Celeste Scotti

Recapitulation of endochondral bone formation using human adult mesenchymal stem cells as a paradigm for developmental engineering.

Mesenchymal stem/stromal cells (MSC) are typically used to generate bone tissue by a process resembling intramembranous ossification, i.e., by direct osteoblastic differentiation. However, most bones develop by endochondral ossification, i.e., via remodeling of hypertrophic cartilaginous templates. To date, endochondral bone formation has not been reproduced using human, clinically compliant cell sources. Here, we aimed at engineering tissues from bone marrow-derived, adult human MSC with an intrinsic capacity to undergo endochondral ossification. By analogy to embryonic limb development, we hypothesized that successful execution of the endochondral program depends on the initial formation of hypertrophic cartilaginous templates. Human MSC, subcutaneously implanted into nude mice at various stages of chondrogenic differentiation, formed bone trabeculae only when they had developed in vitro hypertrophic tissue structures. Advanced maturation in vitro resulted in accelerated formation of larger bony tissues. The underlying morphogenetic process was structurally and molecularly similar to the temporal and spatial progression of limb bone development in embryos. In particular, Indian hedgehog signaling was activated at early stages and required for the in vitro formation of hypertrophic cartilage. Subsequent development of a bony collar in vivo was followed by vascularization, osteoclastic resorption of the cartilage template, and appearance of hematopoietic foci. This study reveals the capacity of human MSC to generate bone tissue via an endochondral program and provides a valid model to study mechanisms governing bone development. Most importantly, this process could generate advanced grafts for bone regeneration by invoking a “developmental engineering” paradigm.

Engineering of a functional bone organ through endochondral ossification

Embryonic development, lengthening, and repair of most bones proceed by endochondral ossification, namely through formation of a cartilage intermediate. It was previously demonstrated that adult human bone marrow-derived mesenchymal stem/stromal cells (hMSCs) can execute an endochondral program and ectopically generate mature bone. Here we hypothesized that hMSCs pushed through endochondral ossification can engineer a scaled-up ossicle with features of a “bone organ,” including physiologically remodeled bone, mature vasculature, and a fully functional hematopoietic compartment. Engineered hypertrophic cartilage required IL-1β to be efficiently remodeled into bone and bone marrow upon subcutaneous implantation. This model allowed distinguishing, by analogy with bone development and repair, an outer, cortical-like perichondral bone, generated mainly by host cells and laid over a premineralized area, and an inner, trabecular-like, endochondral bone, generated mainly by the human cells and formed over the cartilaginous template. Hypertrophic cartilage remodeling was paralleled by ingrowth of blood vessels, displaying sinusoid-like structures and stabilized by pericytic cells. Marrow cavities of the ossicles contained phenotypically defined hematopoietic stem cells and progenitor cells at similar frequencies as native bones, and marrow from ossicles reconstituted multilineage long-term hematopoiesis in lethally irradiated mice. This study, by invoking a “developmental engineering” paradigm, reports the generation by appropriately instructed hMSC of an ectopic “bone organ” with a size, structure, and functionality comparable to native bones. The work thus provides a model useful for fundamental and translational studies of bone morphogenesis and regeneration, as well as for the controlled manipulation of hematopoietic stem cell niches in physiology and pathology.

The Benefit of Synthetic Versus Biological Patch Augmentation in the Repair of Posterosuperior Massive Rotator Cuff Tears A 3-Year Follow-up Study

Background: Rotator cuff repair typically results in a satisfactory, although variable, clinical outcome. However, anatomic failure of the repaired tendon often occurs. Hypothesis: Patch augmentation can improve the results of open rotator cuff repair by supporting the healing process, protecting the suture, and reducing friction in the subacromial space. Study Design: Cohort study; Level of evidence, 3. Methods: A total of 152 patients with a posterosuperior massive rotator cuff tear were treated by open repair only (control group; n = 51; mean age, 67.06 ± 4.42 years), open repair together with collagen patch augmentation (collagen group; n = 49; mean age, 66.53 ± 5.17 years), or open repair together with polypropylene patch augmentation (polypropylene group; n = 52; mean age, 66.17 ± 5.44 years) and were retrospectively studied. Patients were evaluated preoperatively and after 36 months with a visual analog scale (VAS) and the University of California, Los Angeles (UCLA) shoulder rating scale and by measuring elevation of the scapular plane and strength with a dynamometer. The VAS and UCLA scores were also obtained 2 months postoperatively. Tendon integrity was assessed after 1 year by ultrasound. Patients were homogeneous as per the preoperative assessment. Results: After 2 months, results (mean ± standard deviation) for the control, collagen, and polypropylene groups, respectively, were as follows: VAS scores were 6.96 ± 1.11, 6.46 ± 1.02, and 4.92 ± 0.90, while UCLA scores were 11.29 ± 1.46, 11.40 ± 1.51, and 19.15 ± 1.99. After 36 months, the mean scores for the respective groups were 3.66 ± 1.05, 4.06 ± 1.02, and 3.28 ± 1.10 for the VAS and 14.88 ± 1.98, 14.69 ± 1.99, and 24.61 ± 3.22 for the UCLA scale. In addition, after 36 months, elevation on the scapular plane was 140.68° ± 9.84°, 140.61° ± 12.48°, and 174.71° ± 8.18°, and abduction strength was 8.73 ± 0.54 kg, 9.03 ± 0.60 kg, and 13.79 ± 0.64 kg for the control, collagen, and polypropylene groups, respectively. The retear rate after 12 months was 41% (21/51) for the control group, 51% (25/49) for the collagen group, and 17% (9/52) for the polypropylene group. In particular, the reduced 12-month retear rate and the increased UCLA scores, abduction strength, and elevation at 3-year follow-up were statistically significant for patients treated with a polypropylene patch compared with those treated with repair only or with a collagen patch. Conclusion: Polypropylene patch augmentation of rotator cuff repair was demonstrated to significantly improve the 36-month outcome in terms of function, strength, and retear rate.

Adult human neural crest-derived cells for articular cartilage repair.

HOX-negative, differentiated neural crest–derived adult cells from the nasal septum display self-renewal capacity and environmental plasticity and are compatible for articular cartilage repair. Cells from Nose Repair Tissue in Joint Cartilage repair remains a yet unmet clinical need, with few viable cell therapy options available. Taking cells from the knee or ankle to repair worn cartilage requires additional surgery and, in turn, pain and healing for the patient. As such, a new, accessible cell source would greatly benefit these patients. Here, Pelttari and colleagues looked up the nose for cells that may have the capacity to regenerate cartilage. Nasal septum cells arise from the neuroectoderm—the tissue that gives rise to the nervous system—and are better at repairing tissues than their mesoderm counterparts. These regenerative capabilities have been attributed to a lack of homeobox (HOX) gene expression. The authors therefore investigated whether nasal chondrocytes (HOX-negative, neuroectoderm origin) were compatible with an articular cartilage environment, like the knee joint (HOX-positive, mesoderm origin). The authors discovered that adult human nasal chondrocytes were able to self-renew and also, to their surprise, adopt a HOX-positive profile upon implantation into a mesoderm environment; in goats, this led to repair of experimental articular cartilage defects. In an ongoing clinical trial, human nasal chondrocytes have been shown to be safe once transplanted, suggesting translation of this new, easy-to-access cell source for repairing damaged joints. In embryonic models and stem cell systems, mesenchymal cells derived from the neuroectoderm can be distinguished from mesoderm-derived cells by their Hox-negative profile—a phenotype associated with enhanced capacity of tissue regeneration. We investigated whether developmental origin and Hox negativity correlated with self-renewal and environmental plasticity also in differentiated cells from adults. Using hyaline cartilage as a model, we showed that adult human neuroectoderm-derived nasal chondrocytes (NCs) can be constitutively distinguished from mesoderm-derived articular chondrocytes (ACs) by lack of expression of specific HOX genes, including HOXC4 and HOXD8. In contrast to ACs, serially cloned NCs could be continuously reverted from differentiated to dedifferentiated states, conserving the ability to form cartilage tissue in vitro and in vivo. NCs could also be reprogrammed to stably express Hox genes typical of ACs upon implantation into goat articular cartilage defects, directly contributing to cartilage repair. Our findings identify previously unrecognized regenerative properties of HOX-negative differentiated neuroectoderm cells in adults, implying a role for NCs in the unmet clinical challenge of articular cartilage repair. An ongoing phase 1 clinical trial preliminarily indicated the safety and feasibility of autologous NC–based engineered tissues for the treatment of traumatic articular cartilage lesions.

Surgical treatment of chronic acromioclavicular dislocation: Comparison between two surgical procedures for anatomic reconstruction

INTRODUCTION Surgical treatment of chronic complete acromioclavicular (AC) joint dislocation is still debated and no gold standard surgical procedure has been identified. MATERIALS AND METHODS A retrospective series of 90 patients treated for AC dislocations is reported here. Patients were divided into three groups: group 1 receiving AC reconstruction with a Dacron vascular prosthesis; group 2 receiving AC reconstruction with LARS(®) artificial ligament; group 3 receiving conservative treatment. Follow-up was performed after 1, 6 and 15 months with plain radiographs, UCLA, SPADI and modified UCLA acromioclavicular rating scales. RESULTS Patients treated surgically presented significant better functional outcome compared to patients treated conservatively with overall positive results in 93.3% of patients for group 2 and 53.3% of patients for group 1. However, reconstruction with Dacron vascular prosthesis presented an unacceptable high complications rate (43.3%). CONCLUSION Our results show that anatomic AC reconstruction with LARS(®) artificial ligament resulted in both satisfactory functional outcome and low complication rate. Therefore, we recommend this procedure for the treatment of chronic complete AC dislocations.

Engineering human cell-based, functionally integrated osteochondral grafts by biological bonding of engineered cartilage tissues to bony scaffolds

In this study, we aimed at developing and validating a technique for the engineering of osteochondral grafts based on the biological bonding of a chondral layer with a bony scaffold by cell-laid extracellular matrix. Osteochondral composites were generated by combining collagen-based matrices (Chondro-Gide) containing human chondrocytes with devitalized spongiosa cylinders (Tutobone) using a fibrin gel (Tisseel). We demonstrate that separate pre-culture of the chondral layer for 3 days prior to the generation of the composite allows for (i) more efficient cartilaginous matrix accumulation than no pre-culture, as assessed histologically and biochemically, and (ii) superior biological bonding to the bony scaffold than 14 days of pre-culture, as assessed using a peel-off mechanical test, developed to measure integration of bilayered materials. The presence of the bony scaffold induced an upregulation in the infiltrated cells of the osteoblast-related gene bone sialoprotein, indicative of the establishment of a gradient of cell phenotypes, but did not affect per se the quality of the cartilaginous matrix in the chondral layer. The described strategy to generate osteochondral plugs is simple to be implemented and--since it is based on clinically compliant cells and materials--is amenable to be readily tested in the clinic.

Animal models for meniscus repair and regeneration.

The meniscus plays an important role in knee function and mechanics. Meniscal lesions, however, are common phenomena and this tissue is not able to achieve spontaneous successful repair, particularly in the inner avascular zone. Several animal models have been studied and proposed for testing different reparative approaches, as well as for studying regenerative methods aiming to restore the original shape and function of this structure. This review summarizes the gross anatomy, function, ultrastructure and biochemical composition of the knee meniscus in several animal models in comparison with the human meniscus. The relevance of the models is discussed from the point of view of basic research as well as of clinical translation for meniscal repair, substitution and regeneration. Finally, the advantages and disadvantages of each model for various research directions are critically discussed. Copyright

A tissue engineered osteochondral plug : an in vitro morphological evaluation

Articular cartilage lesions have a poor intrinsic healing potential. The repair tissue is often fibrous, having insufficient biomechanical properties, which could frequently lead to the development of early osteoarthritis. In the last decade, tissue engineering approaches addressed this topic in order to restore joint function with a differentiated and functional tissue. Many biomaterials and techniques have been proposed and some of them applied in clinical practice, even though several concerns have been raised on the quality of the engineered tissue and on its integration in the host joint. In this study, we focused on engineering in vitro a biphasic composite made of cellular fibrin glue and a calcium–phosphate scaffold. Biphasic composites are the latest products of tissue engineering applied to articular cartilage and they seem to allow a more efficient integration of the engineered tissue with the host. However, a firm in vitro bonding between the two components of the composite is a necessary condition to validate this model. Our study demonstrated a gross and microscopic integration of the two components and a cartilage-like quality of the newly formed matrix. Moreover, we noticed an improvement of this integration and GAGs production during the in vitro culture.

Pseudoaneurysm overlying an osteochondroma: a noteworthy complication

Pseuodaneurysms are an extremely rare complication of osteochondromas. We describe a case of traumatic pseudoaneurysm of the brachial artery presenting as a soft tissue mass in a patient who was treated for an osteochondroma 3 years earlier. This case demonstrates that radiographic follow-up of large osteochondromas is mandatory and that, in patients with soft tissue masses and a history of osteochondroma, pseudoaneurysms should be included in the differential diagnosis.

Stem Cells for Bone Regeneration: From Cell-Based Therapies to Decellularised Engineered Extracellular Matrices

Currently, autologous bone grafting represents the clinical gold standard in orthopaedic surgery. In certain cases, however, alternative techniques are required. The clinical utility of stem and stromal cells has been demonstrated for the repair and regeneration of craniomaxillofacial and long bone defects although clinical adoption of bone tissue engineering protocols has been very limited. Initial tissue engineering studies focused on the bone marrow as a source of cells for bone regeneration, and while a number of promising results continue to emerge, limitations to this technique have prompted the exploration of alternative cell sources, including adipose and muscle tissue. In this review paper we discuss the advantages and disadvantages of cell sources with a focus on adipose tissue and the bone marrow. Additionally, we highlight the relatively recent paradigm of developmental engineering, which promotes the recapitulation of naturally occurring developmental processes to allow the implant to optimally respond to endogenous cues. Finally we examine efforts to apply lessons from studies into different cell sources and developmental approaches to stimulate bone growth by use of decellularised hypertrophic cartilage templates.