Development of a novel minimally invasive technique to washout necrotic bone marrow content from epiphyseal bone: A preliminary cadaveric bone study

Mesenchymal Stem Cell Therapy for Bone Repair of Human Hip Osteonecrosis with Bilateral Match-Control Evaluation: Impact of Tissue Source, Cell Count, Disease Stage, and Volume Size on 908 Hips

We investigated the impact of mesenchymal stem cell (MSC) therapy on treating bilateral human hip osteonecrosis, analyzing 908 cases. This study assesses factors such as tissue source and cell count, comparing core decompression with various cell therapies. This research emphasizes bone repair according to pre-treatment conditions and the specificities of cell therapy in osteonecrosis repair, indicating a potential for improved bone repair strategies in hips without femoral head collapse. This study utilized a single-center retrospective analysis to investigate the efficacy of cellular approaches in the bone repair of osteonecrosis. It examined the impact on bone repair of tissue source (autologous bone marrow concentrate, allogeneic expanded, autologous expanded), cell quantity (from none in core decompression alone to millions in cell therapy), and osteonecrosis stage and volume. Excluding hips with femoral head collapse, it focused on patients who had bilateral hip osteonecrosis, both pre-operative and post-operative MRIs, and a follow-up of over five years. The analysis divided these patients into seven groups based on match control treatment variations in bilateral hip osteonecrosis, primarily investigating the outcomes between core decompression, washing effect, and different tissue sources of MSCs. Younger patients (<30 years) demonstrated significantly better repair volumes, particularly in stage II lesions, than older counterparts. Additionally, bone repair volume increased with the number of implanted MSCs up to 1,000,000, beyond which no additional benefits were observed. No significant difference was observed in repair outcomes between different sources of MSCs (BMAC, allogenic, or expanded cells). The study also highlighted that a 'washing effect' was beneficial, particularly for larger-volume osteonecrosis when combined with core decompression. Partial bone repair was the more frequent event observed, while total bone repair of osteonecrosis was rare. The volume and stage of osteonecrosis, alongside the number of injected cells, significantly affected treatment outcomes. In summary, this study provides comprehensive insights into the effectiveness and variables influencing the use of mesenchymal stem cells in treating human hip osteonecrosis. It emphasizes the potential of cell therapy while acknowledging the complexity and variability of results based on factors such as age, cell count, and disease stage.

Local BMP2 hydrogel therapy for robust bone regeneration in a porcine model of Legg-Calvé-Perthes disease

Legg-Calvé-Perthes disease is juvenile idiopathic osteonecrosis of the femoral head (ONFH) that has no effective clinical treatment. Previously, local injection of bone morphogenetic protein-2 (BMP2) for ONFH treatment showed a heterogeneous bone repair and a high incidence of heterotopic ossification (HO) due to the BMP2 leakage. Here, we developed a BMP2-hydrogel treatment via a transphyseal bone wash and subsequential injection of BMP2-loaded hydrogel. In vitro studies showed that a hydrogel of gelatin-heparin-tyramine retained the BMP2 for four weeks. The injection of the hydrogel can efficiently prevent leakage. With the bone wash, the injected hydrogel had a broad distribution in the head. In vivo studies on pigs revealed that the BMP2-hydrogel treatment produced a homogeneous bone regeneration without HO. It preserved the subchondral contour and restored the subchondral endochondral ossification, although it increased growth plate fusions. In summary, the study demonstrated a promising BMP2-hydrogel treatment for ONFH treatment, especially for teenagers.

Ex vivo study of detergent-assisted intraosseous bone wash treatment of osteonecrosis

Avascular necrosis (AVN) involves ischemic cell death of the bone. AVN leaves an abundance of necrotic lipids and debris in the bone marrow, which instigates inflammatory bone repair. Consequently, the necrotic bone microenvironment stimulates excessive bone resorption, leading to joint deformities and osteoarthritis. Here, we performed a detergent-assisted bone wash using poloxamer 407 (P407) to clean the necrotic bone environment by removing lipids and necrotic debris. The new concept was tested using an established ex vivo AVN model of porcine cadaver humeral heads. The P407 wash was performed using P407 solution and followed with saline via two intraosseous needles. Visual inspection and image analyses of average pixel light intensity showed that the P407 wash produced a better-cleaned bone than the saline wash. Analyses of the collected bone wash solution showed a two-fold increase in triglycerides (101 vs. 53 mmol/head, p = 0.006) and a 10-fold increase in the dry weight of the removed debris (1.34 vs. 0.13 g/head, p = 0.02) with the P407 wash compared to saline. The histological evaluation showed significantly decreased Oil-Red-O (fats) staining in the P407-washed bone compared with the saline-washed bone. The in vitro assays of Alizarin red and qPCR showed the P407 wash neither altered the osteogenic behaviors of porcine bone marrow-derived mesenchymal cells (pBMMCs) nor raised inflammatory responses of porcine bone marrow-derived macrophages (pBMMs). In conclusion, detergent-assisted bone wash using P407 produced a better removal of nonsoluble debris from the bone marrow space than the saline wash without causing changes to osteogenesis or inflammatory reactions.

Local Administration of Bone Morphogenetic Protein-2 Using a Hydrogel Carrier for Robust Bone Regeneration in a Large Animal Model of Legg-Calvé-Perthes disease

Legg-Calvé-Perthes disease is juvenile idiopathic osteonecrosis of the femoral head (ONFH) that has no effective clinical resolutions. Previously, local injection of bone morphogenetic protein-2 (BMP2) for ONFH treatment showed a heterogeneous bone repair and a high incidence of heterotopic ossification (HO) due to the BMP2 leakage. Here, we developed a BMP2-hydrogel treatment via a transphyseal bone wash and subsequential injection of BMP2-loaded hydrogel. In vivo studies showed that a hydrogel of gelatin-heparin-tyramine retained the BMP2 for four weeks. The injection of the hydrogel can efficiently prevent leakage. With the bone wash, the injected hydrogel had a broad distribution in the head. In vivo studies on pigs revealed that the BMP2-hydrogel treatment produced a homogeneous bone regeneration without HO. It preserved the subchondral contour and restored the subchondral endochondral ossification, although it increased growth plate fusions. In summary, the study demonstrated a promising BMP2-hydrogel treatment for ONFH treatment, especially for teenagers.

Damage associated molecular patterns in necrotic femoral head inhibit osteogenesis and promote fibrogenesis of mesenchymal stem cells

In Legg-Calvé-Perthes disease (LCPD), a loss of blood supply to the juvenile femoral head leads to extensive cell death and release of damage-associated molecular patterns (DAMPs). Over time chronic inflammatory repair process is observed with impaired bone regeneration. Increased fibrous tissue and adipose tissue are seen in the marrow space with decreased osteogenesis in a piglet model of LCPD, suggesting inhibition of osteoblastic differentiation and stimulation of fibroblastic and adipogenic differentiation of mesenchymal stem cell (MSC) during the healing process. Little is known about the DAMPs present in the necrotic femoral head and their effects on MSC differentiation. The purpose of this study was to characterize the DAMPs present in the femoral head following ischemic osteonecrosis and to determine their effects on MSC differentiation. Necrotic femoral heads were flushed with saline at 48 h, 2 weeks and 4 weeks following the induction of ischemic osteonecrosis in piglets to obtain necrotic bone fluid (NBF). Western blot analysis of the NBF revealed the presence of prototypic DAMP, high mobility group box 1 (HMGB1), and other previously described DAMPs: biglycan, 4-hydroxynonenal (4-HNE), and receptor activator of NF-κB ligand (RANKL). ELISA of the NBF revealed increasing levels of inflammatory cytokines IL1β, IL6 and TNFα with the temporal progression of osteonecrosis. To determine the effects of NBF on MSC differentiation, we cultured primary porcine MSCs with NBF obtained by in vivo necrotic bone flushing method. NBF inhibited osteoblastic differentiation of MSCs with significantly decreased OSX expression (p = 0.008) and Von Kossa/Alizarin Red staining for mineralization. NBF also significantly increased the expression of proliferation markers Ki67 (p = 0.03) and PCNA (p < 0.0001), and fibrogenic markers Vimentin (p = 0.02) and Fibronectin (p = 0.04). Additionally, NBF treated MSC cells showed significantly elevated RANKL/OPG secretion ratio (p = 0.003) and increased expression of inflammatory cytokines IL1β (p = 0.006) and IL6 (p < 0.0001). To specifically assess the role of DAMPs in promoting the fibrogenesis, we treated porcine fibroblasts with artificial NBF produced by bone freeze-thaw method. We found increased fibroblastic cell proliferation in an NBF dose-dependent manner. Lastly, we studied the effect of HMGB1, a prototypic DAMP, and found that HMGB1 partially contributes to MSC proliferation and fibrogenesis. In summary, our findings show that DAMPs and the inflammatory cytokines present in the necrotic femoral head inhibit osteogenesis and promote fibrogenesis of MSCs, potentially contributing to impaired bone regeneration following ischemic osteonecrosis as observed in LCPD.

Minimally Invasive Necrotic Bone Washing Improves Bone Healing After Femoral Head Ischemic Osteonecrosis: An Experimental Investigation in Immature Pigs

BACKGROUND

Ischemic osteonecrosis of the femoral head produces necrotic cell debris and inflammatory molecules in the marrow space, which elicit a chronic inflammatory repair response. The purpose of this study was to determine the effects of flushing out the necrotic cell debris and inflammatory proteins on bone repair in a piglet model of ischemic osteonecrosis.

METHODS

Osteonecrosis of the femoral head of the right hindlimb was induced in 12 piglets by tying a ligature tightly around the femoral neck. One week after the surgery, 6 animals were treated with a percutaneous 3-needle bone washing procedure and non-weight-bearing (NWB) of the right hindlimb (wash group). The total saline solution wash volume was 450 mL per femoral head. Serial wash solutions were collected and analyzed. The remaining 6 animals were treated with NWB only (NWB group). At 8 weeks after the surgery, the femoral heads were assessed using radiography, micro-computed tomography (micro-CT), and histological analysis. In addition, we compared the results for these piglets with our published results for 6 piglets treated with multiple epiphyseal drilling (MED) plus NWB without bone washing (MED group).

RESULTS

Necrotic cells and inflammatory proteins were present in the bone wash solution collected 1 week after ischemia induction. The protein and triglyceride concentrations decreased significantly with subsequent washing (p < 0.005). At 8 weeks after ischemia induction, the wash group had a significantly higher bone volume than the MED or NWB group (p < 0.0001). Histological bone-formation measures were also significantly increased in the wash group compared with the MED group (p = 0.002) or NWB group (p < 0.0001) while macrophage numbers were significantly decreased in the wash group.

CONCLUSIONS

The percutaneous 3-needle procedure flushed out cell debris and inflammatory proteins from the necrotic femoral heads, decreased osteoclasts and macrophages, and increased bone formation following induction of ischemic osteonecrosis.

CLINICAL RELEVANCE

We believe that this is the first study to investigate the concept of washing out the necrotic femoral head to improve bone healing. The minimally invasive procedure may be useful to improve the necrotic bone environment and bone repair following ischemic osteonecrosis.