Treatment of a congenital pseudarthrosis of the tibia by osteogenic protein-1 (bone morphogenetic protein-7): a case report

Congenital Pseudarthrosis of the Tibia Associated With Cleidocranial Dysostosis: Case Report and Literature Review

CASE

We describe a case of 2 individually rare diseases existing comorbidly in the form of congenital pseudarthrosis of the tibia (CPT) coincident with cleidocranial dysostosis and provide a review of the literature, including the sole preexisting documented coincidence.

CONCLUSION

Understanding, treatment, and surgical protocol of CPT have changed considerably since this comorbidity was last reported. Updates include synostosis, periosteal grafting, the use of bone morphogenetic protein, and bisphosphonates. Our case varies from the previous in associated disorder and family history. The relationship between CBFA1 and RUNX2 genes may hold the key, but further study is needed.

rhBMP-2 and Intramedullary Fixation in Congenital Pseudarthrosis of the Tibia

BACKGROUND

In congenital pseudarthrosis of the tibia, use of intramedullary (IM) fixation and autogenous bone graft has long been the standard of care. This study was undertaken to determine whether the addition of rhBMP-2 to this treatment method further enhances healing potential.

METHODS

Twenty-one patients with congenital pseudarthrosis of the tibia were evaluated. Fifteen of these patients had neurofibromatosis type 1 (NF1). All had IM fixation and autogenous bone graft, followed by a BMP-soaked collagen sponge wrapped around both the fracture site and bone graft. A minimum 2 years' follow-up was required.

RESULTS

Follow-up averaged 7.2 years (range, 2.1 to 12.8 y). Sixteen of 21 tibias achieved bone union following the index surgery, at an average 6.6 months postoperatively. The 5 persistent nonunions occurred in NF1 patients. Further surgery was undertaken in these 5 NF1 patients, including the use of BMP. One of the 5 healed, 1 had persistent nonunion, and 3 eventually had amputation. Of the 16 patients who healed initially following the index surgery, 5 refractured (3 had NF1). Of these 5 patients, the IM fixation at the index surgery did not cross the ankle joint, and refracture occurred at the rod tip in 4. Three of these 5 patients healed following further surgery, 1 had persistent nonunion, and 1 had amputation. All of those with eventual amputation had NF1. No deleterious effects related to the use of BMP-2 were recognized in any patient.

CONCLUSIONS

The addition of rhBMP-2 appears to be helpful in shortening the time required to achieve fracture union in those who healed, but its use does not insure that healing will occur.

LEVEL OF EVIDENCE

Level IV-therapeutic, case series.

Interaction of colon cancer cells with glycoconjugates triggers complex changes in gene expression, glucose transporters and cell invasion

Glycan metabolism balance is critical for cell prosperity, and macromolecule glycosylation is essential for cell communication, signaling and survival. Thus, glycotherapy may be a potential cancer treatment. The aim of the present study was to determine whether combined synthetic glycoconjugates (GCs) induce changes in gene expression that alter the survival of colon cancer cells. The current study evaluated the effect of the GCs N‑acetyl‑D‑glucosamine modified polyamidoamine dendrimer and calix[4]arene scaffold on cancer cell proliferation, apoptosis, invasion and sensitivity to immune cell‑mediated killing. Using reverse transcription‑quantitative polymerase chain reaction, the expression of genes involved in the aforementioned processes was measured. It was determined that GCs reduce the expression of the glucosaminyltransferases Mgat3 and Mgat5 responsible for surface glycosylation and employed components of the Wnt signaling pathway Wnt2B and Wnt9B. In addition, the calix[4]arene‑based GC reduced cell colony formation; this was accompanied by the downregulation of the metalloproteinase Mmp3. By contrast, the dendrimer‑based GC affected the expression of the glucose transporter components Sglt1 and Egfr1. Therefore, to the best of our knowledge, the present study is the first to reveal that N‑acetyl‑D‑glucosamine‑dendrimer/calix[4]arene GCs alter mRNA expression in a comprehensive way, resulting in the reduced malignant phenotype of the colon cancer cell line HT‑29.

The reduced osteogenic potential of Nf1-deficient osteoprogenitors is EGFR-independent

Neurofibromatosis type 1 (NF1) is a common genetic disorder caused by mutations in the NF1 gene. Recalcitrant bone healing following fracture (i.e. pseudarthrosis) is one of the most problematic skeletal complications associated with NF1. The etiology of this condition is still unclear; thus, pharmacological options for clinical management are limited. Multiple studies have shown the reduced osteogenic potential of Nf1-deficient osteoprogenitors. A recent transcriptome profiling investigation revealed that EREG and EGFR, encoding epiregulin and its receptor Epidermal Growth Factor Receptor 1, respectively, were among the top over-expressed genes in cells of the NF1 pseudarthrosis site. Because EGFR stimulation is known to inhibit osteogenic differentiation, we hypothesized that increased EREG and EGFR expression in NF1-deficient skeletal progenitors may contribute to their reduced osteogenic differentiation potential. In this study, we first confirmed via single-cell mRNA sequencing that EREG over-expression was associated with NF1 second hit somatic mutations in human bone cells, whereas Transforming Growth Factor beta 1 (TGFβ1) expression was unchanged. Second, using ex-vivo recombined Nf1-deficient mouse bone marrow stromal cells (mBMSCs), we show that this molecular signature is conserved between mice and humans, and that epiregulin generated by these cells is overexpressed and active, whereas soluble TGFβ1 expression and activity are not affected. However, blocking either epiregulin function or EGFR signaling by EGFR1 or pan EGFR inhibition (using AG-1478 and Poziotinib respectively) did not correct the differentiation defect of Nf1-deficient mBMSCs, as measured by the expression of Alpl, Ibsp and alkaline phosphatase activity. These results suggest that clinically available drugs aimed at inhibiting EGFR signaling are unlikely to have a significant benefit for the management of bone non-union in children with NF1 PA.

Complication Rates After Bone Morphogenetic Protein (BMP) Use in Orthopaedic Surgery in Children: A Concise Multicenter Retrospective Cohort Study

BACKGROUND

The use of bone morphogenetic protein (BMP) has been associated with a number of complications in adult patients. However, this association is less established in children. The aim of this study was to evaluate the safety of BMP use in children by determining the complication rates after BMP use at multiple institutions.

METHODS

In a retrospective study (2000 to 2013), the medical records of all patients who received BMP at any of the 5 institutions were reviewed. Demographic information, preoperative data, and postoperative follow-up data were collected on those patients who were under the age of 18 at the time of surgery.

RESULTS

A total of 312 pediatric patients underwent surgery with BMP application during the study period. The surgical procedures consisted of 228 spinal fusions, 39 pars repairs, 33 nonunion repair, and 12 other various procedures. Overall 21% (65/312) of patients who had BMP utilized had a complication. Fifty-five percent (36/65) of patients with a complication required a revision surgery. The average follow-up was 27 months (range, 3 to 96 mo); 80% of patients had a follow-up period of >12 months. The average age at the time of surgery was 13 years (range, 1 to 17 y). Males and females were almost equally represented in the study: 143 males (46%) and 168 females (54%). Of the patients who received BMP, 9% had minor complications and 13% had major complications. Wound dehiscence without infection was the most common minor complication and occurred in 59% (16/27) of patients with minor complications. Infection and implant failures were the most frequent major complications, occurring in 38% (15/39) and 33% (13/39) of patients with major complications, respectively. Five of 312 (2%) patients had neurological injury, 3 of which were only temporary.

CONCLUSIONS

This multicenter study demonstrates a relatively high rate of complications after the use of BMP in children. However, further study is needed to attribute the complications directly to the use of BMP.

LEVEL OF EVIDENCE

Level IV.

Bone morphogenetic protein-2 for the treatment of congenital pseudarthrosis of the tibia or persistent tibial nonunion in children and adolescents: A retrospective study with a minimum 2-year follow-up

There is a lack of studies reporting on rhBMP-2 application in pediatric orthopaedics, although few reports demonstrated promising results of the use of rhBMP-2 in children, especially for spine fusion and for the treatment of congenital pseudarthrosis of the tibia. The objectives of this study were (1) to examine clinical and radiographic healing after rhBMP-2 application for the treatment of congenital pseudarthrosis of the tibia (CPT) or persistent tibial nonunion in children and adolescents, and (2) to investigate the safety of rhBMP-2 use in these cases. Therefore we reviewed the medical records of ten patients with a mean age of 8.6 years (2.3-21) with CPT (n = 7) or persistent tibial nonunion for at least six months (n = 3) who had been treated with rhBMP-2. Nine of ten patients had union at final follow-up, after a mean of 72.9 months (25-127). In the CPT group, primary healing of the pseudarthrosis occurred in six of seven patients at a mean of 5.2 months (3-12). Repeat rhBMP-2 application was performed in three patients; two patients had one additional application each, and one patient had three additional applications. Complications that may be attributed to the use of rhBMP-2 were seen in two of fifteen applications, including a compartmemt syndrome and a hematoma. In this retrospective case series rhBMP-2 has been used successfully to treat CPT or persistent tibial nonunion in pediatric patients. However, prospective randomized controlled trials are warranted to investigate the long-term efficacy and safety of rhBMP-2 use in these cases.

Computational modeling of bone fracture non-unions: four clinically relevant case studies

The human skeleton has a remarkable regeneration capacity. Nevertheless, 5-10 % of the bone fractures fails to heal and develops into a non-union which is a challenging orthopedic complication requiring complex and expensive treatment. This review paper will discuss four different computational models, each capturing a particular clinical case of non-union: non-union induced by reaming of the marrow canal and periosteal stripping, non-union due to a large interfragmentary gap, non-union due to a genetic disorder [i.e. NF1 related congenital pseudoarthrosis of the tibia (CPT)] and non-union due to mechanical overload. Together, the four computational models are able to capture the etiology of a wide range of fracture non-union types and design novel treatment strategies thereof. Further research is required to corroborate the computational models in both animal and human settings and translate them from bench to bed side.

Combined MEK inhibition and BMP2 treatment promotes osteoblast differentiation and bone healing in Nf1Osx -/- mice

Neurofibromatosis type I (NF1) is an autosomal dominant disease with an incidence of 1/3000, caused by mutations in the NF1 gene, which encodes the RAS/GTPase-activating protein neurofibromin. Non-bone union after fracture (pseudarthrosis) in children with NF1 remains a challenging orthopedic condition to treat. Recent progress in understanding the biology of neurofibromin suggested that NF1 pseudarthrosis stems primarily from defects in the bone mesenchymal lineage and hypersensitivity of hematopoietic cells to TGFβ. However, clinically relevant pharmacological approaches to augment bone union in these patients remain limited. In this study, we report the generation of a novel conditional mutant mouse line used to model NF1 pseudoarthrosis, in which Nf1 can be ablated in an inducible fashion in osteoprogenitors of postnatal mice, thus circumventing the dwarfism associated with previous mouse models where Nf1 is ablated in embryonic mesenchymal cell lineages. An ex vivo-based cell culture approach based on the use of Nf1(flox/flox) bone marrow stromal cells showed that loss of Nf1 impairs osteoprogenitor cell differentiation in a cell-autonomous manner, independent of developmental growth plate-derived or paracrine/hormonal influences. In addition, in vitro gene expression and differentiation assays indicated that chronic ERK activation in Nf1-deficient osteoprogenitors blunts the pro-osteogenic property of BMP2, based on the observation that only combination treatment with BMP2 and MEK inhibition promoted the differentiation of Nf1-deficient osteoprogenitors. The in vivo preclinical relevance of these findings was confirmed by the improved bone healing and callus strength observed in Nf1osx (-/-) mice receiving Trametinib (a MEK inhibitor) and BMP2 released locally at the fracture site via a novel nanoparticle and polyglycidol-based delivery method. Collectively, these results provide novel evidence for a cell-autonomous role of neurofibromin in osteoprogenitor cells and insights about a novel targeted approach for the treatment of NF1 pseudoarthrosis.

Bone morphogenetic protein and orthopaedic surgery: can we legitimate its off-label use?

PURPOSE

Bone morphogenetic proteins (BMP) are recombinant osteoinductive proteins with their primary role being to promote bone formation. The off-label use of BMP in orthopaedic surgery has dramatically increased. However, reports of complications with BMP have emerged, and the safety of these proteins in orthopaedics is questioned. The purpose of this review was to evaluate safe situations in which BMP should be used and situations in which their use should be restricted.

METHOD

We recorded all studies from PubMed database from 2002 (date of first authorisation for both BMPs) until January 2014 using "BMP" or "bone morphogenetic protein". Then we screened and extracted all studies dealing with orthopaedic surgery. All situations in which BMP were used, even cases reports, were considered, and complications reported were then listed.

RESULTS

Situations in which it seems safe and efficient to use BMP are long-bone nonunions, or arthrodesis as an alternative or combined to autograft in small-bone loss. Surgeons and patients should be aware of transient aseptic wound swelling when BMP is located superficially. The use of BMP in spine surgery for intersomatic fusion is efficient but should be restricted to approaches that respect the vertebral canal to avoid neurological complications.

CONCLUSION

This review is an off-label map of BMP use in orthopaedics during the past 10 years. Our results could provide a useful tool to help decisions around when to use a BMP in a specific complex, and sometimes off-label, situation.

Asfotase-α improves bone growth, mineralization and strength in mouse models of neurofibromatosis type-1

Mineralization of the skeleton depends on the balance between levels of pyrophosphate (PPi), an inhibitor of hydroxyapatite formation, and phosphate generated from PPi breakdown by alkaline phosphatase (ALP). We report here that ablation of Nf1, encoding the RAS/GTPase–activating protein neurofibromin, in bone–forming cells leads to supraphysiologic PPi accumulation, caused by a chronic ERK–dependent increase in genes promoting PPi synthesis and extracellular transport, namely Enpp1 and Ank. It also prevents BMP2–induced osteoprogenitor differentiation and, consequently, expression of ALP and PPi breakdown, further contributing to PPi accumulation. The short stature, impaired bone mineralization and strength in mice lacking Nf1 in osteochondroprogenitors or osteoblasts could be corrected by enzyme therapy aimed at reducing PPi concentration. These results establish neurofibromin as an essential regulator of bone mineralization, suggest that altered PPi homeostasis contributes to the skeletal dysplasiae associated with neurofibromatosis type-1 (NF1), and that some of the NF1 skeletal conditions might be preventable pharmacologically.

Effectiveness of recombinant human bone morphogenetic protein-7 in the management of congenital pseudoarthrosis of the tibia: a randomised controlled trial

PURPOSE

Despite the popularity and an increased use of bone morphogenetic protein to improve bone healing in patients with congenital pseudoarthrosis of the tibia (CPT), no previous study has compared its efficacy against any other procedure.

METHODS

We randomised 20 consecutive patients (mean age 4.1 years) with CPT (Crawford type IV) associated with neurofibromatosis type 1(NF1) and no previous history of surgery into two groups. Group 1 received recombinant human bone morphogenetic protein-7 (rhBMP-7) along with intramedullary Kirschner (K)-wire fixation and autologous bone grafting; group 2 received only K wire and grafting. Outcome measures were time to achieve union, Johnston grade, tibial length and the American Orthopaedic Foot and Ankle Society (AOFAS) score, which were evaluated preoperatively and at five year follow-up.

RESULTS

Study results showed that patients in group 1 achieved primary bone union at a mean of 14.5 months [standard error (SE) 5.2], whereas group 2 took a mean of 17.11 months (SE 5.0). However, the log-rank test showed no difference in healing times between groups at all time points (P = 0.636). There was a statistically significant pre- to post operative improvement (P < 0.05) within groups for the other outcome measures.

CONCLUSION

In a five year follow-up, these results suggest that rh-BMP-7 and autologous bone grafting is no better than autologous grafting alone.

The clinical use of bone morphogenetic proteins revisited: a novel biocompatible carrier device OSTEOGROW for bone healing

PURPOSE

The purpose of this study was to revise the clinical use of commercial BMP2 (Infuse) and BMP7 (Osigraft) based bone devices and explore the mechanism of action and efficacy of low BMP6 doses in a novel whole blood biocompatible device OSTEOGROW.

METHODS

Complications from the clinical use of BMP2 and BMP7 have been systemically reviewed in light of their role in bone remodeling. BMP6 function has been assessed in Bmp6-/- mice by μCT and skeletal histology, and has also been examined in mesenchymal stem cells (MSC), hematopoietic stem cells (HSC) and osteoclasts. Safety and efficacy of OSTEOGROW have been assessed in rats and rabbits.

RESULTS

Clinical use issues of BMP2 and BMP7 have been ascribed to the limited understanding of their role in bone remodeling at the time of device development for clinical trials. BMP2 and BMP7 in bone devices significantly promote bone resorption leading to osteolysis at the endosteal surfaces, while in parallel stimulating exuberant bone formation in surrounding tissues. Unbound BMP2 and BMP7 in bone devices precipitate on the bovine collagen and cause inflammation and swelling. OSTEOGROW required small amounts of BMP6, applied in a biocompatible blood coagulum carrier, for stimulating differentiation of MSCs and accelerated healing of critical size bone defects in animals, without bone resorption and inflammation. BMP6 decreased the number of osteoclasts derived from HSC, while BMP2 and BMP7 increased their number.

CONCLUSIONS

Current issues and challenges with commercial bone devices may be resolved by using novel BMP6 biocompatible device OSTEOGROW, which will be clinically tested in metaphyseal bone fractures, compartments where BMP2 and BMP7 have not been effective.

Congenital pseudarthrosis of the tibia: the results of an evolving protocol of management

PURPOSE

This retrospective cohort study assesses the outcomes of a protocol of management, based on the recommendations of the European Paediatric Orthopaedic Society (EPOS) multi-centre study, for the management of congenital pseudarthrosis of the tibia.

METHODS

Utilising an incremental protocol of bracing, intramedullary rods and circular frame fixation with or without bone morphogenetic protein-2 (BMP-2), 11 patients had reached skeletal maturity or had follow up of 5 years from radiological union of the pseudarthrosis. Demographic data, deformity parameters before and after treatment, and functional outcome scores were recorded.

RESULTS

Ten of the 11 patients successfully healed and two sustained a refracture. All deformity parameters improved and a mean leg length discrepancy of 2.5 cm (range 0-7.5 cm) existed at the time of the last follow up. Some pseudarthroses healed with deformity correction and rod insertion alone. Six of the 11 patients had a confirmed diagnosis of neurofibromatosis and nine had sustained a fracture before 4 years of age. Refracture was associated with malalignment after healing.

CONCLUSION

This method of treatment provides a successful stepwise protocol for the management of this complex disorder, avoiding the use of aggressive limb reconstruction techniques at a young age in some cases. Level of evidenceCase series Level IV.

Controversies in the management of congenital pseudarthrosis of the tibia and fibula

Congenital pseudarthrosis of the tibia (CPT) is a rare but well recognised condition. Obtaining union of the pseudarthrosis in these children is often difficult and may require several surgical procedures. The treatment has changed significantly since the review by Hardinge in 1972, but controversies continue as to the best form of surgical treatment. This paper reviews these controversies.

Cite this article: Bone Joint J 2013;95-B:1027–34.

Masquelet's procedure and bone morphogenetic protein in congenital pseudarthrosis of the tibia in children: a case series and meta-analysis

PURPOSE

A type 2 recombinant human bone morphogenetic protein (rhBMP2) and Masquelet's procedure were used in three children presenting with congenital pseudarthrosis of the tibia (CPT). Recent studies on CPT suggested the presence in situ of pathologic tissues promoting pseudarthrosis. The authors hypothesized that large segmental resection of pseudarthrosis could improve prognosis of the CPT. Masquelet's procedure and rhBMP2 have been advocated for the treatment of long bone defect.

METHOD

The authors report three cases of CPT in children treated with Masquelet's procedure and application of rhBMP2. They analyzed all published cases of CPT similarly treated.

RESULTS

In the present study, Masquelet's procedure did not improve the results in the treatment of CPT, but segmental bone reconstruction was possible. Bone healing was obtained in three out of the five applications of rhBMP2. In one case, the patient's parents asked for leg amputation. Analysis of the 33 published cases with the application of BMP in CPT points to a 62 % healing rate in this pathology.

CONCLUSION

The authors confirmed that segmental bone reconstruction is possible in CPT using Masquelet's procedure. In the literature, the success rate of the application of rhBMP in CPT appears to be lower than the healing rate usually reported without BMP. Nevertheless, the strict selection of patients, limited number of cases, and their heterogeneity make interpreting the results difficult. However, the theoretical risk which the children are exposed to during the use of BMP makes rigorous selection of the indications necessary. Finally, the interest of rhBMP2 application in Masquelet's procedure remained to be proven.

Congenital pseudarthrosis of the tibia

Congenital pseudarthrosis of the tibia (CPT) is an uncommon disease with various clinical presentations ranging from simple anterolateral tibial angulation to complete non-union with extensive bone defects. Classifications of radiographic findings include atrophic or hypertrophic pseudarthosis as well as cystic or dystrophic lesions. Although the relationship between CPT and type 1 neurofibromatosis is well known, the exact pathogenesis still remains unclear. The fibrous soft tissue found in the pseudarthosis and the abnormal periosteum are certainly a key to the pathology, possibly due to decreased osteogenic capacities and impaired local vascularization. Treatment of CPT is still challenging in pediatric orthopedics because of bone union difficulties, persistant angulation, joint stiffness and sometimes severe limb length discrepancy sequellae. Numerous treatments based on biological and/or mechanical concepts, surgical or not, have been reported with variable success rates. Vascularized fibular grafts and the Ilizarov technique have greatly transformed the prognosis of CPT. Despite these steps forward, repeated surgical procedures are often necessary to obtain bone union and the risk of amputation is never entirely eliminated. The effectiveness of new treatments (bone morphogenetic protein, bone marrow stromal cell grafts, pulsed electromagnetic fields, induced membrane technique…) still requires to be confirmed. Combining these new techniques with existing treatments may improve the final prognosis of CPT, which nevertheless remains poor.

Distal tibial fracture repair in a neurofibromatosis type 1-deficient mouse treated with recombinant bone morphogenetic protein and a bisphosphonate

Congenital pseudarthrosis of the tibia is an uncommon manifestation of neurofibromatosis type 1 (NF1), but one that remains difficult to treat due to anabolic deficiency and catabolic excess. Bone grafting and more recently recombinant human bone morphogenetic proteins (rhBMPs) have been identified as pro-anabolic stimuli with the potential to improve the outcome after surgery. As an additional pharmaceutical intervention, we describe the combined use of rhBMP-2 and the bisphosphonate zoledronic acid in a mouse model of NF1-deficient fracture repair. Fractures were generated in the distal tibiae of neurofibromatosis type 1-deficient (Nf1(+/-)) mice and control mice. Fractures were open and featured periosteal stripping. All mice received 10 μg rhBMP-2 delivered in a carboxymethylcellulose carrier around the fracture as an anabolic stimulus. Bisphosphonate-treated mice also received five doses of 0.02 mg/kg zoledronic acid given by intraperitoneal injection. When only rhBMP but no zoledronic acid was used to promote repair, 75% of fractures in Nf1(+/-) mice remained ununited at three weeks compared with 7% of controls (p < 0.001). Systemic post-operative administration of zoledronic acid halved the rate of ununited fractures to 37.5% (p < 0.07). These data support the concept that preventing bone loss in combination with anabolic stimulation may improve the outcome following surgical treatment for children with congenital pseudarthosis of the tibia and NF1.

Combined treatment of congenital pseudarthrosis of the tibia, including recombinant human bone morphogenetic protein-2: a case series

The use of recombinant human bone morphogenetic protein-2 (rhBMP-2) for the treatment of congenital pseudarthrosis of the tibia has been investigated in only one previous study, with promising results. The aim of this study was to determine whether rhBMP-2 might improve the outcome of this disorder. We reviewed the medical records of five patients with a mean age of 7.4 years (2.3 to 21) with congenital pseudarthrosis of the tibia who had been treated with rhBMP-2 and intramedullary rodding. Ilizarov external fixation was also used in four of these patients. Radiological union of the pseudarthrosis was evident in all of them at a mean of 3.5 months (3.2 to 4) post-operatively. The Ilizarov device was removed after a mean of 4.2 months (3.0 to 5.3). These results indicate that treatment of congenital pseudarthrosis of the tibia using rhBMP-2 in combination with intramedullary stabilisation and Ilizarov external fixation may improve the initial rate of union and reduce the time to union. Further studies with more patients and longer follow-up are necessary to determine whether this surgial procedure may significantly enhance the outcome of congenital pseudarthrosis of the tibia, considering the refracture rate (two of five patients) in this small case series.

[Percutaneous administration of recombinant human bone morphogenetic protein-7 (rhBMP-7) after callus distraction. Two case reports]

Two cases of increased bone density after callus distraction are described following percutaneous administration of 3.5 mg recombinant bone morphogenetic protein-7 (rhBMP-7). Both patients underwent segmental resection and segmental transport for osteomyelitis of the long bones (femur and tibia) but no callus maturation occurred. After percutaneous administration of rhBMP-7 the callus density increased in both cases.

Complications associated with the use of bone morphogenetic protein in pediatric patients

BACKGROUND

Recombinant human bone morphogenetic protein (rhBMP) has been found to be a powerful adjunct to healing nonunions and obtaining fusions. Despite the apparent clinical efficacy and good safety profile reported with rhBMP use in adults, there is little data regarding the safety of this product in pediatric patients. We evaluated the use of rhBMP-2 in pediatric patients to determine if any complications were associated with its use.

METHODS

We performed a retrospective review of 81 patients, all less then 18 years old, in whom rhBMP-2 was used. Theoretical complications associated with rhBMP-2 use were compiled based on a review of the published literature on rhBMP-2. A review of each patient's chart and radiographs was performed to record the occurrences of complications, which may have been associated with the use of rhBMP-2.

RESULTS

A total of 16 complications were found, which may have been attributed to the use of rhBMP-2. There were no incidences of systemic toxicity associated with rhBMP-2 use. Nine patients were noted to have some local operative site problem, 3 deep infections were noted, 1 patient was found to have a postoperative compartment syndrome, 2 patients were found to have neurologic complications (1 with progressive myelopathy and 1 with weakness and dural fibrosis), and 1 patient with neurofibromatosis and previously diagnosed intracranial gliomas was found to have subsequent enlargement of these gliomas. In reviewing these complications, only the case of dural fibrosis and subsequent weakness was thought to possibly be directly related to the use of rhBMP-2.

CONCLUSION

We found few complications in pediatric patients, which were felt to be directly attributable to the use of rhBMP-2. As such, rhBMP-2 use seems to be relatively safe in this young patient population. Due to the current use of this product in pediatric patients in an "off-label" fashion, we recommend a thorough discussion of the possible risks and benefits of this product with the family before its use.

LEVEL OF EVIDENCE

Therapeutic studies-Level IV.

Enhancement of difficult nonunion in children with osteogenic protein-1 (OP-1): early experience

Numerous studies have described the use of osteogenic protein-1 (OP-1) in adults, but there are few reports in children. The objectives of this short-term followup cohort study were (1) to examine clinical and radiographic healing of persistent nonunions after OP-1 application in children; and (2) to determine the safety of OP-1 use in this sample. Clinical healing was defined by absence of pain and tenderness at the nonunion site and the ability to fully weight bear on the affected limb. Radiographic healing was determined by bony bridging of the nonunion site in at least one view. Safety was defined as the absence of major adverse events, including allergic reactions, infections, local inflammatory reactions, and heterotopic ossification. OP-1 was used in 19 patients who had an operative procedure for the bridging of persistent nonunions between 1999 and 2007. The mean age was 11.6 years (range, 4.8-20.3 years). Thirteen patients had persistent nonunion after one or more previous surgeries, prior to the initial OP-1 application. A single dose of 3.5 mg of OP-1 mixed with 1 g of Type I bovine collagen was applied to 23 sites of 19 patients. Three patients received additional OP-1 applications. Healing occurred clinically and radiographically in 17 of the 23 sites. Complications included four superficial pin site infections, one deep infection, and two fractures. No major local adverse event related to OP-1 application was noted in our sample. Our findings suggest OP-1 stimulates healing of persistent nonunions without major adverse events in our patient population.

LEVEL OF EVIDENCE

Level IV, case series. See the guidelines online for a complete description of levels of evidence.

Biologic characteristics of fibrous hamartoma from congenital pseudarthrosis of the tibia associated with neurofibromatosis type 1

BACKGROUND

Fibrous hamartoma is a key pathologic component of congenital pseudarthrosis of the tibia, a challenging and disabling bone disorder. We investigated the biologic characteristics of fibrous hamartoma cells in order to better understand the pathogenesis of this rare disease.

METHODS

Fibrous hamartoma tissues were surgically excised at the time of osteosynthesis from seven patients with congenital pseudarthrosis of the tibia associated with neurofibromatosis type 1. Distal tibial periosteum was also harvested as control tissue during tibial derotation osteotomy from two other patients with cerebral palsy and one patient with idiopathic internal tibial torsion. Fibroblast-like cells were enzymatically dissociated and cultured from these tissues. Immunophenotypes were investigated for positive (CD44 and CD105) and negative (CD45 and CD14) mesenchymal lineage cell markers, and the mRNA expressions of bone morphogenetic protein(BMP)-2, BMP-4, and their receptors were assayed by reverse transcription-polymerase chain reaction. After rhBMP-2 treatment, the changes in alkaline phosphatase activity, and in the mRNA expressions of type-I collagen (COL1A1), alkaline phosphatase, and osteocalcin genes, were assayed with use of an RNase protection assay. The mRNA expressions of receptor activator of nuclear factor-kappa B ligand (RANKL) and osteoprotegerin (OPG) were quantitatively assayed with use of real-time RT-PCR. Osteoclastic differentiation of RAW(264.7) cells in coculture with fibrous hamartoma cells was evaluated.

RESULTS

All fibrous hamartoma and tibial periosteal cells tested were CD44+/CD105+/CD45-/CD14- and expressed the mRNAs of BMP-2, BMP-4, and their receptors. The baseline mRNA expressions of COL1A1, alkaline phosphatase, and osteocalcin genes in the fibrous hamartoma cells were diverse. These gene expressions were upregulated by BMP treatment in tibial periosteal cells but did not change or were downregulated in fibrous hamartoma cells. Fibrous hamartoma cells expressed higher levels of RANKL and lower levels of OPG than did tibial periosteal cells. Coculture with fibrous hamartoma cells enhanced osteoclastic differentiation of RAW(264.7) cells.

CONCLUSIONS

Fibrous hamartoma cells maintain some of the mesenchymal lineage cell phenotypes, but do not undergo osteoblastic differentiation in response to BMP. They are more osteoclastogenic than are tibial periosteal cells.

[Malformations of the lower extremities]

Malformations with deficiencies of the lower extremities are rare. They are usually caused by toxic influences during pregnancy between the 4th and the 12th week of gestation. Some malformations have a genetic origin. The total incidence of congenital deficiencies of the lower extremities is approximately 18 in 100,000 newborns. The most common deficiencies are fibular hemimelias, followed by congenital femoral deficiencies and tibial hemimelias. Hemimelias are often associated with deficient toes or ray defects. Congenital pseudarthrosis of the tibia is less common, but this diagnosis is underestimated in epidemiological studies in neonates, because the fracture usually only occurs at walking age. Other deficiencies such as bladder exstrophy with pelvic defects, split feet and defects in association with hereditary skeletal dysplasias (Apert syndrome, constriction band syndrome) are extremely rare. Various treatment options are available, including shoe elevation, orthotic or prosthetic devices, realignment osteotomy, arthrodesis, rotationplasty, amputation and surgical leg lengthening. Complex deformities should be treated by a team of specialists such as orthopedic surgeons, orthotists, physiotherapists, psychologists and possibly other surgeons too.

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.

Recent insights into bone development, homeostasis, and repair in type 1 neurofibromatosis (NF1)

Neurofibromatosis type 1 (NF1) is one of the most common single gene syndromes and is typified by a range of characteristic but variably penetrant manifestations. The orthopaedic manifestations of congenital pseudarthrosis of the tibia (CPT) and scoliosis, along with other skeletal defects including sphenoid wing dysplasia, rib penciling, and gracile bones have been classically associated with NF1. Added to this, several recent studies have reported a high prevalence of osteoporosis or osteopenia in NF1 cohorts. Clues to the underlying molecular and cellular deficiencies that cause these bony defects can be gleaned from genetically modified mouse models of Nf1 gene deficiency. These studies suggest that a variety of different cell lineages may be adversely affected by Nf1 haploinsufficiency or by double inactivation of the Nf1 gene. Osteoblasts, osteoclasts, chondrocytes, fibroblasts, and vascular endothelial cells all express the Nf1 gene product, neurofibromin, and may be functionally compromised when levels are decreased or absent. This paper reviews the current literature on NF1 bone development, homeostatic regulation, and repair, and highlights some emerging themes that may have relevance for managing orthopaedic disorders that can arise in individuals with NF1.

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 microg 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.