Human bone morphogenetic protein allografting for reconstruction of femoral nonunion

Preliminary Evaluation of BMP-2 Expression and Histological Characteristics During Apexification with Calcium Hydroxide and Mineral Trioxide Aggregate

Histological characteristics and bone morphogenetic protein-2 (BMP-2) expression were evaluated in apexification procedures using calcium hydroxide [Ca (OH)2] and mineral trioxide aggregate (MTA). In three of four quadrants of the mouth, monkey (Macaca fascicularis) teeth were infected by pulpal exposure to saliva. After 90 days, each group was treated with Ca (OH)2 or MTA. Infected, untreated teeth were used as negative controls and normally developing teeth were used as positive controls. Areas within the apical region of each sample were scored based upon histological findings and BMP-2 expression. Overall, BMP-2 expression in all areas was similar in the Ca (OH)2, MTA, and infection/no treatment groups, which tended to be more immunoreactive for BMP-2 than the untreated group. Use of MTA in combination with Ca (OH)2 may initiate regeneration of the periodontium more quickly than either material used alone, but further studies involving MTA use in apical closure are indicated.

Bone mass effects of a BMP4 gene polymorphism in postmenopausal women

The pathogenesis of osteoporosis involves both genetic and environmental factors. On the basis of linkage data suggesting gene effects on bone density at chromosome 14q and data locating the BMP4 gene to 14q, we performed a positional candidate study to examine a possible association of BMP4 gene polymorphisms, hip bone density (n = 1012) and fracture rates (n = 1232) in postmenopausal women (mean age 75). On genotype analysis of the three selected single nucleotide polymorphisms (SNP), the 6007C > T polymorphism was associated with total and intertrochanteric hip BMD and BMD was lower in the 32% of subjects homozygous for the C allele. This polymorphism codes for a nonsynonymous amino acid change with the T allele coding for valine, while the C allele codes for alanine. The difference in BMD was 3.1% (TT vs. CC) and 2.3% (CT versus CC) for the total hip (P = 0.023), and 3.7% (TT vs. CC) and 2.8% (CT versus CC) for the intertrochanter site (P = 0.012). Haplotype analysis demonstrated 6 haplotypes of frequency greater than 2%. A major haplotype defined by G-C-T alleles in SNPs -5826G > A, 3564C > T and 6007C > T respectively, showed association with high bone mass. No SNP showed association with fracture rates. We conclude that a polymorphism found in the BMP4 gene, affecting amino acid sequence, is associated with hip bone density in postmenopausal women, presumably via regulation of anabolic effects on the skeleton.

The effect of different mineral frames on ectopic bone formation in mouse hind leg muscles induced by native reindeer bone morphogenetic protein

INTRODUCTION

Bone morphogenetic proteins (BMPs) require carrier material for slow release and framing material for osteoconduction.

MATERIALS AND METHODS

The effect of a frame on early bone formation induced by partially purified native reindeer BMP in composite implants containing 3 mg of BMP, type IV collagen and tricalcium phosphate (TCP/Col/BMP) or hydroxyapatite (HA/Col/BMP) or biphasic tricalcium phosphate-hydroxyapatite (TCP/HA/Col/BMP) or biocoral (NC/Col/BMP) was evaluated using a mouse hind leg muscle pouch model. Collagen with native reindeer BMP (Col/BMP) and corresponding implants without native reindeer BMP served as controls. Evaluation was done by incorporation of 45Ca, radiographically and histologically 3 weeks after the implantation.

RESULTS

None of the implants without native reindeer BMP were able to induce new bone visible on radiographs. The area of new bone formation in the Col/BMP (p=0.026) and TCP/HA/Col/BMP (p=0.012) groups was significantly greater than in the TCP/Col/BMP group. The optical density of the new bone area was significantly greater in the TCP/HA/Col/BMP group than in the TCP/Col/BMP (p=0.036) or Col/BMP (p=0.02) groups. 45Ca incorporation was many times greater in all the groups containing native reindeer BMP than in the corresponding groups without BMP. In the Col/BMP (p=0.046) and TCP/HA/Col/BMP (p=0.046) groups, 45Ca incorporation was significantly greater than in the TCP/Col/BMP group. No significant differences were found in any parameters between HA/Col/BMP and NC/Col/BMP groups and the other BMP-containing groups.

CONCLUSIONS

Hydroxyapatite, biocoral and biphasic tricalciumphosphate-hydroxyapatite are equally good as framing material for native reindeer BMP, while tricalciumphosphate is somewhat worse. Osteoinduction of native reindeer BMP works well with collagen alone.

Osteoinductivity of commercially available demineralized bone matrix. Preparations in a spine fusion model

BACKGROUND

Although autogenous bone is the most widely used graft material for spinal fusion, demineralized bone matrix preparations are available as alternatives or supplements to autograft. They are prepared by acid extraction of most of the mineralized component, with retention of the collagen and noncollagenous proteins, including growth factors. Differences in allograft processing methods among suppliers might yield products with different osteoinductive activities. The purpose of this study was to compare the efficacy of three different commercially available demineralized bone matrix products for inducing spinal fusion in an athymic rat model.

METHODS

Sixty male athymic rats underwent spinal fusion and were divided into three groups of eighteen animals each. Group I received Grafton Putty; Group II, DBX Putty; and Group III, AlloMatrix Injectable Putty. A control group of six animals (Group IV) underwent decortication alone. Six animals from each of the three experimental groups were killed at each of three intervals (two, four, and eight weeks), and the six animals from the control group were killed at eight weeks. At each of the time-points, radiographic and histologic analysis and manual testing of the explanted spines were performed.

RESULTS

The spines in Group I demonstrated higher rates of radiographically evident fusion at eight weeks than did the spines in Group III or Group IV (p < 0.05). Manual testing of the spines at four weeks revealed variable fusion rates (five of six in Group I, two of six in Group II, and none of six in Group III). At eight weeks, all six spines in Group I, three of the six in Group II, and no spine in Group III or IV had fused. Histologic analysis of the spines in Groups I, II, and III demonstrated varying amounts of residual demineralized bone matrix and new bone formation. Group-I spines demonstrated the most new bone formation.

CONCLUSIONS

This study demonstrated differences in the osteoinductive potentials of commercially available demineralized bone matrices in this animal model.

The effect of the presence of muscle tissue in a bone healing site

PURPOSE

The recovery of a bone fracture is a process that is not yet fully understood. The literature conflicts on the results obtained by the interposition of foreign tissue inside a damaged bone. The objective of the present study was to ascertain the effect of placing muscle tissue between the stumps of a fractured bone.

METHOD

The study was carried out on 10 rabbits divided into 2 groups (n = 5): Group 1--partial fracture of the humerus and interposition of muscle tissue; Group 2--complete fracture of the humerus and interposition of muscle tissue. The fractured limb of all animals was immobilized for 8 weeks. At the end of this time, the rabbits were killed and their operated humeri were carefully removed for roentgenological and histological assessment.

RESULTS

All humeri of Group 1 recovered their integrity and normal aspect. However, the healing of the humeri of Group 2 was not perfect. Gross angulation of the bone diaphysis occurred in all animals, and immature trabecular bone, osteochondral tissue, and persistence of muscle tissue substituted normal bone.

CONCLUSIONS

Interposed muscle does not affect partial bone fracture healing but causes instability in a complete fracture.

Influence of ethylene oxide sterilization on the activity of native reindeer bone morphogenetic protein

We studied the effects of ethylene oxide sterilization (Steri-Vac 4XL, temperature 29 degrees C, exposure time 4 h 10 min, ethylene oxide concentration 860 mg/l) on the osteoinductivity of partially purified native reindeer bone morphogenetic protein (BMP) in a hind leg muscle pouch model of male NMRI mice. BMP was administered in implants containing 3 mg in a collagen carrier. Implants without sterilization and without BMP served as controls. New bone formation was evaluated based on the calcium yield, radiographic and histological examination 3 weeks after implantation. The implants without BMP were not able to induce new bone visible in radiographs. In the sterilized BMP group, the mean area of new bone was 35% ( p=0.004) and density 32% ( p=0.000) smaller than in the nonsterilized group. Calcium yield was 20% lower in the sterilized group than in the nonsterilized group, but this difference was not significant ( p=0.22). It was many times lower in the group without BMP than in the above-mentioned groups ( p=0,001). We conclude that ethylene oxide gas sterilization reduces the bone-forming activity of native reindeer BMP by one third.

Ilizarov compression over a nail for aseptic femoral nonunions that have failed exchange nailing: a report of five cases

OBJECTIVE

To evaluate a new operative treatment of femoral nonunion following failed exchange nailing.

DESIGN

Retrospective review, consecutive series. SETTING Office-based orthopaedic practice.

PATIENTS

Five consecutive patients (ages 31-67 years) were referred in with a femoral nonunion following exchange nailing an average of 28 months (range 11-55) after the initial traumatic injury. The patients had undergone an average of 5 (range 2-8) previous surgeries on the femur. No patient had signs or history of bone infection or segmental bone loss at presentation. All patients had diaphyseal or diaphyseal-metaphyseal oligotrophic nonunions and had failed an average of 2 (range 1-3) previous exchange nailings.

INTERVENTION

Slow compression (0.25 to 0.50 mm per day) of the nonunion site over a new, smaller diameter nail using an Ilizarov external fixator.

MAIN OUTCOMES MEASUREMENTS

Clinical and radiographic evidence of bone union, ambulation, pain, residual deformity, or shortening.

RESULTS

All nonunions healed without the need for further nonunion surgery. The external fixator was removed at an average of 133 days (range 86-238 days). No deep infections occurred in any patient. All patients experienced some degree of pin site irritation. At the most recent follow-up (average 45 months; range 12-75 months), all patients had improved their functional ambulatory status and had discontinued or decreased the use of assistive devices to walk. All patients were full weight bearing. Average pain, as rated on a 0 to 10 Visual Analogue Scale, decreased from 8 of 10 before treatment to 1 of 10 after treatment. No patient experienced a clinically significant worsening of leg length discrepancy.

CONCLUSIONS

Slow compression over an intramedullary nail using external fixation successfully promotes the healing of problematic femoral nonunions that have failed one or more prior exchange nailings.

Efficacy of allogenic bone implants in a series of consecutive elective foot procedures

To show the efficacy of an allogenic bone graft in elective foot surgery, the authors report on 39 consecutive procedures in which allograft was implanted in 26 patients during a 30-month period. These procedures were performed for a variety of conditions, including arthrodesis, segmental lengthening, and treatment of nonunion. Allograft material consisted of freeze-dried tricortical iliac crest or demineralized bone matrix used either alone or as a composite. Allograft incorporation in all surgical procedures was retrospectively analyzed. Of 39 consecutive implant procedures, there were 38 healed sites (97%) and 1 nonunion (3%). After radiographic and clinical evaluation of allograft incorporation, the authors conclude that allogenic bone graft is a viable option for a multitude of foot conditions.

Recombinant human bone morphogenetic protein-2 for treatment of open tibial fractures: a prospective, controlled, randomized study of four hundred and fifty patients

BACKGROUND

The treatment of open fractures of the tibial shaft is often complicated by delayed union and nonunion. The objective of this study was to evaluate the safety and efficacy of the use of recombinant human bone morphogenetic protein-2 (rhBMP-2; dibotermin alfa) to accelerate healing of open tibial shaft fractures and to reduce the need for secondary intervention.

METHODS

In a prospective, randomized, controlled, single-blind study, 450 patients with an open tibial fracture were randomized to receive either the standard of care (intramedullary nail fixation and routine soft-tissue management [the control group]), the standard of care and an implant containing 0.75 mg/mL of rhBMP-2 (total dose of 6 mg), or the standard of care and an implant containing 1.50 mg/mL of rhBMP-2 (total dose of 12 mg). The rhBMP-2 implant (rhBMP-2 applied to an absorbable collagen sponge) was placed over the fracture at the time of definitive wound closure. Randomization was stratified by the severity of the open wound. The primary outcome measure was the proportion of patients requiring secondary intervention because of delayed union or nonunion within twelve months postoperatively.

RESULTS

Four hundred and twenty-one (94%) of the patients were available for the twelve-month follow-up. The 1.50-mg/mL rhBMP-2 group had a 44% reduction in the risk of failure (i.e., secondary intervention because of delayed union; relative risk = 0.56; 95% confidence interval = 0.40 to 0.78; pairwise p = 0.0005), significantly fewer invasive interventions (e.g., bone-grafting and nail exchange; p = 0.0264), and significantly faster fracture-healing (p = 0.0022) than did the control patients. Significantly more patients treated with 1.50 mg/mL of rhBMP-2 had healing of the fracture at the postoperative visits from ten weeks through twelve months (p = 0.0008). Compared with the control patients, those treated with 1.50 mg/mL of rhBMP-2 also had significantly fewer hardware failures (p = 0.0174), fewer infections (in association with Gustilo-Anderson type-III injuries; p = 0.0219), and faster wound-healing (83% compared with 65% had wound-healing at six weeks; p =0.0010).

CONCLUSIONS

The rhBMP-2 implant was safe and, when 1.50 mg/mL was used, significantly superior to the standard of care in reducing the frequency of secondary interventions and the overall invasiveness of the procedures, accelerating fracture and wound-healing, and reducing the infection rate in patients with an open fracture of the tibia.

Bone morphogenetic proteins and spinal fusion

Bone morphogenetic proteins (BMPs) have increasingly become a focus of research in the laboratory, with animal models, and in human clinical trials for the treatment of spinal disorders. Basic science research has elucidated the putative mechanism of action of BMPs, and the efficacy of BMPs in inducing bone formation has been evaluated in multiple animal models of anterior and posterior spinal fusion. Not only has BMP been shown to improve the quality and amount of bone formation when used as a supplement to autograft, it has also been shown to promote superior fusion in the absence of autograft, even in high-risk fusion models involving the use of nicotine or nonsteroidal antiinflam-matory agents. Both completed and ongoing clinical trials have demonstrated the efficacy of recombinant BMP, leading to the first BMP product being approved for clinical use earlier this year.

Animal models and clinical trials have also been used to evaluate the safety of BMPs. Although few complications have been reported, BMPs can induce heterotopic bone formation, especially when placed adjacent to exposed neural elements. Potentially more serious, antibody formation has been seen in up to 38% of patients in some clinical trials. No clinical sequelae have been reported despite the development of antibodies against BMP, a naturally occurring human protein implicated in processes other than osteoinduction.

The future directions of biological manipulation of the osteoinduction process include further understanding of the interactions of the BMP subtypes, the interactions of BMP with its receptors, and exploring other molecules capable of osteoinduction.

Purified bovine BMP extract and collagen for spine arthrodesis: preclinical safety and efficacy

STUDY DESIGN

Rabbit and nonhuman primate posterolateral intertransverse process spinal fusions were performed.

OBJECTIVES

To determine the preclinical safety and efficacy of bBMPx product (a composite of collagen and bovine bone morphogenetic protein extract) mixed with demineralized bone matrix for posterolateral intertransverse process spinal fusions.

SUMMARY OF BACKGROUND DATA

A dose response of bovine BMP extract with collagen in demineralized bone matrix has demonstrated spinal fusion to a rate of 100% in a rabbit spinal fusion model. This study furthers the research to demonstrate safety in the rabbit and efficacy of bovine BMP extract for spinal fusion applications in nonhuman primates. Additionally, preliminary human clinical data are presented.

METHODS

For the safety portion of the study, 45 New Zealand white rabbits underwent posterolateral intertransverse process spinal fusion after laminectomy. Nine additional rabbits served as nontreated control subjects. Graft material (autograft or bBMPx product) was placed in the gutters in 30 animals, and no material was used in 15 animals. The animals were observed for abnormal physical activity, then killed at 8, 29, or 57 days. Histologic evaluation was performed on explanted spines. In the nonhuman primate efficacy studies, 54 rhesus macaques also underwent bilateral posterolateral intertransverse process fusion. bBMPx product with varying bovine BMP extract doses was implanted bilaterally. The animals were killed at 4, 8, 12, 18, or 24 weeks. Plain radiograph, computed tomography scanning, and histology were performed.

RESULTS

The rabbit safety study demonstrated that any spinal cord compression or degeneration was caused by the inflammatory response after surgery and was equivalent in all groups. These issues resolved over time. Efficacy data demonstrated an autograft fusion rate of only 21% in the rhesus macaques. The bovine BMP extract demonstrated a dose response in which 3 mg per side gave twice the fusion rate as autograft.

CONCLUSIONS

bBMPx product is safe and effective as an autograft substitute for posterolateral intertransverse process spinal fusion. Clinical studies are underway.

Demineralized bone matrix and native bone morphogenetic protein in orthopaedic surgery

The recognition that demineralized bone matrix could induce bone formation when placed in mammalian skeletal muscle led to preclinical studies of crude native insoluble bone morphogenetic protein and noncollagenous protein, followed by the clinical application of demineralized bone matrix, chemosterilized autolyzed antigen-extracted allogenic bone, and autolyzed antigen-extracted allogenic bone matrix gelatin. Cultural norms and regulatory agencies influence the availability of different demineralized bone matrix preparations in different parts of the world, but there is continued interest in the biologic structure of native insoluble bone morphogenetic protein and noncollagenous protein aggregates and the applied science of osteoinduction and osteoconduction in reconstructive orthopaedic surgery. Demineralized bone matrix is not widely available in Asia, but tissue processing facilities in the United States distribute demineralized bone matrix materials with different carriers, handling properties, and possibly osteoinductive potential. The purpose of the current study was to review the development and use of various preparations of demineralized bone matrix materials.