劉達(dá),謝慶云,鄭偉,康夏,張波,權(quán)毅,周江軍,雷偉,潘顯明
·基礎(chǔ)研究·
骨質(zhì)疏松綿羊腰椎內(nèi)不同椎弓根螺釘界面的顯微CT研究
劉達(dá),謝慶云,鄭偉,康夏,張波,權(quán)毅,周江軍,雷偉,潘顯明
目的通過顯微CT技術(shù)比較骨質(zhì)疏松綿羊腰椎內(nèi)可膨脹椎弓根螺釘(EPS)與骨水泥強(qiáng)化螺釘(PMMA-PS)的界面情況。方法健康成年雌性綿羊8只,成功建立骨質(zhì)疏松模型后將每只綿羊的腰椎(L1-L6)隨機(jī)分為3個(gè)不同置釘組(采用相同的方法制備釘?shù)?,普通椎弓根螺釘(CPS)組經(jīng)釘?shù)老蜃刁w內(nèi)擰入CPS,PMMA-PS組在擰入CPS之前向釘?shù)纼?nèi)注入骨水泥(PMMA)1.0ml,EPS組經(jīng)釘?shù)老蜃刁w內(nèi)擰入EPS。分別于術(shù)后6周和12周處死綿羊,對(duì)螺釘及周圍骨組織進(jìn)行顯微CT掃描,通過三維重建和骨組織計(jì)量學(xué)方法評(píng)價(jià)釘?shù)澜缑媲闆r。結(jié)果術(shù)后6周和12周時(shí)CPS組和EPS組中骨小梁與螺釘直接接觸,形成了“釘-骨”界面,PMMA-PS組中螺釘被PMMA嚴(yán)密包裹,形成了“釘-PMMA-骨”界面。EPS組螺釘?shù)那岸蚊涢_形成“爪狀”結(jié)構(gòu),擠壓并顯著改善了周圍骨質(zhì)的質(zhì)量。從術(shù)后6周到12周,CPS組和PMMA-PS組中螺釘周圍的骨質(zhì)質(zhì)量無明顯變化,未見PMMA降解吸收,PMMA-PS組中形成了二次界面。術(shù)后12周時(shí)EPS膨脹部分周圍的骨質(zhì)條件較術(shù)后6周有顯著提高,形成了良好的“釘-骨”界面。結(jié)論在骨質(zhì)疏松綿羊腰椎內(nèi),EPS通過膨脹擠壓刺激周圍骨質(zhì)生長,在術(shù)后早期顯著提高了局部骨質(zhì)的質(zhì)量,隨著擠壓應(yīng)力的持續(xù)存在,局部骨質(zhì)質(zhì)量在后期進(jìn)一步改善,形成了良好的生物性界面,為螺釘?shù)倪h(yuǎn)期穩(wěn)定提供了良好的骨質(zhì)基礎(chǔ)。
骨質(zhì)疏松;椎弓根螺釘;聚甲基丙烯酸;腰椎;顯微CT
目前,椎弓根螺釘系統(tǒng)已經(jīng)廣泛用于治療脊柱骨折、畸形及退行性疾病[1-3],但骨質(zhì)疏松時(shí)椎弓根螺釘?shù)墓潭◤?qiáng)度明顯降低,嚴(yán)重影響預(yù)后。為有效增強(qiáng)骨質(zhì)疏松條件下螺釘?shù)陌殉至?,本課題組前期設(shè)計(jì)了可膨脹的椎弓根螺釘(expansive pedicle screw,EPS),可顯著提高螺釘?shù)墓潭◤?qiáng)度[4-8],且不增加螺釘在椎弓根內(nèi)的長度和直徑,能有效降低因改進(jìn)螺釘設(shè)計(jì)帶來的諸多風(fēng)險(xiǎn)。大量研究顯示,縱然傳統(tǒng)的骨水泥(polymethylmethacrylate,PMMA)存在許多不足,但憑借其出色的力學(xué)強(qiáng)度和強(qiáng)化作用,目前仍被用于強(qiáng)化螺釘?shù)姆€(wěn)定性[8-11]。釘?shù)澜缑媲闆r是螺釘穩(wěn)定固定的前提條件,特別是在體內(nèi),釘?shù)澜缑娴淖兓苯記Q定了螺釘?shù)葍?nèi)固定的動(dòng)態(tài)穩(wěn)定性和遠(yuǎn)期穩(wěn)定性。因此,對(duì)于椎弓根螺釘釘?shù)澜缑娴难芯坑兄谏钊肓私饴葆斣隗w內(nèi)穩(wěn)定的機(jī)制。目前,有關(guān)EPS和PMMA強(qiáng)化螺釘(polymethylmethacrylate-augmented pedicle screw,PMMA-PS)界面的優(yōu)劣,國內(nèi)外研究甚少。本研究旨在通過顯微CT三維重建和骨組織計(jì)量學(xué)方法評(píng)價(jià)不同椎弓根螺釘在骨質(zhì)疏松綿羊腰椎中釘?shù)澜缑娴奈⒂^情況,以期為進(jìn)一步研究其在體內(nèi)穩(wěn)定的機(jī)制提供依據(jù)。
1.1 實(shí)驗(yàn)材料及儀器 普通椎弓根螺釘(conventional pedicle screw,CPS)長度20.0mm,直徑4.5mm(圖1A)。EPS長度20.0mm,直徑4.5mm,中央空腔直徑1.0mm。螺釘前半段有一縱向裂隙,通過中央空腔將內(nèi)栓插入螺釘后使螺釘?shù)那岸闻蛎?圖1B、C)。CPS 64枚,EPS(含配套內(nèi)栓、壓棒和頂絲)32枚,所有螺釘均由醫(yī)用鈦合金制成,由山東樞法模-威高骨科醫(yī)療器械公司提供。PMMA(天津合成材料工業(yè)研究所生產(chǎn))用于強(qiáng)化螺釘。雙能X線吸收骨密度儀(Lunar Corp,Madison,WI,USA)由成都軍區(qū)總醫(yī)院內(nèi)分泌科提供。eXplore Locus SP 型Micro-CT(Healthcare,GE,USA)由西京醫(yī)院全軍骨科研究所提供。
1.2 動(dòng)物及模型建立 健康成年雌性綿羊8只,體重55.7±5.6kg,年齡5.5±0.7歲,均已過生育哺乳期,由成都軍區(qū)總醫(yī)院實(shí)驗(yàn)動(dòng)物中心提供。所有涉及動(dòng)物實(shí)驗(yàn)的操作均嚴(yán)格遵守國家及成都軍區(qū)總醫(yī)院關(guān)于動(dòng)物實(shí)驗(yàn)的醫(yī)學(xué)倫理學(xué)規(guī)定。采用速眠新(0.1ml/kg)麻醉成功后,取俯臥位測(cè)量綿羊去勢(shì)前腰椎的骨密度(bone mineral density,BMD),然后對(duì)所有綿羊行雙側(cè)卵巢切除術(shù)。術(shù)前半小時(shí)及術(shù)后肌注頭孢唑啉鈉1.0g,2次/d,共3d。術(shù)后1個(gè)月開始肌注甲潑尼龍0.45mg/(kg.d),連續(xù)注射9個(gè)月后逐漸減量至停止(共10個(gè)月),觀察1個(gè)月無不良反應(yīng)后再次測(cè)量綿羊腰椎BMD,下降>25%時(shí)確定為脊柱骨質(zhì)疏松動(dòng)物模型建立成功[12]。
圖1 普通椎弓根螺釘(CPS)和膨脹式椎弓根螺釘(EPS) Fig. 1 The conventional pedicle screw and expansive pedicle screw of vertebral archA. Conventional pedicle screw (CPS); B. Components of expansive pedicle screw (EPS), including EPS, bolt, rod and nut; C. Assembled EPS
1.3 實(shí)驗(yàn)方法 骨質(zhì)疏松綿羊取俯臥位,速眠新0.1ml/kg肌內(nèi)注射麻醉成功后,沿腰部正中切口逐層切開,分離顯露腰椎(L1-L6)的椎板及橫突。采用人字嵴頂點(diǎn)法確定進(jìn)釘點(diǎn),與棘突成40°角方向制備釘?shù)?,深度?0mm。透視確定定位針位置良好。每只綿羊的L1-L6隨機(jī)分入3個(gè)不同的置釘組。CPS組:經(jīng)釘?shù)老蜃刁w內(nèi)直接擰入CPS;PMMA-PS組:向釘?shù)雷⑷隤MMA(1.0ml)后再擰入CPS;EPS組:經(jīng)釘?shù)老蜃刁w內(nèi)直接擰入EPS。依次縫合切口。圍術(shù)期給予頭孢唑啉鈉預(yù)防感染。密切觀察術(shù)后動(dòng)物生命體征、飲食、雙下肢活動(dòng)及切口愈合情況。術(shù)后6周和12周隨機(jī)處死4只綿羊,取出帶有螺釘?shù)难?,游離成單個(gè)椎體。每個(gè)腰椎隨機(jī)選擇一側(cè)椎弓根螺釘進(jìn)行釘?shù)赖娘@微CT三維重建和骨組織計(jì)量學(xué)分析。
1.4 顯微CT三維重建 用特制的環(huán)鉆沿螺釘?shù)拈L軸鉆取以螺釘為中心、直徑約1.5cm的圓柱狀標(biāo)本。在44mm_tube_21μm_270min_ss條件下對(duì)螺釘及周圍的骨質(zhì)進(jìn)行顯微CT掃描和重建,觀察各組中的釘?shù)澜缑媲闆r。掃描和重建條件:分辨率21μm,旋轉(zhuǎn)角度200°,旋轉(zhuǎn)角度增量0.5°,電壓80kV,電流80μA,曝光時(shí)間2960ms,幀平均數(shù)6,像素組合為1×1;黑白掃描校正;Hounsfeild刻度校正;重建條紋標(biāo)準(zhǔn)化校正軟件,Micro View三維重建處理軟件(GE Healthcare,USA)。
1.5 骨組織計(jì)量學(xué)分析 取CPS組和EPS組中螺釘周圍相同位置、相同體積的區(qū)域?yàn)楦信d趣區(qū)域(RIO,圖2),設(shè)定重建閾值為1000,進(jìn)行骨計(jì)量學(xué)分析。數(shù)據(jù)庫產(chǎn)生的主要參數(shù)包括:①組織骨密度(tissue mineral density,TMD),即單位體積內(nèi)高于設(shè)定界值的骨量,以mg/cm3表示;②骨體積分?jǐn)?shù)(bone volume fraction,BVF),即骨小梁的體積(BV)除以ROI的體積(TV),以百分比(%)表示;③骨表面積體積比(bone surface/bone volume,BS/BV),即骨小梁的表面積(BS)除以骨的體積(BV),以mm–1表示;④骨小梁厚度(trabecular thickness,Tb.Th),以μm表示;⑤骨小梁數(shù)目(trabecular number,Tb.N),以mm–1表示;⑥骨小梁間隙(trabecular spacing,Tb.Sp),以μm表示。
圖2 CPS和EPS周圍骨組織計(jì)量學(xué)分析Fig. 2 Histomorphometric analysis of bone tissue around CPS and EPSA. CPS; B. EPS. The yellow region is region of interest (ROI)
1.6 統(tǒng)計(jì)學(xué)處理 采用SPSS 16.0軟件進(jìn)行數(shù)據(jù)分析。計(jì)量資料以表示,處理前后綿羊腰椎BMD的比較采用配對(duì)t檢驗(yàn),同組中兩時(shí)間點(diǎn)間及兩組間釘?shù)乐車怯?jì)量學(xué)參數(shù)的比較采用獨(dú)立樣本t檢驗(yàn)。P<0.05為差異有統(tǒng)計(jì)學(xué)意義。
2.1 大體觀察 麻醉清醒后綿羊可站立,術(shù)后第2天可自行行走。術(shù)后飲食、雙下肢活動(dòng)及切口情況均未見明顯異常。術(shù)后2周切口甲級(jí)愈合,予以拆線。術(shù)后未見脊髓、神經(jīng)壓迫癥狀。
2.2 綿羊腰椎BMD 建模前后綿羊腰椎的BMD分別為1.14±0.10g/cm2和0.83±0.07g/cm2,差異有統(tǒng)計(jì)學(xué)意義(P<0.05),建模后BMD平均下降27.2%,表明骨質(zhì)疏松綿羊模型建立成功。
2.3 顯微CT三維重建 顯微CT三維重建清楚地顯示了各組中螺釘界面的情況。在術(shù)后6周和12周時(shí),CPS組中骨小梁直接與螺釘表面接觸,釘骨之間形成了“釘-骨”界面(圖3A、圖4A);PMMA-PS組中,螺釘被PMMA嚴(yán)密包裹,PMMA存在于釘骨之間及釘?shù)乐車墓撬枨粌?nèi),阻礙了骨小梁與螺釘?shù)闹苯咏佑|,釘骨之間形成了“釘-PMMA-骨”界面(圖3B、圖4B);EPS組中,骨小梁直接與螺釘表面接觸形成了“釘-骨”界面,螺釘?shù)那岸嗣黠@膨脹,擠壓并刺激局部骨小梁生長,使螺釘前段周圍骨質(zhì)的質(zhì)量較CPS組有顯著改善(圖3C、圖4C)。肉眼觀察,CPS組和PMMA-PS組中螺釘周圍的骨質(zhì)質(zhì)量(骨小梁數(shù)量和密度)在術(shù)后6周和12周時(shí)均未見明顯差異,PMMA-PS組螺釘周圍的PMMA未見明顯降解吸收,而術(shù)后12周時(shí)EPS膨脹部分周圍的骨質(zhì)質(zhì)量較術(shù)后6周有明顯改善。
圖3 術(shù)后6周釘?shù)澜缑娴膍icro-CT三維重建結(jié)果Fig. 3 3D micro-CT reconstruction of interface between bone and screw 6-week post-operationA, B and C. CPS group, PMMA-PS group and EPS group, respectively. Brown, green and white color represent bone trabecula, screw and PMMA, respectively. (Resolution 21μm, 2048×2048)
2.4 骨組織計(jì)量學(xué)分析 術(shù)后6周和12周時(shí)EPS組螺釘前段周圍骨小梁的TMD、BVF、Tb.Th和Tb.N均明顯高于CPS組,而BS/BV和Tb.Sp明顯低于CPS組,差異有統(tǒng)計(jì)學(xué)意義(P<0.05)。術(shù)后12周時(shí)CPS組的TMD、BVF、Tb.Th和Tb.N與術(shù)后6周比較有不同程度提高,而BS/BV和Tb.Sp與術(shù)后6周比較出現(xiàn)不同程度降低,但差異均無統(tǒng)計(jì)學(xué)意義(P>0.05)。術(shù)后12周時(shí)EPS組的TMD、BVF、Tb.Th和Tb.N均明顯高于術(shù)后6周時(shí),Tb.Sp明顯低于術(shù)后6周時(shí),差異有統(tǒng)計(jì)學(xué)意義(P<0.05),而BS/BV與術(shù)后6周時(shí)比較差異無統(tǒng)計(jì)學(xué)意義(P>0.05,表1)。
圖4 術(shù)后12周釘?shù)澜缑娴膍icro-CT三維重建結(jié)果Fig. 4 3D micro-CT reconstruction of interface between bone and screw 12-week post-operationA, B and C. CPS group, PMMA-PS group and EPS group, respectively. Brown, green and white color represent bone trabecula, screw and PMMA, respectively. (Resolution 21μm, 2048×2048)
為了避免因增加螺釘直徑和長度導(dǎo)致的諸多風(fēng)險(xiǎn),本課題組前期研制出了前段可膨脹的椎弓根螺釘(EPS)。體外生物力學(xué)實(shí)驗(yàn)證實(shí),與USS、Tenor、CDH等普通螺釘相比,EPS的穩(wěn)定性分別提高48.4%、40.8%和25.3%[4],且在骨質(zhì)疏松尸體腰椎中的穩(wěn)定性接近傳統(tǒng)的PMMA強(qiáng)化方法[5]。在骨質(zhì)疏松綿羊體內(nèi)進(jìn)行的力學(xué)研究顯示,EPS可顯著提高骨質(zhì)疏松綿羊腰椎椎弓根螺釘?shù)姆€(wěn)定性,達(dá)到了與目前臨床上常用的PMMA強(qiáng)化方法近似的固定效果,且隨著時(shí)間延長,EPS的穩(wěn)定性顯著提高[8]。然而,螺釘?shù)姆€(wěn)定性取決于釘?shù)澜缑娴膹?qiáng)度,體內(nèi)釘?shù)澜缑娴膭?dòng)態(tài)變化直接影響螺釘在體內(nèi)的穩(wěn)定性,目前國內(nèi)尚無有關(guān)動(dòng)物體內(nèi)EPS與PMMA-PS釘?shù)澜缑媲闆r的比較研究。因此,為了進(jìn)一步探索螺釘穩(wěn)定的微觀機(jī)制,本研究在骨質(zhì)疏松綿羊體內(nèi)比較了EPS與PMMA-PS釘?shù)澜缑娴奈⒂^結(jié)構(gòu)。
表1 釘?shù)乐車切×河?jì)量學(xué)分析(±s,n=8)Tab. 1 Histomorphometric analysis of bone tissue around screw (x±s, n=8)
表1 釘?shù)乐車切×河?jì)量學(xué)分析(±s,n=8)Tab. 1 Histomorphometric analysis of bone tissue around screw (x±s, n=8)
(1)P<0.05 compared with CPS group; (2)P<0.05 compared with 6-week
12-week CPS group EPS group CPS group EPS group TMD(mg/cm3) 387.46±40.74 447.83±43.13(1) 423.43±46.89 506.06±50.27(1)(2)BVF(%) 44.05±7.46 57.05±8.37(1) 51.92±8.24 67.55±9.40(1)(2)BS/BV(mm–1) 15.02±3.51 11.01±2.31(1) 12.05±2.71 8.90±1.82(1)Tb.Th(μm) 153.84±25.68 227.85±38.27(1) 184.57±36.96 276.24±48.19(1)(2)Tb.N(mm–1) 2.11±0.22 2.53±0.28(1) 2.35±0.29 2.90±0.34(1)(2)Tb.Sp(μm) 281.18±39.09 234.37±30.73(1) 257.18±34.45 201.25±25.61(1)(2)Parameters 6-week
顯微CT技術(shù)自問世以來,憑借較高的分辨率在骨組織微觀結(jié)構(gòu)研究中得到了廣泛應(yīng)用。顯微CT可對(duì)骨組織進(jìn)行精細(xì)的三維平掃及立體重建,分辨率可達(dá)微米水平,同時(shí)它還能準(zhǔn)確地測(cè)量骨組織形態(tài)計(jì)量學(xué)定量參數(shù),如骨小梁厚度、骨小梁數(shù)量、骨小梁間隙、組織骨密度等[13],從而可以更客觀、準(zhǔn)確、全面地反映標(biāo)本的骨質(zhì)質(zhì)量[14-15]。顯微CT還可根據(jù)不同材料的密度進(jìn)行多種成分的三維重建疊加,進(jìn)一步觀察多種成分物質(zhì)之間的相互關(guān)系,也便于觀察內(nèi)固定與周圍骨組織的整合情況。Aldini等[16]應(yīng)用該技術(shù)對(duì)釘?shù)乐車墓琴|(zhì)進(jìn)行骨組織計(jì)量學(xué)分析發(fā)現(xiàn),骨質(zhì)疏松綿羊腰椎內(nèi)螺釘周圍的骨小梁厚度和骨小梁體積分?jǐn)?shù)明顯低于正常綿羊。本課題組在動(dòng)物體內(nèi)實(shí)驗(yàn)中通過三維重建和骨計(jì)量學(xué)分析發(fā)現(xiàn),硫酸鈣骨水泥可以促進(jìn)釘?shù)乐車墓琴|(zhì)生長,改善螺釘與周圍骨質(zhì)的接觸,形成了更為優(yōu)化的“釘-骨”界面[17]。
目前顯微CT技術(shù)已經(jīng)成為內(nèi)固定界面研究的主要方法之一。前期研究中本課題組設(shè)計(jì)出用于綿羊腰椎的小型EPS和CPS,并在離體綿羊腰椎標(biāo)本中進(jìn)行了實(shí)驗(yàn),結(jié)果顯示,EPS前段膨脹擠壓周圍的骨質(zhì),增加了局部的骨質(zhì)密度,形成了早期的“機(jī)械性穩(wěn)定”,顯著提高了螺釘?shù)目v向和橫向穩(wěn)定性,而在離體標(biāo)本中EPS形成的“釘-骨”界面明顯優(yōu)于PMMA-PS形成的“釘-PMMA-骨”界面[6-7]?;谏鲜鲅芯浚緦?shí)驗(yàn)進(jìn)一步在骨質(zhì)疏松綿羊腰椎內(nèi)動(dòng)態(tài)觀察和比較了EPS和PMMA-PS的釘骨界面情況,結(jié)果顯示,EPS前段脹開的兩瓣擠壓局部骨質(zhì)并刺激骨小梁生長,改善了螺釘局部的骨質(zhì)質(zhì)量(骨小梁數(shù)量和骨小梁密度),在術(shù)后6周和12周兩個(gè)時(shí)間點(diǎn)均明顯優(yōu)于CPS前段周圍的骨質(zhì)質(zhì)量。同時(shí),由于EPS的前段持續(xù)擠壓周圍骨質(zhì),隨著時(shí)間延長,EPS膨脹部分周圍的骨小梁數(shù)量及骨小梁空間排列明顯改善,后期(術(shù)后12周時(shí))EPS前段周圍的骨質(zhì)質(zhì)量和釘骨界面情況較術(shù)后早期(6周時(shí))均有明顯提高。此外,術(shù)后12周EPS局部骨小梁的TMD、Tb.Th、Tb.N和BVF均明顯高于術(shù)后6周,而Tb.Sp明顯低于術(shù)后6周;術(shù)后12周EPS前段周圍骨組織的質(zhì)量較術(shù)后6周明顯提高,這為螺釘?shù)倪h(yuǎn)期穩(wěn)定性提供了良好的骨質(zhì)環(huán)境。CPS則不存在這方面的優(yōu)勢(shì),從術(shù)后6~12周螺釘局部的骨質(zhì)質(zhì)量并無明顯改變。EPS前段周圍骨質(zhì)質(zhì)量和微觀結(jié)構(gòu)的變化,進(jìn)一步解釋了前期力學(xué)實(shí)驗(yàn)的結(jié)果,即EPS螺釘?shù)姆€(wěn)定性在術(shù)后6周和12周時(shí)均明顯高于CPS,且隨著時(shí)間延長,EPS螺釘?shù)姆€(wěn)定性也有進(jìn)一步提高,而CPS螺釘無明顯變化。
PMMA-PS組中螺釘被PMMA嚴(yán)密包裹,PMMA存在于螺釘周圍的骨小梁間隙中,提高了局部的組織密度。然而,從術(shù)后6周到12周,螺釘周圍的PMMA未見明顯降解、吸收,PMMA存留于釘骨之間阻礙了骨小梁與螺釘?shù)闹苯咏佑|,難以形成釘骨之間的生物性整合,形成了二次界面,為螺釘?shù)倪h(yuǎn)期穩(wěn)定性埋下了隱患。由于PMMA與周圍骨小梁呈犬牙交錯(cuò)的狀態(tài),很難用密度分割法將兩者完全單獨(dú)重建,這可能嚴(yán)重影響骨計(jì)量學(xué)分析,所以本研究未對(duì)PMMA-PS周圍的骨組織進(jìn)行計(jì)量學(xué)分析和比較研究。另外,考慮到標(biāo)本的非同一性,本研究未對(duì)螺釘穩(wěn)定性與釘?shù)拦墙M織計(jì)量學(xué)參數(shù)進(jìn)行相關(guān)性分析。
綜上所述,本研究結(jié)果表明,在骨質(zhì)疏松綿羊腰椎內(nèi),EPS通過膨脹擠壓刺激周圍骨質(zhì)生長,在術(shù)后早期明顯提高了局部的骨質(zhì)質(zhì)量,隨著擠壓應(yīng)力的持續(xù)存在,局部的骨質(zhì)質(zhì)量在后期進(jìn)一步改善,形成了良好的生物性界面,為螺釘?shù)倪h(yuǎn)期穩(wěn)定提供了良好的骨質(zhì)基礎(chǔ)。
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Comparison of interfaces of different pedicle screws with micro-CT technique in lumbar vertebrae with osteoporosis of sheep
LIU Da1, XIE Qing-yun1, ZHENG Wei1, KANG Xia1, ZHANG Bo1, QUAN Yi1, ZHOU Jiang-jun2, LEI Wei3*, PAN Xianming1*1Department of Orthopedics, General Hospital of Chengdu Command, Chengdu 610083, China
2Department of Orthopedics, 184 Hospital of PLA, Yingtan, Jiangxi 335000, China
3Department of Orthopedics, Xijing Hospital, Fourth Military Medical University, Xi’an 710032, China
*< class="emphasis_italic">Corresponding authors. PAN Xian-ming, E-mail: xianmingpan@163.com; LEI Wei, E-mail: leiweispine@163.com
s. PAN Xian-ming, E-mail: xianmingpan@163.com; LEI Wei, E-mail: leiweispine@163.com
This work was supported by the National Natural Science Foundation of China (81301606), and the Foundation of the General Hospital of Chengdu Command (2013YG-B015)
ObjectiveTo compare the changes in interfaces of expandable pedicle screw (EPS) and polymethylmethacrylateenhanced pedicle screw (PMMA-PS) after being used in osteoporotic sheep lumbar vertebrae with micro-CT technique.MethodsSix lumbar vertebrae (L1-L6) in each sheep were randomly divided into three different screw-insertion groups (two vertebrae with four pedicles in each group) after reproduction of osteoporosis in sheep. After making the pilot hole using the same method, CPS was inserted through the pilot hole into vertebral body in CPS group, while PMMA (1.0ml) was injected into the pilot hole prior to the insertion of CPS in PMMA-PS group, and EPS was inserted through pedicle into vertebral body in EPS group. All the sheep were sacrificed, and lumbar vertebrae (L1-L6) were harvested respectively at the 6- and 12-week postoperatively. The micro-CT three dimensional reconstruction and histomorphometric analysis were performed to evaluate the interfacial conditions.ResultsIt was clearly demonstrated that interface was formed where the bone trabeculae was directly in contact with the screw to form "screw-bone" interface in both CPS and EPS groups both 6 weeks and 12 weeks after the operation. The screw was fully surrounded by PMMA and formed "screw-PMMA-bone" interface in PMMA-PS group. The anterior part of EPS expanded in vertebral body to form a clawlike structure, pressing against the surrounding bone trabeculae, thus significantly improved the local bone quality(amount and density of bone trabeculae). From 6 weeks to 12 weeks after the operation, there was no visual difference in bone quality around the screw in both CPS and PMMA-PS groups. There was no degradation and absorption of PMMA, and it led to form the second non-biological interface in PMMA-PS group. Nevertheless, bone quality around expanding part of EPS at 12-week post-operation was significantly improved compared with that at 6-week post-operation, thus forming a good "screw-bone" interface.ConclusionsEPS can improve the bone quality around the anterior part of screw through expanding compression in early stage in lumbar vertebrae of osteoporotic sheep. With a continuous compression stress in anterior part of EPS, it may result in a significant improvement in the local bone quality in late stage by forming a good biological interface, thus providing a good osseous foundation for long-term stability.
osteoporosis; pedicle screw; polymethylmethacrylate; lumbar vertebrae; micro-CT
R681.4
A
0577-7402(2015)07-0535-05
10.11855/j.issn.0577-7402.2015.07.05
2014-11-25;
2015-06-08)
(責(zé)任編輯:胡全兵)
國家自然科學(xué)基金青年基金(81301606);成都軍區(qū)總醫(yī)院院管課題(2013YG-B015)
劉達(dá),醫(yī)學(xué)博士,主治醫(yī)師。主要從事脊柱外科的基礎(chǔ)與臨床研究
610083 成都 成都軍區(qū)總醫(yī)院骨科(劉達(dá)、謝慶云、鄭偉、康夏、張波、權(quán)毅、潘顯明);335000 江西鷹潭 解放軍184醫(yī)院骨科(周江軍);710032 西安 第四軍醫(yī)大學(xué)西京醫(yī)院骨科(雷偉)
潘顯明,E-mail:xianmingpan@163.com;雷偉,E-mail:leiweispine@163.com