Mechanical variables affecting balloon kyphoplasty outcome – a finite element study

Abstract

It is still unclear how a vertebral fracture should be stabilised and strengthened without endangering the remaining intact bone of the augmented vertebra or the adjacent vertebrae. Numerical modelling may provide insight. To date, however, few finite element (FE) spine models have been developed which are both multi-segmental and capture a more complete anatomy of the vertebrae. A 3-D, two-functional unit, CT-based, lumbar spine, FE model was developed and used to predict load transfer and likelihood of fracture following balloon kyphoplasty. The fractured anterior wall and injected cement were modelled in a two-functional spinal unit model with osteoporotic bone properties. Parameters investigated included: cement stiffness, cement volume and height restoration. Models were assessed based on stresses and a user-defined fracture-predicting field. Augmentation altered the stress distribution; shielding was dependent on positioning of the cement; and fracture algorithm found incomplete height restoration to increase the likelihood of fracture, particularly in adjacent vertebrae.

Height Restoration and Preservation in Osteoporotic Vertebral Compression Fractures

“…This confirms results from other clinical trials. 32 In contrast, adequate intravertebral cement interdigitation and distribution such as in VP procedures seem not to have this effect. This might result in a potentially better cement interdigitation and consecutive superior biological healing process.…”

Cement interdigitation and bone-cement interface after augmenting fractured vertebrae: A cadaveric study

“…An additional negative impact of bone destructive techniques that use a balloon (balloon kyphoplasty and VBS) represents the stress-shielding effect, which has been described in the literature. 17 Good interdigitation and distribution of the cement within the vertebrae like in vertebroplasty procedures seem not to have this effect. 18 Combining this previous knowledge with our results, which (like the effect of stress shielding) point toward persisting instability, bone resorption, and cement dislocation, whether one should use balloon kyphoplasty–like procedures seems debatable.…”

Percutaneous Vertebroplasty for Cephalad Vertebral Fractures After Instrumented Lumbar Fusion

“…24 After augmentation, stresses predominantly transferred along new stiffer load paths to counteract the structural changes. Dabirrahmani et al 24 reported a biomechanical study related to cement augmentation and stress shielding.…”