Long-term results of deep defects in articular cartilage. A scanning electron microscope study

Biomaterials for articular cartilage tissue engineering: Learning from biology

Articular cartilage is commonly described as a tissue that is made of up to 80% water, is devoid of blood vessels, nerves, and lymphatics, and is populated by only one cell type, the chondrocyte. At first glance, an easy tissue for clinicians to repair and for scientists to reproduce in a laboratory. Yet, chondral and osteochondral defects currently remain an open challenge in orthopedics and tissue engineering of the musculoskeletal system, without considering osteoarthritis. Why do we fail in repairing and regenerating articular cartilage? Behind its simple and homogenous appearance, articular cartilage hides a heterogeneous composition, a high level of organisation and specific biomechanical properties that, taken together, make articular cartilage a unique material that we are not yet able to repair or reproduce with high fidelity. This review highlights the available therapies for cartilage repair and retraces the research on different biomaterials developed for tissue engineering strategies. Their potential to recreate the structure, including composition and organisation, as well as the function of articular cartilage, intended as cell microenvironment and mechanically competent replacement, is described. A perspective of the limitations of the current research is given in the light of the emerging technologies supporting tissue engineering of articular cartilage.

STATEMENT OF SIGNIFICANCE

The mechanical properties of articular tissue reflect its functionally organised composition and the recreation of its structure challenges the success of in vitro and in vivo reproduction of the native cartilage. Tissue engineering and biomaterials science have revolutionised the way scientists approach the challenge of articular cartilage repair and regeneration by introducing the concept of the interdisciplinary approach. The clinical translation of the current approaches are not yet fully successful, but promising results are expected from the emerging and developing new generation technologies.

Open Reduction Internal Fixation of Isolated Chondral Fragments Without Osseous Attachment in the Knee: A Case Series

Background:

Isolated chondral fractures of the knee are a rare and challenging problem, typically occurring with an acute traumatic event such as dislocation of the patella or ligamentous injury. Historically, repair of unstable chondral fragments without osseous attachment has not been recommended due to concerns about the limited healing potential of cartilage.

Purpose:

To describe a technique for fixation of large isolated chondral fractures of the knee and present 3 cases where large chondral fragments without osseous attachment were fixed successfully with chondral darts and biologic adhesive.

Study Design:

Case series; Level of evidence, 4.

Methods:

The senior author reviewed his case logs for all patients on whom he performed open reduction and internal fixation on large isolated cartilage fragments without osseous attachment. Three were extracted from his review. The clinical and radiographic outcomes were retrospectively reviewed.

Results:

Successful results and complete healing was obtained in all 3 patients. This procedure can be done in the setting of concurrent injury, such as anterior cruciate ligament tear, using single- or multistaged chondral repair and ligament reconstruction techniques.

Conclusion:

Isolated chondral fragment repair techniques provide the orthopaedic surgeon an additional option for treating these challenging injuries. Primary fixation can be accomplished for what have been historically considered “unsalvageable” fragments.

Preclinical evaluation of a novel implant for treatment of a full-thickness distal femoral focal cartilage defect

A novel, nonresorbable, monolithic composite structure ceramic, developed using a partially stabilized zirconia ceramic common to implantable devices, was used in a cementless weight-bearing articular implant to test the feasibility of replacing a region of degenerated or damaged articular cartilage in the knee as part of a preclinical study using male mongrel dogs lasting up to 24 weeks. Gross/histological cartilage observations showed no differences among control, 12-week and 24-week groups, while pull-out tests showed an increase in maximum pull-out load over time relative to controls. Hence, the use of a novel ceramic implant as a replacement for a focal cartilage defect leads to effective implant fixation within 12 weeks and does not cause significant degradation in opposing articular cartilage in the time frame evaluated.

Advanced Strategies for Articular Cartilage Defect Repair

Articular cartilage is a unique tissue owing to its ability to withstand repetitive compressive stress throughout an individual's lifetime. However, its major limitation is the inability to heal even the most minor injuries. There still remains an inherent lack of strategies that stimulate hyaline-like articular cartilage growth with appropriate functional properties. Recent scientific advances in tissue engineering have made significant steps towards development of constructs for articular cartilage repair. In particular, research has shown the potential of biomaterial physico-chemical properties significantly influencing the proliferation, differentiation and matrix deposition by progenitor cells. Accordingly, this highlights the potential of using such properties to direct the lineage towards which such cells follow. Moreover, the use of soluble growth factors to enhance the bioactivity and regenerative capacity of biomaterials has recently been adopted by researchers in the field of tissue engineering. In addition, gene therapy is a growing area that has found noteworthy use in tissue engineering partly due to the potential to overcome some drawbacks associated with current growth factor delivery systems. In this context, such advanced strategies in biomaterial science, cell-based and growth factor-based therapies that have been employed in the restoration and repair of damaged articular cartilage will be the focus of this review article.

Preclinical Studies for Cartilage Repair: Recommendations from the International Cartilage Repair Society

Investigational devices for articular cartilage repair or replacement are considered to be significant risk devices by regulatory bodies. Therefore animal models are needed to provide proof of efficacy and safety prior to clinical testing. The financial commitment and regulatory steps needed to bring a new technology to clinical use can be major obstacles, so the implementation of highly predictive animal models is a pressing issue. Until recently, a reductionist approach using acute chondral defects in immature laboratory species, particularly the rabbit, was considered adequate; however, if successful and timely translation from animal models to regulatory approval and clinical use is the goal, a step-wise development using laboratory animals for screening and early development work followed by larger species such as the goat, sheep and horse for late development and pivotal studies is recommended. Such animals must have fully organized and mature cartilage. Both acute and chronic chondral defects can be used but the later are more like the lesions found in patients and may be more predictive. Quantitative and qualitative outcome measures such as macroscopic appearance, histology, biochemistry, functional imaging, and biomechanical testing of cartilage, provide reliable data to support investment decisions and subsequent applications to regulatory bodies for clinical trials. No one model or species can be considered ideal for pivotal studies, but the larger animal species are recommended for pivotal studies. Larger species such as the horse, goat and pig also allow arthroscopic delivery, and press-fit or sutured implant fixation in thick cartilage as well as second look arthroscopies and biopsy procedures.

The effects of lesion size and location on subchondral bone contact in experimental knee articular cartilage defects in a bovine model

PURPOSE

To determine how femoral condyle chondral defect size and location influence subchondral bone contact within the defect.

METHODS

Full-thickness, circular chondral defects (0.2 to 5.07 cm²) were created in 9 healthy bovine knees. Knees were loaded to 1,000 N, and subchondral bone contact area measurements were recorded with a Tekscan sensor and I-Scan software (Tekscan, Boston, MA). A MATLAB program (The MathWorks, Natick, MA) was designed to compute defect area and the area within the defect showing subchondral bone contact. One-sample t tests with Bonferroni correction were performed for medial and lateral defects at each defect size to determine when statistically significant (P < .05) contact occurred; the smallest defect size exhibiting significant contact was considered a threshold area.

RESULTS

The threshold at which significant subchondral bone contact occurred was different for medial and lateral defects. Contact within all defects was not observed below a defect area of 0.97 cm². The threshold at which significant (P < .05) contact occurred was 1.61 cm² and 1.99 cm² for lateral and medial condyle defects, respectively.

CONCLUSIONS

Subchondral bone contact within experimental femoral condyle chondral defects is dependent on defect size and intra-articular location. In our bovine model, lateral condyle defects have significant subchondral bone contact at a smaller defect size than medial defects.

CLINICAL RELEVANCE

Current algorithms use size as a primary factor in management of chondral defects of the knee. Although the consequences of subchondral bone contact on femoral condyle articular cartilage defect progression are unknown, the results of this study supplement current algorithms and suggest consideration of defect location, in addition to size, in the management of chondral defects of the knee.

Repair of full-thickness femoral condyle cartilage defects using allogeneic synovial cell-engineered tissue constructs

OBJECTIVE

Synovium-derived stem cells (SDSCs) have proven to be superior in cartilage regeneration compared with other sources of mesenchymal stem cells. We hypothesized that conventionally passaged SDSCs can be engineered in vitro into cartilage tissue constructs and the engineered premature tissue can be implanted to repair allogeneic full-thickness femoral condyle cartilage defects without immune rejection.

METHODS

Synovial tissue was harvested from rabbit knee joints. Passage 3 SDSCs were mixed with fibrin glue and seeded into non-woven polyglycolic acid (PGA) mesh. After 1-month incubation with growth factor cocktails, the premature tissue was implanted into rabbit knees to repair osteochondral defects with Collagraft as a bone substitute in the Construct group. Fibrin glue-saturated PGA/Collagraft composites were used as a Scaffold group. The defect was left untreated as an Empty group.

RESULTS

SDSCs were engineered in rotating bioreactor systems into premature cartilage, which displayed the expression of sulfated glycosaminoglycan (GAG), collagen II, collagen I, and macrophages. Six months after implantation with premature tissue, cartilage defects were full of smooth hyaline-like cartilage with no detectable collagen I and macrophages but a high expression of collagen II and GAG, which were also integrated with the surrounding native cartilage. The Scaffold and Empty groups were resurfaced with fibrous-like and fibrocartilage tissue, respectively.

CONCLUSION

Allogeneic SDSC-based premature tissue constructs are a promising stem cell-based approach for cartilage defects. Although in vitro data suggest that contaminated macrophages affected the quality of SDSC-based premature cartilage, effects of macrophages on in vivo tissue regeneration and integration necessitate further investigation.

The potential of IGF-1 and TGFbeta1 for promoting "adult" articular cartilage repair: an in vitro study

Research into articular cartilage repair, a tissue unable to spontaneously regenerate once injured, has focused on the generation of a biomechanically functional repair tissue with the characteristics of hyaline cartilage. This study was undertaken to provide insight into how to improve ex vivo chondrocyte amplification, without cellular dedifferentiation for cell-based methods of cartilage repair. We investigated the effects of insulin-like growth factor 1 (IGF-1) and transforming growth factor beta 1 (TGFbeta1) on cell proliferation and the de novo synthesis of sulfated glycosaminoglycans and collagen in chondrocytes isolated from skeletally mature bovine articular cartilage, whilst maintaining their chondrocytic phenotype. Here we demonstrate that mature differentiated chondrocytes respond to growth factor stimulation to promote de novo synthesis of matrix macromolecules. Additionally, chondrocytes stimulated with IGF-1 or TGFbeta1 induced receptor expression. We conclude that IGF-1 and TGFbeta1 in addition to autoregulatory effects have differential effects on each other when used in combination. This may be mediated by regulation of receptor expression or endogenous factors; these findings offer further options for improving strategies for repair of cartilage defects.

Animal models for osteoarthritis: processes, problems and prospects

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