Pedicle Screw Pitch Design: 3D-Printed Injectable Bone Substitute for Spinal Osteoporosis

This study aims to determine the effect of pitch variations on pedicle screws for spinal osteoporosis applications. Five variations of pedicle screw pitch (1.75; 2.00; 2.25; 2.50; 2.75 mm) were printed with filaments made of Polylactide Acid (PLA) using a 3D-printing with the Fused Deposition Modelling (FDM) technique. The materials mixed to make the Injectable Bone Substitute (IBS) paste injected into the pedicle screw were Hydroxyapatite (HA), gelatin, hydroxypropyl methylcellulose (HMPC), and alendronate. The pull-out test results showed that the pedicle screw with a pitch of 2.75 mm had the highest value, namely 24.568 ± 0.431 N for screws without IBS paste and 44.814 ± 0.939 N for screws with IBS paste. The results showed that the pedicle screw with the larger pitch had better pull-out and torsional test values, but the larger pitch made the characterization of the bending test decreased. Thus, it can be stated that a pedicle screw with a large pitch is suitable for spinal osteoporosis applications.