Elsevier

The Spine Journal

Volume 5, Issue 1, January–February 2005, Pages 45-54
The Spine Journal

Clinical Studies
Restoring geometric and loading alignment of the thoracic spine with a vertebral compression fracture: effects of balloon (bone tamp) inflation and spinal extension

https://doi.org/10.1016/j.spinee.2004.05.248Get rights and content

Abstract

Background context

In patients with osteoporosis, changes in spinal alignment after a vertebral compression fracture (VCF) are believed to increase the risk of fracture of the adjacent vertebrae. The alterations in spinal biomechanics as a result of osteoporotic VCF and the effects of deformity correction on the loads in the adjacent vertebral bodies are not fully understood.

Purpose

To measure 1) the effect of thoracic VCFs on kyphosis (geometric alignment) and the shift of the physiologic compressive load path (loading alignment), 2) the effect of fracture reduction by balloon (bone tamp) inflation in restoring normal geometric and loading alignment and 3) the effect of spinal extension alone on fracture reduction and restoration of normal geometric and loading alignment.

Study design/setting

A biomechanical study using six fresh human thoracic specimens, each consisting of three adjacent vertebrae with all soft tissues and bony structures intact.

Methods

In order to reliably create fracture, cancellous bone in the middle vertebral body was disrupted by inflation of bone tamps. After removal of the bone tamps, the specimen was compressed using bilateral loading cables until a fracture was observed with anterior vertebral body height loss of ≥25%. Fracture reduction was performed under a compressive preload of 250 N first under the application of extension moments, and then using inflatable bone tamps. The vertebral body heights, kyphotic deformity of the fractured vertebra and adjacent segments and location of compressive load (cable) path in the fractured and adjacent vertebral bodies were measured on video-fluoroscopic images.

Results

The VCF caused anterior wall height loss of 37±15%, middle-height loss of 34±16%, segmental kyphosis increase of 14±7.0 degrees and vertebral kyphosis increase of 13±5.5 degrees (p<.05). The compressive load path shifted anteriorly by about 20% of anteroposterior end plate width in the fractured and adjacent vertebrae (p=.008). Bone tamp inflation restored the anterior wall height to 91±8.9%, middle-height to 91±14% and segmental kyphosis to within 5.6±5.9 degrees of prefracture values. The compressive load path returned posteriorly relative to the postfracture location in all three vertebrae (p=.004): the load path remained anterior to the prefracture location by about 9% to 11% of the anteroposterior end plate width. With application of extension moment (6.3±2.2 Nm) until segmental kyphosis and compressive load path were fully restored, anterior vertebral body heights were improved to 85±8.6% of prefracture values. However, the middle vertebral body height was not restored and vertebral kyphotic deformity remained significantly larger than the prefracture values (p<.05).

Conclusions

The anterior shift of the compressive load path in vertebral bodies adjacent to VCF can induce additional flexion moments on these vertebrae. This eccentric loading may contribute to the increased risk of new fractures in osteoporotic vertebrae adjacent to an uncorrected VCF deformity. Bone tamp inflation under a physiologic preload significantly reduced the VCF deformity (anterior and middle vertebral body heights, segmental and vertebral kyphosis) and returned the compressive load path posteriorly, approaching the prefracture alignment. Application of extension moments also was effective in restoring the prefracture geometric and loading alignment of adjacent segments, but the middle height of the fractured vertebra and vertebral kyphotic deformity were not restored with spinal extension alone.

Introduction

Vertebral compression fractures (VCFs) in the elderly are an important public health problem because of the large size of the affected population and because of the devastating influence of VCFs on morbidity, mortality and social costs. The majority of osteoporotic VCFs occur in the thoracolumbar junction (T12–L1) and the mid-thoracic spine (T7–T8) [1], [2], [3]. Thoracic VCFs typically lead to increased kyphosis, which may worsen over time in persons with prevalent VCFs [4]. Spinal kyphosis resulting from osteoporotic VCFs has been shown to adversely affect quality of life, physical function, mental health and survival [5], [6], [7]. Furthermore, the occurrence of prior VCFs with the resulting kyphotic deformity is a strong risk factor for additional vertebral fractures in osteoporotic patients [3]. The increased risk of fracture is thought to be the result of alterations in spinal load distribution as a consequence of a kyphotic deformity [8].

In recent years, as we have gained an understanding of the adverse consequences of spinal kyphosis, the kyphoplasty procedure has been developed in an attempt to treat the fracture pain and spinal deformity resulting from osteoporotic VCFs. With this procedure, an inflatable bone tamp (IBT) is percutaneously introduced into the fractured vertebral body and is then inflated in an attempt to reduce the fracture deformity. The reported percentage of kyphosis reduction in clinical studies has ranged from 39% to 65% [9], [10], [11], [12], [13], while the restoration of vertebral body height ranged from 35% to 68% [10], [12], [14]. Spinal extension inducing “postural reduction” of VCFs has also been reported and in a prospective study of 41 consecutive patients with 65 VCFs who underwent vertebroplasty, McKiernan et al. [15] achieved improvement of kyphotic deformity in 23 fractures using spinal extension. In a recent, prospective clinical study Kim et al. [16] have described the ability of postural reduction (using a pillow under the VCF level) in achieving significant correction of the anterior vertebral body height and vertebral kyphotic deformity in 90% of acute osteoporotic compression fractures the onset of which was less than 8 weeks.

Restoration of the vertebral height and sagittal alignment are believed to mitigate adverse biomechanical consequences of osteoporotic VCFs [15]; however, there are no biomechanical data on how the VCF deformity and its correction affect the loads in the adjacent vertebral bodies. Proponents of kyphoplasty have suggested that by restoring normal spinal alignment the risk of new VCFs in adjacent vertebrae may be reduced. Although previous laboratory studies have investigated the reduction of osteoporotic VCF with balloon kyphoplasty [17], [18], [19], [20], these studies were performed on individual vertebral bodies. As a result, the effects of balloon kyphoplasty on the angular alignment and loading of adjacent segments under physiologic compressive preloads have not been reported.

We hypothesized that 1) kyphotic deformity caused by a thoracic VCF will shift the physiologic compressive load path anteriorly in the fractured vertebra as well as in the adjacent vertebrae and (2) deformity correction will restore the load path to its prefracture alignment. The specific objectives of this study were to measure 1) the effect of thoracic VCFs on segmental kyphosis (geometric alignment) and the shift of the physiologic compressive load path (loading alignment), 2) the effect of fracture reduction by balloon (bone tamp) inflation in restoring normal geometric and loading alignment and 3) the effect of spinal extension alone on fracture reduction and restoration of geometric and loading alignment.

Section snippets

Specimens

Fresh frozen human cadaveric thoracic spines from two women and three men (age, 81±10 years) were used. The specimens were radiographically screened to ensure that there were no previous fractures. They were thawed at room temperature (20 C), 24 hours before testing. The paravertebral muscles were dissected, while keeping the discs, ligaments and posterior bony structures intact.

Six thoracic specimens were obtained from five donor spines. Each test specimen consisted of three adjacent vertebrae

Fracture loads

The mean (±1 SD) value of the applied load for fracture creation was 528±164 N. No fractures in the adjacent vertebral bodies were observed in any of the specimens.

Geometric alignment

In the middle vertebral body of the prefracture specimens, the mean (±SD) values of anterior, middle and posterior vertebral body heights were 21.9±3.2 mm, 20.2±4.1 mm and 25.4±3.1 mm, respectively. The prefracture vertebral kyphosis was 5.8±1.7 degrees, and the segmental kyphosis was 1.0±3.6 degrees.

The thoracic VCF caused

Discussion

The presence of VCFs with the resulting kyphotic deformity is a strong risk factor for additional vertebral fractures. The increased fracture risk is thought to be the result of altered spinal alignment and loading as a consequence of the VCF. The purpose of this study was to investigate the effects of a thoracic vertebral compression fracture as well as fracture reduction using bone tamp inflation on the angular alignment and loading of adjacent segments under physiologic compressive preloads.

Conclusions

The anterior shift of the compressive load path in vertebral bodies adjacent to VCF can induce additional flexion moments on these vertebrae. This eccentric loading may contribute to the increased risk of new fractures in osteoporotic vertebrae adjacent to an uncorrected VCF deformity. Bone tamp inflation under a physiologic preload significantly reduced the VCF deformity (anterior and middle vertebral body heights, segmental and vertebral kyphosis) and returned the compressive load path

References (33)

  • I.N. Gaitanis et al.

    Balloon kyphoplasty for the treatment of pathological vertebral compressive fractures

    Eur Spine J

    (2004)
  • R. Garfin et al.

    New technologies in spine. Kyphoplasty and vertebroplasty for the treatment of painful osteoporotic compression fractures

    Spine

    (2001)
  • J. Ledlie et al.

    Balloon kyphoplasty: one-year outcomes in vertebral body height restoration, chronic pain and activity levels

    J Neurosurg

    (2003)
  • I.H. Lieberman et al.

    Initial outcome and efficacy of “kyphoplasty” in the treatment of painful osteoporotic vertebral compression fractures

    Spine

    (2001)
  • F.M. Phillips et al.

    Early radiographic and clinical results of balloon kyphoplasty for the treatment of osteoporotic vertebral compression fractures

    Spine

    (2003)
  • S. Dudeney et al.

    Kyphoplasty in the treatment of osteolytic vertebral compression fractures as a result of multiple myeloma

    J Clin Oncol

    (2002)
  • Cited by (35)

    • Safety and Efficacy Studies of Vertebroplasty with Dual Injections for the Treatment of Osteoporotic Vertebral Compression Fractures: Preliminary Report

      2020, Academic Radiology
      Citation Excerpt :

      It is consistent with previous work that PVP only could achieve partial height restoration from other group (38) and from our group (15,21). PVP could not restore geometric and loading alignments of the fractured vertebral body, decrease their additional buckling torque, and recover the equilibrium dispersive ability of the intervertebral disc to bearing load (39,40). This work also confirmed the wide agreement that PKP treatment has better height restoration ability than PVP treatment due to the use of commercial inflatable bone tamp or Sky-bone expander.

    • Orthoses for Osteoporosis

      2018, Atlas of Orthoses and Assistive Devices, Fifth Edition
    • Inducing targeted failure in cadaveric testing of 3-segment spinal units with and without simulated metastases

      2018, Medical Engineering and Physics
      Citation Excerpt :

      If so, it can be assumed that the measured failure load corresponds to the strength of that particular vertebra. Overall, the failure loads found in this study ranged between 1275 N and 3929 N. Previous studies in which 3-segment spinal units, either with simulated spinal metastases or not, were loaded until failure reported failure loads ranging from approximately 500 N to 8000 N [14–18]. Thus, the failure loads obtained in the current study fall well within the range previously reported.

    • Biomechanics of vertebral bone augmentation

      2010, Neuroimaging Clinics of North America
      Citation Excerpt :

      The investigators concluded that bone tamp inflation significantly reduced deformity of the vertebral body height and kyphosis and resulted in return of the load path to near prefracture alignment. Hyperextension alone improved vertebral body deformity and load path alignment, without restoring middle vertebral height and kyphotic deformity.4 Correction of kyphosis of the fractured vertebral body does not necessarily correlate with overall kyphosis correction.

    • Clinical and radiographic results of balloon kyphoplasty for treatment of vertebral body metastases and multiple myelomas

      2010, Journal of Clinical Neuroscience
      Citation Excerpt :

      The number of metastases was determined by MRI using T1-weighted, T2-weighted and diffusion MRI. The segmental kyphosis angle, the angle formed by the intersection of lines parallel to the superior endplate of the upper vertebra and the inferior endplate of the lower vertebra, was determined from plain radiographs.26,27 The fracture types, vertebral body posterior wall integrity and evidence of epidural tumor extension were evaluated by MRI and CT scans.

    • Vertebral Augmentation: What is the Role of Vertebroplasty and Kyphoplasty?

      2009, Evidence-Based Orthopaedics: The Best Answers to Clinical Questions
    View all citing articles on Scopus

    FDA device/drug status: approved for this indication (inflatable bone tamp).

    Support in whole or in part was received from The Department of Veteran Affairs, Washington, DC. Nothing of value received from a commercial entity related to this research.

    View full text