Heterotopic ossification after local steroid injection.

Pachydermodactyly (PDD) is a rare, benign disease associated with progressive swelling of the periarticular soft tissue of phalangeal hand joints typically treated with local steroid injections. We present a case of a 37-year-old man with PDD treated with local steroid injections. He later developed heterotopic ossification and para-articular calcifications in the injection sites. Heterotopic ossification is not associated with PDD nor is it a recognised complication of local steroid injections. This is the first case in literature of heterotopic ossification occurring after local steroid injection and brings to attention a new potential complication of a widely performed procedure.

Leptin accelerates the pathogenesis of heterotopic ossification in rat tendon tissues via mTORC1 signaling.

Leptin, an adipocyte-derived cytokine associated with bone metabolism, is believed to play a critical role in the pathogenesis of heterotopic ossification (HO). The effect and underlying action mechanism of leptin were investigated on osteogenic differentiation of tendon-derived stem cells (TDSCs) in vitro and the HO formation in rat tendons. Isolated rat TDSCs were treated with various concentrations of leptin in the presence or absence of mTORC1 signaling specific inhibitor rapamycin in vitro. A rat model with Achilles tenotomy was employed to evaluate the effect of leptin on HO formation together with or without rapamycin treatment. In vitro studies with TDSCs showed that leptin increased the expression of osteogenic biomarkers (alkaline phosphatase, runt-related transcription factor 2, osterix, osteocalcin) and enhanced mineralization of TDSCs via activating the mTORC1 signal pathway (as indicated by phosphorylation of p70 ribosomal S6 kinase 1 and p70 ribosomal S6). However, mTORC1 signaling blockade with rapamycin treatment suppressed leptin-induced osteogenic differentiation and mineralization. In vivo studies showed that leptin promoted HO formation in the Achilles tendon after tenotomy, and rapamycin treatment blocked leptin-induced HO formation. In conclusion, leptin can promote TDSC osteogenic differentiation and heterotopic bone formation via mTORC1 signaling in both vitro and vivo model, which provides a new potential therapeutic target for HO prevention.

Peripheral denervation participates in heterotopic ossification in a spinal cord injury model.

We previously reported the development of a new acquired neurogenic HO (NHO) mouse model, combining spinal cord transection (SCI) and chemical muscle injury. Pathological mechanisms responsible for ectopic osteogenesis after central neurological damage are still to be elucidated. In this study, we first hypothesized that peripheral nervous system (PNS) might convey pathological signals from injured spinal cord to muscles in NHO mouse model. Secondly, we sought to determine whether SCI could lead to intramuscular modifications of BMP2 signaling pathways. Twenty one C57Bl6 mice were included in this protocol. Bilateral cardiotoxin (CTX) injection in hamstring muscles was associated with a two-stage surgical procedure, combining thoracic SCI with unilateral peripheral denervation. Volumes of HO (Bone Volume, BV) were measured 28 days after surgery using micro-computed tomography imaging techniques and histological analyses were made to confirm intramuscular osteogenesis. Volume comparisons were conducted between right and left hind limb of each animal, using a Wilcoxon signed rank test. Quantitative polymerase chain reaction (qPCR) was performed to explore intra muscular expression of BMP2, Alk3 and Id1. Nineteen mice survive the complete SCI and peripheral denervation procedure. When CTX injections were done right after surgery (n = 7), bilateral HO were detected in all animals after 28 days. Micro-CT measurements showed significantly increased BV in denervated paws (1.47 mm3 +/- 0.5) compared to contralateral sides (0.56 mm3 +/-0.4), p = 0.03. When peripheral denervation and CTX injections were performed after sham SCI surgery (n = 6), bilateral HO were present in three mice at day 28. Quantitative PCR analyses showed no changes in intra muscular BMP2 expression after SCI as compared to control mice (shamSCI). Peripheral denervation can be reliably added to spinal cord transection in NHO mouse model. This new experimental design confirms that neuro inflammatory mechanisms induced by central or peripheral nervous system injury plays a key role in triggering ectopic osteogenesis.

Heterotopic ossification related to the use of recombinant human BMP-2 in osteonecrosis of femoral head.

Despite the wide use of recombinant human bone morphogenetic protein-2 (rhBMP-2) in bone defect, its application in treating osteonecrosis of femoral head (ONFH) is yet to be elucidated. The heterotopic ossification (HO) after rhBMP-2 usage in some orthopedic surgeries has been reported previously; however, only a few studies describe this complication in the treatment of ONFH.The present study investigated whether the rhBMP-2 application would increase the risk of HO formation in selected ONFH patients with nonvascularized bone grafting surgery and enhance the surgical results of nonvascularized bone grafting as compared to patients who did not receive intraoperative rhBMP-2.A retrospective analysis was performed on 94 patients (141 hips) who, with Association Research Circulation Osseous (ARCO) stages IIb, IIc, and IIIa ONFH, underwent nonvascularized bone grafting surgery. The first 46 patients (66 hips) received intraoperative rhBMP-2. The postoperative radiographic results (X-ray and CT scan) and Harris hip score (HHS) were reviewed in each patient to record the incidence of HO formation and evaluate the clinical efficacy of rhBMP-2, respectively.HO formation frequently occurred in patients receiving intraoperative rhBMP-2 (8/66 hips) than those not receiving the protein (1/75 hips) (P = .02). HHS improved from preoperatively at the final follow-up (P < .01) in the BMP-positive group, with a survival rate of 83.3%. In the BMP-negative group, the HHS improved from preoperatively at the end of the follow-up (P < .01), and the survival rate was 72.0%.rhBMP-2 has osteoinductive property and might serve as an adjuvant therapy in the surgical treatment of ONFH. However, the incidence of HO formation might increase when used in high doses.

Ectopic bone formation with joint impingement after posterior lumbar fusion with rhBMP-2.

Recombinant human bone morphogenetic protein-2 (rhBMP-2) was recently licensed for local administration during posterior lumbar fusion. In this indication, considerable uncertainty remains about the nature and mechanisms of the many adverse effects of rhBMP-2, such as ectopic bone formation. We report a case of ectopic bone formation with impingement on a facet joint and incapacitating low back pain after minimally invasive transforaminal L5-S1 interbody fusion with local application of rhBMP-2 (InductOs(®)). Revision surgery was eventually performed to alleviate the symptoms by removing the ectopic bone. Caution is in order regarding the use of rhBMP-2 during posterior lumbar fusion. Every effort should be made to minimise the risk of complications.

Ectopic osteogenesis and scaffold biodegradation of nano-hydroxyapatite-chitosan in a rat model.

The bone-formation and scaffold-biodegradation processes have not been fully characterized. This study aimed to determine the osteogenic ability of nHA-CS osteo-induced bone marrow mesenchymal stem cell (BMSC) composites and to explore the relationship between bone formation and scaffold biodegradation. The nHA-CS osteo-induced BMSC composites (nHA-CS+cells group) and the nHA-CS scaffolds (nHA-CS group) were implanted into the femoral spatium intermusculare of SD rats. At 2, 4, 6, 8, and 12 weeks post-implantation, the rat femurs were scanned using computerized tomography (CT), and the CT values of the implants were measured and comparatively analyzed. The implants were then harvested and subjected to hematoxylin and eosin (HE) and Masson's trichrome staining, and the percentages of bone area, scaffold area and collagen area were compared between the two groups. The CT values of the implants were higher in the nHA-CS+cells group than the nHA-CS group at the same time points (P < 0.05). Histological analysis revealed that de novo bone and collagen formation in the pores of the scaffolds gradually increased from 2 weeks post-implantation in both groups and that the scaffold gradually degraded as bone formation proceeded. However, more de novo bone and collagen formation and scaffold degradation occurred in the nHA-CS+cells group than in the nHA-CS group at the same time points (P < 0.05). In conclusion, nHA-CS osteo-induced BMSC composites are promising bone tissue engineering substitutes, and osteo-induced BMSCs can significantly enhance the osteogenic ability and play an active role in the degradation of nHA-CS scaffolds on par with bone formation.

Novel mouse model of spinal cord injury-induced heterotopic ossification.

Heterotopic ossification (HO) develops in about 20% to 30% of patients with spinal cord injury (SCI) and significantly impairs their rehabilitation. There is no effective prevention or treatment for this condition at this time. Our current understanding of its etiology and pathophysiology is limited partially due to the lack of clinically relevant animal models. In this study, we report a novel mouse model of SCI-induced HO by administering a subthreshold dose of bone morphogenetic protein (BMP)-2 to muscles in mice after SCI. Micro-computed tomography scanning showed that an intramuscular injection of 0.25 micrograms of BMP-2 causes significant HO in mice with SCI but not in control (sham surgery) mice. Our analysis of gene expression showed significantly increased BMP signaling in quadriceps following SCI, suggesting that BMP signaling may play a role in SCI-induced HO. Administering 0.25 micrograms of BMP-2 to the front arms of the mice with SCI also results in the development of significant HO but not in control mice. This suggests that SCI causes a systematic osteogenic effect, which is not limited to paralyzed limbs. This novel mouse model will serve as a powerful tool in exploring the molecular mechanisms of SCI-induced HO, which may lead to novel treatment for this disease.

Recombinant human bone morphogenetic protein-2-induced ossification of the ligamentum flavum in rats and the associated global modification of histone H3.

OBJECT: The primary object of this investigation was to study recombinant human bone morphogenetic protein-2 (rhBMP-2)-induced ossification of the ligamentum flavum and associated histone H3 modification in a rat model. In an additional set of studies the authors investigated spinal cord and behavioral changes in the same model. METHODS: The authors report on 2 separate sets of studies. A total of 90 rats were used for the 2 sets of studies (45 each); in each study, a lyophilized rhBMP-2 and collagen mixture (20 µg rhBMP-2 and 200 µl collagen) was implanted in the lumbar extradural space in 18 rats; another 18 animals were used for a sham-operation control group and underwent implantation of lyophilized collagen without rhBMP-2 at the same level; an additional 9 animals were used as untreated controls. Lumbar spinal samples were harvested from the rhBMP-2 groups and the shamoperation control groups at 1 week, 3 weeks, and 9 weeks after the operation. Samples were also obtained from untreated controls at the same time points. All samples were scanned using micro-CT and then made into paraffinembedded sections. The sections from the first set of 45 rats were stained using elastica van Gieson and toluidine blue, and the expression of histone modifications (H3K9ac, H3K18ac, H3K4me3, and H3K36me3) and osteogenic transcription factors (osterix, Runx2) was detected by immunohistochemistry. In the second set of studies, hindlimb motor function was assessed at 1 week, 3 weeks, and 9 weeks after surgery. After behavioral evaluation, samples were harvested, scanned using micro-CT, and then made into paraffin-embedded sections. The sections were stained using Luxol fast blue. The expression of NeuN was also detected using immunohistochemistry. RESULTS: Ossification was seen in the rhBMP-2 group from 1 week after insertion, and the volume of ossified mass increased at 3 and 9 weeks. There was no ossification seen in the sham-surgery and normal controls. The pathological changes of ossification involved ligament degeneration, cartilage formation, and, finally, bone replacement. Spinal cord evaluation showed a significant decrease in white matter content and number of neurons at 9 weeks after operation in the rhBMP-2-treated group (compared with findings in the sham-surgery and control groups as well as findings at the earlier time points in the rhBMP-2 group). Using immunohistochemical staining, histone modifications (H3K9ac, H3K18ac, H3K4me3, and H3K36me3) and osteogenic transcription factors (osterix, Runx2) all were found to be expressed in the fibrocartilage area of the rat ossified ligamentum flavum samples (rhBMP2 group). CONCLUSIONS: This rhBMP-2-induced OLF is a typical endochondral ossification, which is similar to clinical OLF. The compressed spinal cord around the ossification site showed signs of a chronic degenerative process. Histone H3 modifications (H3K9ac, H3K18ac, H3K4me3, and H3K36me3) may play an important role in OLF.

Voriconazole-associated soft tissue ossification: an undescribed cause of glenohumeral joint capsulitis.

Voriconazole-related periostitis has been increasingly described in the literature over the last several years as a recognizable disease entity, especially in lung transplant patients. This relationship should be considered when approaching immunosuppressed patients presenting with diffuse bone pain and imaging findings of periostitis. We present a case of voriconazole-associated periostitis, capsular and enthesial ossification and glenuhumeral capsulitis in a patient with a hematologic malignancy. To the authors' knowledge, soft tissue ossification associated with voriconazole has not been described in the radiology literature.

Neuroforaminal chondrocyte metaplasia and clustering associated with recombinant bone morphogenetic protein-2 usage in transforaminal lumbar interbody fusion.

BACKGROUND CONTEXT: Recombinant human bone morphogenetic protein-2 (rhBMP-2) is commonly used to augment posterior and interbody spinal fusion techniques and has many reported side effects. Neuroforaminal heterotopic ossification (HO) is a known cause of postoperative leg pain, but the pathohistologic composition of this material is not well understood. PURPOSE: The purpose of this article was to report the histologic composition of a case of HO and lumbar radiculopathy after transforaminal lumbar interbody fusion with rhBMP-2. STUDY DESIGN/SETTING: This is a case report. PATIENT SAMPLE: This is a single patient case report. OUTCOME MEASURES: The outcomes considered were physician-recorded clinical, physiological, and functional measures. METHODS: A retrospective review of a single patient was performed. Clinical, radiographic, and pathologic specimens were reviewed and are reported. RESULTS: A 69-year-old woman presented with low back pain and right leg radicular pain associated with L4-L5 stenosis and a recurrent facet cyst. After attempted nonsurgical care, she underwent an L4-L5 revision decompression with interbody and posterolateral fusions including off-label rhBMP-2. Postoperatively, her symptoms resolved for approximately 7 months but then returned in association with right L4-L5 foraminal HO. The ectopic tissue was notably larger than suggested by preoperative computed tomographic scan. It was decompressed, which then improved her symptoms. Histologic examination of the specimen revealed three discrete tissue types: a nonspecific fibrovascular stroma; immature osteoid and woven bone; and chondrocyte metaplasia with chondrocyte clustering. CONCLUSIONS: Neuroforaminal HO formation is a reported side effect associated with the off-label use of rhBMP-2 for posterior lumbar interbody fusion. The mechanism of formation and the composition of this material are not well understood but may involve a chondrocyte differentiation pathway.

Allogeneic morphogenetic protein vs. recombinant human bone morphogenetic protein-2 in lumbar interbody fusion procedures: a radiographic and economic analysis.

BACKGROUND: Since the introduction of rhBMP-2 (Infuse) in 2002, surgeons have had an alternative substitute to autograft and its related donor site morbidity. Recently, the prevalence of reported adverse events and complications related to the use of rhBMP-2 has raised many ethical and legal concerns for surgeons. Additionally, the cost and decreasing reimbursement landscape of rhBMP-2 use have required identification of a viable alternative. Osteo allogeneic morphogenetic protein (OsteoAMP) is a commercially available allograft-derived growth factor rich in osteoinductive, angiogenic, and mitogenic proteins. This study compares the radiographic fusion outcomes between rhBMP-2 and OsteoAMP allogeneic morphogenetic protein in lumbar interbody fusion spine procedures. METHODS: Three hundred twenty-one (321) patients from three centers underwent a transforaminal lumbar interbody fusion (TLIF) or lateral lumbar interbody fusion (LLIF) procedure and were assessed by an independent radiologist for fusion and radiographically evident complications. The independent radiologist was blinded to the intervention, product, and surgeon information. Two hundred and twenty-six (226) patients received OsteoAMP with autologous local bone, while ninety-five (95) patients received Infuse with autologous local bone. Patients underwent radiographs (x-ray and/or CT) at standard postoperative follow-up intervals of approximately 1, 3, 6, 12, and 18 months. Fusion was defined as radiographic evidence of bridging across endplates, or bridging from endplates to interspace disc plugs. Osteobiologic surgical supply costs were also analyzed to ascertain cost differences between OsteoAMP and rhBMP-2. RESULTS: OsteoAMP produced higher rates of fusion at 6, 12, and 18 months (p ≤ 0.01). The time required for OsteoAMP to achieve fusion was approximately 40% less than rhBMP-2 with approximately 70% fewer complications. Osteobiologic supply costs were 80.5% lower for OsteoAMP patients (73.7% lower per level) than for rhBMP-2. CONCLUSIONS: Results of this study indicate that OsteoAMP is a viable alternative to rhBMP-2 both clinically and economically when used in TLIF and LLIF spine procedures.

Complications associated with posterior and transforaminal lumbar interbody fusion.

Posterior lumbar interbody fusion and transforaminal lumbar interbody fusion are commonly performed to obtain a 360° arthrodesis through a posterior-only approach. These techniques are currently used in the management of spondylolisthesis, degenerative scoliosis, pseudarthrosis, recurrent disk herniation, and chronic low back pain with associated degenerative disk disease. Several adverse events have been described, including intraoperative neurologic injury, implant migration or subsidence, dural tears, infection, heterotopic ossification, BMP-related radiculitis, and osteolysis. Although the use of newer materials (eg, bone morphogenetic proteins) and procedures (eg, minimally invasive surgery) is on the rise, they are associated with unique concerns. Understanding the potential adverse events and steps that can be taken to prevent, detect, and manage complications is critical in patient counseling and perioperative decision making.

Hedgehog signaling inhibition by the small molecule smoothened inhibitor GDC-0449 in the bone forming prostate cancer xenograft MDA PCa 118b.

BACKGROUND: Hedgehog signaling is a stromal-mesenchymal pathway central to the development and homeostasis of both the prostate and the bone. Aberrant Hedgehog signaling activation has been associated with prostate cancer aggressiveness. We hypothesize that Hedgehog pathway is a candidate therapeutic target in advanced prostate cancer. We confirm increased Hedgehog signaling in advanced and bone metastatic castrate resistant prostate cancer and examine the pharmacodynamic effect of Smoothened inhibition by the novel reagent GDC-0449 in an experimental prostate cancer model. METHODS: Hedgehog signaling component expression was assessed in tissue microarrays of high grade locally advanced and bone metastatic disease. Male SCID mice subcutaneously injected with the bone forming xenograft MDA PCa 118b were treated with GDC-0449. Hedgehog signaling in the tumor microenvironment was assessed by proteomic and species specific RNA expression and compared between GDC-0449 treated and untreated animals. RESULTS: We observe Hedgehog signaling in high grade locally advanced and bone marrow infiltrating disease. Evidence of paracrine activation of Hedgehog signaling in the tumor xenograft, was provided by increased Sonic Hedgehog expression in human tumor epithelial cells, coupled with increased Gli1 and Patched1 expression in the murine stromal compartment, while normal murine stroma did not exhibit Hh signaling expression. GDC-0449 treatment attenuated Hh signaling as evidenced by reduced expression of Gli1 and Ptch1. Reduction in proliferation (Ki67) was observed with no change in tumor volume. CONCLUSIONS: GDC-0449 treatment is pharmacodynamically effective as evidenced by paracrine Hedgehog signaling inhibition and results in tumor cell proliferation reduction. Understanding these observations will inform the clinical development of therapy based on Hedgehog signaling inhibition.

Effects of autogenous growth factors on heterotopic bone formation of osteogenic cells in small animal model.

AIMS: This study used a new approach to investigate the effective concentrations of growth factors released from platelet concentrate (PC) on the bone formation capacity of osteogenically differentiated rat bone marrow stromal cells (rBMSCs). MATERIALS AND METHODS: Rat BMSCs and whole blood were harvested from 40 adult male Spraque-Dawly rats. Rat BMSCs were expanded in an osteogenic medium and seeded on inert collagenous bovine bone matrix (ICBM). Growth factors released from degranulated PC (GFs) containing TGF-ß1 1 (25ng/ml)-10ng (250ng/ml) and rhBMP-2 400ng (10µg/ml) were suspended in 40µl platelet poor plasma (PPP) and applied on the ICBM-rBMSC constructs or ICBM only, respectively. The constructs were then transplanted in autologous hosts for 4 weeks. Concurrently, osteoblastic differentiation of rBMSCs on ICBM-rBMSC-PPP constructs was characterized in vitro. RESULTS: Rat BMSCs in osteogenic medium exhibited phenotypes of mature osteoblasts. The amount of newly formed bone among groups of ICBM-rBMSC-PPP with and without GFs was not significantly different (p>0.05) and was significantly lower than a group of ICBM-PPP-BMP-2 (p<0.05). CONCLUSIONS: Autogenous GFs had no effect on the capacity of rBMSCs to form new bone. The ability to measure the bone formation capacity of transplanted autologous cells and growth factors in a small animal model was demonstrated.

Promoting fusion in minimally invasive lumbar interbody stabilization with low-dose bone morphogenic protein-2--but what is the cost?

BACKGROUND: Using bone morphogenic protein (BMP) to augment fusion in spine surgery is widespread and lends itself in particular to minimally invasive lumbar fusion, where the surface area for fusion is significantly less than the equivalent open procedure. PURPOSE: Here we described the use of very low-dose BMP in promoting fusion in minimally invasive lumbar interbody fixation but also highlight some of the potential complications of BMP-2 use and techniques available to reduce or avoid them. STUDY DESIGN: Prospective observational study of consecutive patients undergoing minimally invasive lumbar interbody fusion with percutaneous pedicle screws. PATIENT SAMPLE: Thirty patients aged between 22 and 78 years (mean 53 years). OUTCOME MEASURES: Thin-slice lumbar computed tomography scanning with multiplanar reconstruction at 6 and 12 months postoperative. METHODS: Thirty-six spinal levels were instrumented in total, of which four underwent posterior lumbar interbody fusion and 32 underwent transforaminal lumbar interbody fusion. Bone graft harvested locally was placed in the disc space with low-dose BMP-2 (1.4 mg per level). RESULTS: Thirty-three of 36 spinal levels showed complete fusion at a mean postoperative scan time of 7.1 months. Two levels demonstrated partial fusion at 6 months, which was complete at 12 months. There was one case of nonunion at 12 months, which also demonstrated vertebral body osteolysis. Despite very low-dose BMP-2, two cases of asymptomatic heterotopic ossification were observed, and there were two cases of perineural cyst formation, one of whom required revision of the interbody cage. CONCLUSIONS: The use of BMP with autograft in the disc space during minimally invasive lumbar interbody fusion is associated with a high rate of early fusion. Even with very low-dose BMP used in this study, complications related to BMP usage were not avoided completely.