Mechanical And Histological Analysis Of Bone-Pedicle Screw Interface In Vivo: Titanium Versus Stainless Steel

Objectives:To investigate the differences in bone interface between titanium and stainless steel pedicle screws in the lumbar spine. Methods:Eighteen adult mini-pigs who underwent total laminectomy, posterolateral spinal fusion(L₄-L₅)were randomly selected to receive stainless steel - (9) or titanium pedicle screw devices (9). In both groups the devices were CCD (Sofamore Danek) type with the same size and shape. The postoperative observation time was 3 months. Screws from L₄ were harvested along their long axis with pedicle for histomorphometric study. Bone-screw interface and bone volume from thread were examined using linear intercept techniques. Mechanical testing (torsional test and pull out test) was performed on the screws from L₅ Result:The titanium screw group had a significantly higher maximum torque (p<0.05) and angle related stiffness (p<0.05) measured by torsional test. In the pull-out tests, no differences were found between the two groups in relation to the maximum load, stiffness and energy to failure. Direct bone contact with the screw in percentage was 29.4% for stainless steel and 43.8% for titanium (p<0.05). No differences in the bone purchase between the vertebral body part and pedicle part were found. Conclusion:...