INTRODUCTION: Osteoporotic fracture reduces vertebral stiffness and alters spinal load‐sharing. Vertebroplasty partially reverses these changes at the fractured level, but may act to increase deformations and stress at adjacent levels. We examined this possibility.
METHODS: Fourteen pairs of three‐vertebra cadaver spine specimens (67‐92 yr) were loaded to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep loaded at 1.0kN for 1hr. In 17 specimens where the upper or lower vertebra fractured, compressive stress distributions were measured in the disc between adjacent non‐fractured vertebrae by pulling a pressure transducer through the disc whilst under 1.0kN load. These "stress profiles" were obtained at each stage of the experiment (in flexion and extension) in order to quantify intradiscal pressure (IDP) and compressive loadbearing by anterior (FA) and posterior (FP) halves of the vertebral body and by the neural arch (FN). Elastic deformations in adjacent vertebrae were measured using an optical MacReflex system.
RESULTS: No differences were found between Cortoss and PMMA so all data were pooled. Following fracture, IDP fell by 26% in extension (P=0.004). FA decreased from 55% to 36% of the applied load in flexion (P=0.002) and from 36% to 27% in extension (P=0.002). FN increased from 17% to 31% in flexion (P=0.006) and from 22% to 37% in extension (P=0.008). Vertebroplasty significantly reversed these mechanical changes but had no significant effect on elastic deformations of adjacent vertebrae.
DISCUSSION: Vertebral fracture transferred compressive load from the anterior vertebral body to the posterior vertebral body and neural arch of adjacent (nonfractured) vertebrae. Vertebroplasty largely restored normal load‐sharing without increasing deformations of adjacent vertebrae. Beneficial effects of vertebroplasty are not at the expense of increasing adjacent level fracture risk.