Human nonunion tissues display differential gene expression in comparison to physiological fracture callus.

The healing of bone fractures can become aberrant and lead to nonunions which in turn have a negative impact on patient health. Understanding why a bone fails to normally heal will enable us to make a positive impact in a patient's life. While we have a wealth of molecular data on rodent models of fracture repair, it is not the same with humans. As such, there is still a lack of information regarding the molecular differences between normal physiological repair and nonunions. This study was designed to address this gap in our molecular knowledge of the human repair process by comparing differentially expressed genes (DEGs) between physiological fracture callus and two different nonunion types, hypertrophic (HNU) and oligotrophic (ONU). RNA sequencing data revealed over ∼18,000 genes in each sample. Using the physiological callus as the control and the nonunion samples as the experimental groups, bioinformatic analyses identified 67 and 81 statistically significant DEGs for HNU and ONU, respectively. Out of the 67 DEGs for the HNU, 34 and 33 were up and down-regulated, respectively. Similarly, out of the 81 DEGs for the ONU, 48 and 33 were up and down-regulated, respectively. Additionally, we also identified common genes between the two nonunion samples; 8 (10.8 %) upregulated and 12 (22.2 %) downregulated. We further identified many biological processes, with several statistically significant ones. Some of these were related to muscle and were common between the two nonunion samples. This study represents the first comprehensive attempt to understand the global molecular events occurring in human nonunion biology. With further research, we can perhaps decipher new molecular pathways involved in aberrant healing of human bone fractures that can be therapeutically targeted.

Stem Cells and Their Derivatives: An Implication for the Regeneration of Nonunion Fractures.

Despite advances in biomedical research, fracture nonunion rates have remained stable throughout the years. Long-bone fractures have a high likelihood of nonunion, but the specific biological pathways involved in this severe consequence are unknown. Fractures often heal in an organized sequence, including the production of a hematoma and an early stage of inflammation, the development of a soft callus and hard callus, and eventually the stage of bone remodeling. Deficient healing can result in a persistent bone defect with instability, discomfort, and loss of function. In the treatment of nonunions, mesenchymal stem cells (MSCs) prove to be a promising and safe alternative to the standard therapeutic strategies. Moreover, novel scaffolds are being created in order to use a synergistic biomimetic technique to rapidly generate bone tissue. MSCs respond to acellular biomimetic matrices by regenerating bone. Extracellular vesicles (EVs) derived from MSCs have recently gained interest in the field of musculoskeletal regeneration. Although many of these techniques and technologies are still in the preclinical stage and have not yet been approved for use in humans, novel approaches to accelerate bone healing via MSCs and/or MSC derivatives have the potential to reduce the physical, economic, and social burdens associated with nonhealing fractures and bone defects. In this review, we focus on providing an up-to-date summary of recent scientific studies dealing with the treatment of nonunion fractures in clinical and preclinical settings employing MSC-based therapeutic techniques.

The promotive role of USP1 inhibition in coordinating osteogenic differentiation and fracture healing during nonunion.

BACKGROUND: Nonunion is a failure of fracture healing and a major complication after fractures. Ubiquitin-specific protease 1 (USP1) is a deubiquitinase that involved in cell differentiation and cell response to DNA damage. Herein we investigated the expression, function and mechanism of USP1 in nonunion. METHODS AND RESULTS: Clinical samples were used to detect the USP1 expression in nonunion. ML323 was selected to inhibit USP1 expression throughout the study. Rat models and mouse embryonic osteoblasts cells (MC3T3-E1) were used to investigate the effects of USP1 inhibition on fracture healing and osteogenesis in vivo and in vitro, respectively. Histological changes were examined by micro-computerized tomography (Micro-CT), hematoxylin & eosin (H&E) staining and Masson staining. Alkaline phosphatase (ALP) activity detection and alizarin red staining were used for osteogenic differentiation observation. The expression of related factors was detected by quantitative real-time PCR, western blot or immunohistochemistry (IHC). It was shown that USP1 was highly expressed in nonunion patients and nonunion rats. USP1 inhibition by ML323 promoted fracture healing in nonunion rats and facilitated the expression of osteogenesis-related factors and the signaling of PI3K/Akt pathway. In addition, USP1 inhibition accelerated osteogenic differentiation and promoting PI3K/Akt signaling in MC3T3-E1 cells. CONCLUSIONS: USP1 inhibition plays a promotive role in coordinating osteogenic differentiation and fracture healing during nonunion. PI3K/Akt may be the downstream pathway of USP1.

miR-1323 suppresses bone mesenchymal stromal cell osteogenesis and fracture healing via inhibiting BMP4/SMAD4 signaling.

BACKGROUND: Atrophic non-union fractures show no radiological evidence of callus formation within 3 months of fracture. microRNA dysregulation may underlie the dysfunctional osteogenesis in atrophic non-union fractures. Here, we aimed to analyze miR-1323 expression in human atrophic non-union fractures and examine miR-1323's underlying mechanism of action in human mesenchymal stromal cells. METHODS: Human atrophic non-union and standard healing fracture specimens were examined using H&E and Alcian Blue staining, immunohistochemistry, qRT-PCR, immunoblotting, and ALP activity assays. The effects of miR-1323 mimics or inhibition on BMP4, SMAD4, osteogenesis-related proteins, ALP activity, and bone mineralization were analyzed in human mesenchymal stromal cells. Luciferase reporter assays were utilized to assay miR-1323's binding to the 3'UTRs of BMP4 and SMAD4. The effects of miR-1323, BMP4, and SMAD4 were analyzed by siRNA and overexpression vectors. A rat femur fracture model was established to analyze the in vivo effects of antagomiR-1323 treatment. RESULTS: miR-1323 was upregulated in human atrophic non-union fractures. Atrophic non-union was associated with downregulation of BMP4 and SMAD4 as well as the osteogenic markers ALP, collagen I, and RUNX2. In vitro, miR-1323 suppressed BMP4 and SMAD4 expression by binding to the 3'UTRs of BMP4 and SMAD4. Moreover, miR-1323's inhibition of BMP4 and SMAD4 inhibited mesenchymal stromal cell osteogenic differentiation via modulating the nuclear translocation of the transcriptional co-activator TAZ. In vivo, antagomiR-1323 therapy facilitated the healing of fractures in a rat model of femoral fracture. CONCLUSIONS: This evidence supports the miR-1323/BMP4 and miR-1323/SMAD4 axes as novel therapeutic targets for atrophic non-union fractures.

Ras associated with diabetes may play a role in fracture nonunion development in rats.

BACKGROUND: Rad is the prototypic member of a subfamily of Ras-related small G-proteins and is highly expressed in the skeletal muscle of patients with type II diabetes. Our previous microarray analysis suggested that Rad may mediate fracture nonunion development. Thus, the present study used rat experimental models to investigate and compare the gene and protein expression patterns of both Rad and Rem1, another RGK subfamily member, in nonunions and standard healing fractures. METHODS: Standard healing fractures and nonunions (produced via periosteal cauterization at the fracture site) were created in the femurs of 3-month-old male Sprague-Dawley rats. At post-fracture days 7, 14, 21, and 28, the fracture callus and fibrous tissue from the standard healing fractures and nonunions, respectively, were harvested and screened (via real-time PCR) for Rad and Rem1 expression. The immunolocalization of both encoded proteins was analyzed at post-fracture days 14 and 21. At the same time points, hematoxylin and eosin staining was performed to identify the detailed tissue structures. RESULTS: Results of real-time PCR analysis showed that Rad expression increased significantly in the nonunions, compared to that in the standard healing fractures, at post-fracture days 14, 21, and 28. Conversely, immunohistochemical analysis revealed the immunolocalization of Rad to be similar to that of Rem1 in both fracture types at post-fracture days 14 and 21. CONCLUSIONS: Rad may mediate nonunion development, and thus, may be a promising therapeutic target to treat these injuries.

VEGF-loaded mineral-coated microparticles improve bone repair and are associated with increased expression of epo and RUNX-2 in murine non-unions.

A poor vascular supply of the fracture gap is a key factor for the development of atrophic non-unions. Mineral-coated microparticles (MCM) represent a sophisticated carrier system for the delivery of vascular endothelial growth factor (VEGF). Hence, we investigated whether VEGF-loaded MCM improve bone repair in non-unions. For this purpose, we analyzed binding and release kinetics of MCM for VEGF in vitro. Moreover, we applied VEGF-loaded or -unloaded MCM in a murine non-union model in vivo and studied the process of bone healing by means of biomechanical, radiological, histomorphometric, and Western blot techniques. MCM-free non-unions served as controls. The binding efficiency of MCM for VEGF was 46 ± 3% and the release profile revealed an initial minor burst release followed by a sustained release over a 50-day study period, thus, mimicking the physiological expression profile of VEGF during bone healing. In vivo, bone defects treated with VEGF-loaded MCM exhibited a higher bending stiffness, a higher fraction of bone volume/tissue volume and a larger callus area on days 14 and 70 when compared to the other groups. Western blot analyses on day 14 revealed a higher expression of VEGF, erythropoietin (EPO), and runt-related transcription factor 2, but not of EPO-receptor in bone defects treated with VEGF-loaded MCM. These findings demonstrate that the use of MCM for VEGF delivery shows great potential due to the ability to maintain protein stability and functionality in vivo. Moreover, the application of VEGF-loaded MCM represent a promising strategy for the treatment of non-unions. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Periosteal Mesenchymal Progenitor Dysfunction and Extraskeletally-Derived Fibrosis Contribute to Atrophic Fracture Nonunion.

Atrophic nonunion represents an extremely challenging clinical dilemma for both physicians and fracture patients alike, but its underlying mechanisms are still largely unknown. Here, we established a mouse model that recapitulates clinical atrophic nonunion through the administration of focal radiation to the long bone midshaft 2 weeks before a closed, semistabilized, transverse fracture. Strikingly, fractures in previously irradiated bone showed no bony bridging with a 100% nonunion rate. Radiation triggered distinct repair responses, separated by the fracture line: a less robust callus formation at the proximal side (close to the knee) and bony atrophy at the distal side (close to the ankle) characterized by sustained fibrotic cells and type I collagen-rich matrix. These fibrotic cells, similar to human nonunion samples, lacked osteogenic and chondrogenic differentiation and exhibited impaired blood vessel infiltration. Mechanistically, focal radiation reduced the numbers of periosteal mesenchymal progenitors and blood vessels and blunted injury-induced proliferation of mesenchymal progenitors shortly after fracture, with greater damage particularly at the distal side. In culture, radiation drastically suppressed proliferation of periosteal mesenchymal progenitors. Radiation did not affect hypoxia-induced periosteal cell chondrogenesis but greatly reduced osteogenic differentiation. Lineage tracing using multiple reporter mouse models revealed that mesenchymal progenitors within the bone marrow or along the periosteal bone surface did not contribute to nonunion fibrosis. Therefore, we conclude that atrophic nonunion fractures are caused by severe damage to the periosteal mesenchymal progenitors and are accompanied by an extraskeletal, fibro-cellular response. In addition, we present this radiation-induced periosteal damage model as a new, clinically relevant tool to study the biologic basis of therapies for atrophic nonunion. © 2018 American Society for Bone and Mineral Research.

[Expression of transforming growth factor 1 and bone morphogenetic protein 9 in human nonunion tissues and its clinical significance].

OBJECTIVE: To examine the expression of transforming growth factor 1(TGF-ß1) and bone morphogenetic protein-9 (BMP-9) in human nonunion tissues, and to evaluate the clinical significance.
 Methods: The number of hypertrophic nonunion tissue samples and atrophic nonunion tissue samples were collected from Department of Orthopedics, the Second Xiangya Hospital of Central South University and Suzhou Kowloon Hospital Affiliated to School of Medicine of Shanghai Jiao Tong University between 2010 and 2014. Semi-quantification of SP immunohistochemical method and pathological image analysis software IPP6.0 were used to analyze the expression of TGF-ß1 and BMP-9. Nonunion type, patients' age and nonunion time were statistical analyzed.
 Results: The absorbance values of TGF-ß1 and BMP-9 in the hypertrophic nonunion tissues were 0.3236±0.0390 and 0.1337±0.0400, respectively; while the absorbance values ofTGF-ß1 and BMP-9 in the atrophic nonunion tissues were 0.3191±0.0369 and 0.1373±0.0423, respectively, with no significant difference between the two types of tissues (both P>0.05). There was also no significant difference in patients' age and bone nonunion time between them (all P>0.05).
 Conclusion: There is no significant difference in osteogenic potential between the hypertrophic nonunion tissues and the atrophic nonunion tissues.

MiR-133a inhibits fracture healing via targeting RUNX2/BMP2.

OBJECTIVE: To analyze the mechanism of miR-133a in inhibiting fracture healing through regulating runt-related transcription factor 2 (RUNX2) signaling pathway. PATIENTS AND METHODS: A total of 80 patients with fracture admitted to our hospital from January 2016 to January 2017 were divided into 2 groups according to nonunion fracture or healing fracture: nonunion fracture group (n = 40) and control group (n= 40). After admission, patients underwent the surgery, respectively, and the bone tissues were taken for stand-by application. The expression level of bone morphogenetic protein 2 (BMP2) was detected using the immunohistochemical method, the expression level of RUNX2 protein was detected by Western blotting, and the expression level of micro ribonucleic acid (miR)-133a was detected by quantitative polymerase chain reaction (qPCR). Moreover, the bioinformatics method was used to predict the target gene of miR-133a, and the luciferase reporter gene was used to detect the binding of miR-133a to RUNX2. RESULTS: Compared with those in control group, the expression of BMP2 and the relative expressions of RUNX2 protein and miR-133a were significantly decreased; the differences were statistically significant (p < 0.05). Pearson correlation analysis showed that miR-133a was negatively correlated with RUNX2. After overexpression of miR-133a, the expression level of RUNX2 was decreased, but it was increased significantly after interference in miR-133a. Besides, it was found in dual-luciferase reporter assay that miR-133a bound to RUNX2. CONCLUSIONS: MiR-133a inhibits the bone formation through inhibiting the RUNX2/BMP2 signaling pathway, thereby negatively regulating the fracture healing.

Valores de vitamina D en fracturas no consolidadas / Vitamin D levels in non-union fractures

Introducción: La falta de consolidacion de una fractura es, en general, un fenomeno multifactorial. El objetivo de este estudio fue estimar los valores de referencia de vitamina D (25OHD3) en fracturas que no consolidaron, estudiar su asociacion con la edad y su localizacion. Materiales y Métodos: Estudio prospectivo, de observacion y descriptivo en 29 pacientes con fracturas no consolidadas. Se determinaron las concentraciones sericas de vitamina D (25OHD3) junto con los estudios prequirurgicos. Se calcularon modelos generalizados para estimar los efectos de la edad y la localizacion, y detectar grupos de pacientes con niveles inferiores al valor recomendado. Resultados: El 68,9% de los pacientes tenia concentraciones sericas promedio de vitamina D inferiores al valor normal (30,0 ng/ml), que se asociaron inversamente con la edad, 40 anos fue el punto de corte a partir del cual otras caracteristicas, como la localizacion de la fractura (en huesos que afectan a los miembros inferiores), condicionan conjuntamente la falta de consolidacion. Conclusiones: La mayoria de los pacientes cuya fractura no consolido tenia deficiencia de vitamina D y este fenomeno es marcado a partir de los 40 anos de edad. Es importante identificar a los pacientes con mayor riesgo de presentar este deficit en las primeras etapas del tratamiento de las fracturas, ya que el aporte de este micronutriente es un factor reconocido para disminuir el riesgo de falta de consolidacion. Nivel de Evidencia: IV

Introduction: Absence of bone union after a fracture is generally multifactorial phenomenon. The objective of this study was to determine reference vitamin D values (25OHD3) in non-unions, and to study their association with age and localization. Methods: A prospective, observational and descriptive study was performed to evaluate 29 patients with non-union fractures. Serum vitamin D levels (25OHD3) were determined together with standard preoperative studies. Generalized models were used to estimate the effects of age and location, as well as to detect the group of patients with vitamin D levels lower than recommended. Results: The 68.9% had serum levels of vitamin-D lower than the normal value (30 ng/mL), which was inversely associated with age, being the age of 40 the cutoff point from which other characteristics, such as location, conditioned simultaneously the non-union. Conclusions: Most patients with a non-union fracture had vitamin D deficiency, and this phenomenon was more evident in patients >40 years. Prompt identification of patients with increased risk of presenting this deficiency is important, as treatment could reduce the incidence of fractures that evolve into a non-union. Level of Evidence: IV

Cell-based Assay System for Predicting Bone Regeneration in Patient Affected by Aseptic Nonunion and Treated with Platelet Rich Fibrin.

BACKGROUND: Regenerative strategies based on the use of platelet concentrates as an autologous source of growth factors (GF) has been proposed to promote the healing of long bone nonunions. However, the relatively high failure rate stimulates interest in growing knowledge and developing solutions to obtain the best results from the regenerative approach. OBJECTIVE: In this study we evaluated whether a cell-based assay system could be able to recognize patients who will benefit or not from the use of autologous platelet preparations. METHOD: The autologous serum was used in culture medium to promote the osteogenic differentiation of normal bone-marrow stromal cells (BMSC). Blood samples were collected from 16 patients affected by aseptic long bone nonunion who were candidates to the treatment with autologous platelet-rich fibrin. The osteoinductive effect was detected by measuring the BMSC proliferation, the mineralization activity, and the expression of bone-related genes. Serum level of basic fibroblast growth factor (bFGF) was considered as a representative marker of the delivery of osteogenic GFs from platelets. Laboratory results were related to the characteristics of the disease before the treatment and to the outcome at 12 months. RESULTS: Serum samples from "good responders" showed significantly higher levels of bFGF and were able to induce a significantly higher proliferation of BMSC, while no significant differences were observed in terms of osteoblast differentiation. CONCLUSION: BMSC-based assay could be a useful tool to recognize patients who have a low probability to benefit from the use of autologous platelet concentrate to promote the healing of long bone nonunion.

Hypoxia and Reactive Oxygen Species Homeostasis in Mesenchymal Progenitor Cells Define a Molecular Mechanism for Fracture Nonunion.

Fracture nonunion is a major complication of bone fracture regeneration and repair. The molecular mechanisms that result in fracture nonunion appearance are not fully determined. We hypothesized that fracture nonunion results from the failure of hypoxia and hematoma, the primary signals in response to bone injury, to trigger Bmp2 expression by mesenchymal progenitor cells (MSCs). Using a model of nonstabilized fracture healing in transgenic 5'Bmp2BAC mice we determined that Bmp2 expression appears in close association with hypoxic tissue and hematoma during the early phases of fracture healing. In addition, BMP2 expression is induced when human periosteum explants are exposed to hypoxia ex vivo. Transient interference of hypoxia signaling in vivo with PX-12, a thioredoxin inhibitor, results in reduced Bmp2 expression, impaired fracture callus formation and atrophic-like nonunion by a HIF-1α independent mechanism. In isolated human periosteum-derived MSCs, BMP2 expression could be induced with the addition of platelets concentrate lysate but not with hypoxia treatment, confirming HIF-1α-independent BMP2 expression. Interestingly, in isolated human periosteum-derived mesenchymal progenitor cells, inhibition of BMP2 expression by PX-12 is accomplished only under hypoxic conditions seemingly through dis-regulation of reactive oxygen species (ROS) levels. In conclusion, we provide evidence of a molecular mechanism of hypoxia-dependent BMP2 expression in MSCs where interference with ROS homeostasis specifies fracture nonunion-like appearance in vivo through inhibition of Bmp2 expression. Stem Cells 2016;34:2342-2353.

Bone morphogenetic protein 2 and decorin expression in old fracture fragments and surrounding tissues.

Bone morphogenetic protein 2 (BMP-2) can promote fracture healing. Although the complex role BMP-2 in bone formation is increasingly understood, the role of endogenous BMP-2 in nonunion remains unclear. Decorin (DCN) can promote the formation of bone matrix and calcium deposition to control bone morphogenesis. In this study, tissue composition and expression of BMP-2 and DCN were detected in different parts of old fracture zones to explore inherent anti-fibrotic ability and osteogenesis. Twenty-three patients were selected, including eight cases of delayed union and 15 cases of nonunion. Average duration of delayed union or nonunion was 15 months. Fracture fragments and surrounding tissues, including bone grafts, marrow cavity contents, and sticking scars, were categorically sampled during surgery. Through observation and histological testing, component comparisons were made between fracture fragments and surrounding tissue. The expression levels of DCN and BMP-2 in different tissues were detected by immunohistochemical staining and real-time polymerase chain reaction. The expression of DCN and BMP- 2 in different parts of the nonunion area showed that, compared with bone graft and marrow cavity contents, sticking scars had the highest expression of BMP-2. Compared with the marrow cavity contents and sticking scars, bone grafts had the highest expression of DCN. The low antifibrotic and osteogenic activity of the nonunion area was associated with non-co-expression of BMP-2 and DCN. Therefore, the co-injection of osteogenic factor BMP and DCN into the nonunion area can improve the induction of bone formation and enhance the conversion of the old scar, thereby achieving better nonunion treatment.

Profiling microRNA expression in fracture nonunions: Potential role of microRNAs in nonunion formation studied in a rat model.

MicroRNAs (miRNAs ) are small non-coding RNAs that regulate gene expression. We hypothesised that the functions of certain miRNAs and changes to their patterns of expression may be crucial in the pathogenesis of nonunion. Healing fractures and atrophic nonunions produced by periosteal cauterisation were created in the femora of 94 rats, with 1:1 group allocation. At post-fracture days three, seven, ten, 14, 21 and 28, miRNAs were extracted from the newly generated tissue at the fracture site. Microarray and real-time polymerase chain reaction (PCR) analyses of day 14 samples revealed that five miRNAs, miR-31a-3p, miR-31a-5p, miR-146a-5p, miR-146b-5p and miR-223-3p, were highly upregulated in nonunion. Real-time PCR analysis further revealed that, in nonunion, the expression levels of all five of these miRNAs peaked on day 14 and declined thereafter. Our results suggest that miR-31a-3p, miR-31a-5p, miR-146a-5p, miR-146b-5p and miR-223-3p may play an important role in the development of nonunion. These findings add to the understanding of the molecular mechanism for nonunion formation and may lead to the development of novel therapeutic strategies for its treatment.

Biological and molecular profile of fracture non-union tissue: current insights.

Delayed bone healing and non-union occur in approximately 10% of long bone fractures. Despite intense investigations and progress in understanding the processes governing bone healing, the specific pathophysiological characteristics of the local microenvironment leading to non-union remain obscure. The clinical findings and radiographic features remain the two important landmarks of diagnosing non-unions and even when the diagnosis is established there is debate on the ideal timing and mode of intervention. In an attempt to understand better the pathophysiological processes involved in the development of fracture non-union, a number of studies have endeavoured to investigate the biological profile of tissue obtained from the non-union site and analyse any differences or similarities of tissue obtained from different types of non-unions. In the herein study, we present the existing evidence of the biological and molecular profile of fracture non-union tissue.

[Expression of bone morphogenetic protein 2 in human nonunion tissue and the clinical significance].

OBJECTIVE: To explore the difference of bone formation potential between hypertrophic nonunion tissue and atrophic nonunion tissue, which may be beneficial to nonunion therapy. METHODS: From October 2010 to March 2014, 40 nonunion tissue samples were collected in Department of Orthopedics, Second Xiangya Hospital. The samples were divided into a hypertrophic nonunion group (n=20) and an atrophic nonunion group (n=20) according to nonunion character; or a 20 to 35 years old group (n=18), a 36 to 50 years old group (n=18), a more than 50 years old group (n=4) according to different ages; or a 9-12 months group (n=21), 13-24 months group (n=14) and a more than 24 months group (n=5) according to different nonunion time. Semi-quantification was performed by SP immunohistochemical method and IPP6.0 was used to analyze the expression of bone morphogenetic protein-2 (BMP-2) through measuring the mean optical density. RESULTS: The mean optical density of BMP-2 was 0.1540±0.0408 in hypertrophic nonunion tissue, 0.1372±0.0372 in atrophic nonunion tissue, there was no significant difference between the 2 groups (P>0.05). The mean optical density of BMP-2 was 0.1477±0.0379 in the 20 to 35 years old group, 0.1419±0.0399 in the 35 to 50 years old group, 0.1456±0.0595 in the more than 50 years old group, there was no significant difference among the three groups (P>0.05). The mean optical density of BMP-2 was 0.1449±0.0366 in the 9-12 months group, 0.1472±0.0400 in the 13-24 months group, 0.1445±0.0541 in the more than 24 months group, there was no significant difference among the 3 groups (P>0.05). CONCLUSION: The present results suggest that the hypertrophic nonunion tissue share similar osteogenic potential with the atrophic nonunion tissue.

Comparison of radiographic appearance and bone scintigraphy in fracture nonunions.

Many surgeons assess the biological activity of fracture nonunions by the presence or absence of callus on radiographs. However, the assessment of biological activity by radiographic appearance alone is controversial. Bone scintigraphy reflects blood flow and new bone formation; therefore, it is useful in assessing such biological activity in nonunion cases. This retrospective study compared radiographs with Tc-99m bone scintigraphy in 48 patients with uninfected nonunions. Positive uptake was observed in all cases. The uptake patterns were classified into 4 types: type 1, intense, uniform uptake; type 2A, a definite photon-deficient cleft between 2 areas of intense uptake; type 2B, a photon-deficient area other than type 2A; and type 3, an intermediate pattern with uneven, distributed uptake. The percentage of type 1 with intense uptake does not decrease with time, and type 2 does not increase. When uptake was compared in patients with a nonunion and a united fracture, higher uptake in nonunion was seen in 46% and lower uptake was seen in 27%. All cases of hypertrophic and more than half of oligotrophic nonunions were type 1. Type 2 was seen in 17% of oligotrophic, 67% of comminuted, 100% of defect, and 57% of atrophic nonunions. Poor callus visualization may not preclude biological activity. Long duration from injury may not equate to declines in biological activity. Comparing uptake in nonunions and united fractures in the same patient may help to assess biological activity. The photon-deficient area is helpful to assess the necessity of bone graft or other osteogenic supplementation.

Decreased pool of mesenchymal stem cells is associated with altered chemokines serum levels in atrophic nonunion fractures.

Nonunion fractures can cause severe dysfunction and are often difficult to treat mainly due to a poor understanding of their physiopathology. Although many aspects of impaired fracture healing have been extensively studied, little is known about the cellular and molecular mechanisms leading to atrophic nonunion. Therefore, the aim of the present study was to assess the pools and biological functions of bone marrow-derived mesenchymal stem cells (hMSCs) and circulating endothelial progenitor cells (EPCs) in atrophic nonunion patients compared to healthy subjects, and the systemic levels of growth factors involved in the recruitment, proliferation and differentiation of these cells. In nonunions, the pool of hMSCs was decreased and their proliferation delayed. However, once committed, hMSCs from nonunions were able to proliferate, differentiate into osteoblastic cells and mineralize in vitro as efficiently as hMSCs from healthy subjects. In parallel, we found altered serum levels of chemokines and growth factors involved in the chemotaxis and proliferation of hMSCs such as leptin, interleukin-6 (IL-6) and its soluble receptor, platelet-derived growth factor-BB (PDGF-BB), stem cell factor (SCF) and insulin-like growth factor-1 (IGF-1). Moreover, we showed that the number of EPCs and their regulating growth factors were not affected in nonunion patients. If nonunion is generally attributed to a vascular defect, our results also support a role for a systemic mesenchymal and osteogenic cell pool defect that might be related to alterations in systemic levels of factors implicated in their chemotaxis and proliferation.

Impaired fracture healing associated with amino acid disturbances.

BACKGROUND: Five percent to 10% of all fracture patients experience an inadequate healing process that results in a nonunion of fracture parts. Previous experimental studies have indicated the importance of sufficient nitric oxide production from arginine during normal fracture healing. However, during conditions of stress, such as inflammation, arginine availability can become limited, which may lead to a nonunion as a result of insufficient callus formation. OBJECTIVE: The aim of this study was to measure callus and plasma amino acid concentrations in patients with and without a fracture nonunion. DESIGN: Amino acid concentrations in plasma and callus were measured with HPLC in atrophic nonunions (n = 12) and compared with those in hypertrophic nonunions (n = 12), acute fractures (n = 15), and healed fractures (n = 8). RESULTS: Arginine (61 compared with 180 µmol/mg; P < 0.0001), citrulline (13 compared with 44 µmol/mg; P < 0.0001), and ornithine (25 compared with 149 µmol/mg; P < 0.0001) in callus were significantly lower in atrophic-nonunion patients than in healed-fracture patients. In hypertrophic nonunions, arginine was significantly higher and ornithine was lower than in healed fractures. Plasma arginine concentrations were significantly lower in patients with hypertrophic nonunions (62 µmol/L; P < 0.001) and acute-fracture patients (41 µmol/L; P < 0.001) but not in atrophic-nonunion patients. Plasma ornithine concentrations were lower in all groups than in acute-fracture patients. CONCLUSIONS: Amino acid concentrations were significantly changed in nonunion patients. Atrophic nonunions had lower concentrations of all amino acids, whereas hypertrophic nonunions had higher arginine and lower ornithine concentrations at fracture sites than did healed-fracture and acute-fracture patients.

Enhancement of fracture healing with the diamond concept: the role of the biological chamber.

Bone regeneration presents a unique challenge to both clinicians and scientists. Recently, a vast amount of knowledge has been attained with regard to the molecular mediators, cell populations and the overall cascade of events participating in the bone repair processes. For the treatment of bone non-unions or bone defects, the 'diamond concept' for biological enhancement supports the implantation of mesenchymal stem cells, a scaffold and a growth factor. Prior to the implantation of any or all of these materials however, the surgeon must develop the ideal biological environment (non-union bed) where molecular and physiological processes will evolve facilitating an early and successful osteogenesis leading to bone continuity and functional restoration of the affected limb. At the end of the surgical procedure the non-union bed should have been transformed to a 'biological chamber' active enough to support efficiently all the necessary physiological processes for a successful outcome. The notion of creating the optimum 'biological chamber' represents the centre of the highest biological activity and in a sense the heart of the diamond concept.