A case of pedicle screw loosening treated by modified transpedicular screw augmentation with polymethylmethacrylate

Abstract

We report a case of pedicle screw loosening treated by modified transpedicular screw augmentation technique using polymethylmethacrylate (PMMA), which used the anchoring effect of hardened PMMA. A 56-year-old man who had an L3/4/5 fusion operation 3 years ago complained of continuous low back pain after this operation. The computerized tomography showed a radiolucent halo around the pedicle screw at L5. We augmented the L5 pedicle screw with modified pedicle screw augmentation technique using PMMA and performed an L3/4/5 pedicle screw fixation without hook or operation field extension. This modified technique is a kind of transpedicular stiffness augmentation using PMMA for the dead space around the loosed screw. After filling the dead space with 1-2 cc of PMMA, we inserted a small screw. Once the PMMA hardened, we removed the small screw and inserted a thicker screw along the existing screw threading to improve the pedicle screws' pullout strength. At 10 months' follow-up, x-ray showed strong fusion of L3/4/5. The visual analogue scale (VAS) of his back pain was improved from 9 to 5. This modified transpedicular screw augmentation with PMMA using anchoring effect is a simple and effective surgical technique for pedicle screw loosening. However, clinical analyses of long-term follow-up and biomechanical studies are needed.

Keywords: Instrument failure; Osteoporosis; PMMA; Pedicle screw loosening; Pseudoarthrosis; Surgical technique.

Fig. 1

X-ray and computerized tomography (CT) of the case. A : Lateral lumbar X-ray shows a radiolucent halo around L5 pedicle screw (arrow). B : Pre-reoperative CT of the L5 pedicle showing the radiolucent halos around the screws (arrows). C : Post-reoperative anterior-posterior (AP) X-ray checked 10 months after reoperation shows the pedicle screw fixation of L3/4/5 with the intertransverse bone fusion (arrow head). Each peri-implant hollow is filled with PMMA and a new screw (arrows). D : Post-reoperative CT reveals the halos are filled with radiopaque bone cement (arrows) and new pedicle screws. E and F : flexion and extension lateral view of lumbar spine checked 10 months after reoperation showed strong fixation between instruments and vertebral bodys.

Fig. 2

Consecutive schematic illustrations of the modified transpedicular screw augmentation procedure and operation findings. A : The vacant pedicle hole after removal of the loose pedicle screw. B : The PMMA insertion process. When the PMMA's viscosity became like toothpaste, we filled the dead space with about 1 cc of PMMA. C : The inserted PMMA hardens with the small pilot screw inserted. D : The inner thread created by the small screw is presented after the small pilot screw was removed. E : Intra-operative photograph shows the inner thread (white arrow) after removing the small pilot screw. F : The cracks (red arrows), caused by inserting the thicker permanent screw, gives the screw greater holding power (anchor bolt effect). G and H : Illustrations of axial and coronal section after thicker permanent screw insertion. We suppose the thicker permanent screw has greater expansile forces (red arrows) and holding powers (blue arrows) throughout its whole surface.