Different composition of leucocytes in cortical and cancellous bone healing in a mouse model

Abstract

ObjectivesCortical and cancellous bone healing processes appear to be histologically different. They also respond differently to anti-inflammatory agents. We investigated whether the leucocyte composition on days 3 and 5 after cortical and cancellous injuries to bone was different, and compared changes over time using day 3 as the baseline.MethodsTen-week-old male C56/Bl6J mice were randomized to either cancellous injury in the proximal tibia or cortical injury in the femoral diaphysis. Regenerating tissues were analyzed with flow cytometry at days 3 and 5, using panels with 15 antibodies for common macrophage and lymphocyte markers. The cellular response from day 3 to 5 was compared in order to identify differences in how cancellous and cortical bone healing develop.ResultsBetween day 3 and 5, the granulocytes increased in the cancellous model, whereas the lymphocytes (T cells, B cells, NK cells) and monocytes (CD11b+, F4/80+, CD206+, CD14+) increased in the cortical model.ConclusionThese results suggest an acute type of inflammation in cancellous bone healing, and a more chronic inflammation in cortical healing. This might explain, in part, why cancellous healing is faster and more resistant to anti-inflammatory drugs than are diaphyseal fractures.Cite this article: L. Tätting, O. Sandberg, M. Bernhardsson, J. Ernerudh, P. Aspenberg. Different composition of leucocytes in cortical and cancellous bone healing in a mouse model. Bone Joint Res 2018;7:620–628. DOI: 10.1302/2046-3758.712.BJR-2017-0366.R2.

Inflammation in Cancellous and Cortical Bone Healing

“…The separation of monocytes and granulocytes can otherwise be hard as both may be high in side scatter (SSC) and positive for CD11b (Rose et al 2012). An increase in granulocytes is a dominating feature of early inflammation in both cortical and cancellous bone healing (Tätting et al 2018b). It is not known, however, if depletion of Ly6G bearing cells would have a similar effect in a cancellous model.…”

“…Many times, no clear hematoma could be seen in the osteotomy as one would expect, and the surrounding muscle is quick to attach to the traumatized bone. To overcome these technical shortcomings in studying cortical bone healing, we devised a model where the femoral cortex was milled away longitudinally for a short distance (Figure 3 on page 16), first published in Tätting et al (2018b). The reaming injury to the cortex models trauma to bone with a major cortical component.…”

Healing Processes in Cancellous Bone

“…For a study in mice, 68 we had developed a model to study the influx of inflammatory cells in a cortical bone defect. In the model, we removed a portion of the cortical bone in the femur midshaft to get into the marrow compartment before the marrow was scooped out ( Figure 12A).…”

A novel mouse model to study fracture healing of the proximal femur

“…3 Furthermore, recent research has demonstrated that there are significant differences between the fracture healing process in metaphyseal and diaphyseal bone. Tätting et al 4 revealed increased numbers of lymphocytes and monocytes and decreased numbers of granulocytes when comparing the inflammatory response after fracture in diaphyseal vs metaphyseal bone. Further studies demonstrate different effects of both antiresorptive and osteoanabolic treatment strategies including Wnt/β-catenin activation, parathyroid hormone application, and bisphosphonate injections on metaphyseal and diaphyseal bone healing.…”

“…Most of these studies used drill hole defects in the mouse femur or tibia. [4][5][6][7]14 However, drill hole defects lack biomechanical stimulation at the fracture site and furthermore, no fracture implants are used for this approach. This might critically influence the type of healing.…”