Core Decompression and Autologous Bone Marrow Concentrate for Treatment of Femoral Head Osteonecrosis: A Randomized Prospective Study.

The aim of this study was to investigate the safety of injection of bone marrow aspirate concentrate during core decompression and to study its clinical (visual analogue scale; Harris-Hip-score) and radiological outcomes (magnetic resonance imaging). In this prospective and randomized clinical trial we evaluated 24 consecutive patients with non-traumatic femoral head necrosis (FHN) during a period of two years after intervention. In vitro analysis of mesenchymal stem cells was performed by evaluating the fibroblast colony forming units (CFU-Fs). Postoperatively, significant decrease in pain associated with a functional benefit lasting was observed. However, there was no difference in the clinical outcome between the two study groups. Over the period of two years there was no significant difference between the head survival rate between both groups. In contrast to that, we could not perceive any significant change in the volume of FHN in both treatment groups related to the longitudinal course after treating. The number of CFU showed a significant increase after centrifugation. This trial could not detect a benefit from the additional injection of bone marrow concentrate with regard to bone regeneration and clinical outcome in the short term.

What should be the characteristics of the ideal bone graft substitute? Combining scaffolds with growth factors and/or stem cells.

Reconstruction of large bone defects or non-unions resulting from biochemical disorders, tumour resections or complicated fractures is still a challenge for orthopaedic and trauma surgery. On the one hand, autografts harbour most features of ideal bone graft substitutes but on the other hand, they have a lot insurmountable disadvantages. An ideal bone graft substitute should be biomechanically stable, able to degrade within an appropriate time frame, exhibit osteoconductive, osteogenic and osteoinductive properties and provide a favourable environment for invading blood vessels and bone forming cells. Whilst osteoconductivity of biomaterials for bone tissue engineering strategies can be directed by their composition, surface character and internal structure, osteoinductive and osteogenic features can be provided by growth factors originally participating in fracture healing and/or multipotent mesenchymal stromal/stem cells (MSC) capable of rebuilding bone and marrow structures. In this review, aspects of the clinical application of the most commonly used growth factors for bone repair, the bone morphogenetic proteins (BMPs), and the potential use of human MSC for clinical application will be discussed.

Chondrogenic pre-induction of human mesenchymal stem cells on beta-TCP: enhanced bone quality by endochondral heterotopic bone formation.

New techniques to heal bone defects include the combination of bone substitute materials with mesenchymal stem cells (MSC). To find solutions not hampered by low material resorbability or high donor variability of human MSC, the potency of such composites is usually evaluated by heterotopic bone formation assays in immunocompromised animals. The aim of this study was to investigate whether resorbable phase-pure beta-tricalcium-phosphate (beta-TCP) could support heterotopic bone formation by MSC comparable to partially resorbable hydroxyapatite/tricalcium-phosphate (HA/TCP). Furthermore, in light of disappointing results with osteogenic in vitro priming of MSC, we tested whether chondrogenic pre-induction of constructs may allow for enhanced bone formation by triggering the endochondral pathway. beta-TCP granules of three different sizes and HA/TCP were seeded with MSC and transplanted subcutaneously into immunocompromised mice either immediately or after a chondrogenic pre-induction for 6 weeks. After 8 weeks, explants were analysed by histology. beta-TCP seeded with unprimed MSC revealed intramembranous bone formation without haematopoietic marrow with 3.8-fold more bone formed with granules smaller than 0.7 mm than with 0.7-1.4mm particles (p< or =0.018). Chondrogenic pre-induction of beta-TCP/MSC composites resulted in collagen type II and proteoglycan-rich cartilage-like tissue which, after transplantation, underwent endochondral ossification, yielding ectopic bone produced by human cells while haematopoietic marrow was derived from the mouse. Transdifferentiation of MSC-derived chondrocytes to osteoblasts or direct osteogenesis of cartilage-resident MSC is postulated to explain the human origin of new bone. In conclusion, beta-TCP was significantly more osteo-permissive (p=0.004) than HA/TCP for human MSC, and chondrogenic priming of beta-TCP/MSC represented a superior approach capable of supporting full bone formation, including marrow organization.

Influence of defective bone marrow osteogenesis on fracture repair in an experimental model of senile osteoporosis.

Bone marrow osteogenesis in senile osteoporotic bone is impaired and, as such, may have significant implications on the successful outcome of fracture repair. Here we utilize a well-established murine model of senile osteoporosis, the P6 strain of senescence-accelerated mice (SAMP6), to investigate fracture healing in aged osteoporotic bone. A femoral osteotomy was created in SAMP6 and in non-osteoporotic age-matched control R1 senescence-resistant mice (SAMR1). The course of fracture healing was evaluated over a period of 42 days using quantitative microCT and histological analysis. The differentiation capabilities of bone mesenchymal progenitor cells derived from SAMP6 and SAMR1 mice was examined, and their osteogenic potential determined. Although preliminary in vitro analysis confirmed that bone marrow-derived stem cells (BMSC) isolated from SAMP6 mice had a reduced osteogenic capacity, no significant deficit in fracture repair as determined by quantitative microCT could be detected. This was supported by histology assessment, where complete bridging of the fracture gap was evident by day 28 and was fully healed day 42 in both SAMP6 and SAMR1 mice. Further in vitro studies revealed that periosteal-derived progenitor cells (PDPC) isolated from SAMP6 mice had an osteogenic potential comparable to that observed in SAMR1 mice. In conclusion, fracture healing in SAMP6 mice is not detrimentally affected by impairment of BMSC osteogenesis, suggesting that bone marrow-mediated repair processes are dispensable for normal bone healing in this senile osteoporotic fracture model. Furthermore, the influence of PDPC in the repair process may partly explain the absence of any detectable deficits in fracture repair in SAMP6 mice.

Calcification or dedifferentiation: requirement to lock mesenchymal stem cells in a desired differentiation stage.

A current challenge in mesenchymal stem cell (MSC)-based cartilage repair is to solve donor and tissue-dependent variability of MSC cultures and to prevent chondrogenic cells from terminal differentiation like in the growth plate. The aim of this study was to select the best source for MSC which could promise stable cartilage formation in the absence of hypertrophy and ectopic in vivo mineralization. We hypothesized that MSC from synovium are superior to bone marrow- and adipose tissue-derived MSC since they are derived from a joint tissue. MSC were characterized by flow cytometry. MSC pellets were cultured under chondrogenic conditions and differentiation was evaluated by histology, gene expression analysis, and determination of alkaline phosphatase activity (ALP). After chondrogenic induction, pellets were transplanted subcutaneously into SCID mice. MSC from bone marrow, adipose tissue, and synovium revealed similar COL2A1/COL10A1 mRNA levels after chondrogenic induction and were positive for collagen-type-X. Bone marrow-derived and adipose tissue-derived MSC showed significantly higher ALP activity than MSC from synovium. Low ALP-activity before transplantation of pellets correlated with marginal calcification of explants. Surprisingly, non-mineralizing transplants specifically lost their collagen-type II, but not collagen-type I deposition in vivo, or were fully degraded. In conclusion, the lower donor-dependent ALP activation and reduced mineralization of synovium-derived heterotopic transplants did not lead to stable ectopic cartilage as known from articular chondrocytes, but correlated with fibrous dedifferentiation or complete degeneration of MSC pellets. This emphasizes that beside appropriate induction of differentiation, locking of MSC in the desired differentiation state is a major challenge for MSC-based repair strategies.

Xenopus Paraxial Protocadherin regulates morphogenesis by antagonizing Sprouty.

Xenopus Paraxial Protocadherin (xPAPC) has signaling functions that are essential for convergent extension (CE) movements and tissue separation during gastrulation. PAPC modulates components of the planar cell polarity (PCP) pathway, but it is not clear how PAPC is connected to beta-catenin-independent Wnt-signaling. By yeast two-hybrid screen, we found that the intracellular domain of PAPC interacts with Sprouty (Spry), an inhibitor of CE movements. Upon binding to PAPC, Spry function is inhibited and PCP signaling is enhanced. Our data indicate that PAPC promotes gastrulation movements by sequestration of Spry and reveal a novel mechanism by which protocadherins modulate beta-catenin-independent Wnt-signaling.