaments, facets and arches removed. Disc height, intradiscal pressure and disc contour were time dependently measured.

FINDINGS

Load application reduced the disc height by 1.14 mm. The further decrease showed a typical creep behavior whereas the intradiscal pressure slightly but significantly decreased from 0.49 to 0.48 MPa. Cross-sectional disc contours showed that bulging was largest anterolateral followed by the anterior region. The creeping also increased the disc circumference. This effect varied region dependently having a maximum of 0.1 mm posterolateral.

INTERPRETATION

Results suggest that geometries of biological tissues should be obtained within one minute avoiding superimposing creep effects. This new method might be used to evaluate disc injuries, degeneration and disc treatments. Measuring disc contours under different loads and conditions yields the outer annular strain distribution. This is a prerequisite for the development of cell seeded and tissue engineered implants.

Reproduction of the Lumbar Lordosis: A Comparison of Standing Radiographs Versus Supine Magnetic Resonance Imaging Obtained with Straightened Lower Extremities

OBJECTIVE

This study investigates whether it is possible to reproduce the lumbar lordosis in the upright position during magnetic resonance imaging (MRI) by positioning the patient supine with straightened lower extremities and investigates intra- and interexaminer reliability of measurements of the lumbar lordosis on radiographs and MRI.

METHODS

This was an observational study, which included an intra- and interexaminer reliability study. The lumbar lordosis was measured digitally on radiographs taken from 22 patients in an upright standing position, and 22 MRI scans of the same patients lying supine with straightened lower extremities. These measurements were compared statistically. Intra- and interexaminer reliability was calculated applying the Bland and Altman method.

RESULTS

The lumbar lordosis in the standing position was reproduced in the straightened supine position with a median deviation of 3 degrees . Intra- and interexaminer reliability was better for MRI than for radiographs. The mean differences were close to 0, especially for interexaminer reliability during MRI. On radiographs, there was a higher agreement on interexaminer than on intra-examiner reliability.

CONCLUSION

The findings of this study show that lumbar lordosis in the upright position can be reproduced by positioning the patient supine with straightened lower extremities.

The effect of lumbar flexion and extension on disc contour abnormality measured quantitatively on magnetic resonance imaging

STUDY DESIGN

Experimental study with subjects as their own control.

OBJECTIVE

To determine if lumbar disc contour abnormality dimensions, measured quantitatively, differ in flexed, neutral or extended positions.

SUMMARY OF BACKGROUND DATA

MRIs obtained lying supine are used to determine the degree of lumbar disc contour abnormality (bulging or herniation). Variations in positioning are suspected to influence this assessment.

METHODS

Lumbar MR images for 26 male volunteers (24-74 years of age), with or without low back pain, were obtained with the subjects lying in neutral, maximal flexion, and maximal extension positions allowable within a conventional 1.5T MR scanner. Quantitative measures of anterior and posterior disc contour abnormality were obtained for each position.

RESULTS

Statistically significant differences in disc angles were obtained between positions (2-5 degrees) for all levels. Posterior contour abnormality was significantly smaller in flexion and extension than in the neutral position (9.5%-30.1%). Posterior contour abnormality in extension was similar or smaller than in flexion. Anterior contour abnormality was significantly smaller in extension than flexion and smaller in the neutral position than flexion.

CONCLUSION

Spine position should be standardized when assessing disc contour abnormality with MRI. The largest measured disc contour abnormalities when lying supine in a standard MR scanner are observed in the neutral position, as opposed to flexion or extension.

Morphometric analysis of the roots and neural foramina of the lumbar vertebrae

BACKGROUND

There have been few anatomic studies on the foramina and roots of the lumbar region, and those available in human specimens are usually based on computed tomography and magnetic resonance imaging methods.

METHODS

Using the recent breakthroughs in microscopic anatomic dissections, the roots and vertebral foramina of the lumbar region were examined in 15 cadavers. Morphometric analysis of the roots and vertebral foramina of 80 lumbar vertebral objects was conducted.

RESULTS

The transverse and sagittal diameters of the lumbar intervertebral foramina were measured at each vertebral level. The median diameter of the lumbar neural foramina was 8.8 +/- 1.7 mm for the transverse and 19.4 +/- 2.7 mm for the sagittal planes. The widest median diameter of roots was 3.9 mm in the L4 root, and the narrowest was 3.3 mm in the L1 root.

CONCLUSION

Quantitative measurements of the diameters of the neural foramina and roots of the lumbar region in anatomic dissection models may provide a deeper understanding about the pathologies of this region and influence the success of surgical interventions.

Anterior lumbar fusion with paired BAK standard and paired BAK Proximity cages: subsidence incidence, subsidence factors, and clinical outcome

BACKGROUND CONTEXT

Anterior lumbar interbody fusion (ALIF) procedures have a known incidence of subsidence. The individual risk of subsidence for specific lumbar levels in ALIF procedures has not been determined.

PURPOSE

To evaluate the incidence of subsidence with two ALIF constructs. A paired Bagby and Kuslich (BAK) standard cage construct is compared with a paired BAK Proximity construct (Sulzer Spine-Tech, Minneapolis, MN). Study purpose is to evaluate lumbar intervertebral disc subsidence including the subsidence incidence for each disc level and with single- and two-level constructs. Also evaluated is the site of maximal subsidence within each end plate, risk with increased reaming depth, fusion incidence and clinical outcome.

STUDY DESIGN

A consecutive series of 70 fused levels fused with paired standard BAK cages is compared with a subsequent series of 70 fused levels using paired Proximity BAK cages.

PATIENT SAMPLE

The study population is derived from a consecutive series of ALIF procedures completed by a single surgeon. In 1998 the construct was changed from dual-standard to dual-Proximity cages. In the year 2000 there were 52 patients with a 2-year follow-up. These were matched to the previous 52 patients with dual-standard construct.

OUTCOME MEASURES

Clinical outcome was determined using pre- and postoperative Oswestry questionnaires. Postoperative questionnaires were completed at the yearly follow-up. Radiographic outcome was determined by fusion status and evaluation of subsidence. Also evaluated was reaming depth and cage size for each fused level.

METHODS

A total of 52 patients with ALIF procedures using paired BAK standard cages (the SS group) were studied with a group of 52 patients using paired BAK Proximity cages (the PP group). The study population was derived from an ongoing prospective study of consecutive ALIF fusion procedures completed by a single surgeon. Disc height measurements were used to determine subsidence. Reaming depth, fusion status and the site of maximal subsidence were all recorded. Clinical outcome was determined with a pre- and postoperative Oswestry functional questionnaire.

RESULTS

Subsidence greater than 2 mm was noted in 5 of the 70 SS fused levels and in 9 of the 70 fused PP levels. Subsidence was always at the L4-L5 level in the SS subsided levels. Subsidence was in two-level fusions in all but one of the SS constructs. Subsidence was at the L4-L5 level in eight of the nine subsided PP levels. Subsidence was associated with increased reaming depth and the use of larger cage sizes. Subsidence was usually in the posterior and superior end plate. The clinical outcome was not affected by subsidence. Subsidence incidence was not associated with the age, sex or weight of the patient.

CONCLUSIONS

There is a statistically significant increased incidence of subsidence at the L4-L5 level as opposed to other fused lumbar levels in ALIF fusions with BAK cage constructs. There is an increased incidence of subsidence with the PP constructs. Subsidence also is associated with increased reaming depth and with larger cage sizes. The lowest risk for subsidence was with single-level dual-standard cage constructs.