Clinical and radiological outcomes 5 years after matrix-induced autologous chondrocyte implantation in patients with symptomatic, traumatic chondral defects

Knee Joint Preservation in Tactical Athletes: A Comprehensive Approach Based upon Lesion Location and Restoration of the Osteochondral Unit

The unique physical demands of tactical athletes put immense stress on the knee joint, making these individuals susceptible to injury. In order to ensure operational readiness, management options must restore and preserve the native architecture and minimize downtime, while optimizing functionality. Osteochondral lesions (OCL) of the knee have long been acknowledged as significant sources of knee pain and functional deficits. The management of OCL is predicated on certain injury characteristics, including lesion location and the extent of subchondral disease. Techniques such as marrow stimulation, allograft and autologous chondrocyte implantation are examined in detail, with a focus on their application and suitability in tactical athlete populations. Moreover, the restoration of the osteochondral unit (OCU) is highlighted as a central aspect of knee joint preservation. The discussion encompasses the biomechanical considerations and outcomes associated with various cartilage restoration techniques. Factors influencing procedure selection, including lesion size, location, and patient-specific variables, are thoroughly examined. Additionally, the review underscores the critical role of post-operative rehabilitation and conditioning programs in optimizing outcomes. Strengthening the surrounding musculature, enhancing joint stability, and refining movement patterns are paramount in facilitating the successful integration of preservation procedures. This narrative review aims to provide a comprehensive resource for surgeons, engineers, and sports medicine practitioners engaged in the care of tactical athletes and the field of cartilage restoration. The integration of advanced preservation techniques and tailored rehabilitation protocols offers a promising avenue for sustaining knee joint health and function in this demanding population.

Autologous minced cartilage repair for chondral and osteochondral lesions of the knee joint demonstrates good postoperative outcomes and low reoperation rates at minimum five-year follow-up

PURPOSE

Minced cartilage is a one-step, autologous procedure with promising short-term results. The aim of the present study was to evaluate mid-term results in a patient cohort with chondral and osteochondral lesions in the knee joint treated with minced cartilage.

METHODS

From 2015 through 2016, a total of 34 consecutive patients were treated with a single-step, autologous minced cartilage for knee chondral and osteochondral lesions. Numeric analogue scale (NAS) for pain and knee function were obtained prior to surgery and at 12, 24 and 60 months postoperatively. Secondary outcomes, including Lysholm score, Tegner activity score, and the International Knee Documentation Committee (IKDC) score, were recorded at final follow-up. MRI examinations of patients with unplanned radiological follow-up were analysed using the MOCART (Magnetic Resonance Observation of Cartilage Repair Tissue) score.

RESULTS

A total of 28 patients (44.1% females, age at surgery: 29.5 ± 11.5 years) were available at a mean follow-up of 65.5 ± 4.1 months. Mean defect size was 3.5 ± 1.8 cm2. NAS for pain decreased from a median of 7 (range: 2-10) preoperatively to 2 (0-8) postoperatively. NAS knee function improved from a median of 7 (range: 2-10) to 3 (0-7) after five years, respectively. Satisfactory Lysholm (76.5 ± 12.5), IKDC (71.6 ± 14.8) and Tegner activity (4, range 3-9) scores were reported at final follow-up. Of all patients, 21(75%) and 19 (67.9%) reached or exceeded the PASS for the IKDC- and Lysholm score at final follow-up, respectively. The average overall MOCART 2.0 scores for all postoperatively performed MRIs (n = 23) was 62.3 ± 17.4. Four (14.2%) postoperative complications were directly linked to minced cartilage, one (3.5%) of which required revision surgery.

CONCLUSION

One-step, autologous minced cartilage repair of chondral and osteochondral lesions of the knee without the necessity for subchondral bone treatment demonstrated good patient-reported outcomes, low complication rates, and graft longevity at mid-term follow-up. Minced cartilage represents a viable treatment option to more traditional cartilage repair techniques even in mid-term.

LEVEL OF EVIDENCE

Level III.

Single-stage autologous cartilage repair results in positive patient-reported outcomes for chondral lesions of the knee: a systematic review

AIM

This article aims to perform a systematic review of the clinical literature regarding the efficacy of single-stage autologous cartilage repair.

METHODS

A systematic review of the literature was performed using PubMed, Scopus, Web of Science, and the Cochrane Library. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed.

RESULTS

Twelve studies were identified; however, due to overlapping patient cohorts, nine studies were included for data extraction and analysis. Six studies applied minced cartilage, while three studies utilized enzymatically processed cartilage. Two authorship groups described single-stage techniques that exclusively utilized cartilage from the debrided lesion rim, while the remaining groups either utilized healthy cartilage or combined healthy cartilage with cartilage debrided from lesion rim. Among the included techniques, scaffold augments were used in four studies, and three studies implemented bone autograft augmentation. When summarizing patient reported outcome measures for the included studies, single-stage autologous cartilage repair demonstrated an average improvement ranging from 18.7 ​± ​5.3 to 30.0 ​± ​8.0 amongst the Knee Injury and Osteoarthritis Outcome Scores subsections, 24.3 ​± ​10.5 for the International Knee Documentation Committee subjective score, and 41.0 ​± ​10.0 for Visual Analogue Scale-Pain.

CONCLUSION

Single-stage autologous cartilage repair is a promising technique with positive clinical data to date. The current study highlights the overall improvement in patient reported outcomes after repair for chondral defects to the knee with average follow-up ranging from 12 to 201 months and also the heterogeneity and variability of the single-stage surgical technique. Further discussion on the standardization of practices for a cost-effective single-stage augmented autologous cartilage technique is needed. In the future, a well-designed randomized controlled trial is needed to explore the efficacy of this therapeutic modality relative to established intervention.

LEVEL OF EVIDENCE

Systematic review; Level IV.

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.

Autologous and Allogeneic Cytotherapies for Large Knee (Osteo)Chondral Defects: Manufacturing Process Benchmarking and Parallel Functional Qualification

Cytotherapies are often necessary for the management of symptomatic large knee (osteo)-chondral defects. While autologous chondrocyte implantation (ACI) has been clinically used for 30 years, allogeneic cells (clinical-grade FE002 primary chondroprogenitors) have been investigated in translational settings (Swiss progenitor cell transplantation program). The aim of this study was to comparatively assess autologous and allogeneic approaches (quality, safety, functional attributes) to cell-based knee chondrotherapies developed for clinical use. Protocol benchmarking from a manufacturing process and control viewpoint enabled us to highlight the respective advantages and risks. Safety data (telomerase and soft agarose colony formation assays, high passage cell senescence) and risk analyses were reported for the allogeneic FE002 cellular active substance in preparation for an autologous to allogeneic clinical protocol transposition. Validation results on autologous bioengineered grafts (autologous chondrocyte-bearing Chondro-Gide scaffolds) confirmed significant chondrogenic induction (COL2 and ACAN upregulation, extracellular matrix synthesis) after 2 weeks of co-culture. Allogeneic grafts (bearing FE002 primary chondroprogenitors) displayed comparable endpoint quality and functionality attributes. Parameters of translational relevance (transport medium, finished product suturability) were validated for the allogeneic protocol. Notably, the process-based benchmarking of both approaches highlighted the key advantages of allogeneic FE002 cell-bearing grafts (reduced cellular variability, enhanced process standardization, rationalized logistical and clinical pathways). Overall, this study built on our robust knowledge and local experience with ACI (long-term safety and efficacy), setting an appropriate standard for further clinical investigations into allogeneic progenitor cell-based orthopedic protocols.

Five-Year Outcomes After Implantation of a Scaffold-Free Tissue-Engineered Construct Generated From Autologous Synovial Mesenchymal Stromal Cells for Repair of Knee Chondral Lesions

Background

In an earlier study, a scaffold-free tissue-engineered construct (TEC) derived from autologous synovial membrane mesenchymal stromal cells (MSCs) was developed and demonstrated to be safe and effective for cartilage repair at 2 years postoperatively.

Purpose

To investigate clinical outcomes and magnetic resonance imaging (MRI) findings at 5 years after implantation.

Study Design

Case series; Level of evidence, 4.

Methods

This was an observational first-in-human study limited to 5 patients (age, 28-46 years) with symptomatic knee chondral lesions (size, 1.5-3.0 cm2) on the medial femoral condyle, lateral femoral condyle, or femoral groove. Synovial MSCs were isolated from arthroscopic biopsy specimens and cultured to develop a TEC that matched the lesion size. The TECs were then implanted into chondral defects without fixation and assessed at up to 5 years postoperatively. The patients were clinically evaluated using the visual analog scale for pain, Lysholm score, Tegner score, and Knee injury and Osteoarthritis Outcome Score. An MRI scan evaluation was also performed for morphologic and compositional quality of the repair tissue at both 2 and 5 years of follow-up.

Results

All clinical scores were significantly improved from the preoperative evaluation to the 2- and 5-year follow-ups and the results were stable over time. The MRI scan evaluation showed cartilage defects filled with newly generated tissues with good tissue integration to adjacent host cartilage over time. The cartilage thickness and surface smoothness of the repair cartilage were maintained up to 5 years postoperatively. The MOCART (magnetic resonance observation of cartilage repair tissue) 2.0 Knee Scores remained high at 5 years, although the total points decreased slightly.

Conclusion

The results highlight the efficacy and feasibility of autologous scaffold-free TEC derived from synovial MSCs for regenerative cartilage repair via a sutureless and simple implantation procedure, showing good clinical outcomes and MRI findings with stable results at midterm follow-up. Further follow-up will be needed to assess the long-term quality of the repair tissue.

Marine Gelatin-Methacryloyl-Based Hydrogels as Cell Templates for Cartilage Tissue Engineering

Marine-origin gelatin has been increasingly used as a safe alternative to bovine and porcine ones due to their structural similarity, avoiding the health-related problems and sociocultural concerns associated with using mammalian-origin materials. Another benefit of marine-origin gelatin is that it can be produced from fish processing-products enabling high production at low cost. Recent studies have demonstrated the excellent capacity of gelatin-methacryloyl (GelMA)-based hydrogels in a wide range of biomedical applications due to their suitable biological properties and tunable physical characteristics, such as tissue engineering applications, including the engineering of cartilage. In this study, fish gelatin was obtained from Greenland halibut skins by an acidic extraction method and further functionalized by methacrylation using methacrylic anhydride, developing a photosensitive gelatin-methacryloyl (GelMA) with a degree of functionalization of 58%. The produced marine GelMA allowed the fabrication of photo-crosslinked hydrogels by incorporating a photoinitiator and UV light exposure. To improve the biological performance, GelMA was combined with two glycosaminoglycans (GAGs): hyaluronic acid (HA) and chondroitin sulfate (CS). GAGs methacrylation reaction was necessary, rendering methacrylated HA (HAMA) and methacrylated CS (CSMA). Three different concentrations of GelMA were combined with CSMA and HAMA at different ratios to produce biomechanically stable hydrogels with tunable physicochemical features. The 20% (w/v) GelMA-based hydrogels produced in this work were tested as a matrix for chondrocyte culture for cartilage tissue engineering with formulations containing both HAMA and CSMA showing improved cell viability. The obtained results suggest these hybrid hydrogels be used as promising biomaterials for cartilage tissue engineering applications.

Perspective in Achieving Stratified Articular Cartilage Repair Using Zonal Chondrocytes

Articular cartilage is composed of superficial, medial, and deep zones, which endow the tissue with biphasic mechanical properties to withstand shearing force and compressional loading. The tissue has very limited self-healing capacity once it is damaged due to its avascular nature. To prevent the early onset of osteoarthritis, surgical intervention is often needed to repair the injured cartilage. Current noncell-based and cell-based treatments focus on the regeneration of homogeneous cartilage to achieve bulk compressional properties without recapitulating the zonal matrix and mechanical properties, and often oversight in aiding cartilage integration between host and repair cartilage. It is hypothesized that achieving zonal architecture in articular cartilage tissue repair could improve the structural and mechanical integrity and thus the life span of the regenerated tissue. Engineering stratified cartilage constructs using zonal chondrocytes have been hypothesized to improve the functionality and life span of the regenerated tissues. However, stratified articular cartilage repair has yet to be realized to date due to the lack of an efficient zonal chondrocyte isolation method and an expansion platform that would allow both cell propagation and phenotype maintenance. Various attempts and challenges in achieving stratified articular cartilage repair in a clinical setting are evaluated. In this review, different perspectives on achieving stratified articular cartilage repair using zonal chondrocytes are described. The effectiveness of different zonal chondrocyte isolation and zonal chondrocyte phenotype maintenance methodologies during expansion are compared, with the focus on recent advancements in zonal chondrocyte isolation and expansion that could present a possible strategy to overcome the limitation of applying zonal chondrocytes to facilitate zonal architecture development in articular cartilage regeneration. Impact Statement The zonal properties of articular cartilage contribute to the biphasic mechanical properties of the tissues. Recapitulation of the zonal architecture in regenerated articular cartilage has been hypothesized to improve the mechanical integrity and life span of the regenerated tissue. This review provides a comprehensive discussion on the current state of research relevant to achieving stratified articular cartilage repair using zonal chondrocytes from different perspectives. This review further elaborates on a zonal chondrocyte production pipeline that can potentially overcome the current clinical challenges and future work needed to realize stratified zonal chondrocyte implantation in a clinical setting.

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.

Prognostic factors for the management of chondral defects of the knee and ankle joint: a systematic review

Purpose

Different surgical techniques to manage cartilage defects are available, including microfracture (MFx), autologous chondrocyte implantation (ACI), osteoarticular auto- or allograft transplantation (OAT), autologous matrix-induced chondrogenesis (AMIC). This study investigated the patient-related prognostic factors on the clinical outcomes of surgically treated knee and ankle cartilage defects.

Methods

This study followed the PRISMA statement. In May 2022, the following databases were accessed: PubMed, Google Scholar, Embase, and Scopus. All the studies investigating the outcomes of surgical management for knee and/or talus chondral defects were accessed. Only studies performing mesenchymal stem cells transplantation, OAT, MFx, ACI, and AMIC were considered. A multiple linear model regression analysis through the Pearson Product–Moment Correlation Coefficient was used.

Results

Data from 184 articles (8905 procedures) were retrieved. Female sex showed a positive moderate association with visual analogue scale at last follow-up (P = 0.02). Patient age had a negative association with the American Orthopaedic Foot and Ankle Score (P = 0.04) and Lysholm Knee Scoring Scale (P = 0.03). BMI was strongly associated with graft hypertrophy (P = 0.01). Greater values of VAS at baseline negatively correlate with lower values of Tegner Activity Scale at last follow-up (P < 0.0001).

Conclusion

The clinical outcomes were mostly related to the patients’ performance status prior surgery. A greater BMI was associated with greater rate of hypertrophy. Female sex and older age evidenced fair influence, while symptom duration prior to the surgical intervention and cartilage defect size evidenced no association with the surgical outcome. Lesion size and symptom duration did not evidence any association with the surgical outcome.

Fixation of the Membrane during Matrix-Induced Autologous Chondrocyte Implantation in the Knee: A Systematic Review

Introduction: It is unclear whether the type of membrane used for matrix-assisted autologous chondrocyte implantation (mACI) influences results. A systematic review was conducted to investigate the midterm results of the three most common types of membrane fixation for mACI. Methods: This systematic review was conducted according to the 2020 PRISMA checklist. PubMed, Google Scholar, Embase, and Scopus online databases were accessed in August 2022. All the prospective clinical trials reporting outcomes of mACI in the knee were considered. Studies that describe the modality of membrane fixation (glued, glued, and sutured, no fixation) used for mACI were eligible. Studies that conducted a minimum of 12 months of follow-up were considered. The outcomes of interest were the Tegner Activity Scale and International Knee Documentation Committee (IKDC) score. The rate of failure and revisions were also collected. Results: Data from 26 studies (1539 procedures; 554 of 1539 (36%) were women) were retrieved. The mean follow-up was 42.6 (12 to 84) months. No difference between the groups was found in terms of mean duration of symptoms, age, BMI, gender, and defect size (P > 0.1). No difference was found in terms of the Tegner score (P = 0.3). When no fixation was used, a statistically significant higher IKDC compared to the other groups (P = 0.02) was evidenced. No difference was found in the rate of failure (P = 0.1). The no-fixation group evidenced a statistically significant lower rate of revisions (P = 0.02). Conclusions: No membrane fixation for mACI in the knee scored better than the fastening techniques at the midterm follow-up.

Particulated Juvenile Articular Cartilage and Matrix-Induced Autologous Chondrocyte Implantation Are Cost-Effective for Patellar Chondral Lesions

PURPOSE

To compare the cost-effectiveness of nonoperative management, particulated juvenile allograft cartilage (PJAC), and matrix-induced autologous chondrocyte implantation (MACI) in the management of patellar chondral lesions.

METHODS

A Markov model was used to evaluate the cost-effectiveness of three strategies for symptomatic patellar chondral lesions: 1) nonoperative management, 2) PJAC, and 3) MACI. Model inputs (transition probabilities, utilities, and costs) were derived from literature review and an institutional cohort of 67 patients treated with PJAC for patellar chondral defects (mean age 26 years, mean lesion size 2.7 cm²). Societal and payer perspectives over a 15-year time horizon were evaluated. The principal outcome measure was the incremental cost-effectiveness ratio (ICER) using a $100,000/quality-adjusted life year (QALY) willingness-to-pay threshold. Sensitivity analyses were performed to assess the robustness of the model and the relative effects of variable estimates on base case conclusions.

RESULTS

From a societal perspective, nonoperative management, PJAC, and MACI cost $4,140, $52,683, and $83,073 and were associated with 5.28, 7.22, and 6.92 QALYs gained, respectively. PJAC and MACI were cost-effective relative to nonoperative management (ICERs $25,010/QALY and $48,344/QALY, respectively). PJAC dominated MACI in the base case analysis by being cheaper and more effective, but this was sensitive to the estimated effectiveness of both strategies. PJAC remained cost-effective if PJAC and MACI were considered equally effective.

CONCLUSIONS

In the management of symptomatic patellar cartilage defects, PJAC and MACI were both cost-effective compared to nonoperative management. Because of the need for one surgery instead of two, and less costly graft material, PJAC was cheaper than MACI. Consequently, when PJAC and MACI were considered equally effective, PJAC was more cost-effective than MACI. Sensitivity analyses accounting for the lack of robust long-term data for PJAC or MACI demonstrated that the cost-effectiveness of PJAC versus MACI depended heavily on the relative probabilities of yielding similar clinical results.

LEVEL OF EVIDENCE

III, economic and decision analysis.

Three-dimensional Culture and Chondrogenic Differentiation of Mesenchymal Stem Cells in Interconnected Collagen Scaffolds

Interconnected scaffolds are useful for promoting the chondrogenic differentiation of stem cells. Collagen scaffolds with interconnected pore structures were fabricated with poly(lactic acid-co-glycolic acid) (PLGA) sponge templates. The PLGA-templated collagen scaffolds were used to culture human bone marrow-derived mesenchymal stem cells (hMSCs) to investigate their promotive effect on the chondrogenic differentiation of hMSCs. The cells adhered to the scaffolds with a homogeneous distribution and proliferated with culture time. The expression of chondrogenesis-related genes was upregulated, and abundant cartilaginous matrices were detected. After subcutaneous implantation, the PLGA-templated collagen scaffolds further enhanced the production of cartilaginous matrices and the mechanical properties of the implants. The good interconnectivity of the PLGA-templated collagen scaffolds promoted chondrogenic differentiation. In particular, the collagen scaffolds prepared with large pore-bearing PLGA sponge templates showed the highest promotive effect.

Matrix-induced autologous chondrocyte implantation (mACI) versus autologous matrix-induced chondrogenesis (AMIC) for chondral defects of the knee: a systematic review

INTRODUCTION

Chondral defects of the knee are common and their treatment is challenging.

SOURCE OF DATA

PubMed, Google scholar, Embase and Scopus databases.

AREAS OF AGREEMENT

Both autologous matrix-induced chondrogenesis (AMIC) and membrane-induced autologous chondrocyte implantation (mACI) have been used to manage chondral defects of the knee.

AREAS OF CONTROVERSY

It is debated whether AMIC and mACI provide equivalent outcomes for the management of chondral defects in the knee at midterm follow-up. Despite the large number of clinical studies, the optimal treatment is still controversial.

GROWING POINTS

To investigate whether AMIC provide superior outcomes than mACI at midterm follow-up.

AREAS TIMELY FOR DEVELOPING RESEARCH

AMIC may provide better outcomes than mACI for chondral defects of the knee. Further studies are required to verify these results in a clinical setting.

Membrane scaffolds for matrix-induced autologous chondrocyte implantation in the knee: a systematic review

INTRODUCTION

Chondral defects of the knee are common and their management is challenging.

SOURCE OF DATA

Current scientific literature published in PubMed, Google scholar, Embase and Scopus.

AREAS OF AGREEMENT

Membrane-induced autologous chondrocyte implantation (mACI) has been used to manage chondral defects of the knee.

AREAS OF CONTROVERSY

Hyaluronic acid membrane provides better outcomes than a collagenic membrane for mACI in the knee at midterm follow-up is controversial.

GROWING POINTS

To investigate whether hyaluronic acid membrane may provide comparable clinical outcomes than collagenic membranes for mACI in focal defects of the knee.

AREAS TIMELY FOR DEVELOPING RESEARCH

Hyaluronic acid membrane yields a lower rate of failures and revision surgeries for mACI in the management of focal articular cartilage defects of the knee compared with collagenic scaffolds at midterm follow-up. No difference was found in patient reported outcome measures (PROMs). Further comparative studies are required to validate these results in a clinical setting.

Algorithm for Treatment of Focal Cartilage Defects of the Knee: Classic and New Procedures

OBJECTIVE

To create a treatment algorithm for focal grade 3 or 4 cartilage defects of the knee using both classic and novel cartilage restoration techniques.

DESIGN

A comprehensive review of the literature was performed highlighting classic as well as novel cartilage restoration techniques supported by clinical and/or basic science research and currently being employed by orthopedic surgeons.

RESULTS

There is a high level of evidence to support the treatment of small to medium size lesions (<2-4 cm2) without subchondral bone involvement with traditional techniques such as marrow stimulation, osteochondral autograft transplant (OAT), or osteochondral allograft transplant (OCA). Newer techniques such as autologous matrix-induced chondrogenesis and bone marrow aspirate concentrate implantation have also been shown to be effective in select studies. If subchondral bone loss is present OAT or OCA should be performed. For large lesions (>4 cm2), OCA or matrix autologous chondrocyte implantation (MACI) may be performed. OCA is preferred over MACI in the setting of subchondral bone involvement while cell-based modalities such as MACI or particulated juvenile allograft cartilage are preferred in the patellofemoral joint.

CONCLUSIONS

Numerous techniques exist for the orthopedic surgeon treating focal cartilage defects of the knee. Treatment strategies should be based on lesion size, lesion location, subchondral bone involvement, and the level of evidence supporting each technique in the literature.

Cell-laden injectable microgels: Current status and future prospects for cartilage regeneration

Injectable hydrogels have been employed extensively as versatile materials for cartilage regeneration due to their excellent biocompatibility, tunable structure, and ability to accommodate bioactive factors, as well as their ability to be locally delivered via minimally invasive injection to fill irregular defects. More recently, in vitro and in vivo studies have revealed that processing these materials to produce cell-laden microgels can enhance cell-cell and cell-matrix interactions and boost nutrient and metabolite exchange. Moreover, these studies have demonstrated gene expression profiles and matrix regeneration that are superior compared to conventional injectable bulk hydrogels. As cell-laden microgels and their application in cartilage repair are moving closer to clinical translation, this review aims to present an overview of the recent developments in this field. Here we focus on the currently used biomaterials and crosslinking strategies, the innovative fabrication techniques being used for the production of microgels, the cell sources used, the signals used for induction of chondrogenic differentiation and the resultant biological responses, and the ability to create three-dimensional, functional cartilage tissues. In addition, this review also covers the current clinical approaches for repairing cartilage as well as specific challenges faced when attempting the regeneration of damaged cartilage tissue. New findings related to the macroporous nature of the structures formed by the assembled microgel building blocks and the novel use of microgels in 3D printing for cartilage tissue engineering are also highlighted. Finally, we outline the challenges and future opportunities for employing cell-laden microgels in clinical applications.

Typical MRI-pattern suggests peak maturation of the ACI graft 2 years after third-generation ACI: a systematic review

PURPOSE

The purpose of the present article was (1) to systematically review the current literature and (2) to collect data regarding the postoperative magnetic resonance imaging (MRI) appearance of third-generation autologous chondrocyte implantation (ACI) grafts and (3) to provide an overview of imaging findings at various postoperative time points.

METHODS

A systematic review of the literature in Medline (Pubmed) and Embase was performed using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Articles which reported the post-operative MRI morphological outcomes following the use of third-generation ACI for treatment of knee cartilage lesions were included. All MRI results were allocated to six different time intervals: ≤ 3 months, > 3-6 months, > 6 months-1 year, > 1 year-2 years, > 2-5 years and > 5 years after surgery.

RESULTS

A total of 22 studies were included and the study populations ranged from 13 to 180 patients adding up to a total of 951 patients. Parameters such as defect fill, border integration, surface contour, graft morphology and integrity of the subchondral lamina all improve gradually with a peak two years following surgery suggesting complete graft maturation at this time point. After this peak, a statistically insignificant decline is noted for most of the parameters. Signal intensity was found to gradually shift from hyperintense to isointense in the first 36 months and to hypointense later on. Contrarily, subchondral bone edema is not only a postoperative feature of the procedure but also can reappear or persist up to ten years after surgery. As graft failures can appear after two years, consequently, the MRI composite score is also affected.

CONCLUSION

Recurring patterns in postoperative MRI appearance were observed in certain parameters including defect filling, graft signal intensity and structure, border integration of the graft while parameters like subchondral bone tend to be unpredictable. Given the heterogenous findings in terms of clinical correlation, and relating that aspect to the patterns found in this review, an MRI is justified at three months, one year, two years and five years after surgery, unless the clinical symptomatology and individual patient needs dictate otherwise.

LEVEL OF EVIDENCE

IV.

Reliability of the MOCART score: a systematic review

BACKGROUND

The present systematic review analysed the available literature to assess reliability of the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score in the evaluation of knee and ankle osteochondral lesions.

METHODS

All the studies using the MOCART score for knee and/or talus chondral defects were accessed in March 2021. A multivariate analysis was performed to assess associations between the MOCART score at last follow-up and data of patients at baseline, clinical scores and complications. A multiple linear model regression analysis was used.

RESULTS

The MOCART score evidenced no association with patient age (P = 0.6), sex (P = 0.1), body mass index (P = 0.06), defect size (P = 0.9), prior length of symptoms (P = 0.9) or visual analogue scale (P = 0.07). For chondral defects of the knee, no statistically significant association was found between the MOCART score and the International Knee Documentation Committee (P = 0.9) and with the Lysholm Knee Scoring Scales (P = 0.2), Tegner Activity Scale (P = 0.2), visual analogue scale P = 0.07), rate of failure (P = 0.2) and revision (P = 0.9). For chondral defect of the talus, no statistically significant associations were found between the MOCART score and the American Orthopedic Foot and Ankle Score (P = 0.3), Tegner Activity Scale (P = 0.4), visual analogue scale (P = 0.1), rate of failure (P = 0.1) and revision (P = 0.7).

CONCLUSION

The MOCART score demonstrated no association with patient characteristics and with the surgical outcome in patients who underwent surgical management for knee and talus chondral defects.

LEVEL OF EVIDENCE

Level IV.

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.

Clinical evaluation after matrix-associated autologous chondrocyte transplantation : a comparison of four different graft types

Aims

The aim of this retrospective study was to determine if there are differences in short-term clinical outcomes among four different types of matrix-associated autologous chondrocyte transplantation (MACT).

Methods

A total of 88 patients (mean age 34 years (SD 10.03), mean BMI 25 kg/m² (SD 3.51)) with full-thickness chondral lesions of the tibiofemoral joint who underwent MACT were included in this study. Clinical examinations were performed preoperatively and 24 months after transplantation. Clinical outcomes were evaluated using the International Knee Documentation Committee (IKDC) Subjective Knee Form, the Brittberg score, the Tegner Activity Scale, and the visual analogue scale (VAS) for pain. The Kruskal-Wallis test by ranks was used to compare the clinical scores of the different transplant types.

Results

The mean defect size of the tibiofemoral joint compartment was 4.28 cm² (SD 1.70). In total, 11 patients (12.6%) underwent transplantation with Chondro-Gide (matrix-associated autologous chondrocyte implantation (MACI)), 40 patients (46.0%) with Hyalograft C (HYAFF), 21 patients (24.1%) with Cartilage Regeneration System (CaReS), and 15 patients (17.2%) with NOVOCART 3D. The mean IKDC Subjective Knee Form score improved from 35.71 (SD 6.44) preoperatively to 75.26 (SD 18.36) after 24 months postoperatively in the Hyalograft group, from 35.94 (SD 10.29) to 71.57 (SD 16.31) in the Chondro-Gide (MACI) group, from 37.06 (SD 5.42) to 71.49 (SD 6.76) in the NOVOCART 3D group, and from 45.05 (SD 15.83) to 70.33 (SD 19.65) in the CaReS group. Similar improvements were observed in the VAS and Brittberg scores.

Conclusion

Two years postoperatively, there were no significant differences in terms of outcomes. Our data demonstrated that MACT, regardless of the implants used, resulted in good clinical improvement two years after transplantation for localized tibiofemoral defects.

Cite this article: Bone Joint Res 2021;10(7):370–379.

Autologous Chondrocyte Implantation and Mesenchymal Stem Cells for the Treatments of Chondral Defects of the Knee- A Systematic Review

BACKGROUND

There is still a lack of consensus about the best treatment of chondral defects of the knee. We conducted a systematic PRISMA review to evaluate clinical outcomes of Autologous Chondrocyte Implantation (ACI) and Mesenchymal Stem Cell (MSC) injections for the treatment of focal chondral defects of the knee.

METHODS

A systematic review of literature was performed according to the PRISMA guidelines. All the articles reporting data on ACI and MSC treatments for chondral defects of the knee were considered for inclusion. The main databases were accessed: PubMed, Medline, CINAHL, Cochrane, Embase and Google Scholar. The statistical analysis was performed using the Review Manager Software.

RESULTS

In the p-ACI group (987 knees), the Cincinnati Score improved by 18.94% (p=0.1), VAS by 38% (p=0.01), Tegner score by 19.11% (p=0.03), Lysholm score by 22.40% (p=0.01), IKCD by 27.36% (p=0.003). In the c-ACI group (444 knees), the Cincinnati Score improved by 23.80% (p=0.08), KOOS by 23.48% (p=0.03), VAS by 33.2% (p=0.005), IKDC by 33.30% (p=0.005). In the m-ACI group (599 knees), the Cincinnati Score improved by 26.80% (p=0.08), KOOS by 31.59% (p=0.1), VAS by 30.43% (p=0.4), Tegner score by 23.1% (p=0.002), Lysholm score by 31.14% (p=0.004), IKCD by 30.57% (p<0.001). In the MSCs group (291 knees), the KOOS improved by 29.7% (p=0.003), VAS by 41.89% (p<0.001), Tegner score by 25.81% (p=0.003), Lysholm score by 36.96% (p<0.001), IKCD by 30.57% (p=0.001).

CONCLUSION

Both ACI and MSC therapies can be considered as a concrete solution to treat focal chondral defects of the knee.

Arthroscopy versus mini-arthrotomy approach for matrix-induced autologous chondrocyte implantation in the knee: a systematic review

BACKGROUND

Matrix-induced autologous chondrocyte implantation (mACI) can be performed in a full arthroscopic or mini-open fashion. A systematic review was conducted to investigate whether arthroscopy provides better surgical outcomes compared with the mini-open approach for mACI in the knee at midterm follow-up.

METHODS

This systematic review was conducted following the PRISMA guidelines. The literature search was performed in May 2021. All the prospective studies reporting outcomes after mACI chondral defects of the knee were accessed. Only studies that clearly stated the surgical approach (arthroscopic or mini-open) were included. Only studies reporting a follow-up longer than 12 months were eligible. Studies reporting data from combined surgeries were not eligible, nor were those combining mACI with less committed cells (e.g., mesenchymal stem cells).

RESULTS

Sixteen studies were included, and 770 patients were retrieved: 421 in the arthroscopy group, 349 in the mini-open. The mean follow-up was 44.3 (12-60) months. No difference between the two groups was found in terms of mean duration of symptoms, age, body mass index (BMI), gender, defect size (P > 0.1). No difference was found in terms of Tegner Score (P = 0.3), Lysholm Score (P = 0.2), and International Knee Documentation Committee (IKDC) Score (P = 0.1). No difference was found in the rate of failures (P = 0.2) and revisions (P = 0.06).

CONCLUSION

Arthroscopy and mini-arthrotomy approaches for mACI in knee achieve similar outcomes at midterm follow-up.

LEVEL OF EVIDENCE

II, systematic review of prospective studies.

Surgical Management of Osteochondral Defects of the Knee: An Educational Review

PURPOSE OF REVIEW

Numerous surgical techniques are available to treat osteochondral defects of the knee. The aim of this review is to analyse these procedures, including their methodology, outcomes and limitations, to create a treatment algorithm for optimal management.

RECENT FINDINGS

Osteochondral defects of the knee significantly alter the biomechanics of the joint. This can cause symptomatic and functional impairment as well as considerable risk of progressive joint degeneration. Surgical interventions aim to restore a congruent, durable joint surface providing symptomatic relief and reducing the risk of early arthritic changes. These methods include fixation, chondroplasty, microfracture, autologous matrix-induced chondrogenesis, autograft transplants, allograft transplants and autologous chondrocyte implantation. There is currently much debate as to which of these methods provides optimal treatment of osteochondral defects. The overall evidence supports the use of each technique depending on the individual characteristics of the lesion. New technologies provide exciting prospects; however, long-term outcomes for these are not yet available.

Repopulation of decellularised articular cartilage by laser-based matrix engraving

BACKGROUND

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

METHODS

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

FINDINGS

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

INTERPRETATION

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

FUNDING

Austrian Research Promotion Agency FFG ("CartiScaff" #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08).

Third-Generation Autologous Chondrocyte Implantation at the Knee Joint Using the Igor Scaffold: A Case Series With 2-Year Follow-up

Background:

For large, locally restricted cartilage defects in young patients, third-generation matrix-supported autologous chondrocyte implantation (ACI) with a variety of scaffolds has shown good mid- to long-term results.

Purpose/Hypothesis:

This study aimed to monitor the clinical and radiological outcomes of patients who received ACI at the knee joint using the Igor scaffold (IGOR–Institute for Tissue and Organ Reconstruction) at 2-year follow-up. Our hypothesis was that there would be improvements in postoperative subjective scores and cartilage repair tissue quality.

Study Design:

Case series; Level of evidence, 4.

Methods:

A total of 21 patients (12 male and 9 female) were available for 2-year follow-up after third-generation ACI using the Igor scaffold. All were clinically assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS), Tegner Activity Scale, Brittberg score, International Knee Documentation Committee (IKDC) Subjective Knee Form, Noyes Sports Activity Rating Scale, and visual analog scale for pain. For morphological evaluation, the magnetic resonance observation of cartilage repair tissue (MOCART) and MOCART 2.0 scores were calculated using 3-T magnetic resonance imaging performed at 3, 6, 12, and 24 months postoperatively. Results were compared between baseline and 24 months postoperatively.

Results:

After 2 years, the clinical and radiological scores showed good to excellent results in the majority of patients. On the IKDC, 10 patients were graded as excellent, 4 as good, 5 as fair, and 2 as severe; on the KOOS, 7 patients were graded as excellent, 8 as good, 4 as fair, and 2 as severe. From baseline to latest follow-up, visual analog scale pain scores decreased from 5.6 ± 3.2 (mean ± SD) to 1.5 ± 2; KOOS results increased from 51 ± 20.7 to 75.2 ± 15.4; and the Tegner score improved from 2.2 ± 1.8 to 4.3 ± 1.3. The MOCART and MOCART 2.0 scores were comparable at 2-year follow-up, with mean values of 74 ± 10 and 78 ± 13, respectively. Satisfactory filling and integration were found in 90.5%. Overall, 16 of 21 patients (76.1%) were satisfied with the surgery and would undergo the procedure again.

Conclusion:

Third-generation ACI using the Igor scaffold showed improvements in clinical and radiological results that were comparable with other scaffolds for patients with large traumatic or degenerative cartilage defects. Patients reported a decrease in pain and an increase in activity, with the majority reporting good results.

Repopulation of decellularised articular cartilage by laser-based matrix engraving

Background

In spite of advances in the treatment of cartilage defects using cell and scaffold-based therapeutic strategies, the long-term outcome is still not satisfying since clinical scores decline years after treatment. Scaffold materials currently used in clinical settings have shown limitations in providing suitable biomechanical properties and an authentic and protective environment for regenerative cells. To tackle this problem, we developed a scaffold material based on decellularised human articular cartilage.

Methods

Human articular cartilage matrix was engraved using a CO₂ laser and treated for decellularisation and glycosaminoglycan removal. Characterisation of the resulting scaffold was performed via mechanical testing, DNA and GAG quantification and in vitro cultivation with adipose-derived stromal cells (ASC). Cell vitality, adhesion and chondrogenic differentiation were assessed. An ectopic, unloaded mouse model was used for the assessment of the in vivo performance of the scaffold in combination with ASC and human as well as bovine chondrocytes. The novel scaffold was compared to a commercial collagen type I/III scaffold.

Findings

Crossed line engravings of the matrix allowed for a most regular and ubiquitous distribution of cells and chemical as well as enzymatic matrix treatment was performed to increase cell adhesion. The biomechanical characteristics of this novel scaffold that we term CartiScaff were found to be superior to those of commercially available materials. Neo-tissue was integrated excellently into the scaffold matrix and new collagen fibres were guided by the laser incisions towards a vertical alignment, a typical feature of native cartilage important for nutrition and biomechanics. In an ectopic, unloaded in vivo model, chondrocytes and mesenchymal stromal cells differentiated within the incisions despite the lack of growth factors and load, indicating a strong chondrogenic microenvironment within the scaffold incisions. Cells, most noticeably bone marrow-derived cells, were able to repopulate the empty chondrocyte lacunae inside the scaffold matrix.

Interpretation

Due to the better load-bearing, its chondrogenic effect and the ability to guide matrix-deposition, CartiScaff is a promising biomaterial to accelerate rehabilitation and to improve long term clinical success of cartilage defect treatment.

Funding

Austrian Research Promotion Agency FFG (“CartiScaff” #842455), Lorenz Böhler Fonds (16/13), City of Vienna Competence Team Project Signaltissue (MA23, #18-08)

Knee articular cartilage injury treatment with matrix-induced autologous chondrocyte implantation (MACI): correlation at 24 and 120 months between clinical and radiological findings using MR arthrography

OBJECTIVE

To evaluate the long-term evolution of matrix-induced autologous chondrocyte implantation (MACI) with magnetic resonance (MR) arthrography and verify the correlation between radiological and clinical findings.

MATERIALS AND METHODS

Twenty-six patients (20 m/6f) were diagnosed with knee chondral injuries and treated with MACI implantation. Each patient received MR arthrography and clinical examination at mid-term (range 22-36 months) and long term (range 96-194 months) after surgery. MR arthrography was performed with dedicated coil and a 1.5-Tesla MR unit. The modified MOCART scale was used to evaluate the status of chondral implants. Implant coating, integration to the border zone, and the surface and structure of the repaired tissue were evaluated. Presence of bone marrow oedema was evaluated. The Cincinnati Knee Rating System (CKRS) was used for clinical assessment.

RESULTS

At long term, 4/26 patients had complete alignment; 5/26 had a complete integration of the margins; in 4/26 cases, the implant surface was undamaged; in 14/26 cases, the reparative tissue was homogeneous. In 9/26 cases, the implant showed isointense signal compared to articular cartilage, while the presence of subchondral bone oedema was documented in 19/26 cases. The average radiological score decreased from 59.2 (mid-term) to 38.6 (long term). The average clinical score decreased from 8.9 to 8.3.

CONCLUSIONS

Decrease in clinical results was not significant (0.6 points p = .06), but mMOCART scores decreased significantly (p = .00003). Although imaging studies showed deterioration of the grafts, the patients did not have significant clinical deterioration (231/250).

Management of Large Focal Chondral and Osteochondral Defects in the Knee

Large, focal articular cartilage defects of the knee (> 4 cm²) can be a source of significant morbidity and often require surgical intervention. Patient- and lesion-specific factors must be identified when evaluating a patient with an articular cartilage defect. In the management of large cartilage defects, the two classically utilized cartilage restoration procedures are osteochondral allograft (OCA) transplantation and cell therapy, or autologous chondrocyte implantation (ACI). Alternative techniques that are available or currently in clinical trials include a hyaluronan-based scaffold plus bone marrow aspirate concentrate, a third-generation autologous chondrocyte implant, and an aragonite-based scaffold. In this review, we will focus on OCA and ACI as the mainstay in management of large chondral and osteochondral defects of the knee. We will discuss the techniques and associated clinical outcomes for each, while including a brief mention of alternative treatments. Overall, cartilage restoration techniques have yielded favorable clinical outcomes and can be successfully employed to treat these challenging large focal lesions.

Alternative and complementary therapies in osteoarthritis and cartilage repair

Osteoarthritis (OA) is the most common joint condition and, with a burgeoning ageing population, is due to increase in prevalence. Beyond conventional medical and surgical interventions, there are an increasing number of ‘alternative’ therapies. These alternative therapies may have a limited evidence base and, for this reason, are often only afforded brief reference (or completely excluded) from current OA guidelines. Thus, the aim of this review was to synthesize the current evidence regarding autologous chondrocyte implantation (ACI), mesenchymal stem cell (MSC) therapy, platelet-rich plasma (PRP), vitamin D and other alternative therapies. The majority of studies were in knee OA or chondral defects. Matrix-assisted ACI has demonstrated exceedingly limited, symptomatic improvements in the treatment of cartilage defects of the knee and is not supported for the treatment of knee OA. There is some evidence to suggest symptomatic improvement with MSC injection in knee OA, with the suggestion of minimal structural improvement demonstrated on MRI and there are positive signals that PRP may also lead to symptomatic improvement, though variation in preparation makes inter-study comparison difficult. There is variability in findings with vitamin D supplementation in OA, and the only recommendation which can be made, at this time, is for replacement when vitamin D is deplete. Other alternative therapies reviewed have some evidence (though from small, poor-quality studies) to support improvement in symptoms and again there is often a wide variation in dosage and regimens. For all these therapeutic modalities, although controlled studies have been undertaken to evaluate effectiveness in OA, these have often been of small size, limited statistical power, uncertain blindness and using various methodologies. These deficiencies must leave the question as to whether they have been validated as effective therapies in OA (or chondral defects). The conclusions of this review are that all alternative interventions definitely require clinical trials with robust methodology, to assess their efficacy and safety in the treatment of OA beyond contextual and placebo effects.

Cost-efficacy of Knee Cartilage Defect Treatments in the United States

BACKGROUND

Multiple knee cartilage defect treatments are available in the United States, although the cost-efficacy of these therapies in various clinical scenarios is not well understood.

PURPOSE/HYPOTHESIS

The purpose was to determine cost-efficacy of cartilage therapies in the United States with available mid- or long-term outcomes data. The authors hypothesized that cartilage treatment strategies currently approved for commercial use in the United States will be cost-effective, as defined by a cost <$50,000 per quality-adjusted life-year over 10 years.

STUDY DESIGN

Systematic review.

METHODS

A systematic search was performed for prospective cartilage treatment outcome studies of therapies commercially available in the United States with minimum 5-year follow-up and report of pre- and posttreatment International Knee Documentation Committee subjective scores. Cost-efficacy over 10 years was determined with Markov modeling and consideration of early reoperation or revision surgery for treatment failure.

RESULTS

Twenty-two studies were included, with available outcomes data on microfracture, osteochondral autograft, osteochondral allograft (OCA), autologous chondrocyte implantation (ACI), and matrix-induced ACI. Mean improvement in International Knee Documentation Committee subjective scores at final follow-up ranged from 17.7 for microfracture of defects >3 cm² to 36.0 for OCA of bipolar lesions. Failure rates ranged from <5% for osteochondral autograft for defects requiring 1 or 2 plugs to 46% for OCA of bipolar defects. All treatments were cost-effective over 10 years in the baseline model if costs were increased 50% or if failure rates were increased an additional 15%. However, if efficacy was decreased by a minimum clinically important amount, then ACI (periosteal cover) of femoral condylar lesions ($51,379 per quality-adjusted life-year), OCA of bipolar lesions ($66,255) or the patella ($66,975), and microfracture of defects >3 cm² ($127,782) became cost-ineffective over 10 years.

CONCLUSION

Currently employed treatments for knee cartilage defects in the United States are cost-effective in most clinically acceptable applications. Microfracture is not a cost-effective initial treatment of defects >3 cm². OCA transplantation of the patella or bipolar lesions is potentially cost-ineffective and should be used judiciously.

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.

Fluorescent Nanodiamonds Enable Long-Term Detection of Human Adipose-Derived Stem/Stromal Cells in an In Vivo Chondrogenesis Model Using Decellularized Extracellular Matrices and Fibrin Glue Polymer

Clinically available materials, including allogeneic irradiated costal cartilage and fibrin glue polymer, were used as scaffolds for in vivo chondrogenic differentiation of human adipose-derived stem/stromal cells (hASCs) in the attempt to develop a more efficient treatment over current methods. Current studies include the use of growth-factor stimulation, tissue engineering, and biocompatible materials; however, most methods involve complicated processes and pose clinical limitations. In this report, the xenografts in the experimental group composed of a diced decellularized cartilage extracellular matrix (ECM), hASCs, and fibrin glue polymer were implanted into the subcutaneous layer of nude mice, and the results were compared with two groups of controls; one control group received implantation of decellularized cartilage ECM and fibrin glue polymer, and the other control group received implantation of hASCs mixed with fibrin glue polymer. To evaluate whether hASCs had in vivo chondrogenesis in the xenografts, hASCs were labeled with fluorescent nanodiamonds (FNDs), a biocompatible and photostable nanomaterial, to allow for long-term detection and histological analysis. Increased cellularity, glycosaminoglycan, and collagen deposition were found by the histological examination in the experimental group compared with control groups. With the background-free detection technique and time-gated fluorescence imaging, the numbers and locations of the FND-labeled hASCs could be detected by confocal microscopy. The chondrocyte-specific markers, such as aggrecan and type II collagen, were colocalized with cells containing signals of FNDs which indicated in vivo chondrogenesis of hASCs. Taken together, functional in vivo chondrogenesis of the hASCs could be achieved by clinically available decellularized cartilage ECM and fibrin glue polymer in the nude mice model without in vitro chondrogenic induction. The fluorescent signals of FNDs in hASCs can be detected in histological analysis, such as hematoxylin and eosin staining (H&E staining) without the interference of the autofluorescence. Our study may warrant future clinical applications of the combination of decellular cartilage ECM, fibrin glue polymer, and hASCs for cartilage repair.

Weight-Supported Walking Assist Device for Knee Osteoarthritis Patients

Knee osteoarthritis patients have pain in their knee and it can become difficult to walk depending on the progress of symptoms. After performing chondrocyte implantation, it is necessary to reduce the load on the knee joint until the implanted cartilage is integrated. The purposes of this study were to develop a device that enables the user to walk and reduced the weight on the knee joint and to confirm basic performance of the device through experiments. The device was composed of a seat for supporting the body weight of the user, a prosthetic knee, and the floor reaction force sensor shoes. Experiments were conducted to confirm the basic performance of the device. As a result, an able-bodied participant who wore the device was able to walk while unloading two-thirds of their body weight onto their knee. As a result of gait analysis, it was found that the gait did not change significantly even when the device was worn.

Is implantation of autologous chondrocytes superior to microfracture for articular-cartilage defects of the knee? A systematic review of 5-year follow-up data

BACKGROUND

Autologous chondrocyte implantation (ACI) and microfracture are two of the main surgical treatment options for articular cartilage lesions of the knee. Consensus regarding the best clinical options to repair knee cartilage lesions is lacking. We undertook a systematic review to clarify the clinical efficacy of ACI and microfracture at minimum mean 5-year follow-up.

METHODS

A literature search was conducted using the MEDLINE, Embase and Cochrane Library databases up to August 2018. Only comparative clinical studies of ACI and microfracture for the treatment of articular cartilage lesions of the knee with level I/Ⅱ evidence were included. Clinical outcomes and the prevalence of treatment failure from each study were extracted and compared. The methodological quality of the included studies was analyzed by means of the PEDro scale.

RESULTS

Five comparative studies (three randomized controlled trials and two prospective cohort studies) met our eligibility criteria. ACI and microfracture elicited significant improvement in clinical outcomes after 5 years. However, better clinical results with significant differences were found with modified versions of ACI (ACI with a modified collagen membrane [ACI-C] or matrix-applied chondrocyte implantation [MACI]) than with microfracture as determined by the Knee Injury and Osteoarthritis Outcome Score, activities of daily living assessment, Tegner Activity Scale score, and the International Knee Documentation Committee objective and subjective scores. No significant difference was observed in the treatment failure rate between these two methods within a particular study.

CONCLUSIONS

Currently, the best-available evidence suggests that some clinical outcomes of articular cartilage lesions of the knee treated with modified versions of ACI (ACI-C or MACI) can significantly improve patient outcomes at the mid-term follow-up of 5 years compared with those obtained using microfracture.

Clinical outcome and subchondral bone edema presence at two-year follow-up after high density autologous chondrocyte implantation treatment in the knee

BACKGROUND

Recently, a new approach of autologous chondrocyte implantation technique (using as biomaterial a collagen type i/iii membrane) based on increasing cell density called HD-ACI (High Density Autologous Chondrocyte Implantation) has been described. The objective of this paper was to study the clinical outcome and incidence of subchondral bone oedema in patients with cartilage lesions in the knee treated with HD-ACI at 1-2 years of follow-up.

METHODS

This is a retrospective study performed with forty patients with chondral injuries grade iii-iv. All patients were treated with HD-ACI with a cellular dose of 5×10⁶ chondrocytes /cm² of lesion. The subjective perception of improvement of symptoms and functionality was measured with the IKDC score (International Knee Documentation Committee). The presence of bone oedema was assessed at 6, 12 and 24 months of follow-up by magnetic resonance imaging.

RESULTS

IKDC values showed a significant improvement at 12 and 24 months (P<.001). The mean difference of IKDC between the baseline visit and 12 months was 26.3 points, and 31.6 points at 24 months. Twenty-seven point five percent of the patients presented subchondral bone oedema at 2 years of follow-up.

CONCLUSIONS

HD-ACI is an effective and safe treatment that improves pain, clinical perception and functionality of the joint. No correlation was found between the presence of bone oedema and the patients' clinical outcome.

Repopulation of an auricular cartilage scaffold, AuriScaff, perforated with an enzyme combination

Biomaterials currently in use for articular cartilage regeneration do not mimic the composition or architecture of hyaline cartilage, leading to the formation of repair tissue with inferior characteristics. In this study we demonstrate the use of "AuriScaff", an enzymatically perforated bovine auricular cartilage scaffold, as a novel biomaterial for repopulation with regenerative cells and for the formation of high-quality hyaline cartilage. AuriScaff features a traversing channel network, generated by selective depletion of elastic fibers, enabling uniform repopulation with therapeutic cells. The complex collagen type II matrix is left intact, as observed by immunohistochemistry, SEM and TEM. The compressive modulus is diminished, but three times higher than in the clinically used collagen type I/III scaffold that served as control. Seeding tests with human articular chondrocytes (hAC) alone and in co-culture with human adipose-derived stromal/stem cells (ASC) confirmed that the network enabled cell migration throughout the scaffold. It also guides collagen alignment along the channels and, due to the generally traverse channel alignment, newly deposited cartilage matrix corresponds with the orientation of collagen within articular cartilage. In an osteochondral plug model, AuriScaff filled the complete defect with compact collagen type II matrix and enabled chondrogenic differentiation inside the channels. Using adult articular chondrocytes from bovine origin (bAC), filling of even deep defects with high-quality hyaline-like cartilage was achieved after 6 weeks in vivo. With its composition and spatial organization, AuriScaff provides an optimal chondrogenic environment for therapeutic cells to treat cartilage defects and is expected to improve long-term outcome by channel-guided repopulation followed by matrix deposition and alignment. STATEMENT OF SIGNIFICANCE: After two decades of tissue engineering for cartilage regeneration, there is still no optimal strategy available to overcome problems such as inconsistent clinical outcome, early and late graft failures. Especially large defects are dependent on biomaterials and their scaffolding, guiding and protective function. Considering the currently used biomaterials, structure and mechanical properties appear to be insufficient to fulfill this task. The novel scaffold developed within this study is the first approach enabling the use of dense cartilage matrix, repopulate it via channels and provide the cells with a compact collagen type II environment. Due to its density, it also provides better mechanical properties than materials currently used in clinics. We therefore think, that the auricular cartilage scaffold (AuriScaff) has a high potential to improve future cartilage regeneration approaches.

Matrix-Induced Autologous Chondrocyte Implantation With Autologous Bone Grafting for Osteochondral Lesions of the Femoral Trochlea

Matrix-induced autologous chondrocyte implantation is a 2-stage surgical procedure used to treat symptomatic, full-thickness chondral lesions of the knee. This third-generation autologous chondrocyte implantation (ACI) technique improves on the limitations of previous methods, including the risk of uneven chondrocyte distribution at the time of implantation and graft hypertrophy. Given the compliant properties of the scaffold, the graft can be easily shaped to treat irregular chondral defects and applied to articular surfaces with multiplanar geometry (e.g., patella, trochlea). Although ACI techniques are ideally suited to treat chondral surface defects, the ACI "sandwich" technique can be used to treat large osteochondral defects with significant bone loss (>8 mm). Historically, this procedure uses autologous bone graft to replace areas of osseous deficiency along with 2 type I/III collagen bilayer membranes to securely contain the cultured chondrocytes within the defect. We present an analogous technique for the treatment of osteochondral lesions of the femoral trochlea using a single matrix-induced ACI scaffold and autologous bone grafting for a segmental osseous defect.

Effect of gelatin source and photoinitiator type on chondrocyte redifferentiation in gelatin methacryloyl-based tissue-engineered cartilage constructs

This work investigates neocartilage formation in bovine and porcine gelatin methacryloyl-based hydrogels photocrosslinked using ultraviolet or visible light photoinitiator systems.

Cartilage regeneration using arthroscopic flushing fluid-derived mesenchymal stem cells encapsulated in a one-step rapid cross-linked hydrogel

Many attempts have been made to repair articular cartilage defects, including mesenchymal stem cell (MSC)-based tissue engineering strategies. Although this approach shows promise, optimizing MSC sources and their delivery is challenging. This study was designed to test the feasibility of using MSCs found in the human arthroscopic flushing fluid (AFF) for cartilage regeneration, by incorporating them into a newly developed one-step rapid cross-linking hyper-branched polyPEGDA/HA hydrogel. AFF-MSCs were isolated from the original intra-articular flushing fluid of 10 patients prior to arthroscopic procedures. The hydrogel was fabricated with hyper-branched polyPEGDA and thiolated hyaluronic acid (HA). In vitro assays demonstrated that AFF-MSCs possessed the typical MSC morphology and phenotype, and maintained chondrogenic differentiation properties when encapsulated within the hydrogel. The AFF-MSC/hydrogel composite could significantly repair full-thickness cartilage defects generated in a rat model after 8 weeks of implantation; smooth cartilage was formed with evidence of hyaline cartilage formation. These data suggest that human AFF-MSCs are a novel and abundant MSC source that have high therapeutic value for cartilage regeneration.

STATEMENT OF SIGNIFICANCE

Many attempts have been made to repair the defects of articular cartilage, including mesenchymal stem cell (MSC)-based tissue engineering strategies. Optimizing MSC sources and their delivery approaches still remain clinically challenging. Recent studies determined that MSCs derived from synovium and synovial fluid exhibited superior chondrogenic potential. However, no feasible methods to harvest these human tissues and cells have been impeding them for clinical application. Hereby, we explored a simple and easy accessible approach to obtain a new stem cell source from arthroscopic flushing fluid (AFF-MSCs), which probably contains plenty of MSCs from synovium and synovial fluid. Further experiments demonstrated that encapsulation of these stem cells with one-step rapid cross-linked polyPEGDA/HA hydrogel held very encouraging potential for cartilage regeneration.

Autologous liquid platelet rich fibrin: A novel drug delivery system

There is currently widespread interest within the biomaterial field to locally deliver biomolecules for bone and cartilage regeneration. Substantial work to date has focused on the potential role of these biomolecules during the healing process, and the carrier system utilized is a key factor in their effectiveness. Platelet rich fibrin (PRF) is a naturally derived fibrin scaffold that is easily obtained from peripheral blood following centrifugation. Slower centrifugation speeds have led to the commercialization of a liquid formulation (liquid-PRF) resulting in an upper plasma layer composed of liquid fibrinogen/thrombin prior to clot formation that remains in its liquid phase for approximately 15 min until injected into bodily tissues. Herein, we introduce the use of liquid PRF as an advanced local delivery system for small and large biomolecules. Potential target molecules including large (growth factors/cytokines and morphogenetic/angiogenic factors), as well as small (antibiotics, peptides, gene therapy and anti-osteoporotic) molecules are considered potential candidates for enhanced bone/cartilage tissue regeneration. Furthermore, liquid-PRF is introduced as a potential carrier system for various cell types and nano-sized particles that are capable of limiting/by-passing the immune system and minimizing potential foreign body reactions within host tissues following injection.

STATEMENT OF SIGNIFICANCE

There is currently widespread interest within the biomaterial field to locally deliver biomolecules for bone and cartilage regeneration. This review article focuses on the use of a liquid version of platelet rich fibrin (PRF) composed of liquid fibrinogen/thrombin as a drug delivery system. Herein, we introduce the use of liquid PRF as an advanced local delivery system for small and large biomolecules including growth factors, cytokines and morphogenetic/angiogenic factors, as well as antibiotics, peptides, gene therapy and anti-osteoporotic molecules as potential candidates for enhanced bone/cartilage tissue regeneration.

Matrix-Applied Characterized Autologous Cultured Chondrocytes Versus Microfracture: Five-Year Follow-up of a Prospective Randomized Trial

BACKGROUND

Matrix-based cell therapy improves surgical handling, increases patient comfort, and allows for expanded indications with better reliability within the knee joint. Five-year efficacy and safety of autologous cultured chondrocytes on porcine collagen membrane (MACI) versus microfracture for treating cartilage defects have not yet been reported from any randomized controlled clinical trial.

PURPOSE

To examine the clinical efficacy and safety results at 5 years after treatment with MACI and compare these with the efficacy and safety of microfracture treatment for symptomatic cartilage defects of the knee.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

This article describes the 5-year follow-up of the SUMMIT (Superiority of MACI Implant Versus Microfracture Treatment) clinical trial conducted at 14 study sites in Europe. All 144 patients who participated in SUMMIT were eligible to enroll; analyses of the 5-year data were performed with data from patients who signed informed consent and continued in the Extension study.

RESULTS

Of the 144 patients randomized in the SUMMIT trial, 128 signed informed consent and continued observation in the Extension study: 65 MACI (90.3%) and 63 microfracture (87.5%). The improvements in Knee injury and Osteoarthritis Outcome Score (KOOS) Pain and Function domains previously described were maintained over the 5-year follow-up. Five years after treatment, the improvement in MACI over microfracture in the co-primary endpoint of KOOS pain and function was maintained and was clinically and statistically significant ( P = .022). Improvements in activities of daily living remained statistically significantly better ( P = .007) in MACI patients, with quality of life and other symptoms remaining numerically higher in MACI patients but losing statistical significance relative to the results of the SUMMIT 2-year analysis. Magnetic resonance imaging (MRI) evaluation of structural repair was performed in 120 patients at year 5. As in the 2-year SUMMIT (MACI00206) results, the MRI evaluation showed improvement in defect filling for both treatments; however, no statistically significant differences were noted between treatment groups.

CONCLUSION

Symptomatic cartilage knee defects 3 cm² or larger treated with MACI were clinically and statistically significantly improved at 5 years compared with microfracture treatment. No remarkable adverse events or safety issues were noted in this heterogeneous patient population.

Biophysical stimulation improves clinical results of matrix-assisted autologous chondrocyte implantation in the treatment of chondral lesions of the knee

PURPOSE

The purpose of the present study was to evaluate the effects of pulsed electromagnetic fields (PEMFs) on clinical outcome in patients who underwent arthroscopic matrix-assisted autologous chondrocyte implantation (MACI) for chondral lesions of the knee.

METHODS

Thirty patients affected by grade III and IV International Cartilage Repair Society chondral lesions of the knee underwent MACI. After surgery, patients were randomly assigned to either experimental group (PEMFs 4 h per day for 60 days) or control group . Clinical outcome was evaluated through International Knee Documentation Committee (IKDC) subjective knee evaluation form, Visual Analog Scale, Short Form-36 (SF-36) and EuroQoL before surgery and 1, 2, 6, and 60 months postoperative.

RESULTS

Mean size of chondral lesion was 2.4 ± 0.6 cm² in the PEMFs group and 2.5 ± 0.5 cm² in the control one. No differences were found between groups at baseline. IKDC score increased in both groups till 6 months, but afterward improvement was observed only in the experimental group with a significant difference between groups at 60 months (p = 0.001). A significant difference between groups was recorded at 60 months for SF-36 (p = 0.006) and EuroQol (p = 0.020). A significant pain reduction was observed in the experimental group at 1-, 2- and 60-month follow-up.

CONCLUSION

Biophysical stimulation with PEMFs improves clinical outcome after arthroscopic MACI for chondral lesions of the knee in the short- and long-term follow-up. Biophysical stimulation should be considered as an effective tool in order to ameliorate clinical results of regenerative medicine. The use of PEMFs represents an innovative therapeutic approach for the survival of cartilage-engineered constructs and consequently the success of orthopaedic surgery.

LEVEL OF EVIDENCE

II.

Applications of Tissue Engineering in Joint Arthroplasty: Current Concepts Update

Research in tissue engineering has undoubtedly achieved significant milestones in recent years. Although it is being applied in several disciplines, tissue engineering's application is particularly advanced in orthopedic surgery and in degenerative joint diseases. The literature is full of remarkable findings and trials using tissue engineering in articular cartilage disease. With the vast and expanding knowledge, and with the variety of techniques available at hand, the authors aimed to review the current concepts and advances in the use of cell sources in articular cartilage tissue engineering.

Failure of Autologous Chondrocyte Implantation

Long-term results of autologous chondrocyte implantation and matrix-assisted autologous chondrocyte transplantation in the knee are satisfying, but not enough attention has been paid to the evaluation of failures. Thus, a systematic review of the literature was performed, underlining a failure rate in the 58 included articles of 14.9% among 4294 patients, most of them occurring in the first 5 years after surgery, and with no difference between autologous chondrocyte implantation and matrix-assisted autologous chondrocyte transplantation. Failures are very heterogenously defined in the current literature. A widely accepted definition is needed, and a comprehensive definition taking into consideration the patient's perception of the outcome, not just the surgeon's or researcher's point of view, would be advisable. Finally, there is no agreement on the most appropriate treatment of failures, and further studies are needed to give better indications to properly manage patients failed after cartilage procedures.

LEVEL OF EVIDENCE

Level IV.