Repair of focal cartilage defects with scaffold-assisted autologous chondrocyte grafts: clinical and biomechanical results 48 months after transplantation

Harnessing Nanomedicine for Cartilage Repair: Design Considerations and Recent Advances in Biomaterials

Cartilage injuries are escalating worldwide, particularly in aging society. Given its limited self-healing ability, the repair and regeneration of damaged articular cartilage remain formidable challenges. To address this issue, nanomaterials are leveraged to achieve desirable repair outcomes by enhancing mechanical properties, optimizing drug loading and bioavailability, enabling site-specific and targeted delivery, and orchestrating cell activities at the nanoscale. This review presents a comprehensive survey of recent research in nanomedicine for cartilage repair, with a primary focus on biomaterial design considerations and recent advances. The review commences with an introductory overview of the intricate cartilage microenvironment and further delves into key biomaterial design parameters crucial for treating cartilage damage, including microstructure, surface charge, and active targeting. The focal point of this review lies in recent advances in nano drug delivery systems and nanotechnology-enabled 3D matrices for cartilage repair. We discuss the compositions and properties of these nanomaterials and elucidate how these materials impact the regeneration of damaged cartilage. This review underscores the pivotal role of nanotechnology in improving the efficacy of biomaterials utilized for the treatment of cartilage damage.

Cartilage Tissue Engineering in Practice: Preclinical Trials, Clinical Applications, and Prospects

Articular cartilage defects significantly compromise the quality of life in the global population. Although many strategies are needed to repair articular cartilage, including microfracture, autologous osteochondral transplantation, and osteochondral allograft, the therapeutic effects remain suboptimal. In recent years, with the development of cartilage tissue engineering, scientists have continuously improved the formulations of therapeutic cells, biomaterial-based scaffolds, and biological factors, which have opened new avenues for better therapeutics of cartilage lesions. This review focuses on advances in cartilage tissue engineering, particularly in preclinical trials and clinical applications, prospects, and challenges.

Suppressing Chondrocyte Hypertrophy to Build Better Cartilage

Current clinical strategies for restoring cartilage defects do not adequately consider taking the necessary steps to prevent the formation of hypertrophic tissue at injury sites. Chondrocyte hypertrophy inevitably causes both macroscopic and microscopic level changes in cartilage, resulting in adverse long-term outcomes following attempted restoration. Repairing/restoring articular cartilage while minimizing the risk of hypertrophic neo tissue formation represents an unmet clinical challenge. Previous investigations have extensively identified and characterized the biological mechanisms that regulate cartilage hypertrophy with preclinical studies now beginning to leverage this knowledge to help build better cartilage. In this comprehensive article, we will provide a summary of these biological mechanisms and systematically review the most cutting-edge strategies for circumventing this pathological hallmark of osteoarthritis.

Instabilities induced by mechanical loading determine the viability of chondrocytes grown on porous scaffolds

Tissue-engineered cartilage constructs have shown promise to treat focal cartilage defects in multiple clinical studies. Notably, products in clinical use or in late-stage clinical trials often utilize porous collagen scaffolds to provide mechanical support and attachment sites for chondrocytes. Under loading, both the local mechanical responses of collagen scaffolds and the corresponding cellular outcomes are poorly understood, despite their wide use. As such, the architecture of collagen scaffolds varies significantly among tissue-engineered cartilage products, but the effects of such architectures on construct mechanics and cell viability are not well understood. This study investigated the effects of local mechanical responses of collagen scaffolds on chondrocyte viability in tissue-engineered cartilage constructs. We utilized fast confocal microscopy combined with a strain mapping technique to analyze the architecture-dependent instabilities under quasi-static loading and subsequent chondrocyte death in honeycomb and sponge scaffolds. More specifically, we compared the isotropic and the orthotropic planes for each type of collagen scaffold. Under compression, both planes exhibited elastic, buckled, and densified deformation modes. In both loading directions, cell death was minimal in regions that experienced elastic deformation mode and a trend of increase in buckled mode. More interestingly, we saw a significant increase in cell death in densified mode. Overall, this study suggests that local instabilities are directly correlated to chondrocyte death in tissue-engineered cartilage constructs, highlighting the importance of understanding the architecture-dependent local mechanical responses under loading.

2D Magnetic Microswimmers for Targeted Cell Transport and 3D Cell Culture Structure Construction

Cell delivery using magnetic microswimmers is a promising tool for targeted therapy. However, it remains challenging to rapidly and uniformly manufacture cell-loaded microswimmers that can be assembled into cell-supporting structures at diseased sites. Here, rapid and uniform manufacturable 2D magnetic achiral microswimmers with pores were fabricated to deliver bone marrow mesenchymal stem cells (BMSCs) to regenerate articular-damaged cartilage. Under actuation with magnetic fields, the BMSC-loaded microswimmers take advantage of the achiral structure to exhibit rolling or swimming motions to travel on smooth and rough surfaces, up inclined planes, or in the bulk fluid. Cell viability, proliferation, and differentiation tests performed days after cell seeding verified the microswimmers' biocompatibility. Long-distance targeting and in situ assemblies into 3D cell-supporting structures with BMSC-loaded microswimmers were demonstrated using a knee model and U-shaped wells. Overall, combining the advantages of preparing an achiral 2D structured microswimmer with magnetically driven motility results in a platform for cell transport and constructing 3D cell cultures that can improve cell delivery at lesion sites for biomedical applications.

Progress and prospect of technical and regulatory challenges on tissue-engineered cartilage as therapeutic combination product

Hyaline cartilage plays a critical role in maintaining joint function and pain. However, the lack of blood supply, nerves, and lymphatic vessels greatly limited the self-repair and regeneration of damaged cartilage, giving rise to various tricky issues in medicine. In the past 30 years, numerous treatment techniques and commercial products have been developed and practiced in the clinic for promoting defected cartilage repair and regeneration. Here, the current therapies and their relevant advantages and disadvantages will be summarized, particularly the tissue engineering strategies. Furthermore, the fabrication of tissue-engineered cartilage under research or in the clinic was discussed based on the traid of tissue engineering, that is the materials, seed cells, and bioactive factors. Finally, the commercialized cartilage repair products were listed and the regulatory issues and challenges of tissue-engineered cartilage repair products and clinical application would be reviewed.

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Tissue engineered cartilage, a promising strategy for articular cartilage repair.

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Nearly 20 engineered cartilage repair products in clinic based on clinical techniques.

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Combination product, the classification of tissue-engineered cartilage.

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Key regulatory compliance issues for combination products.

Progress of Microfluidic Hydrogel-Based Scaffolds and Organ-on-Chips for the Cartilage Tissue Engineering

Cartilage degeneration is among the fundamental reasons behind disability and pain across the globe. Numerous approaches have been employed to treat cartilage diseases. Nevertheless, none have shown acceptable outcomes in the long run. In this regard, the convergence of tissue engineering and microfabrication principles can allow developing more advanced microfluidic technologies, thus offering attractive alternatives to current treatments and traditional constructs used in tissue engineering applications. Herein, the current developments involving microfluidic hydrogel-based scaffolds, promising structures for cartilage regeneration, ranging from hydrogels with microfluidic channels to hydrogels prepared by the microfluidic devices, that enable therapeutic delivery of cells, drugs, and growth factors, as well as cartilage-related organ-on-chips are reviewed. Thereafter, cartilage anatomy and types of damages, and present treatment options are briefly overviewed. Various hydrogels are introduced, and the advantages of microfluidic hydrogel-based scaffolds over traditional hydrogels are thoroughly discussed. Furthermore, available technologies for fabricating microfluidic hydrogel-based scaffolds and microfluidic chips are presented. The preclinical and clinical applications of microfluidic hydrogel-based scaffolds in cartilage regeneration and the development of cartilage-related microfluidic chips over time are further explained. The current developments, recent key challenges, and attractive prospects that should be considered so as to develop microfluidic systems in cartilage repair are highlighted.

Recent Advances in "Functional Engineering of Articular Cartilage Zones by Polymeric Biomaterials Mediated with Physical, Mechanical, and Biological/Chemical Cues"

Articular cartilage (AC) plays an unquestionable role in joint movements but unfortunately the healing capacity is restricted due to its avascular and acellular nature. While cartilage tissue engineering has been lifesaving, it is very challenging to remodel the complex cartilage composition and architecture with gradient physio-mechanical properties vital to proper tissue functions. To address these issues, a better understanding of the intrinsic AC properties and how cells respond to stimuli from the external microenvironment must be better understood. This is essential in order to take one step closer to producing functional cartilaginous constructs for clinical use. Recently, biopolymers have aroused much attention due to their versatility, processability, and flexibility because the properties can be tailored to match the requirements of AC. This review highlights polymeric scaffolds developed in the past decade for reconstruction of zonal AC layers including the superficial zone, middle zone, and deep zone by means of exogenous stimuli such as physical, mechanical, and biological/chemical signals. The mimicked properties are reviewed in terms of the biochemical composition and organization, cell fate (morphology, orientation, and differentiation), as well as mechanical properties and finally, the challenges and potential ways to tackle them are discussed.

Biological Reconstruction of Localized Full-Thickness Cartilage Defects of the Knee: A Systematic Review of Level 1 Studies with a Minimum Follow-Up of 5 Years

OBJECTIVE

The objective of this study was to evaluate the best available mid- to long-term evidence of surgical procedures for the treatment of localized full-thickness cartilage defects of the knee.

DESIGN

Systematic review using Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines of Level 1 randomized clinical trials (RCTs), meta-analyses of RCTs and systematic reviews with a minimum follow-up of 5 years. Data extracted included patient demographics, defect characteristics, clinical and radiological outcomes, as well as treatment failures.

RESULTS

Six RCTs and 3 Level 1 systematic reviews were included. Two RCTs compared microfracture (MFx) to periosteum-covered autologous chondrocyte implantation (ACI-P), 1 to matrix-associated ACI (M-ACI) and 2 to osteochondral autograft transplantation (OAT). One study compared OAT to collagen membrane covered ACI (ACI-C). The 3 Level 1 systematic reviews/meta-analyses assessed the outcome of MFx, OAT, and various ACI methods in RCTs. OAT showed significantly better outcomes compared with MFx. In the 2 RCTs comparing ACI-P and MFx, no significant differences in clinical outcomes were seen, whereas significantly better outcomes were reported for M-ACI versus MFx in 1 study including patients with larger defects (5 cm²), and for ACI-C versus OAT in terms of Cincinnati Score. Higher failure rates were reported for MFx compared with OAT and for OAT compared with ACI-C, while no significant differences in failure rates were observed for ACI-P compared to MFx.

CONCLUSION

Restorative cartilage procedures (ACI-C or M-ACI and OAT) are associated with better long-term clinical outcomes including lower complication and failure rates when compared with reparative techniques (MFx). Among the restorative procedures, OAT seems to be inferior to ACI especially in larger defects after longer follow-up periods.

LEVEL OF EVIDENCE

Level I: Systematic review of Level I studies.

Four cases report: Treatment of knee joint cartilage defects using autologous chondrocyte patch implantation

INTRODUCTION

Autologous chondrocyte implantation (ACI) is a crucial method for the treatment of defects in articular cartilage. However, the extant methods for the preparation of autologous chondrocyte patch are relatively complicated and money-consuming. Therefore, an efficient, reliable, easy-to-follow, and cost-effective technique is needed to overcome constraints. This case report aims to introduce an autologous chondrocyte patch fabrication technique to repair knee joint cartilage defects and report our typical cases with a 2-year follow-up.

CASE PRESENTATION

We described four cases in which patients complained of knee joint pain. According to radiological examination, the patients were diagnosed as knee joint cartilage defect. Arthroscopy and autologous chondrocyte patch implantation were performed as well as a 2-year follow up of patients. The autologous chondrocyte patch for knee joint cartilage repair was fabricated using a "sandwich" technique. The preoperative and postoperative knee function was evaluated by four subjective evaluation systems. MRI was performed for all patients to achieve more intuitionistic observation of the postoperative radiological changes of defect sites. The quality of repaired tissue was evaluated by Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART). Postoperative follow-up showed improvement in clinical and MOCART scores for all patients. However, one patient complained of knee joint pain after walking for a long time or recreational activities from 12- to 18-month postoperatively. The location of pain for this patient was not in accordance with the location of cartilage defect.

CONCLUSION

The patients undergoing autologous chondrocyte patch implantation demonstrated clinical improvement and good quality of repaired tissue postoperatively. The procedure is an efficient and cost-effective treatment for knee joint cartilage defect in this report. In addition, patients with osteoarthritis carry the risk of a poor outcome after the procedure, and whether to have a procedure should be considered carefully.

Highlights on Advancing Frontiers in Tissue Engineering

The field of tissue engineering continues to advance, sometimes in exponential leaps forward, but also sometimes at a rate that does not fulfill the promise that the field imagined a few decades ago. This review is in part a catalog of success in an effort to inform the process of innovation. Tissue engineering has recruited new technologies and developed new methods for engineering tissue constructs that can be used to mitigate or model disease states for study. Key to this antecedent statement is that the scientific effort must be anchored in the needs of a disease state and be working toward a functional product in regenerative medicine. It is this focus on the wildly important ideas coupled with partnered research efforts within both academia and industry that have shown most translational potential. The field continues to thrive and among the most important recent developments are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies that warrant special attention. Developments in the aforementioned areas as well as future directions are highlighted in this article. Although several early efforts have not come to fruition, there are good examples of commercial profitability that merit continued investment in tissue engineering. Impact statement Tissue engineering led to the development of new methods for regenerative medicine and disease models. Among the most important recent developments in tissue engineering are the use of three-dimensional bioprinting, organ-on-a-chip, and induced pluripotent stem cell technologies. These technologies and an understanding of them will have impact on the success of tissue engineering and its translation to regenerative medicine. Continued investment in tissue engineering will yield products and therapeutics, with both commercial importance and simultaneous disease mitigation.

The immune microenvironment in cartilage injury and repair

The ability of articular cartilage to repair itself is limited because it lacks blood vessels, nerves, and lymph tissue. Once damaged, it can lead to joint swelling and pain, accelerating the progression of osteoarthritis. To date, complete regeneration of hyaline cartilage exhibiting mechanical properties remains an elusive goal, despite the many available technologies. The inflammatory milieu created by cartilage damage is critical for chondrocyte death and hypertrophy, extracellular matrix breakdown, ectopic bone formation, and progression of cartilage injury to osteoarthritis. In the inflammatory microenvironment, mesenchymal stem cells (MSCs) undergo aberrant differentiation, and chondrocytes begin to convert or dedifferentiate into cells with a fibroblast phenotype, thereby resulting in fibrocartilage with poor mechanical qualities. All these factors suggest that inflammatory problems may be a major stumbling block to cartilage repair. To produce a milieu conducive to cartilage repair, multi-dimensional management of the joint inflammatory microenvironment in place and time is required. Therefore, this calls for elucidation of the immune microenvironment of cartilage repair after injury. This review provides a brief overview of: (1) the pathogenesis of cartilage injury; (2) immune cells in cartilage injury and repair; (3) effects of inflammatory cytokines on cartilage repair; (4) clinical strategies for treating cartilage defects; and (5) strategies for targeted immunoregulation in cartilage repair. STATEMENT OF SIGNIFICANCE: Immune response is increasingly considered the key factor affecting cartilage repair. It has both negative and positive regulatory effects on the process of regeneration and repair. Proinflammatory factors are secreted in large numbers, and necrotic cartilage is removed. During the repair period, immune cells can secrete anti-inflammatory factors and chondrogenic cytokines, which can inhibit inflammation and promote cartilage repair. However, inflammatory factors persist, which accelerate the degradation of the cartilage matrix. Furthermore, in an inflammatory microenvironment, MSCs undergo abnormal differentiation, and chondrocytes begin to transform or dedifferentiate into fibroblast-like cells, forming fibrocartilage with poor mechanical properties. Consequently, cartilage regeneration requires multi-dimensional regulation of the joint inflammatory microenvironment in space and time to make it conducive to cartilage regeneration.

Magnetic resonance observation of cartilage repair tissue (MOCART) 2.0 for the evaluation of retropatellar autologous chondrocyte transplantation and correlation to clinical outcome

BACKGROUND

Matrix-associated chondrocyte transplantation (MACT) has become an established treatment option for cartilage defects.

OBJECTIVE

Three objectives were defined: first, to evaluate retropatellar cartilage grafts using Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) 2.0 score; second, to determine whether clinical outcome correlates with specific parameters or overall results; third, to screen those parameters for their ability to predict a clinical outcome of Delta IKDC ≥ 20 as a threshold for good clinical response at 12 months.

METHODS

38 patients were included of whom all underwent retropatellar MACT. MRI was performed 3, 6 and 12 months postoperatively. The clinical status was determined using International Knee Documentation Committee Subjective Form (IKDC). Correlations of MOCART 2.0 parameters and Delta IKDC scores were quantified by nonparametric Spearman's R. Those parameters with significant correlations (p < 0.05) were screened for their ability to predict a clinical outcome of Delta IKDC ≥ 20 at 12 months.

RESULTS

Significant correlations were identified for the parameters MOCART total _{6 months} (p < 0.05), Surface _{6 months} (p < 0.05), Surface _{12 months} (p < 0.05), Structure _{6 months} (p < 0.01), Structure _{12 months} (p < 0.05), Subchondral changes _{3 months} (p < 0.0001), Subchondral changes _{6 months} (p < 0.05) and Subchondral changes _{12 months} (p < 0.05). Among all MRI score parameters, Subchondral changes _{3 months} achieved the highest accuracy of 0.76 (0.62-0.86) in predicting Delta IKDC ≥ 20 after 12 months.

CONCLUSION

Some of the MOCART 2.0 parameters show significant correlation with Delta IKDC scores in the postoperative course after retropatellar MACT, which seems to depend on the time interval between surgery and MRI acquisition.

Good clinical outcomes after patellar cartilage repair with no evidence for inferior results in complex cases with the need for additional patellofemoral realignment procedures: a systematic review

PURPOSE

Focal, patellar cartilage defects are a challenging problem as most cases have an underlying multifactorial pathogenesis. This systematic review of current literature analysed clinical results after regenerative cartilage repair of the patella with a special focus on the assessment and treatment of existing patellofemoral malalignment.

METHODS

A systematic review was conducted to identify articles reporting clinical results after cartilage regenerative surgeries of the patella using the PubMed and Scopus database. The extracted data included patient-reported outcome measures (PROMS) and whether cartilage repair was performed alone or in combination with concomitant surgeries of underlying patellofemoral co-pathologies. In cases of isolated cartilage repair, specific exclusion criteria regarding underlying co-pathologies were screened. In cases of concomitant surgeries, the type of surgeries and their specific indications were extracted.

RESULTS

A total of 35 original articles were included out of which 27 (77%) were cohort studies with level IV evidence. The most frequently used technique for cartilage restoration of the patella was autologous chondrocyte implantation (ACI). Results after isolated cartilage repair alone were reported by 15 (43%) studies. Of those studies, 9 (60%) excluded patients with underlying patellofemoral malalignment a priori and 6 (40%) did not analyse underlying co-pathologies at all. Among the studies including combined surgeries, the most frequently reported concomitant procedures were release of the lateral retinaculum, reconstruction of the medial patellofemoral ligament (MPFL), and osteotomy of the tibial tubercle. In summary, these studies showed lower preoperative PROMS but similar final PROMS in comparison with the studies reporting on isolated cartilage repair. The most frequently used PROMS were the IKDC-, Lysholm- and the Modified Cincinnati Score.

CONCLUSION

This comprehensive literature review demonstrated good clinical outcomes after patellar cartilage repair with no evidence of minor results even in complex cases with the need for additional patellofemoral realignment procedures. However, a meaningful statistical comparison between isolated patellar cartilage repair and combined co-procedures is not possible due to very heterogeneous patient cohorts and a lack of analysis of specific subgroups in recent literature.

LEVEL OF EVIDENCE

Level IV.

In Vitro Cartilage Regeneration with a Three-Dimensional Polyglycolic Acid (PGA) Implant in a Bovine Cartilage Punch Model

Resorbable polyglycolic acid (PGA) chondrocyte grafts are clinically established for human articular cartilage defects. Long-term implant performance was addressed in a standardized in vitro model. PGA implants (+/- bovine chondrocytes) were placed inside cartilage rings punched out of bovine femoral trochleas (outer Ø 6 mm; inner defect Ø 2 mm) and cultured for 84 days (12 weeks). Cartilage/PGA hybrids were subsequently analyzed by histology (hematoxylin/eosin; safranin O), immunohistochemistry (aggrecan, collagens 1 and 2), protein assays, quantitative real-time polymerase chain reactions, and implant push-out force measurements. Cartilage/PGA hybrids remained vital with intact matrix until 12 weeks, limited loss of proteoglycans from "host" cartilage or cartilage-PGA interface, and progressively diminishing release of proteoglycans into the supernatant. By contrast, the collagen 2 content in cartilage and cartilage-PGA interface remained approximately constant during culture (with only little collagen 1). Both implants (+/- cells) displayed implant colonization and progressively increased aggrecan and collagen 2 mRNA, but significantly decreased push-out forces over time. Cell-loaded PGA showed significantly accelerated cell colonization and significantly extended deposition of aggrecan. Augmented chondrogenic differentiation in PGA and cartilage/PGA-interface for up to 84 days suggests initial cartilage regeneration. Due to the PGA resorbability, however, the model exhibits limitations in assessing the "lateral implant bonding".

Accurate Reporting of Concomitant Procedures Is Highly Variable in Studies Investigating Knee Cartilage Restoration

OBJECTIVE

Successful clinical outcomes following cartilage restoration procedures are highly dependent on addressing concomitant pathology. The purpose of this study was to document methods for evaluating concomitant procedures of the knee when performed with articular cartilage restoration techniques, and to review their reported findings in high-impact clinical orthopedic studies. We hypothesized that there are substantial inconsistencies in reporting clinical outcomes associated with concomitant procedures relative to outcomes related to isolated cartilage repair.

DESIGN

A total of 133 clinical studies on articular cartilage repair of the knee were identified from 6 high-impact orthopedic journals between 2011 and 2017. Studies were included if they were primary research articles reporting clinical outcomes data following surgical treatment of articular cartilage lesions with a minimum sample size of 5 patients. Studies were excluded if they were review articles, meta-analyses, and articles reporting only nonclinical outcomes (e.g., imaging, histology). A full-text review was then used to evaluate details regarding study methodology and reporting on the following variables: primary cartilage repair procedure, and the utilization of concomitant procedures to address additional patient comorbidities, including malalignment, meniscus pathology, and ligamentous instability. Each study was additionally reviewed to document variation in clinical outcomes reporting in patients that had these comorbidities addressed at the time of surgery.

RESULTS

All studies reported on the type of primary cartilage repair procedure, with autologous chondrocyte implantation (ACI) noted in 43% of studies, microfracture (MF) reported in 16.5%, osteochondral allograft (OCA) in 15%, and osteochondral autograft transplant (OAT) in 8.2%. Regarding concomitant pathology, anterior cruciate ligament (ACL) reconstruction (24.8%) and meniscus repair (23.3%) were the most commonly addressed patient comorbidities. A total of 56 studies (42.1%) excluded patients with malalignment, meniscus injury, and ligamentous instability. For studies that addressed concomitant pathology, 72.7% reported clinical outcomes separately from the cohort treated with only cartilage repair. A total of 16.5% of studies neither excluded nor addressed concomitant pathologies. There was a significant amount of variation in the patient reported outcome scores used among the studies, with the majority of studies reporting International Knee Documentation Committee (IKDC) and Knee Injury and Osteoarthritis Outcomes Score (KOOS) in 47.2% and 43.6% of articles, respectively.

CONCLUSIONS

In this study on knee cartilage restoration, recognition and management of concomitant pathology is inadequately reported in approximately 28% of studies. Only 30% of articles reported adequate treatment of concomitant ailments while scoring their outcomes using one of a potential 18 different scoring systems. These findings highlight the need for more standardized methods to be applied in future research with regard to inclusion, exclusion, and scoring concomitant pathologies with regard to treatment of cartilage defects in the knee.

Multifunctional Biodegradable Microrobot with Programmable Morphology for Biomedical Applications

We described a magnetic chitosan microscaffold tailored for applications requiring high biocompatibility, biodegradability, and monitoring by real-time imaging. Such magnetic microscaffolds exhibit adjustable pores and sizes depending on the target application and provide various functions such as magnetic actuation and enhanced cell adhesion using biomaterial-based magnetic particles. Subsequently, we fabricated the magnetic chitosan microscaffolds with optimized shape and pore properties to specific target diseases. As a versatile tool, the capability of the developed microscaffold was demonstrated through in vitro laboratory tasks and in vivo therapeutic applications for liver cancer therapy and knee cartilage regeneration. We anticipate that the optimal design and fabrication of the presented microscaffold will advance the technology of biopolymer-based microscaffolds and micro/nanorobots.

Third generation autologous chondrocyte implantation is a good treatment option for athletic persons

PURPOSE

Autologous chondrocyte implantation is an established method for the treatment of joint cartilage damage. However, to date it has not been established that autologous chondrocyte implantation is an appropriate procedure for cartilage defects therapy in athletic persons. The aim of this study is to analyze if third-generation autologous chondrocyte implantation is an appropriate treatment for athletic persons with full cartilage defect of the knee joints.

METHODS

A total of 84 patients were treated with third-generation autologous chondrocyte implantation (NOVOCART^® 3D). The mean follow-up time was 8 years (5-14). Sports activity was measured via UCLA Activity Score and Tegner Activity Scale before the onset of knee pain and postoperatively in an annual clinical evaluation. 41 athletic persons and 43 non-athletic persons (UCLA-Cut-off: 7; Tegner Activity Scale-Cut-off: 4) were analyzed. Patient reported outcomes were captured using IKDC subjective, KOOS, Lysholm score and VAS score on movement.

RESULTS

Patient reported outcomes (IKDC, VAS at rest, VAS on movement) showed significant improvement (p < 0.001) postoperatively. Athletic persons demonstrated significantly better results than non-athletic persons in the analyzed outcome scores (IKDC: p < 0.01, KOOS: p < 0.01, Lysholm score: p < 0.01). 96.4% of the patients were able to return to sport and over 50% returned or surpassed their preinjury sports level. The remaining patients were downgraded by a median of two points on the UCLA- and 2.5 on the Tegner Activity Scale. A shift from high-impact sports to active events and moderate or mild activities was found. Furthermore, it was shown that preoperative UCLA score and Tegner Activity Scale correlated significantly with the patient reported outcome postoperatively.

CONCLUSION

Autologous chondrocyte implantation is a suitable treatment option for athletic persons with full-thickness cartilage defects in the knee. The return to sports activity is possible, but includes a shift from high-impact sports to less strenuous activities.

Review of Synthetic and Hybrid Scaffolds in Cartilage Tissue Engineering

Cartilage tissue is under extensive investigation in tissue engineering and regenerative medicine studies because of its limited regenerative potential. Currently, many scaffolds are undergoing scientific and clinical research. A key for appropriate scaffolding is the assurance of a temporary cellular environment that allows the cells to function as in native tissue. These scaffolds should meet the relevant requirements, including appropriate architecture and physicochemical and biological properties. This is necessary for proper cell growth, which is associated with the adequate regeneration of cartilage. This paper presents a review of the development of scaffolds from synthetic polymers and hybrid materials employed for the engineering of cartilage tissue and regenerative medicine. Initially, general information on articular cartilage and an overview of the clinical strategies for the treatment of cartilage defects are presented. Then, the requirements for scaffolds in regenerative medicine, materials intended for membranes, and methods for obtaining them are briefly described. We also describe the hybrid materials that combine the advantages of both synthetic and natural polymers, which provide better properties for the scaffold. The last part of the article is focused on scaffolds in cartilage tissue engineering that have been confirmed by undergoing preclinical and clinical tests.

Evolution of hydrogels for cartilage tissue engineering of the knee: A systematic review and meta-analysis of clinical studies

INTRODUCTION

In recent years, studies have boosted our knowledge about the biology and disorders of articular cartilage. In this regard, the design of hydrogel-based scaffolds has advanced to improve cartilage repair. However, the efficacy of knee cartilage repair using hydrogels remains unclear. The aim of systematic review and meta-analysis was to scrutinize the efficiency of hydrogel-based therapy in correcting cartilage defects of knee (femoral condyle, patella, tibia plateau and trochlea).

METHODS

The search was conducted in PubMed to gather articles published from 2004/1/1 to 2019/10/01, addressing the effects of implant of hydrogel on knee joint cartilage regeneration. The Cochrane Collaboration's tool for estimating the risk of bias was applied to check the quality of articles. The clinical data for meta-analysis was recorded using the visual analog scale (VAS), Lysholm score, WOMAC, and IKDC. The guidelines of Cochrane Handbook for Systematic Reviews of Interventions were utilized to conduct the review and meta-analysis in the RevMan 5.3 software.

RESULTS

The search resulted in 50 clinical trials that included 2846 patients, 986 of whom received cell-based hydrogel implants while 1860 patients used hydrogel without cell. There were significant differences comparing the pain scores based on the VAS (MD: -2.97; 95% CI: -3.15 to -2.79, P<0.00001) and WOMAC (MD: -25.22; 95% CI: -31.22 to -19.22, P<0.00001) between pre- and post-treatment with hydrogels. Furthermore, there were significant improvements in the functional scores based on the IKDC total score (MD: 30.67; P<0.00001) and the Lysholm knee scale (MD: 29.26; 95% CI: 26.74 to 31.78, P<0.00001). According to the Lysholm and IKDC score and after cumulative functional analysis, there was a significant improvement in this parameter (MD: 29.25; 95% CI: 27.26 to 31.25, P<0.00001).

CONCLUSIONS

This meta-analysis indicated clinically and statistically significant improvements in the pain score (VAS and WOMAC) and the functional score (IKDC and Lysholm) after the administration of hydrogel compared to pretreatment status. So, the current evidence shows the efficiency of hydrogel-based therapy in correcting and repairing knee cartilage defects.

Clinical Application of the Basic Science of Articular Cartilage Pathology and Treatment

The joint is an organ with each tissue playing critical roles in health and disease. Intact articular cartilage is an exquisite tissue that withstands incredible biologic and biomechanical demands in allowing movement and function, which is why hyaline cartilage must be maintained within a very narrow range of biochemical composition and morphologic architecture to meet demands while maintaining health and integrity. Unfortunately, insult, injury, and/or aging can initiate a cascade of events that result in erosion, degradation, and loss of articular cartilage such that joint pain and dysfunction ensue. Importantly, articular cartilage pathology affects the health of the entire joint and therefore should not be considered or addressed in isolation. Treating articular cartilage lesions is challenging because left alone, the tissue is incapable of regeneration or highly functional and durable repair. Nonoperative treatments can alleviate symptoms associated with cartilage pathology but are not curative or lasting. Current surgical treatments range from stimulation of intrinsic repair to whole-surface and whole-joint restoration. Unfortunately, there is a relative paucity of prospective, randomized controlled, or well-designed cohort-based clinical trials with respect to cartilage repair and restoration surgeries, such that there is a gap in knowledge that must be addressed to determine optimal treatment strategies for this ubiquitous problem in orthopedic health care. This review article discusses the basic science rationale and principles that influence pathology, symptoms, treatment algorithms, and outcomes associated with articular cartilage defects in the knee.

Patient-Reported and Magnetic Resonance Imaging Outcomes of Third-Generation Autologous Chondrocyte Implantation After 10 Years

PURPOSE

To evaluate the long-term clinical and radiologic outcomes of third-generation autologous chondrocyte implantation (ACI) for the treatment of focal cartilage defects of the knee.

METHODS

Data capture was carried out between 2004 and 2018. Included were patients with cartilage defects of the knee joint with an International Cartilage Repair Society grade of III or higher treated with third-generation ACI who had a minimum follow-up period of 10 years. International Knee Documentation Committee scores and assessment of pain at rest and on movement using visual analog scale scores were captured preoperatively and at 6 months postoperatively, as well as annually thereafter. In addition, we performed magnetic resonance imaging examinations in 13 cases after 10 years. The MOCART (Magnetic Resonance Observation of Cartilage Repair Tissue) score was used to evaluate the ACI cartilage.

RESULTS

A total of 54 patients met the inclusion criteria. Of these, 30 reached the 10-year follow-up point and were included in this assessment. At 10 years postoperatively, all clinical outcome parameters showed a statistically significant improvement compared with the preoperative situation, with a responder rate of 70%. The average MOCART (Magnetic Resonance Observation of Cartilage Repair Tissue) score after 10 years was 59.2 points (range, 20-100 points), and over 60% of the evaluated patients showed good integration of the implant at 10 years postoperatively.

CONCLUSIONS

The clinical and radiologic findings of this study show that third-generation ACI is a suitable and effective option in the treatment of full-thickness cartilage defects of the knee. At 10 years after surgery, third-generation ACI shows stable results and leads to significant improvement in all clinical outcome parameters. Despite these results, revision surgery after third-generation ACI is common and was needed in 23% of patients in this study.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Clinical Application Status of Articular Cartilage Regeneration Techniques: Tissue-Engineered Cartilage Brings New Hope

Hyaline articular cartilage lacks blood vessels, lymphatics, and nerves and is characterised by limited self-repair ability following injury. Traditional techniques of articular cartilage repair and regeneration all have certain limitations. The development of tissue engineering technology has brought hope to the regeneration of articular cartilage. The strategies of tissue-engineered articular cartilage can be divided into three types: “cell-scaffold construct,” cell-free, and scaffold-free. In “cell-scaffold construct” strategies, seed cells can be autologous chondrocytes or stem. Among them, some commercial products with autologous chondrocytes as seed cells, such as BioSeed®-C and CaReS®, have been put on the market and some products are undergoing clinical trials, such as NOVOCART® 3D. The stem cells are mainly pluripotent stem cells and mesenchymal stem cells from different sources. Cell-free strategies that indirectly utilize the repair and regeneration potential of stem cells have also been used in clinical settings, such as TruFit and MaioRegen. Finally, the scaffold-free strategy is also a new development direction, and the short-term repair results of related products, such as NOVOCART® 3D, are encouraging. In this paper, the commonly used techniques of articular cartilage regeneration in surgery are reviewed. By studying different strategies and different seed cells, the clinical application status of tissue-engineered articular cartilage is described in detail.

Cartilage damage at the time of anterior cruciate ligament reconstruction is associated with weaker quadriceps function and lower risk of future ACL injury

PURPOSE

To determine whether articular cartilage damage noted at the time of primary anterior cruciate ligament reconstruction (ACLR) affects the likelihood of achieving ≥ 90% symmetry for isokinetic extension strength at 6 months after surgery or risk of recurrent ACL injury.

METHODS

Five hundred and eight patients underwent primary ACLR and diagnostic arthroscopy. All identified cartilage lesions were graded using the Outerbridge system. All patients underwent isokinetic strength testing. The association between cartilage Outerbridge grade and a ≥ 90% Limb Symmetry Index (LSI) and recurrent ACL injury risk at mean 38.7 month follow-up (SD 31.8) was evaluated via multivariate regression analysis.

RESULTS

Grade 2 or higher damage was present in 394 (77.5%) of patients, grade 3 or higher in 143 (28.1%) and grade 4 in 83 (16.4%) at time of ACLR. Ipsilateral ACLR graft rupture occurred in 31 (6.1%) of patients. Contralateral ACL injury occurred in 19 (3.7%). Patients with grade 2 or higher damage were significantly less likely to meet an LSI goal of ≥ 90% for fast (300°/s) isokinetic extension. There was no association with slow isokinetic extension. Cartilage lesion severity at or beyond grade 2 had a similar effect on isokinetic testing results regardless of compartment involvement or performance of microfracture. Patients with grade 2-4 cartilage damage were less likely to sustain a second ipsilateral ACL injury or a contralateral native ACL injury.

CONCLUSIONS

Cartilage damage seen at time of ACL reconstruction is common and associated with lower likelihood of achieving ≥ 90% symmetry for isokinetic extension strength at 6 months after surgery. However, lower recurrent ACL injury rates are seen in patients with concurrent cartilage damage. These data may inform future clinical decisions regarding operative managment of recurrent ACL injuries.

LEVEL OF EVIDENCE

III.

Association Between Isokinetic Knee Strength and Perceived Function and Patient Satisfaction With Sports and Recreational Ability After Matrix-Induced Autologous Chondrocyte Implantation

Background:

Returning to a sound level of activity after matrix-induced autologous chondrocyte implantation (MACI) is important to patients. Evaluating the patient’s level of satisfaction with his or her sports and recreational ability is critical.

Purpose:

To investigate (1) satisfaction with sports and recreational ability after MACI and (2) the role that knee strength plays in self-reported knee function and satisfaction.

Study Design:

Case-control study; Level of evidence, 3.

Methods:

Isokinetic knee strength was assessed in 97 patients at 1, 2, and 5 years after MACI to calculate hamstrings-quadriceps ratios and peak knee extensor and flexor torque limb symmetry indices (LSIs). The Sports and Recreation subscale of the Knee injury and Osteoarthritis Outcome Score (KOOS Sports/Rec) was completed. A satisfaction scale was used to evaluate how satisfied the patients were with their ability to return to recreational activities and their ability to participate in sport. Associations between knee strength LSI, KOOS Sports/Rec, and satisfaction with recreational and sporting activities were assessed through use of multivariable linear and logistic regression, with adjustment for confounders. Mediation analysis was conducted to assess the extent to which self-reported knee function mediated associations between strength LSI and satisfaction.

Results:

Satisfaction with the ability to return to recreational activities was achieved in 82.4%, 85.6%, and 85.9% of patients at 1, 2, and 5 years, respectively, and satisfaction with sports participation was achieved in 55.7%, 73.2%, and 68.5% of patients at 1, 2, and 5 years, respectively. Knee extension torque LSIs were associated with KOOS Sports/Rec after adjustment for confounders over 1, 2, and 5 years (5-year regression coefficient, 6.0 points; 95% CI, 1.4-10.7; P = .012). KOOS Sports/Rec was associated with the likelihood of being satisfied at all time points (recreation: 5-year adjusted odds ratio [OR], 2.26; 95% CI, 1.48-3.46; P < .001; and sports: 5-year adjusted OR, 1.98; 95% CI, 1.47-2.68; P < .001). In a multivariable mediation model, the knee extension torque LSI was associated with satisfaction directly (standardized coefficient, 0.16; 95% CI, 0.03-0.28; P = .017) and indirectly via KOOS Sports/Rec (standardized coefficient, 0.19; 95% CI, 0.01-0.38; P = .027), the latter representing 55% of the total association of knee extension torque LSI with satisfaction.

Conclusion:

Knee extensor symmetry was associated with satisfaction in recreational and sporting ability, both directly and indirectly, via self-reported sports and recreation–related knee function. Restoring strength deficits after MACI is important for achieving optimal outcomes.

Gold nanoparticles for the in situ polymerization of near-infrared responsive hydrogels based on fibrin

Non-invasiveness and relative safety of photothermal therapy, which enables local hyperthermia of target tissues using a near infrared (NIR) laser, has attracted increasing interest. Due to their biocompatibility, amenability of synthesis and functionalization, gold nanoparticles have been investigated as therapeutic photothermal agents. In this work, hollow gold nanoparticles (HGNP) were coated with poly-l-lysine through the use of COOH-Poly(ethylene glycol)-SH as a covalent linker. The functionalized HGNP, which peak their surface plasmon resonance at 800 nm, can bind thrombin. Thrombin-conjugated HGNP conduct in situ fibrin polymerization, facilitating the process of generating photothermal matrices. Interestingly, the metallic core of thrombin-loaded HGNP fragmentates at physiological temperature. During polymerization process, matrices prepared with thrombin-loaded HGNP were loaded with genetically-modified stem cells that harbour a heat-activated and ligand-dependent gene switch for regulating transgene expression. NIR laser irradiation of resulting cell constructs in the presence of ligand successfully triggered transgene expression in vitro and in vivo. STATEMENT OF SIGNIFICANCE: Current technological development allows synthesis of gold nanoparticles (GNP) in a wide range of shapes and sizes, consistently and at scale. GNP, stable and easily functionalized, show low cytotoxicity and high biocompatibility. Allied to that, GNP present optoelectronic properties that have been exploited in a range of biomedical applications. Following a layer-by-layer functionalization approach, we prepared hollow GNP coated with a positively charged copolymer that enabled thrombin conjugation. The resulting nanomaterial efficiently catalyzed the formation of fibrin hydrogels which convert energy of the near infrared (NIR) into heat. The resulting NIR-responsive hydrogels can function as scaffolding for cells capable of controlled gene expression triggered by optical hyperthermia, thus allowing the deployment of therapeutic gene products in desired spatiotemporal frameworks.

Comparative Effectiveness of Cartilage Repair With Respect to the Minimal Clinically Important Difference

BACKGROUND

Recent studies demonstrated a 5% increase in cartilage repair procedures annually in the United States. There is currently no consensus regarding a superior technique, nor has there been a comprehensive evaluation of postoperative clinical outcomes with respect to a minimal clinically important difference (MCID).

PURPOSE

To determine the proportion of available cartilage repair studies that meet or exceed MCID values for clinical outcomes improvement over short-, mid-, and long-term follow-up.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

A systematic review was performed via the Medline, Scopus, and Cochrane Library databases. Available studies were included that investigated clinical outcomes for microfracture (MFX), osteoarticular transfer system (OATS), osteochondral allograft transplantation, and autologous chondrocyte implantation/matrix-induced autologous chondrocyte implantation (ACI/MACI) for the treatment of symptomatic knee chondral defects. Cohorts were combined on the basis of surgical intervention by performing a meta-analysis that utilized inverse-variance weighting in a DerSimonian-Laird random effects model. Weighted mean improvements in International Knee Documentation Committee (IKDC), Lysholm, and visual analog scale for pain (VAS pain) scores were calculated from preoperative to short- (1-4 years), mid- (5-9 years), and long-term (≥10 years) postoperative follow-up. Mean values were compared with established MCID values per 2-tailed 1-sample Student t tests.

RESULTS

A total of 89 studies with 3894 unique patients were analyzed after full-text review. MFX met MCID values for all outcome scores at short- and midterm follow-up with the exception of VAS pain in the midterm. OATS met MCID values for all outcome scores at all available time points; however, long-term data were not available for VAS pain. Osteochondral allograft transplantation met MCID values for IKDC at short- and midterm follow-up and for Lysholm at short-term follow-up, although data were not available for other time points or for VAS pain. ACI/MACI met MCID values for all outcome scores (IKDC, Lysholm, and VAS pain) at all time points.

CONCLUSION

In the age of informed consent, it is important to critically evaluate the clinical outcomes and durability of cartilage surgery with respect to well-established standards of clinical improvement. MFX failed to maintain VAS pain improvements above MCID thresholds with follow-up from 5 to 9 years. All cartilage repair procedures met MCID values at short- and midterm follow-up for IKDC and Lysholm scores; ACI/MACI and OATS additionally met MCID values in the long term, demonstrating extended maintenance of clinical benefits for patients undergoing these surgical interventions as compared with MFX.

Long-Term Clinical and MRI Results of Matrix-Assisted Autologous Chondrocyte Implantation for Articular Cartilage Defects of the Knee

OBJECTIVE

To evaluate the long-term clinical and radiological outcome of matrix-assisted autologous chondrocyte implantation (mACI) for articular cartilage defects in the knee joint.

DESIGN

Clinical evaluation was assessed in 21 patients with full-thickness cartilage defects, International Cartilage Repair Society (ICRS) grade IV. Clinical scoring was performed preoperatively and 12 years after transplantation using the International Knee Documentation Committee (IKDC) score, the Lysholm score, the Knee injury and Osteoarthritis Outcome Score (KOOS), and the Noyes sports activity rating scale. Morphologic evaluation of the repair tissue was assessed by magnetic resonance imaging (MRI) in 14 patients using the Kreuz-Henderson score.

RESULTS

Clinical evaluation revealed significant improvement in the IKDC, the Lysholm, the KOOS, and the Noyes score. Morphological evaluation by MRI showed moderate to complete defect filling in 10 of 14 patients, demonstrating normal to nearly normal values in mean 74.29% of all assessed parameters. Significant correlation of the parameter cartilage signal and clinical outcome was found with the IKDC, Lysholm, and KOOS subscales ADL (activities of daily living) and QoL (quality of life).

CONCLUSIONS

The clinical and radiological outcomes 12 years after transplantation suggest the confirmation of the promising results of the mid-term follow-up. This study therefore provides first indications that the implantation of mACI might be a suitable option for long-term cartilage repair. Future controlled studies need to address the exact parameters influencing the long-term outcome of mACI.

Meniscus-shaped cell-free polyglycolic acid scaffold for meniscal repair in a sheep model

Since loss of meniscus is correlated with an increasing risk for osteoarthritis, meniscal scaffolds are proposed as new strategies. Development of a suitable scaffold has to take into account differing meniscus thickness, exposure to compressive and tensile forces combined with high porosity and biocompatibility of the material. After physical testing of three flat scaffolds composed of different modified polyglycolic acid (PGA) fibers, a three-dimensional meniscus-shaped PGA-hyaluronan implant was generated. Micro-computed tomography showed 90% porosity in the outer area with 50% in the inner area of the implant. Biocompatibility and expression of meniscus typical cartilaginous genes were shown for human meniscus cells cultivated in the implant with 10% human serum or 5% platelet-rich plasma for 14 days in vitro. The proof-of-concept study in sheep demonstrated proteoglycan- and collagen type I-rich repair tissue formation in partial meniscectomy combined with a meniscus-shaped PGA-hyaluronan implant after 6 months. In contrast, the control showed nearly no repair tissue formation. Thus, meniscus-shaped PGA-hyaluronan implants might be a suitable therapeutic approach to support repair tissue formation in partial meniscectomy.

Fresh osteochondral grafting in the United States: the current status of tissue banking processing

The use of musculoskeletal allografts has become increasingly popular among surgeons. The purpose of this review is to highlight the procurment and delievery process of fresh osteochondral allografts in the United States. The four distributors of fresh osteochondral allografts in the United States were contacted. Surveys containing quantitative and qualitative sections concerning the procurement and processing of osteochondral allograft tissue were obtained. Our results showed an average of 13 ± 4.24 years of experience with osteochondral allografts. The average donor age ranged from 13.5 ± 3 to 37.5 ± 5 years, with an average age of 27 ± 2.83 years. All donors were between ages 12 and 45 years old. The percentage of screened donors that were accepted for allograft transplant was consistent at 70-75% for 3 out of the 4 tissue banks. The percentage of grafts that expire without implantation ranged from 20% to 29%. Maximum shipping time varied between 24 and 96 hours. Each tissue bank used its own proprietary storage medium. The time from donor death to the harvest of allograft tissue was < 24 hours. The most commonly requested osteochondral allograft tissue for all banks was the medial femoral condyle. The market share of fresh allografts is as follows: Joint Restoration Foundation (JRF) 59.9%, Muskuloskeletal Transplant Foundation (MTF) 15.3%, LifeNet Health (LN) 14.5%, and Regeneration Technology Incorporated (RTI) 10.2%, with approximately 4700 fresh allografts distributed in 2018. This compiled data from the four tissue banks that supply fresh osteochondral allograft in the United States  provides important background information for patients and orthopaedic surgeons.

Rehabilitation before regenerative cartilage knee surgery: a new prehabilitation guideline based on the best available evidence

INTRODUCTION

Focal cartilage defects are an increasingly relevant clinical problem especially in athletes. Cartilage regenerative surgery (CRS) including microfracture and autologous chondrocyte implantation (ACI) to treat such isolated cartilage defects in the knee joint has been well established in the last two decades. In contradiction to high-level evidence concerning the surgical technique, cell-related issues, and clinical results, the knowledge about the optimal rehabilitation process is still sparse although the importance of optimizing the rehabilitation process has recently led to new research focus in this field. The preoperative time frame may be used to start rehabilitation which may fasten the postoperative recovery and optimize clinical outcome ("Prehabilitation"-PREHAB). The aim of this article, therefore, was to review the available literature on prehabilitation concepts and to present a prehabilitation guideline for CRS patients based on the best evidence available.

METHODS

A systemic literature research was conducted on rehabilitation for cartilage regenerative surgery as well as prehabilitation in knee joint procedures. From the available literature a prehabilitation concept was generated and tested in 10 ACI patients.

RESULTS

As the literature search found no studies addressing prehabilitation in CRS patients, an evidence-based PREHAB program has been compiled based on the available evidence from (a) studies addressing postoperative rehabilitation in CRS patients and (b) PREHAB studies on other knee procedures including TKA. This presented prehabilitation guideline has been tested in > 50 CRS patients and was found to be feasible as all of the patients showed a good compliance and were able to perform the protocol as suggested.

CONCLUSION

The presented PREHAB regimen may serve clinicians as a guideline for early rehabilitation of their CRS patients. Obviously, further research is mandatory to quantify its clinical effect and to demonstrate its cost-effectiveness and benefits in surgically treated patients.

Chasing Chimeras - The elusive stable chondrogenic phenotype

The choice of the best-suited cell population for the regeneration of damaged or diseased cartilage depends on the effectiveness of culture conditions (e.g. media supplements, three-dimensional scaffolds, mechanical stimulation, oxygen tension, co-culture systems) to induce stable chondrogenic phenotype. Herein, advances and shortfalls in in vitro, preclinical and clinical setting of various in vitro microenvironment modulators on maintaining chondrocyte phenotype or directing stem cells towards chondrogenic lineage are critically discussed. Chondrocytes possess low isolation efficiency, limited proliferative potential and rapid phenotypic drift in culture. Mesenchymal stem cells are relatively readily available, possess high proliferation potential, exhibit great chondrogenic differentiation capacity, but they tend to acquire a hypertrophic phenotype when exposed to chondrogenic stimuli. Embryonic and induced pluripotent stem cells, despite their promising in vitro and preclinical data, are still under-investigated. Although a stable chondrogenic phenotype remains elusive, recent advances in in vitro microenvironment modulators are likely to develop clinically- and commercially-relevant therapies in the years to come.

Cartilage Defect Treatment Using High-Density Autologous Chondrocyte Implantation: Two-Year Follow-up

OBJECTIVE

The aim of this work was to study the short- and mid-term effectiveness and safety of high-density autologous chondrocyte implantation (HD-ACI) in the first 50 patients with knee cartilage damage treated in our unit.

DESIGN

Fifty consecutive patients with cartilage lesions (Outerbridge grade III-IV) in the knee treated with HD-ACI were included in this study. Chondrocytes were isolated from a nonbearing cartilage area biopsy and were cultured until 40 to 50 million cells were obtained. Five million chondrocytes per cm² of a porcine collagen type I/III membrane were implanted covering the defect. Procedure effectiveness was assessed by evaluating pain, swelling, and range of mobility (flexion and extension) at 6-, 12-, and 24-month follow-up. The International Knee Documentation Committee (IKDC) subjective evaluation form was used to evaluate symptoms and functions of the knee.

RESULTS

The percentage of patients with pain and swelling decreased progressively in the following visits, with differences being statistically significant ( P < 0.001 and P = 0.040, respectively). IKDC scores improved progressively throughout the 24-month follow-up ( P < 0.001). Thus, the mean IKDC score improvement was 26.3 points (95% confidence interval [CI] = 18.2-34.4 points) at 12 months and 31.0 points (95% CI = 22.9-39 points) at 24 months. No significant differences were found when performing extension ( P = 0.112). Flexion significantly improved by 25.1° at 24-month follow-up ( P = 0.013).

CONCLUSIONS

HD-ACI is a safe and effective technique for the treatment of cartilage defects, improving clinical and subjective perception of knee functionality. These preliminary results encourage future studies comparing this technique with traditional ACI.

Orthopaedic regenerative tissue engineering en route to the holy grail: disequilibrium between the demand and the supply in the operating room

Orthopaedic disorders are very frequent, globally found and often partially unresolved despite the substantial advances in science and medicine. Their surgical intervention is multifarious and the most favourable treatment is chosen by the orthopaedic surgeon on a case-by-case basis depending on a number of factors related with the patient and the lesion. Numerous regenerative tissue engineering strategies have been developed and studied extensively in laboratory through in vitro experiments and preclinical in vivo trials with various established animal models, while a small proportion of them reached the operating room. However, based on the available literature, the current strategies have not yet achieved to fully solve the clinical problems. Thus, the gold standards, if existing, remain unchanged in the clinics, notwithstanding the known limitations and drawbacks. Herein, the involvement of regenerative tissue engineering in the clinical orthopaedics is reviewed. The current challenges are indicated and discussed in order to describe the current disequilibrium between the needs and solutions made available in the operating room. Regenerative tissue engineering is a very dynamic field that has a high growth rate and a great openness and ability to incorporate new technologies with passion to edge towards the Holy Grail that is functional tissue regeneration. Thus, the future of clinical solutions making use of regenerative tissue engineering principles for the management of orthopaedic disorders is firmly supported by the clinical need.

Treatment of a Focal Articular Cartilage Defect of the Talus with Polymer-Based Autologous Chondrocyte Implantation: A 12-Year Follow-Up Period

Autologous chondrocyte implantation (ACI) is a first-line treatment option for large articular cartilage defects. Although well-established for cartilage defects in the knee, studies of the long-term outcomes of matrix-assisted ACI to treat cartilage defects in the ankle are rare. In the present report, we describe for the first time the long-term clinical and radiologic results 12 years after polymer-based matrix-assisted ACI treat a full-thickness talar cartilage defect in a 25-year-old male patient. The clinical outcome was assessed using the visual analog scale and Freiburg ankle score, magnetic resonance imaging evaluation using the Henderson-Kreuz scoring system and T2 mapping. Clinical assessment revealed improved visual analog scale and Freiburg ankle scores. The radiologic analysis and T2 relaxation time values indicated the formation of hyaline-like repair tissue. Polymer-based autologous chondrocytes has been shown to be a safe and clinically effective long-term treatment of articular cartilage defects in the talus.

Synthetic Poly(Vinylalcohol)-Based Membranes for Cartilage Surgery and Repair

Cell-based therapies for cartilage repair are continually being developed to treat osteoarthritis. The cells are either introduced directly by intra-articular injection or via a cell-seeded matrix scaffold. Here, poly(vinylalcohol)-based membranes are developed to be used for mesenchymal stem cell implantation in cartilage repair procedures, having controllable physicochemical properties such as porosity, mechanical strength, and permeability, and a unique self-sealing property. The membranes possess a bilayer structure with a less porous layer providing mechanical strength and selective permeability, exhibit an elastic modulus of between 0.3 and 0.9 MPa, and are permeable to molecules <40 kDa, which is in the range of cartilage permeability. Three different peptide ligands with the sequences Ac-GCGYGRGDSPG, Ac-GCG(OPG)4REGOFG(OPG)4, and Ac-GCG(OPG)7, respectively, are conjugated to the membranes and subject to in vitro cell adhesion and differentiation assays. Col I/Col II gene expression ratios indicated that the collagen-mimetic peptide, Ac-GCG(OPG)7, best supported mesenchymal stem cell differentiation into the chondrogenic lineage. Although low retention of the membrane is observed in vivo in a rabbit knee model, results suggest that the membrane was able to facilitate mesenchymal stem cell implantation and differentiation to chondrocytes. These PVA-based membranes provide a feasible, synthetic, off-the-shelf material for the delivery of stem cells, and can be modified for other surgical applications.

Ex vivo model unravelling cell distribution effect in hydrogels for cartilage repair

The implantation of chondrocyte-laden hydrogels is a promising cartilage repair strategy. Chondrocytes can be spatially positioned in hydrogels and thus in defects, while current clinical cell therapies introduce chondrocytes in the defect depth. The main aim of this study was to evaluate the effect of spatial chondrocyte distribution on the reparative process. To reduce animal experiments, an ex vivo osteochondral plug model was used and evaluated. The role of the delivered and endogenous cells in the repair process was investigated.

Full thickness cartilage defects were created in equine osteochondral plugs. Defects were filled with (A) chondrocytes at the bottom of the defect, covered with a cell-free hydrogel, (B) chondrocytes homogeneously encapsulated in a hydrogel, and (C, D) combinations of A and B with different cell densities. Plugs were cultured for up to 57 days, after which the cartilage and repair tissues were characterized and compared to baseline samples. Additionally, at day 21, the origin of cells in the repair tissue was evaluated.

Best outcomes were obtained with conditions C and D, which resulted in well-integrated cartilage-like tissue that completely filled the defect, regardless of the initial cell density. A critical role of the spatial chondrocyte distribution in the repair process was observed. Moreover, the osteochondral plugs stimulated cartilage formation in the hydrogels when cultured in the defects. The resulting repair tissue originated from the delivered cells.

These findings confirm the potential of the osteochondral plug model for the optimization of the composition of cartilage implants and for studying repair mechanisms.

A Magnetically Actuated Microscaffold Containing Mesenchymal Stem Cells for Articular Cartilage Repair

This study proposes a magnetically actuated microscaffold with the capability of targeted mesenchymal stem cell (MSC) delivery for articular cartilage regeneration. The microscaffold, as a 3D porous microbead, is divided into body and surface portions according to its materials and fabrication methods. The microscaffold body, which consists of poly(lactic-co-glycolic acid) (PLGA), is formed through water-in-oil-in-water emulsion templating, and its surface is coated with amine functionalized magnetic nanoparticles (MNPs) via amino bond formation. The porous PLGA structure of the microscaffold can assist in cell adhesion and migration, and the MNPs on the microscaffold can make it possible to steer using an electromagnetic actuation system that provides external magnetic fields for the 3D locomotion of the microscaffold. As a fundamental test of the magnetic response of the microscaffold, it is characterized in terms of the magnetization curve, velocity, and 3D locomotion of a single microscaffold. In addition, its function with a cargo of MSCs for cartilage regeneration is demonstrated from the proliferation, viability, and chondrogenic differentiation of D1 mouse MSCs that are cultured on the microscaffold. For the feasibility tests for cartilage repair, 2D/3D targeting of multiple microscaffolds with the MSCs is performed to demonstrate targeted stem cell delivery using the microscaffolds and their swarm motion.

Quadriceps Strength in Patients With Isolated Cartilage Defects of the Knee: Results of Isokinetic Strength Measurements and Their Correlation With Clinical and Functional Results

Background:

Recent studies have found a significant deficit of maximum quadriceps strength after autologous chondrocyte implantation (ACI) of the knee. However, it is unclear whether muscular strength deficits in patients with cartilage damage exist prior to operative treatment.

Purpose:

To isokinetically test maximum quadriceps muscle strength and quantify the impact of possible strength deficits on functional and clinical test results.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

To identify clinically relevant muscular strength deficits, 24 patients (5 females, 19 males; mean age, 34.5 years; body mass index, 25.9 kg/m²) with isolated cartilage defects (mean onset, 5.05 years; SD, 7.8 years) in the knee joint underwent isokinetic strength measurements. Maximal quadriceps strength was recorded in 3 different testing modes: pure concentric contraction (flexors and extensors alternating work; con1), concentric-eccentric (only the extensors work concentrically and eccentrically; con2), and eccentric contraction in the alternating mode (ecc). Results were compared for functional performance (single-leg hop test), pain scales (visual analog scale [VAS], numeric rating scale [NRS]), self-reported questionnaires (International Knee Documentation Committee [IKDC], Knee Injury and Osteoarthritis Outcome Scale [KOOS]), and defect size (cm²).

Results:

Compared with the uninjured leg, significantly lower quadriceps strength was detected in the injured leg in all isokinetic working modes (con1 difference, 27.76 N·m [SD 17.47; P = .003]; con2 difference, 21.45 N·m [SD, 18.45; P =.025]; ecc difference, 29.48 N·m [SD, 21.51; P = .001]), with the largest deficits found for eccentric muscle performance. Moderate negative correlations were observed for the subjective pain scales NRS and VAS. The results of the IKDC and KOOS questionnaires showed low, nonsignificant correlations with findings in the isokinetic measurement. Moreover, defect sizes (mean, 3.13 cm²) were of no importance regarding the prediction of the strength deficit. The quadriceps strength deficit between the injured and the uninjured leg was best predicted by the results of the single-leg hop test.

Conclusion:

Patients with isolated cartilage defects of the knee joint have significant deficits in quadriceps muscle strength of the injured leg compared with the uninjured leg. The single-leg hop test may be used to predict quadriceps strength deficits. Future research should address whether preoperative strength training in patients with cartilage defects of the knee could be effective and should be taken into consideration in addition to surgical treatment.

Poly (lactic acid)-based biomaterials for orthopaedic regenerative engineering

Regenerative engineering converges tissue engineering, advanced materials science, stem cell science, and developmental biology to regenerate complex tissues such as whole limbs. Regenerative engineering scaffolds provide mechanical support and nanoscale control over architecture, topography, and biochemical cues to influence cellular outcome. In this regard, poly (lactic acid) (PLA)-based biomaterials may be considered as a gold standard for many orthopaedic regenerative engineering applications because of their versatility in fabrication, biodegradability, and compatibility with biomolecules and cells. Here we discuss recent developments in PLA-based biomaterials with respect to processability and current applications in the clinical and research settings for bone, ligament, meniscus, and cartilage regeneration.

Cell-based tissue engineering strategies used in the clinical repair of articular cartilage

One of the most important issues facing cartilage tissue engineering is the inability to move technologies into the clinic. Despite the multitude of current research in the field, it is known that 90% of new drugs that advance past animal studies fail clinical trials. The objective of this review is to provide readers with an understanding of the scientific details of tissue engineered cartilage products that have demonstrated a certain level of efficacy in humans, so that newer technologies may be developed upon this foundation. Compared to existing treatments, such as microfracture or autologous chondrocyte implantation, a tissue engineered product can potentially provide more consistent clinical results in forming hyaline repair tissue and in filling the entirety of the defect. The various tissue engineering strategies (e.g., cell expansion, scaffold material, media formulations, biomimetic stimuli, etc.) used in forming these products, as collected from published literature, company websites, and relevant patents, are critically discussed. The authors note that many details about these products remain proprietary, not all information is made public, and that advancements to the products are continuously made. Nevertheless, by understanding the design and production processes of these emerging technologies, one can gain tremendous insight into how to best use them and also how to design the next generation of tissue engineered cartilage products.

Cell-based tissue engineering strategies used in the clinical repair of articular cartilage

One of the most important issues facing cartilage tissue engineering is the inability to move technologies into the clinic. Despite the multitude of current research in the field, it is known that 90% of new drugs that advance past animal studies fail clinical trials. The objective of this review is to provide readers with an understanding of the scientific details of tissue engineered cartilage products that have demonstrated a certain level of efficacy in humans, so that newer technologies may be developed upon this foundation. Compared to existing treatments, such as microfracture or autologous chondrocyte implantation, a tissue engineered product can potentially provide more consistent clinical results in forming hyaline repair tissue and in filling the entirety of the defect. The various tissue engineering strategies (e.g., cell expansion, scaffold material, media formulations, biomimetic stimuli, etc.) used in forming these products, as collected from published literature, company websites, and relevant patents, are critically discussed. The authors note that many details about these products remain proprietary, not all information is made public, and that advancements to the products are continuously made. Nevertheless, by understanding the design and production processes of these emerging technologies, one can gain tremendous insight into how to best use them and also how to design the next generation of tissue engineered cartilage products.

Application of cell and biomaterial-based tissue engineering methods in the treatment of cartilage, menisci and ligament injuries

Over 20 years ago it was realized that the traditional methods of the treatment of injuries to joint components: cartilage, menisci and ligaments, did not give satisfactory results and so there is a need of employing novel, more effective therapeutic techniques. Recent advances in molecular biology, biotechnology and polymer science have led to both the experimental and clinical application of various cell types, adapting their culture conditions in order to ensure a directed differentiation of the cells into a desired cell type, and employing non-toxic and non-immunogenic biomaterial in the treatment of knee joint injuries. In the present review the current state of knowledge regarding novel cell sources, in vitro conditions of cell culture and major important biomaterials, both natural and synthetic, used in cartilage, meniscus and ligament repair by tissue engineering techniques are described, and the assets and drawbacks of their clinical application are critically evaluated.

Cartilage failures. Systematic literature review, critical survey analysis, and definition

PURPOSE

While midterm results of matrix-assisted autologous chondrocyte transplantation (MACT) are now available, less attention has been paid to the evaluation of failures of this surgical approach. Aim of this study was to analyse how "failures" are generally defined in cartilage surgery, in order to understand how the survival rate may change according to different definitions of failure.

METHODS

A systematic review on MACT in the knee was conducted to report failure rates as well as different failure definitions in the available literature. Afterwards, we analysed the survival curve at 8.5-year follow-up of a survey of 193 patients treated with MACT. Using different definitions to identify failures, we compared how the survival rate changed according to the different definitions of failure.

RESULTS

The systematic review on 93 papers showed that the average failure rate reported on 3,289 patients was 5.2 % at a mean 34 months of follow-up. However, 41 studies (44.1 %) did not even consider this aspect, and failures were variously defined, thus generating confusing data that make a meta-analysis or a study comparison meaningless. The failure analysis of the MACT survey showed that the survival curve changed significantly depending on the definition applied; in fact, the failure rate ranged from 3.6 to 33.7 %. According to a critical literature and survey analysis, we proposed a combined surgical- and improvement-based definition which led to a failure rate of 25.9 % at midterm/long-term follow-up.

CONCLUSION

Nowadays, failure definitions of cartilage treatments differ in scientific articles, thus generating confusion and heterogeneous data even when applied to the same cohort of patients. While the literature analysis shows a low number of failures, this study demonstrated that if properly addressed with a comprehensive definition, the real failure rate of cartilage surgical procedures in the knee is higher than previously reported. Recognizing failures would give a better understanding and a more realistic prognosis to patients and physicians seeking treatment for cartilage lesions.

LEVEL OF EVIDENCE

IV.

A conceptual framework for a sports knee injury performance profile (SKIPP) and return to activity criteria (RTAC)

Injuries to the knee, including intra-articular fractures, ligamentous ruptures, and meniscal and articular cartilage lesions, are commonplace within sports. Despite advancements in surgical techniques and enhanced rehabilitation, athletes returning to cutting, pivoting, and jumping sports after a knee injury are at greater risk of sustaining a second injury. The clinical utility of objective criteria presents a decision-making challenge to ensure athletes are fully rehabilitated and safe to return to sport. A system centered on specific indicators that can be used to develop a comprehensive profile to monitor rehabilitation progression and to establish return to activity criteria is recommended to clear athletes to begin a progressive and systematic approach to activities and sports. Integration of a sports knee injury performance profile with return to activity criteria can guide clinicians in facilitating an athlete's safe return to sport, prevention of subsequent injury, and life-long knee joint health.

Incidence, degree, and development of graft hypertrophy 24 months after matrix-induced autologous chondrocyte implantation: association with clinical outcomes

BACKGROUND

Graft hypertrophy is a common occurrence after periosteal, collagen-covered and matrix-induced autologous chondrocyte implantation (MACI).

PURPOSE/HYPOTHESIS

The purpose of this study was to investigate the incidence, development, and degree of graft hypertrophy at 24 months after MACI. The hypothesis was that graft hypertrophy would not be associated with clinical outcome at 24 months.

STUDY DESIGN

Case series, Level of evidence, 4.

METHODS

This study was undertaken in 180 consecutive patients (113 male, 67 female) after MACI in the knee. All patients were assessed clinically using the Knee injury and Osteoarthritis Outcome Score (KOOS) and underwent magnetic resonance imaging (MRI) at 3, 12, and 24 months after surgery. The incidence of hypertrophy relevant to anatomic graft site was investigated, as was the progressive change in hypertrophic studies postoperatively. The degree of tissue overgrowth in hypertrophic cases was investigated, as was its association with patient clinical outcome at 24 months after surgery.

RESULTS

Of the 180 patients, 50 demonstrated a hypertrophic graft at 1 or more postoperative time points. This included 9 grafts (5.0%) at 3 months and 32 grafts (18.7%) at 12 months. At 24 months, 47 grafts (26.1%)-43 (32.1%) tibiofemoral and 4 (8.7%) patellofemoral-were hypertrophic. Patients with hypertrophic grafts at 24 months (n = 47) were younger (P = .051), they had a lower body mass index (BMI; P = .069), and significantly fewer of them had patellofemoral grafts (P = .007) compared with patients who had grafts with full (100%) tissue infill (n = 61). There were no significant differences in any of the KOOS subscales between patients with graft hypertrophy or full (100%) tissue infill at 24 months after surgery, while the severity of graft hypertrophy was not associated with KOOS subscales at 24 months.

CONCLUSION

Hypertrophic grafts after MACI were common and continued to develop through to 24 months after surgery. Hypertrophic growth was associated with being younger and having a lower BMI, was more common on the femoral condyles, and overall was not associated with clinical outcome at 24 months after surgery. However, further research with longer term follow-up is required to evaluate the effect of persistent hypertrophy on graft stability and to assess the use of early surgical intervention to prevent such failure.

Significantly worse isokinetic hamstring-quadriceps ratio in patellofemoral compared to condylar defects 4 years after autologous chondrocyte implantation

PURPOSE

Detailed biomechanical analysis including isokinetic muscle strength measurements after autologous chondrocyte implantation (ACI) are still rare, but might be of crucial importance for long-term outcomes. The present prospective study was performed to evaluate whether defect location had any influence on clinical and biomechanical outcomes 4 years after ACI.

METHODS

Forty-four patients with full-thickness cartilage defects ICRS grade III B and C underwent ACI and were assigned to two groups, the femoral condyle group or the patellofemoral joint group. Clinical scores were gathered preoperatively and 6, 12 and 48 months after implantation using the International Knee Documentation Committee (IKDC) score and the International Cartilage Repair Society (ICRS) form. Isokinetic strength measurements were performed 48 months postoperatively comparing healthy and operated knee joint of each patient.

RESULTS

Clinical scores (ICRS, IKDC) showed continuous significant (p < 0.05) improvement over the study period for both groups. Isokinetic muscle strength measurements showed significantly reduced maximum strength capacities for the operated knee joint compared to the healthy knee in both groups (p < 0.05). Hamstring-quadriceps ratios of the operated extremity revealed a significant change in physiological muscle balancing (ratios >1.0) based on significantly impaired extensor muscle strength in the patellofemoral joint group.

CONCLUSION

All patients showed significant strength deficits on the operated extremity 4 years after ACI. Furthermore, the patellofemoral compartment in particular showed significantly worse hamstring-quadriceps ratios compared to condylar defects. Consequently, more efforts should be made to restore muscular strength especially of the quadriceps and the rehabilitation protocol should be adjusted accordingly.

LEVEL OF EVIDENCE

II.