Autoimmune arthritis deteriorates bone quantity and quality of periarticular bone in a mouse model of rheumatoid arthritis

This study showed that autoimmune arthritis induces especially severe osteoporosis in the periarticular region adjacent to inflamed joints, suggesting that arthritis increases the fragility fracture risk near inflamed joints, which is frequently observed in patients with RA.

INTRODUCTION

Periarticular osteoporosis near inflamed joints is a hallmark of early rheumatoid arthritis (RA). Here we show that rheumatic inflammation deteriorates the bone quality and bone quantity of periarticular bone, thereby decreasing bone strength and toughness in a mouse model of RA.

METHODS

Female BALB/c mice and SKG mice, a mutant mouse model of autoimmune arthritis on the BALB/c background, were used. At 12 weeks of age, BALB/c mice underwent either Sham surgery or bilateral ovariectomy (OVX), and SKG mice underwent intraperitoneal injection of mannan to induce arthritis. Eight weeks later, the mice were killed and the femurs and tibias were subjected to micro-computed tomography, Fourier transform infrared (FTIR) spectroscopic imaging, X-ray diffraction, histology, and mechanical testing.

RESULTS

SKG mice developed significant trabecular bone loss in both the distal metaphysis of the femur and the lumbar vertebral body, but the extent of the bone loss was more severe in the distal metaphysis. Neither SKG nor OVX mice exhibited changes in the geometry and matrix properties of the diaphysis of the femur, whereas SKG mice, but not OVX mice, did exhibit changes in these properties in the distal metaphysis of the femur. Bone strength and fracture toughness of the distal metaphysis of the tibia adjacent to the inflamed ankle joint were significantly decreased in SKG mice.

CONCLUSIONS

Autoimmune arthritis induces periarticular osteoporosis, characterized by deterioration of cortical bone geometry and quality as well as by trabecular bone loss, leading to severe bone fragility in periarticular bone adjacent to inflamed joints.

Chondroprotective effects of high-molecular-weight cross-linked hyaluronic acid in a rabbit knee osteoarthritis model

OBJECTIVES

We hypothesized that high-molecular-weight (MW) cross-linked (CL) hyaluronic acid (HA) improves joint lubrication and has an enhanced chondroprotective effect. We examined the histopathological changes and friction coefficients in osteoarthritic knee joints after injecting high-MW CL HA.

DESIGN

A bilateral anterior cruciate ligament transection (ACLT) model in 20 Japanese white rabbits was used. From week 5 after transection, low-MW HA (0.8 × 10(6) Da; HA80) or high-MW CL HA (6 × 10(6) Da; HA600) was injected weekly into 10 right knee for 3 weeks; normal saline (NS) was injected into the 10 left knee. A sham operation was undertaken to exclude spontaneous osteoarthritis (OA) in five knees. Results were evaluated with macroscopy, histopathology (Kikuchi's score), biomechanical testing, and rheological assessment of the joint fluid viscoelasticity. Statistical analysis was performed using one-way analysis of variance with a 95% confidence interval (CI) (P < 0.05).

RESULTS

The macroscopic findings showed severely damaged cartilage in 30% of the NS group and 20% of the HA80 and HA600 groups and intact cartilage in 100% of the sham group. The histological scores and friction coefficients of the HA600 group were significantly lower than those of the NS group (P = 0.007 and P = 0.002, respectively). Viscoelasticity measurements of the joint fluid showed no significant differences between the three treatment groups.

CONCLUSION

High-MW CL HA exerts potential chondroprotective effects and produces superior friction coefficients. Our results suggest that HA600 delays the progression of OA effectively and improves joint lubrication significantly.

A constitutive modeling of the human lumbar intervertebral disc and forward-backward bending simulation

This paper presents a constitutive law of the lumbar intervertebral disc to be described mathematically with the finite deformation theory. Mechanical behavior of the cadaveric lumbar disc obtained from continuous cyclic compression-tension tests and continuous cyclic axial torsion tests was formulated by the constitutive equation with a semi-circular shaped model. These equations were formulated with or without taking the nucleus pulposus into account. It was also confirmed that forward-backward bending behavior of the disc could be simulated numerically from these equations.

Phase lag of the intersegmental motion in flexion-extension of the lumbar and lumbosacral spine. An in vivo study

STUDY DESIGN

The lumbar and lumbosacral segmental motions were analyzed in vivo using cineradiographic method.

OBJECTIVES

To reveal the in vivo motion behavior of the lumbar and lumbosacral segments and their contribution to the whole lumbar motion.

SUMMARY OF BACKGROUND DATA

Relation between the lumbar motion and hip joint motion has been well investigated. The lumbar motion preceded the hip flexion in forward bending and delayed from extension of the hip joints in backward bending. However, it remains unclear how the lumbar and lumbosacral segmental motion contributed to the whole lumbar motion in vivo.

METHODS

Eight healthy male subjects participated in this study. The lower lumbar and lumbosacral motion (L3-S1) was recorded using cineradiography during flexion and extension. Each trunk motion was carried out from the neutral position to the maximum position. Segmental rotation and translation were measured sequentially at the L3-L4, L4-L5, and L5-S1 motion segments.

RESULTS

Intersegmental motion lags were observed between the lumbar and lumbosacral motion segments during flexion. The lower lumbar and lumbosacral motion (L3-S1) was initiated at the L3-L4 motion segment. The L4-L5 segmental motion delayed from the L3-L4 motion by an average of 6 degrees and preceded the L5-S1 motion by an average of 8 degrees. In extension, motions in the L3-L4 and L4-L5 segments were small, and the L5-S1 segmental motion only contributed to the total lower lumbar motion.

CONCLUSIONS

The lumbar and lumbosacral segmental motions occurred not simultaneously but stepwise from the upper level with intersegmental motion lags during flexion. These intersegmental motion lags were much larger than the neutral zone in vitro, which implied the neutral zone in vivo should be different from the neutral zone in vitro.

A mathematical expression of three-dimensional configuration of the scoliotic spine

Three-dimensional configuration of the scoliotic spine was mathematically expressed by a spatial curve passing through each vertebral centroid ("vertebral body line"). Three-dimensional location of the vertebral centroid was determined from digitization on the frontal and sagittal roentgenograms. Cobb angle, which is clinically used for measuring scoliosis curvature, was calculated in space to evaluate scoliosis deformity three-dimensionally. In forty-five scoliotic spines, regardless of curvature and curve patterns, the spinal configurations were excellently approximated by vertebral body lines. Vertebral body lines swerved from the sagittal plane at the end vertebrae, but aligned on a certain plane within the scoliosis region. Three-dimensional Cobb angle, which was larger than that in the frontal plane, can be utilized to evaluate the scoliosis deformity.

Effects of degeneration on the elastic modulus distribution in the lumbar intervertebral disc

STUDY DESIGN

Local elastic moduli of sliced intervertebral disc specimens were studied after establishing the relation between the elastic modulus and indentation behaviors by model tests using polyurethane specimens.

OBJECTIVES

This study presents a method to quantify the distribution of compressive elastic moduli in the lumbar intervertebral disc and to clarify the effects of degeneration on the distribution.

SUMMARY OF BACKGROUND DATA

No study has been performed to evaluate the distribution of axial compressive elastic moduli, which is supposed to relate previous biomechanical, biological, and biochemical findings regarding the intervertebral disc.

METHODS

Local compressive elastic moduli of the intervertebral disc were estimated by indentation tests. To evaluate the distribution of elastic moduli, indentation tests were performed at nodal points of a 10 mm x 10 mm network on a specimen. Nine cadaveric lumbar discs (L3-L4 and L4-L5) with various degrees of degeneration were tested. The age of subjects ranged 39 to 90 years (mean, 58.4 years).

RESULTS

The distribution of elastic moduli in normal discs was symmetric about the midsagittal plane. The mean elastic modulus in the nucleus pulposus was 5.8 kPa and those of the anterior and posterior anulus fibrosus were 110.7 and 75.8 kPa, respectively. The elastic moduli in the lateral portions were the lowest in the normal anulus, and were close to the values of the nucleus. Compared to normal discs, degenerated discs showed irregular distributions of elastic moduli. The elastic moduli of the degenerated nucleus were higher than those in normal discs.

CONCLUSIONS

The distribution of elastic moduli is much different between discs with and without degeneration.

A cineradiographic study on the lumbar disc deformation during flexion and extension of the trunk

To reveal deformation behaviour of normal lumbar discs (L((3/4)), L((4/5)) andL(5)/S(1), the lumbar spines of eight asymptomatic volunteers were examined cineradiographically during flexion and extension of the trunk. Disc deformation could be evaluated by displacement of the superior corners of the disc, which were measured with respect to the upper surface of the adjacent lower vertebra. Furthermore the in-vivo strain distribution of each lumbar disc was analysed by the finite element method and in-vivo measurement of the disc deformation. During flexion, deformation of the lumbar disc increased rapidly after a certain delay from the start of trunk motion and reached maximum value before the finish of trunk motion. It was also confirmed that time lags were present between the onsets of disc deformation. Namely, each disc deformed not simultaneously but stepwise from the upper to the lower level with time lags during flexion. When the lower disc deformation started, the strain at the adjacent upper discs had already reached more than half of the value at full flexion. RELEVANCE: The present study revealed one of the phenomena of lumbar spinal kinematics, which will provide helpful information to clinical problems such as evaluation of spinal instability.

A biomechanical definition of spinal segmental instability taking personal and disc level differences into account

The biomechanical definition of spinal segmental instability has not been clarified sufficiently, because of the great personal and level differences in intervertebral disc deformation. This article proposes a new method of judging spinal segmental instability regardless of these differences, using lateral functional radiographs. The linear relationship between the disc geometry and the disc deformation was confirmed in the normal intervertebral discs. The degree of spinal segmental instability could be evaluated statistically by calculating a regression residual from the regression line of the normal discs. Strain distributions of an intervertebral disc in the sagittal plane also were investigated to make sure of the differences in the deformation behaviors between normal spines and unstable lumbar spines. Although normal lumbar spines showed the consistent deformation pattern, the patterns of the unstable lumbar spines were different.

The mechanical properties of the human L4-5 functional spinal unit during cyclic loading. The structural effects of the posterior elements

Cyclic axial compression-tension tests and cyclic torsional tests were performed on ten fresh human L4-5 functional spinal units to investigate the structural effects of the posterior elements on the mechanical properties of L4-5 functional spinal units. The stiffness of the functional spinal unit increased with the increase of displacement under every loading. This was same in the intact functional spinal units and the functional spinal units after removal of each posterior element, respectively. All the posterior elements contributed to the compressive, tensile, and torsional stiffness of L4-5 functional spinal units. The apophyseal joints had a significant effect on the compressive and torsional stiffness. The effect of the apophyseal joints on the torsional stiffness became greater according to the extent of displacement, whereas their effect on the compressive stiffness was constant. The posterior ligaments (supraspinous and interspinous ligaments) had a significant effect on the tensile stiffness.

Influence of disc degeneration on mechanism of thoracolumbar burst fractures

In order to clarify the pathomechanism of thoracolumbar burst fractures and to evaluate the influence of disc degeneration and bone mineral density, a biomechanical study was performed using cadaveric spines. Eleven motion segments of thoracolumbar spines from human cadavers were compressed vertically until a fracture occurred. In addition, bone mineral density and degree of disc degeneration were determined for each specimen. Compression of 7 of 11 specimens resulted in the typical burst fracture characterized by retropulsion of a bony fragment into the spinal canal and an increase of the interpedicular distance. All seven specimens showed disruptions of the middle end plate and disc materials in the vertebral body. The fracture line was located between the middle of the end plate and the middle of the posterior wall cortex. No burst fractures were seen in the specimens with severely degenerated discs and osteoporosis. In order to confirm the stress state in a vertebra that induces the burst fracture, finite element analysis of one motion segment was also carried out under the same mechanical conditions as the experiments in this study. As a result of calculation for the healthy disc, the highest stresses under axial compression were concentrated in the following areas: the middle of the end plate, the cancellous bone under the nucleus pulposus, and the middle of the posterior wall cortex. This implies that the above regions are more vulnerable to vertical compressive load. In the analysis of specimens with severely degenerated discs, stresses were very low at the end plate and cancellous bone under the nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)