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Concept: Knee cartilage replacement therapy

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Untreated articular cartilage defects may lead to chronic joint degeneration and functional disability. In the past decade, several cartilage repair techniques have emerged for the treatment of cartilage lesions. Among these techniques, mosaicplasty was introduced by the senior author into the clinical practice in 1992. This article does not intend to give a review or a comparison of currently existing surgical techniques which aim to repair symptomatic focal defects; however, it focuses on the procedures used in the everyday practice in the authors' institute, namely microfracture, mosaicplasty, autologous chondrocyte implantation (ACI), osteochondral allograft transplantation and biodegradable osteochondral scaffolds. It gives a brief summary of these well-described techniques, summarizes the authors' clinical experience and available data on the clinical outcome, and the rehabilitation protocol following different procedures, with a special emphasis on mosaicplasty.

Concepts: Organ transplant, Articular cartilage damage, Chondrocyte, Knee, Knee cartilage replacement therapy, Articular cartilage repair, Cartilage, Autologous chondrocyte implantation

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Cartilage therapy for focal articular lesions of the knee has been implemented for more than a decade, and it is becoming increasingly available. What do we know on the healing response of cartilage lesions? What do we know on the treatment of focal cartilage lesions of the knee and the prognostic factors involved? PubMed articles related to articular cartilage regeneration of the knee in clinical studies were searched from January 2006 to November 2012, using the following key words: articular cartilage, regeneration, clinical studies, and knee. A total of 44 reports were found. They showed the following possibilities for the treatment of focal lesions of the articular cartilage of the knee: cartilage regeneration and repair including cartilage reparation with gene-activated matrices, autologous chondrocyte implantation (ACI) and matrix-induced ACI (MACI), microfracture, osteochondral autograft transfer (mosaicplasty), biological approaches (scaffolds, mesenchymal stem cells-MSCs, platelet-rich plasma, growing factors-GF, bone morphogenetic proteins-BMPs, magnetically labeled synovium-derived cells-M-SDCs, and elastic-like polypeptide gels), osteotomies, stem-cell-coated titanium implants, and chondroprotection with pulsed electromagnetic fields. Untreated cartilage lesions on the femoral condyles had a superior healing response compared to those on the tibial plateaus, and in the patellofemoral joint. Clinical outcome regarding the treatment of medial defects is better than that of the lateral defects. Improvement from baseline was better for patients < or = 30 years compared with patients > or = 30 years. ACI, MACI, and mosaicplasty have shown similar results. The results of comparative clinical studies using ACI have shown some superiority over conventional microfracturing in medium or large defects and in long-term durability. Some biological methods such as scaffolds, MSCs, GF, M-SDCs, BMPs, and elastic-like polypeptide gels still need more research.

Concepts: Chondrocyte, Collagen, Articular cartilage repair, Bone, Knee cartilage replacement therapy, Knee, Autologous chondrocyte implantation, Cartilage

27

The regeneration capacity of articular cartilage is very limited. Therefore, cartilage defects heal poorly and are known as prearthrotic lesions. Autologous Matrix-Induced Chondrogenesis (AMIC) is an innovative treatment concept for localized full-thickness cartilage defects. This technique combines the well-established microfracturing with a collagen I/III scaffold fixated by fibrin glue.

Concepts: Knee cartilage replacement therapy, Bone, Autologous chondrocyte implantation, Knee, Collagen, Cartilage

27

This article reviews the basics of articular cartilage biology, which provide a necessary foundation for understanding the evolving field of articular cartilage injury and repair. The currently popular treatment options for osteochondral injury (microfracture, osteochondral autograft transfer system, osteochondral allograft, autologous chondrocyte implantation, and the use of scaffolds with autologous chondrocyte implantation) document the significant advances made in this area in the past 2 decades. Integration of newly available information and technology derived from advances in molecular biology and tissue engineering holds even greater promise for continued advances in optimal management of this challenging problem.

Concepts: Biology, Knee cartilage replacement therapy, Evolution, DNA, Extracellular matrix, Molecular biology, Cartilage, Autologous chondrocyte implantation

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PURPOSE: Graft hypertrophy is a major complication in the treatment for localized cartilage defects with autologous chondrocyte implantation (ACI) using periosteal flap and its further development, Novocart (a matrix-based ACI procedure). The aim of the present study is to investigate individual criteria for the development of graft hypertrophy by NOVOCART 3D implantation of the knee in the post-operative course of 2 years. METHODS: Forty-one consecutive patients with 44 isolated cartilage defects of the knee were treated with NOVOCART 3D implants. Individual criteria and defect-associated criteria were collected. Follow-up MRIs were performed at 3, 6, 12 and 24 months. The NOVOCART 3D implants were measured and classified. The modified MOCART Score was used to evaluate quality and integration of the NOVOCART 3D implants in MRI. RESULTS: Graft hypertrophy was observed in a total of 11 patients at all post-operative time points. We were able to show that NOVOCART 3D implantation of cartilage defects after acute trauma and osteochondritis dissecans (OCD) led to a significantly increased proportion of graft hypertrophy. No other individual criteria (age, gender, BMI) or defect-associated criteria (concomitant surgery, second-line treatment, defect size, fixation technique) showed any influence on the development of graft hypertrophy. The modified MOCART Score results revealed a significant post-operative improvement within 2 years. CONCLUSION: The aetiology of cartilage defects appears to have a relevant influence for the development of graft hypertrophy. Patients, who were treated with NOVOCART 3D implants after an acute event (acute trauma or OCD), are especially at risk for developing a graft hypertrophy in the post-operative course of two years. LEVEL OF EVIDENCE: Case series, Level IV.

Concepts: Knee replacement, Knee cartilage replacement therapy, Knee, Magnetic resonance imaging, Osteochondritis dissecans, Cartilage, Autologous chondrocyte implantation

22

Chondral injuries are short of self-healing ability and need to surgical repair after articular cartilage injury. Conventional treatment includes debridement and drainage under arthroscope, micro-fracture, osteochondral autograft transplantation (OATS), mosaiplasty and osteochondral allografts (OCA), autologous chondrocyte implantation (ACI). Debridement and drainage could remove pain factor, and has advantages of simple operation, wide clinical application and early clinical effect. Micro-fracture and osteochondral autograft transplantation is suitable for small area of cartilage repair, while the further effect showed that fibrous cartilage permeated by drill could decrease postoperative clinical effect. Osteochondral autograft transplantation has better advantages for reconstruction complete of wear-bearing joint. Autologous chondrocyte implantation and allogeneic cartilage transplantation are suitable for large area of cartilage defect, postoperative survival of allogeneic cartilage transplantation is effected by local rejection reaction and decrease further clinical effect. Cartilage tissue engineering technology could improve repair quality of autologous chondrocyte implantation, and make repair tissue close to transparent cartilage, but has limit to combined subchondral bone plate, reactive bone edema, bone loss and bad axis of lower limb. New technology is applied to cartilage injury, and has advantages of less trauma, simple operation, rapid recover, good clinical effect and less cost;and could be main method for treat cartilage injury with surgical repair technology. How to improve repair quality with compression resistance and abrasive resistance are expected to be solved.

Concepts: Knee, Knee cartilage replacement therapy, Bone, Articular cartilage repair, Extracellular matrix, Organ transplant, Autologous chondrocyte implantation, Cartilage

3

For a long time, cartilage has been a major focus of the whole field of tissue engineering, both because of the constantly growing need for more effective options for joint repair and the expectation that this apparently simple tissue will be easy to engineer. After several decades, cartilage regeneration has proven to be anything but easy. With gratifying progress in our understanding of the factors governing cartilage development and function, and cell therapy being successfully used for several decades, there is still a lot to do. We lack reliable methods to generate durable articular cartilage that would resemble the original tissue lost to injury or disease. The question posed here is whether the answer would come from the methods using cells, biomaterials, or tissue engineering. We present a concise review of some of the most meritorious efforts in each area, and propose that the solution will most likely emerge from the ongoing attempts to recapitulate certain aspects of native cartilage development. While an ideal recipe for cartilage regeneration is yet to be formulated, we believe that it will contain cell, biomaterial, and tissue engineering approaches, blended into an effective method for seamless repair of articular cartilage.

Concepts: Materials science, Engineering, Knee cartilage replacement therapy, Biocompatibility, Tissue engineering, Biomaterial, Cartilage, Extracellular matrix

3

Mesenchymal stem cells (MSCs) have emerged as a promising option to treat articular defects and early osteoarthritis (OA) stages. However, both their potential and limitations for a clinical use remain controversial. Thus, the aim of this systematic review was to examine MSCs treatment strategies in clinical settings, in order to summarize the current evidence of their efficacy for the treatment of cartilage lesions and OA.Among the 60 selected studies, 7 were randomized, 13 comparative, 31 case series, and 9 case reports; 26 studies reported the results after injective administration, whereas 33 used surgical implantation. One study compared the two different modalities. With regard to the cell source, 20 studies concerned BMSCs, 17 ADSCs, 16 BMC, 5 PBSCs, 1 SDSCs, and 1 compared BMC versus PBSCs. Overall, despite the increasing literature on this topic, the evidence is still limited, in particular for high-level studies. On the other hand, the available studies allow to draw some indications. First, no major adverse events related to the treatment or to the cell harvest have been reported. Second, a clinical benefit of using MSCs therapies has been reported in most of the studies, regardless of cell source, indication, or administration method. This effectiveness has been reflected by clinical improvements and also positive MRI and macroscopic findings, whereas histologic features gave more controversial results among different studies. Third, young age, lower BMI, smaller lesion size for focal lesions, and earlier stages of OA joints have been shown to correlate with better outcomes, even though the available data strength does not allow to define clear cutoff values. Finally, definite trends can be observed with regard to the delivery method: currently cultured cells are mostly being administered by i.a. injection, while one-step surgical implantation is preferred for cell concentrates. In conclusion, while promising results have been shown, the potential of these treatments should be confirmed by reliable clinical data through double-blind, controlled, prospective and multicenter studies with longer follow-up, and specific studies should be designed to identify the best cell sources, manipulation, and delivery techniques, as well as pathology and disease phase indications.

Concepts: Knee cartilage replacement therapy, Bone marrow, Articular cartilage repair, Knee, Cartilage, Mesenchyme, Mesenchymal stem cell, Stem cell

1

Partial joint repair is a surgical procedure where an artificial material is used to replace localised chondral damage. These artificial bearing surfaces must articulate against cartilage, but current materials do not replicate both the biphasic and boundary lubrication mechanisms of cartilage. A research challenge therefore exists to provide a material that mimics both boundary and biphasic lubrication mechanisms of cartilage. In this work a polymeric network of a biomimetic boundary lubricant, poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), was incorporated into an ultra-tough double network (DN) biphasic (water phase + polymer phase) gel, to form a PMPC triple network (PMPC TN) hydrogel with boundary and biphasic lubrication capability. The presence of this third network of MPC was confirmed using ATR-FTIR. The PMPC TN hydrogel had a yield stress of 26 MPa, which is an order of magnitude higher than the peak stresses found in the native human knee. A preliminary pin on plate tribology study was performed where both the DN and PMPC TN hydrogels experienced a reduction in friction with increasing sliding speed which is consistent with biphasic lubrication. In the physiological sliding speed range, the PMPC TN hydrogel halved the friction compared to the DN hydrogel indicating the boundary lubricating PMPC network was working. A biocompatible, tough, strong and chondral lubrication imitating PMPC TN hydrogel was synthesised in this work. By complementing the biphasic and boundary lubrication mechanisms of cartilage, PMPC TN hydrogel could reduce the reported incidence of chondral damage opposite partial joint repair implants, and therefore increase the clinical efficacy of partial joint repair.

Concepts: Materials science, Knee cartilage replacement therapy, Cartilage, Lubricant, Lubrication, Boundary lubrication, Tribology, Knee

1

Articular cartilage injuries experienced at an early age can lead to the development of osteoarthritis later in life. In situ 3D printing is an exciting and innovative bio-fabrication technology that enables the surgeon to deliver tissue- engineering techniques at the time and location of need. We have created a hand- held 3D printing device (Biopen) that allows the simultaneous co-axial extrusion of bioscaffold and cultured cells directly into the cartilage defect in vivo in a single session surgery. This pilot study assesses the ability of the Biopen to repair a full thickness chondral defect and the early outcomes in cartilage regeneration, and compares these results to other treatments in a large animal model. A standardised critical-sized full thickness chondral defect was created in the weight-bearing surface of the lateral and medial condyles of both femurs of 6 sheep. Each defect was treated with one of the following treatments: (i) hand- held in situ 3D printed bioscaffold using the Biopen (HH group), (ii) pre- constructed bench-based printed bioscaffolds (BB group), (iii) micro-fractures (MF group) or (iv) untreated (Control, C group). At 8 weeks after surgery, macroscopic, microscopic and biomechanical tests were performed. Surgical 3D bio-printing was performed in all animals without any intra- or post- operative complication. The HH Biopen allowed early cartilage regeneration. Results of this study show that real-time, in vivo bioprinting with cells and scaffold is a feasible means of delivering a regenerative medicine strategy in a large animal model to regenerate articular cartilage. This article is protected by copyright. All rights reserved.

Concepts: Carcinoma in situ, Knee cartilage replacement therapy, Regeneration, Articular cartilage repair, In vivo, In situ, Surgery, Cartilage