**5. Mesenchymal stromal cell transplantation for the treatment of FHN**

Reports of poor results using concentrated bone marrow transplantation combined with core decompression may reflect the low population of osteogenic cells in bone marrow of patients with FHN. Hernigou et al. [22] reported the osteogenic cell number to be low in patients with a history of steroid and alcohol use, as well as in patients who had undergone organ trans‐ plantation. Mesenchymal stromal cells (MSCs) may provide a solution to the problem of low osteogenic cell number.

MSCs hold promise for their use in regeneration of tissues of the musculoskeletal system [37]. MSCs are plastic dish-adherent cells that differentiate into osteogenic, chondrogenic, and adipogenic cell lineages, *in vitro* [38, 39]. The adherent cells can be easily proliferated, yielding a large number of cells [38]. The high proliferation nature of these cells in *in vitro* cultures could provide an effective compensation for low cell numbers [39]. MSCs can also differentiate into vascular endothelial cells [40]. This property to differentiate into vascular tissue would be useful to treat the avascular component of FHN. MSCs can be isolated from many tissues, including bone marrow, fat, and synovium [41]. The ideal source for MSC differentiation and proliferation remains controversial, with isolation of MSCs from bone marrow having been shown to be stable [42]. The technique to aspirate bone marrow is also well established [43] and relatively safe.

Zhao et al. [44] conducted a clinical trial on the use of MSCs for the treatment of FHN, with salient finding summarized in **Figure 2** and **Table 2**. Zhao et al. compared outcomes of transplanting cultured MSCs and bone marrow cells, in combination with core decompression, in patients with the early stage of FHN (i.e., ARCO stage 1 or 2). After 60-month follow-up, 4% of hip treated with MSCs progressed to collapse, compared to 23% of cases in the bone marrow treatment group. Rastogi et al. [45] also conducted a comparison of outcomes for treatment using cultured MSCs and bone marrow for transplantation in patients with the early (stages 1 and 2) and advanced (stage 3) stages of FHN. In contrast to Zhao et al., Rastogi et al. did not identify a significant difference in the rate of collapse between the two treatment groups, with a rate of collapse of 0% for both groups for stage 1 hips and 18% for stage 2 hips, and a rate of 20% for stage 3 hips for the MSC group, compared to 25% for the bone marrow group. Persiani et al. [46] reported that core decompression with MSCs transplantation was not a sufficient treatment for patients with advanced stages of FHN. Aoyama et al. [47] and Kawate et al. [48] performed curettage of the necrotic bone and packed beta-tricalcium phosphate with MSCs and a vascularized bone graft to treat patients with advanced stages of FHN. Aoyama et al. reported no progression to collapse for hips in stage 3A, while 50% of the hips in stage 3B progressed to collapse. In their 12-week follow-up, Kawate et al. did not report any progression to collapse of hips in stage 3 or 4 FHN.

### **6. The cell type used for the treatment of FHN**

al. [36] performed curettage of the necrotic bone, instead of core decompression, packing the free bone graft with concentrated bone marrow cells. Progression to collapse was prevented

> Wang BL (2010) Chotivichit A (2012) Mao Q (2013) Ma Y (2014)

Tabatabaee RM (2015) Hernigou P (2002)

Martin JR (2013) Kang JS (2013)

Yamasaki T (2010)

Rastogi S (2013) Persiani P (2015)

**5. Mesenchymal stromal cell transplantation for the treatment of FHN**

Reports of poor results using concentrated bone marrow transplantation combined with core decompression may reflect the low population of osteogenic cells in bone marrow of patients with FHN. Hernigou et al. [22] reported the osteogenic cell number to be low in patients with a history of steroid and alcohol use, as well as in patients who had undergone organ trans‐ plantation. Mesenchymal stromal cells (MSCs) may provide a solution to the problem of low

MSCs hold promise for their use in regeneration of tissues of the musculoskeletal system [37]. MSCs are plastic dish-adherent cells that differentiate into osteogenic, chondrogenic, and adipogenic cell lineages, *in vitro* [38, 39]. The adherent cells can be easily proliferated, yielding a large number of cells [38]. The high proliferation nature of these cells in *in vitro* cultures could provide an effective compensation for low cell numbers [39]. MSCs can also differentiate into

Liu Y (2013)

**Radiographic stages (ARCO)**

**Stage 1 Stage 2 Stage 3 Stage 4**

**3A 3B**

Aoyama T (2014)

Kawate K (2006)

in 75% of their patients in stage 2 and 100% in stage 3.

Core decompression + bioderived material

Core decompression + bioactive scaffold

MSCs Core decompression Zhao D (2012)

Curretage + bone graft + bioactive scaffold

MSC, mesenchymal stem cell.

osteogenic cell number.

Core decompression Gangji V (2004)

Curretage + bone graft Wang T (2014)

**Table 2.** Cell therapy according to the grade of osteonecrosis of the femoral head.

**Cell source Combined surgical technique**

96 Advanced Techniques in Bone Regeneration

Bone marrow cells

> It is clear that transplantation of cells that can be differentiated to osteogenic cells is effective for the treatment of FHN. Preparation of concentrated bone marrow cells is easy, of low risk and of low cost. However, when the necrotic lesion is broad, preparation of a large number of cells is needed [49]. The condition of the host tissue influences the number and quality of osteogenic cells harvested [49]. Therefore, it is a great benefit that MSCs can be differentiated into both osteogenic and vascular endothelial cells [40]. The cytokine and paracrine effect of MSCs is important in yielding a large number of differentiated MSC cell lineages *in vitro* [50, 51]. However, the differentiation property of MSCs is highly influenced by the conditions of the host, such as age, disease, medication, etc. [52]. Peripheral CD34-positive MSCs may be another source for the treatment of FHN. They have the potential to differentiate into osteo‐ genic and vascular endothelial cells and are easily prepared by *in vivo* induction of granulocyte colony-stimulating factors [53]. Despite the different possible sources of MSCs, remodeling of the osteonecrotic bone is an issue that remains to be solved. In healthy bone tissue, the balance between bone formation and bone resorption is under precise regulation [54]. In contrast, in pathological conditions, such as osteoporosis, prolonged fracture repair, and osteonecrosis,

there is a dysregulation of the balance between osteoclast and osteoblast activity [35, 54]. In FHN, both living osteoclast and osteoblast cells are reduced in number. Therefore, pathogenic tissue, such as necrotic bone, should be removed as a component of treatment to facilitate bone remodeling. MSCs have the ability not only to differentiate into osteogenic cells, but they can also stimulate the osteoclastogenesis [55–57]. Therefore, the cytokine effect of MSCs induces a healthy remodeling regulation.
