Autologous bone graft is thought to contain growth fac-tors such as bone morphogenetic proteins BMPs.1 These proteins have been shown to induce bone formation through endochondral mechan
Trang 1Of the various bone-graft materials
available, autologous bone graft is
the standard for arthrodesis of the
spine The relative superiority of
autologous bone grafting is due to
its osteoinductive, as well as its
osteoconductive and osteogenic,
properties Autologous bone graft
is thought to contain growth
fac-tors such as bone morphogenetic
proteins (BMPs).1 These proteins
have been shown to induce bone
formation through endochondral
mechanisms, leading to their
possi-ble use in isolated form to achieve
spinal fusion and to repair
long-bone fractures.2,3
In 1979, Urist et al4first showed
that proteins with bone
morpho-genetic properties could be extracted
from animal cortical bone by
diges-tion of the demineralized cortical
bone matrix with bacterial collage-nase and solubilization of the digest in a neutral mixture of salt and ethylene glycol The BMP ex-tracted in this manner was found not to be species-specific; that is, BMP extracted from a rabbit in-duced new bone in rats and there-fore might do so in man as well
Bauer and Urist5 then isolated human BMP (by using a 4M guani-dine hydrochloride solution) that was capable of inducing bone for-mation in the thigh muscles of athymic nude mice
Since that time, more BMP types, better isolation techniques, and the advent of recombinant cloning techniques have made the use of BMP in the clinical setting a reality Currently, the use of BMP
in humans is restricted to trials
evaluating its use in achieving spinal arthrodesis6and in treating nonunions and other difficult problems Possible future uses for BMPs include enhancement or re-placement of autologous bone graft, treatment of delayed union
or nonunion, compensation for patient factors such as nicotine use, facilitation of spinal or recon-structive arthrodeses, supplemen-tation of biologic ingrowth, and management of osteonecrosis and certain pathologic osteopenias.7
Additionally, current basic science research is evaluating the efficacy
in animal models of a single dose
of recombinant human BMP-2 (rhBMP-2) versus the use of mar-row cells genetically transformed
to produce BMP-2
Dr Zlotolow is Clinical Research Fellow, Department of Orthopaedic Surgery, The Rothman Institute at Thomas Jefferson University, Philadelphia Dr Vaccaro is Associate Professor of Orthopaedic Surgery, The Rothman Institute Mr Salamon is Research Assistant, Thomas Jefferson University Dr Albert is Associate Professor of Orthopaedic Surgery, The Rothman Institute.
Reprint requests: Dr Vaccaro, The Rothman Institute, 925 Chestnut Street, Philadelphia,
PA 19107.
Copyright 2000 by the American Academy of Orthopaedic Surgeons.
Abstract
The attainment of a stable arthrodesis is critical to the successful management
of some types of spinal disorders Autologous iliac-crest bone graft has been the
most commonly utilized substance associated with predictable healing in spinal
fusion applications Although alternative graft substances exist, these have not
been shown to be as uniformly effective in achieving spinal fusion Because of
the morbidity associated with bone autograft harvest, there is increasing
inter-est in alternative graft substances and especially in the osteoinductive abilities
of bone morphogenetic proteins (BMPs) Several animal models have
demon-strated that BMP-containing allograft or synthetic carrier medium is as effective
as or superior to autograft bone in promoting spinal fusion Furthermore, the
limited number of human trials utilizing BMPs to treat nonunions in the
appendicular skeleton indicate that the results found in animal models will be
reproducible in the clinical setting.
J Am Acad Orthop Surg 2000;8:3-9
The Role of Human Bone Morphogenetic
Proteins in Spinal Fusion
Dan A Zlotolow, MD, Alexander R Vaccaro, MD, Michael L Salamon, and Todd J Albert, MD
Trang 2The BMPs, with the exception of
BMP-1, are grouped as a family
within the transforming growth
factor β (TGF-β) superfamily of
dimeric, disulfide cross-linked
growth and differentiation factors
(Table 1) Although BMPs have
been studied primarily for their
osteoinductive properties, they
may also be found in extraskeletal
tissues, where they function to
reg-ulate the development of other
organ systems.8 The sole criterion
for BMP classification is the
induc-tion of ectopic bone formainduc-tion in a
standard in vivo rodent assay
sys-tem Individual BMPs are grouped
on the basis of their amino acid
sequences and molecular structural
components
The BMP family encompasses
more than 12 proteins, 9 of which
have demonstrated an ability to
induce ectopic bone formation in
an in vivo assay system.9 The
BMPs used for the initial basic and
clinical research endeavors were
originally extracted from
deminer-alized human cortical matrix A
number of extraction schemes have
been developed, but all are
com-plex and do not reliably yield
usable quantities of BMP, as only 1
to 2 µg of BMPs are present in a
kilogram of cortical bone
Further-more, the presence of contaminants
in these extracts is of some concern
in this era of blood-transmissible
infections.7
The application of recombinant
DNA technology in the
manufac-turing of genetically engineered
BMPs as early as 19882has allowed
for a virtually limitless supply of a
few rhBMPs (e.g., rhBMP-2, -4, and
-6,Genetic Institute, Cambridge,
Mass; OP-1 rhBMP-7, Stryker
Bio-tech, Natick, Mass) for basic
re-search and clinical trial
applica-tions Despite this, the mechanism
of action and the role of each of the
seemingly redundant BMPs remain
controversial What little is known about these proteins has been stud-ied mostly in in vitro assay systems and in clinical trials in animals
Osteoinductive Properties
Analogous to the cascade theory of bone formation witnessed in em-bryonic endochondral ossification and fracture callus formation, BMPs induce bone formation in a stepwise fashion The sequence includes chemotaxis of progenitor cells, proliferation of mesenchymal cells, differentiation of chondro-cytes, calcification of cartilage matrix, angiogenesis and vascular invasion, bone differentiation and mineralization, and bone remodel-ing and marrow differentiation
Once formed, the bone seems to function as typical endochondral bone, responsive to both internal and external stimuli.8
The BMPs may themselves act in
a stepwise fashion The presence of one BMP may induce the expres-sion of other BMPs Moreover, two different BMPs may join to form disulfide-linked heterodimers, and these heterodimers may bind and activate BMP receptors with greater affinity than that of BMP homo-dimers The combinations of BMP-2 with BMP-7 and BMP-2 with BMP-6 have been shown to be five- to ten-fold more potent in inducing carti-lage and bone formation than BMP-2 alone.10 This, along with the dis-covery of a joint BMP-2ÐBMP-4 re-ceptor, suggests that BMPs may function as heterodimers in vivo.11
Alternatively, BMP-2 and BMP-4 may induce endochondral bone for-mation, while BMP-6 may preferen-tially induce direct membranous bone formation There is evidence that BMP-7 stimulates mRNA levels
of BMP-6 while decreasing mRNA levels of BMP-2 and BMP-4,12 and that BMP-2 stimulates BMP-3 and BMP-4 mRNA levels.13 Boden et al14
found that physiologic levels of the glucocorticoid triamcinolone ace-tonide promoted osteoblast differen-tiation from fetal calvarial cells by inducing BMP-6 production The effects of the glucocorticoid could be blocked by BMP-6 antisense DNA (antisense DNA blocks sister-strand mRNA translation), indicating that BMP-6 mRNA translation to protein
is a necessary step downstream of glucocorticoid production in the osteoinductive pathway Further-more, BMP-6 was found to be 2 to 2.5 times more potent than either BMP-2 or BMP-4, and to not be as potentiated by a glucocorticoid infu-sion as the other two.15
The cascade of bone osteoinduc-tion may be initiated by a BMP, leading to the controlled expres-sion of other BMPs, which may then work synergistically to stimu-late bone formation In sponta-neous bone formation, the gluco-corticoid may be the principal or early signaling molecule, and may initiate a signal amplification cas-cade beginning with BMP-6 Due
to its function early in the cascade, BMP-6 appears to be the ideal osteoinductive protein for investi-gation in clinical trials
Segmental-Defect Models
The potential of BMPs was initially investigated by utilizing segmental-defect animal models In 1982, Takagi and Urist16showed that extracted bovine BMP could be
Table 1 Family Groups Within the TGF-β
Superfamily
TGF-βfamily Inhibin/activin family MŸllerian inhibiting substance family
Decapentaplegic BMP family
Trang 3used to heal large femoral
diaphy-seal defects in rats The authors
used an omega pin to distract the
two ends of the femur and to block
the migration of osteoinductive and
osteoconductive elements within
the marrow Although a variety of
graft materials were evaluated,
including variable doses of BMP
without a carrier, only the defects
treated with BMP and autologous
marrow healed 100% of the time
The earliest experimental studies
of rhBMP-2 also involved
iatrogeni-cally produced bone defects in an
animal model Yasko et al17found
that rhBMP-2 combined with bone
marrow in a rat segmental
femoral-defect model produced union at a
rate of 100%, three times superior to
the rates achieved with autogenous
cancellous bone graft Similar
bone-defect studies have been
con-ducted in rabbit tibia and ulna,
sheep femur, and canine spine and
mandible Toriumi et al18 showed
that rhBMP-2 could effectively
in-duce bone formation in the
man-dible, which embryologically follows
the intramembranous pathway,
un-like previous studies that focused
on endochondrally derived bones
Early results in human clinical trials
for tibial nonunions suggest
out-comes equivalent to those obtained
with use of autologous bone graft
Posterior Lumbar Spine
Fusion
Posterior lumbar fusions in humans,
unlike anterior fusions, may not be
loaded in compression and therefore
occur less predictably Clinically
im-proving the rate of posterior fusion
may require use of an
osteoinduc-tive substance such as autograft or
BMP At the present time, the only
human BMPs tested in clinical
ani-mal spine fusion models have been
rhBMP-2 and rhBMP-7 In addition
to investigating the efficacy of BMPs,
studies of these substances have
pro-vided information on the optimal delivery system or carrier, potential complications, and the effects of dosage manipulation on fusion rate and success
Early Results
As early as 1989, Lovell et al19
evaluated the effect of extracted BMP
on experimental posterior inter-vertebral spine fusions in mature mongrel dogs Radiologic and histo-morphometric evaluation showed that the fusion levels augmented with BMP had two to three times more new-bone formation than con-trol levels Fusion occurred at 71% of the levels treated with the BMP but only 14% of the control levels How-ever, the polylactic-acid polymer car-rier utilized was not resorbed com-pletely, suggesting that a better carrier material needs to be found
Schimandle et al20demonstrated higher fusion tensile strength and stiffness in rabbit posterior lumbar-spine fusions supplemented with rhBMP-2 as compared with those in animals that received autogenous iliac-crest bone graft All animals treated with rhBMP-2 demonstrated solid fusion, as evaluated by manual palpation and radiographic exami-nation, compared with only 42% of the autograft animals In another study, performed in a posterolateral intertransverse-process model in rabbits, rhBMP-2 was shown to reverse the inhibitory effects of the nonsteroidal anti-inflammatory drug ketorolac on fusion rate.21
Dose Response
Using rhBMP-2 with a collagen carrier in a canine spinal fusion model, David et al22showed a dose-dependent osteoinductive effect, with a 100% clinical and radio-graphic fusion rate Using a canine fusion model, Sandhu et al23 dem-onstrated that rhBMP-2, delivered
at a dose of 2,300 µg in a porous polylactic-acid polymer, was supe-rior to autologous iliac-crest bone
graft in achieving a single-level lumbar arthrodesis In a later study, this group investigated the dosage level at which no further osteoinduction was achieved Re-combinant human BMP-2 was implanted at multiple doses, in-cluding 58, 115, 230, 460, and 920
µg Histologically, abundant bone formation occurred in all specimens containing rhBMP-2 by 3 months.24
The data from this study and the one using 2,300 µg of rhBMP-2 showed no mechanical, radiographic,
or histologic variations in the quality
of intertransverse-process fusion re-sulting from a 40-fold increase in rhBMP-2 dosage (58 µg to 2,300 µg) The rhBMP-2 dosage require-ment for successful fusion was also investigated by Boden et al25 in a primate model of laparoscopic anterior lumbar interbody arthro-desis in which a titanium-threaded interbody fusion cage was used Before insertion, the cages were soaked in either high-dose (1,500 µg/mL) or low-dose (750 µg/mL) rhBMP-2 Although bone formation and spinal fusion were achieved at both doses tested, the higher dose produced a more rapid fusion re-sponse In humans, the optimal dosage based on the optimal carrier remains to be determined, although dose-response studies have been carried out in nonspinal locations
in humans
Carrier Medium
The role of the carrier medium is
to allow the BMP molecules to be applied in an easily reproducible localized fashion and to prevent rapid uncontrolled diffusion into the surrounding tissues The ideal car-rier medium would be biocompatible, completely resorbable, structurally stable, and easy to manipulate A variety of media, including biologic substances, polymers of different types, and even titanium sponges, have been investigated in the ap-pendicular skeleton
Trang 4Sheehan et al26examined various
carrier media in posterior lumbar
spine fusions in an adult female
ca-nine model Using the same
surgi-cal approach, the authors compared
four different treatments:
autoge-nous iliac-crest bone alone, bovine
type I collagen gel and autogenous
iliac-crest bone, type I collagen gel
combined with autogenous
iliac-crest bone and rhBMP-2, and
con-trol (sham) without an implant
There was considerably more bone
formation at the sites containing
rhBMP-2 than at the sites
contain-ing autogenous iliac-crest bone
graft either alone or combined with
the collagen gel carrier
Biome-chanical testing of the explants
demonstrated superior strength of
the rhBMP-2 fusion sites
Fischgrund et al27evaluated the
augmentation of autograft by using
rhBMP-2 combined with various
car-rier media in a canine lumbar spine
fusion model The carrier media
included a collagen ÒsandwichÓ
made of collagen sheets, collagen
ÒmorselsÓ (collagen sheets cut into
small pieces), open-pore polylactic
acid, and a polylactic acidÐglycolic
acid sponge sandwich, with
auto-graft alone or in combination with
rhBMP-2 as controls Greater
in-creases in bone fusion mass were
recorded at all levels that involved
rhBMP-2 as compared with levels
containing autograft alone In
addi-tion, carriers that were combined
with morselized bone graft offered
easier technical handling and
appli-cation during the operative
proce-dure Use of the polylactic acidÐ
glycolic acid sponge sandwich as a
carrier was associated with a greater
incidence of voids within the fusion
mass compared with the use of
colla-gen sandwich, collacolla-gen morsels,
open-pore polylactic acid, or
auto-graft with rhBMP-2 alone
Ulti-mately, no important difference in
the efficacy of the various carrier
media could be determined from this
study However, the addition of
rhBMP-2 to autograft enhanced the volume and maturity of the resulting fusion mass
The most recent studies suggest that another approach to the use of BMP-2 in spinal fusions may be pos-sible Rather than utilizing a single dose at the time of surgery, geneti-cally transformed marrow cells were implanted, which produced continuously generated quantities
of BMP-2 Boden et al28transplanted marrow cells in rats with cDNA for
an osteoinductive protein and had a 100% fusion rate, compared with 0%
for controls Similar results were observed with adenoviral vectorÐ transformed, BMP-2Ðproducing marrow cells in a rat fusion model;
the effects were comparable to those obtained with implanted rhBMP-2.29
Decortication and Minimally Invasive Techniques
The value of host-bone decortica-tion was studied by Sandhu et al30
in a dog intertransverse-process fusion model in which rhBMP-2 was used The argument for the necessity of decortication to achieve fusion is that it unmasks marrow elements, osteoinductive proteins, inflammatory cells, the local blood supply (including the initial hema-toma), and osteogenic cells at the fusion site In that study, there was
no statistical difference in the clini-cal and radiographic fusion rates between decorticated and non-decorticated fusion sites Further-more, as the dosage of rhBMP-2 was increased, there was little his-tologic discrimination between fusions in decorticated spines and those in nondecorticated spines
Boden et al31 demonstrated the feasibility, efficacy, and safety of a minimally invasive application of rhBMP-2 delivered in a collagen sponge carrier in both a rabbit and
a nonhuman primate (rhesus
mon-key) intertransverse-process model This technique minimizes the mor-bidity of paraspinal muscle dener-vation and devascularization seen with open intertransverse-process fusion techniques while providing effective fusion
In a subsequent study, Boden et
al32again utilized the minimally invasive video-assisted lateral inter-transverse-process approach in rhe-sus monkeys with a different carrier Instead of a collagen carrier, which was criticized for its nonrigidity and its lack of predictability of rhBMP dose delivery, the researchers used
a rectangular-block ceramic carrier made of hydroxyapatite (60%) and tricalcium phosphate (40%) with 9
mg of rhBMP-2 At follow-up, the intertransverse processes in all five monkeys had fused solidly, com-pared with only three of four mon-keys in which a collagen carrier had been utilized
Anterior Interbody Fusion
Results of successful interbody fusions were reported by Hecht et
al,33who studied the application of rhBMP-2 delivery by means of an ab-sorbable collagen sponge carrier within a freeze-dried cortical-dowel allograft in a nonhuman primate (rhesus macaque) model (Fig 1) The rates of new-bone formation and ultimate fusion success were superior with the use of rhBMP-2 compared with autogenous cancel-lous iliac-crest graft and freeze-dried cortical-dowel allograft (Fig 2) Successful fusion was achieved in all three animals in the rhBMP-2 group, whereas two of the three control animals had pseudarthro-ses (Fig 3)
The benefits of rhBMP-2 in stim-ulating a successful fusion response have also been demonstrated re-cently by Zdeblick et al34in a goat model In that study, animals treated with cervical interbody cages filled
Trang 5with rhBMP-2 in a collagen sponge
demonstrated more predictable
bone growth than those treated
with local bone alone
Human Studies
Johnson et al35were among the first
to use BMP in human clinical
stud-ies, evaluating the role of BMPs in
the treatment of femoral nonunions
Twelve patients with an average of
4.3 surgical procedures each for
intractable femoral nonunions were
treated with internal fixation and
extracted human BMP implants
All went on to have a successful
union at an average of 5 months
Johnson and Urist36evaluated 15
patients with posttraumatic atrophic
femoral nonunions treated with a
one-stage lengthening procedure
(mean lengthening, 2.8 cm)
involv-ing the use of an implant of
allo-geneic antigen-extracted autolyzed
human bone perfused with
par-tially purified hBMP Fourteen
pa-tients healed primarily with no
negative side effects from the
allo-geneic graft material, such as
infec-tion, allergic reacinfec-tion, or tissue
re-jection
Recently, Muschler et al37
re-ported on the first US prospective
human clinical trial of rhBMP-7, in
which they evaluated its efficacy when coupled to a collagen carrier in the treatment of complicated tibial nonunions In that study, both groups were treated with a reamed tibial nail, preparation of the nonunion site, and placement of autogenous bone graft or the rhBMP-7 device
The researchers found no clinically relevant difference in outcomes with regard to pain, return to full
weight-bearing status, and avoidance of surgery between the rhBMP-7 group and the autogenous iliac-crest bone grafting group Unfortunately, the study design did not utilize a control group with no graft material; there-fore, the effect of rhBMP-7 relative to that of the surgical procedure alone could not be discerned
An unpublished Food and Drug Administration pilot study utilizing
Figure 1 Computed tomographic scans of the L5-S1 interspace in primates, obtained 3 months after attempted anterior interbody fusion
with allograft Axial (A) and sagittal (B) reconstructions of a control animal that received a cortical-dowel allograft with iliac-crest
auto-graft placed inside the dowel Minimal bone formation is demonstrated within the center of the dowel, with minimal incorporation of the
cortical allograft C and D, Images of an animal that received a cortical-dowel allograft with a collagen sponge containing rhBMP-2 placed
within the dowel Extensive bone formation is depicted within the center of the dowel, as well as extensive incorporation of the allograft with fusion at the L5-S1 interspace (Courtesy of Jeffrey S Fischgrund, MD, Southfield, Mich.)
Figure 2 A,Histologic analysis 6 months after attempted L5-S1 fusion with cortical allo-graft and cancellous autoallo-graft within the autoallo-graft in a rhesus monkey The alloallo-graft is still visible, and fibrous tissue is noted at the site of attempted fusion (Mallory azan, origi-nal magnification ×14) B, Similar histologic analysis of tissue from another animal that
received rhBMP-2 within the cortical allograft At the 6-month evaluation, solid fusion is demonstrated across the interspace, with normal trabecular bone Note complete incorpo-ration of the allograft with preservation of the space available for the exiting spinal nerves (Courtesy of Jeffrey S Fischgrund, MD, Southfield, Mich.)
Trang 6rhBMP-2 with anterior spinal cages
in the lumbar spine has reached the
1-year follow-up period
Prelimi-nary results were presented at the
1998 meeting of the North
Ameri-can Spine Society and the 1999
meeting of the American Academy
of Orthopaedic Surgeons The
re-searchers demonstrated 100%
heal-ing by 6 months in 11 patients who
received rhBMP-2 and collagen
without any autograft.6 Another
human clinical trial with allograft bone dowels used as rhBMP-2 car-riers is in progress
Human clinical trials of the use of rhBMP-7 are taking place in Aus-tralia, Sweden, and Denmark, with a special focus on utilizing rhBMP-7
in lieu of autograft bone for various operative procedures in the spine
The first such study of the use of rhBMP-7 in the United States is al-ready under way
Summary
Although the in vivo role of each BMP is unclear, the ability of BMPs to stimulate bone formation
is no longer in question Various studies, most recently human clin-ical trials, have demonstrated that BMPs not only can potentiate heal-ing after autologous bone graftheal-ing but also may be able to replace that procedure It is unlikely, however, that BMPs will replace rigid fixation in spine surgery, except in cases of minimal instabil-ity The use of BMPs in a small number of human trials suggests that rhBMPs may be safe for use in human subjects, although further investigation is necessary before widespread use can be sanctioned Currently, the costs of BMPs (an estimated $3,000 to $5,000 per dose) limit their use to experimen-tal studies and selected cases of nonunion or those with a high probability of nonunion However,
as this technology matures, the cost will likely drop precipitously and allow BMPs to be used in other aspects of orthopaedic surgery In theory, BMPs will be as inexpen-sive to produce as recombinant human insulin or any recombinant vaccine and will likely be as widely used The results of the work that has been done with rhBMPs are encouraging, suggesting that the conventional techniques of spinal surgery may change dramatically
in the not too distant future
Figure 3 A,Microradiograph demonstrating persistence of a cortical allograft 3 months
after attempted L5-S1 fusion in a rhesus monkey B, Microradiograph of another animal
that received rhBMP-2 within the cortical allograft Note solid fusion across the interspace,
with trabecular bone formation (Courtesy of Jeffrey S Fischgrund, MD, Southfield, Mich.)
References
1 Elima K: Osteoinductive proteins.
Ann Med 1993;25:395-402.
2 Wozney JM, Rosen V, Celeste AJ, et al:
Novel regulators of bone formation:
Molecular clones and activities.
Science 1988;242:1528-1534.
3 Einhorn TA, Lane JM, Burstein AH,
Kopman CR, Vigorita VJ: The healing
of segmental bone defects induced by
demineralized bone matrix: A
radio-graphic and biomechanical study J Bone Joint Surg Am 1984;66:274-279.
4 Urist MR, Mikulski A, Lietze A:
Solubilized and insolubilized bone
morphogenetic protein Proc Natl Acad Sci USA 1979;76:1828-1832.
5 Bauer FC, Urist MR: Human osteosar-coma-derived soluble bone
morpho-genetic protein Clin Orthop 1981;154:
291-295.
6 Boden SD, Zdeblick TA, Sandhu HS, Heim SE: The use of BMP-2 in inter-body fusion cages: Definitive evidence
of osteoinduction in humans Pre-sented at the 66th Annual Meeting of the American Academy of Ortho-paedic Surgeons, Anaheim, Calif, February 5, 1999.
7 Riley EH, Lane JM, Urist MR, Lyons
KM, Lieberman JR: Bone
Trang 7morpho-genetic protein-2: Biology and
applica-tions Clin Orthop 1996;324:39-46.
8 Reddi AH: Bone and cartilage
differ-entiation Curr Opin Genet Dev 1994;4:
737-744.
9 Israel DI, Nove J, Kerns KM,
Mout-satsos IK, Kaufman RJ: Expression and
characterization of bone
morphogenet-ic protein-2 in Chinese hamster ovary
cells Growth Factors 1992;7:139-150.
10 Israel DI, Nove J, Kerns KM, et al:
Heterodimeric bone morphogenetic
proteins show enhanced activity in
vitro and in vivo Growth Factors 1996;
13:291-300.
11 Mayer H, Scutt AM, Ankenbauer T:
Subtle differences in the mitogenic
effects of recombinant human bone
morphogenetic proteins -2 to -7 on
DNA synthesis on primary
bone-forming cells and identification of
BMP-2/4 receptor Calcif Tissue Int
1996;58:249-255.
12 Honda Y, Knutsen R, Strong DD,
Sampath TK, Baylink DJ, Mohan S:
Osteogenic protein -1 stimulates
mRNA levels of BMP-6 and decreases
mRNA levels of BMP-2 and -4 in
human osteosarcoma cells Calcif Tissue
Int 1997;60:297-301.
13 Chen D, Harris MA, Rossini G, et al:
Bone morphogenetic protein 2 (BMP-2)
enhances BMP-3, BMP-4, and bone cell
differentiation marker gene expression
during the induction of mineralized
bone matrix formation in cultures of
fetal rat calvarial osteoblasts Calcif
Tissue Int 1997;60:283-290.
14 Boden SD, Hair G, Titus L, et al:
Glucocorticoid-induced differentiation
of fetal rat calvarial osteoblasts is
mediated by bone morphogenetic
pro-tein-6 Endocrinology
1997;138:2820-2828.
15 Boden SD, McCuaig K, Hair G, et al:
Differential effects and glucocorticoid
potentiation of bone morphogenetic
protein action during rat osteoblast
differentiation in vitro Endocrinology
1996;137:3401-3407.
16 Takagi K, Urist MR: The role of bone
marrow in bone morphogenetic
pro-tein-induced repair of femoral massive
diaphyseal defects Clin Orthop 1982;
171:224-231.
17 Yasko AW, Lane JM, Fellinger EFJ,
Rosen V, Wozney JM, Wang EA: The
healing of segmental bone defects,
induced by recombinant human bone
morphogenetic protein (rhBMP-2): A
radiographic, histological, and
biome-chanical study in rats J Bone Joint Surg
Am 1992;74:659-670.
18 Toriumi DM, Kotler HS, Luxenberg
DP, Holtrop ME, Wang EA: Mandib-ular reconstruction with a recombi-nant bone-inducing factor: Functional, histologic, and biomechanical
evalua-tion Arch Otolaryngol Head Neck Surg
1991;117:1101-1112.
19 Lovell TP, Dawson EG, Nilsson OS, Urist MR: Augmentation of spinal fusion with bone morphogenetic
pro-tein in dogs Clin Orthop 1989;243:
266-274.
20 Schimandle JH, Boden SD, Hutton WC:
Experimental spinal fusion with re-combinant human bone
morphogenet-ic protein-2 Spine 1995;20:1326-1337.
21 Martin GJ, Boden SD: BMP-2 reverses the inhibitory effect of ketorolac, a non-steroidal anti-inflammatory drug (NSAID), on posterolateral lumbar intertransverse process spine fusion.
Presented at the 65th Annual Meeting
of the American Academy of Ortho-paedic Surgeons, New Orleans, March
19, 1998.
22 David SM, Murakami T, Tabor OB, et al: Lumbar spinal fusion using recom-binant human bone morphogenetic protein (rhBMP-2): A randomized, blinded, and controlled study Pre-sented before the International Society for the Study of the Lumbar Spine, Helsinki, Finland, June 18-22, 1995.
23 Sandhu HS, Kanim LEA, Kabo JM, et al: Evaluation of rhBMP-2 with an OPLA carrier in a canine
posterolater-al (transverse process) spinposterolater-al fusion
model Spine 1995;20:2669-2682.
24 Sandhu HS, Kanim LEA, Kabo JM, et al: Effective doses of recombinant human bone morphogenetic protein-2
in experimental spinal fusion Spine
1996;21:2115-2122.
25 Boden SD, Horton WC, Martin G, Truss TR, Sandhu H: Laparoscopic anterior spinal arthrodesis with rhBMP-2 in a titanium interbody threaded cage Presented at the 32nd Annual Meeting of the Scoliosis Research Society, St Louis, September 25-27, 1997.
26 Sheehan JP, Kallmes DF, Sheehan JM,
et al: Molecular methods of enhancing
lumbar spine fusion Neurosurgery
1996;39:548-554.
27 Fischgrund JS, James SB, Chabot MC,
et al: Augmentation of autograft using rhBMP-2 and different carrier media
in the canine spinal fusion model J Spinal Disord 1997;10:467-472.
28 Boden SD, Titus L, Hair G, Liu Y, Viggeswarapu M, Nanes MS: Lumbar spine fusion by local gene therapy with
a cDNA encoding a novel osteoinduc-tive protein (LMP-1) Presented at the
66th Annual Meeting of the American Academy of Orthopaedic Surgeons, Anaheim, Calif, February 6, 1999.
29 Wang JC, Yoo S, Kanim LEA, et al: Gene therapy for spinal fusion: Trans-formation of marrow cells with an adenoviral vector to produce BMP-2 Presented at the 29th Annual Meeting
of the Scoliosis Research Society, San Diego, Calif, September 23, 1999.
30 Sandhu HS, Kanim LEA, Toth JM, et al: Experimental spinal fusion with recombinant human bone morpho-genetic protein-2 without decortication
of osseous elements Spine 1997;22:
1171-1180.
31 Boden SD, Moskovitz PA, Morone
MA, Toribitake Y: Video-assisted lat-eral intertransverse process arthrode-sis: Validation of a new minimally invasive lumbar spinal fusion tech-nique in the rabbit and nonhuman
pri-mate (rhesus) models Spine 1996;21:
2689-2697.
32 Boden SD, Moskovitz PA, Martin G: Video-assisted lateral intertransverse process arthrodesis: Validation of a new minimally invasive lumbar spinal fusion technique in the non-human primate (rhesus) model Presented at the 12th Annual Meeting of the North American Spine Society, New York, October 25, 1997.
33 Hecht BP, Fischgrund JS, Herkowitz
HN, Penman L, Toth J: The use of rhBMP-2 to promote spinal fusion in a non-human primate anterior inter-body fusion model utilizing a freeze-dried allograft cylinder Presented at the 12th Annual Meeting of the North American Spine Society, New York, October 22-25, 1997.
34 Zdeblick TA, Ghanayem AJ, Rapoff
AJ, et al: Cervical interbody fusion cages: An animal model with and without bone morphogenetic protein.
Spine 1998;23:758-766.
35 Johnson EE, Urist MR, Finerman GA: Bone morphogenetic protein augmen-tation grafting of resistant femoral
nonunions: A preliminary report Clin Orthop 1988;230:257-265.
36 Johnson EE, Urist MR: One-stage lengthening of femoral nonunion aug-mented with human bone
morpho-genetic protein Clin Orthop 1998;347:
105-116.
37 Muschler GF, Perry CR, Cole JD, et al: Treatment of established tibial non-unions using human recombinant osteogenic protein-1 Presented at the 65th Annual Meeting of the American Academy of Orthopaedic Surgeons, New Orleans, March 20, 1998.