[Evaluation of neointimal coverage and thrombosis at 3 months and 2 years post sirolimus-eluting stent implantation by optical coherence tomography].

OBJECTIVE: To evaluate the short- and long-term prevalence of persistent uncovered struts and in-stent thrombus after sirolimus-eluting stent (SES) implantation by optical coherence tomography (OCT). METHODS: OCT was performed for 31 SES in 21 patients at 3 months and for 30 SES in 21 patients at 2 years post SES implantation. Thickness of new intima inside each strut was measured and thickness equal to 0 microm was defined as an uncovered strut. Existence of in-stent thrombus was also evaluated. RESULTS: A total of 4545 struts and 3707 struts were evaluated at 3 months and at 2 years post SES implantation, respectively. New intima at 2 years was significantly thicker than that at 3 months [(71 +/- 93) microm vs. (29 +/- 41) microm, P < 0.01]. Percent of uncovered struts at 2 years was significantly lower than that at 3 months (5% vs. 15%, P < 0.01). Prevalence of uncovered struts was similar at 2 years and at 3 months (81% vs.95%, P > 0.05). Subclinical thrombus was recognized in 14% patients at 3 months and 2 years post SES implantation. CONCLUSIONS: Neointimal coverage inside the SES is a continuous process and the number of uncovered struts decreased from 3 months to 2 years after SES implantation. Few uncovered struts could still be visualized in the majority of patients at 2 years post SES implantation.

[Finite element analysis of stress changes of posterior spinal pedicle screw infixation].

OBJECTIVE: To evaluate the mechanical response of L3-L4 segment after posterior interfixation with a transpedicle screw system. METHODS: Spiral CT machine was used to conduct continuous parallel scan on the L3-L4 section of a 40-year-old healthy male Chinese. The image data thus obtained were introduced into MIMICS software to reconstruct the 2-D data into volume data and obtain 3-D models of every element.. Pro/3-D model construction software system was used to simulate the 3-D entity of L3-L4 fixed by screw robs through spinal pedicle via posterior approach that was introduced into the finite element software ABAQUS to construct a 3-D finite element model. The stress changes on the vertebrae and screw under the axial pressure of 0.5 mPa was analyzed. RESULTS: Under the evenly distributed pressure the displacement of the L4 model was 0.00125815 mm, with an error of only 0.8167% from the datum displacement. The convergence of the model was good. The stress of the fixed vertebral body, intervertebral disc, and internal fixators changed significantly. The stress concentration zone of the intervertebral disc turned from the posterolateral side to anterolateral side. The stress produced by the fixed vertebral bodies decreased significantly. Obvious stress concentration existed in the upper and lower sides of the base of screw and the fixed screw at the upper vertebral body bore greater stress than the lower vertebral body. CONCLUSIONS: Integration of computer aided device and finite element analysis can successfully stimulate the internal fixation of L3-IA visa posterior approach and observe the mechanic changes in the vertebral column more directly.