ABSTRACT
Objective To investigate the biomechanical effects of interbody cage height on cervical spine during anterior cervical discectomy and fusion (ACDF) surgery, so as to provide references for selection of interbody cage. Methods The finite element model of normal cervical spine (C2-7) was built and validated, and the cages with different height (5, 6, 7, 8 mm) were implanted into C5-6 disc (cage5, 6, 7, 8 model). All the models were loaded with pure moment of 1.5 N•m to produce flexion, extension, blending and axial torsion motions on the cervical spine, and the effects of cage height on range of motion (ROM), facet joint stress, intervertebral pressure in cervical spine were investigated. Results The intervertebral angle at the fusion segment increased by 0.68°with per 1 mm-increase of height. The ROM at C5-6 after cage implantation was less than 0.44°. The influence of cage height on ROM in C4-5 was greater than that in C6-7, and the changes of ROM in non-fusion segments were less than 7.3%. The cage height variation had a smaller impact on the facet joint stress and intervertebral pressure. The stresses in the capsular ligament, cage and screw-plate system increased gradually with the increase of cage height, and these stresses in the cage6, 7, 8 models were much higher than those in the cage5 model. Conclusions For patients who need implanting fusion cage, the cage height should be 0-1 mm greater than the original intervertebral space height.
ABSTRACT
Objective To investigate the biomechanical effects of interbody cage height on cervical spine during anterior cervical discectomy and fusion (ACDF) surgery,so as to provide references for selection of interbody cage.Metheds The finite element model of normal cervical spine (C2-7) was built and validated,and the cages with different height (5,6,7,8 mm) were implanted into C5-6 disc (cage 5,6,7,8 model).All the models were loaded with pure moment of 1.5 N · m to produce flexion,extension,lateral bending and axial rotation motions on cervical spine,and the effects of cage height on range of motion (ROM),facet joint stress,intervertebral pressure in cervical spine were investigated.Results The intervertebral angle at the fusion segment increased by 0.68° with per 1 mm-increase in height.The ROM in C5-6 after cage implantation was smaller than 0.44°.The influence of cage height on ROM in C4-5 was greater than that in C6-7,and the changes of ROM in non-fusion segments were smaller than 7.3％.The cage height variation had a smaller impact on the facet joint stress and intervertebral pressure.The stresses in the capsular ligament,cage and screw-plate system increased gradually with the increase of cage height,and the stresses in cage 6,7,8 models were much higher than those in cage 5 model.Conclusions For patients who need implanting fusion cage,the cage height should be 0-1 mm greater than the original intervertebral space height.
ABSTRACT
Objective To investigate the biomechanical effects of interbody cage height on cervical spine during anterior cervical discectomy and fusion (ACDF) surgery,so as to provide references for selection of interbody cage.Metheds The finite element model of normal cervical spine (C2-7) was built and validated,and the cages with different height (5,6,7,8 mm) were implanted into C5-6 disc (cage 5,6,7,8 model).All the models were loaded with pure moment of 1.5 N · m to produce flexion,extension,lateral bending and axial rotation motions on cervical spine,and the effects of cage height on range of motion (ROM),facet joint stress,intervertebral pressure in cervical spine were investigated.Results The intervertebral angle at the fusion segment increased by 0.68° with per 1 mm-increase in height.The ROM in C5-6 after cage implantation was smaller than 0.44°.The influence of cage height on ROM in C4-5 was greater than that in C6-7,and the changes of ROM in non-fusion segments were smaller than 7.3％.The cage height variation had a smaller impact on the facet joint stress and intervertebral pressure.The stresses in the capsular ligament,cage and screw-plate system increased gradually with the increase of cage height,and the stresses in cage 6,7,8 models were much higher than those in cage 5 model.Conclusions For patients who need implanting fusion cage,the cage height should be 0-1 mm greater than the original intervertebral space height.
ABSTRACT
AIM: To better reveal the changing process of macula area after photodynamic therapy (PDT), the changes of tomographic imaging on macular fovea optical coherence tomography ( OCT ) scan at different follow- up time points after treating age-related macular degeneration ( AMD) by PDT were investigated. METHODS: This cohort study included 30 eyes of 26 patients diagnosed as AMD. The dosage of verteporfin was calculated according to manufacturer's instruction. All participants got FFA, ICG, OCT scan and best corrected visual acuity before and followed up for 2wk, 1, 2, 3mo after PDT. The standard five lines combined with 6 lines OCT scan covered key parts of lesion and the scan locations before and after were kept the same. The bilaminar foveal thickness (BFT), outer high reflectivity band thickness ( OHRBT ) , and the total area of intraretinal fluid ( IRF ) and subretinal fluid ( SRF ) were measured at different time points. The relationship between the changes and follow up time was analyzed. Statistical analysis of the data was performed using SPSS for windows version 13. 0. RESULTS: There months after treatment, an improvement of 2 lines or better on the Snellen chart was achieved on 22 eyes, visual acuity of 3 eyes without significant change, 3 eyes got decreased, 2 cases lost follow up. The average macular thickness of improved 22 eyes before treatment was 722. 5±55. 6μm, 2wk after treatment, 708. 3±45. 3μm, 1mo, 584. 4±49. 3μm, 2mo, 430. 7±50. 2μm and 180. 6 ±36. 3μm at 3mo. The OHRBT before and after treatment respectively were 302. 3 ±50-2μm, 277. 5±42. 3μm, 202. 7±40. 1μm, 180. 6±35. 7μm, 100. 8±22. 9μm. The total area of both IRF and SRF was estimated as 0. 34±0. 12mm2 , 0. 25±0. 07mm2 , 0. 10±0-05mm2 , 0. 08±0. 04mm2 , 0. 05±0. 01mm2 . CONCLUSION:SRF and retinal edema of patients with AMD were absorbed 1mo after PDT, and the BFT, OHRBT were significantly tend to be thin.