Analysis of bone cement distribution around fenestrated pedicle screws in low bone quality lumbosacral vertebrae

Purpose To study the exact distribution of bone cement around augmented fenestrated pedicle screws in both lumbar and sacral vertebrae of patients with low bone quality. Methods A total of 37 patients with instrumented lumbar fusion were investigated. 3D computed tomography virtual models of the injected cement and screws were obtained. The models were computed for their centroid (i.e. their average mass centre point), and their coordinates ( x , y , z ) were projected on their respective screw-transversal and screw-longitudinal planes for further analysis. Results The results showed better bone cement homogeneous distribution around the screws in lumbar (L4 and L5) than in sacral (S1) vertebrae. In the lumbar region, the centroids were transversally projected near the transversal centre of symmetry of the screws. On the other hand, in the sacral region, the cement flowed preferentially outside the centre of symmetry of the screws, into the sacral ala. Conclusions The results confirm the different flow behaviours of bone cement in lumbar versus sacra vertebrae. The computer methodology followed in this study helps to understand the clinical monitoring observations and lays the foundations for better positioning of the screws and specific vertebrae-oriented screw designs.