Anterior support reduces the stresses on the posterior instrumentation after pedicle subtraction osteotomy: a finite-element study.

STUDY
DESIGN: The investigation was based on finite-element simulations.
OBJECTIVE: Pedicle subtraction osteotomy (PSO) is an effective but technical demanding surgical technique, associated with a high risk of rod failure. The present study aims at investigating the role of the anterior support in combination with PSO, with a numerical comparative analysis.
METHODS: An osteotomy was simulated at the L3 level of a lumbosacral spine. An implantation of various combinations of devices for the anterior (1 or 2 cages of different material) and posterior stabilization (1 or 2 rods) was then performed. ROM, loads, and stresses acting on the rods were calculated.
RESULTS: A 4-8% reduction of the ROM was obtained introducing one or two cages in the instrumented model. However, the anterior support had only a minor influence on the ROM. The load on the posterior instrumentation decreased up to 8% using one cage and about 15% with two anterior devices. A 20-30% reduction of the stresses on the rods was calculated inserting one cage and up to 50% using two cages. Following the introduction of the anterior support, the greatest stress reduction was observed in the model having two cages and spinal fixators with two rods.
CONCLUSIONS: The use of cages is crucial to ensure anterior support and decrease loads and stresses on the posterior instrumentation.