Posterolateral lumbar fusion using Escherichia coli-derived rhBMP-2/hydroxyapatite in the mini pig.
BACKGROUND CONTEXT
Hydroxyapatite (HA) is used as a bone graft extender for posterolateral spinal fusion in human. It is also useful as a recombinant human bone morphogenetic protein (rhBMP)-2 carrier because of its high affinity for rhBMP-2.


PURPOSE
To assess the osteoinductivity of Escherichia coli-derived rhBMP-2 (E-BMP-2) using HA granules as a carrier and to evaluate the bone-forming ability depending on the different dosages of E-BMP-2.


STUDY DESIGN
A mini-pig lumbar posterolateral fusion model using microcomputed tomography (μCT) scanning.


PATIENT SAMPLE
Thirty-one adult male mini pigs were randomized into a single control group (n=8) without E-BMP-2 and two experimental groups with two different doses of E-BMP-2 (1 mg per side, n=8 and 3 mg per side, n=15).


OUTCOME MEASURES
Outcome was measured by plain radiography, manual palpation, CT, three-dimensional μCT, and histologic examinations.


METHODS
Bilateral intertransverse process arthrodesis was performed, and E-BMP-2 (0, 1.0, 3.0 mg per side) was implanted into the intertransverse space using HA granules as a carrier.


RESULTS
Three mini pigs were removed because of death. Among 28 experimental subjects, 19 animals achieved solid bony union. The fusion rates were 37.5% for control group, 71.4% for 1 mg group, and 84.6% for 3 mg group. Fusion rates were significantly different among groups (p=.031). However, there was no statistically significant difference in fusion rates between 1 and 3 mg groups (p=.587). Thirty-eight intertransverse fusion masses of 19 subjects underwent μCT scanning. The bone volumes determined by μCT were 12,603±3,240 mm(3) for control group, 18,718±3,000 mm(3) for 1 mg group, and 26,768±7,256 mm(3) for 3 mg group, and the difference between groups was statistically significant (p<.001).


CONCLUSIONS
This study shows that E-BMP-2 has osteoinductive activity in dose-dependent fashion, and porous HA granule is suitable for E-BMP-2 carrier in a porcine posterolateral fusion model. These preliminary findings suggest that E-BMP-2-adsorbed porous HA granules could be a novel effective bone graft substitute.
['Kong|Chang-Bae|CB|', 'Lee|Jae Hyup|JH|', 'Baek|Hae-Ri|HR|', 'Lee|Choon-Ki|CK|', 'Chang|Bong-Soon|BS|']
D000818:Animals D055396:Bone Morphogenetic Protein 2 D016025:Bone Transplantation D004337:Drug Carriers D017886:Durapatite D006801:Humans D008159:Lumbar Vertebrae D008297:Male D011994:Recombinant Proteins D013123:Spinal Fusion D013552:Swine D013556:Swine, Miniature D016212:Transforming Growth Factor beta
Hydroxyapatite Mini pig Osteoinductivity Posterolateral fusion Escherichia coli–derived rhBMP-2