SPINE Volume 26, Number 2, pp 151–156
©2001, Lippincott Williams & Wilkins, Inc.
An Ex Vivo Biomechanical Evaluation of an Inflatable
Bone Tamp Used in the Treatment of
Compression Fracture
Stephen M. Belkoff, PhD,* John M. Mathis, MD,† David C. Fenton, MS,*
Robert M. Scribner, BS,§ Mark E. Reiley, MD,¶ and Karen Talmadge, PhD§
Study Design. Ex vivo biomechanical study using os-
teoporotic cadaveric vertebral bodies.
Objectives. To determine if the inflatable bone tamp
(tamp) restores height to compressed vertebral bodies
and to compare the biomechanical properties of isolated,
fractured osteoporotic vertebral bodies treated by kypho-
plasty (tamp) or vertebroplasty.
Summary of Background Data. Previous biomechani-
cal studies have shown that vertebroplasty increases ver-
tebral body strength and restores vertebral body stiffness,
but does not restore vertebral body height lost as a result
of compression fracture.
Methods. Compression fractures were experimentally
created in 16 osteoporotic VBs assigned to either the
tamp or percutaneous vertebroplasty group. The tamp
treatment consisted of inserting balloon-like devices into
the vertebral body, inflating the bone tamp, and filling the
void with Simplex P (Howmedica, Rutherford, NJ) bone
cement. The percutaneous vertebroplasty treatment con-
sisted of directly injecting Cranioplastic bone cement
(CMW, Blackpool, UK) into the vertebral body. Pre- and
posttreatment heights were measured, and the repaired
vertebral bodies were recompressed to determine post-
treatment strength and stiffness values.
Results. The tamp treatment resulted in significant
restoration (97%) of vertebral body height lost after com-
pression, whereas percutaneous vertebroplasty treat-
ment resulted in a significantly lower restoration of lost
height (30%) (P 0.05). Both treatments resulted in sig-
nificantly stronger vertebral bodies relative to their initial
state (P 0.05). The tamp treatment restored vertebral
body stiffness to initial values, but the percutaneous ver-
tebroplasty treatment did not (P 0.05).
Conclusions. Tamp treatment resulted in significantly
greater height restoration than did percutaneous verte-
broplasty, without loss of vertebral body strength or stiff-
ness. [Key words: biomechanical evaluation, compres-
sion fractures, inflatable bone tamp, kyphoplasty,
osteoporosis, vertebroplasty] Spine 2001;26:151–156
More than 200,000 symptomatic osteoporotic compres-
sion fractures of the vertebrae, primarily in elderly
women, occur in the United States each year.
20,21
These
fractures are the source of substantial pain and can lead
to disability and poor quality of life.
17,18,22,27
Until re-
cently, treatment of these fractures has been by nonop-
erative means.
17
In the mid-1980s, percutaneous trans-
pedicular vertebroplasty (PVP) was developed in France
9
and is now gaining acceptance in the United States. This
technique consists of injecting cement into the cancellous
bone of the fractured vertebral body (VB),
5,9
presumably
to stabilize the fracture.
1,6,28
The procedure has not un-
dergone prospective investigation, but findings in retro-
spective clinical studies indicate that it results in good
pain relief and has a low complication rate.
3,4,10,13
Al-
though the technique increases strength and restores VB
stiffness,
1,2,28
it does not restore VB height. A new de-
vice, the inflatable bone tamp (referred to hereinafter as
tamp), has been developed as a means of restoring height
(Figure 1). Height restoration has the potential benefit of
reducing postfracture kyphosis and its associated sequel-
ae.
15,16,18,26,27
The tamp is placed inside the VB under
fluoroscopic guidance through a percutaneously intro-
duced cannula. The tamp is inflated, thereby compress-
ing the cancellous bone, creating a void, and concur-
rently lifting the end plates in an en masse reduction.
After tamp removal, the void can be filled under lower
pressure than that needed for PVP. This procedure has
been termed kyphoplasty.
Little information exists about the biomechanics of
kyphoplasty. In a recent report
29
the investigators sug-
gest that kyphoplasty results in compliance reduction
(i.e., restoration of normal spine kinematics) similar to
that achieved by PVP, but height restoration was not a
primary focus of that investigation. The purpose of the
current study was to determine whether the tamp re-
stores VB height in simulated compression fractures and
whether the procedure results in VB strength and stiff-
ness values different from those obtained using PVP
alone.
Methods
Sixteen VBs (T12–L1) from eight fresh spines harvested from
female cadavers (average age at death, 84 11 years; range,
60 –96 years; Maryland State Anatomy Board, Baltimore, MD)
were evaluated. Bone mineral density was measured by the
dual-energy x-ray absorptiometry method (Lunar DPX-IQ; Lu-
nar Corp., Madison, WI). Rice bags were placed beneath the
From the *Orthopaedic Biomechanics Laboratory, Department of Or-
thopaedic Surgery, The University of Maryland at Baltimore, Balti-
more, Maryland; the †Department of Neuroradiology, The Johns
Hopkins Hospital, Baltimore, Maryland; §Kyphon, Inc., Santa Clara,
California; and ¶The Berkeley Orthopedic Medical Group, Berkeley,
California.
Supported by a grant from Kyphon, Inc., Santa Clara, California.
Acknowledgment date: October 5, 1999.
First revision date: January 21, 2000.
Acceptance date: April 6, 2000.
Device status category: 13.
Conflict of interest category: 15, 17.
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