Delivery of recombinant human bone morphogenetic protein-2 using a compression-resistant matrix in posterolateral spine fusion in the rabbit and in the non-human primate.
METHODS
A rabbit and rhesus monkey model of posterolateral intertransverse process spine arthrodesis was used.


OBJECTIVE
To test two new soft tissue compression resistant ceramic/collagen sponge carriers for recombinant human bone morphogenetic protein-2.


BACKGROUND
After determining that a plain collagen sponge was too compressible for large animals in a posterolateral fusion application, the authors demonstrated good bone induction using biphasic ceramic phosphate granules (60% hydroxyapatite/40% tricalcium phosphate) as the carrier matrix for recombinant human bone morphogenetic protein 2 in rhesus monkeys. A limitation of 60:40 biphasic ceramic phosphate was its slow resorption time caused by the high hydroxyapatite content, making radiographic detection of new bone formation very difficult.


METHODS
Adult New Zealand white rabbits (n = 14) underwent posterolateral spine arthrodesis at L5-L6 using 5:95 biphasic ceramic phosphate (5% hydroxyapatite/95% tricalcium phosphate) impregnated Type I collagen sponges (17 x 35 x 2.5 mm, two per side) loaded with 0.86 mg recombinant human bone morphogenetic protein 2. Additional rabbits (n = 14) received 60:40 hydroxyapatite-tricalcium phosphate granules as the carrier for bone morphogenetic protein 2. Adult rhesus monkeys (n = 6) underwent posterolateral arthrodesis at L4-L5 with ceramic/collagen sponge carrier loaded with 9 mg recombinant human bone morphogenetic protein 2 per side. Two monkeys received ceramic/collagen sponges containing 15:85 biphasic ceramic phosphate (15% hydroxyapatite/85% tricalcium phosphate) with two pieces per side; two received sponges containing 5:95 biphasic ceramic phosphate with two pieces per side, and two received sponges containing 5:95 biphasic ceramic phosphate with four pieces per side. The rabbits were killed after 5 weeks and the monkeys after 24 weeks; the spines were evaluated by manual palpation, radiographs, tensile mechanical testing (rabbits only), and histology.


RESULTS
The recombinant human bone morphogenetic protein 2 delivered in the 5:95 biphasic ceramic phosphate/collagen sponge achieved fusion in 100% of rabbits and had improved handling properties compared with the biphasic ceramic phosphate granules. Biomechanical results with 5:95 biphasic ceramic phosphate/collagen carrier were comparable to those obtained with the 60:40 biphasic ceramic phosphate granules and superior to those of autogenous bone graft (P < 0.05). The recombinant human bone morphogenetic protein 2 delivered in the 15:85 or the 5:95 biphasic ceramic phosphate/collagen sponge carrier (two pieces per side) induced fusion in nonhuman primates with normal bone histology, less residual ceramic, and more bone in the center of the carrier matrix in comparison with BCO granules alone. The 15:85 biphasic ceramic phosphate/collagen sponge resulted in fusion mass sizes closer to the original size of the matrix implanted than did the 5:95 biphasic ceramic phosphate/collagen sponge, which was considered a desirable feature. The monkeys with 9 mg recombinant human bone morphogenetic protein 2 spread over four sponges per side instead of two had half the effective recombinant human bone morphogenetic protein 2 concentration per sponge and inferior results.


CONCLUSIONS
The new compression-resistant biphasic ceramic phosphate/collagen sponge matrices were biologically compatible with recombinant human bone morphogenetic protein 2 bone formation, resulted in biomechanically stiffer fusion masses than autograft, better space maintenance than plain collagen sponges, and improved handling and radiographic resorption properties over the ceramic carriers previously tested.
Suh
Dan Y
DY
Neurosurgery, Emory University School of Medicine, The Atlanta VA Medical Center, The Yerkes Regional Primate Center, Atlanta, Georgia, USA.
Boden
Scott D
SD
Louis-Ugbo
John
J
Mayr
Matthew
M
Murakami
Hideki
H
Kim
Hak-Sun
HS
Minamide
Akihito
A
Hutton
William C
WC
D000818:Animals; D001696:Biomechanical Phenomena; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000008:administration & dosage*; D002130:Calcium Phosphates / Q000008:administration & dosage; D002516:Ceramics; D024042:Collagen Type I / Q000008:administration & dosage; D019245:Compressive Strength; D004333:Drug Administration Routes; D004337:Drug Carriers / Q000008:administration & dosage*; D004353:Drug Evaluation, Preclinical; D017886:Durapatite / Q000008:administration & dosage; D006801:Humans; D020007:Implants, Experimental / Q000009:adverse effects; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000601:surgery; D008161:Lumbosacral Region; D008253:Macaca mulatta; D023421:Models, Animal; D010012:Osteogenesis / Q000187:drug effects; D011817:Rabbits; D011994:Recombinant Proteins / Q000008:administration & dosage*; D013123:Spinal Fusion / Q000379:methods*; D015503:Surgical Sponges; D014057:Tomography, X-Ray Computed; D016212:Transforming Growth Factor beta; D016896:Treatment Outcome
C525718:BMP2 protein, human; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D002130:Calcium Phosphates; D024042:Collagen Type I; D004337:Drug Carriers; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; C485817:beta-tricalcium phosphate; C499469:recombinant human bone morphogenetic protein-2; D017886:Durapatite; C018392:tricalcium phosphate