Study of stress distribution in pedicle screws along a continuum of diameters: a three-dimensional finite element analysis.

OBJECTIVE

To create a three-dimensional finite element model to identify the biomechanically optimal diameter of pedicle screws for placement in L1 vertebral bone.

METHODS

The effects of pedicle screws with different diameters on the maximum Von Mises stress in L1 vertebra bone were evaluated by a finite element method. Pedicle screw diameters ranging from 4.0 to 6.5 mm were assessed.

RESULTS

The simulation showed that, under axially oriented pullout forces, stress was decreased in all models when the diameter of screws was in the range of 4.0 mm to 6.5 mm. With a standard external load and a 6.5 mm diameter screw, load transferred to cortical and cancellous bone was reduced by 47.24% and 34.28%, respectively, and displacement of the screw was reduced by 21.35%. When the diameter was ≥5.0 mm, the variable of stress was stable in all models.

CONCLUSION

When the diameter of the screws is in the range of 4.0 mm to 6.5 mm, increasing the diameter of pedicle screw can improve the distribution of axial pullout stress on the screws, cortical bone and cancellous bone. Provided the bone mass permits it, pedicle screws with a diameter of not less than 5.0 mm should be chosen.