Use of recombinant human bone morphogenetic protein-2 to achieve posterolateral lumbar spine fusion in humans: a prospective, randomized clinical pilot trial: 2002 Volvo Award in clinical studies

Posterolateral Lumbar Fusion by Tissue Engineered Bone

Posterolumbar fusion, which involves placing a bone graft in the posterolateral portion of the spine, has been applied to patients with lumbar instability due to structural defects or regressive degeneration. However, harvesting cancellous bone from the ilium is associated with severe postoperative pain, and patients experience more pain at the harvest site than at the graft site, thus resulting in poor patient satisfaction. If a tissue engineering approach was used to produce autogenous bone ex vivo with culture techniques, spinal fusion could be performed without damaging normal tissues. In all patients, 10 to 20 mL of bone marrow fluid was collected from the ilium and cultured in MEM containing autologous serum or fetal bovine serum and an antibiotic. After two weeks in primary culture, the marrow mesenchymal cells were seeded onto porous beta-TCP block, and tissue engineered bone were fabricated as we reported previously. Decompressive laminectomy and posterolateral lumbar fusion with use of the tissue engineered bone thus obtained were then done. In all patients, the implanted artificial bone survived and bone regeneration was detected radiographically, and the clinical symptoms were improved. Short term follow-up has shown that the bone implants were effective in all of the patients. There were no adverse reactions related to implantation. The use of this tissue engineered bone makes it possible to perform osteogenetic treatment without harvesting autogenous bone, thus avoiding pain and pelvic deformity at the site of bone collection and reducing the burden on the patient.

In Vivo Evaluation of Porous Hydroxyapatite/Collagen Composite as a Carrier of OP-1 in a Rabbit PLF Model

Transplantation surgeries of autologous bone require a second surgery with inherent risks. To avoid these risks, we developed a multi porous implant of hydroxyapatite/collagen composite with desirable biophysical properties (flexibility, elasticity and compression resistance) for use with OP-1 as a graft implant. In this study, we tested the efficacy of this multi porous implant as OP-1 carrier using rabbit posterolateral lumbar fusion model (PLF). PLFs were performed in the following 4 groups of 8 New Zealand white rabbits each: autograft, HAp/Col alone, HAp/Col plus 0.3 mg OP-1, and HAp/Col plus 1.2 mg OP-1. At 5 weeks, fusion masses were analyzed by radiographic and biomechanical tests. Implants consisting of HAp/Col plus OP-1 were more effective than autologous bone in promoting spinal fusion. Low dose and high dose OP-1 were equally effective.

A prospective randomized study of posterolateral lumbar fusion using osteogenic protein-1 (OP-1) versus local autograft with ceramic bone substitute: emphasis of surgical exploration and histologic assessment

STUDY DESIGN

A prospective, randomized and controlled study.

OBJECTIVES

To evaluate the osteoinductive property of Osteogenic Protein-1 (OP-1 or BMP-7) and fusion rate in human instrumented posterolateral lumbar fusion through radiographic examination, surgical exploration, and histologic assessment.

SUMMARY OF BACKGROUND DATA

The use of osteoinductive agents is a current topic in spinal fusion. Numerous preclinical investigations have demonstrated efficacy of osteoinductive proteins in spinal fusion, but few human clinical studies have been reported.

METHODS

Nineteen patients with L3-L4 or L4-L5 degenerative spondylolisthesis underwent posterolateral lumbar fusion using pedicle screw instrumentation. The patients were randomized to receive either OP-1 Putty (3.5 mg OP-1/g of collagen matrix per side) alone (n = 9), or local autograft with HA-TCP granules (n = 10). Fusion status was evaluated using plain radiography and CT scan. Radiographic fusion criteria included less than 5 degrees of angular motion, less than 2 mm of translation, and evidence of bridging bone in the posterolateral lumbar area in which the graft materials were placed following decortication. After a minimum 1-year follow-up, the patients who showed radiographic evidence of fusion underwent instrumentation removal and surgical exploration of the fusion site. Biopsy specimens were taken from the fusion mass and evaluated histologically.

RESULTS

Radiographic fusion rate was 7 of 9 OP-1 patients and 9 of 10 control patients. Based on surgical exploration of these 16 patients, new bone formation was macroscopically observed in the posterolateral lumbar region in all cases; however, solid fusion was observed in 4 of 7OP-1 and 7 of 9 HA-TCP/autograft patients. Histologic assessment demonstrated viable bone in 6 of 7 OP-1 patients. All the control (HA-TCP/autograft) specimens contained viable bone and fibrous tissue surrounding ceramic granules, suggesting slow incorporation of the graft material.

CONCLUSIONS

In a human posterolateral lumbar spine trial, OP-1 reliably induced viable amounts of new bone formation, but the fusion success rate evaluated by surgical exploration was only 4 of 7.

Application of bone morphogenetic proteins in spinal fusion

We are now entering an exciting new era in spinal surgery where the inherent osteoinductive capacity of the body has been harnessed for bone formation for therapeutic purposes. Recombinant bone morphogenetic proteins have been extensively studied in both the pre-clinical and clinical arena for spinal fusion with considerable success. The challenges facing spine surgeons now is the development of site-specific carriers and optimal doses for these growth factors. This review highlights the recent advances in this regard.

LIM mineralization protein-1 potentiates bone morphogenetic protein responsiveness via a novel interaction with Smurf1 resulting in decreased ubiquitination of Smads

Development and repair of the skeletal system and other organs is highly dependent on precise regulation of bone morphogenetic proteins (BMPs), their receptors, and their intracellular signaling proteins known as Smads. The use of BMPs clinically to induce bone formation has been limited in part by the requirement of much higher doses of recombinant proteins in primates than were needed in cell culture or rodents. Therefore, control of cellular responsiveness to BMPs is now a critical area that is poorly understood. We determined that LMP-1, a LIM domain protein capable of inducing de novo bone formation, interacts with Smurf1 (Smad ubiquitin regulatory factor 1) and prevents ubiquitination of Smads. In the region of LMP responsible for bone formation, there is a motif that directly interacts with the Smurf1 WW2 domain and can effectively compete with Smad1 and Smad5 for binding. We have shown that small peptides containing this motif can mimic the ability to block Smurf1 from binding Smads. This novel interaction of LMP-1 with the WW2 domain of Smurf1 to block Smad binding results in increased cellular responsiveness to exogenous BMP and demonstrates a novel regulatory mechanism for the BMP signaling pathway.

The use of heparan sulfate to augment fracture repair in a rat fracture model

Fracture healing is a complex process regulated by numerous growth and adhesive factors expressed at specific stages during healing. The naturally occurring, cell surface-expressed sugar, heparan sulfate (HS), is known to bind to and potentiate the effects of many classes of growth factors, and as such, may be a potential candidate therapy for enhancing bone repair. This study investigated the local application of bone-derived HS in the repair of rat femoral fractures. After 2 weeks, there was a significant increase in the callus size of rats administered with 5 microg HS compared to the control and 50 microg HS groups, presumably due to increased trabecular bone volume rather than increased cartilage production. In addition, 5 microg HS increased the expression of ALP, Runx2, FGF-1, IGF-II, TGF-beta1, and VEGF. It is hypothesized that these increases resulted from changes in HS-mediated receptor/ligand interactions that increase local growth factor production to augment bone formation. The findings of this study demonstrate the anabolic potential of HS in bone repair by recruiting and enhancing the production of endogenous growth factors at the site of injury.

Adverse effects associated with high-dose recombinant human bone morphogenetic protein-2 use in anterior cervical spine fusion

STUDY DESIGN

A retrospective review of patients who underwent an anterior cervical fusion using recombinant human bone morphogenetic protein (rhBMP)-2 with an absorbable collagen sponge (INFUSE; Medtronic Sofamor Danek, Minneapolis, MN).

OBJECTIVE

To ascertain the complication rate after the use of high-dose INFUSE in anterior cervical fusions.

SUMMARY OF BACKGROUND DATA

The rhBMP-2 has been primarily investigated in lumbar spine fusions, where it has significantly enhanced the fusion rate and decreased the length of surgery, blood loss, and hospital stay.

METHODS

We present 151 patients who underwent either an anterior cervical discectomy and fusion (n = 138) or anterior cervical vertebrectomy and fusion (n = 13) augmented with high-dose INFUSE between July 2003 and March 2004. The rhBMP-2 (up to 2.1 mg/level) was used in the anterior cervical discectomy and fusions.

RESULTS

A total of 35 (23.2%) patients had complications after the use of high-dose INFUSE in the cervical spine. There were 15 patients diagnosed with a hematoma, including 11 on postoperative day 4 or 5, of whom 8 were surgically evacuated. Thirteen individuals had either a prolonged hospital stay (> 48 hours) or hospital readmission because of swallowing/breathing difficulties or dramatic swelling without hematoma.

CONCLUSIONS

A significant rate of complications resulted after the use of a high dose of INFUSE in anterior cervical fusions. We hypothesize that in the cervical area, the putative inflammatory effect that contributes to the effectiveness of INFUSE in inducing fusion may spread to adjacent critical structures and lead to increased postoperative morbidity. A thorough investigation is warranted to determine the optimal dose of rhBMP-2 that will promote cervical fusion and minimize complications.

Bone morphogenetic protein activities are enhanced by 3',5'-cyclic adenosine monophosphate through suppression of Smad6 expression in osteoprogenitor cells

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor (TGF)-beta superfamily, and some display potent osteogenic activity both in vivo and in vitro. The BMP signaling cascade involving BMP receptors at the cell membrane and intracellular messengers (Smads) has been elucidated, but the regulatory mechanisms of BMP signaling have not been clarified. We previously found that pentoxifyline (PeTx), a nonspecific inhibitor of phosphodiesterase (PDE), and rolipram, a PDE-4-specific inhibitor, enhance BMP-4-induced osteogenic differentiation of mesenchymal cells, probably through the elevation of intracellular cyclic adenosine monophosphate (cAMP) accumulation and modulation of BMP signaling pathways as enhanced BMP-4 action was reproduced by addition of dibutylyl-cAMP (dbcAMP). However, the precise mechanisms underlying the enhancing effects of those agents on BMP signaling were not completely revealed. As already reported, BMPs utilize a specific intracellular signaling cascade to target genes via R-Smads (Smad1,5,8), Co-Smad (Smad4) and I-Smads (Smad6,7). One possibility for cAMP-mediated effects on BMP signaling might be suppression of I-Smads expression since these proteins form a negative feedback loop in BMP signaling. To examine this possibility, changes in I-Smad (Smad6) expression on addition of dbcAMP or PeTx were examined in a bone-marrow-derived osteogenic cell line (ST2). Alkaline phosphatase activity in ST2 cells was consistently induced by BMP-4 treatment (300 ng/ml), and Smad6 mRNA expression was also induced by BMP-4 treatment. Although concurrent treatment of ST2 cells with BMP-4 and dbcAMP elicited further activation of alkaline phosphatase, addition of dbcAMP reduced BMP-4-induced Smad6 expression in a dose-dependent manner. Furthermore, detection of phosphorylated Smad1/5/8 on Western blotting analysis was prolonged, suggesting prolonged kinase activity of BMP receptors through suppressed expression of Smad6. Elevated intracellular cAMP might thus enhance BMP signaling by suppressing Smad6 induction and prolonging intracellular BMP signaling.

Nutritional modulators of bone remodeling during aging

Bone mass declines progressively with age in both men and women from the age of approximately 30 y. Increased longevity will inevitability be associated with an increase in the incidence of osteoporosis, its associated complications, and incurred health care costs. Current pharmacologic approaches focus on inhibiting bone resorption in those with osteoporosis but do little to improve bone mass. Increased understanding of the cellular events responsible for normal bone formation has led to multiple pathways that can be targeted to positively influence bone mass. Bone morphogenetic proteins (BMPs) have been shown to stimulate bone formation, and the BMP2 gene was recently linked to osteoporosis. BMP-2 therefore represents one potential molecular target to identify new agents to simulate bone formation. Research is accumulating on the positive effects of dietary sources that stimulate the BMP2 promoter and their effects on bone formation. Flavonoids and statins occur naturally in food products and have been shown to promote bone formation. It may be possible to influence peak bone mass by dietary means and to decrease the risk of osteoporosis in later life. To ease the future burden of osteoporosis, focusing on prevention will be key, and this could include dietary interventions to stimulate bone formation.

Safety of transforaminal lumbar interbody fusion and intervertebral recombinant human bone morphogenetic protein-2

OBJECT

Recombinant human bone morphogenetic protein-2 (rhBMP-2) is being increasingly used for spinal fusion. There are few data regarding its clinical safety, effectiveness, and clinical outcome when applied on an absorbable collagen sponge (ACS) in conjunction with allograft for transforaminal lumbar interbody fusion (TLIF).

METHODS

Seventy-four consecutive patients undergoing TLIF for degenerative disc disease were divided into five groups depending on whether the patient underwent a minimally invasive or open approach, as well as the number of spinal levels surgically treated. Surgery-related data, fusion results, complications, and clinical outcome were evaluated. The mean follow-up duration was 20.6 months (range 14-28 months). The radiographic fusion rate was 100% at 12 and 24 months after the surgery. No bone overgrowth or other complications related to BMP use were demonstrated.

CONCLUSIONS

Analysis of the results demonstrated that TLIF combined with a BMP-2-soaked ACS is a feasible, effective, and safe method to promote lumbar fusion. There were no significant intergroup differences in clinical outcome between patients who underwent open compared with minimally invasive procedures. Patient satisfaction rates, however, were higher in the minimally invasive procedure group. The efficacy of BMP-2 was not dependent on which approach was used or the number of spinal levels that were treated.

Bone morphogenetic protein receptors and bone morphogenetic protein signaling are controlled by tumor necrosis factor-α in human bone cells

Bone morphogenetic proteins (BMP) stimulate osteoblast differentiation by signal transduction via three BMP receptors (BMPR-IA, -IB and -II), whereas the inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha) has been shown to suppress osteoblast differentiation. Although the mechanisms which regulate the BMPR are not yet known, it is possible that they may be negatively controlled by TNF-alpha, thereby inhibiting BMP-induced osteoblast differentiation. To test this hypothesis, we have examined the effects of TNF-alpha on BMPR-IA, -IB and -II expression and the functional consequences of this cytokine on BMPR-mediated functions in human bone cells. The results showed that although TNF-alpha down-regulated BMPR-IA and -II transcripts, it increased the level of BMPR-IB mRNA via a MAPK-dependent pathway. In marked contrast, however, TNF-alpha nevertheless caused marked down-regulation of the expression of the BMPR-IB surface antigen specifically. Moreover, the cytokine-induced decrease in BMPR-IB expression was found to be associated with the concurrent presence of a 'soluble' form of this antigen in supernatants of TNF-alpha-treated cultures. Furthermore, the TNF-alpha-induced loss of BMPR-IB was found to ablate BMP-2-stimulated bone cell functions, including phosphorylation of Smad1/5/8, alkaline phosphatase activity and osteocalcin expression. In conclusion, our study has provided evidence, for the first time, that BMPR can be differentially modulated by TNF-alpha at both the post-transcriptional and post-translational levels, with the TNF-alpha-induced shedding of the BMPR-IB antigen associated with a significantly diminished response to BMP-2 in vitro.

Nell-1 induced bone formation within the distracted intermaxillary suture

Maxillary bone deficiencies, such as cleft palate and underdeveloped maxilla that require bone graft or regeneration after orthopedic or surgical expansion, pose a significant biomedical burden. Nell-1 is a secreted molecule that possesses chordin-like domains and induces cranial suture bone growth and osteoblast differentiation. To accelerate bone formation in acutely distracted palatal sutures, rat organ cultures were stimulated with Nell-1 or BMP-7 for 8 days in vitro. We hypothesized that Nell-1 stimulation to the distracted palatal suture would accelerate bone formation. Distracted palates of 4-week-old male rats were maintained in an organ culture system, and tissue was either unstimulated or stimulated with Nell-1 or BMP-7 for 8 days. MicroCT was conducted to quantitate bone formation, while alcian blue staining was conducted for cartilage localization. Immunohistochemistry of Sox9 for chondrocyte proliferation, type X collagen for hypertrophic cartilage in endochondral bone formation, and bone sialoprotein for bone formation was conducted to characterize the cellular mechanism of newly developed tissues. Distracted palates cultured in the presence of Nell-1 or BMP-7 produced statistically significantly (P < 0.05) more bone and cartilage within the intermaxillary suture, relative to unstimulated control samples. While both BMP-7 and Nell-1 induced similar bone formation in the distracted suture, BMP-7 induced both chondrocyte proliferation and differentiation, while Nell-1 accelerated chondrocyte hypertrophy and endochondral bone formation. While both Nell-1 and BMP-7 are effective in forming bone in the distracted palatal suture, they are suggested to have distinctively different mechanisms. The ability of Nell-1 to accelerate bone formation within the palate suture demonstrates the versatility of Nell-1 within the craniofacial complex as well as an exciting advance in palate suture defect healing.

Treatment of glenoid loosening and bone loss due to osteolysis with glenoid bone grafting

Twenty-four patients underwent conversion of a total shoulder replacement to a humeral head replacement with glenoid bone grafting for glenoid loosening due to osteolysis. Of the 24 patients, 18 (75%) had satisfactory pain relief at a mean follow-up of 33.4 months (range, 24-63 months). Four had good pain relief with conversion back to total shoulder replacement at a mean of 11 months (range, 9-15 months) after the index procedure, thus bringing the rate of overall satisfactory pain relief to 92%. Two patients continued to report significant pain and were not satisfied with the procedure. Significant functional motion improvements were not seen (P > .05). Graft subsidence was seen in 10 of 20 cases (50%). Bone grafting of glenoid defects in revision arthroplasty provides satisfactory improvement in terms of pain relief and, by improving bone stock, allows for placement of a glenoid component at a later date if there is persistent pain. However, high rates of graft subsidence are concerning.

Growth factor delivery for bone tissue repair: an update

Growth factors (GFs) are endogenous proteins capable of acting on cell-surface receptors and directing cellular activities involved in the regeneration of new bone tissue. The specific actions and long-term effects of GFs on bone-forming cells have resulted in exploration of their potential for clinical bone repair. The concerted efforts have led to the recent approval of two GFs, bone morphogenetic protein-2 and osteogenic protein-1, for clinical bone repair, and human parathryroid hormone (1-34) for augmentation of systemic bone mass. This review provides a selective summary of recent (2001-2004) attempts for GF delivery in bone tissue regeneration. First, a summary of non-human primate studies involving local regeneration and repair is provided, with special emphasis on the range of biomaterials used for GF delivery. Next, efforts to administer GFs for systemic augmentation of bone tissue are summarised. Finally, an alternative means of GF delivery, namely the delivery of genes coding for osteogenic proteins, rather than the delivery of the proteins, is summarised from rodent models. To conclude, future avenues of research considered promising to enhance the clinical application of GFs are discussed.

De novo osteogenesis from human ligamentum flavum by adenovirus-mediated bone morphogenetic protein-2 gene transfer

STUDY DESIGN

In vitro and in vivo experiment using degenerated human ligamentum flavum (LF) and Type 5 adenovirus construct with bone morphogenetic protein-2 (BMP-2) cDNA.

OBJECTIVES

To demonstrate in vitro and in vivo osteogenic effect of BMP-2 gene transfer to human LF and to propose genetically modified LF as a substitute for autogenous bone graft in spinal fusion.

SUMMARY OF BACKGROUND DATA

Spinal fusion is still considered to be an important option for treating various spinal disorders. To induce solid spinal fusion, osteoinductive and/or osteoconductive agents have been widely adopted. Autogenous LF, however, has never been seriously considered as a carrier for ex vivo osteoinductive gene therapy for spinal fusion.

METHODS

In vitro experiment: Degenerated human LF was harvested and cultured. Type 5 adenovirus lacZ (Ad/lacZ) and BMP-2 construct (Ad/BMP-2) were produced. LF cell cultures were then exposed to Ad/BMP-2. Expressions of osteocalcin and BMP-2 mRNA were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). Western blot analysis was performed to detect osteocalcin protein. Alkaline phosphatase and von Kossa stains were used to detect osteogenic markers and bone nodule formation, respectively. In vivo experiment: Human LF tissues treated with Ad/lacZ, Ad/BMP-2, and saline were implanted into the subcutaneous tissue of nude mice. After 4 weeks, nude mice were radiographed and killed. Implanted LF tissues were harvested and histologically stained.

RESULTS

LF cell cultures with Ad/BMP-2 revealed strong expression of BMP-2 and osteocalcin mRNA in RT-PCR and osteocalcin protein in western blot analysis. LF cell culture with saline showed baseline expression of BMP-2, osteocalcin mRNA, and osteocalcin protein, respectively. Furthermore, LF cell culture with Ad/BMP-2 demonstrated the expression of alkaline phosphatase and bone nodule formation in the aforementioned histochemical stain. LF tissues with Ad/BMP-2 revealed de novo osteogenesis in nude mice, whereas LF with Ad/lacZ or saline showed only remaining LF tissue without sign of bone formation.

CONCLUSION

Human LF cells transduced with Ad/BMP-2 exhibited the expression of osteogenic phenotype and bone nodule formation. Additionally, genetically modified human LF with BMP-2 cDNA clearly demonstrated de novo osteogenesis, which supports the concept that biologically modified LF can be a substitute for autogenous bone graft in spinal fusion surgery.

Effect of recombinant human bone morphogenetic protein-2 in an experimental model of spinal fusion in a radiated area

STUDY DESIGN

An animal model of posterolateral intertransverse process spine fusion was used.

OBJECTIVES

To investigate whether recombinant human bone morphogenetic protein-2 (rhBMP-2) can overcome the adverse effects of radiation treatment (RT) on spine fusion.

SUMMARY OF BACKGROUND DATA

Spinal metastases are common. Some of these patients are candidates for spinal cord decompression and vertebral reconstruction; however, radiation has significant adverse effects on bone healing.

METHODS

A posterolateral fusion model was used with rhBMP-2 or iliac crest bone graft (ICBG). Eighty one-year-old rabbits were divided into eight groups: 1) RT 14 days before surgery, rhBMP-2; 2) RT 14 days before surgery, ICBG; 3) RT 2 days after surgery, rhBMP-2; 4) RT 2 days after surgery, ICBG; 5) RT 14 days after surgery, rhBMP-2; 6) RT 14 days after surgery, ICBG; 7) no RT, rhBMP-2; 8) no RT, ICBG. Animals were killed approximately 35 days after surgery. Manual palpation was the definitive test of fusion. Biomechanical and histologic assessments were also performed.

RESULTS

All rhBMP-2 groups had significantly greater fusion rates versus respective ICBG control groups: 1 (86%) versus 2 (0%) (P = 0.005), 3 (100%) versus 4 (0%) (P < 0.0001), 5 (100%) versus 6 (0%) (P < 0.0001), and 7 (100%) versus 8 (60%) (P = 0.003). Stiffness and ultimate strength did not differ significantly between the experimental and control groups. Histologic assessment confirmed new bone formation in the fusion masses from rhBMP-2 groups.

CONCLUSIONS

Use of rhBMP-2 produced a significantly greater rate of fusion compared with ICBG in a previously radiated area in an animal model, without the morbidity of ICBG harvesting and without the risk of inadvertently using autograft contaminated by micrometastases.

Stimulation of gene expression and loss of anular architecture caused by experimental disc degeneration--an in vivo animal study

STUDY DESIGN

An external compression model was used to evaluate gene and protein expression in intervertebral discs with moderate disc degeneration.

OBJECTIVE

To determine messenger ribonucleic acid and protein expression levels of relevant disc components.

SUMMARY OF BACKGROUND DATA

An animal model of mechanically induced disc degeneration was developed and characterized histologically. However, little is known at the molecular level in moderate disc degeneration.

METHODS

There were 8 New Zealand white rabbits subjected to monosegmental posterior compression to induce moderate disc degeneration. Twelve animals served as controls or sham controls. Discs were analyzed using immunohistochemistry for collagen type 1 (COL1), COL2, aggrecan, and bone morphogenetic protein-2/4 (BMP-2/4). For gene analysis, conventional and quantitative polymerase chain reactions were used for COL1A2, COL2A1, aggrecan, BMP-2, biglycan, decorin, osteonectin, fibromodulin, fibronectin, matrix metalloproteinase-13 (MMP-13), and tissue inhibitor of MMP-1. Gene expression for nontreated, sham-treated, and compressed discs was quantified in relation to the housekeeping gene glyceraldehyde-3-phosphate dehydrogenase.

RESULTS

Immunohistochemistry of compressed discs showed a loss of anular architecture, and a significant reduction of BMP-2/4 and COL2 positive cells. Gene expression analysis showed a significant up-regulation of COL1A2, osteonectin, decorin, fibronectin, tissue inhibitor of MMP-1, BMP-2, and MMP-13 in compressed discs.

CONCLUSIONS

Experimental moderate disc degeneration is characterized by a loss of BMP-2/4 and COL2 positive cells, although gene expression of disc constituents, catabolic enzymes, and growth factors is stimulated to reestablish disc integrity.

Coralline hydroxyapatite and laminectomy-derived bone as adjuvant graft material for lumbar posterolateral fusion

OBJECT

The purpose of this study was to evaluate the effectiveness of coralline hydroxyapatite (CHA) and laminectomy-derived bone as an adjuvant graft material when combined with autogenous iliac bone graft (AIBG) in posterolateral fusion (PLF).

METHODS

This prospective, case-control study involved 58 patients who underwent lumbar instrumentation-augmented PLF for degenerative spinal stenosis-induced segmental instability between July 2000 and June 2001. The patients were divided into three groups. Laminectomy bone and AIBG were placed in the right intertransverse process space in Group 1 (20 patients), CHA and AIBG were placed in Group 2 (19 patients), and laminectomy bone and CHA were placed in Group 3 (19 patients). Pure autogenous iliac cancellous bone graft was placed in the left intertransverse process space in all three groups of patients. Successful fusion was determined by two spine surgeons after examining the plain, anteroposterior, bilateral oblique, and lateral flexion-extension radiographs. If the examiners did not agree on fusion status, fine-cut computerized tomography scans of the fusion mass were used to make the final decision. The chi-square test was used to compare the fusion rate at different time intervals among the three groups.

CONCLUSIONS

Pure AIBG placed in left intertransverse process space was associated with the best fusion rate. After 6 months, CHA produced a comparable result to laminectomy-derived bone when combined with AIBG. When laminectomy bone was mixed with CHA, the combination failed to yield a satisfactory fusion rate (57.9%) even 1 year after surgery if no AIBG was added.

Discovery and development of BMPs

In the early 1970s, the isolation and identification of bone morphogenetic proteins (BMPs) was a major breakthrough for the understanding of the distinct biological events occurring during bone formation. Not surprising, since their discovery, BMPs have been perhaps one of the most intensively studied group of factors in various physiological processes. The prompt development of recombinant BMPs and various delivery methods made BMPs currently available for clinical use. Research and clinical studies on BMPs are ongoing, aiming to refine further our understanding of their activities in vivo and to optimise and expand their clinical use in humans.

Carrier materials for spinal fusion

BACKGROUND CONTEXT

The rise in spinal fusion procedures has led to an increase in the available number and variety of bone graft substitutes. As our understanding of the biologic processes that influence bony fusion has improved, appreciation for the role of the carrier material involved in bone grafts has also increased.

PURPOSE

The abundance of products available leaves a surgeon with many choices. Knowledge of the current advances will allow for more critical review of the literature and improved decision making when choosing bone graft materials.

STUDY DESIGN/SETTING

Review of the English-language literature.

METHODS

A critical review of basic science, animal and human studies that investigate the types and role of carrier materials used in spine surgery.

RESULTS

The myriad of carrier material available to the spine surgeon is related to the many options in bone graft material. Allograft is an important osteoconductive agent but has its disadvantages especially in regard to disease transmission and immunogenicity. Collagen in various forms is an effective carrier for bone morphogenic protein and autogenous stem cells and can be easily combined with other bone graft materials. Synthetic options include hydroxyapatite and calcium phosphate ceramic materials with different formulations; all are osteoconductive only but can be combined with osteoinductive and/or osteogenic components. Bioabsorbable carriers are effective for use with bone morphogenic protein and can also be used in multiple forms and settings.

CONCLUSIONS

Many bone graft carriers exist, and multiple studies have shown their efficacy. It appears that no one carrier is ideal but each situation might influence the choice of one carrier over another.

Cell technologies for spinal fusion

For a successful spinal fusion to occur, several vital elements are necessary. They consist of the presence of the bone-forming cell (osteoblast) or its precursor, the appropriate biological signals directing bone synthesis, and a biocompatible scaffold on which the process can occur. The most critical of these components is the osteoblast or its precursor, the mesenchymal stem cell (MSC), both of which possess the ability to form bone. As a result, many current techniques attempt to maximize the benefits derived from harvesting the ready source of MSCs from bone marrow, while minimizing the associated complications. These cellular technologies seek to improve on the harvest and concentration of the MSCs or enhance their delivery and action. This review focuses on the terminology, historical underpinnings, and current research rationale and techniques and discusses the possible future of these technologies.

Vascular endothelial growth factor gene-activated matrix (VEGF165-GAM) enhances osteogenesis and angiogenesis in large segmental bone defects

Healing of fractures is dependent on vascularization of bone, which is in turn promoted by VEGF. It was shown that 0.1 and 1 mg of pVEGF165-GAM led to a significant increase in vascularization and bone regeneration in defects that would otherwise have led to atrophic nonunions.

INTRODUCTION

One reason for lack of bone healing in nonunions is the absence of vascularization. In skeletogenesis, which is tightly linked to angiogenesis, vascular endothelial growth factor (VEGF) promotes the vascularization of the growth plate and transformation of cartilage to bone. We postulate that a gene-activated matrix (GAM), created with a plasmid coding for human VEGF165, coated on a collagen sponge could efficiently accelerate bone healing in large segmental defects.

MATERIALS AND METHODS

Sixty New Zealand white rabbits received a 15-mm critical size defect on one radius, which was filled with either 0.1 or 1 mg plasmid-DNA as GAM. Radiographs were obtained every 3 weeks. After 6 or 12 weeks, animals were killed. New bone was measured by microCT scans. Vascularity was measured using anti-CD31 staining of endothelial cells in 18 regions of interest per implant.

RESULTS

Scaffold and control plasmid showed no defect healing, whereas most of the animals in the VEGF groups showed partial or total bone regeneration. Significantly more bone was found in the VEGF groups, with no significant differences between the 0.1- and 1-mg groups. Immunohistochemical staining of endothelial cells revealed that the VEGF groups showed two to three times the number of vessels and a significantly larger endothelial area after 6 weeks. Twelve weeks after surgery, the amount of vascularization decreased, whereas more new bone was detectable.

CONCLUSIONS

The rabbit critical size defect was appropriate in size to produce atrophic nonunions. We showed that angiogenesis and osteogenesis can be promoted by a VEGF165-GAM that is an appropriate tool to induce bone healing in atrophic nonunions.

Application of recombinant BMP-7 on persistent upper and lower limb non-unions

The purpose of this study was to evaluate the efficacy and safety of recombinant bone morphogenetic protein 7 (rhBMP-7 or OP-1) as a bone-stimulating agent in the treatment of persistent fracture non-unions. Twenty-five consecutive patients [19 males, mean age 39.4 years (range: 18-79)] with 26 fracture non-unions were treated with rhBMP-7. There were 10 tibial non-unions, eight femoral, three humeral, three ulnar, one patellar, and one clavicular non-union. The mean follow-up was 15.3 months. The mean number of operations performed prior to rhBMP-7 application was 3.2, with autologous bone graft and bone marrow injection being used in 10 cases (38.5%). Both clinical and radiological union occurred in 24 (92.3%) cases, within a mean time of 4.2 months and 5.6 months, respectively. Of the remaining two cases, one patient ultimately underwent a below knee amputation, secondary to recurrence of deep sepsis. The other patient with recalcitrant ulnar non-union although the radiological union was incomplete, declined further intervention, as he was asymptomatic. No complications or adverse effects from the use of rhBMP-7 were encountered. This study supports the view that the application of rhBMP-7 as a bone-stimulating agent is safe and a power adjunct to be considered in the surgeon's armamentarium for the treatment of these challenging clinical conditions.

Clinical applications of BMP-7: the UK perspective

Treatment of fracture non-union is a challenging situation in skeletal surgery. Since the discovery of bone morphogenetic proteins (BMPs) by Urist preclinical research as well as clinical trials has shown the efficacy of these molecules in bone healing enhancement. Recombinant bone morphogenetic protein became available in UK during August 2001. We evaluated the type of indications and the efficacy of BMP-7 in a variety of clinical conditions including persistent fracture non-unions, augmentation of periprosthetic fracture treatment and osteotomies, enhancement of fracture healing following acetalular reconstruction, distraction osteogenesis, free fibular graft and arthrodesis of joints. Out of 653 cases, the overall success rate was 82% (535 cases). No local or systemic adverse effects were encountered. The role of BMP's as a bone stimulating agent is safe, well established and could be considered as a power adjunct in the surgeon's armamentarium for the treatment of these challenging clinical conditions.

Bone morphogenetic proteins for spinal fusion

BACKGROUND CONTEXT

In 1965, Marshall Urist discovered that the extracellular matrix of bone contains the ability to induce new bone formation. This substance was later named bone morphogenetic protein (BMP). Since that time, BMPs have been extensively studied. Molecular clones have since been characterized and expressed as complementary DNAs (cDNAs). BMPs have recently been used in a multitude of mammalian clinical studies, including many recent human studies, for the purpose of evaluating their function in bone healing and spinal arthrodesis. BMPs are currently the most effective substitute available for bone graft as a means to eliminate the morbidity of iliac crest bone graft harvest and increase the rate of successful spinal arthrodesis.

PURPOSE

The purpose of this article is to review the history and recent advancements in the use of BMPs in spinal arthrodesis models, as well as discuss the possible future use of BMPs in this clinical setting.

STUDY DESIGN/SETTING

The setting of this review article is centered on classic and recent literature of BMPs with emphasis on anterior as well as posterolateral spinal arthrodesis.

METHODS

The classic and recent primary literature about BMPS and their clinical use in human and nonhuman mammals for spinal fusion was reviewed. Special emphasis is placed on animal and human studies of both recombinant human bone morphogenetic protein-2 (rhBMP-2) and recombinant human osteogenic protein-1 (rhOP-1, rhBMP-7).

RESULTS

BMPs are able to promote solid fusion in the spine in both the anterior and the posterolateral environments in animal studies and early human trials. Human trials to date have also shown an acceptable safety profile with the clinical use of these proteins.

CONCLUSIONS

Animal studies and early human trials of BMPs support the ability of these growth factors to enhance or replace autograft bone for spinal arthrodesis. Studies have shown this promotion of fusion in both the anterior interbody and the posterolateral environments. Future use of these factors is likely to continue to expand in clinical as well as research arenas.

Surgery for degenerative lumbar spondylosis

BACKGROUND

Surgical investigations and interventions account for large health care utilisation and costs, but the scientific evidence for most procedures is still limited.

OBJECTIVES

Degenerative conditions affecting the lumbar spine are variously described as lumbar spondylosis or degenerative disc disease (which we regarded as one entity) and may be associated with back pain and associated leg symptoms, instability, spinal stenosis and/or degenerative spondylolisthesis. The objective of this review was to assess current scientific evidence on the effectiveness of surgical interventions for degenerative lumbar spondylosis.

SEARCH STRATEGY

We searched CENTRAL, MEDLINE, PubMed, Spine and ISSLS abstracts, with citation tracking from the retrieved articles. We also corresponded with experts. All data found up to 31 March 2005 are included.

SELECTION CRITERIA

Randomised (RCTs) or quasi-randomised trials of surgical treatment of lumbar spondylosis.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial quality and extracted data from published papers. Additional information was sought from the authors if necessary.

MAIN RESULTS

Thirty-one published RCTs of all forms of surgical treatment for degenerative lumbar spondylosis were identified. The trials varied in quality: only the more recent trials used appropriate methods of randomization, blinding and independent assessment of outcome. Most of the earlier published results were of technical surgical outcomes with some crude ratings of clinical outcome. More of the recent trials also reported patient-centered outcomes of pain or disability, but there is still very little information on occupational outcomes. There was a particular lack of long term outcomes beyond two to three years. Seven heterogeneous trials on spondylolisthesis, spinal stenosis and nerve compression permitted limited conclusions. Two new trials on the effectiveness of fusion showed conflicting results. One showed that fusion gave better clinical outcomes than conventional physiotherapy, while the other showed that fusion was no better than a modern exercise and rehabilitation programme. Eight trials showed that instrumented fusion produced a higher fusion rate (though that needs to be qualified by the difficulty of assessing fusion in the presence of metal-work), but any improvement in clinical outcomes is probably marginal, while there is other evidence that it may be associated with higher complication rates. Three trials with conflicting results did not permit any conclusions about the relative effectiveness of anterior, posterior or circumferential fusion. Preliminary results of two small trials of intra-discal electrotherapy showed conflicting results. Preliminary data from three trials of disc arthroplasty did not permit any firm conclusions.

AUTHORS' CONCLUSIONS

Limited evidence is now available to support some aspects of surgical practice. Surgeons should be encouraged to perform further RCTs in this field.

Mechanism of osteogenic induction by FK506 via BMP/Smad pathways

FK506 is an immunosuppressant that exerts effects by binding to FK506-binding protein 12 (FKBP12). Recently, FK506 has also been reported to promote osteogenic differentiation when administered locally or in vitro in combination with bone morphogenetic proteins (BMPs), although the underlying mechanism remains unclarified. The present study initially showed that FK506 alone at a higher concentration (1muM) induced osteogenic differentiation of mesenchymal cell lines, which was suppressed by adenoviral introduction of Smad6. FK506 rapidly activates the BMP-dependent Smads in the absence of BMPs, and the activation was blocked by Smad6. Overexpression of FKBP12, which was reported to block the ligand-independent activation of BMP type I receptor A (BMPRIA), suppressed Smad signaling induced by FK506, but not that induced by BMP2. BMPRIA and FKBP12 bound to each other, and this binding was suppressed by FK506. These data suggest that FK506 promotes osteogenic differentiation by activating BMP receptors through interacting with FKBP12.

Augmentation of bone morphogenetic protein-induced bone mass by local delivery of a prostaglandin E EP4 receptor agonist

Recombinant human bone morphogenetic protein (rhBMP) is viewed as a therapeutic cytokine because of its ability to induce bone. However, the high doses of rhBMP required for bone induction in humans remain a major hurdle for the therapeutic application of this protein. The development of a methodology that would effectively overcome the weak responsiveness to human BMP is highly desired. In the present study, we investigate the ability of a prostaglandin E EP4 receptor selective agonist (EP4A) to augment the bone-inducing ability of BMP in a biodegradable delivery system. A block copolymer composed of poly-D,L-lactic acid with random insertion of p-dioxanone and polyethylene glycol (PLA-DX-PEG, polymer) was used as the delivery system. Polymer discs containing rhBMP-2 and EP4A were implanted into the left dorsal muscle pouch of mice to examine the dose-dependent effects of EP4A. Fifty mice were divided into 5 groups based on the contents of rhBMP and EP4 in the polymer (group 1; BMP 5 microg EP4A 0 microg, group 2; BMP 5 microg EP4 3 microg, group 3; BMP 5 microg EP4 30 microg, group 4; BMP 5 microg EP4 300 microg, group 5; BMP 0 microg EP4 30 microg, n=10 each). All implants were harvested, examined radiologically, and processed for histological analysis 3 weeks after surgery. On dual-energy X-ray absorptiometry (DXA) analysis, the bone mineral content (BMC) of the ossicles was 6.52+/-0.80 (mg), 9.36+/-1.89, 14.21+/-1.27, and 18.75+/-2.31 in groups 1, 2, 3, and 4 respectively. In terms of BMC, the values of groups 3 and 4 were significantly higher than those of group 1. The mean BMC value of group 4 was approximately 3 times higher than that of group 1. No significant difference in body weight was noted among the groups during the experimental period. In summary, the presence of a prostaglandin E EP4 receptor selective agonist in the carrier polymer enhanced the bone-inducing capacity of rhBMP-2 with no apparent systemic adverse effects.

Preparation and biological characteristics of recombinant human bone morphogenetic protein-2-loaded dextran-co-gelatin hydrogel microspheres, in vitro and in vivo studies

Hydrogels are based on hydrophilic polymers which are cross-linked to prevent dissolution in water. Because hydrogels can contain large amounts of water, they are interesting devices for the delivery of protein drugs. In this contribution, biodegradable dextran-co-gelatin hydrogel microspheres (DG-MPs) are described which are based on physical interactions and are particularly suitable for the controlled delivery of pharmaceutically active proteins. The unique feature of this preparation system is that the hydrogel microsphere formation takes place in an all-aqueous solution, by which the use of organic solvents is avoided. We investigated the preparation and biological activities of recombinant human bone morphogenetic protein-2 (rhBMP2)-loaded dextran-co-gelatin hydrogel microspheres (rhBMP2-DG-MPs), which aimed to keep rhBMP2's biological activity and to achieve a long-term sustained release of rhBMP2. The microspheres' average diameter was about 20-40 microm and rhBMP2 release in vitro could be maintained for >10 days. Cytology studies showed that using rhBMP2-DG-MPs could promote the proliferation and osteoblastic differentiation of periodontal ligament cells better than using rhBMP2 aqueous solution. By a freeze-drying method, rhBMP2-DG-MPs could be adhered in chitosan membranes for guided tissue regeneration use, namely functionalized membranes. To evaluate bone regeneration induced by rhBMP2-DG-MPs, an animal experiment with canine class III furcation defects was adopted and the results indicated that using rhBMP2-DG-MPs incorporating scaffolds and functionalized membranes could gain more periodontal tissue regeneration than using scaffolds and general membranes soaked with concentrated rhBMP2 aqueous solution. Therefore, those studies demonstrate the potential of DG-MPs in the sustained delivery of low dosages of rhBMP2 to periodontal defects.

Bone morphogenic proteins: applications in spinal surgery

The prospect of predictable and reliable oseteogenesis without the need for secondary bone grafting to treat a wide spectrum of spinal disorders is tremendously appealing. Recombinant human bone morphogenic proteins (rhBMP) have been the subject of extensive basic science, animal, and clinical research as a potential therapeutic modality to promote bony fusion. Animal studies and prospective, randomized clinical trials have demonstrated the efficacy of rhBMPs as an adjunct or substitute to autogenous bone graft in the specific treatment of certain spinal conditions. The future role of rhBMPs in spinal surgery applications remains to be determined and will be dependent upon future investigations evaluating 1) the efficacy in a variety of spinal conditions and environments, 2) the optimal dose and delivery system, 3) the long-term safety profile (immunogenicity, antibody formation), and 4) the cost effectiveness of these therapeutic growth factors.

Pregnancy-associated plasma protein-a is involved in matrix mineralization of human adult mesenchymal stem cells and angiogenesis in the chick chorioallontoic membrane

Pregnancy-associated plasma protein A (PAPP-A) is an IGF binding protein 4 protease that can function to increase local IGF-I bioavailability. Aside from its assumed role during pregnancy, in vitro and in vivo studies have indicated roles for PAPP-A in IGF-I-mediated wound healing, vascular repair, and bone formation. Because bone morphogenetic protein 2 (BMP-2) is known to up-regulate Igf-I gene expression, we hypothesized that PAPP-A may be involved in BMP-2 mechanisms in bone formation. To test this hypothesis, we quantified gene expression of Papp-A in response to BMP-2 treatment and runt-related transcription factor 2, Osterix, and Igf-I in response to PAPP-A protein treatment in human adult mesenchymal stem cells. Our results demonstrate that BMP-2 directly up-regulated Papp-A gene and protein expression. Purified PAPP-A protein directly up-regulated runt-related transcription factor 2 and Igf-I gene expression but not Osterix. When added in combination with recombinant human BMP-2, PAPP-A increased matrix mineralization in the absence of dexamethasone. PAPP-A further demonstrated an angiogenic effect in the chick chorioallontoic membrane, which implicates a critical developmental role and possible therapeutic potential. Our findings suggest that PAPP-A functions in the formation of mineralized tissues through direct up-regulation of key genes. Furthermore, PAPP-A is involved in the formation of new blood vessels, which is essential for proper bone regeneration.

Use of bone morphogenetic protein-2 for adult spinal deformity

STUDY DESIGN

Prospective, single-center, nonblinded clinical and radiographic analysis of consecutive adult deformity patients treated with recombinant human bone morphogenetic protein-2 (rhBMP-2) without iliac or rib bone graft supplementation.

OBJECTIVES

To determine the ability of rhBMP-2 to achieve both anterior and posterior spinal fusion in patients undergoing multilevel fusions for adult spinal deformity.

SUMMARY OF BACKGROUND DATA

The literature concerning one-level anterior fusions, and potentially one-level posterior fusions, using rhBMP-2 has demonstrated clinical efficacy. No published data exist on the use of rhBMP-2 in multilevel spine fusions.

METHODS

Prospective analysis of patients treated with rhBMP-2 in multilevel anterior and posterior fusions with a minimum 1-year follow-up. There were a total of 95 patient samples (70 total patients; 25 patients had rhBMP-2 used circumferentially): 46 anterior fusions (Group 1), 41 posterior fusions (Group 2), and 8 patients were "compassionate use" fusions (Group 3). In the anterior fusion group (n = 46), mean rhBMP-2/level was 10.8 mg in titanium mesh cages without any bone graft or other substance. The posterior fusion group had only local bone graft, no harvested rib or iliac bone graft (n = 41). The mean rhBMP-2/level was 13.7 mg. The "compassionate use" group (n = 8 patients) consisted of patients who had prior surgeries, prior iliac harvesting, and substantial comorbidities and therefore a higher concentration and different carrier was used. No local bone graft, no harvested bone was used. The mean rhBMP-2/level was 28.6 mg. The median dose was 40 mg for Group 3.

RESULTS

For the anterior fusion group (n = 46), operative levels were deemed fused in 89 of the 93 (96%) levels. For the posterior fusion group (n = 41), a solid fusion was assessed in 110 of the 118 (93%) operative levels. For the "compassionate-use" patients, the overall fusion rate was 100% (52 of 52 operative levels).

CONCLUSIONS

With the use of rhBMP-2, a high rate of apparent fusion was observed for anterior (96%) and posterior (93%) fusions in adult spinal deformity patients. Use of rhBMP-2 results in a promising early fusion rate without the graft harvest site morbidity.

Surgical treatment for the painful motion segment: matching technology with the indications: posterior lumbar fusion

STUDY DESIGN

A convenience literature-based review of the different techniques of posterior lumbar fusion.

OBJECTIVE

To describe the history, specific techniques, and outcomes of different methods of posterior lumbar fusion. The specific methods that were described include 1) uninstrumented posterior, posterolateral, and facet fusion, and 2) instrumented fusion using pedicle screws or facet screws.

SUMMARY OF BACKGROUND DATA

There are various posterior fusion techniques available for the treatment of degenerative lumbar spine conditions. Each individual technique has specific technical demands, indications, advantages, and disadvantages which should be taken into consideration when performing these procedures.

METHODS

The published scientific literature on the different methods of posterior lumbar fusion was reviewed. The history, indications, advantages, disadvantages, and clinical and radiographic outcomes were described based on the literature search.

RESULTS/CONCLUSIONS

Posterior fusion techniques have been and will continue to be among the most commonly performed procedures in lumbar spine surgery. The different methods of fusion are well defined, as are the possible complications and outcomes. They are effective techniques when performed on appropriately selected patients by a surgeon knowledgeable in the techniques and indications. Further studies are needed regarding promising but relatively unproven developments such as minimally invasive surgery and the use of osteoinductive agents.

Surgical treatment of the painful motion segment: matching technology with indications

STUDY DESIGN

Literature review of current bone graft technology and bone graft substitutes used in spinal fusion applications.

OBJECTIVE

We reviewed current bone graft technologies and identified the range of bioactive properties that each possesses, such as osteoconductivity, osteoinductivity, and structural, load-bearing capabilities that can be used to either augment or replace autogenous bone graft in spinal fusions.

SUMMARY OF BACKGROUND DATA

Bioactive materials are used in spinal fusion applications to encourage bone formation across an intervertebral motion segment. To be an effective replacement for autogenous bone grafts, a bioactive material must possess the properties of osteoinduction and osteoconduction.

METHODS

Literature review.

RESULTS

Platelet gel concentrates deliver nonspecific cytokines that influence local cells at the implantation site. Demineralized bone matrix acts as a bone graft enhancer that excludes fibrous tissue of muscle interposition in a fusion mass and is a mildly osteoinductive material. Bone morphogenetic proteins are an integral part of natural bone formation response. They function as differentiation factors that act on mesenchymal stem cells to induce bone formation.

CONCLUSIONS

Patient-derived therapies such as platelet gel concentrates contain cytokines that play a role in bone formation; however, none of them is capable of inducing the entire bone formation cascade. Clinical use of these concentrates could possibly interfere with new bone formation. The use of bone marrow aspiration and concentration techniques has not been convincingly studied in spinal fusions in lower order animal or human clinical studies. Demineralized bone matrix contains small and variable amounts of naturally occurring bone morphogenetic proteins. These products can only function as bone graft extenders. Recombinant bone morphogenetic protein products contain much more highly concentrated and focused amounts of bone morphogenetic proteins, and some have been shown to be clinically effective bone graft replacements.

Minimal access surgical techniques in the management of the painful lumbar motion segment

STUDY DESIGN

Review article.

OBJECTIVES

To provide an overview of current minimally invasive lumbar fusion techniques.

SUMMARY OF BACKGROUND DATA

Minimally invasive lumbar fusion techniques have only recently been developed. The goals of these procedures are to reduce approach-related soft tissue injury while allowing the surgery to be conducted in an effective manner. METHODS.: Pertinent literature and the authors' clinical experience are reviewed.

RESULTS

Minimally invasive techniques have been developed for intertransverse process, posterior lumbar interbody, and transforaminal lumbar interbody fusions. The indications, advantages, and disadvantages of each technique are described. It is emphasized that while they appear promising, the clinical results of these techniques remain preliminary with few long-term studies available for critical review.

CONCLUSIONS

Preliminary clinical evidence suggests that minimally invasive lumbar fusion techniques will benefit patients with spinal disorders.

Estrogen-dependent actions of bone morphogenetic protein-7 on spine fusion in rats

STUDY DESIGN

Intertransverse process spinal fusion using recombinant human bone morphogenetic protein-7 (rhBMP-7) was performed in intact and ovariectomized female rats.

OBJECTIVES

To examine fusion rates in intact and ovariectomized female rats using rhBMP-7 to determine if spine fusion is dependent on estrogen status.

SUMMARY OF BACKGROUND DATA

Rat spinal fusion has been established as a consistent, efficient model for posterolateral intertransverse process fusion. Previous experiments have confirmed the efficacy of pellets containing the carrier, insoluble collagen bone matrix (ICBM), and rhBMP-7 to augment intertransverse process single level fusion in a rat model. Studying these implications in an osteoporosis model is of clinical value because there are many patients undergoing spinal fusion surgery that have osteoporotic bone disease, and there is a steady increase in this group of patients.

METHODS

A total of 15 ovariectomized and 15 intact Sprague-Dawley female rats were randomly assigned to groups receiving 25 mg ICBM alone, 25 mg ICBM + 10 microg rhBMP-7, and 25 mg ICBM + 30 microg rhBMP-7. Spinal fusion was evaluated by manual motion testing at each lumbar segment, radiographic evaluation using the Lenke grading system, and histology.

RESULTS

Ovariectomized and intact rats receiving 25 mg carrier ICBM alone did not show spinal fusion. With 25 mg ICBM + 10 microg rhBMP-7, there was not a significant difference in fusion rates between intact and ovariectomized rats (P = 0.63). Ovariectomized rats receiving 25 mg ICBM + 30 microg rhBMP-7 showed significantly lower fusion rates than intact rats (P = 0.013).

CONCLUSION

These data suggest that spinal fusion using rhBMP-7 is estrogen-dependent in rats. At the dosages used, rhBMP-7 was unable to overcome the inhibitory effects of estrogen deficiency on spinal fusion.

Initial fusion rates with recombinant human bone morphogenetic protein-2/compression resistant matrix and a hydroxyapatite and tricalcium phosphate/collagen carrier in posterolateral spinal fusion

STUDY DESIGN

Prospective, randomized, unblinded study of iliac crest bone graft (ICBG) versus recombinant human bone morphogenetic protein-2/compression resistant matrix (rhBMP-2/CRM)in a posterolateral instrumented fusion procedure.

OBJECTIVES

Document initial radiographic characteristics, based on computed tomography, with rhBMP-2/CRM for posterolateral fusion at 6 and 12-month intervals.

SUMMARY OF BACKGROUND DATA

As the acceptance of INFUSE bone graft as an ICBG replacement becomes more widespread, surgeons have begun to study applications for rhBMP-2 in posterior spinal fusion. Preclinical studies have examined variables including carrier composition, rhBMP-2 concentration, and rhBMP-2 dose. Pilot studies have been performed with encouraging initial results.

METHODS

Patients with single level lumbar degenerative disease were enrolled in a randomized study of ICBG versus rhBMP-2/CRM in a posterolateral instrumented fusion procedure. Computed tomography scans at 6 and 12 months were graded as demonstrating no fusion (grade 1), partial or limited unilateral fusion (grade 2), partial or limited bilateral fusion (grade 3), solid unilateral fusion (grade 4), or solid bilateral fusion (grade 5).

RESULTS

At our institution, 74 patients (38 rhBMP-2/CRM, 36 ICBG) reached minimum 1-year follow-up and were included in this analysis. Mean fusion grade (scale1-5) at 6 months after surgery was 4.35 in the rhBMP-2/CRM group versus 3.09 in the ICBG group (P < 0.0001). At 1 year after surgery mean fusion grade was 4.62 in the rhBMP-2/CRM group versus 3.77 in the ICBG group (P < 0.0023).

CONCLUSIONS

These early results are encouraging and suggest a more rapid incorporation and development of the fusion mass with rhBMP-2/CRM than iliac crest autograft in a single level posterior instrumented fusion.

Experimental spinal fusion with recombinant human bone morphogenetic protein-2 delivered by a synthetic polymer and beta-tricalcium phosphate in a rabbit model

STUDY DESIGN

An experimental animal study to achieve posterolateral intertransverse process spine fusion with recombinant bone morphogenetic protein in combination with a new delivery system.

OBJECTIVE

To evaluate the efficacy of a new synthetic biodegradable bone-inducing material containing recombinant human bone morphogenetic protein-2 (rhBMP-2) as a bone-graft substitute for posterolateral intertransverse process fusion in a rabbit model.

SUMMARY OF BACKGROUND DATA

rhBMP-2, a powerful bone-inducing cytokine, has been used as a bone graft substitute in combination with animal-derived collagen to achieve spinal fusion in animal models. However, the minimum dose of rhBMP-2 required to obtain solid posterolateral intertransverse process fusion was high on the basis of previous reports (>100 microg in rabbit models). To improve the efficacy, performance of rhBMP-2, and the safety of the delivery system for this protein, a more sophisticated system is required.

METHODS

To fabricate one implant for one-side L4-L5 intertransverse process fusion, beta-tricalcium phosphate (beta-TCP) powder (300 microg), a polymer gel (PLA-DX-PEG block copolymer; 300 microg) and rhBMP-2 (7.5, 15, or 30 microg) were mixed and manually shaped to resemble a rod. Through a posterolateral approach, two implants were placed on both sides (1 per side) by surgery so as to bridge the transverse processes of adult New Zealand white rabbits (n = 27). In control animals, implants without rhBMP or autogenous cortico-cancellous bone chips from the iliaccrest were placed in a similar location. The lumbar vertebrae were recovered 6 weeks after surgery. The posterolateral fusion was examined by manual palpation, radiography, biomechanical testing, and histology.

RESULTS

Rabbits that received 15 or 30 microg of rhBMP-2 showed consistent fusion. However, solid fusion was seen in 2 of 5 rabbits with autografting and rabbits that received 7.5 microg of rhBMP-2. Fusion was not observed in the rabbits that did not receive rhBMP-2.

CONCLUSIONS

Consistent spinal fusion was obtained by implanting a biodegradable bone-inducing implant composed of beta-TCP, PLA-DX-PEG, and rhBMP-2 within a period of 6 weeks. The rhBMP-2 doses required for the spinal fusion were significantly lower than those reported previously.

Healing of critically sized femoral defects, using genetically modified mesenchymal stem cells from human adipose tissue

The FDA has approved the clinical use of recombinant bone morphogenetic proteins (BMPs). However, the use of recombinant BMPs in humans has required large doses of the proteins to be effective, which suggests that the delivery method of bone morphogenetic proteins needs to be optimized. Gene therapy is an alternative method to deliver such recombinant proteins, and gene transfer techniques have been tested on a variety of cell types including bone marrow cells, skin fibroblasts, peripheral blood monocytes, and muscle-derived cells. In this study, we sought to determine the ability of BMP-2-producing human adipose-derived mesenchymal stem cells to heal a critically sized femoral defect in a nude rat model. After approval by the human subjects protection committee, human adipose tissue was obtained from healthy donors. The lipoaspirate was processed as previously described (De Ugarte, D.A., et al. Cells Tissues Organs 174, 101, 2003). Cells were grown in culture and infected with a BMP-2-carrying adenovirus. Five million cells were applied to a collagen- ceramic carrier and implanted into femoral defects as previously described (Zuk, P.A., et al. Mol. Biol. 13, 4279, 2002). All animals were killed at 8 weeks. Femora were dissected out and underwent radiographic, histologic, and biomechanical analysis. Eleven of the 12 femora in the group treated with human processed lipoaspirate (HPLA) cells genetically modified to overexpress BMP-2 had healed at 8 weeks. This was assessed by radiographs, by mechanical testing, and by histology. The one femur that did not heal had a subacute infection. All eight of the femora treated with the rhBMP-2-impregnated collagen-ceramic carrier healed. No statistically significant difference was detected between these two groups. Evaluation of the control groups: group II (collagen- ceramic carrier with HPLA cells) and group III (collagen-ceramic carrier alone) showed that none of the femora had healed by 8 weeks. Our results indicate that HPLA cells genetically modified by adenoviral gene transfer to overexpress BMP-2 can induce bone formation in vivo and heal a critically sized femoral defect in an athymic rat. The HPLA cells alone did not induce significant bone formation. However, when combined with an osteoinductive factor these cells may be an effective method for enhancing bone healing and the tissue engineering of bone.

Anterior cervical discectomy and fusion involving a polyetheretherketone spacer and bone morphogenetic protein

OBJECT

The authors reviewed clinical and radiographic outcomes in patients who had undergone anterior cervical discectomy and fusion (ACDF) involving the placement of polyetheretherketone (PEEK) spacers filled with recombinant human bone morphogenetic protein (rhBMP)-2.

METHODS

Data obtained in 24 cases were retrospectively evaluated. The follow-up period ranged from 12 to 16 months (mean 13 months). Fifteen patients presented with radiculopathy, eight with myeloradiculopathy, and one with quadriparesis. Single-level ACDF was performed in 12 patients, two-level ACDF in nine, and three-level ACDF in three. Clinical outcomes were assessed using Odom criteria, and fusion was assessed by examining flexion-extension radiographs and computerized tomography scans in cases in which arthrodesis was questionable. Follow-up data were available for 23 patients. One patient died of medical complications unrelated to surgery 4 weeks after ACDF. Clinical outcomes were rated as good/excellent in 22 patients (95%) and fair in one (5%). Solid radiographically documented fusion, with evidence of solid bridging bone and no instability on flexion-extension x-ray films, was present in all cases. Complications included transient recurrent laryngeal nerve injury in one case, transient C-5 paresis in one, cerebrospinal fluid leakage in one, and transient dysphagia in two.

CONCLUSIONS

Analysis of the results indicated that ACDF involving an rhBMP-2-filled PEEK spacer leads to good clinical outcomes (by Odum criteria) and solid fusion (even in multilevel cases) while avoiding the complications associated with harvesting iliac crest bone grafts.

Strut allograft union and remodeling using rhBMP-2 in a spinal corpectomy model

STUDY DESIGN

Growth factor in a collagen sponge carrier was compared to autograft, both packed within an allograft strut following corpectomy in a bovine spinal model.

OBJECTIVE

To evaluate incorporation of cortical strut allografts after lumbar corpectomy, comparing augmentation with recombinant human bone morphogenetic protein-2 (rhBMP-2) to local autograft.

SUMMARY OF BACKGROUND DATA

Autogenous strut grafts are the gold standard for successful fusion in reconstruction following corpectomy; however, significant donor site morbidity can occur. Recent studies describing consistently successful anterior interbody fusions with BMP augmentation suggest an exciting prospect of unlimited and potent grafting material for these difficult fusions.

METHODS

Sixteen calves underwent L3 corpectomy with instrumented strut allograft reconstruction. The rhBMP-2 impregnated collagen sponges filled the empty medullary canal of the allograft in 8 animals. Eight animals had the allograft strut filled with local autogenous bone. After 4 months, the lumbar spines were harvested for radiographic, biomechanical, and histologic evaluation.

RESULTS

Computerized tomography revealed allograft fusion in 7 of 8 autograft specimens and 8 of 8 BMP specimens. The BMP treated group had denser bone at the ends of the cortical allograft, but a central void persisted. Autograft filled struts maintained a more uniform distribution of less organized bone throughout the strut canal. Histologic assessment verified remodeling and incorporation of the allografts for both groups. Biomechanical testing confirmed no significant difference in fusion strength between groups.

CONCLUSIONS

Large cortical strut allografts (after lumbar corpectomy) supplemented with rhBMP-2 had incorporation and fusion strength comparable to allografts enhanced with cancellous autograft.

Developmental anomalies of the cervical spine in patients with fibrodysplasia ossificans progressiva are distinctly different from those in patients with Klippel-Feil syndrome: clues from the BMP signaling pathway

STUDY DESIGN

A radiographic analysis of the cervical spine of 70 patients diagnosed with fibrodysplasia ossificans progressiva (FOP) and 33 diagnosed with Klippel-Feil (KF) syndrome was conducted.

OBJECTIVES

The objectives of this study were to describe cervical spine abnormalities in patients with FOP, to compare and contrast those findings with the malformations in patients with KF syndrome, and to examine the possible etiology of these abnormalities.

SUMMARY OF BACKGROUND DATA

Congenital features of diseases often provide seminal clues to underlying etiology and developmental pathways. While progressive metamorphosis of connective tissue to heterotopic bone is the most dramatic and disabling feature of FOP, less severe congenital anomalies of the skeleton are also present. Vertebral fusions observed in KF are consistent with defects in embryonic segmentation.

METHODS

The cervical spine plain films of 70 FOP patients and 33 KF patients with documented congenital abnormalities were reviewed.

RESULTS

Generalized neck stiffness and decreased range of motion were noted in most children with FOP. In the FOP patient group, characteristic anomalies, including large posterior elements, tall narrow vertebral bodies,and fusion of the facet joints between C2 and C7, were observed. Most notably, these characteristic anomalies of the cervical spine in patients with FOP were distinctly different from those of 33 patients with KF that were examined but were strikingly similar to those seen in mice with homozygous deletions of the gene-encoding noggin, a bone morphogenetic protein (BMP) antagonist.

CONCLUSIONS

FOP patients exhibit a characteristic set of congenital spine malformations. While the noggin gene (NOG) is not mutated in patients who have FOP, these findings extend a growing body of evidence implicating overactivity of the BMP signaling pathway in the molecular pathogenesis of FOP.

Guidelines for the performance of fusion procedures for degenerative disease of the lumbar spine. Part 16: bone graft extenders and substitutes

Despite the large volume of animal data regarding the use of synthetic bone graft substitutes or extenders, there are very few data regarding the use of these substances for fusion in lumbar degenerative disease. The best available data indicate that rhBMP-2 is a viable alternative to autograft bone for interbody fusion procedures. This same substance may also be a viable alternative to autograft for PLF; however, definitive medical evidence is not yet available. There is little, if any, medical evidence to support the use of other biological agents at the present time. As promising new compounds are brought to market, well-designed cohort studies and randomized trials will be required to determine the actual usefulness of these compounds in clinical practice. It is important not to generalize the results obtained with one preparation or application to different preparations or applications. The use of synthetic calcium phosphate ceramics as graft extenders appears to be reasonable in certain situations. The medical evidence available regarding their use is limited and of poor quality. Further study will be required to establish their utility for use in spinal fusion.

The use of cultured bone marrow cells in type I collagen gel and porous hydroxyapatite for posterolateral lumbar spine fusion

STUDY DESIGN

Posterolateral lumbar transverse process fusion was completed using the cultured bone marrow cells in type I collagen gel and porous hydroxyapatite.

OBJECTIVE

To compare the efficacy of cultured bone marrow cells with that of bone morphogenetic protein (BMP) as a graft alternative to autologous bone for posterolateral spine fusion.

SUMMARY OF BACKGROUND DATA

The clinical application of BMP for spinal fusion may be limited by high dose and cost. Recently, mesenchymal stem cells have been studied in various fields because of their capability to differentiate into various cells, including those in the osteogenic lineage.

METHODS

Thirty adult rabbits were used. Each underwent single-level, bilateral, posterolateral intertransverse process fusions at L4-L5. The animals were divided into 4 groups, each according to the material implanted: (1) autologous bone (autograft, n = 9); (2) porous hydroxyapatite (HA) particles and type I collagen sheet with 100 microg rhBMP-2 (BMP-HA, n = 7); (3) bone marrow cells (1 x 10(6) cells/mL, low-marrow-HA, n = 7); and (4) bone marrow cells (1 x 10(8) cells/mL, high-marrow-HA, n = 7). Before implantation for groups 3 and 4, fresh bone marrow cells from the iliac crest of each animal were cultured in a standard medium for 2 weeks. For one additional week, the marrow cells were cultured in 10(-8) M dexamethasone, type I collagen gel, and HA. Animals were euthanized 6 weeks after surgery. Spinal fusions were evaluated by radiograph, manual palpation, and histology.

RESULTS

The fusion rates were 4 of 7 in the autograft group, 7 of 7 in the BMP-HA group, 0 of 7 in the low-marrow-HA group, and 5 of 7 in the high-marrow-HA group. The histology in the BMP-HA and high-marrow-HA groups showed that grafted HA fragments were connected with mature new bone. The pores of HA fragments were filled up with bone matrix. In the low-marrow-HA group, fibrous tissue was predominant in the grafted fragments.

CONCLUSIONS

This study shows that the cultured bone marrow cells can act as a substitute for autograft or BMP in spine fusion. The current formulation may yield improved fusion success and better quality of fusion bone as compared to autograft.

Application of bone morphogenetic proteins in orthopaedic practice: their efficacy and side effects

Bone morphogenetic proteins (BMPs) have been extensively studied since the discovery of agents within bone that could induce bone formation at ectopic sites by Urist in the 1960s. Extensive preclinical research has been carried out showing the efficacy of these products in promoting bone healing. Clinical trials are encouraging, with meta-analysis of results revealing better rates of healing than treatment with autologous bone grafting (risk ratio [RR]: 0.845; 95% confidence interval [CI]: 0.772 - 0.924; p < 0.001 for clinical outcome and RR: 0.884; 95% CI: 0.825 - 0.948; p < 0.001 for radiological outcome). Preclinical and clinical safety assessments have revealed little evidence of toxic effects and there have been few reports of adverse events related to their use. A small rate of immunological reaction following administration, resulting in antibody formation, has been observed in some patients, without clinical consequence, although the long-term implications of this are unknown. Ongoing research is revealing that BMPs act on an extremely wide range of body tissues in a variety of manners and this is far from fully understood. It should be noted, however, that given the role of BMP as a differentiation factor, the production of undifferentiated neoplastic tissue seems unlikely. It has also been shown in an animal model that artificially administered BMP can cross the placenta and subsequently be detected in the growing embryo. As this area has been little investigated, use in pregnancy is currently contraindicated. Until the long-term safety profile is more fully documented it would seem sensible to continue to carefully control use and monitor patients closely. However, the current evidence is very promising.

Surgery for degenerative lumbar spondylosis

BACKGROUND

Surgical investigations and interventions account for large health care utilisation and costs, but the scientific evidence for most procedures is still limited.

OBJECTIVES

Degenerative conditions affecting the lumbar spine are variously described as lumbar spondylosis or degenerative disc disease (which we regarded as one entity) and may be associated with back pain and associated leg symptoms, instability, spinal stenosis and/or degenerative spondylolisthesis. The objective of this review was to assess current scientific evidence on the effectiveness of surgical interventions for degenerative lumbar spondylosis.

SEARCH STRATEGY

We searched CENTRAL, MEDLINE, PubMed, Spine and ISSLS abstracts, with citation tracking from the retrieved articles. We also corresponded with experts. All data found up to 31 March 2004 are included.

SELECTION CRITERIA

Randomised (RCTs) or quasi-randomised trials of surgical treatment of lumbar spondylosis.

DATA COLLECTION AND ANALYSIS

Two authors assessed trial quality and extracted data from published papers. Additional information was sought from the authors if necessary.

MAIN RESULTS

Thirty-one published RCTs of all forms of surgical treatment for degenerative lumbar spondylosis were identified. The trials varied in quality: only the more recent trials used appropriate methods of randomization, blinding and independent assessment of outcome. Most of the earlier published results were of technical surgical outcomes with some crude ratings of clinical outcome. More of the recent trials also reported patient-centered outcomes of pain or disability, but there is still very little information on occupational outcomes. There was a particular lack of long term outcomes beyond two to three years. Seven heterogeneous trials on spondylolisthesis, spinal stenosis and nerve compression permitted limited conclusions. Two new trials on the effectiveness of fusion showed conflicting results. One showed that fusion gave better clinical outcomes than conventional physiotherapy, while the other showed that fusion was no better than a modern exercise and rehabilitation programme. Eight trials showed that instrumented fusion produced a higher fusion rate (though that needs to be qualified by the difficulty of assessing fusion in the presence of metal-work), but did not improve clinical outcomes, while there is other evidence that it may be associated with higher complication rates. Three trials with conflicting results did not permit any conclusions about the relative effectiveness of anterior, posterior or circumferential fusion. Preliminary results of two small trials of intra-discal electrotherapy showed conflicting results. Preliminary data from three trials of disc arthroplasty did not permit any firm conclusions.

AUTHORS' CONCLUSIONS

Limited evidence is now available to support some aspects of surgical practice. Surgeons should be encouraged to perform further RCTs in this field.

Experimental anterior lumbar interbody fusion with an osteoinductive bovine bone collagen extract

STUDY DESIGN

A randomized experimental porcine anterior lumbar interbody fusion.

OBJECTIVE

To determine the osteoinductive potential of a bovine bone derived collagen lyophilisate for anterior interbody spinal fusion in an animal model.

SUMMARY OF BACKGROUND DATA

Complications associated with autologous bone graft harvesting are still major concerns when performing spinal fusion surgery. A new formulation of bovine bone collagen-protein extracts (Colloss) has been shown to be effective in animal studies as a bone graft enhancer. The present study further tested its osteogenic potential in the anterior spinal fusion cage in a controlled animal study.

METHODS

Twelve normal Danish landrace pigs of 50 kg each were chosen as experimental animals. Lumbar spine interbody fusion of L3-L4, L4-L5 using titanium alloy cages was performed on each pig with pedicle screws instrumentation. Cages packed with either autograft or Colloss were randomly assigned to the two levels. Pigs were followed up to 3 months. After termination, the spine segments were evaluated by radiograph, micro-CT, and histomorphometry

RESULTS

Ten pigs completed the study. Implant breakage, loosening, or spinal deformity was not observed after 12 weeks on radiograph examination. Micro-CT evaluations demonstrated that cages with Colloss had the same fusion rate (9 of 10) as those with autograft, further evaluation of bone volume (BV/TV), and trabecular thickness (Tb Th) also showed no different between them. Histologically, both autograft and Colloss levels had 80% (8 of 10) fusion rate. Histomorphometric results revealed that the only difference was the Colloss-filled cages had a higher cartilage tissue volume (P < 0.04).

CONCLUSION

Colloss was effective as a bone graft substitute. It achieved the same fusion rate and the samepercentage of new bone formation as that of autologous iliac bone graft in this demanding porcine anterior spinal fusion model after 12 weeks.

Twisted gastrulation and chordin inhibit differentiation and mineralization in MC3T3-E1 osteoblast-like cells

Bone morphogenetic proteins (BMPs) are potent inducers of osteoblast differentiation. The accessibility of BMP ligands for binding to their receptors is regulated by secreted proteins Twisted gastrulation (Tsg) and Chordin (Chd). Tsg antagonizes BMP signaling by forming ternary complexes with Chd and BMPs, thereby preventing BMPs from binding to their receptors. In addition to the anti-BMP function, Tsg also has pro-BMP activity, partly mediated by cleavage and degradation of Chd, which releases BMPs from ternary complexes. The roles of Tsg and Chd in osteoblast differentiation are not known. Therefore, in the present study, we investigated the effect of exogenous Tsg and Chd on osteoblast differentiation and mineralization using a well-characterized subclone of MC3T3-E1 osteoblast-like cells. Our results show that Tsg and Chd are expressed in MC3T3-E1 osteoblast-like cells. While Tsg mRNA levels decrease during osteoblast differentiation, Chd levels are found to increase. Tsg and Chd proteins accumulate in the cell culture media as the osteoblasts differentiate. Exogenous Tsg and Chd inhibit osteoblast differentiation and mineralization. Osteocalcin (OCN) mRNA levels decrease following both Tsg and Chd treatment. Tsg and Chd also inhibit alkaline phosphatase (ALP) activity in a dose-dependent manner. To provide insight into the mechanism of Tsg and Chd action, we investigated the effect of Tsg and Chd on BMP activity by determining phosphorylated Smad1 (pSmad1) levels. We show that both Tsg and Chd can independently and in combination reduce pSmad1 levels in MC3T3-E1 cells treated with BMP4. Further, BMP2 partially reverses the inhibitory effect of Tsg and Chd on ALP activity. Taken together, these results suggest that Tsg and Chd are involved in osteoblast differentiation and mineralization by regulating BMP signaling.