不同后枕颈角对枕颈融合时下颈椎运动范围和椎间压力的影响

Effects of different posterior occipitocervical angles on the range of motion and intradiscal pressure of subaxial cervical spine in occipitocervical fusion

目的:分析以不同后枕颈角(posterior occipitocervical angle,POCA)行枕颈固定时下颈椎的运动范围(range of motion,ROM)和椎间压力(intradiscal pressure,IDP),探讨枕颈融合(occipitocervical fusion,OCF)术中POCA的选择策略。方法:选取8具新鲜冰冻人体枕颈部标本(C0~T1,头端包括枕骨粗隆以下的颅底骨性结构),年龄为25~45岁,男4具,女4具,X线透视排除骨性异常及破坏。剔除附着的肌肉、脂肪组织,完整保留各种韧带、关节囊及椎间盘,作为正常组。将标本置于2N·m载荷下,运用伺服液压材料测试系统、光电运动分析系统及微型压力传感器测量C3/4、C4/5、C5/6、C6/7运动节段在前屈、后伸、左旋及左侧弯4个方向上的ROM以及IDP。后将标本以不同POCA行枕颈固定作为实验组,5组分别为:中立位组(POCA=111°)、中立位-标准差(standard deviation,SD)组(POCA=101°)、中立位+SD组(POCA=121°)、中立位-2SD组(POCA=91°)及中立位+2SD组(POCA=131°)。固定节段为C0、C2及C3。各实验组均采用位移控制模式进行实验,测量4个运动节段在4个方向上的ROM及IDP。结果:枕颈固定以后,C0~C34个方向上的ROM较正常组均显著减小(P<0.001)。POCA的变化对4个运动节段前屈和后伸方向上的ROM及IDP的影响呈现一定的规律性:前屈方向上,随着POCA的增大,各节段的ROM及IDP呈递减趋势;后伸方向上,随着POCA的增大,各节段的ROM呈递增趋势,而IDP呈减小趋势。POCA固定于中立位时,各运动节段前屈、后伸方向上的ROM虽明显大于正常组,但未出现POCA过小时前屈方向上或过大时后伸方向上极度增大的ROM,且IDP与正常组之间无显著差异(P>0.05)。而在左旋及左侧弯方向上,随POCA变化4个运动节段的ROM较正常组显著增加,但其对ROM及IDP的影响无规律性。结论:OCF术中,POCA于中立位固定时,下颈椎的ROM、IDP最接近正常状态。

Objectives:To analyze the range of motion(ROM)and intradiscal pressure(IDP)of lower cervical spine in occipitocervical fixation with different posterior occipitocervical angles(POCA),and explore the selection strategy of POCA in occipitocervical fusion(OCF)surgery.Methods:8 fresh frozen human occipitocervical cadaveric specimens(C0-T1,cephalic end included the bony structure of the skull base below the occipital tuberosity)were selected,including 4 males and 4 females,aged 25-45 years,and bone abnormalities and destruction were excluded with X-ray fluoroscopy.The speciemens were removed of muscles and fat tissues and preserved with ligaments,joint capsules and intervertebral discs as the normal group.Specimens were loaded with 2N·m in a servo-hydraulic materials testing system for measuring the ROM and IDP of C3/4,C4/5,C5/6 and C6/7 in the directions of flexion,extension,left torsion and left lateral bending with the help of optoelectronic motion analysis system and miniature pressure transducers.Then,the specimens were subjected to occipitocervical fixation with different POCAs as 5 experimental groups,which were:neutral position group(POCA=111°),neutral position-standard deviation(SD)group(POCA=101°),neutral position+SD group(POCA=121°),neutral position-2SD group(POCA=91°),and neutral position+2SD group(POCA=131°).The fixed segments were C0,C2 and C3.All experimental groups used the displacement control protocol to perform experiment,and the ROM and IDP of C3/4,C4/5,C5/6 and C6/7 in four directions were measured.Results:After occipitocervical fixation,ROM in the four directions of C0-C3 was significantly reduced compared with the normal group(P<0.001).Of the four directions,the change of POCA had regular impacts on ROM and IDP of the 4 segments in flexion and extension:in flexion,with the increase of POCA,ROM and IDP of each segment showed a decreasing trend;In extension,with the increase of POCA,ROM of each segment showed an increasing trend,while IDP showed a decreasing trend.When POCA was in the neutral position,ROM in flexion or extension of each segment was significantly greater than that of normal group,yet there was no extremely increased ROM in flexion as POCA was too little or in extension as POCA was too large,and there was no significant difference of IDP compared with that of the normal group(P>0.05).The change of POCA had no regular effect on ROM and IDP of 4 segments in left torsion and left lateral bending,although ROM increased significantly compared with that of the normal group.Conclusions:In OCF surgery,fixing POCA in a neutral position,the ROM and IDP of subaxial cervical spine are approximately normal.