Maximizing bone formation in posterior spine fusion using rhBMP‐2 and zoledronic acid in wild type and NF1 deficient mice

Spinal pseudarthrosis is a well described complication of spine fusion surgery in NF1 patients. Reduced bone formation and excessive resorption have been described in NF1 and anti‐resorptive agents may be advantageous in these individuals. In this study, 16 wild type and 16 Nf1^+/? mice were subjected to posterolateral fusion using collagen sponges containing 5 µg rhBMP‐2 introduced bilaterally. Mice were dosed twice weekly with 0.02 mg/kg zoledronic acid (ZA) or sterile saline. The fusion mass was assessed for bone volume (BV) and bone mineral density (BMD) by microCT. Co‐treatment using rhBMP‐2 and ZA produced a significant increase (p < 0.01) in BV of the fusion mass compared to rhBMP‐2 alone in both wild type mice (+229%) and Nf1^+/? mice (+174%). Co‐treatment also produced a significantly higher total BMD of the fusion mass compared to rhBMP‐2 alone in both groups (p < 0.01). Despite these gains with anti‐resorptive treatment, Nf1^+/? deficient mice still generated less bone than wild type controls. TRAP staining on histological sections indicated an increased osteoclast surface/bone surface (Oc.S/BS) in Nf1^+/? mice relative to wild type mice, and this was reduced with ZA treatment. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1090–1094, 2014.

     

Preliminary experience with the combined use of recombinant bone morphogenetic protein and bisphosphonates in the treatment of congenital pseudarthrosis of the tibia

Purpose  

Congenital pseudarthrosis of the tibia (CPT) is a rare but serious disorder in children. No single approach has clearly emerged as superior in terms of operative procedure, fixation, optimal time for surgery or adjunctive pharmaceutical intervention. CPT is frequently associated with neurofibromatosis type 1 (NF1), a condition featuring deficient bone anabolism and excessive catabolism. We have therefore combined the use of bone morphogenetic proteins (BMP) with bisphosphonates (BP) as an adjunct to surgical intervention.     

Recombinant human bone morphogenetic protein‐type 2 (rhBMP‐2) enhances local bone formation in the lumbar spine of osteoporotic sheep

The failure of orthopedic implants in osteoporotic patients is attributed to the lack of sufficient bone stock and regenerative capacity but most treatments for osteoporosis fail to address this issue. rhBMP‐2 is known to promote bone formation under normal conditions but has not been used clinically in the osteoporotic condition. Osteoporosis was induced in 19 ewes using ovariectomy, low calcium diet, and steroid injection. After induction, the steroid was withdrawn and pellets containing inert carrier with rhBMP‐2 in either slow or fast‐release formulation were implanted into the lumbar vertebrae of each animal. After 2, 3, and 6 months the spines were harvested and assessed for changes in BMD and histomorphometric indices. BMD did not change after cessation of steroid treatment. After 2 months BV/TV increased in the vicinity of the pellets containing the fast‐release rhBMP‐2 and was sustained for the duration of the study. Focal voids surrounding all implants, particularly the slow‐release formulation, were observed initially but resolved with time. Increased BV/TV adjacent to rhBMP‐2 pellets suggests it could be used for localized treatment of osteoporosis. Refinement of the delivery system and supplementary treatments may be necessary to overcome the initial catabolic effects of rhBMP‐2. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1390–1397, 2013.     

Models of tibial fracture healing in normal and Nf1‐deficient mice

Delayed union and nonunion are common complications associated with tibial fractures, particularly in the distal tibia. Existing mouse tibial fracture models are typically closed and middiaphyseal, and thus poorly recapitulate the prevailing conditions following surgery on a human open distal tibial fracture. This report describes our development of two open tibial fracture models in the mouse, where the bone is broken either in the tibial midshaft (mid‐diaphysis) or in the distal tibia. Fractures in the distal tibial model showed delayed repair compared to fractures in the tibial midshaft. These tibial fracture models were applied to both wild‐type and Nf1‐deficient (Nf1^+/?) mice. Bone repair has been reported to be exceptionally problematic in human NF1 patients, and these patients can also spontaneously develop tibial nonunions (known as congenital pseudarthrosis of the tibia), which are recalcitrant to even vigorous intervention. pQCT analysis confirmed no fundamental differences in cortical or cancellous bone in Nf1‐deficient mouse tibiae compared to wild‐type mice. Although no difference in bone healing was seen in the tibial midshaft fracture model, the healing of distal tibial fractures was found to be impaired in Nf1^+/? mice. The histological features associated with nonunited Nf1^+/? fractures were variable, but included delayed cartilage removal, disproportionate fibrous invasion, insufficient new bone anabolism, and excessive catabolism. These findings imply that the pathology of tibial pseudarthrosis in human NF1 is complex and likely to be multifactorial. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:1053–1060, 2008     

Effect of recombinant human bone morphogenetic protein‐2 on a novel lung cancer spine metastasis model in rodents

Lung cancer is the second most prevalent cancer. Spinal metastases are found in 30–90% of patients with death attributed to cancer. Due to bony destruction caused by metastases, surgical intervention is often required to restore spinal alignment and stability. While some research suggests that BMP‐2 may possess tumorigenic effects, other studies show possible inhibition of cancer growth. Thirty‐six athymic rats underwent intraosseous injection of lung adenocarcinoma cells into the L5 vertebral body. Cells were pre‐treated with vehicle control (Group A) or rhBMP‐2 (Group B) prior to implantation. At 4 weeks post‐implantation, in vivo bioluminescent imaging (BLI) was performed to confirm presence of tumor and quantify signal. Plain radiographs and microComputed Tomography (microCT) were employed to establish and quantitate osteolysis. Histological analysis characterized pathologic changes in the vertebral body. At 4 weeks post‐implantation, BLI showed focal signal in the L5 vertebral body in 93% of Group A animals and 89% of Group B animals. Average tumor burden by BLI radiance was 7.43 × 10³ p/s/cm²/sr (Group A) and 1.11 × 10⁴ p/s/cm²/sr (Group B). Radiographs and microCT demonstrated osteolysis in 100% of animals showing focal BLI signal. MicroCT demonstrated significant bone loss in both groups compared to age‐matched controls but no difference between study groups. Histological analysis confirmed tumor invasion in the L5 vertebral body. These findings provide a reliable in vivo model to study isolated spinal metastases from lung cancer. Statement of Clinical Significance: The data support the notion that exposure to rhBMP‐2 does not promote the growth of A549 lung cancer spine lesions. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1274–1281, 2016.     

Open tibial fractures grade IIIC treated successfully with external fixation,negative‐pressure wound therapy and recombinant human bone morphogenetic protein 7

The aim of the therapy in open tibial fractures grade III was to cover the bone with soft tissue and achieve healed fracture without persistent infection. Open tibial fractures grade IIIC with massive soft tissue damage require combined orthopaedic, vascular and plastic–reconstructive procedures. Negative‐pressure wound therapy (NPWT), used in two consecutive cases with open fracture grade IIIC of the tibia diaphysis, healed extensive soft tissue defect with exposure of the bone. NPWT eventually allowed for wound closure by split skin graft within 21–25 days. Ilizarov external fixator combined with application of recombinant human bone morphogenetic protein‐7 at the site of delayed union enhanced definitive bone healing within 16–18 months.     

Modeling bone morphogenetic protein and bisphosphonate combination therapy in wild‐type and Nf1 haploinsufficient mice

Recombinant bone morphogenetic proteins (BMPs) show promise in treating the orthopedic complications associated with neurofibromatosis type 1 (NF1), such as congenital pseudarthrosis of the tibia. Minimal scientific information regarding the effects of BMP in the context of NF1 is available. As abnormalities in both bone formation and resorption have been documented in Nf1‐deficient mice, we hypothesized that inadequate BMP‐induced bone formation could be augmented by cotreatment with the bisphosphonate zoledronic acid (ZA). First, primary osteoblasts isolated from wild type (Nf1^+/+) and Nf1‐deficient (Nf1^+/?) mice were cultured in the presence and absence of BMP‐2. While Nf1^+/? cells exhibited less osteogenic potential than Nf1^+/+ cells, alkaline phosphatase expression and matrix mineralization for both genotypes were enhanced by BMP‐2 treatment. To model this response in vivo, 20 µg BMP‐2 was implanted intramuscularly into the quadriceps of mice to induce heterotopic bone. Radiographs revealed significantly less net bone formation in Nf1^+/? mice compared to Nf1^+/+ controls. To test the effect of an antiresorptive agent, mice were cotreated twice weekly from postoperative day 3 with 0.02 mg/kg ZA or with saline. ZA treatment led to a synergistic increase in the amount of heterotopic bone in both Nf1^+/+ and Nf1^+/? mice compared with saline controls, as measured by DEXA and histomorphometry. Thus, the anabolic deficiency noted in Nf1^+/? mice is amenable to stimulation by BMP‐2, but mineralized tissue formation remains below that of Nf1^+/+ controls. Bisphosphonate combination therapy is superior to BMP therapy alone in terms of net bone production in vivo in both wild‐type and Nf1‐deficient mice. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:65–74, 2008     

Effects of sequential treatment with intermittent parathyroid hormone and zoledronic acid on particle‐induced implant loosening: Evidence from a rat model

Particle‐induced implant loosening is a major challenge to long‐term survival of joint prostheses. Administration of intermittent parathyroid hormone (PTH) has shown potential in the treatment of cases of early‐stage periprosthetic osteolysis, while sequential administration of intermittent PTH (iPTH) and bisphosphonates (Bps) has achieved significant effects on treatment of postmenopausal osteoporosis. The objective of this study was to determine whether sequential treatment could preserve bone mass and implant fixation during a pathological course of peri‐implant osteolysis in a rat model. Ninety male Sprague Dawley rats were randomly divided into nine groups, four of which were used for confirmation of establishment of the peri‐implant osteolysis model at two time points, while the other five were used to determine the efficiency of the sequential treatment on peri‐implant osteolysis. Implant fixation and peri‐implant bone mass were evaluated using biomechanical testing, micro‐CT analysis, and histology at 6 and 12 weeks postoperative. The biomechanical test demonstrated that the maximum loading force during a push‐out test was significantly elevated in the sequential treatment group compared to the osteolysis group and iPTH withdrawal group at 12 weeks. Peri‐implant bone morphology also indicated a robust increase in bone volume in the sequential treatment group. Sequential administration of iPTH and Bps was effective in preventing experimental peri‐implant osteolysis, resulting in improved implant fixation and increased peri‐implant bone volume. Clinical significance: The innovative application of sequential treatment in peri‐implant osteolysis could be used clinically to improve the prognosis of patients with early‐stage periprosthetic osteolysis. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1489–1497, 2019.     

Effect of rhBMP‐2 on tibial plateau fractures in a canine model

This study was to determine the efficacy of recombinant human bone morphogenetic protien‐2 (rhBMP‐2)/calcium phosphate matrix (CPX) paste to accelerate healing in a canine articular fracture model with associated subchondral defect. rhBMP‐2/CPX (BMP), CPX alone (CPX) or autogenous bone graft (ABG) was administered to a canine articular tibial plateau osteotomy with a subchondral defect in each of 21 female dogs. The unoperated contralateral limbs served as controls. Ground reaction forces, synovial fluid, radiographic changes, mechanical testing, bone density, and histology of bone and synovium were analyzed at 6 weeks after surgery. Radiographic analysis demonstrated that the BMP and CPX groups showed improved bony healing compared to the ABG group at week 6. Histomorphometric analysis demonstrated that the BMP group had significantly increased trabecular bone volume compared to the CPX and ABG groups. Mechanical testing revealed that the BMP group had significantly greater maximum failure loads than the ABG group. Histological analysis demonstrated that the BMP group had significantly less sub‐synovial inflammation than CPX group. This study demonstrated that rhBMP‐2/CPX accelerated healing of articular fractures with subchondral defect compared to ABG in most of the parameters evaluated, and had less subsynovial inflammation than the CPX alone in a canine model. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 27: 466–471, 2009     

ACL reconstruction using bone‐tendon‐bone graft engineered from the semitendinosus tendon by injection of recombinant BMP‐2 in a rabbit model

We attempted to generate a bone‐tendon‐bone structure by injecting human‐type recombinant human bone morphogenetic protein‐2 (rhBMP‐2) into the semitendinosus tendon, and an anterior cruciate ligament (ACL) defect was reconstructed by grafting the engineered bone‐tendon‐bone graft. Two ossicles with a separation distance of 1 cm were generated within the left semitendinosus tendon of a rabbit 6 weeks after the injection of rhBMP‐2 (15 µg at each site). The engineered bone‐tendon‐bone graft was transplanted in order to reconstruct the ACL by passing the graft through the bone tunnels. In the control group, the ACL was reconstructed with the semitendinosus tendon without BMP‐2 using the same methods as those used in the experimental group. The animals were harvested at 4 or 8 weeks after surgery and examined by radiographic, histological, and biomechanical methods. In the experimental group, ossicles in the bone‐tendon‐bone graft were successfully integrated into the host bone of the femur and tibia. Histological analysis revealed that characteristic features identical to the normal direct insertion morphology had been restored. Biomechanical pull‐out testing showed that the ultimate failure load and stiffness of the reconstructed ACL in the experimental group were significantly higher than those in the control group at both 4 and 8 weeks (p < 0.05). These results indicate the potential of regenerative reconstruction of the ACL, and the reconstruction resulted in the restoration of morphology and function equivalent to those of the normal ACL. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1923–1930, 2011     

Controlled‐release of bone morphogenetic protein‐2 from a microsphere coating applied to acid‐etched Ti6AL4V implants increases biological bone growth in vivo

A central clinical challenge regarding the surgical treatment of bone and joint conditions is the eventual loosening of an orthopedic implant as a result of insufficient bone ingrowth at the bone–implant interface. We investigated the in vivo effectiveness of a coating containing recombinant human bone morphogenetic protein‐2 (rhBMP‐2)‐loaded microspheres applied to acid‐etched Ti6Al4V cylinders for implantation. Three groups of rabbits (24 per group) were used for implantation: (1) acid‐etched Ti6Al4V implants coated with a mixture of rhBMP‐2‐loaded microspheres (125 ng rhBMP‐2/mg microspheres) and α‐butyl cyanoacrylate; (2) acid‐etched, uncoated implants; and (3) bare, smooth uncoated implants. After implantation, 12 rabbits from each group were used for bone ingrowth determination at 4, 5, 6, 7, 8, and 12 weeks (2 rabbits per time point), while the remainder were used for histological analysis and push‐out testing at 12 weeks. Scanning electron microscopy showed significant improvement in bone growth of the rhBMP‐2 microspheres/α‐butyl cyanoacrylate group compared with the other groups (p < 0.01). Histological analysis and push‐out testing also demonstrated enhanced bone growth of the rhBMP‐2 group over that in the other two groups (p < 0.01). The rhBMP‐2 group showed the most significant bone growth, suggesting that coating acid‐etched implants with a mixture of rhBMP‐2‐loaded microspheres and α‐butyl cyanoacrylate may be an effective method to improve the osseointegration of orthopedic implants. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:744–751, 2014.     

Recombinant human bone morphogenetic protein‐7 enhances fracture healing in an ischemic environment

Ischemia predisposes orthopedic trauma patients to delayed fracture healing or nonunion. The goal of this study was to test the ability of bone morphogenetic protein 7 (BMP7) to stimulate fracture repair in an ischemic environment. Ischemic fractures were generated in male adult mice by resecting the femoral artery prior to the creation of a nonstabilized tibia fracture. Recombinant human BMP7 (rhBMP7, 50 µg) was injected into the fracture site immediately after surgery. At 7 days after injury, more tissue vascularization was observed in rhBMP7 treated fractures. Histomorphometric analyses revealed that rhBMP7 induced more cartilage at day 7, more callus and bone at days 14 and 28, and more adipose tissue and fibrous tissue at days 7, 14, and 28 compared to controls (n = 5/group/time). At day 28, all fractures treated with rhBMP7 (50 µg, n = 5) healed, whereas only three of five control fractures exhibited slight bony bridging. In addition, we found that rhBMP7 (both 10 and 50 µg) significantly increased the amount of cartilage compared to controls in stabilized fractures, confirming its chondrogenic effect. Lastly, using bone marrow transplantation, we determined that no donor‐derived osteocytes or chondrocytes were present in rhBMP7‐treated fractures, suggesting rhBMP7 did not recruit mesenchymal stem cells from the bone marrow to the fracture site. In conclusion, our results indicate that rhBMP7 is a promising treatment for fractures with severely disrupted blood supply. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:687–696, 2010     

Enhancement of recombinant human BMP‐7 bone formation with bmp binding peptide in a rodent femoral defect model

Bone morphogenetic binding peptide (BBP) is an 18.5 kDa fragment of a bone matrix protein peptide. A rat femoral defect model was used to test the effect of BBP combined with recombinant human bone morphogenetic protein‐7 (rhBMP‐7) to induced bone healing. Two doses of BBP (500 and 1000 µg) were tested with two doses of rhBMP‐7 (2 and 5 µg), and the results were compared with a positive control (10 µg rhBMP‐7). Bone healing was evaluated by radiology, manual palpation, microcomputed tomography, and histology. The high dose of 10 µg of rhBMP‐7 resulted in a consistent 100% bone union rate and a mature histological appearance on histology, and was used as a positive control. When 1000 µg of BBP was combined with lower doses of BMP‐7 (2 µg rhBMP‐7 or 5 µg rhBMP‐7) significant differences were seen in radiographic scores, manual palpation, and bone volume, when compared to 2 µg rhBMP‐7 or 5 µg rhBMP‐7 alone. The combination of 1000 µg of BBP and 5 µg rhBMP‐7 also achieved 100% fusion rate, induced a larger amount of bone formation, and yielded similar maturity of bone marrow when compared with the high dosage 10 µg rhBMP‐7 group. This study demonstrated that when combined together, BBP can enhance the bone healing of rhBMP‐7. Improved healing imparted by the addition of BBP may result in lesser amounts of rhBMP‐7 needed to achieve union in the clinical setting. © 2010 OrthopaedicResearchSociety.PublishedbyWileyPeriodicals, Inc.JOrthopRes29:753–759,2011     

Chondroprotective effect of high‐dose zoledronic acid: An experimental study in a rabbit model of osteoarthritis

To address the need to impact the subchondral bone‐articular cartilage interaction for the treatment of degenerative osteoarthritis (OA), bisphosphonates may be used as a means to inhibit the subchondral bone resorption. The purpose of the present study is to evaluate the chondroprotective effect of zoledronic acid (ZOL) in a model of OA. Eighteen adult male rabbits underwent an anterior cruciate ligament transection and were separated into two groups: ZOL group (n = 10) received 0.6 mg/kg intravenous injection of ZOL on day 1, 15, and 29 and placebo group (n = 8) received saline. The animals were euthanized at 8 weeks. Macroscopically, the ZOL group had significantly milder ulcerations, cartilage softening and fibrillation compared to the placebo group. Microscopically, morphology of the articular cartilage was better in the ZOL treated group compared with the placebo group, without complete disorganization in any section of the ZOL group. Furthermore, the chondrocytes in the ZOL treated group were mainly cloning, indicating cartilage repairing and regeneration process, while in the placebo group hypocellularity predominated. Additionally, subchondral necrosis was evident in some specimens of the placebo group. Zoledronic acid, in a high‐dose regimen, proved to be chondroprotective in a well‐established animal model of OA. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:1646–1651, 2014.     

Generation of tendon-to-bone interface "enthesis" with use of recombinant BMP-2 in a rabbit model.

The anatomical structure at bone-tendon and bone-ligament interfaces is called the enthesis. Histologically, the enthesis is characterized by a transitional series of tissue layers from the end of the tendon to bone, including tendon, fibrocartilage, calcified fibrocartilage, and bone. This arrangement yields stronger direct connection of the soft tissues to bone. In surgical repair, the enthesis has proven difficult to reproduce, and the success of ligament-bone bonding has depended on the fibrous attachment that forms after any ligament reconstructions. In this study, we attempted to generate a direct-insertion enthesis in two stages. First, recombinant human bone morphogenetic protein-2 (rhBMP-2) was injected into the flexor digitorum communis tendon in the rabbit hind limb to induce ectopic ossicle formation. In a second step, the resultant tendon/ossicle complex was then surgically transferred onto the surface of the rabbit tibia to generate a stable tendon-bone junction. One month following surgery, histomorphological examination confirmed direct insertion of tendon-bone structures in the proximal tibia of the rabbit. Ultimate failure loads of the BMP-2-generated tendon-bone junction were significantly higher than in the control group (p < 0.01). These findings suggest that it is possible to successfully regenerate a direct tendon-to-bone enthesis. Use of this approach may enable successful reconstruction of joints rendered unstable after ligamentous rupture or laxity after anterior cruciate ligament injury.     

Repair of rat calvarial defects using Si‐doped hydroxyapatite scaffolds loaded with a bone morphogenetic protein‐2‐related peptide

Tissue engineering promises therapies ideal for treating conventional large bone injuries and defects. In the present study, we developed a novel Si‐HA scaffold loaded with a synthetic BMP‐2‐related peptide, P28, and tested its ability to repair a critical‐sized calvarial defect. We created a calvarial defect (5 mm in diameter) in the parietal bone of 32 rats and implanted one of the following biomaterials: No implant (control), Si‐HA, P28/Si‐HA, or rhBMP‐2/Si‐HA. As assessed by micro CT imaging and histological evaluations, the P28/Si‐HA scaffold promoted bone recovery to a similar degree as the rhBMP‐2/Si‐HA scaffold. In addition, both P28/Si‐HA and rhBMP‐2/Si‐HA promoted recovery better than Si‐HA alone. The novel P28/Si‐HA scaffold might represent a promising biomaterial for future bone tissue engineering applications. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1874–1882, 2016.     

A clonal translocation t(10;21) in an optic glioma of a patient with neurofibromatosis type 1 (NF 1)

Summary An 11-year-old boy affected by neurofibromatosis type 1 is presented with severely impaired vision on the right eye (0.1). MRI demonstrated a 2.3×1.8 cm tumour of the optic chiasma. After open biopsy cytogenetic analysis was performed on primary cultures of this optic glioma (grade I). A clonal translocation t(10;21)(q 21.2;21.1) was detected in 66% of the metaphases analysed. The boy received fractioned irradiation with a total tumour dose of 60 Gy. The ultimate MRI taken 18 month after radiotherapy showed no residual tumour. The vision on the right improved to 0.2, but decreased on the left to 0.6. The patient attends high school with no impairment in his daily life.     

An injectable composite material containing bone morphogenetic protein‐2 shortens the period of distraction osteogenesis in vivo

To investigate new methods that can decrease the duration of bone transport (BT) distraction osteogenesis, we injected composite materials containing recombinant human bone morphogenetic protein‐2 (BMP‐2) and induced the generation of a callus bridge by rapid segmental transport (4 mm/day) in a rabbit bone defect model. The composite materials consisted of BMP‐2 (0, 30, or 100 µg), β‐tricalcium phosphate powder (βTCP, 100 mg/animal; particle size, <100 µm), and polyethylene glycol (PEG; 40 mg/animal). A paste of equivalent composition was percutaneously injected at the lengthening and the docking sites after surgery and after BT, respectively. The radiographic, mechanical, and histological examinations 12 weeks post‐operative revealed that the generation of bridging callus in the presence and in the absence of BMP‐2 was significantly different. The callus mass in the bone defect region was adequately and consistently developed in the presence of 100 µg of BMP (administered for 6 weeks), and the bones were consolidated in 12 weeks. Such an adequate callus formation was not observed in the control animals without BMP‐2 treatment. The result of this experimental study suggests the potential application of BMP‐2 in accelerating callus formation and in enabling rapid bone transporting, thereby shortening the treatment period for the repair of diaphyseal bone defects by distraction osteogenesis. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:452–456, 2011     

Effect of bone morphogenetic protein 2 on tendon‐to‐bone healing in a canine flexor tendon model

Tendon‐to‐bone healing is typically poor, with a high rate of repair‐site rupture. Bone loss after tendon‐to‐bone repair may contribute to poor outcomes. Therefore, we hypothesized that the local application of the osteogenic growth factor bone morphogenetic protein 2 (BMP‐2) would promote bone formation, leading to improved repair‐site mechanical properties. Intrasynovial canine flexor tendons were injured in Zone 1 and repaired into bone tunnels in the distal phalanx. BMP‐2 was delivered to the repair site using either a calcium phosphate matrix (CPM) or a collagen sponge (COL) carrier. Each animal also received carrier alone in an adjacent repair to serve as an internal control. Repairs were evaluated at 21 days using biomechanical, radiographic, and histologic assays. Although an increase in osteoid formation was noted histologically, no significant increases in bone mineral density occurred. When excluding functional failures (i.e., ruptured and gapped repairs), mechanical properties were not different when comparing BMP‐2/CPM groups with carrier controls. A significantly higher percentage of BMP‐2 treated specimens had a maximum force <20 N compared to carrier controls. While tendon‐to‐bone healing can be enhanced by addressing the bone loss that typically occurs after surgical repair, the delivery of BMP‐2 using the concentrations and methods of the current study did not improve mechanical properties over carrier alone. The anticipated anabolic effect of BMP‐2 was insufficient in the short time frame of this study to counter the post‐repair loss of bone. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1702–1709, 2012     

Enhanced effects of BMP‐binding peptide combined with recombinant human BMP‐2 on the healing of a rodent segmental femoral defect

BMP‐binding peptide (BBP) enhances the osteogenic activity of recombinant human bone morphogenetic protein‐2 (rhBMP‐2), but the mechanism underlying the enhancement remains unclear. We aimed to elucidate the potential enhanced efficacy of BBP using critical‐sized segmental femoral bone defects in rats. Seventy defects in seven groups of rats were filled with various amounts (0, 2, 5, and 10 µg) of rhBMP‐2 with or without 1000 µg BBP. Radiographs were obtained after 4 and 8 weeks. The animals were euthanized at 8 weeks, and femoral specimens were assessed manually, evaluated for bone volume using microcomputed tomography, and subjected to histological or biomechanical analysis. Although 10 µg rhBMP‐2 yielded consistent results in terms of bone healing and quality of bone repair across the segmental defect, lower doses of rhBMP‐2 failed to induce satisfactory bone healing. However, the combined administration of lower doses of rhBMP‐2 and BBP induced the formation of significantly large amounts of bone. Our results suggest that the combined administration of rhBMP‐2 and BBP facilitates bone healing and has potential clinical applications. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:258–264, 2010