| Background and objective. The structure disorder and dysfunction of lumbar facet joint is an important reason for chronic low back pain. Because of its deep location, complex shape and small size, the research on the micro-structure was rare. This thesis is to study the components of the facet joint in detail, in order to investigate its morphological characteristics and the variation, so as to understand the relationship between the structure and local stress distribution, and the difference between asymptomatic and symptomatic patients.Methods. A total of 90 volunteers and 12 lumbar specimens from cadavers were included in this study. Each of the volunteers underwent proton density-weighted sequence MRI scanning and CT scanning. The images of facet joints were analyzed using custom software coded by Visual C++. Region of interest was processed by a multi-threshold technique, three dimensions reconstruction and point clouds dataset conversion algorithm.Each facet joint of the lumbar sample was scanned by MicroCT to investigate the structure of the cancellous bone. Then the capsule was opened to observe describe in detail degenerative changes of the articular cartilage. The mainly evaluation indicators were as follows①In vivo measurement of the subchondral cortical bone thickness. One of the specific MRI image at each level was selected for analyses. The subchondral cortical bone region was defined by a multi-threshold technique; each contour line was conversed to point clouds dataset. The thickness of subchondral cortical bone was calculated by the least distance between the two point clouds datasets.②In vivo measurement of the 3-dimensional distribution of the subchondral cortical bone thickness. The CT imaging of each facet joint were binarized and each contour line of subchondral cortical bone surface was converted to linear point cloud dataset then reconstructed to planar point clouds dataset. The thickness of subchondral cortical bone at each region was calculated by the least distance between the two point clouds datasets.③In vivo measurement of the distribution of facet joint space width. The CT imaging of each facet joint were binarized and each contour line of the facet joint surface was converted to linear point cloud dataset then reconstructed to planar point clouds dataset. The width of facet joint space at each region was calculated by the least distance between two point clouds datasets.④In vivo measurement of the surface area of the facet joint. After got the point clouds dataset, the area of the basal polygon face was calculated by using 2 adjacent points in one plane and 1 point in the adjacent plane. The area of the entire facet joint surface was calculated by summating the area of the polygons throughout the joint surface.⑤In vitro investigation of the cancellous bone structure. Using Scanco software to reconstruct the MicroCT imaging of the facet joint cancellous bone, and to analyze the structural parameters.⑥In vitro investigation of the articular cartilage degeneration features. The capsule of the facet joint was opened to observe the features of the degenerated cartilage directly. Analyzed the degree of the degeneration and its location.Result. Comparing the difference of parameters between superior and inferior facet joint, different regions of the articular process, male and female. Study the changing trend of each parameter by levels and age periods. Looking for the difference between symptomatic and asymptomatic persons.①The thickness of subchondral cortical bone. The averaged thickness was 1.56±0.37 mm, there was no difference between left and right facet. The thickness of subchondral cortical bone was larger by level and increased age. The thickness in superior facet was significantly larger than that in inferior facet. The thickness in male was significantly larger than that in female.②Three dimensional distribution of subchondral cortical bone. At superior facet, the largest thickness was located at the cranial region, while at inferior facet it located at caudal region. The thickness of subchondral cortical bone was significantly small at central region. The difference was more obvious at lower spinal levels.③Three dimensional distribution of the facet joint space width. The averaged thickness was 1.46±0.08mm. It got smaller by decreased age, and more obvious after the age of 40 years old. The width was significantly larger at female than that at male. It was also significantly smaller at low back pain patients. At each facet joint, the space at cranial region was significantly larger than that at caudal region, and it was also significantly larger at the central region. These difference was obvious at the lower three spinal levels.④The surface area of the facet joint. The averaged area was 173.2±3.6mm2, it was larger by increased level and age, more obvious at the lowest two levels and at the age more than 40. The area was significantly larger at low back pain patients than that at normal ones. And the superior facet was significantly larger than inferior facet at low back pain patients, except L5S1 level.⑤The three dimensional structural features of the cancellous bone:The cancellous bone in the superior facet was plate-like structure while it was rod-like structure in the inferior facet which means the cancellous bone was stronger at superior facet. At superior facet, the cancellous bone was significantly compact at cranial and caudal region while it was significantly loose at central region. At inferior facet, it was also significantly compact at cranial and caudal region while loose at central region. The density was larger by the increased of spinal levels, which reached its peak value at L4/5 levels and slightly lower at L5S1 level.⑥The feature of the degeneration of the articular cartilage:The incidence of cartilage degeneration was high, and it was increasing by the increased age and levels. The most serious level was L4/5. The degeneration of superior facet was more significantly than that of inferior facet. The degeneration was more significant at the surrounding region. The incidence of cartilage degeneration in superior articular process from high to low was cranial, caudal, dorsal, abdominal and central. While this order at inferior facet was caudal, cranial, dorsal, abdominal and central region.After comprehensive analysis, we found that①There were interrelated and interact on each structure of facet joint. At the position where the cartilage degenerated seriously, the subchondral cortical bone also showed thicker, and the cancellous bone seem more compact.②At low back pain patients, the facet joint space width was significantly smaller, the facet joint area was significantly larger, and there also was significantly difference between the area of superior and inferior facet.③The above difference was more significant with a variety of factors, such as age more than 40 years old, male or postmenopausal female, L4/5 level, superior and inferior facet didn't match and so on.Conclusions. This study:①Created a non-invasive and accurate method for lumbar facet joint structure measurement.②Revealed the distribution and variation of the micro structure of the lumbar facet joint. The reason of this difference was correlated with the shape of facet joint surface, the stress on the joint and the degeneration of this joint. It was the reflection of the long-term loading on the facet joint. The research on these structures will be helpful for further physiological and pathological study.
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