CONCLUSIONS: Insertion of an oversized disc prosthesis resulted in

a biomechanical response that was similar to the fused spine condition.

In spinal arthroplasty, over-correction of disc angulation and height may

compromise subsequent disc mobility and function.

FDA DEVICE/DRUG STATUS: Kineflex lumbar disc prosthesis: Inves-

tigational/not approved.

CONFLICT OF INTEREST: Authors (DD, KF) Grant/Research Sup-

port: Spinal Motion.

doi: 10.1016/j.spinee.2006.06.302

P44. Assessment of Posterolateral Fusion Rates With BMP-2

and Resorbable Ceramic Granules

Edward Sun, MD1, James Reynolds, MD2, Paul Slosar, Jr., MD1,

Noel Goldthwaite, MD1; 1San Francisco Spine Institute, Daly City, CA,

USA; 2Spine Care Medical Group Inc., Daly City, CA, USA

BACKGROUND CONTEXT: The use of rhBMP-2 with resorbable ce-

ramic granules has been shown to have superior fusion rate compared with

iliac crest bone graft. However, the clinical studies often utilize high doses

of rhBMP-2 (40 mg/level). The rate of fusion using commercially available

doses of rhBMP-2 (5 to 15 mg/level) has not been reported. In addition, the

use of rhBMP-2 in posterolateral fusion for patients with failed previous

spinal fusions has not been examined.

PURPOSE: To assess the posterolateral fusion rate using rhBMP-2 and

resorbable ceramic granules in a consecutive group of patients undergoing

either primary or revision posterior spinal surgery.

STUDY DESIGN/SETTING: Retrospective review at a single institution.

PATIENT SAMPLE: All patients who underwent posterolateral fusions

using rhBMP-2 (at 1.5 mg/cc concentration) and resorbable ceramic gran-

ules (15% HA/85% beta-tricalcium phosphate) were identified by com-

puter database with minimum 12-month follow-up.

OUTCOME MEASURES: Radiographic analysis of the fusion rate using

CT scan.

METHODS: All patients had CT scans with 2-mm cuts 12 months after

surgery. Fusion status was graded using modified Bridwell-Lenke criteria:

solid bilateral fusion with trabeculated transverse processes (grade I), thick

unilateral fusion mass (grade II), defects in fusion mass bilaterally (grade

III), or definite graft resorption (grade IV).

RESULTS: Twenty-five patients were identified from a computer database

with mean follow-up of 15 months. Average patient age was 53 (range 35-

83), and 18 patients (72%) had prior spinal procedures. Majority had failed

back surgery syndrome with pseudoarthrosis (8 patients) or adjacent level

degeneration (8 patients). Concurrent iliac crest bone graft was used in

24% of patients. Fusion status was rated as grade I in 11 patients (44%),

grade II in 12 patients (48%), and grade III in 2 patients (8%). None of

the patients had grade IV fusion. Patients without prior lumbar surgery

had statistically higher bilateral solid fusion rate (grade I) compared with

those with prior surgeries (p!.05). The use of spinal instrumentation and

concurrent use of iliac crest bone graft also showed a trend towards higher

fusion rate although the difference was not statistically significant (pO.05).

CONCLUSIONS: The use of rhBMP-2 and ceramic granules can be ef-

fective in inducing posterolateral fusion even in patients with failed previ-

ous spinal fusion. However, only 44% of patients achieved solid bilateral

intertransverse fusion and an additional 48% achieved solid unilateral in-

tertransverse fusion. The rate of bilateral pseudoarthrosis was 8% in this

group of patients.

FDA DEVICE/DRUG STATUS: rhBMP-2: Not approved for this

indication.

CONFLICT OF INTEREST: Author (ES) Grant/Research Support:

Medtronic.

doi: 10.1016/j.spinee.2006.06.303

P45. How Increasing Lumbar Disc Space Height Affects the Lumbar

Facet Joint

Jiayong Liu, MD, Nabil A. Ebraheim, MD, Steve P. Haman, MD, Chris

G. Sanford, Jr., BS, Richard A. Yeasting, PhD; Medical University of Ohio,

Toledo, OH, USA

BACKGROUND CONTEXT: The surgeon often destructs the disc space

in order to implant a larger artificial disc in an attempt to keep the artificial

disc stable. However, it is hypothesized by the current authors that such

a procedure can have an adverse effect on the facet joints and may result

in instability at this level. No study has addressed the effect that increasing

disc space height has on the facet joints.

PURPOSE: Demonstrate how facet joint articulation is affected by in-

creasing disc space height in the lumbar spine.

STUDY DESIGN/SETTING: A computer-simulated prospective study

involving computed tomography images of lumbar spine cadaveric

specimens.

PATIENT SAMPLE: CT images of 15 cadaveric lumbar spine specimens

were used. Five of these 15 were dissected for validation and standardiza-

tion of measurements.

OUTCOME MEASURES: Sagittal plane CT images were used to mea-

sure the change in the facet joint articulation overlap and facet joint space

after incremental increases in lumbar disc space height.

METHODS: Computerized tomography images in the plane passing

through the center of the L3 to S1 facet joints (sagittal plane) on the right

and left sides were obtained for 15 cadaveric lumbar spine specimens. The

articulation overlap of the facet joint at L3-4, L4-5, and L5-S1 were

measured with Aquarius Image software at the CT scanner’s TeraRecon

Aquarius Workstation. The images were then manipulated. A 1-mm incre-

mental increase to a total 5 mm from L3 to S1 disc spaces was performed

to simulate an increase of the disc space height. NIH Image J software

(V1.33m) was then used to measure the change of the facet joint articula-

tion overlap in the sagittal plane on both sides at normal and each displace-

ment level. The joint space was also measured at each 1-mm increase in

disc space height. Validation was done on 5 of the 15 whole lumbar spine

specimens by comparing the same distances on the spine using the Aquar-

ius Image software at the CT scanner’s TeraRecon Aquarius Workstation,

the NIH Image J software, and a ruler directly on the specimen.

RESULTS: No significant difference was found between the measure-

ments on the CT images and the gross specimens (pO.05). In 15 speci-

mens, the mean facet joint articulation overlap in the sagittal plane was

16.2961.20 mm (left) and 16.2261.16 (right) at the L3-4 level,

17.8161.18 mm (left) and 17.7461.18 mm (right) at the L4-5 level, and

18.1861.18 mm (left) and 18.2361.15 mm (right) at the L5-S1 level.

There was no significant difference between the measured values on the

left and right sides (pO.05). Each 1-mm incremental increase in disc space

at the L3-4 level translated to a decrease in the facet joint articulation over-

lap in the sagittal plane by approximately 6% while the mean facet joint

Fig. 1. Normalized motion for oversized disc and fused spine conditions.

105SProceedings of the NASS 21st Annual Meetings / The Spine Journal 6 (2006) 1S–161S