brace, and except for the Miami J at C1-C2, all braces also significantly

(p!.05) reduced sagittal plane translation during flexion and extension.

When moving from a neutral upright position to supine, intervertebral

levels in the upper cervical spine tended to move into a more extended po-

sition whereas the lower cervical levels moved into a more flexed position.

There were a few significant differences with respect to intervertebral mo-

tion control when comparing the upright position relative to supine, but the

magnitude of the motion was generally small. The Aspen, Philadelphia,

PMT, and Miami J were all cervical orthoses and tended to perform sim-

ilarly. The Minerva, Halo, and SOMI were cervicothoracic braces that

tended to perform similarly and generally restricted motion to a greater

extent than did the cervical braces.

CONCLUSIONS: Some contemporary cervical braces can reduce head

and intervertebral motion significantly more than others when subjects

try to flex and extend their neck. Data from this investigation can help

clinicians select between these braces. Additionally, none of the braces

appeared to create significant motion in the spine when the subjects lay

supine on a hard surface while wearing the brace.

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

CONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2006.06.336

Fig. 1. Intervertebral rotation was significantly reduced by the cervical

braces.

145SProceedings of the NASS 21st Annual Meeting / The Spine Journal 6 (2006) 1S–161S

P128. A Rat Osteoporotic Spine Model for the Evaluation of

Bioresorbable Bone Cements

Mark Wang, MD, PhD1, Jennifer Massie, MS2, Andrew Perry, MD1,

Lichun Lu, PhD3, Yaszemski Michael, MD, PhD3, Steven Garfin, MD1,

Choll Kim, MD, PhD1; 1University of California, San Diego, San Diego,

CA, USA; 2VA Medical Center San Diego, San Diego, CA, USA; 3Mayo

Clinic, MN, USA

BACKGROUND CONTEXT: As the aging population increases, the ris-

ing prevalence of osteoporosis-related spine fractures will have a dramatic

impact on health care. Currently treatment relies on systemic medications

to increase bone mineral density. However, an adjunctive treatment strat-

egy is to target specific areas that are prone to osteoporotic fractures.

We term this strategy the ‘‘local treatment of osteoporosis’’, or osteoplasty,

involving the percutaneous injection of bioactive bone cements into bones

at risk of sustaining osteoporotic fractures. To accomplish this goal, a

suitable in vivo system is needed to evaluate the behavior of potential

biomaterials in an osteoporotic animal model.

PURPOSE: The purpose of this study was to evaluate the ovarectomized

(OVX) rat as an appropriate system for the in vivo evaluation of bone

cement performance in the osteoporotic spine.

STUDY DESIGN/SETTING: 1) Bone histomorphometric study, 2) Bio-

mechanical vertebral compression study.

PATIENT SAMPLE: N/A.

OUTCOME MEASURES: N/A.

METHODS: Female Sprague Dawley rats, 8 weeks, were ovarectomized

(OVX, n54) and maintained on a low calcium diet for 3 mos. Normal

nonovarectomized female rats (NL, n54) of similar age and size were

maintained on regular feed. Micro-CT analysis was performed on lumbar

(L5-L7) and tail vertebrae (T5-T7) of both groups, and the following bone

histomorphometric parameters were determined: BMD, average cortical

thickness (ACT), average trabecular thickness (TbTh), and average trabec-

ular spacing (TbSp). Failure force and stiffness were determined as verte-

bral bodies (OVX, n511; NL, n511) underwent failure testing under axial

compression at 0.1 mm/s (Fig. 1). Tail vertebrae derived from OVX rats

exhibited decreased BMD (Fig. 1A), decreased cortical thickness (B), de-

creased trabecular thickness (C), and increased trabecular spacing (D)

compared with non-OVX controls (CT) (*p!.05, **p!.01).

RESULTS: OVX tail vertebrae demonstrated an 18% decrease in BMD,

a 28% decrease in diaphyseal ACT, a 55% decrease in TbTh, and a 2.4 fold

increase in TbSp compared with CT (p!.05). Additionally, lumbar verte-

brae exhibited a 21% decrease in BMD, a 24% decrease in anterior body

ACT, a 48% decrease in TbTh, and a 4.7 fold increase in TbSp (p!.05).

Failure testing of OVX tail vertebral bodies revealed a 29% decrease in

force to failure and a 60% decrease in stiffness compared with CT

(p!.01) (Fig. 2). Dorsal exposure of tail vertebral bodies is minimally in-

vasive and provides excellent exposure (Fig. 2A). After creating a surgical

defect, cement can be easily injected and placed along the longitudinal axis

of the tail vertebrae (Fig. 2B).

CONCLUSIONS: The utilization of the rat osteoporotic spine for applied

orthopedic spine studies provides an efficient and convenient model for

spinal osteoporosis model compared with the lumbar spine. The tail verte-

brae can be readily exposed for the subsequent injection of bone cement,

yielding a greater bone-biomaterial interface for histological analysis. In

this study, we propose that the osteoporotic rat tail spine provides an ap-

propriate model for the evaluation of bone cement performance within

the osteoporotic spine, and, ultimately, allows for the future investigation

of potential biomaterials designed for the percutaneous augmentation of

the osteoporotic vertebral body.

Fig. 1. OVX effect on bone mineral density and microarchitecture in tail

vertebrae analyzed by bone histomorphometry.

Fig. 2. Surgical exposure of tail vertebrae and subsequent cement

injection.

P130. Radiation Dose Reduction Using Isocentric 3-D Fluoroscopic

Navigation for Percutaneous Kyphoplasty

Sigita Burneikiene, MD1, Alan Villavicencio, MD1, Ketan Bulsara, MD2,

Jeffrey Thramann, MD1; 1Boulder Neurosurgical Associates, Boulder, CO,

USA; 2University of Missouri, Columbia, MO, USA

BACKGROUND CONTEXT: Percutaneous stabilization of vertebral

body fractions is being increasingly utilized throughout the world. An

146S Proceedings of the NASS 21st Annual Meeting / The Spine Journal 6 (2006) 1S–161S

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

CONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2006.06.337

P129. Experimental Spinal Fusion Using a Highly Porous Slow

Release Carrier with Recombinant Human Bone Morphogenetic

Protein-2 in a Rabbit Model

Elisabeth Hustert, PhD, Susanne Pippig, PhD, Michael Siedler, PhD,

Andreas Schuetz, PhD, Carola Dony, PhD; Scil Technology GmbH,

Martinsried, Germany

BACKGROUND CONTEXT: Various bone growth factor activated bio-

materials have been used in the past for substitution of autogenous bone

grafts to achieve spinal fusion in animal models and humans. Because

these are mostly not satisfactory due to a high dose of the growth factor

necessary (such as recombinant bone morphogenetic protein-2 [rhBMP-

2]) and the limitation of the biomaterial itself, a new osteoconductive

delivery system with an improved bioavailability of the bone-inducing

substance was developed.

PURPOSE: The purpose of this study was to evaluate the efficacy of a syn-

thetic biodegradable bone graft substitute containing recombinant bone

morphogenetic protein-2 in a posterolateral intertransverse spinal fusion

rabbit model.

STUDY DESIGN/SETTING: A one-level posterolateral intertransverse

process arthrodesis was performed bilaterally at the L5-L6 level in adult

New Zealand white rabbits.

PATIENT SAMPLE: A total of 32 female and male skeletally mature rab-

bits were analyzed in the present study using 30 and 150 mg rhBMP-2

on a ceramic carrier in addition to several controls.

OUTCOME MEASURES: Manual palpation, radiologic assessment, CT

analysis, and a detailed histological analysis including a histomorphometric

analysis was performed 3 weeks after implantation.

METHODS: Through a posterolateral approach, implants were placed on

both sides to bridge the transverse processes of the New Zealand white rab-

bits. In control animals, implants without rhBMP2, autogeneous bone graft

derived from iliac crest or rhBMP-2 containing collagen were placed in

a similar location. The animals were sacrifized 3 weeks after implantation.

Histological analysis including histomorphometric analysis was performed

on undecalcified samples.

RESULTS: Rabbits that received 150 mg rhBMP-2 showed consistent fu-

sion 3 weeks after implantation. Extensive bone mass formation was ob-

served in rabbits that received 30 mg rhBMP-2. However, solid fusion as

determined by histological analysis was only determined in one animal

at that early time point. Fusion was not observed in rabbits that did not re-

ceive rhBMP-2. The results of this study demonstrated that the success rate

of posterolateral fusion was higher in the group where the new carrier with

150 mg rhBMP-2 was applied compared with all other groups including

a collagen rhBMP-2 group using the same amount of rhBMP-2. Increased

new bone mass, a higher fusion rate, and less immature bone indicate

superiority over autograft and collagen-based biomaterials.

CONCLUSIONS: These data indicate that the new carrier combined with

rhBMP-2 achieved enhanced bioactivity of the biomaterial with a highly

osteoconductive and osteoinductive potential for a more efficient bone for-

mation in spinal fusion compared with control samples. The future work

will focus on a preclinical study in monkeys for analyzing the potential

of the biomaterial in higher animals.

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

CONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2006.06.338

average fluoroscopy time of up to 10.1 minutes has been reported for a

single-level kyphoplasty procedure using biplanar fluoroscopic image

guidance. There are considerable known risks to spinal surgeons and other

ancillary personnel associated with long-term increased radiation exposure

from intraoperative fluoroscopy.

PURPOSE: The purpose of this study was to compare radiation time when

using isocentric (Iso-C) fluoroscopy-based navigation vs. biplanar fluoros-

copy for the pedicle cannulation during a kyphoplasty procedure.

STUDY DESIGN/SETTING: A prospective, nonrandomized clinical

study.

PATIENT SAMPLE: There were 35 patients in the Iso-C fluoroscopy

assisted group and 12 patients in the retrospectively analyzed biplanar

fluoroscopy assisted patients group.

OUTCOME MEASURES: Operative and radiation exposure time.

METHODS: A total operative time and intraoperative fluoroscopy time in

the Iso-C fluoroscopy patients group was compared with a cohort of pa-

tients who underwent the procedure under biplanar fluoroscopy guidance.

RESULTS: The mean duration of surgery was shorter in the isocentric

fluoroscopy guidance patients group compared with the biplanar fluoros-

copy-assisted procedures, 58.6 min (range 36–89 min) versus 69.2 min

(range 44–113 min) for single-level cases, respectively (p50.3). The mean

biplanar fluoroscopy exposure time was 57.4 sec (range, 20–83 sec) for the

isocentric fluoroscopy assisted cases, with an additional 40 seconds fluo-

roscopy time utilized for the 3-D fluoroscopy ‘‘spin’’, compared with

266.6 sec (range, 144–400 sec) for the biplanar fluoroscopy assisted cases.

The difference was statistically significant (p5.0001).

CONCLUSIONS: Use of intraoperative fluoro-based CT guidance for the

pedicle cannulation during percutaneous kyphoplasty potentially increases

safety and significantly reduces radiation exposure for the patient and

surgical staff.

FDA DEVICE/DRUG STATUS: This abstract does not discuss or include

any applicable devices or drugs.

CONFLICT OF INTEREST: No conflicts.

doi: 10.1016/j.spinee.2006.06.339

P131. Pressure: Implications for Expulsion Testing of Intra-Discal

Devices

Oscar Yeh, PhD, Samuel Chow, Maurice Small, Jacob Einhorn,

Greg Lambrecht; Intrinsic Therapeutics, Inc., Woburn, MA, USA

BACKGROUND CONTEXT: An extremely aggressive mechanical envi-

ronment exists in the intervertebral disc. In vivo intra-discal pressures have

been reported to be as high as 23 atm, and maximum axial loads are

thought to be greater than 2.3 kN. Extrusion of prosthetic nuclei in both

cadaveric (20% incidence) and clinical (38% incidence) studies under-

scores the importance of proper testing under these challenging conditions,

particularly as new intra-discal devices are emerging.

PURPOSE: Intra-discal pressure should govern the likelihood that such an

implant would be expelled out of the disc. As such, the overall purpose of

this study was to formulate a methodology for testing an expulsion failure

by: 1) identifying key parameters that affect intra-discal pressure; and 2)

utilizing those parameters to achieve pressures consistent with the highest

reported in vivo values.

STUDY DESIGN/SETTING: Cadaveric biomechanical study.

PATIENT SAMPLE: Fresh-frozen cadaveric lumbar functional spine

units.