椎体骨密度、椎弓根螺钉旋入力矩与拔出力的关系及临床意义

Relationship of Vertebral Body Bone Mineral Density with Insertional Torque and Pull-out Strengths of Pedicle Screws and Its Clinical Significance

目的 探讨椎体骨密度（BMD）、椎弓根螺钉的最大旋入力矩及螺钉最大轴向拔出力，三者之间的关系。方法 随机取青壮年、中年、老年和骨质疏松患者的新鲜椎体标本（L1～L3）各10个共40个，双能X线吸收骨密度仪（dual energy X-ray absorptiometry，DEXA）测试每个椎体BMD；每个椎体一侧椎弓根植入CCD螺钉，另一侧，植入TSRH螺钉；测量螺钉最大旋入力矩，然后轴向拔出螺钉，记录螺钉最大轴向拔出力。结果 四组椎体BMD均值分别为：青壮年组：（0．968±0．07）mg／cm^2，中年组：（0.856±0．08）mg／cm^2，老年组：（0.785±0．07）mg／cm^2，骨质疏松组：（0.491±0．09）mg/cm^2。最大旋入力矩（CCD／TSRH）分别为：青壮年组（1．29±0．13／1．26±0．15）Nm，中年组（1．14±0．15／1．17±0．14）Nm，老年组（0.72±0．09／0．70±0．11）Nm，骨质疏松组（0.56±0．12／0．57±0．10）Nm。最大轴向拔出力（CCD／TSRH）分别为：青壮年组（873．27±96．5／849．36±84．7）Nm，中年组（778．00±90．3／758．72±92．3）Nm，老年组（384．04±36．8／371．28±28．3）Nm，骨质疏松组（316．47±67．6／313．51±62．9）Nm。椎体BMD与最大旋入力矩、最大轴向拔出力呈显著相关（r=0．831和r=0．757，均P〈0.000）。在骨质疏松组，螺钉最大旋入力矩与最大轴向拔出力显著相关（r=0.890，P〈0.000）。结论 BMD是术前预测椎弓根螺钉稳定性的良好指标；在老年骨质疏松患者，螺钉最大旋入力矩能较好反映螺钉的稳定程度。

Objective To explore the relationship of vertebral bone mineral density（ BMD）, and insertional torque of pedicle screws with pull-out strengths and its clinical significancl . Method Forty lumbar vertebrae bodies were randomly derived from young （n= 10） , middle age （n= 10）, older （n= 10）, and older osteoporotic cadevers （n= 10）. Every BMD was measured with dual energggy x-ray absorptiometry DEXA. One CCD pedicle screw of 40mm/6.0mm was implanted into one side of pedicle and one similar size TSRH screw was implanted into the other side. The screws were pulled out from the vertebral bone at 1. 0mm/sec on MTS858. The peak insertional torque and pull-out strengths were measured. Results The average BMD in young,middle age,older and older psteoporotic groups were（0. 968 ±0.07）mg/cm^2, （ 0. 856 ± 0.08）mg/cm^2, （ 0. 785 ±0.07）mg/cm^2, and（0. 491 ± 0.09） mg/cm^2 respectively. The insertional torques（CCD/TSRH） were （1.29±0.13/1.26±0.15）Nm（young group）, （1.14±0.15/1. 17±0.14） Nm（middle age group）, （0.72±0.09/0.70±0.11 ） Nm（older group）, and （0.56±0.12/0. 57±0.10）Nm（older osteoporotic group） ） respectively. The pull-out strengths （ CCD/TSRH ） were （ 873.27 ± 96. 5/849.36 ±84.7 ） Nm （ young group）, （778.00±90. 3/758. 72±92. 3）Nm（middle age group）, （384. 04±36. 8/371.28±28. 3）Nm （older group）, and （316. 47±67.6/ 313. 51 ±62. 9）Nm（older osteoporotic group）respectively. BMD was positively related to insertional torque and pull-out strengths （r=0. 831 and r=0. 757, P 〈0.01）. There was no significant difference in pull-out strengths and peak insertional torque between CCD and TSRH screw types（ P 〉0.05）. Conclusions BMD is a reliable preoperative predictor of preoperative stability of pedicle screw fixation. The peak insertional torque can predict screw loosening and related failures in older osteoporotic patient.