Deformities in the spine often require pedicle screw insertion, which alters the mechanical environment in the spine resulting in implant loosening and failure. This study examined the alteration of the state of strain at the bone-implant interface in the lumbar spine after pedicle screw insertion. Three-dimensional (3D) geometry of the lumber region (L1-S) and CAD model of pedicle screw was subjected at L3-L5 level to finite element (FE) analysis to examine the strain condition at the 6 selected locations at the bone-implant interface using different screw diameters (5 mm and 6 mm), implant materials (stainless steel and titanium), bone conditions (very strong, strong, normal, weak and very weak) and loading conditions (420 N, 490 N and 588 N). Screw diameter was observed to be the most crucial factor in determining the strain environment. The 6 mm diameter screw did not alter the strain environment significantly (p Keywords: lumbar vertebra, spinal implant, pedicle screw, finite element analysis, bone condition