134S Proceedings of the NASS 22nd Annual Meeting / The Spine Journal 7 (2007) 1S–163S

incorporation of allografts into the vertebrae. Finally, perioperative and

long-term complications were noted.

RESULTS: Mean patient age was 56. The average FU was 18 months

(12–42 months). The radiographic fusion rate was 97% of patients (32/33)

and 99% of levels (101/102). Minimal graft settling occurred even though

aggressive remodeling occurs (2 with over 5 deg settling). Graft incorpo-

ration by radiographic criteria was almost uniformly Grade I by the mod-

ified Bridwell-Lenke criteria, which correlates with the almost 100%

fusion rate. With the conservative BMP-use techniques used by surgeons

in our institute, which confines the BMP inside the allografts, there were

no incidents of respiratory complications.

CONCLUSIONS: RhBMP-2 is effective in significantly increasing ante-

rior multi-level cervical fusion rates when used with allograft and dynamic

plating. There is minimal graft settling without significantly affecting cer-

vical lordosis or fusion rate. The radiographic quality of fusion is also im-

proved, with allograft incorporation seen uniformly. When the rhBMP-2

containing sponge is confined entirely within the graft, no untoward

complications related to excessive neck swelling were observed.

FDA DEVICE/DRUG STATUS: rhBMP-2 (INFUSE): Not approved for

this indication.

doi: 10.1016/j.spinee.2007.07.319

P112. Surgical Repair of Pars Interarticularis Defect, 12 Year

Experience

Paul Lin, MD1; 1SUN Orthopaedic Group Inc., Lewisburg, PA, USA

BACKGROUND CONTEXT: Pars interarticularis defect may cause back

and leg pain and neurological compromise is some patients. A potential

outcome is isthmic spondlyolisthesis. Surgical options have included

any combination of the following: neural decompression, interbody or

posterolateral fusion, instrumentation, and reduction. This novel technique

improves the clinical outcome, prevents the development of spondylolis-

thesis and eliminates the need for lumbar fusion.

PURPOSE: The purpose of this paper is to describe the 12 year experi-

ence of the author in performing pars defect repairs. This includes a de-

scription of the evolution of the technique to where it stands today;

a novel approach using rhBMP and a pedicle screw based, compressive

tension band, posterior element fixation.

STUDY DESIGN/SETTING: Analysis of patient outcomes consisted of

review of 23 patients who underwent pars defect repair with a pedicle

based-posterior element fixation.

PATIENT SAMPLE: The patient population consisted of 18 males, and 5

females with an average age of 18 years (range 12-36 years) and a mean

follow-up of 3 years.

OUTCOME MEASURES: The surgery was considered successful if

there was a good clinical outcome, there was no development of spondy-

lolisthesis, and there was significant bone formation at the site of the par

defect. Clinical outcome was based on assessment of preoperative and

postoperative back and leg pain. Radiographic review was used to evaluate

development of spondylolisthesis and bone formation.

METHODS: Patients were evaluated clinically at regular intervals and as-

sessments made regarding use of pain medication, resumption of prior ac-

tivities including athletics, and ability to work if applicable. AP and lateral

radiographs were obtained every 6 months for 2 years. CT scans done prior

to surgery, and recommended at the 1 and 2 year follow-up exam. An in-

dependent radiologist was used for assessment of the development of spon-

dylolisthesis, bone formation at the level of the pars, and whether a union

of the defect had occurred.

RESULTS: Of the 23 patients included in the study, 20 rated their out-

come as ‘‘excellent’’, and 3 ‘‘very good’’. All agreed that the surgery

was worthwhile, and none were using narcotics. None of the 23 patients

had gone on to develop a spondylolisthesis, none required additional sur-

gery. There were no instances of hardware failure or removal. No surgical

complications were reported. Of the 9 patients who underwent repair using

the newer technique of repair using the Dynesys system (pedicle screws,

cord, and spacers) for posterior element fixation, and rhBMP with iliac

crest for graft, 4 went on to show CT evidence of bony healing of the

defect. Of the remaining 5, bone formation was present however a clear

union had not occurred.

CONCLUSIONS: Pars defect repair is an excellent alternative to offer se-

verely symptomatic patients who have failed conservative care. Rather

than fuse across a healthy disc space, this technique allows for a direct

repair of the defect. The literature is sparse regarding techniques that allow

for this. The author has been able to devise a techique that allows for se-

cure fixation of the posterior elements to a pedicle screw, and describes the

evolution of the grafting process to where it is today with autogenous iliac

graft and rhBMP. In the very least, this procedure allows for an excellent

clinical outcome with stabilization of the segment, and in some instances

allows for CT evidence of healing.

FDA DEVICE/DRUG STATUS: Dynesys: Not approved for this indica-

tion; Infuse: Not approved for this indication.

doi: 10.1016/j.spinee.2007.07.320

P113. In Vitro Effects of Recombinant Human GDF-5 on Human

and Rabbit Intervertebral Disc Cells

Cynthia Lee1, Mohamed Attawia1, Chantal Holy., PhD1, Liesbeth Brown1;1Johnson & Johnson Regenerative Therapeutics, Raynham, MA, USA

BACKGROUND CONTEXT: The stimulatory effects of recombinant hu-

man growth and differentiation factor-5 (rhGDF-5) on bovine interverte-

bral disc (IVD) cell biosynthesis in vitro has recently been reported and

in vivo studies have shown that intradiscal injections of rhGDF-5 can have

regenerative effects in a rabbit degeneration model. A link to the potential

efficacy in human patients, however, has been lacking.

PURPOSE: The purpose of this study was to investigate the dose-response

of human and rabbit annulus fibrosus (AF) and nucleus pulposus (NP) cells

to rhGDF-5.

STUDY DESIGN/SETTING: An in vitro experiment using human and

rabbit IVD cells in alginate beads.

METHODS: AF and NP cells from macroscopically normal human and

rabbit lumbar IVDs (n52 spines/species) were enzymatically isolated us-

ing sequential protease and collagenase digestion. Following expansion in

monolayer, cells were encapsulated in alginate beads and cultured in the

presence of 0, 30, 100, 200, or 500 ng/ml rhGDF-5 (BIOPHARM, GmbH).

On days 7 and 21, beads were harvested for DNA and GAG analysis (n53

groups of 9 beads for each dose and timepoint). On days 3 and 21, addi-

tional beads were harvested for gene expression analysis of aggrecan

(agg), collagen Ia2 (col1), collagen IIa1 (col2), collagen X (colX), and de-

corin (dcn) by real-time RT-PCR (n53 groups of 9 beads for each dose and

timepoint).

RESULTS: Biochemistry: There was no significant effect of rhGDF-5 on

DNA content. GAG accumulation for human AF cells was not affected by

rhGDF-5 on day 7, but was increased by day 21 for all rhGDF-5 doses. The

GAG content in human NP beads was increased with all rhGDF-5 concen-

trations by day 7 and sustained through day 21. In contrast, rabbit AF cells

showed a dose-dependent increase in GAG accumulation (on day 7 for one

donor and only on day 21 for the other) and no significant increase in NP

GAG accumulation over the 21 days. Gene Expression: The most dramatic

effects of rhGDF-5 on gene expression were seen for agg and col2 on day

21. Human AF cells showed an apparent peak in expression of these 2

genes at 100 ng/ml for one donor and a dose-dependent increase of the

same 2 genes through the 500 ng/ml dose for the other donor. Human

NP cells had an increase in gene expression with all doses of rhGDF-5,

with little difference from 100-500 ng/ml for one donor and from 30-

500 ng/ml for the other donor. For rabbit AF cells, the relative increase

in gene expression with rhGDF-5 treatment was seen at all dose levels,

was much greater than for humans, and the dose-dependent nature of the