Biomechanical comparison of different techniques in primary spinal surgery in osteoporotic cadaveric lumbar vertebrae: Expansive pedicle screw versus polymethylmethacrylate-augmented pedicle screw

Introduction: Transpedicular fixation can be challenging in the osteoporotic spine. Expansive pedicle screw (EPS) and polymethylmethacrylate- augmented pedicle screw (PMMA-PS) were both used to increase screw stability. However, there are a little or no biomechanical comparisons of EPS and PMMA-PS, especially in primary spinal surgery in osteoporotic vertebrae. The purpose of this study was to compare the stability of EPS and PMMA-PS in primary spinal surgery. Materials and methods: Fifteen osteoporotic vertebrae were randomly divided into three groups. The conventional pedicle screw (CPS) was inserted in CPS group, the pilot hole was filled with PMMA followed by CPS insertion in PMMA-PS group, and EPS was inserted in EPS group. Twenty-four hours later, X-ray and CT examination and biomechanical tests were performed to all vertebrae. Results: In PMMA-PS group, PMMA existed in bone tissue around the CPS in both vertebral body and pedicle of vertebral arch, and PMMA surrounding the screw formed a spindle-shaped structure in vertebral body. In EPS group, anterior part of EPS presented an obvious expansion in vertebral body and formed a clawlike structure. Screw stabilities in PMMA-PS and EPS groups were significantly enhanced compared with those in CPS group (P < 0.05). However, there was no significant difference between PMMA-PS and EPS groups (P > 0.05). Conclusion: Expansive pedicle screw can markedly enhance screw stability with a similar effect to the traditional method of screw augmentation with PMMA in primary surgery in osteoporotic vertebrae. In addition, EPS can overcome pedicle fracture, leakage and compression caused by lager screw and augmentation with PMMA. We propose that EPS is an effective, safe and easy method and has a great application potential in augmentation of screw stability in osteoporosis in clinic.