ABSTRACT
Abstract Objective We aimed to study the "in vitro" pullout strength of SpineGuard/Zavation Dynamic Surgical Guidance Z-Direct Screw (DSG Screw, SpineGuard Inc, Boulder, Colorado, USA), a screw designed to be inserted using a direct insertion technique. Methods Dynamic Surgical Guidance Screws of 5.5 and 6.5 mm were introduced into polyurethane blocks with a density of 10 PCF (0,16g/cm3). According to the experimental group, screws were inserted without pilot hole, with pilot without tapping, undertapping and line-to-line tapping. Screw pullout tests were performed using a universal test machine after screw insertion into polyurethane blocks. Results Screws inserted directly into the polyurethane blocks without pilot hole and tapping showed a statistically higher pullout strength. Insertion of the screw without tapping or with undertapping increases the pullout screw strength compared with lineto-line tapping. Conclusion Dynamic Surgical Guidance Screw showed the highest pullout strength after its insertion without pilot hole and tapping.
Resumo Objetivo Nosso objetivo foi estudar a resistência à extração "in vitro" do parafuso SpineGuard/Zavation Dynamic Surgical Guidance Z-Direct (Parafuso DSG Guia Cirúrgico Dinâmico, SpineGuard Inc, Boulder, Colorado, USA), um parafuso projetado para ser inserido utilizando a técnica de inserção direta. Métodos Os parafusos DSG de 5,5 e 6,5 mm foram introduzidos em blocos de poliuretano com densidade de 10 PCF (0,16g/cm3). De acordo com o grupo experimental, os parafusos foram inseridos sem um orifício piloto, com um orifício piloto sem o macheamento, com macheamento e com macheamento linha a linha. Os testes de extração do parafuso foram realizados em uma máquina de teste universal, após a inserção do parafuso em blocos de poliuretano. Resultados Os parafusos inseridos diretamente nos blocos de poliuretano sem o orifício piloto e o macheamento mostraram uma resistência à extração estatisticamente maior. A inserção do parafuso sem o macheamento ou com o macho de menor diâmetro aumenta a resistência à extração do parafuso em comparação com o macheamento linha a linha. Conclusão O parafuso DSG apresentou a maior resistência à extração após a inserção sem o orifício piloto e o macheamento.
Subject(s)
Spinal Fusion , Biomechanical Phenomena/physiology , Bone Screws , Pedicle ScrewsABSTRACT
ABSTRACT Purpose: To investigate the relationship between biomechanical properties of the cornea and postoperative refractive changes in patients with low-level astigmatism after cataract surgery. Methods: This prospective study recruited patients undergoing cataract surgery involving 2.8-mm superior incisions. Biomechanical properties of the cornea were evaluated preoperatively using the Ocular Response Analyzer, and corneal profiles were evaluated using a Scheimpflug system (Pentacam HR). Topographic astigmatism, total corneal aberrations (TCA) and higher-order corneal aberrations (HOCA) analyses were performed preoperatively and during 1- and 3-month postoperative exams. The incidences of surgically-induced astigmatism (SIA) and HOCAs were calculated using vector analyses. Associations of the preoperative biomechanical properties of the cornea with SIA and HOCAs were evaluated. Results: This study included 28 eyes of 28 patients. The preoperative corneal hysteresis (CH) was 8.68 ± 1.86 mmHg, and the corneal resistance factor (CRF) was 8.66 ± 1.61 mmHg. At the 1-month postoperative evaluation, significant changes were observed in HOCAs (p=0.023), TCAs (p=0.05), astigmatism (p=0.02), and trefoil (p=0.033); in contrast, differences in coma (p=0.386) and spherical aberration (SA) were not significant (p=0.947). At the 3-month visit, significant changes were only observed in TCAs (p=0.02) and HOCAs (p=0.012). No relationships between the preoperative corneal hysteresis and corneal resistance factor and postoperative SIA and HOCA were identified, other than a positive correlation between the 3-month postoperative incidence of corneal hysteresis and spherical aberration. Conclusions: Despite the observed lack of relationships of preoperative biomechanical properties of the cornea with SIA and postoperative aberrations (except for SA), further studies involving larger patient groups are needed to explore the unexpected refractive deviations after cataract surgery.
RESUMO Objetivo: Investigar a relação entre as propriedades biomecânicas da córnea e as mudanças refrativas pós-operatórias em pacientes com baixa astigmatismo após a cirurgia de catarata. Método: Neste estudo prospectivo, recrutamos os pacientes submetidos a cirurgia de catarata com incisões superiores de 2,8 mm. As propriedades biomecânicas da córnea foram avaliadas no pré-operatório pelo Ocular Response Analyzer (ORA, Reichert, EUA) e o perfil corneano foi avaliado por um sistema Scheimpflug (Pentacam HR, Oculus Optikgeräte, GmbH). As avaliações do astigmatismo topográfico e das aberrações corneanas de alta ordem (HOCA) foram feitas no pré-operatório e no 1º e 3º mês pós-operatório. O astigmatismo induzido cirurgicamente (SIA) e aberrações corneanas de alta ordem foram calculados pela análise vetorial. Associações das propriedades biomecânicas da córnea no pré-operatório com astigmatismo induzido cirurgicamente e aberrações corneanas de alta ordem foram avaliadas. Resultados: O estudo foi realizado em 28 olhos de 28 pacientes. A histerese corneana (CH) pré-operatória foi 8,68 ± 1,86 mmHg, e o fator de resistência da córnea (CRF) foi de 8,66 ± 1,61 mmHg. No pós-operatório de 1 mês houve mudanças significativas aberrações corneanas de alta ordem (p=0,023), aberração total (p=0,05), astigmatismo (p=0,02) e trifóglio (p=0,033), mas as diferenças em coma (p=0,386) e aberração esférica (SA) foram insignificantes (p=0,947). No terceiro mês, a única mudança significativa foi em RMS total (p=0,02) e aberração total (p=0,012). Não houve relação entre histerese corneana e o fator de resistência da córnea pré-operatórios e astigmatismo induzido cirurgicamente e aberrações corneanas de alta ordem pós-operatórios, além de uma correlação positiva entre o histerese corneana e o aberração esférica do 3º mês pós-operatório. Conclusões: Apesar de não haver relação entre as propriedades biomecânicas pré-operatórias da córnea e astigmatismo induzido cirurgicamente e aberrações (exceto SA) após a cirurgia em nosso estudo, são necessários mais estudos com grupos de pacientes maiores de explicar os erros refrativos inesperados após a cirurgia de catarata.
Subject(s)
Humans , Male , Female , Adult , Middle Aged , Aged , Postoperative Complications/etiology , Astigmatism/etiology , Cataract Extraction/adverse effects , Cornea/surgery , Lens Implantation, Intraocular/adverse effects , Corneal Wavefront Aberration/etiology , Postoperative Period , Biomechanical Phenomena , Prospective Studies , Preoperative PeriodABSTRACT
Background Corneal refractive surgery has significant effects on corneal biomechanical properties.However,there are few study on large scale population with corneal biomechanical properties in the myopic population before corneal refractive surgery.Objective This study was to evaluate the change of corneal biomechanical properties and influence factors in myopic eyes using ocular response analyzer (ORA).Methods A prospective cohort study was carried out in Beijing Tongren Eye Center from April 2010 to January 2011.Corneal hysteresis (CH) and corneal resistance factor (CRF) were detected using ORA in 1 792 eyes of 896 myopic subjects who were going to receive corneal refractive surgery under the informed consent.According to different spherical equivalent (SE) the eyes were grouped into-0.25-＜-3.0 D group,-3.0-＜-6.0 D group,-6.0-＜-9.0 D group,-9.0-＜-12.0 D group,-12.0-＜-15.0 D group and ≥-15.0 D group and according to different central corneal thickness (CCT),the eyes were grouped into ＜500 μm group,500-＜550 μm group,550-＜600 μm group and≥600 μm group.The CH value and CRF value in different SE groups or different CCT groups were compared,and the factors influencing CH and CRF were analyzed by Pearson correlation analysis.Results The mean CH and CRF value were (9.84±1.52)mmHg (1 mmHg =0.133 kPa) and (10.46±1.71) mmHg,respectively in the myopic eyes.The CH values were (10.35±1.53),(10.07±1.55),(9.81±1.46),(9.71±1.59),(9.35±1.55) and (9.23±1.28) mmHg in the-0.25-＜-3.0 D group,-3.0-＜-6.0 D group,-6.0-＜-9.0 D group,-9.0-＜-12.0 D group,-12.0-＜-15.0 D group and ≥-15.0 D group,respectively,showing a significant difference among the groups (F=20.69,P＜0.01),and the CH values in the-6.0-＜-9.0 D group,-9.0-＜-12.0 D group,-12.0-＜-15.0 D group and ≥-15.0 D group were significantly lower than those in the-6.0-＜-9.0 D group,-9.0-＜-12.0 D group (all at P＜0.01).There was no significant difference in the CRF values among different SE groups (F =0.65,P =0.49).CH and CRF values were increasing with the raise of CCT,with evidently differences among the CCT＜500 μm group,500 μm ≤ CCT＜550 μm group,550 μm≤ CCT＜600 μm group and CCT≥ 600 μm group (CH:F=110.99,P＜0.01;CRF:F =84.35,P＜0.01),and the CH and CRF values were significantly higher in the 550 μm ≤ CCT＜600 μm group and CCT ≥600 μm group than those in the CCT＜500 μm group (all at P＜0.01).CH showed a positive correlation with SE (r =0.24,P＜0.01),and no significant correlation between CRF and SE (r =0.03,P =0.20).The CH and CRF showed the positive correlations with the CCT (r=0.42,0.57,both at P＜0.01).In addition,CH and CRF values increased as the increases of SE,corneal curvature (CC) and CCT values,with the regression equation of CH =-7.87+0.08SE+0.16CC+0.02CCT (R2=0.26,P＜0.01) and CRF=-11.42+0.14CC+0.03CCT (R2=0.34,P＜0.01),respectively.The CH and CRF did not change with the age and gender in the subjects.Conclusions Corneal biomechanical properties including CH and CRF were positively correlated with CCT,CC and SE.
ABSTRACT
Background The novel dynamic biomechanical device Corvis ST can measure a variety of corneal deformation parameters and record the dynamic process of cornea deformation.Understanding various corneal deformation parameters is of important clinical significance for morphological and functional prediction for myopic eyes in corneal refractive surgery.However,the range and meaning of corneal deformation parameters in myopic eyes are still unknown.Objective This study was to establish the range of corneal defamation parameters by Corvis ST and explore its clinical significance in myopic eyes.Methods A descriptive study was designed under the approval of Ethic Committee of Tianjin Eye Hospital and informed consent of patients.This study protocol complied with Helsinki Declaration.Four hundred and seventy-seven eyes of 257 myopic patients who were going to receive corneal refractive surgery were included in Tianjin Eye Hospital from June 2014 to January 2015.The corneal deformation parameters including the first applanation time (1st A-time),first applanation lengh (1 st A-length),first applanation velocity (1 st A-velocity),second applanation time (2nd A-time),second applanation length (2nd A-length),second applanation velocity (2nd A-velocity),highest concavity time (HC-time),highest concavity deformation amplitude (HC-DA),highest concavity peak distance (HC-PD),highest concavity radius (HC-R),non-contact intraocular pressure (IOPnct) and the central corneal thickness (CCTst) were measured by Corvis ST.Corneal structural parameters including CCT and corneal curvature were measured by 3-D anterior segment analysis system (Pentacam),and corneal biomechanical parameters including corneal resistance factor (CRF),corneal hysteresis (CH),intraocular pressure mimic Goldmann (IOPg) and intraocular pressure of corneal compensation (IOPcc) were measured by Ocular Response Analyzer (ORA).The distributions of the data were tested with the Shapiro-Wilk test and 95％ confidence intervals (CI) were calculated.The correlations of the variables were evaluated by Pearson correlation coefficient and Spearman rank correlation coefficient.Multiple linear regression was used to analyze the changes of 1st A-time,2nd A-time and HC-DA with corneal morphology and biomechanical parameters.Resnlts Only 1st A-time,2ndA-time,HC-time,HC-DA,CCTst and IOPnct showed the normality distribution in corneal deformation parameters.The positive correlations were found between 1st A-time,1st A-length,2nd A-length,2nd A-velocity,HC-R with CCT (r=0.338,rs=0.129,rs=0.282,rs =0.374,r=0.306,all at P＜0.01),while 1st A-velocity,2nd A-time,HC-D and HC-PD showed the negative correlations with CCT (rs =-0.235,r=-0.130,r=-0.259,r=-0.226,all at P＜0.01).CRF and CH showed positive correlations with 1st A-time,2nd A-length,2nd A-velocity,HC-time,HC-R and negative correlations with HC-PD,△A-length (all at P＜0.05).1st A-time,2nd A-time and HC-DA changed with CRF and IOPcc with the regression formations of 1st A-time =6.185+0.066CRF+0.034IOPec (F=300.123,P =0.000),2nd A-time=23.397-0.074IOPec-0.044CRF (F=227.979,P=0.000) and HC-DA =1.523-0.017IOPcc-0.017CRF (F=152.662,P=0.000).The CCTst,IOPst and IOPnct values by Corvis ST were significantly lower than CCT by Pentacam ([548.23±26.31] μm,IOPg ([15.02±2.72]mmHg and ([16.02-±2.56]mmHg) by ORA respectively (t =11.00,2.919,6.815,all at P ＜ 0.01).Conclusions The corneal deformation parameters by Corvis ST can quantitatively describe corneal biomechanical properties in myopic eyes.Both IOP and the corneal steep curvature of the 3 mm center area (K2) affect the deformation response of cornea.The reliability of Corvis ST in the measurement of CCT and IOP remains to be further studied.