Stress Distribution at the Bone-cement Interface Changes during Kyphoplasty Rehabilitation

Abstract

Abstract-Balloon Kyphoplasty uses an inflatable bone tamp and cement augmentation to repair vertebral compression fractures. A recent clinical study observed a 78% re-collapse rate in patients showing a radiolucent phenomenon at the bonecement interface following Kyphoplasty. Two experimental studies showed significant height loss following Balloon Kyphoplasty under cyclical loads. The present study investigates the alteration in load angle corresponding to this height loss and its effect on load transfer to the bone-cement interface. A validated finite element model of a human thoracolumbar spine was segmented into a single L1 vertebral body and modified to replicate bilateral Balloon Kyphoplasty. Cement was modeled using prolate spheroids surrounded by an interface region divided into anterior, middle and posterior sections. Interface thickness was calculated using a mathematical model with a bone volume fraction of 0.3 and 50% bone compaction. An 800N load was applied at angles of 0 o and 20 o from the vertebral axis. Results indicate that a change in the applied load angle significantly alters the principal stress components and directions across the interface region. This alteration in loading must be considered in the context of the highly compliant interface region and therefore is hypothesized to be a contributory factor to vertebral recollapse.

Strong similarities in the creep and damage behaviour of a synthetic bone model compared to human trabecular bone under compressive cyclic loading

“…These models have been further utilised to study the micromechanics of the bone cement interface, which is an important feature for augmentation outcomes (Purcell et al, 2014(Purcell et al, , 2013Zhao et al, 2012). Many of these studies utilise an aluminium based open cell structure, which have been found to exhibit favourable properties for the study of cement injection micromechanics in terms of damage evolution and distribution (Guillén et al, 2011).…”

A Multiscale Finite Element Analysis of Balloon Kyphoplasty to Investigate the Risk of Bone-Cement Separation In Vivo

“…To our knowledge only 2 other kyphoplasty models have explicitly represented the interface as a layer of elements surrounding the cement with an intermediary modulus assigned. [35][36][37][38] The majority of macroscale kyphoplasty simulations instead assume an instantaneous transition of elastic properties from bone to cement via shared node bonding of the domains. 39-43 These assumptions would not have been deemed unreasonable before the more recent in vivo observations of bone-cement interface separation.…”

A combined experimental and computational study of mechanical properties after balloon kyphoplasty

“…An important feature of the kyphoplasty treatment is the balloon expansion process, since in addition to decompressing the collapsed vertebra it also creates a cavity surrounded by a periphery of compacted trabeculae displaced by the balloon in the trabecular centrum. [9][10][11] In-vitro studies on human vertebra have found that this zone of compacted trabeculae can impede the subsequent infiltration of injected bone cement, which is necessary for effective load transfer and structure stabilization. 12,13 The adverse consequences of this effect were first reported in vivo by Mazwi et al, when a patient presented with back pain two months after kyphoplasty intervention.…”

“…18 Previous studies have postulated that this re-collapse mechanism could be related to the compaction of trabecular bone during the balloon inflation process, thereby reducing the permeability. [10][11][12]19,20 A hypothesised factor in these recollapse events has been the clear difference in interdigitation patterns, with a 29.5% occurrence of a lumped cement mass in kyphoplasty cases compared to just 4.6% in vertebroplasty cases. 21 A significant proportion of these adverse events have been reported during the first 60 days following the original intervention.…”