Optimization of spinal implant screw for lower vertebra through finite element studies.

ABSTRACT

The increasing older population is suffering from an increase in age-related spinal degeneration that causes tremendous pain. Spine injury is mostly indicated at the lumbar spine (L3-L5) and corresponding intervertebral disks. Finite element analysis (FEA) is now one of the most efficient and accepted tools used to simulate these pathological conditions in computer-assisted design (CAD) models. In this study, L3-L5 spines were modeled, and FEA was performed to formulate optimal remedial measures. Three different loads (420, 490.5, and 588.6 N) based on three body weights (70, 90, and 120 kg) were applied at the top surface of the L3 vertebra, while the lower surface of the L5 vertebra remained fixed. Models of implants using stainless steel and titanium alloy (Ti6Al4V) pedicle screws and rods with three different diameters (4, 5, and 6 mm) were inserted into the spine models. The relative strengths of bone (very weak, weak, standard, strong, and very strong) were considered to determine the patient-specific effect. A total of 90 models were simulated, and von Mises stress and strain, shear stress, and strain intensity contour at the bone-implant interface were analyzed. Results of these analyses indicate that the 6-mm pedicle screw diameter is optimal for most cases. Experimental and clinical validation are needed to confirm these theoretical results.