The Pull-out Strength Research Of Novel Extensible Pedicle Screw

Objective:To discuss the biomechanical properties of novel extensible pedicle screw in vertebralbody and pedicle,and to provide a basis for better performing pedicle-lengtheningosteotomy in clinic.Methods:8formalin preserved antact spine specimens including L2to L5(mean age,66y)were selected and used. The mean bone mineral density was0.802±0.081g/cm2. Allspecimens were examined by X-ray photography to exclude fracture, tumor, tuberculosisand deformity. The lumbar spine specimens were separated into4segmen（tL2，L3，L4andL5）at the levels of intervertebral disc before testing.The specimens were embedded bydenture base poly after cleaning,and then assigned randomly into3groups:Group A,6mmfixed type extensible pedicle screw; Group B,7mm fixed type extensible pedicle screw;Group C,7mm novel extensible pedicle screw.The maximum axial pull-out strength test ofpedicle extended screw in Group A,B and C was performced at HY1080typemulti-function material testing machine.Results:1. The pull-out force of novel extensible pedicle screw was:525.15±59.17N,and itinecreased81.7%than group A（P＜0.05）,and64.72%than group B（P＜0.05）. Thepull-out force of the7mm screw in the vertebral body was:318.81±26.64N,whichincreased10.31%than the6mm screw in the vertebral body(289.03±27.27N)（P＞0.05）.1. The pull-out force of novel extensible pedicle screw was:265.08±27.92N,and itdroped39.08%than group A（P＜0.05）,and44.46%than group B（P＜0.05）. The pull-outforce of the7mm screw in the pedicle was:477.25±29.25N,and it increased9.68%thanthe6mm screw in the pedicle (435.14±35.03N)（P＜0.05）.Conclusions: 1.The fixation rigidity in vertebral body of novel extensible pedicle screw issignificantly better than the conventional6mm and7mm extensible pedicle screws.2.The fixation rigidity in pedicle of novel extensible pedicle screw is significantlyweaker than extensible pedicle screws6mm and7mm extensible pedicle screws.3.The novel extensible pedicle screw still needs to be improved.