Modern Medical Consequences of the Ancient Evolution of a Long, Flexible Lumbar Spine

Modern human bipedality is unique and requires lumbar lordosis, whereas chimpanzees, our closest relatives, have short lumbar spines rendering them incapable of lordosis. To facilitate lordosis, humans have longer lumbar spines, greater lumbosacral angle, dorsally wedged lumbar vertebral bodies, and lumbar zygapophyseal joints with both increasingly coronal orientation and further caudal interfacet distances. These features limit modern lower lumbar spine and lumbosacral joint ailments, albeit imperfectly. The more coronal zygapophyseal orientation limits spondylolisthesis, while increasing interfacet distance may limit spondylolysis. Common back pain, particularly in people who are obese or pregnant, may result from increased lumbar lordosis, causing additional mass transfer through the zygapophyseal joints rather than vertebral bodies. Reduction in lumbar lordosis, such as in flatback syndrome from decreased lumbosacral angle, can also cause back pain. Human lumbar lordosis is necessary for placing the trunk atop the pelvis and presents a balancing act not required of our closest primate relatives.

Influence of morphological variations on cervical spine segmental responses from inertial loading

OBJECTIVES

The objective of this study was to investigate the influence of morphological variations in osteoligamentous lower cervical spinal segment responses under postero-anterior inertial loading.

METHODS

A parametric finite element model of the C5-C6 spinal segment was used to generate models. Variations in the vertebral body and facet depth (anteroposterior), posterior process length, intervertebral disc height, facet articular process height and slope, segment orientation ranging from lordotic to straight, and segment size were parameterized. These variations included male-female differences. A Latin hypercube sampling method was used to select parameter values for model generation. Forces and moments associated with the inertial loading were applied to the generated model segments. The 7 parameters were grouped as local or global depending on the number of spinal components involved in the shape variation. Four output responses representing overall segmental and soft tissue responses were analyzed for each model variation: response angle of the segment, anterior longitudinal ligament stretch, anterior capsular ligament stretch, and facet joint compression in the posterior region. Pearson's correlation coefficient was used to compute the correlations of these output responses with morphological variations.

RESULTS

Fifty models were generated from the parameterized model using a Latin hypercube sampling technique. Variation in response angle among the models was 4° and was most influenced by change in the combined dimension of vertebral body and facet depth, followed by size of the segment. The maximum anterior longitudinal ligament stretch varied between 0.1 and 0.3 and was strongly influenced by the change in the segment orientation. The anterior facet joint region sustained tension, whereas the posterior region sustained compression. For the anterior capsular ligament stretch, the most influential global variation was segment orientation, whereas the most influential local variations were the facet height and facet angle parameters. In the case of posterior facet joint compression, segment orientation was again most influential, whereas among the local variations, the facet angle had the most influence.

CONCLUSION

Shape variations in the intervertebral disc influenced segmental rotation and ligament responses; however, the influence of shape variations in the facet joint was confined to capsular ligament responses. Response angle was most influenced by the vertebral body depth variations, explaining greater segmental rotations in female spines. Straighter spine segments sustained greater posterior facet joint compression, which may offer an explanation for the higher incidence of whiplash-associated disorders among females, who exhibit a straighter cervical spine. The anterior longitudinal ligament stretch was also greater in straighter segments. These findings indicate that the morphological features specific to the anatomy of the female cervical spine may predispose it to injury under inertial loading.

Immunohistochemical investigation of nerve fiber presence and morphology in elderly cervical spine meniscoids

BACKGROUND CONTEXT

Innervation of anatomical structures is fundamental to their capacity to generate nociceptive impulses. Cervical spine meniscoids are hypothesized to be contributors to neck pain; however, their innervation is not comprehensively understood.

PURPOSE

This study aimed to examine the presence and morphology of nerve fibers within cervical spine meniscoids and adjacent joint capsules.

STUDY DESIGN

This is a cross-sectional study.

PATIENT SAMPLE

The sample consists of cervical hemispines of 12 embalmed cadavers (mean [standard deviation] age 82.9 [6.5] years, six female, six left). Either the right or the left half of the cervical spine (hemispine) of each cadaver was included in the sample. So six left sides and six right sides of the cadaver cervical spines made up the 12 hemispines that formed the sample.

METHODS

Cervical spine meniscoids and adjacent joint capsules were excised from lateral atlantoaxial and cervical zygapophyseal (C2-C3 to C6-C7) joints (n=67), then paraffin embedded. Meniscoids were sectioned sagittally (5 µm), slide mounted, and immunohistochemistry was performed using primary antibodies to neurofilament heavy (NF-H) and pan-neurofilament (Pan-NF) to identify nerve tissue. The study was supported by institutional graduate student funding. The authors have no conflicts of interest to declare.

RESULTS

Seventy-seven meniscoids (23 lateral atlantoaxial, 54 cervical zygapophyseal) were extracted and processed (154 sections in total). Sixty-four individual nerve fiber bundles were identified (26 NF-H positive, 38 Pan-NF positive) from 14 meniscoids. Nerves immunoreactive to both NF-H and Pan-NF were identified in 13 of 77 meniscoids (10 of 14 lateral atlantoaxial joint) from 11 joints (eight cadavers). Nerves were always located in joint capsules except three exclusively Pan-NF immunoreactive nerve fiber bundles from two adipose meniscoids.

CONCLUSIONS

The low nerve prevalence in elderly cervical spine meniscoids, with nerves only found in two adipose type meniscoids, suggests these structures may play a minimal role in cervical nociception generation in this demographic. The joint capsules, which were more frequently innervated, appear to be more likely generators of nociception in the elderly. Joint capsule nerves were mostly NF-H positive, indicating potential Aδ-fiber presence.

Clinical Anatomy and Measurement of the Medial Branch of the Spinal Dorsal Ramus

Percutaneous block and neurotomy of the medial branch of the spinal dorsal ramus has shown excellent results in treating facet joint-mediated low back pain. This study aimed to describe the clinical anatomy of the medial branch and its measurements.We dissected the lumbar spine of 12 adult cadavers (24 sides) and measured the distances between the medial branch and various anatomical landmarks. The distances were compared between L1 and L5 vertebrae.The distance between the dorsal ramus bifurcation and the superior border of the root of the transverse process was 3.52 ± 1.15 mm, 3.63 ± 1.36 mm, 3.46 ± 1.31 mm, 3.38 ± 1.24 mm, and 1.87 ± 0.88 for L1 to L5, respectively. The medial branch of the dorsal ramus is enclosed in a fibro-osseous canal bounded by the accessory process, the mammillary process, and the mammilloaccessory ligament.For the percutaneous treatment of block and neurotomy, the first choice of target is the medial branch fibro-osseous canal near to the accessory process. The accessory process is not displayed in x-ray films; therefore, the junction of the superior articular process and the root of the transverse process can be targeted.

The cervical spine of the American barn owl (Tyto furcata pratincola): I. Anatomy of the vertebrae and regionalization in their S-shaped arrangement

BACKGROUND

Owls possess an extraordinary neck and head mobility. To understand this mobility it is necessary to have an anatomical description of cervical vertebrae with an emphasis on those criteria that are relevant for head positioning. No functional description specific to owls is available.

METHODOLOGY/PRINCIPAL FINDINGS

X-ray films and micro-CT scans were recorded from American barn owls (Tyto furcata pratincola) and used to obtain three-dimensional head movements and three-dimensional models of the 14 cervical vertebrae (C1-C14). The diameter of the vertebral canal, the zygapophyseal protrusion, the distance between joint centers, and the pitching angle were quantified. Whereas the first two variables are purely osteological characteristics of single vertebrae, the latter two take into account interactions between vertebrae. These variables change in characteristic ways from cranial to caudal. The vertebral canal is wide in the cranial and caudal neck regions, but narrow in the middle, where both the zygapophyseal protrusion and the distance between joint centers are large. Pitching angles are more negative in the cranial and caudal neck regions than in the middle region. Cluster analysis suggested a complex regionalization. Whereas the borders (C1 and C13/C14) formed stable clusters, the other cervical vertebrae were sorted into 4 or 5 additional clusters. The borders of the clusters were influenced by the variables analyzed.

CONCLUSIONS/SIGNIFICANCE

A statistical analysis was used to evaluate the regionalization of the cervical spine in the barn owl. While earlier measurements have shown that there appear to be three regions of flexibility of the neck, our indicators suggest 3-7 regions. These many regions allow a high degree of flexibility, potentially facilitating the large head turns that barn owls are able to make. The cervical vertebral series of other species should also be investigated using statistical criteria to further characterize morphology and the potential movements associated with it.

[Establishment and validation of three dimensional finite element model of lower cervical bilateral facet locking]

OBJECTIVE

To establish the three dimensional finite element model of bilateral cervical articular process locking and verify its effectiveness.

METHODS

A healthy adult male underwent cervical thin-layer computed tomography (CT) scan. The software programs of Simpleware3.0, Geomagic8.0, Hypermesh9.0, Abaqus6.9 and Rhino4.0 were employed to establish a complete C4, C5 segment (including intervertebral disc and ligament tissue) finite element model. A spring force load of 180 n was applied along the direction of cervical curvature. The locking of articular process was simulated. And its effectiveness was compared with previous experiments.

RESULTS

Detailed anatomy structure of cervical spine was established. Simulated bilateral joints in journey finally formed. The load-displacement situations and experiment results of small joint ligament were consistent. And shear forces and displacement differences of modeling was insignificant.

CONCLUSION

The three dimensional finite element model of bilateral cervical articular process locking has excellent biological fidelity. And it is suitable for clinical applications.

[Feasibility and accuracy of ultrasound-guided methodology in the examination of lumbar spine facet joints]

OBJECTIVE

To investigate the feasibility, accuracy of B ultrasound in the examination of joint space of lumbar spine facet joints compared with CT scan.

METHODS

Ten healthy adult volunteers were enrolled. The joint space of lumbar facet joints was measured by ultrasound. To identify the spinal levels, the posterior parasagittal sonograms were obtained at levels L1 to S1. The lumbar facet joints were delineated with the help of transverse sonograms at each level. Meanwhile, the lumbar facet joints were evaluated by spiral CT on the same plane, reformatted to 1-mm axial slices.

RESULTS

A total of 88 lumbar facet joints from L1 to S1 were clearly visualized in the 10 volunteers. Both ultrasound and CT measurements showed the same average depth and lateral distance of lumbar facet joint space (P > 0.05).

CONCLUSION

The lumbar facet joint space can be accurately demonstrated by ultrasound.

Internal morphology of human facet joints: comparing cervical and lumbar spine with regard to age, gender and the vertebral core

Back pain constitutes a major problem in modern societies. Facet joints are increasingly recognised as a source of such pain. Knowledge about the internal morphology and its changes with age may make it possible to include the facets more in therapeutic strategies, for instance joint replacements or immobilisation. In total, 168 facets from C6/7 and L4/5 segments were scanned in a micro-computed tomography. Image analysis was used to investigate the internal morphology with regard to donor age and gender. Additional data from trabecular bone of the vertebral core allowed a semi-quantitative comparison of the morphology of the vertebral core and the facets. Porosity and pore spacing of the cortical sub-chondral bone does not appear to change with age for either males or females. In contrast, bone volume fraction decreases in females from approximately 0.4 to 0.2 , whereas it is constant in males. Trabecular thickness decreases during the ageing process in females and stays constant in males , whereas trabecular separation increases during the ageing process in both genders. The results of this study may help to improve the understanding of pathophysiological changes in the facet joints. Such results could be of value for understanding back pain and its treatment.

[Comparison between pig lumbar zypapophyseal joint cartilage acquired from multiple magnetic resonance image sequences and gross specimens]

OBJECTIVE

To evaluate the capability and limitation of magnetic resonance image(MRI)for Lumbar zygapophyseal joint cartilage through comparing pig lumbar zygapophyseal joint cartilage acquired from multiple MRI sequences of a 1.5 Tesla MR and gross specimens.

METHODS

Six fresh lumbar spines from adult pigs were sagittaly scanned by Siemens 1.5 Tesla MR. The scan sequences included fast spin echo T1-weighted imaging (FSE T1WI), fast spin echo T2-weighted imaging (FSE T2 weighted T2WI), fat saturation proton density-weighted imaging (FS PDWI), 3-dimensional fast low angle shot imaging (3D-FLASH), and water excitation 3-dimensional fast low angle shot imaging (WE 3D-FLASH). Each scan sequence acquired images from the same layer. The signal-noise ratio (SNR) for articular cartilage, contrast-noise ratio (CNR) for cartilage versus bone cortex, cartilage versus bone marrow, and cartilage versus saline were calculated. Right after the scanning, the lumbar spines were snap-frozen, incised sagittally along the midline lumbar zypapophyseal joints, and photographed to compare the gross specimens with corresponding MRIs. The thickness of sagittal midline center of 6 pairs of lumbar(L₃/L₄) zypapophyseal joint cartilage was measured by vernier caliper. The thickness of the back ventral articular cartilage was added and then compared with corresponding MR images.

RESULTS

3D-FLASH (FA 20°) and WE 3D-FLASH (FA 20°) sequences had significant advantages compared with other sequences in imaging lumbar zypapophyseal joint cartilage, and were mostly close to the real thickness.(1) Comparison of the 4 flip angle (FA 10°, FA 20°, FA 30°, and FA 40°) 3D-FLASH sequences:The highest cartilage SNR and best CNR of cartilage versus bone cortex were both found in the 3D-FLASH(FA 20°) sequence, which was significantly different from the other three 3D-FLASH sequences.The satisfactory CNR of cartilage versus bone marrow, cartilage versus saline were found more in the 3D-FLASH(FA 20°) sequence. (2) Comparison of the 4 flip angle(FA 10°, FA 20°, FA 30°, and FA 40°) WE 3D-FLASH sequences: the highest cartilage SNR,best CNR of cartilage versus bone cortex,and best CNR of cartilage versus bone marrow were found in the WE 3D-FLASH (FA 20°) sequence, which was significantly different from the other three 3D-FLASH sequences. The CNR of cartilage versus saline was found more satisfactory in the WE 3D-FLASH (FA 20°) sequence. (3) The highest cartilage SNR and best CNR of cartilage versus bone cortex were both found in the 3D-FLASH (FA 20°) sequence, which was significantly different from those in the PDWI, FSE T1WI,and FSE T2WI sequences (P<0.05), but with no significance (P>0.05) in the WE 3D-FLASH (FA 20°) sequence. The highest CNR of cartilage versus bone marrow was seen in WE 3D-FLASH (FA 20°) sequence. It was statistically significant compared with that in FS PDWI,FSE T1WI, and T2WI sequences respectively, but the difference was not significant compared with 3D-FLASH (FA 20°) sequence (P>0.05). Both the FS PDWI and T2WI sequences displayed ideal CNR of cartilage versus saline, with no significant difference (P>0.05). The lower SNR of cartilage versus saline was shown in 3D-FLASH (FA 20°) and WE 3D-FLASH (FA 20°) sequence, and the difference was not significant (P>0.05). However, they were significantly different compared with FS PDWI and T2WI sequences (P<0.05). (4) WE 3D-FLASH (FA 20°) and 3D-FLASH (FA 20°) sequences were relatively better than the FS PDWI when comparing the thickness of articular cartilage, which was significantly different from the FS PDWI sequence (P<0.05).

CONCLUSION

The 3D-FLASH sequence and derived WE 3D-FLASH sequence have better definition of cartilage images and are mostly close to the real thickness, which possibly are the optimal scanning sequences for lumbar zypapophyseal joint articular cartilage MR imaging.

C2-fractures: part I. Quantitative morphology of the C2 vertebra is a prerequisite for the radiographic assessment of posttraumatic C2-alignment and the investigation of clinical outcomes

Pertinent literature exists concerning indications, techniques, complications of treatment, and risk factors for nonunion in axis and odontoid fractures; however, there are scarce data regarding the incidence and definition of malunion in these fractures. As a prerequisite for the study of anatomical alignment following surgical and nonsurgical treatment of C2-fractures, an understanding of normal C2 anatomy is essential. Therefore, the authors intended to evaluate morphometrical dimensions of the C2 vertebra. The purpose was to provide normalized quantitative data to enable assessment of malalignment following the treatment of C2-fractures within a classification system. Using digitized cervical spine lateral and transoral odontoid radiographs of 100 consecutive patients without any evidence of traumatic or neoplastic disorders, the authors performed measurements on distinct anatomical structures and investigated morphometrical dimensions of the normal axis vertebra. The incidence of atlantoaxial arthritis was also evaluated. In addition, with the assessment of twenty arbitrarily chosen sets of radiographs by three different observers we calculated the interobserver reliability in terms of intraclass correlation coefficients for each parameter. With calculation of SD and 95% confidence limits, pathological cut-offs were reconstructed from measurements performed resembling non-physiological and pathological limits. Distinct parameters were selected to form a new classification system for radiographical follow-up that focuses on the quantitative C1-2 vertebral alignment. The measurement process resulted in 2,400 data points. Distinct morphometrical parameters, such as a quantitative characterization of the sagittal atlantoaxial congruency, the lateral mass inclination and the type of degenerative changes at the atlantoaxial joint could be demonstrated to be valuable and reliably used within a proposed classification for C2-malunions following C2-fractures. The current study offers a template including recommended radiological measurements for further research on the study of clinical outcome and posttraumatic alignment following C2-fractures.

Ultrasound-guided and CT-navigation-assisted periradicular and facet joint injections in the lumbar and cervical spine: a new teaching tool to recognize the sonoanatomic pattern

BACKGROUND AND OBJECTIVES

The aim of this study is to provide a teaching tool to facilitate the acquirement of periradicular and facet-joint infiltration techniques in the cervical and lumbar spine.

METHODS

On 3 fresh cadavers, a computed tomography (CT) of the lumbar and cervical region was obtained. By use of a dedicated image navigation and reconstruction system, sonographic images were generated and fused with the collected CT data set.

RESULTS

The sonoanatomy can be instantly compared with the correlating CT-images. This new bimodal method allows for simultaneous views of CT and ultrasound images. Multiplanar imaging of ultrasound-guided infiltrations is facilitated.

CONCLUSIONS

This teaching tool provides immediate CT-verification of sonographically identified structures and helps in the identification of bony landmarks, which are necessary for facet-joint and periradicular injections.

Strength of the cervical spine in compression and bending

STUDY DESIGN

Cadaveric motion segment experiment.

OBJECTIVES

To compare the strength in bending and compression of the human cervical spine and to investigate which structures resist bending the most.

SUMMARY OF BACKGROUND DATA

The strength of the cervical spine when subjected to physiologically reasonable complex loading is unknown, as is the role of individual structures in resisting bending.

METHODS

A total of 22 human cervical motion segments, 64 to 89 years of age, were subjected to complex loading in bending and compression. Resistance to flexion and to extension was measured in consecutive tests. Sagittal-plane movements were recorded at 50 Hz using an optical two-dimensional "MacReflex" system. Experiments were repeated 1) after surgical removal of the spinous process, 2) after removal of both apophyseal joints, and 3) after the disc-vertebral body unit had been compressed to failure. Results were analyzed using t tests, analysis of variance, and linear regression. Results were compared with published data for the lumbar spine.

RESULTS

The elastic limit in flexion was reached at 8.5 degrees (SD, 1.7 degrees ) with a bending moment of 6.7 Nm (SD, 1.7 Nm). In extension, values were 9.5 degrees (SD, 1.6 degrees ) and 8.4 Nm (3.5 Nm), respectively. Spinous processes (and associated ligaments) provided 48% (SD, 17%) of the resistance to flexion. Apophyseal joints provided 47% (SD, 16%) of the resistance to extension. In compression, the disc-vertebral body units reached the elastic limit at 1.23 kN (SD, 0.46 Nm) and their ultimate compressive strength was 2.40 kN (SD, 0.96 kN). Strength was greater in male specimens, depended on spinal level and tended to decrease with age.

CONCLUSIONS

The cervical spine has approximately 20% of the bending strength of the lumbar spine but 45% of its compressive strength. This suggests that the neck is relatively vulnerable in bending.

Regional changes in spine posture at lift onset with changes in lift distance and lift style

STUDY DESIGN

Repeated measures experiment.

OBJECTIVE

To determine the effect of changes in horizontal lift distance on the amount of flexion, at lift onset, in different spine regions when using different lift styles.

SUMMARY OF BACKGROUND DATA

By approximating spine bending during lifting as a pure rotation about a single revolute joint, the differential effects of task constraints and instructions on motions of different spine levels will be obscured.

METHODS

Eight participants lifted a 10-kg crate from the floor, 10 times at each of five distances. Participants were instructed to use freestyle (a participant's preferred lift style), squat, or stoop lift styles. Kinematic data were collected from the mid thoracic spine, lower thoracic/upper lumbar spine, mid lumbar spine, and the lower lumbar spine at lift onset. A whole spine angle was also calculated.

RESULTS

Flexion of the lower lumbar spine was not affected by lift distance and style. Differences between lift styles occurred mainly in the mid thoracic and the lower thoracic/upper lumbar regions. With increasing horizontal distance, changes in lift style occurred in the upper three spine regions.

CONCLUSIONS

These results suggest that the tensile strain on tissues in the lower lumbar spine, which can be a cause of injury in lifting, was not affected by lift style or horizontal lift distance when lifting from floor level.

Pathogenesis, diagnosis, and treatment of lumbar zygapophysial (facet) joint pain

Lumbar zygapophysial joint arthropathy is a challenging condition affecting up to 15% of patients with chronic low back pain. The onset of lumbar facet joint pain is usually insidious, with predisposing factors including spondylolisthesis, degenerative disc pathology, and old age. Despite previous reports of a "facet syndrome," the existing literature does not support the use of historic or physical examination findings to diagnose lumbar zygapophysial joint pain. The most accepted method for diagnosing pain arising from the lumbar facet joints is with low-volume intraarticular or medial branch blocks, both of which are associated with high false-positive rates. Standard treatment modalities for lumbar zygapophysial joint pain include intraarticular steroid injections and radiofrequency denervation of the medial branches innervating the joints, but the evidence supporting both of these is conflicting. In this article, the authors provide a comprehensive review of the anatomy, biomechanics, and function of the lumbar zygapophysial joints, along with a systematic analysis of the diagnosis and treatment of facet joint pain.

High-field magnetic resonance imaging of meniscoids in the zygapophyseal joints of the human cervical spine

STUDY DESIGN

Prospective in vitro study of meniscoids in the cervical zygapophysial joints. OBJECTIVES.: To assess the use of high-field magnetic resonance imaging (MRI) as a potential tool for evaluating meniscoids of the cervical zygapophysial joints.

SUMMARY OF BACKGROUND DATA

Pain originating from the cervical spine is a frequent condition. It has been suggested that pathologic conditions of meniscoids within the zygapophysial joints may cause pain.

METHODS

Six zygapophysial joints from one embalmed human body were investigated with a 3.0-T MR unit, equipped with a microimaging-set. MRIs were correlated with microanatomical sections.

RESULTS

High-quality images of the meniscoids were obtained for all joints examined. There was a good correlation between the anatomic features derived from MRI and the microanatomical sections.

CONCLUSIONS

High-field MRI was successfully implemented as a noninvasive method for imaging the meniscoids in cervical zygapophysial joints. The results of this in vitro study indicate that high-field MRI may be feasible in evaluating patients with cervical pain possibly related to meniscoid pathology.

Biomechanical analysis of rotational motions after disc arthroplasty: implications for patients with adult deformities

STUDY DESIGN

An anatomic and biomechanical bench-top basic scientific comparative analysis to determine the appropriateness of total disc replacement (TDR) in a lumbar spine with scoliotic tendencies.

OBJECTIVES

Only limited data are currently available studying the application of disc replacement adjacent to scoliosis fusions. Theoretically, motion preservation should help delay the continuum of lumbar degeneration adjacent to scoliosis fusions and rotationally unstable lumbar segments.

SUMMARY OF BACKGROUND DATA

As a tertiary referral center for failed TDR, we noticed an alarming number of lumbar spinal rotational iatrogenic instability patterns but none occurring in the cervical spine. It is appropriate to analyze the bench-top rotational stability of disc replacement to predict whether this new technology is feasible for a larger prospective clinical study in the treatment of degenerative scoliosis.

METHODS

Measurements were taken from 60 human specimens from the Hamann-Todd Osteological Collection: 1) to determine the rotational arc of influence (AOI) = the angle formed from the center of axial rotation to the outermost extent of the facet joints; and 2) to determine the relative anatomic size discrepancy between the left and right facets proportionately with the cross-sectional area of the intervertebral disc = facet/endplate ratio (FER). Biomechanical testing was performed using fresh frozen human cadaveric spines with the following conditions to determine the rotational stability: 1) intact; 2) resection of ALL, anulus, disc, and PLL simulating the preparation for a TDR; 3) a more radical anular resection; 4) entire 360 degrees anular resection; and 4) insertion of the respective unconstrained-type disc replacement. Using a 6 degrees of freedom spine simulator, unconstrained pure moments of +/-8.0 Nm (lumbar) and +/-3.0 Nm (cervical) were used for axial rotation with quantification of the operative level range of motion and neutral zone, with data normalized to the intact spine condition.

RESULTS

There were anatomic limitations in the lumbar spine that make it less desirable to apply uncon-strained disc replacements; indeed, the spine was at risk for iatrogenic lumbar scoliosis. The anulus fibrosis, anterior longitudinal ligament, and the posterior longitudinal ligament are critical structures in preventing iatrogenic scoliosis. The lumbar facet joints are more posteriorly located and are smaller relative to the intervertebral disc, compared with this association in the cervical spine. Because the facet capsular ligaments are mechanically less effective with lower tensile strength in the lumbar spine, multiple-level arthroplasty tends to accentuate scoliotic tendencies; this is independent of prosthetic design and surgical technique.

DISCUSSION

Implantation of the lumbar TDR never restored the motion segment back to the rotational stability of the intact segment achieving a range of 120% to 140% rotational range of motion compared with the intact condition. This rotational instability proved to be additive as a two-level lumbar TDR resulted in between 240% and 260% increase in rotational instability compared with the intact condition.

CONCLUSION

The neutral zone of the intact cervical spine was restored even using an unconstrained cervical TDR. The greater inherent rotational constraints of the cervical spine make it more amenable to stable multilevel arthroplasty compared with the lumbar spine.

Modified Cervical Laminoforaminotomy Based on Anatomic Landmarks Reduces Need for Bony Removal

We describe a modified keyhole laminoforaminotomy (LF) using anatomic landmarks on the posterior aspect of the cervical vertebral body to decompress the intervertebral foramen with minimal bone removal. Twenty-four procedures were performed at C3-4, C4-5, and C5-6; 12 at C6-7; and 3 at C7-Tl. Facets and laminae structures were identified based on relative surgical perspectives. Bony resection was limited as follows: 1) inferior limit; inferior border of the superior facet; 2) superior limit, superior border of the superior facet; 3) lateral limit, a vertical line linking the junction of the lamina-facet to the lateral end of the superior limit; and 4) lateral aspect of the dural sac. Fluoroscopy was used to confirm that the intervertebral space was reached. The amount of bony removal was quantified for the superior and inferior laminae and facets. The length of the exposed nerve root was measured. The intervertebral foramen was exposed and the intervertebral disc reached in all specimens. Fluoroscopy showed that the center of the exposure remained at the same height with the intervertebral space. The mean length of the nerve root was 4.6 mm; the mean percentage of bony resection was 21.8%, 7.5%, 11.3%, and 11.5% for the superior and inferior laminae and facets, respectively. Opening the intervertebral foramen posteriorly consistently exposed sufficient nerve root length and allowed access to the intervertebral disc. The technique offers the most direct and safest method of decompressing the intervertebral foramen while minimizing bony resection. This simple surgical procedure may help reduce postoperative morbidity.

Effects of anatomic conformation on three-dimensional motion of the caudal lumbar and lumbosacral portions of the vertebral column of dogs

OBJECTIVE

To determine the association between the 3-dimensional (3-D) motion pattern of the caudal lumbar and lumbosacral portions of the canine vertebral column and the morphology of vertebrae, facet joints, and intervertebral disks.

SAMPLE POPULATION

Vertebral columns of 9 German Shepherd Dogs and 16 dogs of other breeds with similar body weights and body conditions.

PROCEDURE

Different morphometric parameters of the vertebral column were assessed by computed tomography (CT) and magnetic resonance imaging. Anatomic conformation and the 3-D motion pattern were compared, and correlation coefficients were calculated.

RESULTS

Total range of motion for flexion and extension was mainly associated with the facet joint angle, the facet joint angle difference between levels of the vertebral column in the transverse plane on CT images, disk height, and lever arm length.

CONCLUSIONS AND CLINICAL RELEVANCE

Motion is a complex process that is influenced by the entire 3-D conformation of the lumbar portion of the vertebral column. In vivo dynamic measurements of the 3-D motion pattern of the lumbar and lumbosacral portions of the vertebral column will be necessary to further assess biomechanics that could lead to disk degeneration in dogs.

Morphometric analysis of the working zone for endoscopic lumbar discectomy

OBJECTIVE

Our study's purpose was to analyze the working zone for the current practice of endoscopic discectomy at the lateral exit zone of the intervertebral foramen (IVF) and to define a safe point for clinical practice.

METHODS

One hundred eighty-six nerve roots of the lumbar IVFs of cadaveric spines were studied. Upon lateral inspection, we measured the distance from the nerve root to the most dorsolateral margin of the disc and to the lateral edge of the superior articular process of the vertebra below at the plane of the superior endplate of the vertebra below. The angle between the root and the plane of the disc was also measured.

RESULTS

The results showed that the mean distance from the nerve root to the most dorsolateral margin of the disc was 3.4 +/- 2.7 mm (range 0.0-10.8 mm), the mean distance from the nerve root to the lateral edge of the superior articular process of the vertebra below was 11.6 +/- 4.6 mm (range 4.1-24.3 mm), and the mean angle between the nerve root and the plane of the disc was 79.1 degrees +/- 7.6 degrees (range 56.0-90.0 degrees ).

CONCLUSIONS

The values of the base of the working zone have a wide distribution. Blind puncture of annulus by the working cannula or obturator may be dangerous. The safer procedure would be the direct viewing of the annulus by endoscopy before annulotomy; the working cannula should be inserted into the foramen as close as possible to the facet joint.

Anatomic Analysis of the Transforaminal Ligament in the Lumbar Intervertebral Foramen

OBJECTIVE:

The objective of this study was to evaluate the clinical significance of the transforaminal ligaments (TFLs) in relation to the area of the lumbar intervertebral foramen (IVF) by analyzing cadaveric spines.

METHODS:

One hundred ninety-eight cadaveric lumbar IVFs were studied, and the existence and type of TFLs were identified. All IVFs were photographed, and the images were saved. The areas of the IVFs and TFLs were measured with the Scion Image for Windows image analysis program.

RESULTS:

TFLs were found in 82.8% of the IVFs. The oblique inferior transforaminal ligament was the most common. The mean area of the IVFs was 155.8 ± 51.1 mm2, and the mean area occupied by the TFLs was 46.3 ± 37.6 mm2. The mean percentage of the IVF area occupied by the TFLs was 28.5 ± 18.8%.

CONCLUSION:

TFLs are common structures in the IVF and may reduce the space available for the spinal nerve root within the IVF. In this circumstance, any compromise of the IVF may impinge on the nerve root.

Facet tropism and interfacet shape in the thoracolumbar vertebrae: characterization and biomechanical interpretation

STUDY DESIGN

Thoracolumbar facet and interfacet linear dimensions were measured and analyzed.

OBJECTIVE

To characterize and analyze the thoracolumbar facet and interfacet size and shape in relation to gender, ethnic group, and age and to detect the extent of normal facet tropism along the thoracolumbar spine.

SUMMARY OF BACKGROUND DATA

Knowledge on facet tropism and interfacet shape is limited in the literature as most data are based on 2-dimensional measurements, small samples, or isolated vertebrae.

METHODS

Facet shape as represented by width, length, width/length ratio and interfacet distances was obtained directly from dry vertebrae of 240 adult human spines. The specimen's osteologic material is part of the Hamann-Todd Osteological Collection housed at the Cleveland Museum of Natural History, Cleveland, OH. A total of 4080 vertebrae (T1-L5) from the vertebral columns of individuals 20 to 80 years of age were measured, using a Microscribe 3-dimensional apparatus (Immersion Co., San Jose, CA). Data were recorded directly on computer software. Statistical analysis included paired t tests and ANOVA.

RESULTS

A significant correlation was found between all thoracolumbar facet dimensions and an individual's height and weight. Facet tropism is a major characteristic of the thoracolumbar spine, the left being longer in the thorax while the right is longer in the lumbar. In general, facet size is age-independent and greater in males compared with females with a significant ethnic component. Facet length is similar for all thoracic vertebrae, whereas it sharply and continuously increases in the lumbar vertebrae. Facet dimension manifests a bipolar distribution along the thoracolumbar vertebrae. Width/length ratio indicates that facets are longer than wider for most verte-brae. The interarticular area manifests a marked inverted trapezoidal shape at T1-T2, a rectangular shape at T3-L3, and an ordinary trapezoidal shape at L4-L5.

CONCLUSIONS

Facet tropism is a normal characteristic in humans, yet it varies along the thoracolumbar spine.

Material Sensitivity Study on Lumbar Motion Segment (L2-L3) Under Sagittal Plane Loadings Using Probabilistic Method

OBJECTIVE

In this study, the probabilistic responses of a three-dimensional finite element L2-L3 motion segment, with and without posterior elements, tested under sagittal plane loadings, are presented. Understanding the effect of biologic uncertainties and variations on the biomechanical response provides an insight into spinal behavior under normal and degenerated conditions.

METHODS

The biologic variability of 19 spinal components (nucleus, annulus, ligament, cortical/cancellous bone, endplate, and ligaments) in the motion segment was incorporated using statistical distributions into the model. A total of 2000 runs were performed using Monte Carlo probabilistic algorithms to compute the probabilistic response.

RESULTS

This study establishes the relative importance of the spinal components in resisting the loading modes. The results show that for an intact motion segment, posterior ligaments are more dominant than intervertebral disc in resisting flexion moment. In extension, the capsular ligaments were found to be the most influential parameter. The intervertebral disc (ie, nucleus and annulus) affects the angular response of the disc body segment more than the hard tissues (ie, cortical and cancellous bone).

CONCLUSIONS

The application of the probabilistic analysis provides a new approach whereby the influences of inherent uncertainties and variations in biologic structures can be studied and the biomechanical response assessed.

Demonstration of the appearance of the paraspinal musculoligamentous structures of the cervical spine using ultrasound

The application of ultrasound in the imaging of the neck has primarily focussed on anterior structures (e.g., thyroid gland). Structures located on the posterior aspect of the neck have received little attention. This study illustrates the capability of modern ultrasound equipment in visualising the musculoligamentous structures of the neck, particularly the paraspinal musculature. Ten healthy adult volunteers (6 female; 4 male) underwent ultrasound examination of the cervical spine. A standardised technique for transducer placement was adopted and successive images of the neck of each subject were obtained. Spatial compound (extended field of view) images were obtained in subjects using one of two different ultrasound systems. Images of structures produced by ultrasound were compared to those achieved with magnetic resonance imaging in three subjects. Identification of key landmarks aided orientation and identification of structures. The internal architecture of the musculoligamentous structures of the cervical spine, especially the posterior neck muscles, was demonstrated well using ultrasound. Our study showed that modern ultrasound equipment is capable of producing clear images of the posterior cervical spine musculature and certain bony features.

Morphologic changes in the cervical neural foramen due to flexion and extension: in vivo imaging study

STUDY DESIGN

Dimensional measurement of cervical neural foramen at various positions, using reformatted computed tomography.

OBJECTIVES

To examine the morphologic changes in the neural foramen during flexion and extension of the cervical spine in vivo.

SUMMARY OF BACKGROUND DATA

Previous cadaveric studies have shown the effect of cervical spinal motion on dimensions of the neural foramen. However, little information is available about dynamic morphologic changes in the cervical neural foramen in vivo.

METHODS

Cervical CT images of seven healthy volunteers were taken at the neutral position, maximum extension, and maximum flexion, and were reconstructed in the oblique plane perpendicular to the long axis of each neural foramen from the C3-C4 to C6-C7 level. Measured parameters included foraminal height, width, cross-sectional area, and segmental sagittal rotation at each spinal level. Differences in neural foraminal dimensions among these positions were analyzed. Correlations of segmental sagittal rotation with differences in dimensions between flexion and extension were analyzed.

RESULTS

Flexion significantly increased the foraminal height (by 1.0 mm; 11%), foraminal width (by 1.0 mm; 16%), and foraminal area (by 12 mm2; 28%) (P < 0.01). Extension significantly decreased the foraminal height (by 0.9 mm; 10%), foraminal width (by 1.4 mm; 22%), and foraminal area (by 8.0 mm2; 17%) (P < 0.01). Segmental sagittal rotation significantly positively correlated with % change in foraminal height (r = 0.434, P < 0.01) and area (r = 0.504, P < 0.01).

CONCLUSIONS

The present results are consistent with those of previous in vitro studies and may explain the clinical observation that cervical extension aggravates symptoms in patients with cervical radiculopathy and that flexion often relieves them.

Kinematics of the subaxial cervical spine in rotation in vivo three-dimensional analysis

STUDY DESIGN

Three-dimensional intervertebral motions of the subaxial cervical spine during head rotation were investigated in healthy volunteers using three-dimensional magnetic resonance imaging (MRI).

OBJECTIVES

To document intervertebral coupled motions of the subaxial cervical spine during rotation.

SUMMARY OF BACKGROUND DATA

In vivo three-dimensional kinematics of the subaxial cervical spine in rotation have not previously been well described, since they are too complicated to follow using conventional radiography or computed tomography techniques.

METHODS

Ten healthy volunteers underwent three-dimensional MRI of the cervical spine in 11 positions with 15 degrees increments during head rotation using a 1.0-T imager. Relative motions of the subaxial cervical spine were calculated by automatically superimposing a segmented three-dimensional MRI of the vertebra in the neutral position over images of each position using volume registration. Three-dimensional motions of adjacent vertebrae were represented with 6 df (6 degrees of freedoms) by Euler angles and translations on the coordinate system defined by Panjabi, then visualized in animations using surface bone models.

RESULTS

Mean axial rotation of the subaxial cervical spine in maximum head rotation (69.5 degrees ) was 2.2 degrees at C2-C3, 4.5 degrees at C3-C4, 4.6 degrees at C4-C5, 4.0 degrees at C5-C6, 1.6 degrees at C6-C7, and 1.5 degrees at C7-T1. Coupled lateral bending with axial rotation was observed in the same direction as axial rotation at all levels (C2-C3, 3.6 degrees ; C3-C4, 5.4 degrees; C4-C5, 5.0 degrees ; C5-C6, 5.3 degrees ; C6-C7, 4.9 degrees ; C7-T1, 1.2 degrees ). Coupled extension with axial rotation occurred in the middle cervical region (C2-C3, 1.4 degrees ; C3-C4, 2.3 degrees ; C4-C5, 1.5 degrees ), while in the lower cervical region, flexion was coupled with axial rotation (C5-C6, 0.9 degrees ; C6-C7, 2.4 degrees ; C7-T1, 3.0 degrees ).

CONCLUSIONS

We investigated intervertebral motions of the subaxial cervical spine during head rotation using a three-dimensional imaging system, and obtained the first accurate depictions of in vivo coupled motion. These findings will be helpful as the basis for understanding abnormal conditions.

Intervertebral motion between flexion and extension in asymptomatic individuals

STUDY DESIGN

Measure and analyze variation in intervertebral motion in asymptomatic subjects.

OBJECTIVES

Gain further insight into intervertebral motion during flexion and extension in asymptomatic individuals, identify factors that contribute to variation in motion, and establish a quantitative database using a clinically practical imaging tool.

SUMMARY OF BACKGROUND DATA

Several authors have reported on normal values for intervertebral motion during flexion and extension of the cervical spine. However, the sources of the wide variations in intervertebral motion are poorly understood.

METHODS

Fluoroscopic images of the cervical spine in maximum flexion and extension were analyzed for 140 asymptomatic volunteers using a validated and clinically applicable image analysis system. Several independent variables were analyzed for their contribution to variation in motion. The dependent variables studied included sagittal plane rotation and translation, and displacements between vertebrae measured at the anterior and posterior aspects of each motion segment.

RESULTS

There was considerable variation in measured intervertebral motion. Intervertebral level and total gross rotation between C2 and C6 significantly affected all measures of intervertebral motion. The intervertebral motion measures were all interrelated. After adjusting for differences in gross motion between C2 and C6, intervertebral levels and the three displacement measures could be used to explain almost 90% of the variation in sagittal plane intervertebral rotations. In addition, the data suggest that currently accepted clinical guidelines for shear should be raised at all levels except C6-C7.

CONCLUSIONS

A database describing intervertebral motion in asymptomatic subjects representing both sexes and a wide age range was established that should aid in interpreting intervertebral motion in patients. Evaluating various aspects of intervertebral motion may improve the clinical efficacy of radiographic flexion-extension studies of the cervical spine.

Poroelastic Analysis of Lumbar Spinal Stability in Combined Compression and Anterior Shear

OBJECTIVE

A three-dimensional poroelastic finite element (FE) L2-L3 model was developed to study lumbar spinal instability and intrinsic parameters in the intervertebral disc (IVD).

METHODS

The FE model took into consideration poroelasticity of the IVD and viscoelasticity of the annulus fibers and ligaments to predict the time-dependent behavior. To simulate a holding task, the motion segment was subjected to a combined loading of constant compressive load (1600 N) and anterior shear (200 N) for 2 hours, and the role of facet joints and ligaments in the biomechanical response was investigated by removal of unilateral/bilateral facets, posterior ligaments (supraspinous and interspinous), and facets and ligaments.

RESULTS

The results show the stabilizing role of the facets and ligaments in resisting anterior shear and sagittal rotation under combined loading over time. The main pathway of fluid movement was found to permeate through the central region of the endplate, and the fluid diffusion occurred earlier at the posterior nucleus than the anterior nucleus. The fluid loss from the nucleus dictated the time-dependent motion under the sustained loading, whereas the intrinsic properties of ligaments/annulus fibers played a role only in the early stage of the loading.

CONCLUSION

The predicted results using poroelastic elements provide new insight into the IVD in providing the spinal stiffness under combined loading.

Facet orientation in the thoracolumbar spine: three-dimensional anatomic and biomechanical analysis

STUDY DESIGN

Thoracolumbar facet orientations were measured and analyzed.

OBJECTIVES

To establish a comprehensive database for facet orientation in the thoracolumbar vertebrae and to determine the normal human condition.

SUMMARY OF BACKGROUND DATA

Most studies on facet orientation have based their conclusions on two-dimensional measurements, in small samples or isolated vertebrae. The amount of normal asymmetry in facet orientation is poorly addressed.

METHODS

Transverse and longitudinal facet angles were measured directly from 240 human vertebral columns (males/females, blacks/whites). The specimens' osteologic material is part of the Hamann-Todd Osteological Collection housed at the Cleveland Museum of Natural History (Cleveland, OH). A total of 4,080 vertebrae (T1-L5) from the vertebral columns of individuals 20 to 80 years of age were measured, using a Microscribe three-dimensional apparatus (Immersion Co., San Jose, CA). Data were recorded directly on computer software. Statistical analysis included paired t tests and analysis of variance. RESULTS.: Facet orientation is independent of gender, age, and ethnic group. Asymmetry in facet orientation is found in the thorax. All thoracolumbar facets are positioned in an oblique plane. In the transverse plane, all facets from T1 to T11 are positioned with an anterior inclination of approximately 25 degrees to 30 degrees from the frontal plane. The facets of T12-L2 are oriented closer to the midsagittal plane of the vertebral body (mean range, 25.89 degrees-33.87 degrees), while the facets of L3-L5 are oriented away from that plane (mean range, 40.40 degrees-56.30 degrees). Facet transverse orientation at the thoracolumbar junction is highly variable (approximately 80% with approximately 101 degrees and approximately 20% with 35 degrees). All facets are oriented more vertically from T1 (approximately 150 degrees) to L5 (approximately 170 degrees). The facet sagittal orientations of the lumbar zygoapophyseal joints are not equivalent. CONCLUSIONS.: Asymmetry in facet orientation is a normal characteristic in the thorax.

Gender- and region-dependent local facet joint kinematics in rear impact: implications in whiplash injury

STUDY DESIGN

Localized facet joint kinematics resulting from whiplash acceleration were analyzed in the dynamic domain during the time of cervical S-curvature using intact head and neck specimens and a pendulum mini-sled loading apparatus.

OBJECTIVES

To determine the effects of gender, impact severity, cervical level, and anatomic joint region on shear and distraction motion of lower cervical facet joints.

SUMMARY OF BACKGROUND DATA

Clinical and experimental studies identify cervical facet joints to be a likely location of whiplash injury. Epidemiologic studies report that female occupants sustain a greater percentage of whiplash injuries. Previous experimental studies have not analyzed facet joint motion as a function of variables such as gender.

METHODS

Intact head and neck complexes were subjected to whiplash acceleration using a pendulum mini-sled apparatus at four impact severities. Facet joint kinematics were analyzed using digital high-resolution video at 1000 frames per second during the time of maximum cervical S-curvature. Shear and distraction motions were analyzed in the ventral and dorsal joint regions from C4-C5 to C6-C7 levels. Analysis of variance techniques were used to analyze biomechanical data.

RESULTS

Intact head and neck complexes sustained cervical S-curvature during whiplash loading. Lower cervical facet joints demonstrated dorsally directed shear motion with distraction in the ventral and compression in the dorsal regions of the joint. Magnitudes of distraction and compression were significantly lower than shear motion (P < 0.05). Facet joint shear and distraction motion increased with impact severity. Lower cervical facet joint shear and distraction motions in female specimens were greater than in male specimens. This difference reached statistical significance at C4-C5 (P < 0.05).

CONCLUSIONS

Secondary to whiplash loading, lower cervical facet joints responded with a shear plus distraction mechanism in the anatomic ventral and shear plus compression mechanisms in the dorsal region. Injury to the ventral region stems from tensile failure of the joint capsule. Injury to the dorsal region stems from pinching of the joint capsule or synovial fold and contact between subchondral bone of superior and inferior facet processes. Because excess spinal motion is biomechanically related to abnormalities and because lower cervical facet joints sustain greater motion in female specimens, this population is more likely to be injured under whiplash loading. Potential contributors for the susceptibility of females to injury, including genotypic (apolipoprotein APOE-epsilon4), hormonal, structural, and tolerance factors, are discussed.

Does osteoarthritis of the lumbar spine cause chronic low back pain?

The lumbar spine is a common location for osteoarthritis. The axial skeleton demonstrates the same classic alterations of cartilage loss, joint instability, and osteophytosis characteristic of symptomatic disease in the appendages. Despite these similarities, questions remain regarding the lumbar spine facet joints as a source of chronic back pain. The facet joints undergo a progression of degeneration that may result in pain. The facet joints have sensory input from two spinal levels that makes localization of pain difficult. Radiographic studies describe intervertebral disc abnormalities in asymptomatic individuals that are associated with, but not synonymous for, osteoarthritis. Patients who do not have osteoarthritis of the facet joints on magnetic resonance scan do not have back pain. Single photon emission computed tomography scans of the axial skeleton are able to identify painful facet joints with increased activity that may be helped by local anesthetic injections. Low back pain is responsive to therapies that are effective for osteoarthritis in other locations. Osteoarthritis of the lumbar spine does cause low back pain.

Human lumbar facet joint capsule strains: I. During physiological motions

BACKGROUND CONTEXT

The lumbar facet joint capsule is innervated with nociceptors and mechanoreceptors, and is thought to play a role in low back pain as well as to function proprioceptively.

PURPOSE

In order to examine the facet capsule's potential proprioceptive role, relationships between intracapsular strain and relative spine position were examined.

STUDY DESIGN/SETTING

Lumbar facet joint capsule strains were measured in human cadaveric specimens during displacement-controlled motions.

METHODS

Ligamentous lumbar spine specimens (n=7) were potted and actuated without inducing a moment at the point of application. Spines were tested during physiological motions of extension, flexion, left and right lateral bending. Intervertebral angulations (IVA) were measured using biaxial inclinometers mounted on adjacent vertebrae. Joint moments were determined from the applied load at T12 and the respective moment arms. Capsule plane strains were measured by optically tracking the displacements of infrared reflective markers glued to capsule surfaces. Statistical differences (p<.05) in moment, IVA and strain were assessed across facet joint levels using analysis of variance and comparison of linear regressions.

RESULTS

The developed moments and IVAs increased monotonically with increasing displacements; the relationships were highly correlated for all four motion types. Although highly variable among specimens, principal strains also increased monotonically in magnitude with increasing displacements during extension and flexion, but were more complex during lateral bending. At a given joint level, the absolute magnitudes of principal strains and IVA were largest during the same motion type.

CONCLUSIONS

Distinct patterns in principal strains and IVA were identified during physiological motions, lending biomechanical support to the theory that lumbar facet joint capsules could function proprioceptively.

Anatomic study of the morphology of human cervical facet joint

STUDY DESIGN

Geometrical properties of the facet joint including cartilage thickness and gap were obtained using human cadaver cervical spinal columns and cryomicrotomy techniques.

OBJECTIVES

To determine the existence of level or gender dependency on facet joint morphology in the human cervical spine.

BACKGROUND DATA

Although measurements of the human cervical spine have been reported in literature, to the best of knowledge of the authors, geometrical data on the facet joint structures such as the cartilage are not available. These data are important to understand the anatomy of the cervical spine and the role of the cartilage in sharing the external load during physiologic and traumatic situations. Furthermore, the data will assist mathematical modelers to accurately simulate this component of the cervical facet joint in finite element analysis of the spine.

MATERIALS AND METHODS

Six unembalmed human cadaver cervical spinal columns were used. A heavy-duty cryomicrotome was used to obtain the geometrical characteristics. The specimens were sectioned in the sagittal plane at 20- to 40-microm intervals. Geometric properties of the facet joint width, cartilage thickness, and cartilage gap (defined as the distance from the ventral-most or dorsal-most region of the facet joint to the location where the cartilage began to appear) were extracted from the anatomic sections that were midsagittal with respect to the facet joints from occiput to T1 levels. Multiple factorial analysis of variance techniques were used to determine the statistical significance of various geometrical parameters obtained from the anatomic sections.

RESULTS

The cartilage gap in the upper cervical spine (UCS) (C1-C2, i.e., UCS, 5.4% +/- 0.8) was lower (P < 0.0001) than the gap in the lower cervical spine (LCS) (C3-C7, i.e., LCS, 16.4% +/- 0.8). The gap at the ventral and dorsal regions was lower in the UCS (ventral 3.8% +/- 0.6, dorsal 7.0% +/- 1.4) than in the LCS (ventral 18.5% +/- 0.9, dorsal 14.2% +/- 1.1) with p values of less than 0.0001 and equal to 0.0004, respectively. Further, the gap in the dorsal region for females (14.7% +/- 1.8) was greater (P = 0.0523) than the gap for males (10.8% +/- 1.1). The overall mean facet cartilage thickness was lower (P = 0.0111) in females (0.6 mm +/- 0.1) than males (0.9 mm +/- 0.2) in the UCS. It was also lower (P = 0.0077) in females (0.4 mm +/- 0.02) than males (0.5 mm +/- 0.03) in the LCS. The facet joint width demonstrated differences only between the UCS and LCS (P < 0.0001), with higher magnitudes in the upper (17.4 mm +/- 0.4) than in the lower (11.3 mm +/- 0.3) region.

CONCLUSIONS

Facet joint morphology varies with the regions of the cervical spine (upper vs. lower), gender (male vs. female), and location (dorsal vs. ventral). Because of the lack of intervertebral discs in the UCS region, variations in these geometrical characteristics affect the biomechanical behaviors of the human spine secondary to external loads. Furthermore, the lack of adequate cartilage in females may expose the underlying adjacent subchondral bone to direct stresses during normal physiologic and traumatic loads.

Clinical anatomy of the fibrous capsule of human lumbar facet joint

OBJECTIVE

To describe the anatomical and histological characteristics of the fibrous capsule of human lumbar facet joints.

METHODS

Specimens of the facet joint capsules were obtained from 5 embalmed cadavers for macroscopic investigation, and microscopic observation of L5 facet joint capsules obtained from 2 fresh cadavers was performed after the specimens were stained by way of resorzinoroseine-van Gieson method.

RESULTS

The outer layer of the fibrous capsule was constituted by dense regular connective tissue that was in turn composed of parallel bundles of collagenous fibers. In the superior part of the joint capsules, the fibers were arranged in the direction different from that taken by the fibers in the inferior part. In the middle layer of the joint capsules, large quantities of elastic fibers were identified in the roots of the capsule.

CONCLUSIONS

The anatomical and histological complexities adapt the lumbar facet joint to better withstand loads from various directions. Immoderate rotatory manipulations may result in capsule injuries, which may aggravate low back pain in some cases.

The lumbar zygapophyseal (facet) joints: a role in the pathogenesis of spinal pain syndromes and degenerative spondylolisthesis

The zygapophyseal joints in the lumbar spine are important structural components contributing to the stability of the lumbar motion segments. Pathology of the zygapophyseal joints in the lumbar spine may be a significant cause of low back pain and segmental instability within the lumbar spine. Management of pathology related to the zygapophyseal joints remains a difficult challenge for the physician caring for patients with spinal disorders. Future investigations with tissue engineering, ligamentous reconstructions, and intervertebral disc replacement or regeneration may have useful applications in the treatment of zygapophyseal joint pathology.

Morphometrical study of the joint surface and capsule of the lumbar zygapophysial joint with special reference to their laterality

Using 26 osteoligamentous lumbar vertebral columns (260 facets), we morphometrically investigated the cartilagenous joint surface, inner capsular surface and capsular thickness. We also examined whether the subcapsular pocket was present and, if present, how far it extended along the joint margin. The proportion of the inner capsular area in the total joint surface area in a facet (the capsular-joint surface ratio) was hypothesized to correspond to the potential looseness (or tightness) of the facet. The absolute data themselves seemed to be useful for better understanding of the joint morphology. However, further evaluations of the differences between segments, left/right differences, individual segmental fluctuation patterns and correlations between parameters provided a novel classification of specimens according to the hypothetical progress of joint degeneration. Criteria for the classification existed in 1) the laterality in parameters defined as more than 100% larger or smaller than the contralateral facet and 2) the drastic segmental difference in parameters over 50% larger or smaller than the adjacent segment. Consequently, three types were identified: 1) outside of the criteria in both area and thickness (-/- type, 9 of 26); 2) the criteria did not fit the area parameters but did fit the thickness parameters (-/+ type, 8); the criteria were filled in both categories of parameters (+/+ type, 9). Notably, in the +/+ types, the capsular thickness and capsular-joint surface ratio correlated significantly (p < 0.01), i.e., the hypothetical loose joint had a thick capsule. We speculated that early joint degeneration starts from the -/- type and advances via the -/+ type to the +/+ type. Considerating these results, we recommended using MR imaging for detailed identification of laterality in the capsular thickness for low-back pain patients to discriminate candidates for future severe degenerative changes of the articular cartilage in the lumbar spine.

Facet joint geometry and intervertebral disk degeneration in the L5-S1 region of the vertebral column in German Shepherd Dogs

OBJECTIVE

To evaluate the possible association between facet joint geometry and intervertebral disk degeneration in German Shepherd Dogs.

ANIMALS

25 German Shepherd Dogs and 11 control dogs of similar body weight and condition.

PROCEDURE

Facet joint angles in the caudal portion of the lumbar region of the vertebral column (L5-S1) were measured by use of computed tomography, and the intervertebral discs were evaluated microscopically. The relationship between facet joint geometry and disk degeneration was evaluated by use of statistical methods.

RESULTS

German Shepherd Dogs had significantly more facet joint tropism than control dogs, but an association with disk degeneration was not found. However, German Shepherd Dogs had a different facet joint conformation, with more sagittally oriented facet joints at L5-L6 and L6-L7 and a larger angle difference between the lumbar and lumbosacral facet joints, compared with control dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

A large difference between facet joint angles at L6-L7 and L7-S1 in German Shepherd Dogs may be associated with the frequent occurrence of lumbosacral disk degeneration in this breed.

Geometric parameters of the in vivo tissues at the lumbosacral joint of young Asian adults

STUDY DESIGN

Magnetic resonance images (MRIs) were used to determine the geometry of the tissues studied.

OBJECTIVE

To investigate the geometric parameters of tissues around the lumbosacral joint.

SUMMARY OF BACKGROUND DATA

Cross-sectional area (CSA), moment arms, and line of action of the tissues located at lumbosacral joint (L5-S1), which are important in the study of spinal mechanics and models for the investigation of low back pain. It was insufficient information to describe the relative dimension of spinal tissues except muscles around the lumbar spine.

METHODS

MRIs from eight asymptomatic young Taiwanese male adults were collected to present CSA, moment arms, and line of action of the tissues located at lumbosacral joint (L5-S1). Four pairs of trunk muscles, erector spinae, rectus abdominis, abdominal oblique externus, and psoas muscles, ligamentum flavum, and facet joints at the bilateral sides were studied.

RESULTS

Spinal tissues at the level of lumbosacral joint were determined. The CSAs of the spinal elements at the L5-S1 normalized by the CSA of trunk ranged from 5.42% (the erector spinae) to 0.14% (the ligamentum flavum). The moment arm of the spinal elements relative to the trunk width and depth ranged from 40.91% (rectus abdominis at the y direction) to 0.38% (ligamentum flavum at the x direction). The profile of geometric elements of lumbosacral joint in the Asian male subjects was similar to the data collected from the white population. The data also showed that right-left symmetry in the aforementioned dimension.

CONCLUSION

Normalized data of the CSA, moment arm, and line of action of the spinal tissues at the L5-S1 joint were reported in vivo through the MRI techniques. The profile of geometric elements of lumbosacral joint in the Asian male subjects did not differ from the white population. In addition to muscles, the geometry of facet joint and ligament was determined, which would be important to the calculation of force distribution on the lumbosacral joint.

Comparative and functional anatomy of the mammalian lumbar spine

As an essential organ of both weight bearing and locomotion, the spine is subject to the conflict of providing maximal stability while maintaining crucial mobility, in addition to maintaining the integrity of the neural structures. Comparative morphological adaptation of the lumbar spine of mammals, especially in respect to locomotion, has however received only limited scientific attention. Specialised features of the human lumbar spine, have therefore not been adequately highlighted through comparative anatomy. Mathematical averages were determined of 14 measurements taken on each lumbar vertebrae of ten mammalian species (human, chimpanzee, orang-utan, kangaroo, dolphin, seal, Przewalski's horse, cheetah, lama, ibex). The revealed traits are analysed with respect to the differing spinal loading patterns. All examined mammalian lumbar spines suggest an exact accommodation to specific biomechanical demands. The lumbar spine has reacted to flexion in a predominant plane with narrowing of the vertebral bodies in quadrupeds. Torsion of the lumbar spine is withstood by an increase in the transverse distance between the inferior articular processes in the upper lumbar spine in primates, but lower lumbar spine in humans, quadrupeds and the seal. Sagittal zygapophyseal joint areas resist torsion in the seal and humans. Ventral shear is resisted by frontal zygapophyseal joint areas in humans and primates, and dorsal shear by encompassing joints in the ibex. The human fifth lumbar vertebra is remarkable in possessing the largest endplate surface area and the widest distance between the inferior articular processes, as an indicator of the high degree of axial load and torsion in bipedalism.

Structure and function of the lumbar intervertebral disk in health, aging, and pathologic conditions

This report is a comprehensive review of the basic and clinical science relating to the morphology and function of the intervertebral disc of the lumbar spine. The purpose is to review the anatomy, physiology, and biomechanics of the intervertebral disc of the lumbar spine in health, with aging, and in pathologic conditions. The complex morphology and ultrastructure of the intervertebral disc of the lumbar spine in the human provide the critical elements that permit normal mobility and transmission of force through the vertebral column. Alterations in this structure are manifest in a variety of clinical conditions routinely encountered in orthopaedic physical therapy practice. These structural and biomechanical changes are related to degenerative changes that occur in association with aging and trauma. Knowledge of the gross morphology and ultrastructure of the intervertebral disc and pathobiologic processes underlying associated conditions is essential to orthopaedic practice.

Types of synovial fold in the cervical facet joint

Few detailed studies of synovial folds of cervical facet joints exist at the moment. This study was performed to provide anatomical data for each synovial fold in the cervical facet joints, using 20 cervical spines from C2 to C7 for dissection. Anatomic evaluation of the synovial folds included the gross morphology, in three dimensions, and the histology. Also, degenerative changes of the lower facet surface on which synovial folds occurred were evaluated. On the basis of gross morphology and histological composition, three types of synovial folds were identified. Type-1 synovial folds, shaped like a crescent, consisted principally of adipose tissue. Type-2 synovial folds had an apical region made up of dense fibrous tissue, with the base and middle region consisting of adipose tissue. In type-2 folds, the size and shape varied, including some elliptic-shaped synovial folds projecting well into the joint cavity. Type-3 synovial folds were thin with ragged free borders, and were formed exclusively of fibrous tissue. This study shows the variable appearance of synovial folds. Speculation was raised that the articular facet impingement of a large synovial fold and the subluxation of a smaller structure may play a possible role in the pathology of some disorders of the neck.

The orientation of the articular facets of the zygapophyseal joints at the cervical and upper thoracic region

Knowledge of the orientation of facet joints in the cervical and upper thoracic region is important for understanding the biomechanical properties and clinical conditions relevant to the neck. The study was undertaken on dry macerated bones from 30 adult male human vertebral columns. The orientation of the superior articular facets in relation to their inclination with the sagittal and transverse planes was examined between C3 and T3 vertebrae in each column. The linear dimensions of the superior articular facets and the width/height ratio were also calculated. The results show that all vertebrae at C3 level and 73% at C4 level displayed posteromedially facing superior articular facets. Similarly at T1 level (C7/T1 joint) and below, all columns showed posterolaterally facing superior articular facets. The level of change in orientation, from posteromedial to posterolateral facing superior facets, was not constant and occurred anywhere between C4 (C3/C4 joint) and T1 (C7/T1 joint). The change in orientation followed 2 different patterns, i.e. sudden or gradual. The C6 vertebra (C5/C6 joint) was the most frequent site to show the transition. The shape of the superior articular facets was circular to oval at C3, C4 and C5 levels and gradually changed to a transversely elongated surface at C7 and T1. These findings correlate well with various cervical movements and associated clinical conditions.

An anatomical investigation of the human cervical facet capsule, quantifying muscle insertion area

Facet capsule injury has been hypothesised as a mechanism for neck pain. While qualitative studies have demonstrated the proximity of neck muscles to the cervical facet capsule, the magnitude of their forces remains unknown owing to a lack of quantitative muscle geometry. In this study, histological techniques were employed to quantify muscle insertions on the human cervical facet capsule. Computerised image analysis of slides stained with Masson's trichrome was performed to characterise the geometry of the cervical facet capsule and determine the total insertion area of muscle fibres into the facet capsule for the C4-C5 and C5-C6 joints. Muscle insertions were found to cover 22.4+/-9.6% of the capsule area for these cervical levels, corresponding to a mean muscle insertion area of 47.6+/-21.8 mm2. The magnitude of loading to the cervical facet capsule due to eccentric muscle contraction is estimated to be as high as 51 N. When taken in conjunction with the forces acting on the capsular ligament due to vertebral motions, these forces can be as high as 66 N. In that regard, these anatomical data provide quantitative evidence of substantial muscle insertions into the cervical facet capsular ligament and provide a possible mechanism for injury to this ligament and the facet joint as a whole.

The location of the pedicle and pars interarticularis in the axis

STUDY DESIGN

This is an anatomic and radiologic study on the lateral mass of the C2 vertebra.

OBJECTIVES

To define the location of the pedicle and pars interarticularis in the C2 vertebra.

SUMMARY OF BACKGROUND DATA

Transpedicular screw fixation of the C2 has been addressed in the literature. However, the use of the anatomic terminology of the pedicle or pars interarticularis (isthmus) in C2 is confusing in most of orthopaedic and neurosurgical literature since C2 is considered a transitional vertebra.

METHODS

Twenty dry C2 vertebrae were obtained for observation of the external anatomy of the C2 from superior, lateral, and inferior views. Six C2 vertebrae were harvested from cadavers and sectioned in the sagittal, horizontal, and coronal planes to observe the internal structures of the lateral mass using high resolution radiographs.

RESULTS

Based on observation, the pedicle of the C2 vertebra is defined as the portion beneath the superior facet and anteromedial to the transverse foramen. The pars interarticularis or isthmus is defined as the narrower portion between the superior and inferior facets. No remarkable difference in bone density and trabecular bone orientation between the pedicle and pars interarticularis was noted.

CONCLUSIONS

It is still more appropriate to call this procedure "transpedicular screw fixation" in the C2 to avoid confusion, although this technique requires placing a screw from the posterior aspect of the inferior articular process through the isthmus and pedicle into the vertebral body.

Sensory innervation of the cervical facet joints in rats

STUDY DESIGN

With a retrograde neurotracing method with Fluoro-Gold (FG; Fluorochrome, Denver, CO), the level of dorsal root ganglions (DRGs) innervating the C1-C2, C3-C4, and C5-C6 facet joints and their pathways were investigated in rats.

OBJECTIVES

To clarify the levels of DRGs and parasympathetic nodose ganglions innervating the cervical facet joints and to determine the pathways from the facet joint to DRGs.

SUMMARY OF BACKGROUND DATA

Patients with cervical facet lesions and whiplash sometimes experience diffuse neck pain, headache, arm, and shoulder pain, but the pattern of sensory innervation of the facet joint is still unclear.

METHODS

Sixty male Sprague-Dawley rats were used. Fluoro-gold crystals (FG) were applied into the C1-C2 (C1-C2 group), C3-C4 (C3-C4 group) and C5-C6 (C5-C6 group) facet joints, and numbers of the labeled neurons in DRGs from C1 to T5 and nodose ganglions were determined. To determine the sensory pathway, bilateral sympathectomy was performed.

RESULTS

Neurons labeled with FG were present in the DRGs from C1 through C8 in the C1-C2 group, from C1 to T2 in the C3-C4 group, and from C3 to T3 in the C5-C6 group without sympathectomy. In the nodose ganglions, 17 FG-labeled neurons were present. The number of the labeled neurons after sympathectomy was not significantly different in the C1, C2, and C3 DRGs in the C1-C2 group, in the C3 and C4 DRGs in the C3-C4 group, and in the C5 and C6 DRGs in the C5-C6 group from that in the groups without sympathectomy. In contrast, the number of labeled neurons in the DRGs was significantly less at the other levels than that in the groups without sympathectomy (P < 0.01).

CONCLUSION

Sensory nerve fibers of the cervical facet joint were derived from the C1-T3 DRGs. Some sensory nerves from the cervical facet joint entered the paravertebral sympathetic trunks and reached the DRGs at multisegmental levels. The present findings regarding the multisegmental innervation to the facet joint may be of importance in the treatment of facet joint syndrome.

Cervical transfacet versus lateral mass screws: a biomechanical comparison

The authors directly the compared biomechanical pullout strength of screws placed in the cervical lateral masses to that of screws placed across the facet joints. Posterior cervical fixation with lateral mass plates is an accepted adjunctive technique for cervical spine fusions. Altered anatomy resulting from congenital malformation, tumor, trauma, infection, or failed lateral mass fixation may limit traditional screw placement options. Transfacet screw placement, which has been studied extensively in the lumbar spine, may offer an alternative when posterior cervical fusion is required. Ten fresh human cadaveric cervical spines (postmortem age range, 69 to 91 years) were harvested. On one side, transfacet screws were placed at the C3-4, C5-6, and C7-T1 levels. On the other side, lateral mass screws were placed at the C3, C5, and C7 levels. The screw insertion technique at each level was randomized for right or left. After screw placement, each set of vertebral bodies were dissected and mounted in a custom jig for axial pullout testing using a servohydraulic testing machine. The load-displacement curves were obtained for each screw pullout. The mean pullout strength for the screws placed across the facets was 467 N (range, 192 to 1,176 N). This compares with 360 N (range, 194 to 750 N) for the lateral mass screws (p = 0.008). At each level, transfacet screws exhibited greater pullout resistance compared with the lateral mass placement, but the difference was most pronounced at the C7-T1 level (lateral mass = 373 N, transfacet = 539 N, p = 0.042). Cervical transfacet screw placement provides pullout resistance that is comparable to, if not greater than, lateral mass placement. This type of placement, although technically difficult, may be an alternative to lateral mass screws in cases with unusual anatomy, stripped screws, or when additional intermediate points of fixation are desired.

Laminotomy/medial facet approach in the excision of thoracic disc herniation

OBJECT

The author describes a technique of thoracic discectomy that has evolved from the posterolateral transfacet and the transpedicular approaches but that spares the pedicle and most of the facet joint.

METHODS

This approach was used to remove a total of 11 discs (T6-12) in seven patients. The follow-up period ranged from 8 months to 3 years. In four patients with axial and/or girdle pain significant improvement was demonstrated. The paraparesis in one patient with myelopathy improved postoperatively; that in another patient improved but recurred 8 months postoperatively. In one patient who experienced preoperative leg weakness, the weakness was slightly increased postoperatively, but this sequela was only transient. There were no other complications, and there were no deaths.

CONCLUSIONS

This technique appears safe and effective. It can be adapted to the conventional laminectomy known to spine surgeons and requires no specialized instruments. Further trials appear warranted.

Transpedicular approach for thoracic disc herniations

OBJECT

Patients with symptomatic herniated thoracic discs may require operation for intractable radiculopathy or functionally disabling myelopathy. In the past, laminectomy was the procedure of choice for the treatment of thoracic herniations, but it was found that the approach was associated with an unacceptably high rate of neurological morbidity. Several strategies have been developed to excise the disc without manipulating the spinal cord. The focus of this paper is the transpedicular approach.

METHODS

The author retrospectively reviewed the cases of 20 consecutive patients presenting with herniated thoracic discs in whom surgery was performed via a transpedicular approach. Fourteen patients presented with acute myelopathy and six with radiculopathy. Of those with myelopathy six of six regained ambulation and six of seven regained normal bladder function. No patient with myelopathy experienced neurological worsening. In four patients presenting with radiculopathy postoperative pain resolved, and in two it remained unchanged. Three minor complications (15%) occurred. No patient suffered postoperative spinal instability-related pain or delayed kyphosis.

CONCLUSIONS

As experience accumulates in the use of multiple approaches for the treatment of thoracic disc herniations, the role of each is becoming more clearly defined. The transpedicular approach is most applicable to lateral or centrolateral calcified or soft discs. The more anterior (transthoracic or thoracoscopic) and lateral (costotransversectomy or lateral extracavitary) approaches may be more useful for excision of central calcified discs.

Anatomy of deer spine and its comparison to the human spine

The anatomical parameters of the thoracic and lumbar regions of the deer spine were evaluated and compared with the existing data of the human spine. The objective was to create a database for the anatomical parameters of the deer spine, with a view to establish deer spine as a valid model for human spine biomechanical experiments in vitro. To date, the literature has supported the use of both calf and sheep spines as a suitable model for human spine experiments as the difficulty in procuring the human cadaveric spines is well appreciated. With the advent of Bovine Spongiform Encephalopathy (BSE) and its likely transmission to human in form of new variant Creutzfeld Jakob disease (CJD), there is a slight risk of transmission to humans through food chain if proper precautions for disposal of specimen are not adhered to. There is also a significant risk of transmission through direct inoculation to the researchers (Wells et al. Vet. Rec., 1998:142:103-106), working with infected bovine and sheep spine. The deer spines are readily available and there are no reported cases of deer being carriers of prion diseases (Ministry of Agriculture, Fisheries and Food, 1998). Six complete deer spines were measured to determine 22 dimensions from the vertebral bodies, endplates, disc, pedicles, spinal canal, transverse and spinous processes, articular facets. This was compared with the existing data of the human spine in the literature. The deer and human vertebrae show many similarities in the lower thoracic and upper lumbar spine, although they show substantial differences in certain dimensions. The cervical spine was markedly different in comparison. The deer spine may represent a suitable model for human experiments related to gross anatomy of the thoracic and lumbar spine. A thorough database has been provided for deciding the validity of deer spine as a model for the human spine biomechanical in vitro experiments.