Recombinant bone morphogenetic protein-7 as an intracorporal bone growth stimulator in unstable thoracolumbar burst fractures in humans: preliminary results

The study presented here is a pilot study in five patients with unstable thoracolumbar spine fractures treated with transpedicular OP-1 transplantation, short segment instrumentation and posterolateral fusion. Recombinant bone morphogenetic protein-7 in combination with a collagen carrier, also referred to as OP-1, has demonstrated ability to induce healing in long-bone segmental defects in dogs, rabbits and monkeys and to induce successful posterolateral spinal fusion in dogs without need for autogenous bone graft. Furthermore OP-1 has been demonstrated to be effective as a bone graft substitute when performing the PLIF maneuver in a sheep model. Five patients with single-level unstable burst fracture and no neurological impairment were treated with intracorporal OP-1 transplantation, posterior fixation (USS) and posterolateral fusion. One patient with osteomalacia and an L2 burst fracture had an additional intracorporal transplantation performed proximal to the instrumented segment, i.e. OP-1 into T 12 and autogenous bone into T 11. Follow-up time was 12–18 months. On serial radiographs, Cobb and kyphotic angles, as well as anterior, middle and posterior column heights, were measured. Serial CT scans were performed to determine the bone mineral density at fracture level. In one case, radiographic and CT evaluation after 3 and 6 months showed severe resorption at the site of transplantation, but after 12 months, new bone had started to fill in at the area of resorption. In all cases there was loss of correction with regard to anterior and middle column height and sagittal balance at the latest follow-up. These preliminary results regarding OP-1 as a bone graft substitute and stimulator of new bone formation have been disappointing, as the OP-1 device in this study was not capable of inducing an early sufficient structural bone support. There are indications to suggest that OP-1 application to a fracture site in humans might result in detrimental enhanced bone resorption as a primary event. Received: 13 February 1999 Revised: 4 August 1999 Accepted: 18 August 1999     

The effect of osteogenic protein-1 on the healing of segmental bone defects treated with autograft or allograft bone.

BACKGROUND: Large amounts of bone graft are frequently used to elicit the healing of bone defects resulting from reconstructive procedures. Autograft and allograft bone are often used, but each has its limitations. Bone morphogenetic proteins (BMPs) improve the healing of segmental bone defects treated with autograft or allograft. The objective of the present study was to determine the effect of implantation of a recombinant osteogenic protein-1 (OP-1) in combination with bone graft on the healing of a critical-sized (2.5-cm) segmental defect in canine ulnae. METHODS: Either autograft bone, allograft bone, osteogenic protein-1 (OP-1) mixed with type-1 bovine collagen, or various combinations of OP-1 and collagen (OP-1 device) mixed with allograft or autograft were implanted in the segmental bone defects. The combinations included 67% bone graft with 33% OP-1 device and 33% bone graft with 67% OP-1 device. The healing of the defects was assessed with radiographic, biomechanical, and histological studies. The animals were killed at twelve weeks postoperatively. RESULTS: The use of the OP-1 device alone or any combination of autograft or allograft bone and the OP-1 device demonstrated improved healing on radiographic, mechanical, and histological studies compared with that demonstrated after use of autograft or allograft bone alone. The highest radiographic and histological grades and the greatest mechanical strength were achieved with the use of 33% allograft and 67% OP-1 device, although no significant differences were observed among the different groups containing the OP-1 device. At twelve weeks postoperatively, the defects treated with any amount of the OP-1 device obtained greater mechanical strength than that obtained by autograft bone alone. CONCLUSIONS: Major bone defects may be treated with allograft bone combined with the OP-1 device, instead of autograft alone, to avoid complications associated with the use of autograft. The combination of allograft bone and the OP-1 device resulted in optimum healing of the defect, according to the radiographic, mechanical, and histological parameters measured in this study. CLINICAL RELEVANCE: The combination of freeze-dried allograft bone with the OP-1 device is an attractive graft material for the treatment of large bone defects. Although similar results were observed when autogenous bone graft was used in combination with the OP-1 device, the results of the present study suggest that allograft, because of its relatively unlimited supply, can be substituted without reduced efficacy. In addition, avoiding the need to harvest autogenous bone eliminates the additional operative time and risk associated with a second surgical procedure.     

The effect of osteogenic protein-1 in instrumented and noninstrumented posterolateral fusion in rabbits.

BACKGROUND CONTEXT: The use of rigid instrumentation combined with bone graft makes intuitive sense given the requirements for vascular ingrowth, bone formation and a stable environment for the cellular events of healing to develop. However, with the advances of potent osteoinductive growth factors, the role of internal fixation may come into question. Whether bone morphogenic proteins (BMPs) would benefit from a more "stable" spinal segment for bone production and modeling remains unknown. In addition, it is unknown whether BMP and rigid fixation may have an additive effect on fusion healing. PURPOSE: This study is proposed to test the hypothesis that rigid fixation in the lumbar spine would be advantageous to achieve fusion for autogenous bone grafting, but fusion would occur regardless of fixation with the use of osteogenic protein (OP)-1. STUDY DESIGN/SETTING: A histologic and radiographic analysis of BMP in a rabbit lumbar fusion model. METHODS: Thirty-two rabbits were randomized into four groups: 1) control animals: in situ posterolateral L5-L6 arthrodesis using autogenous iliac crest bone graft; 2) fixation group: posterolateral arthrodesis L5-L6 with autogenous bone graft and interspinous fixation; 3) OP-1 group: in situ posterolateral L5-L6 arthrodesis using OP-1 and 4) combined OP-1 and fixation group. Radiographic fusion analysis was performed with computed tomography scans at 3 and 12 weeks after surgery. Decalcified histology was performed to assess tissue morphology and cellularity. RESULTS: Minimal evidence of fusion was noted at 3 weeks with autograft or OP-1. By 12 weeks, all OP-1-treated animals had solid fusion, whereas no fusion was noted in autograft animals. The addition of fixation slightly increased radiographic fusion at 3 weeks in autograft and OP-1 groups but did not affect OP-1 animals at 12 weeks where all were fused. Decalcified histologic results confirmed the proliferative bone formation noted with OP-1 and the variable cellular response with autograft. CONCLUSIONS: The results of the present study suggest that the osteoinductive effect of OP-1 may be only minimally enhanced early in the bone healing process but does not appear to be affected in the long term by spinal fixation in the rabbit intertransverse fusion model. Fixation appeared to enhance early fusion in the autograft group.     

Distinct and Overlapping Patterns of Localization of Bone Morphogenetic Protein (BMP) Family Members and a BMP Type II Receptor During Fracture Healing in Rats

Bone morphogenetic proteins (BMPs) and their receptors (BMPRs) are thought to play an important role in bone morphogenesis. The purpose of this study was to determine the locations of BMP-2/-4, osteogenic protein-1 (OP-1, also termed BMP-7), and BMP type II receptor (BMPR-II) during rat fracture healing by immunostaining, and thereby elucidate the possible roles of the BMPs and BMPR-II in intramembranous ossification and endochondral ossification. In the early stage of fracture repair, the expression of BMP-2/-4 and OP-1 was strongly induced in the thickened periosteum near the fracture ends, and coincided with an enhanced expression of BMPR-II. On day 7 after fracture, staining for BMP-2/-4 and OP-1 immunostaining was increased in various types of chondrocytes, and was strong in fibroblast-like spindle cells and proliferating chondrocytes in endochondral bone. On day 14 after fracture, staining with OP-1 antibody disappeared in proliferating and mature chondrocytes, while BMP-2/-4 staining continued in various types of chondrocytes until the late stage. In the newly formed trabecular bone, BMP-2/-4 and OP-1 were present at various levels. BMPR-II was actively expressed in both intramembranous ossification and endochondral ossification. Additionally, immunostaining for BMP-2/-4 and OP-1 was observed in multinucleated osteoclast-like cells on the newly formed trabecular bone, along with BMPR-II. In reference to our previous study of BMP type I receptors (BMPR-IA and BMPR-IB), BMPR-II was found to be co-localized with BMPR-IA and BMPR-IB. BMP-2/-4 and OP-1 antibodies exhibited distinct and overlapping immunostaining patterns during fracture repair. OP-1 may act predominantly in the initial phase of endochondral ossification, while BMP-2/-4 acts throughout this process. Thus, these findings suggested that BMPs acting through their BMP receptors may play major roles in modulating the sequential events leading to bone formation.     

OP-1 Augments Glucocorticoid-inhibited Fracture Healing in a Rat Fracture Model

Glucocorticoids inhibit bone remodeling and fracture healing. We sought to determine whether osteogenic protein 1 (OP-1) can overcome this inhibition in a closed fracture model in the rat. Time-released prednisolone or placebo pellets were implanted subcutaneously; closed femoral fractures were created 2 weeks later in rats. Fractures received sham, OP-1 and collagen, or collagen-only implants. Femurs were harvested at 3, 10, 21, 28, and 42 days postfracture. Fractures were examined radiographically for amount of hard callus; mechanically for torque and stiffness (also expressed as a percentage of the contralateral intact femur); and histomorphometrically for amount of cartilaginous and noncartilaginous soft callus, hard callus, and total callus. Glucocorticoid administration inhibited fracture healing. The application of a devitalized Type I collagen matrix mitigated the inhibitory effects of prednisolone on fracture healing However, further increases in indices of fracture healing were observed when OP-1 was added to the collagen matrix compared with collagen alone. OP-1 and collagen was more effective than collagen alone.     

The Otto Aufranc Award. Strut allograft healing to the femur with recombinant human osteogenic protein-1

Allograft struts are used to reinforce the deficient proximal femur in hip arthroplasty or for fixation of a periprosthetic fracture. Although the use of strut grafts wired or cabled to the proximal femur generally has been successful, the time for healing is slow. The purpose of the current study was to determine whether cortical strut graft healing to the femur could be enhanced by the addition of recombinant human osteogenic protein-1. Fourteen adult dogs underwent bilateral onlay allograft strut procedures to the midfemur using stainless steel cables. In each animal one femur received 500 mg of osteogenic protein-1 device (2.5 mg recombinant human osteogenic protein-1/g Type I collagen) interposed between the graft and host bone. The results showed that the healing of cortical strut grafts to the femur was enhanced dramatically by the addition of the osteogenic protein-1 device. The sites treated with osteogenic protein-1 had significantly greater radiographic, histologic, and microradiographic scores at all times. Rapid formation of new bone and graft incorporation was observed in sites treated with the osteogenic protein-1 device. Strut healing with the osteogenic protein-1 device at 4 weeks postoperative was superior to the healing in control sites at 8 weeks. Improving and accelerating the course of cortical strut graft healing should provide a substantial clinical benefit in lowering the risk of graft nonunion and fracture and shorten the time of protected weightbearing and functional disability.     

Effects of OP-1 and PTH in a new experimental model for the study of metaphyseal bone healing.

The purpose of this study was to establish a reliable model of metaphyseal bone healing and to use this model to investigate the effect of recombinant human osteogenic protein 1 (rhOP-1; BMP-7) and parathyroid hormone fragment (PTH 1-34) on healing. A wedge-shaped osteotomy was created in the distal tibia of 16-week-old female New Zealand White rabbits (n = 20) and was bridged with a custom-made external fixator. Five experimental groups of four animals each were investigated. In groups 1-4 the osteotomy gap was filled with tricalcium phosphate (TCP), and the gap was left unfilled in group 5 ("normal healing"). In group 1, 200 microg OP-1 was mixed in with the TCP. Groups 2 and 3 received daily subcutaneous injections of 10 and 40 microg/kg PTH, respectively, beginning on postoperative day 1. Radiographs were taken weekly. Following sacrifice on postoperative day 28, peripheral quantitative computed tomography (pQCT), histology, and mechanical testing (axial compression and torsion) were performed. Only one animal failed to complete the full 4-week time course, and no infections were encountered. Bone healing occurred in all animals. OP-1 stimulated bone formation locally, while the lower dose of PTH enhanced bone formation systemically (p < 0.05). Tibiae treated with OP-1 exhibited higher torsional strength (p = 0.04) than those in the normal healing group. These results indicate that a reliable and reproducible surgical model of metaphyseal healing has been established. In addition, differences in systemic versus local effects of PTH and OP-1 in accelerating metaphyseal fracture healing were found.     

Osteogenic protein-1 in knee arthritis and arthroplasty

The use of graft materials to restore bone stock and promote healing and implant stabilization is a crucial part of total knee arthroplasty, especially in revision surgery. Recent research has centered on the use of osteoinductive materials to promote bone formation. Osteogenic proteins are members of a superfamily of proteins called transforming growth factor-beta that, either alone or in combination with other regulatory molecules, induce new bone formation. The cloning and genetic expression of recombinant human osteogenic proteins has led to production of quantities sufficient for their clinical use. Recombinant human osteogenic protein-1 has been combined with bone-derived Type I collagen for delivery to an implant site. Preclinical studies have shown that the osteoinductive capacity of autograft and allograft bone and bone graft substitute materials can be notably improved with the addition of osteogenic protein-1. The use of this protein consistently improved the amount and rate of new bone formation compared with graft alone, resulting in earlier graft incorporation and consolidation. In addition, because osteogenic proteins are chondrogenic, they also may have a role in the treatment of cartilage injury and degeneration. Osteogenic protein-1 has been shown to induce hyalinelike cartilage repair of full thickness osteochondral defects in animal models with no degradation of the tissue with time. Although no detailed clinical studies in knee surgery have been reported with the use of osteogenic protein-1, in anecdotal cases its use alone and with bone graft materials indicate results consistent with those obtained in preclinical studies.     

Shock wave application enhances pertussis toxin protein-sensitive bone formation of segmental femoral defect in rats.

Extracorporeal shock waves (ESWs) elicit a dose-dependent effect on the healing of segmental femoral defects in rats. After ESW treatment, the segmental defect underwent progressive mesenchymal aggregation, endochondral ossification, and hard callus formation. Along with the intensive bone formation, there was a persistent increase in TGF-beta1 and BMP-2 expression. Pretreatment with pertussis toxin reduced ESW-promoted callus formation and gap healing, which presumably suggests that Gi proteins mediate osteogenic signaling. INTRODUCTION: Extracorporeal shock waves (ESWs) have previously been used to promote bone repair. In our previous report, we found that ESWs promoted osteogenic differentiation of mesenchymal cells through membrane perturbation and activation of Ras protein. In this report, we show that ESWs elicit a dose-dependent effect on the healing of segmental defects and that Gi proteins play an important role in mediating ESW stimulation. MATERIALS AND METHODS: Rats with segmental femoral defects were subjected to ESW treatment at different energy flux densities (EFD) and impulses. Bone mass (mineral density and calcium content), osteogenic activities (bone alkaline phosphatase activity and osteocalcin content), and immunohistochemistry were assessed. RESULTS: An optimal ESW energy (500 impulses at 0.16 mJ/mm2 EFD) stimulated complete bone healing without complications. ESW-augmented healing was characterized by significant increases (p < 0.01) in callus size, bone mineral density, and bone tissue formation. With exposure to ESW, alkaline phosphatase activity and osteocalcin production in calluses were found to be significantly enhanced (p < 0.05). After ESW treatment, the histological changes we noted included progressive mesenchymal aggregation, endochondral ossification, and hard callus formation. Intensive bone formation was associated with a persistent increase in transforming growth factor-beta 1 (TGF-beta1) and bone morphogenetic protein-2 (BMP-2) expression, suggesting both growth factors were active in ESW-promoted bone formation. We also found that pertussis toxin, an inhibitor of membrane-bound Gi proteins, significantly reduced (p < 0.01) ESW promotion of callus formation and fracture healing. CONCLUSION: ESW treatments enhanced bone formation and the healing of segmental femoral defects in rats. It also seems likely that TGF-beta1 and BMP-2 are important osteogenic factors for ESW promotion of fracture healing, presumably through Gi protein-mediated osteogenic signaling.     

No augmentation of morselized and impacted bone graft by OP-1 in a weight-bearing model

Introduction: Impacted morselized bone allograft is thought to be remodeled to a great extent. We have previously shown that load-bearing increases the remodeling of impacted morselized bone allografts in a rabbit knee prosthesis model. Bone Morphogenic Proteins (BMPs) also stimulate bone formation and bone allograft remodeling. In this study, our aim was to determine whether it was possible to increase further the remodeling of impacted morselized bone allografts by combining load-bearing with a BMP. Experiment: A solution of Osteogenic Protein-1 (OP-1, also called BMP-7) was added to freeze-dried bone allograft chips before impaction grafting in our rabbit knee prosthesis model. 23 skeletally mature rabbits received an uncemented tibial knee prosthetic component inserted into a bed of impacted morselized bone allograft. 12 rabbits were given OP-1-treated allograft (50 µg OP-1 per gram allograft), and 11 rabbits vehicle-treated allograft. Each rabbit received mean 0.53 g graft. The rabbits were killed after 3 or 6 weeks and the grafted region was examined by histomorphometric assessment of the volume fraction of newly formed bone and remaining graft. Results and interpretation: We found that OP-1 did not increase the bone density (graft plus new bone) to any substantial extent. However, we can not exclude that this might be due to a carrier problem, since the OP-1 was added as a solution directly to the dry graft.     

No augmentation of morselized and impacted bone graft by OP-1 in a weight-bearing model

INTRODUCTION: Impacted morselized bone allograft is thought to be remodeled to a great extent. We have previously shown that load-bearing increases the remodeling of impacted morselized bone allografts in a rabbit knee prosthesis model. Bone Morphogenic Proteins (BMPs) also stimulate bone formation and bone allograft remodeling. In this study, our aim was to determine whether it was possible to increase further the remodeling of impacted morselized bone allografts by combining load-bearing with a BMP. EXPERIMENT: A solution of Osteogenic Protein-1 (OP-1, also called BMP-7) was added to freeze-dried bone allograft chips before impaction grafting in our rabbit knee prosthesis model. 23 skeletally mature rabbits received an uncemented tibial knee prosthetic component inserted into a bed of impacted morselized bone allograft. 12 rabbits were given OP-1-treated allograft (50 microg OP-1 per gram allograft), and 11 rabbits vehicle-treated allograft. Each rabbit received mean 0.53 g graft. The rabbits were killed after 3 or 6 weeks and the grafted region was examined by histomorphometric assessment of the volume fraction of newly formed bone and remaining graft. RESULTS AND INTERPRETATION: We found that OP-1 did not increase the bone density (graft plus new bone) to any substantial extent. However, we can not exclude that this might be due to a carrier problem, since the OP-1 was added as a solution directly to the dry graft.     

Osteoinductive agents in reconstructive hip surgery: a look forward

The use of autograft and allograft material to restore bone stock and promote healing and implant stabilization is a crucial part of total hip arthroplasty, especially in the revision situation. Recent research has centered on the use of osteoinductive materials such as osteogenic proteins or bone morphogenetic proteins to promote bone formation. These proteins are members of the transforming growth factor-beta superfamily of proteins that either alone or in combination with other regulatory molecules induce new bone formation. The cloning and genetic expression of recombinant human bone proteins has led to production of quantities sufficient for their clinical development. Preclinical studies have shown that the osteoinductive capacity of autograft and allograft bone can be improved with the addition of osteogenic proteins. Although these proteins are effective alone, their use with cancellous and cortical allograft and autograft consistently improved the amount and rate of new bone formation compared with graft alone resulting in earlier graft incorporation and consolidation. When placed in defects adjacent to porous acetabular components, the use of an osteogenic protein resulted in earlier defect healing and improved component fixation by the enhancement of bone ongrowth and ingrowth. Although no detailed clinical studies have been reported to date, an anecdotal report of their use with and without bone graft indicate results consistent with those obtained in preclinical studies.     

A combination of bisphosphonate and BMP additives in impacted bone allografts

OP-1 increases bone ingrowth distance of new bone into allografts (T?gil et al. 2000), but the bone density after incorporation may be reduced by an increase in resorption (H?istner et al. 2000). Bisphosphonates inactivate osteoclasts and can be used to increase allograft bone density after incorporation (Aspenberg and Astrand 2002). A combination of locally-applied bisphosphonate and OP-1 in the graft could therefore be expected to increase both new bone ingrowth and density. We tested this by using a rat bone chamber model. OP-1 alone increased the ingrowth distance of bone. Clodronate increased final bone density greatly, but reduced the ingrowth distance of new bone into grafts that were extremely impacted. This reduction was improved by adding OP-1. Regardless of graft density, combinations of OP-1 and clodronate included a high final bone density, but the ingrowth distances were shorter than with OP-1 alone. These data indicate that new bone and tissue ingrowth into a compacted graft depends on resorption and that resorption is a prerequisite for the stimulating effect of OP-1 in this experimental set-up. Although the problems associated with the use of OP-1 in impaction grafting may be solved by adding a bisphosphonate, some of the benefits of OP-1 can be lost.     

In vitro and in vivo optimization of impaction allografting by demineralization and addition of rh-OP-1.

Impaction allografting is a bone tissue engineering technique currently used in lower limb reconstruction orthopedic surgery. Our hypothesis was that biological optimization can be achieved by demineralization and addition of osteogenic protein-1 (OP-1) to the allograft. The objective of our in vitro study was to evaluate human mesenchymal stem cell (MSC) proliferation (Alamar Blue assay, titrated thymidine assay, total DNA Hoechst 33258, and scanning electron microscopy) and osteogenic differentiation (alkaline phosphatase assay) in two types of impacted carrier, namely, demineralized bone matrix (DBM) and insoluble collagenous bone matrix (ICBM), with or without OP-1. The objective in vivo was to compare the osteogenic potential of impacted DBM with or without OP-1, with that of impacted fresh frozen allograft (FFA), again with or without OP-1. DBM + OP-1 optimized osteoinduction and significantly improved (p < 0.05) proliferation and differentiation in comparison to the majority of all other graft preparation in vitro. In addition, DBM + OP-1 was significantly superior, with regard to osteogenesis, compared to the impacted FFA alone (p < 0.001), FFA + OP-1 (p = 0.01) and DBM alone (p = 0.02) in vivo. We propose that partial demineralization and addition of OP-1 provides a good method for improving the osteoinductive properties of fresh allograft currently used in the impaction grafting technique.     

A combination of bisphosphonate and BMP additives in impacted bone allografts

OP-1 increases bone ingrowth distance of new bone into allografts (Tägil et al. 2000), but the bone density after incorporation may be reduced by an increase in resorption (Höstner et al. 2000). Bisphosphonates inactivate osteoclasts and can be used to increase allograft bone density after incorporation (Aspenberg and Åstrand 2002). A combination of locally-applied bisphosphonate and OP-1 in the graft could therefore be expected to increase both new bone ingrowth and density. We tested this by using a rat bone chamber model. OP-1 alone increased the ingrowth distance of bone. Clodronate increased final bone density greatly, but reduced the ingrowth distance of new bone into grafts that were extremely impacted. This reduction was improved by adding OP-1. Regardless of graft density, combinations of OP-1 and clodronate included a high final bone density, but the ingrowth distances were shorter than with OP-1 alone. These data indicate that new bone and tissue ingrowth into a compacted graft depends on resorption and that resorption is a prerequisite for the stimulating effect of OP-1 in this experimental set-up. Although the problems associated with the use of OP-1 in impaction grafting may be solved by adding a bisphosphonate, some of the benefits of OP-1 can be lost.     

A comparative dose-response study of cartilage-derived morphogenetic protein (CDMP)-1, -2 and -3 for tendon healing in rats.

Cartilage-derived morphogenetic proteins (CDMPs), belonging to the bone morphogenetic protein (BMP) family, are known to be cartilage and bone inducers as well as to induce tendon and ligament-like tissue. In this study we investigated the influence of CDMP-1, -2 or -3 at four different doses (0, 0.4, 2 and 10 microg) on tendon healing in a rat model, as well as differences in osteogenesis between the different CDMPs and doses.In 110 rats, a 3 mm segment of the Achilles tendon was removed via a 2 mm skin incision. CDMP-1, -2 or -3 was injected into the defect 6 h postoperative. The rats were killed 8 days after operation. The tendon regenerates were tested biomechanically. There was a significant dose-related increase in strength and stiffness with all three CDMPs, but no difference between the CDMPs was found.Another 50 rats were used to compare the highest dose of the CDMPs with controls and osteogenic protein 1 (OP-1), as regards cartilage or bone formation after 4 weeks. Cartilage occurred in all groups, including the controls. Some specimens in all groups contained bone, except the controls. No difference between the CDMPs could be demonstrated. The CDMP-1, CDMP-3 and OP-1 groups contained significantly more calcium than controls. Only the CDMP-2 group and the controls contained significantly less calcium than the OP-1 group.In conclusion, the three CDMPs appeared similar as regards improvement of tendon repair and osteogenicity in this setting.     

Osteogenic activity of OP-1 bone morphogenetic protein (BMP-7) in a human fibular defect.

We performed a prospective, randomised double-blind study in 24 patients undergoing high tibial osteotomy to evaluate the effectiveness of human recombinant osteogenic protein (OP-1) on a collagen type-I carrier in a critically-sized fibular defect. The study had two phases, each evaluated by clinical, radiological and DEXA methods during the first postoperative year. The first concerned the validation of the model of the fibular defect, using positive (demineralised bone) and negative (untreated) controls. The second phase concerned the osteogenic potential of OP-1 on collagen type-I v collagen type-I alone. The results of the first phase established the critically-sized nature of the defect. In the untreated group no bony changes were observed while, in the demineralised bone group, formation of new bone was visible from six weeks onwards. The results of the second phase showed no significant formation of new bone in the presence of collagen alone, while in the OP-1 group, all patients except one showed formation of new bone from six weeks onwards. This proved the osteogenic activity of OP-1 in a validated critically-sized human defect.     

Low-intensity pulsed ultrasound affects RUNX2 immunopositive osteogenic cells in delayed clinical fracture healing

IntroductionOsteogenic cell proliferation and differentiation play an important role in adequate fracture healing, and is target for osteoinductive therapies in delayed fracture healing. The aim of this study was to investigate whether low-intensity pulsed ultrasound enhances fracture healing at the tissue level in patients with a delayed union of the osteotomized fibula through an effect on the presence of RUNX2 immunopositive osteogenic cells. The effect was studied in both atrophic and hypertrophic delayed unions.Materials and methodsBiopsies were obtained from 6 female and 1 male patient (age 43–63) with a delayed union of the osteotomized fibula after a high tibial osteotomy treated for 2–4 months with or without low-intensity pulsed ultrasound in a randomized prospective double-blind placebo-controlled trial. Immunolocalization of RUNX2 protein was performed to identify osteogenic cells. Histomorphometrical analysis was performed to determine the number of cells expressing RUNX2 located within and around the newly formed woven bone at the fracture end (area of new bone formation), and up to 3 mm distant from the fracture end.ResultsCells expressing RUNX2 were present in all histological sections of control and low-intensity pulsed ultrasound-treated bone evaluated. Within the area of new bone formation, RUNX2 immunopositive cells were found in the undifferentiated soft connective tissue, at the bone surface (presumably osteoblasts), and within the newly formed woven bone. Low-intensity pulsed ultrasound treatment of fibula delayed unions significantly reduced the number of RUNX2 immunopositive cells within the soft connective tissue at the fracture ends, whereas the number of RUNX2 immunopositive cells at the bone surface was not affected. The number of RUNX2 immunopositive cells was similar for the atrophic and hypertrophic delayed unions.ConclusionsImmunolocalization of RUNX2 positive cells in delayed unions of the fibula reveals that delayed clinical fracture healing does not result in impairment of osteogenic cell proliferation and/or differentiation at the tissue level, even if delayed unions are clinically regarded as atrophic. Reduced number of osteogenic RUNX2 immunopositive cells within the soft connective tissue, and unchanged number of RUNX2 immunopositive cells at the bone surface, implicate that low-intensity pulsed ultrasound does not increase osteogenic cell presence, but likely affects osteogenic cell differentiation.     

A 2-year follow-up pilot study evaluating the safety and efficacy of op-1 putty (rhbmp-7) as an adjunct to iliac crest autograft in posterolateral lumbar fusions

The ability of bone morphogenetic proteins (BMPs) to induce bone formation has led to a multitude of investigations into their use as bone graft substitutes in spinal surgery. The purpose of this multi-center clinical pilot study was to evaluate the safety and efficacy of BMP-7 (osteogenic protein 1, OP-1), in the form of a putty, combined with autograft for intertransverse process fusion of the lumbar spine in patients with symptomatic spinal stenosis and degenerative spondylolisthesis following spinal decompression. Twelve patients with spinal stenosis and degenerative lumbar spondylolisthesis underwent a laminectomy and partial or complete medial facetectomy as required for decompression of the neural elements, followed by an intertransverse process fusion by placing iliac crest autograft and OP-1 putty between the decorticated transverse processes. No instrumentation was used. Patients were followed clinically using the Oswestry scale and SF-36 outcome forms, and radiographically using static and dynamic radiographs to assess their fusion status over a 2-year period. Independent and blinded radiologists assessed the films for the presence of bridging bone between the transverse processes and measured translation and angulation on dynamic films using digital calipers. Radiographic outcome was compared to a historical control (autograft alone fusion without instrumentation for the treatment of degenerative spondylolisthesis). All adverse events were recorded prospectively. The results showed eight of the nine evaluable patients (89%) obtained at least a 20% improvement in their preoperative Oswestry score, while five of ten patients (50%) with radiographic follow-up achieved a solid fusion by the criteria used in this study. Bridging bone on the anteroposterior film was observed in seven of the ten patients (70%). No systemic toxicity, ectopic bone formation, recurrent stenosis or other adverse events related to the OP-1 putty implant were observed. A successful fusion was observed in slightly over half the patients in this study, using stringent criteria without adjunctive spinal instrumentation. This study did not demonstrate the statistical superiority of OP-1 combined with autograft over an autograft alone historical control, in which the fusion rate was 45%. There were no adverse events related to the OP-1 putty implant in this study, which supports findings in other studies suggesting the safety of bone morphogenetic proteins in spinal surgery.     

Manipulation of the anabolic and catabolic responses with OP-1 and zoledronic acid in a rat critical defect model.

Bone repair involves both anabolic and catabolic responses. We hypothesized that anabolic treatment with OP-1 (BMP-7) and anti-catabolic treatment with zoledronic acid could be synergistic. In a rat critical defect, this combination therapy produced significant increases in new bone volume and strength. INTRODUCTION: When used to augment bone healing, osteogenic protein 1 (OP-1/BMP-7) and other BMPs stimulate the anabolic response, inducing osteoblast recruitment, differentiation, and bone production. However, BMPs can also upregulate catabolism by direct stimulation of osteoclasts and indirectly by osteoblasts through RANKL/RANK. We hypothesized that if such osteoclastic upregulation were modulated by zoledronic acid (ZA), the combination of OP-1 and ZA should produce increased new bone over OP-1 alone. MATERIALS AND METHODS: Rats with a surgically induced 6-mm femoral critical size defect were separated into five dosing groups: Carrier, Carrier + ZA, OP-1, OP-1 + ZA, and OP-1 + ZA administered 2 weeks after surgery (2W). Carrier +/- 50 microg OP-1 was placed in the defect, and 0.1 mg/kg ZA or saline was administered subcutaneously. Bone repair was analyzed by radiographs, QCT, mechanical testing, histology, and histomorphometry. RESULTS: Carrier alone and Carrier ZA groups did not unite by 8 weeks. Radiological union occurred in all OP-1 groups but was tenuous in some animals treated with OP-1 alone. BMC was increased by 45% in the OP-1 ZA group and 96% in the OP-1 ZA 2W group over OP-1 alone (p < 0.01). Callus volume increased over OP-1 alone by 45% and 86% in the OP-1 ZA and OP-1 ZA 2W groups, respectively (p < 0.01). The increased callus volume in the OP-1 ZA 2W group translated to increases in strength of 107% and stiffness of 148% (p < 0.05). BFR was not significantly different between OP-1 groups regardless of ZA treatment. CONCLUSIONS: ZA treatment significantly increased the BMC, volume, and strength of OP-1-mediated callus in a critical size defect in rats at 8 weeks. Thus, modulation of both anabolic and catabolic responses may optimize the amount and mineral content of callus produced, which could be of clinical benefit in obtaining bone union.