Objective To investigate a special optimized technique for computer aided measure,and provide an anatomical basis for the placement of lag screw in the posterior column of the acetabulum. Methods Eighty accurate hemi-pelvis models were reconstructed from 40 CT data sets.The optimization objective function,for improving the placement of lag screw,was built by adaptively sampling the weighted distance of screws to the acetabulum boundary according to surgical requirements,and the two end points of the screw were modified iteratively to reduce the objective value under constraints.The statistical measure data were provided according to new anatomical reference landmarks for clinical use. Results The optimal entry point for lag screw fixation in the posterior column was located(18.90?1.19) mm above the line connecting the anterior borderline of the sacroiliac joint with the notch between the anterior superior iliac spine and the anterior inferior iliac spine,and the connecting line was divided by the perpendicular project point with a proportion of 2∶3.The mean inclination of the lag screw was(85.99?2.04)? for angle with the line connecting the entry point with the notch between the anterior superior iliac spine and the anterior inferior iliac spine,and(37.54?1.55)? for angle with the line connecting the entry point with the perpendicular project point;the mean length of the lag screws in the posterior column was(133.07?3.22)mm.Conclusion The automatic optimized technique for the computer aided measure is very efficient and has many advantages over the conventional manual dissection methods,and is convenient to design new anatomical reference landmark systems for clinical use.

Objective To research the connection between the sagittal orientation of facet joints and disc degeneration in lumbar spine and to investigate the contribution of which to development the degenerative spondylolisthesis. Methods A new effective CAD method was used to accurately establish 9 finite element models(FEM)which were assembled respectively with facet-joint angle 65?, 45?, 25?, with normal disc, light degenerative disc and severe degenerative disc. The biomechanical parameters of 9 finite element models were measured under axial compressive load within physiological range. Results Compared with FEMs with facet-joint angle 45? and 25?, anterior displacement of L4 vertebra in FEMs with facet-joint angle 65? was increased, where the maximum von Mises stresses on facet surface, isthmus and the contact force on facet surface in horizontal orientation were obviously increased. Meanwhile, FEMs with facet-joint angle 65? showed a decrease in end-plate bulge and an increase in stress of annular matrix. The stiffness in light degenerative disc FEMs was reduced and the von Mises stresses on facet surface and isthmus was slightly increased compared with the normal disc FEMs. Among all, the FEM with facet-joint angle 65? combined with light degenerative disc showed the poorest resisting anterior shear force. Conclusion Sagittal orientation of facet joints is not only the primary inducement of the degenerative spondylolisthesis but the secondary pathological change of remodeling of the facet-joints induced by the regional stress change. The inherent instability of lumbar motion segment of sagittal orientation of facet joints is influenced by the lumbar disc degeneration. The lumbar disc degeneration has no manifested contribution to the aggravation of the sagittal orientation of facet joints.

BACKGROUND:Spine is relatively complex in structure, shape, material properties, and load bearing. The traditional biomechanical method cannot solve these problems. OBJECTIVE:To investigate the stress distribution of intervertebral disc, zygapophysial joints and vertebral body of degenerative scoliosis, and to provide accordance to the biomechanical mechanism of degenerative scoliosis occurrence and development. METHODS:Based on the successive CT images of spinal column from T12 to superior segment of S1 of degenerative scoliosis patients, the special material properties were attributed to the model to form the integrated and effective three-dimensional finite element model of degenerative scoliosis. The model was loaded on the anteflexion, extension, left lateral bending, right lateral bending, left rotation and right rotation conditons. Then the spinal activity and the stress distribution of intervertebral disc, vertebral body and articular cartilage of zygapophysial joints were calculated and analyzed. RESULTS AND CONCLUSION:The spinal activities of degenerative scoliosis finite element model were less than those of common lumbar spine. The stress distribution of intervertebral disc was inclined to the verge of it and the greatest stress was appeared on the extension motion. The apex of scoliosis was the place of stress concentration and the obvious stress concentration of articular cartilage of zygapophysial joints was appeared on the rotation motion, then fol owed by the extension motion, especial y that of articular cartilage of zygapophysial joints on the apex of scoliosis. Stress concentration is easily appeared on the apex of scoliosis, and the extension and rotation motion can aggravate the development of degenerative scoliosis.

Objective To study and establish a high quality digital 3D anatomical modeling of the mandible with full teeth.Methods A set of accurate digital models of standard anatomical specimens of mandibular teeth were obtained by laser scanning, and the 3D mandible model was reconstructed by CT scan data;then, a registration deformation method based on the geometry and image anatomical landmark was employed to do the registration of each tooth to the mandible model, and finally the tooth enamel , dentin, periodontal ligament were generated .Results A high quality digital 3D anatomical modeling of the mandible with full teeth was built , each tooth had detail crown and whole root , the distinction between the enamel , dentin, periodontal ligament , and any anatomical regions can be zoomed and rotately displayed . Conclusion The digital 3D anatomical modeling of the mandible with full teeth has realistic 3D imaging view and convenient teaching-learning function , and has tremendous apllication futures in the stomatology , maxillofacial and other medical departments .

Objective To investigate the stress changes of intervertebral disk of degenerative scoliosis (DS) after treatment with short-segment internal fixation and fusion.Methods Based on the DS patient's CT images of the successive spinal column from T12 to superior segment of S1,assigning special material attributes to the model and forming the integrated and effective three dimensional finite element model of DS.Treated with the short-segment (one-segment and two-segment) spinal canal decompression +intervertebral bone fusion+pedicle screw internal fixation.Loading the model on the following postures:anteflexion,postextension,left lateral inclination,right lateral incliniation,left rotation and right rotation.Calculating and analyzing the stress distribution of intervertebral disk and comparing to that of the preoperative normal DS model.Results The stress of intervertebral disk after the short-segment internal fixation and fusion was increased than that of preoperation.The rotation motion affected greater to the upper intervertebral disk of fixation segment and the extension motion affected greater to the inferior intervertebral disk of fixation segment.The increase of stress of upper and inferior intervertebral disk of fixation segment treated with one-segment fixation and fusion(average was 6.03,4.58 MPa,separately) was greater than that of the two-segment fixation and fusion (average was 5.24,4.47 MPa,separately),but there was no statisticdifference (P ＞ 0.05).Conclusions The short-segment intemal fixation can increase the intervertebral disk stress of adjacent segment fixation of DS.The effect on the stress of upper and inferior intervertebral disk of fixation segment of one-segment fixation and fusion is greater than that of two-segment fixation and fusion.And the patient should avoid the rotation and extension movements after treated with the short-segment internal fixation and fusion.

Objective To construct a detailed, 3-dimensional, anatomically accurate finite element (FE) model of lumbar L4-L5 segment from CT data with a new kind of computer aided design (CAD) method. Methods A modified "no-seed region segmentation" was done to extract the interest region in the CT scan images and produce a binary image. "Best cross-section planes" accounting for the preferential direction dictated by lumbar spine were placed on the initial iso-surface model, forming a "non-regular piecewise subspace". This subspace and the embedded iso-surface mode were transformed by local affine transforms to a "regular subspace", in which a surface mesh of high quality was generated quickly. Finally a reverse transform procedure was employed to recover the shape feature of the lumbar surface mesh of lumbar L4-L5 in the original 3-dimensional space, which was then imported into ANSYS for the 3-dimensional FE mesh construction. Results All complicated anatomical features of the L4-L5 segment were explicitly represented in the unprecedented finite element model. The predicted results for compression, flexion and extension correlated well with experimental data under similar loading configurations. Conclusion The presented CAD method containing advanced algorithm implements fast and accurate simulation of such complicated geometry with fine mesh representation for lumbar FE analysis.

Objective To investigate a special optimization technique for computer aided measure, and provide anatomical basis for screw internal fixation in the cavitas glenoidalis through the coracoid process of scapula. Methods Thirty accurate scapula models were reconstructed from CT data sets. First, special optimization objective function was designed for single screw internal fixation configuration, and the optimal placement of screw was found automatically under constraints. Then, the placements of double screws internal fixation configuration were searched taking advantage of principal component analysis. Finally, statistical measure data were provided according to new anatomical reference landmarks for clinical use. Results For single screw internal fixation configuration, the distance from the optimal screw entry point P to the acromion process point X was (39.15±2.28) mm, to the coracoid process point Y was (28.66±2.68) mm, to the angulus superior point Z was (61.13±6.57) mm;The angle was (81.27±7.15)° between PX and PY, and (133.27±6.84)° between PX and PZ. The mean inclination of the lag screw was (104.08±4.41)° for the angle with line PX, (101.29±3.51)° with line PY, and (76.23±5.03)° with line PZ. For double screws configuration, the distance from the original single screw entry point P to the screw entry point E was (5.12±1.37)mm,to the screw entry point F was (3.88±0.94)mm. The angle between the long axis of coracoid process and line EF was (27.41±3.51)°. Conclusion The automatic optimization technique for computer aided measure is very efficient and has many advantages over the conventional manual dissection methods, and is convenient to design new anatomical reference landmark system for clinical use.

This paper aims to establish an accurate finite element model of complete lumbar spine with complex lumbar spinal stenosis (LSS), and then to do comparison and analysis of normal model and decompression surgery model. Firstly, we chose some patients with complex LSS and then collected the CT scanned data. Then we generated a complete FE model of Lumbar with complex LSS using a specially designed modeling system, and we also created a normal lumbar model and a decompression treated model. We applied same boundary conditions in all the three models. The results showed that the active movement range of complex LSS was smaller than that of the normal model, but the movement range of the decompression model was larger than that of the normal. There are stress concentration around the endplate and disk at the degenerative intervertebral? disk L4-L5 and adjacent disk L3-L4 for LSS model, and the stress of the decompression model increased more significantly. This simulation demonstrated that the treatment of simple decompression for lumbar spine with complex LSS can release the pain, but may result in unstability and accelerate the degeneration.
Decompression, Surgical ; methods ; Finite Element Analysis ; Humans ; Lumbar Vertebrae ; surgery ; Models, Biological ; Spinal Stenosis ; surgery

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