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Osteoblast precursors and inflammatory cells arrive simultaneously to sites of a trabecular-bone injury
Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Orthopaedics in Linköping.
Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Orthopaedics in Linköping.
2018 (English)In: Acta Orthopaedica, ISSN 1745-3674, E-ISSN 1745-3682, Vol. 89, no 4, p. 457-461Article in journal (Refereed) Published
Abstract [en]

Background and purpose - Fracture healing in the shaft is usually described as a sequence of events, starting with inflammation, which triggers mesenchymal tissue formation in successive steps. Most clinical fractures engage cancellous bone. We here describe fracture healing in cancellous bone, focusing on the timing of inflammatory and mesenchymal cell type appearance at the site of injury. Material and methods - Rats received a proximal tibial drill hole, A subgroup received clodronate-containing liposomes before or after surgery. The tibiae were analyzed with micro-CT and immunohistochemistry 1 to 7 days after injury. Results - Granulocytes (myeloperoxidase) appeared in moderate numbers within the hole at day 1 and then gradually disappeared. Macrophage expression (CD68) was seen on day 1, increased until day 3, and then decreased. Mesenchymal cells (vimentin) had already accumulated in the periphery of the hole on day 1. Mesenchymal cells dominated in the entire lesion on day 3, now producing extracellular matrix. A modest number of preosteoblasts (RUNX2) were seen on day 1 and peaked on day 4. Osteoid was seen on day 4 in the traumatized region, with a distinct border to the uninjured surrounding marrow. Clodronate liposomes given before the injury reduced the volume of bone formation at day 7, but no reduction in macrophage numbers could be detected. Interpretation - The typical sequence of events in shaft fractures was not seen. Mesenchymal cells appeared simultaneously with granulocyte and macrophage arrival. Clodronate liposomes, known to reduce macrophage numbers, seemed to be associated with the delineation of the volume of tissue to be replaced by bone.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD , 2018. Vol. 89, no 4, p. 457-461
National Category
Orthopaedics
Identifiers
URN: urn:nbn:se:liu:diva-150316DOI: 10.1080/17453674.2018.1481682ISI: 000439704100018PubMedID: 29865916OAI: oai:DiVA.org:liu-150316DiVA, id: diva2:1239452
Available from: 2018-08-16 Created: 2018-08-16 Last updated: 2019-05-02
In thesis
1. Healing Processes in Cancellous Bone
Open this publication in new window or tab >>Healing Processes in Cancellous Bone
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Most of what is known about the biological response during fracture healing comes from numerous animal studies with shaft fractures in the long bone. However, most patients suffer from fractures closer to the ends of the long bones, in the hip, or in the vertebrae. These types of fractures mainly involve cancellous bone, while shaft fractures concern cortical bone. Compared to cortical bone whose structure is dense and compact, cancellous bone is of spongy and porous structure. A growing number of studies point towards that cortical and cancellous bone heal differently. To even this imbalance in knowledge between these two types of bone tissue, further studies in cancellous bone are justified.

In this thesis we delved into the quiet unknown processes behind cancellous bone healing.

In the first study we characterized and compared two models for cancellous bone healing in mice and rats: the first model can be used to analyze the morphology and morphometry of the regenerating bone; the second model can measure the mechanical properties of cancellous bone. The two models correspond in their developing patterns during the first week before they diverge. This suggests that these models can be utilized together to evaluate the initial healing in cancellous bone. Furthermore, we saw in the drill hole model that the bone formation is strictly restricted to the traumatized region, with a distinct interface to the adjacent uninjured tissue.

The second study characterized the cellular response during the initial healing phase in cancellous bone. The focus was to follow the spatial location of inflammatory and osteogenic cells over time in a cancellous bone injury. In contrast to shaft fractures (cortical bone), where healing is described as sequential events where inflammatory cells are the first to arrive to the trauma before osteogenic cells are recruited and initiate healing, we could see how inflammatory and osteogenic cells appeared early, simultaneously after a cancellous bone injury. This study showed that cancellous bone differs from how fracture healing is normally described.

In the third study we explored the role of a subpopulation of lymphocytes (CD8 positive cells), earlier studied in shaft fractures. We wanted to see how their absence would affect the healing in a cancellous bone injury. Without CD8+ cells, cancellous bone healing was impaired as expressed via poorer mechanical properties of the regenerated bone tissue.

The fourth and last study issued the influence of uninjured bone marrow on cortical bone healing. We developed a cortical defect model which blocked uninjured marrow from reaching the defect. Without the presence of marrow, the cortical defects ability to regenerate was significantly impaired. This implies that the marrow is important for cortical bone healing.

In conclusion, cancellous bone healing is different from its cortical counterpart and the general perception of fracture healing. We have briefly discerned healing mechanisms in cancellous bone that might be of clinical importance: the restricted cancellous bone formation is something to take into consideration when performing arthrodeses; and importance of marrow in skeletal defects (e.g. pseudarthroses). With this thesis, we hope to promote that further investigating on cancellous bone healing is necessary.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2018. p. 24
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1652
National Category
Orthopaedics Nursing Public Health, Global Health, Social Medicine and Epidemiology
Identifiers
urn:nbn:se:liu:diva-152349 (URN)10.3384/diss.diva-152349 (DOI)9789176851777 (ISBN)
Public defence
2018-12-06, Belladonna, Campus US, Linköping, 13:00 (English)
Opponent
Supervisors
Available from: 2018-10-30 Created: 2018-10-29 Last updated: 2019-09-30Bibliographically approved

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Bernhardsson, Magnus

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Division of Surgery, Orthopedics and OncologyFaculty of Medicine and Health SciencesDepartment of Orthopaedics in Linköping
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