Endochondral fracture healing with external fixation in the Sost knockout mouse results in earlier fibrocartilage callus removal and increased bone volume fraction and strength

Authors

A. Morse, N.Y.C. Yu, L. Peacock, K. Mikulec, I. Kramer, M. Kneissel, M.M. McDonald, D.G. Little

Abstract

Sclerostin deficiency, via genetic knockout or anti-Sclerostin antibody treatment, has been shown to cause increased bone volume, density and strength of calluses following endochondral bone healing. However, there is limited data on the effect of Sclerostin deficiency on the formative early stage of fibrocartilage (non-bony tissue) formation and removal. In this study we extensively investigate the early fibrocartilage callus. Closed tibial fractures were performed on Sost−/− mice and age-matched wild type (C57Bl/6J) controls and assessed at multiple early time points (7, 10 and 14 days), as well as at 28 days post-fracture after bony union. External fixation was utilized, avoiding internal pinning and minimizing differences in stability stiffness, a variable that has confounded previous research in this area.

Normal endochondral ossification progressed in wild type and Sost−/− mice with equivalent volumes of fibrocartilage formed at early day 7 and day 10 time points, and bony union in both genotypes by day 28. There were no significant differences in rate of bony union; however there were significant increases in fibrocartilage removal from the Sost−/− fracture calluses at day 14 suggesting earlier progression of endochondral healing. Earlier bone formation was seen in Sost−/− calluses over wild type with greater bone volume at day 10 (221%, p < 0.01). The resultant Sost−/− united bony calluses at day 28 had increased bone volume fraction compared to wild type calluses (24%, p < 0.05), and the strength of the fractured Sost−/− tibiae was greater than that that of wild type fractured tibiae.

In summary, bony union was not altered by Sclerostin deficiency in externally-fixed closed tibial fractures, but fibrocartilage removal was enhanced and the resultant united bony calluses had increased bone fraction and increased strength.

Link To Article

http://dx.doi.org/10.1016/j.bone.2014.10.018

Changes in the Mechanical Properties and Composition of Bone during Microdamage Repair

Authors

Gang Wang, Xinhua Qu, Zhifeng Yu

Abstract

Under normal conditions, loading activities result in microdamage in the living skeleton, which is repaired by bone remodeling. However, microdamage accumulation can affect the mechanical properties of bone and increase the risk of fracture. This study aimed to determine the effect of microdamage on the mechanical properties and composition of bone. Fourteen male goats aged 28 months were used in the present study. Cortical bone screws were placed in the tibiae to induce microdamage around the implant. The goats were euthanized, and 3 bone segments with the screws in each goat were removed at 0 days, 21 days, 4 months, and 8 months after implantation. The bone segments were used for observing microdamage and bone remodeling, as well as nanoindentation and bone composition, separately. Two regions were measured: the first region (R1), located 1.5 mm from the interface between the screw hole and bone; and the second region (R2), located>1.5 mm from the bone-screw interface. Both diffuse and linear microdamage decreased significantly with increasing time after surgery, with the diffuse microdamage disappearing after 8 months. Thus, screw implantation results in increased bone remodeling either in the proximal or distal cortical bone, which repairs the microdamage. Moreover, bone hardness and elastic modulus decreased with microdamage repair, especially in the proximal bone tissue. Bone composition changed greatly during the production and repair of microdamage, especially for the C (Carbon) and Ca (Calcium) in the R1 region. In conclusion, the presence of mechanical microdamage accelerates bone remodeling either in the proximal or distal cortical bone. The bone hardness and elastic modulus decreased with microdamage repair, with the micromechanical properties being restored on complete repair of the microdamage. Changes in bone composition may contribute to changes in bone mechanical properties.

Link To Article

http://dx.doi.org/10.1371/journal.pone.0108324

Fracture healing using degradable magnesium fixation plates and screws

Authors

Amy Chaya, BS, Sayuri Yoshizawa, DDS, PhD, Kostas Verdelis, DDS, PhD, Sabrina Noorani, MS, B.J. Costello, MD, DMD, Charles Sfeir, DDS, PhD

Abstract

Purpose Internal bone fixation devices made with permanent metals are associated with numerous long-term complications and may require removal. We hypothesized that fixation devices made with degradable magnesium alloys could provide an ideal combination of strength and degradation, facilitating fracture fixation and healing, while eliminating the need for implant removal surgery.

Methods Fixation plates and screws were machined from 99.9% pure magnesium and compared to titanium devices in a rabbit ulna fracture model. Magnesium device degradation and effect on fracture healing and bone formation was assessed after four weeks. Fracture healing with magnesium device fixation was compared to that of titanium devices using qualitative histological analysis and quantitative histomorphometry.

Results Microcomputed tomography showed device degradation after four weeks in vivo. In addition, 2D microCT slices and histological staining showed that magnesium degradation did not inhibit fracture healing or bone formation. Histomorphology revealed no difference in bone bridging fractures fixed with magnesium and titanium devices. Interestingly, abundant new bone was formed around magnesium devices, suggesting a connection between magnesium degradation and bone formation.

Conclusion Our results demonstrate potential for magnesium fixation devices in a loaded fracture environment. Furthermore, these results suggest that magnesium fixation devices may enhance fracture healing by encouraging localized new bone formation.

Link To Article

http://dx.doi.org/10.1016/j.joms.2014.09.007

Activated protein C (APC) can increase bone anabolism via a protease-activated receptor (PAR)1/2 dependent mechanism

Authors

Kaitlin Shen, Ciara M. Murphy, Ben Chan, Mille Kolind, Tegan L. Cheng, Kathy Mikulec, Lauren Peacock, Meilang Xue, Sang-Youel Park, David G. Little, Chris J. Jackson, and Aaron Schindeler

Abstract

Activated Protein C (APC) is an anticoagulant with strong cytoprotective properties that has been shown to promote wound healing. In this study APC was investigated for its potential orthopedic application using a Bone Morphogenetic Protein 2 (rhBMP-2) induced ectopic bone formation model. Local co-administration of 10 µg rhBMP-2 with 10 µg or 25 µg APC increased bone volume at 3 weeks by 32% (N.S.) and 74% (p < 0.01) compared to rhBMP-2 alone. This was associated with a significant increase in CD31+ and TRAP+ cells in tissue sections of ectopic bone, consistent with enhanced vascularity and bone turnover. The actions of APC are largely mediated by its receptors endothelial protein C receptor (EPCR) and protease-activated receptors (PARs). Cultured pre-osteoblasts and bone nodule tissue sections were shown to express PAR1/2 and EPCR. When pre-osteoblasts were treated with APC, cell viability and phosphorylation of ERK1/2, Akt, and p38 were increased. Inhibition with PAR1 and sometimes PAR2 antagonists, but not with EPCR blocking antibodies, ameliorated the effects of APC on cell viability and kinase phosphorylation. These data indicate that APC can affect osteoblast viability and signaling, and may have in vivo applications with rhBMP-2 for bone repair.

Link To Article

http://dx.doi.org/10.1002/jor.22726

Immobilization contributes to exaggerated neuropeptide signaling, inflammatory changes, and nociceptive sensitization after fracture in rats

Authors

Tian-Zhi Guo, Tzuping Wei, Wen-Wu Li, Xiang-Qi Li, J. David Clark, Wade S. Kingery

Abstract

A tibia fracture cast immobilized for 4 weeks can induce exaggerated substance P (SP) and CGRP signaling and neuropeptide-dependent nociceptive and inflammatory changes in the hindlimbs of rats similar to those seen in complex regional pain syndrome (CRPS). Four weeks of hindlimb cast immobilization can also induce nociceptive and vascular changes resembling CRPS. To test our hypothesis that immobilization alone could cause exaggerated neuropeptide signaling and inflammatory changes we tested 5 cohorts of rats; 1) controls, 2) tibia fracture and hindlimb casted, 3) hindlimb casted, no fracture, 4) tibia fracture with intrameduallary pinning, no cast, and 5) tibia fracture with intrameduallary pinning and hindlimb casting. After 4 weeks the casts were removed and hindlimb allodynia, unweighting, warmth, edema, sciatic nerve neuropeptide content, cutaneous and spinal cord inflammatory mediator levels, and spinal c-Fos activation were measured. After fracture with casting there was allodynia, unweighting, warmth, edema, increased sciatic nerve SP and CGRP, increased skin NK1 receptors and keratinocyte proliferation, increased in inflammatory mediator expression in the hindpaw skin (TNF-α, IL-1β, IL-6, NGF) and cord (IL-1β, NGF), and increased spinal c-Fos activation. These same changes were observed after cast immobilization alone, except spinal IL-1β levels were not increased. Treating cast only rats with an NK1 receptor antagonist inhibited development of nociceptive and inflammatory changes. Four weeks after fracture with pinning all nociceptive and vascular changes had resolved and there were no increases in neuropeptide signaling or inflammatory mediator expression.

Link To Article

http://dx.doi.org/10.1016/j.jpain.2014.07.004

A novel role for interferon regulatory factor 1 (IRF1) in regulation of bone metabolism

Authors

Sandra Salem, Chan Gao, Ailian Li, Huifen Wang, Loan Nguyen-Yamamoto, David Goltzman, Janet E. Henderson, and Philippe Gros

Abstract

Increased risk of bone fractures is observed in patients with chronic inflammatory conditions, such as inflammatory bowel disease and rheumatoid arthritis. Members of the Interferon Response Factor family of transcriptional regulators, IRF1 and IRF8, have been identified as genetic risk factors for several chronic inflammatory and autoimmune diseases. We have investigated a potential role for the Irf1 gene in bone metabolism. Here, we report that Irf1−/−mutant mice show altered bone morphology in association with altered trabecular bone architecture and increased cortical thickness and cellularity. Ex vivo studies on cells derived from bone marrow stimulated with Rank ligand revealed an increase in size and resorptive activity of tartrate-resistant acid-positive cells from Irf1−/− mutant mice compared with wild-type control mice. Irf1 deficiency was also associated with decreased proliferation of bone marrow-derived osteoblast precursors ex vivo, concomitant with increased mineralization activity compared with control cells. We show that Irf1 plays a role in bone metabolism and suggest that Irf1 regulates the maturation and activity of osteoclasts and osteoblasts. The altered bone phenotype of Irf1−/− mutants is strikingly similar to that of Stat1−/− mice, suggesting that the two interacting proteins play a critical enabling role in the common regulation of these two cell lineages.

Link To Article

http://dx.doi.org/10.1111/jcmm.12327