Cartilage repair in terms of replacement, or regeneration of damaged or diseased articular cartilage with functional tissue, is the ‘holy grail’ of joint surgery. A wide spectrum of strategies for cartilage repair currently exists and several of these techniques have been reported to be associated with successful clinical outcomes for appropriately selected indications. However, based on respective advantages, disadvantages, and limitations, no single strategy, or even combination of strategies, provides surgeons with viable options for attaining successful long-term outcomes in the majority of patients. As such, development of novel techniques and optimisation of current techniques need to be, and are, the focus of a great deal of research from the basic science level to clinical trials. Translational research that bridges scientific discoveries to clinical application involves the use of animal models in order to assess safety and efficacy for regulatory approval for human use. This review article provides an overview of animal models for cartilage repair. Cite this article: Bone Joint Res 2014;4:89–94

Aims

The aim of this study was to report the outcome of femoral condylar fresh osteochondral allografts (FOCA) with concomitant realignment osteotomy with a focus on graft survivorship, complications, reoperation, and function.

In relation to regenerative therapies in osteoarthritis and cartilage repair, mesenchymal stromal cells (MSCs) have immunomodulatory functions and influence macrophage behaviour. Macrophages exist as a spectrum of pro-(M1) and anti-(M2) inflammatory phenotypic subsets. In the context of cartilage repair, we investigated MSC-macrophage crosstalk, including specifically the priming of cartilage cells by macrophages to achieve a regenerative rather than fibrotic outcome. Human monocytes were isolated from blood cones and differentiated towards M1 and M2 macrophages. Monocytes (Mo), M1 and M2 macrophages were cultured directly and indirectly (trans-well system) with human bone marrow derived MSCs. MSCs were added during M1 polarisation and separately to already induced M1 cells. Outcomes (M1/M2 markers and ligands/receptors) were evaluated using RT-qPCR and flow cytometry. Influence on chondrogenesis was assessed by applying M1 and M2 macrophage conditioned media (CM) sequentially to cartilage derived cells (recapitulating an acute injury environment). RT-qPCR was used to evaluate chondrogenic/fibrogenic gene transcription. The ratio of M2 markers (CD206 or CD163) to M1 markers (CD38) increased when MSCs were added to Mo/M1 macrophages, regardless of culture system used (direct or indirect). Pro-inflammatory markers (including TNFβ) decreased. CXCR2 expression by both M1 macrophages and MSCs decreased when MSCs were added to differentiated M1 macrophages in transwell. When adding initially M1 CM (for 12 hours) followed by M2 CM (for 12 hours) sequentially to chondrocytes, there was a significant increase of Aggrecan and Collagen type 2 gene expression and decrease in fibroblastic cell surface markers (PDPN/CD90). Mo/M1 macrophages cultured with MSCs, directly or indirectly, are shifted towards a more M2 phenotype. Indirect culture suggests this effect can occur via soluble signaling mediators. Sequential exposure of M1CM followed by M2CM to chondrocytes resulted in increased chondrogenic and reduced fibrotic gene expression, suggesting that an acute pro-inflammatory stimulus may prime chondrocytes before repair

Abstract. Objectives. In relation to regenerative therapies in osteoarthritis and cartilage repair, mesenchymal stromal cells (MSCs) have immunomodulatory functions and influence macrophage behaviour. Macrophages exist as a spectrum of pro-(M1) and anti-(M2) inflammatory phenotypic subsets. In the context of cartilage repair, we investigated MSC-macrophage crosstalk, including specifically the priming of cartilage cells by macrophages to achieve a regenerative rather than fibrotic outcome. Methods. Human monocytes were isolated from blood cones and differentiated towards M1 and M2 macrophages. Monocytes (Mo), M1 and M2 macrophages were cultured directly and indirectly (trans-well system) with human bone marrow derived MSCs. MSCs were added during M1 polarisation and separately to already induced M1 cells. Outcomes (M1/M2 markers and ligands/receptors) were evaluated using RT-qPCR and flow cytometry. Influence on chondrogenesis was assessed by applying M1 and M2 macrophage conditioned media (CM) sequentially to cartilage derived cells (recapitulating an acute injury environment). RT-qPCR was used to evaluate chondrogenic/fibrogenic gene transcription. Results. The ratio of M2 markers (CD206 or CD163) to M1 markers (CD38) increased when MSCs were added to Mo/M1 macrophages, regardless of culture system used (direct or indirect). Pro-inflammatory markers (including TNFa) decreased. CXCR2 expression by both M1 macrophages and MSCs decreased when MSCs were added to differentiated M1 macrophages in transwell. When adding initially M1 CM (for 12 hours) followed by M2 CM (for 12 hours) sequentially to chondrocytes, there was a significant increase of Aggrecan and Collagen type 2 gene expression and decrease in fibroblastic cell surface markers (PDPN/CD90). Conclusions. Mo/M1 macrophages cultured with MSCs, directly or indirectly, are shifted towards a more M2 phenotype. Indirect culture suggests this effect can occur via soluble signaling mediators. Sequential exposure of M1CM followed by M2CM to chondrocytes resulted in increased chondrogenic and reduced fibrotic gene expression, suggesting that an acute pro-inflammatory stimulus may prime chondrocytes before repair. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Multiple biochemical biomarkers have been previously investigated for the diagnosis, prognosis and response to treatment of articular cartilage damage, including osteoarthritis (OA). Synovial fluid (SF) biomarker measurement is a potential method to predict treatment response and effectiveness. However, the significance of different biomarkers and their correlation to clinical outcomes remains unclear. This systematic review evaluated current SF biomarkers used in investigation of cartilage degeneration or regeneration in the knee joint and correlated these biomarkers with clinical outcomes following cartilage repair or regeneration interventions. PubMed, Institute of Science Index, Scopus, Cochrane Central Register of Controlled Trials, and Embase databases were searched. Studies evaluating SF biomarkers and clinical outcomes following cartilage repair intervention were included. Two researchers independently performed data extraction and QUADAS-2 analysis. Biomarker inclusion, change following intervention and correlation with clinical outcome was compared. 9 studies were included. Study heterogeneity precluded meta-analysis. There was significant variation in sampling and analysis. 33 biomarkers were evaluated in addition to microRNA and catabolic/anabolic ratios. Five studies reported on correlation of biomarkers with six biomarkers significantly correlated with clinical outcomes following intervention. However, correlation was only demonstrated in isolated studies. This review demonstrates significant difficulties in drawing conclusions regarding the importance of SF biomarkers based on the available literature. Improved standardisation for collection and analysis of SF samples is required. Future publications should also focus on clinical outcome scores and seek to correlate biomarkers with progression to further understand the significance of identified markers in a clinical context

Varus malalignment increases the susceptibility of cartilage to mechanical overloading, which stimulates catabolic metabolism to break down the extracellular matrix and lead to osteoarthritis (OA). The altered mechanical axis from the hip, knee to ankle leads to knee joint pain and ensuing cartilage wear and deterioration, which impact millions of the aged population. Stabilization of the remaining damaged cartilage, and prevention of further deterioration, could provide immense clinical utility and prolong joint function. Our previous work showed that high tibial osteotomy (HTO) could shift the mechanical stress from an imbalanced status to a neutral alignment. However, the underlying mechanisms of endogenous cartilage stabilization after HTO remain unclear. We hypothesize that cartilage-resident mesenchymal stem cells (MSCs) dampen damaged cartilage injury and promote endogenous repair in a varus malaligned knee. The goal of this study is to further examine whether HTO-mediated off-loading would affect human cartilage-resident MSCs' anabolic and catabolic metabolism. This study was approved by IACUC at Xi'an Jiaotong University. Patients with medial compartment OA (52.75±6.85 yrs, left knee 18, right knee 20) underwent open-wedge HTO by the same surgeons at one single academic sports medicine center. Clinical data was documented by the Epic HIS between the dates of April 2019 and April 2022 and radiographic images were collected with a minimum of 12 months of follow-up. Medial compartment OA with/without medial meniscus injury patients with unilateral Kellgren /Lawrence grade 3–4 was confirmed by X-ray. All incisions of the lower extremity healed well after the HTO operation without incision infection. Joint space width (JSW) was measured by uploading to ImageJ software. The Knee injury and Osteoarthritis Outcome Score (KOOS) toolkit was applied to assess the pain level. Outerbridge scores were obtained from a second-look arthroscopic examination. RNA was extracted to quantify catabolic targets and pro-inflammatory genes (QiaGen). Student's t test for two group comparisons and ANOVA analysis for differences between more than 2 groups were utilized. To understand the role of mechanical loading-induced cartilage repair, we measured the serial changes of joint space width (JSW) after HTO for assessing the state of the cartilage stabilization. Our data showed that HTO increased the JSW, decreased the VAS score and improved the KOOS score significantly. We further scored cartilage lesion severity using the Outerbridge classification under a second-look arthroscopic examination while removing the HTO plate. It showed the cartilage lesion area decreased significantly, the full thickness of cartilage increased and mechanical strength was better compared to the pre-HTO baseline. HTO dampened medial tibiofemoral cartilage degeneration and accelerate cartilage repair from Outerbridge grade 2 to 3 to Outerbridge 0 to 1 compared to untreated varus OA. It suggested that physical loading was involved in HTO-induced cartilage regeneration. Given that HTO surgery increases joint space width and creates a physical loading environment, we hypothesize that HTO could increase cartilage composition and collagen accumulation. Consistent with our observation, a group of cartilage-resident MSCs was identified. Our data further showed decreased expression of RUNX2, COL10 and increased SOX9 in MSCs at the RNA level, indicating that catabolic activities were halted during mechanical off-loading. To understand the role of cartilage-resident MSCs in cartilage repair in a biophysical environment, we investigated the differentiation potential of MSCs under 3-dimensional mechanical loading conditions. The physical loading inhibited catabolic markers (IL-1 and IL-6) and increased anabolic markers (SOX9, COL2). Knee-preserved HTO intervention alleviates varus malalignment-related knee joint pain, improves daily and recreation function, and repairs degenerated cartilage of medial compartment OA. The off-loading effect of HTO may allow the mechanoregulation of cartilage repair through the differentiation of endogenous cartilage-derived MSCs

Hyaline articular cartilage has been known to be a troublesome tissue to repair once damaged. Since the introduction of autologous chondrocyte implantation (ACI) in 1994, a renewed interest in the field of cartilage repair with new repair techniques and the hope for products that are regenerative have blossomed. This article reviews the basic science structure and function of articular cartilage, and techniques that are presently available to effect repair and their expected outcomes

Although cartilage repair has been around since the time of open Pridie drilling, clinical outcomes for newer techniques such as arthroscopic debridement, microfracture (MFX), osteochondral autograft transfers (OATS), osteochondral allograft transplantation and Autologous Chondrocyte Implantation (ACI) are still finding their place in treating injured knees. Early mechanical symptoms are best managed by a gentle arthroscopic debridement of loose articular flaps. This allows the surgeon to assess the defect size, location in the tibio-femoral or patellofemoral joint, status of the cartilage overall and patients response to the intervention. If the symptom improvement is not satisfactory to the patient, after assessing background factors that will influence the results of a cartilage repair procedure, (alignment of the patellofemoral joint or axial alignment, ligament stability and status of the meniscus), the surgeon can choose the best procedure for that individual based on the expected outcomes of the various cartilage repair techniques while addressing the background factors. As all the techniques have failures and informed discussion with the patient prior to performing the procedure is critical in avoiding disappointment for the patient and the surgeon. The repair technique used should incorporate considerations of the defect size, location, and the patient age, activity level, expectations and ability to comply with the longer rehabilitation needed for biological procedures as compared to prosthetic implants

Background. Microfracture (MF) and Autologous Chondrocyte Implantation (ACI) are used to repair symptomatic condylar cartilage defects (grade II-IV Outerbridge). Superiority of ACI to MF is still debated. The aim of the study was to conduct a systematic literature review, compare superiority of ACI versus MF in a meta-analysis and investigate the correlation between patient age and outcome of both treatments. Methods. Extended literature search was conducted (papers from January 2001 to present), looking at patient characteristics, pre- and post-operative scores and cartilage repair assessment evaluation. Methodological quality was verified through modified Coleman score and assessment bias. A fixed-effect meta-analysis was conducted, comparing post-operative standardised mean differences between ACI and MF. Pearson correlation coefficient between post-operative score and age was calculated against ACI and MF. Results. of 490 studies systematically analysed, 8 met the inclusion criteria, accounting for 255 patients treated with ACI and 259 with MF. Overall mean postoperative scores were 81.38±8.31 for ACI and 74.9±7.0 for MF, with no significant difference (p=0.13). The average modified Coleman score of the studies was 82.6, with low bias among them. The meta-analysis displayed an overall effect estimate of 0.3 favouring ACI treatment versus MF (95%CI=0.12–0.48, P=0.001). Significant heterogeneity was although observed (I2>70%). Pearson correlation coefficient calculated between mean post-operative score and mean age, surprisingly failed to indicate clear correlation for ACI (r=0.11) and MF (r=0.18) respectively. Conclusions. Minor statistically significant superiority of ACI intervention versus MF in knee cartilage repair was found, together with high levels of heterogeneity, halting the possibility to make full recommendation of ACI versus MF. Level of Evidence. Ia (systematic review and meta-analysis)

Aims. Implantation of ultra-purified alginate (UPAL) gel is safe and effective in animal osteochondral defect models. This study aimed to examine the applicability of UPAL gel implantation to acellular therapy in humans with cartilage injury. Methods. A total of 12 patients (12 knees) with symptomatic, post-traumatic, full-thickness cartilage lesions (1.0 to 4.0 cm. 2. ) were included in this study. UPAL gel was implanted into chondral defects after performing bone marrow stimulation technique, and assessed for up to three years postoperatively. The primary outcomes were the feasibility and safety of the procedure. The secondary outcomes were self-assessed clinical scores, arthroscopic scores, tissue biopsies, and MRI-based estimations. Results. No obvious adverse events related to UPAL gel implantation were observed. Self-assessed clinical scores, including pain, symptoms, activities of daily living, sports activity, and quality of life, were improved significantly at three years after surgery. Defect filling was confirmed using second-look arthroscopy at 72 weeks. Significantly improved MRI scores were observed from 12 to 144 weeks postoperatively. Histological examination of biopsy specimens obtained at 72 weeks after implantation revealed an extracellular matrix rich in glycosaminoglycan and type II collagen in the reparative tissue. Histological assessment yielded a mean overall International Cartilage Regeneration & Joint Preservation Society II score of 69.1 points (SD 10.4; 50 to 80). Conclusion. This study provides evidence supporting the safety of acellular UPAL gel implantation in facilitating cartilage repair. Despite being a single-arm study, it demonstrated the efficacy of UPAL gel implantation, suggesting it is an easy-to-use, one-step method of cartilage tissue repair circumventing the need to harvest donor cells. Cite this article: Bone Joint J 2023;105-B(8):880–887

Osteoarthritis (OA) of the spine and diarthrodial joints is by far the most common cause of chronic disability in people over 50 years of age. The disease has a striking impact on quality of life and represents an enormous societal and economic cost, a burden that will increase greatly as populations age. OA is a complex condition with broad pathology. Damage to the articular cartilage is a consistent feature, accompanied by changes to the subchondral bone and synovium. Progression of the disease involves further degeneration of the articular cartilage, damage to the underlying bone and morphological changes that include subchondral bone thickening, development of cysts, osteophytes and inflammation of the synovium. Enhanced production of proinflammatory cytokines and matrix metalloproteinases accelerates degradation of the articular cartilage. It is striking that no approved pharmacological intervention, biological therapy or procedure prevents the progressive destruction of the OA joint. All current treatments, without exception, produce symptomatic rather than regenerative results. While there have been some exciting developments in the search for OA treatments in the last decade, including matrix metalloproteinase inhibitors, anti-TNF and anti-IL1 drugs for example, none of these has to date emerged as an effective medicinal product. There is thus an urgent and compelling need to identify, validate and test new biological therapeutics. Stromal cell therapy represents one such compelling approach. The results from several early clinical studies have indicated that this approach holds a great deal of promise for the treatment of OA. Most studies have involved direct intraarticular injection of a suspension of mesenchymal stromal cells (MSCs) for treatment of knee OA. Results from a number of controlled patient studies have suggested that this treatment results in an effective repair response. Although data regarding mechanism of action are limited, it appears that the cells have an anti-inflammatory effect, possibly targeting cells within the synovium, rather than a direct cartilage repair effect. Several recent reports have highlighted a dramatic and sustained response in patients receiving MSC treatment. For example, allogeneic expanded adipose-derived MSCs have been shown to be safe and effective in the treatment of complex perianal fistulas in Crohn's disease. Also, allogeneic bone marrow-derived MSCs has a been shown to have a positive effect in pediatric acute graft versus host disease. These observations point to a mechanism of action that involves host immunomodulation, but this needs further examination. Within the field of musculoskeletal disease effective translation of MSC technology has been hindered by a lack of randomized controlled patient studies, severe inconsistencies regarding the preparation and characterization of the cell product, and an incomplete understanding of the therapeutic mechanism. Direct to consumer clinics have flourished in some countries, providing cell treatments to OA patients. Most or all of these utilize unexpanded cell fractions from marrow or fat without even rudimentary product characterization and may report an exaggerated clinical outcome. Data from these clinics is not likely to yield information that will be useful. In fact, a recent systemic review of clinical trials involving MSC treatment in OA indicated that only a limited number of studies provided high quality evidence and long term follow up. Many suffered from a lack of consistency, including a diversity of methods for MSC preparation, and thus did not contribute to a supporting evidence base. There is a compelling need to provide clear and unambiguous clinical proof of concept relating to MSC treatment for OA. The ADIPOA2 study, currently active in Europe, will go some way towards achieving this. This is a 150 patient, phase 2b study designed to to assess the efficacy of a single injection of autologous adipose-derived MSCs in the treatment of mild to moderate OA of the knee, active and unresponsive to conservative therapy for at least 12 months

Articular cartilage repair is assumed to improve by covering the cartilage lesion with a biomaterial scaffold tailored to the specific requirements of the weight-bearing joint surface. We have tested the feasibility of a novel composite collagen-polylactide scaffold rhCo-PLA in cartilage repair. To confirm these results and further challenge the scaffold, we tested it in a large porcine cartilage defect. A critical-sized full-thickness chondral defect was made in the medial femoral condyle of 18 domestic pigs. This technically widest possible defect size of 11×17 mm was determined in a pilot test. Five weeks later, the defect was either treated with the novel rhCo-PLA scaffold or left untreated to heal spontaneously. After four months, the medial condyles were evaluated macroscopically using Goebel's score, in which the worst possible result receives a total of 20 points and imaged with µCT to evaluate subchondral bone. Macroscopic score and subchondral bone microstructure were similar in both study groups. The total Goebel score was higher in spontaneous group (9.75±3.9 for spontaneous and 9.1±3.7 for rhCo-PLA, respectively) but differences between individual animals were large. Subchondral bone volume fraction was 48.2±3.6% for rhCo-PLA and 44.2±3.4% for spontaneous. Trabecular thickness was greater in operated joints (207.9±18.8 µm for spontaneous and 242.9±32.9 µm for rhCo-PLA) than in contralateral non-operated joints (193.3±15.1 µm and 213.4±33.2 µm, respectively). These preliminary data demonstrate that individual differences in the macroscopic appearance were large but there were no significant differences between the two study groups in the score or subchondral bone structure

The parameters to be considered in the selection of a cartilage repair strategy are: the diameter of the chondral defect; the depth of the bone defect; the location of the defect (weight bearing); alignment. A chondral defect less than 3 cm in diameter can be managed by surface treatment such as microfracture, autologous chondrocyte transplantation, mosaicplasty, or periosteal grafting. An osteochondral defect less than 3 cm in diameter and less than 1 cm in depth can be managed by autologous chondrocyte transplantation, mosaicplasty or periosteal grafting. An osteochondral defect greater than 3 cm in diameter and 1 cm in depth is best managed by an osteochondral allograft. If there is an associated knee deformity, then an osteotomy should also be performed with all of the aforementioned procedures. In our series of osteochondral allografts for large post-traumatic knee defects realignment osteotomy is performed about 60% of the time in order to off load the transplant. To correct varus we realign the proximal tibia with an opening wedge osteotomy. To correct valgus, we realign the distal femur with a closing wedge osteotomy. Our results with osteochondral allografts for the large osteochondral defects of the knee have been excellent in 85% of patients at an average follow-up of 10 years. The Kaplan-Meier survivorship at 15 years is 72%. At an average follow-up of 22 years in 58 patients with distal femoral osteochondral allograft, 13 have been revised (22%). The 15-year survivorship was 84%. The results for the hip are early. To date we have performed this procedure on 16 patients. Surgical dislocation of the hip is carried out via a trochanteric osteotomy and the defect defined and trephined out. A press-fit fresh osteochondral allograft is inserted using the trephine technique. We have published our early results on a series of 8 patients with 5 good to excellent results, 1 fair result and 2 failures

Hyaline cartilage defects are a significant clinical problem for which a plethora of cartilage repair techniques are used. One such technique is cartilage replacement therapy using autologous chondrocyte or mesenchymal stem cell (MSC) implantation (ACI). Mesenchymal stem cells are increasingly being used for these types of repair technique because they are relatively easy to obtain and can be expanded to generate millions of cells. However, implanted MSCs can terminally differentiate and produce osteogenic tissue which is highly undesirable, also, MSCs generally only produce fibrocartilage which does not make biomechanically resilient repair tissue, an attribute that is crucial in high weight-bearing areas. Tissue-specific adult stem cells would be ideal candidates to fill the void, and as we have shown previously in animal model systems [Dowthwaite et al, 2004, J Cell Sci 117;889], they can be expanded to generate hundreds of millions of cells, produce hyaline cartilage and they have a restricted differential potential. Articular chondroprogenitors do not readily terminally differentiate down the osteogenic lineage. At present, research focused on isolating tissue-specific stem cells from articular cartilage has met with modest success. Our results demonstrate that using differential adhesion it is possible to easily isolate articular cartilage progenitor populations from human hyaline cartilage and that these cells can be subsequently expanded in vitro to a high population doubling whilst maintaining a normal karyotype. Articular cartilage progenitors maintain telomerase activity and telomere length that are a characteristic of progenitor/stem cells and differentiate to produce hyaline cartilage. In conclusion, we propose the identification and characterisation of a novel articular cartilage progenitor population, resident in human cartilage, which will greatly benefit future cell-based cartilage repair therapies

The past ten years have brought plenty of research and technical innovations and also preliminary clinical success in cartilage repair. The common target of all methods utilised is to produce a sufficiently stable quality of cartilage repair or regenerate. However, yet today clinical, radiological and histological results analysing the different techniques are somewhat contradictory. The different lines of clinically applied and basic research have focused on:. 1) Spontaneous natural filling of the defect with fibro-cartilage of variable solidity. - Abrasion chondroplasty, drilling or microfracturing to allow for mobilisation of progenitor cells and mesenchymal stem cells from the cancellous bone into the defect and develop to a hyaline like cartilage. - Stem cell treatment (in vivo or ex vivo theory of potential technique by which stem cells could be brought to a defect to create cartilage; so far no directly linked product available). 2) Transplantation of osteochondral auto grafts (Mosaicplasty, OATS, SDS, patellar graft) or allograft. 3a) Autologous chondrocyte transplantation and periosteal coverage (ACT) to cover bigger surfaces. 3b) Implantation of second and third generation ex vivo products and create less morbidity but without knowing whether the results are as long-lasting as for the originally described technique (chondrocytes cultured on membranes, MACI, in gels, implantation of a stable three-dimensional de novo cartilage disk or even engineered osteochondral grafts, AMIC: autologous membrane induced chondrogenesis). A fair amount of today’s laboratory research is focusing on the culture of the patients own chondrocytes or his own stem cells. Clinically, some methods can be applied in all indications regardless of size, localisation, depth of the lesion up to the age of fifty years and this is valid for lesions in the knee, the shoulder, the talus, the elbow etc. Other methods like AOCT should not be used for lesions over 2cm in diameter because of donor side morbidity. All methods claim to have an 85% outcome success rate. Regarding the histological content of the successful implants or the reformed cartilage, microfracturing produces a cartilage implant containing a fibrocartilage that looks similar to the hyaline like cartilage of ACI at two years. Mosaicplasty plugs provided great care is applied during insertion avoiding damage of the cylinders and cartilage death-a special instrumentation has been developed with ZIMMER, the Soft Delivery System, SDS to avoid force during impaction. They remain hyaline provided they are inserted without being prone or deep sunken and the surface convexity of the femoral condyle is restored and provided they are inserted tightly next to each other. There is agreement that this is more difficult in arthroscopic techniques. One agrees also that results are dependent on the alignment of the limb. If the compartment treated is overloaded, there is less chance for integration. Osteotomy has therefore a solid position in the armamentarium of the cartilage surgeon- up to 50% of our cases get an osteotomy as part of their treatment regardless of which technique is utilised. As complications in autologous osteochondral grafting we may observe destruction of the hyaline cartilage cap, non integration and pseudarthrosis or fractures of the cylinders (of special risk are smokers), especially when grafts are not inserted tightly to each other and there is lack of stability with fluid leakage out of the cartilage caps. Rarely ossification of the cartilage is observed when a thin capped cylinder retrieved in the peripheral zone of the femoral trochlea is implanted in an area of thick cartilage as in the centre of the patella where the cartilage is 5 mm thick. Donor site pathology in mosaicplasty is an issue of concern mainly if more than six plugs are removed from the femoropatellar joint. This alone can create clinical symptoms. Nicotine abuse, probably for all techniques decreases the rate of success of cartilage repair or regeneration and osteotomy healing. Roughly 300 cases have been treated during the last 10 years. The results were reported in 2002. As an alternate single surgery technique to microfracturing and mosaicplasty we adopted the “Autologous membrane induced chondrogenesis” (AMIC) technique proposed by Behrens that we find especially useful in OCD. In this relatively young technique we curette the defect and apply microfractures to the basis of the osseous defect. Then we gain cancellous bone from the tibial plateau and mix it with fibrin glue, of which 50% of the thrombin portion is replaced by the serum of the patient as a source of growth factor. This paste of bone and enriched fibrin glue is filled in the defect which is then covered by the porcine Chondrogide membrane (Geistlich) that is glued on and which we can as well suture to the defect. The AMIC technique in combination with microfractures can be utilised for the coverage of pure cartilage defects alone where the membrane is glued alone or fixed on the defect in combination with 5-0 resorbable sutures. In the first two weeks following surgery, after treatment is very defensive to avoid loss of the membrane. After two months of crutch walking with 15 kg of weight we observe a nice osseous integration of the graft and a covering layer that looks promising. After 4–6 months activity can be increased depending on the size of the defect. This is a young technique that we adopted in mid 2003 with 30 cases treated so far, therefore strict observation is required over the upcoming years regarding clinical results and durability and also the composition of this neocartilage. So far it seems to be an interesting alternative to Mosaicplasty since it combines principles of cell therapy with an artificial and instant biological containment that acts against the loss of cells thus acting as a internal bioreactor with the patients own growth factor support

PURPOSE. Recently, in tissue engineering several methods using stem cells have been developed to repair chondral and osteochondral defects. Most of these methods rely on the use of scaffolds. Studies in the literature have demonstrated, first in animals and then in humans, that the use of mesenchymal stem cells withdrawn by several methods from adipose tissue allows to regenerate hyaline articular cartilage. In fact, it has been cleared that adipose-derived cells have multipotentiality equivalent to bone marrow-derived stem cells and that they can very easily and very quickly be isolated in large amounts enabling their immediate use in operating room for one-step cartilage repair techniques. The purpose of this study is to evaluate the therapeutic effect of adipose-derived stem cells on cartilage repair and present our experience in the treatment of knee cartilage defects by the novel AMIC REPAIR TECHNIQUE AUGMENTED by immersing the collagen scaffold with mesenchymal stem cells withdrawn from adipose tissue of the abdomen. MATERIALS AND METHODS. Fat tissue processing involves mechanical forces and does not mandatorily require any enzymatic or chemical treatment in order to obtain the regenerative cells from the lipoaspirate. In our study, mesenchymal adipose stem cells were obtained by non-enzymatic filtration or microfragmentation of lipoaspirates of the abdomen adipose tissue that enabled the separation of the stromal vascular fraction and were used in one-step reconstruction of knee cartilage defects by means of this new AUGMENTED AMIC TECHNIQUE. The focal defects underwent bone marrow stimulation microfractures, followed by coverage with collagen double layer resorbable membrane (Chondro-gide. TM. -Geistlich Pharma AG, Wolhusen, Switzerland) soaked in the cells obtained from fat in 18 patients, aged between 31 and 58 years, at the level of the left knee in 10 cases and in the right in eight, with follow-up ranging between 12 and 36 months. RESULTS: Surgical procedures have been completed without technical problems neither intraoperative or early postoperative complications. The evaluation scores (IKDC, KOOS and VAS) showed a significant improvement, more than 30%, at the initial 6 months follow-up and furtherly improved in the subsequent follow-ups. Also the control MRIs showed a progressive filling and maturation of the repair tissue of the defects. CONCLUSIONS. Since we are reporting a short and medium-term experience, it is not, of course, possible to provide conclusive assessment considerations on this technique, as the experience has to mature along with the progression of follow-ups. The simplicity together with the absence of intraoperative difficulties or immediate complications and the experience gained by other authors, first in animals and then in early clinical cases, makes it, however, possible to say that this can be considered one of the techniques to which resort for one-step treatment of cartilage defects in the knee because it improves patient's conditions and has the potential to regenerate hyaline-like cartilage. Future follow-up works will confirm the results

Introduction: Chondral injuries of the knee are commonly seen at arthroscopy, yet there is no consensus on the most appropriate treatment method. However, untreated cartilage injury predisposes to osteoarthritis contributing to pain and disability. For cell-based cartilage repair strategies, an ex vivo expansion phase is required to obtain sufficient cells for therapeutic intervention. Although recent reports demonstrated the central role of oxygen in the function and differentiation of chondrocytes, little is known of the effect of physiological low oxygen concentrations during the expansion of the cells and whether this alters their chondrogenic capacity. Methods: Articular mouse chondrocytes were prepared from the distal femoral condyles of adult mice and chondrocytes were liberated by collagenase type II treatment. Cells were cultured in RPMI 1640 media in monolayer under normoxic or hypoxic conditions (5% O2). Chondrogenic potential was subsequently assessed by plating the cells under micromass conditions and glycosaminoglycan deposition was determined by alcian blue staining. Having determined that oxygen tension infiuences murine chondrocyte expansion and differentiation, similar studies were conducted using adult human chondrocytes taken from knee arthroplasty off-cuts, and Aggrecan (ACAN) gene expression was analyzed using real-time quantitative PCR. Results: Cellular morphology of cells from mouse articular cartilage was improved in hypoxic culture, with a markedly more fibroblastic appearance seen after greater than 2 passages in normoxic conditions. Micromass cultures maintained in hypoxic conditions demonstrated stronger staining with alcian blue, indicating stronger expression of cartilage-associated glycosaminoglycans. Expansions of human chondrocytes under hypoxic conditions led to an ~ 2-fold increase in the expression of ACAN in comparison to cells in normoxic conditions. Differentiation of passage 2 chondrocytes under hypoxic conditions also improved the expression of ACAN when compared to culturing under normoxia. Ten day hypoxic cultures exhibited an ~ 5-fold increase in ACAN expression in comparison to normoxic cultures. Interestingly, ACAN expression normoxic-cultured cells could be increased by > 4-fold by transfer to hypoxic conditions. Conclusions: In vivo, the chondrocytes are adapted to an avascular hypoxic environment. Accordingly, applying 5% O2 in the expansion phase in the course of cell-based cartilage repair strategies may more closely mimic the normal chondrocyte microenvironment and may result in a repair tissue with higher quality by increasing the content of glycosaminoglycans

Purpose: Chondral injuries of the knee are commonly seen at arthroscopy, yet there is no consensus on the most appropriate treatment method. However, untreated cartilage injury predisposes to osteoarthritis contributing to pain and disability. For cell-based cartilage repair strategies, an ex-vivo expansion phase is required to obtain sufficient numbers of cells needed for therapy. Although recent reports demonstrated the central role of oxygen for the function and differentiation of chondrocytes, little is known of the effect of physiological low oxygen concentrations during the expansion of the cells and whether this alters their chondrogenic capacity. Method: Initial studies of chondrocyte expansion were performed in mature mice, with cells expanded at either atmospheric oxygen tension (21%) or 5% 02 in monolayer cultures. Chondrogenic differentiation was subsequently assessed via micromass culture. Having determined that oxygen tension influences murine chondrocyte expansion and differentiation, similar studies were conducted using adult human chondrocytes taken from knee arthroplasty off-cuts, with mRNA expression of select genes involved in the chondrogenic program analyzed by q-PCR. Results: Cellular morphology was improved in hypoxic culture, with a markedly more fibroblastic appearance seen after greater than 2 passages in 21% O2. Micromass cultures maintained in hypoxic conditions demonstrated stronger staining with Alcian blue, indicating stronger expression of cartilaginous glycosaminoglycans. Collagen type II mRNA expression was two-fold higher in cells expanded at 5% as compared to expansion at 21% O2. Micromass cultures grown at 21% O2 showed up to a twofold increase in the tissue content of glycosaminoglycans when formed with cells expanded at 5% instead of 21% O2. However, no differences in the mRNA expression or staining for collagen type II protein were observed in these micromass cultures. Hypoxia (5% O2) applied during micromass cultures gave rise to tissues with low contents of glycosaminoglycans. Conclusion: In-vivo, chondrocytes are adapted to a hypoxic environment. Taking this into account, applying 5% O2 in the expansion phase in the course of cell-based cartilage repair strategies, may result in a repair tissue with higher quality by increasing the content of glycosaminoglycans

We aim to assess the clinical and radiological outcome following cartilage repair in the knee using the TruFit plug (Smith & Nephew). Eleven active sporting patients underwent cartilage repair using TruFit plugs between February 2006 and August 2007. Postoperatively patients were touch weight bearing for 2 weeks and partial until 4 weeks. Data was collected prospectively, patients underwent clinical review and completed Lysholm, IKDC subjective, Tegner, KOOS and SF-36 scores pre-operatively and at 6 monthly intervals. One patient has been excluded from the analysis as she emigrated and was lost to follow up. The remaining 10 patients (mean age 35 years (21–49)) had defects on the medial femoral condyle (n=6), lateral femoral condyle (n=3), and lateral trochlea (n=1). Patients received one (n=5), two (n=3) or three (n=2) plugs and four were primary procedures, and six revision procedures (1 failed OATS, 5 failed microfracture). Eight implantations were performed arthroscopically and, and two were mini-open. All patients were reviewed at 12 months, five were reviewed at 18 months and four have also been reviewed at 24 months. Statistically significant improvements from mean pre-operative scores are seen at 12 months; Lysholm (48.3 to 71), IKDC Subjective (37.7 to 65.1), Tegner (2.4 to 4.6), SF36 physical (39.5 to 50.3) and all components of KOOS. These improvements are maintained at the latest follow up. MRI evaluation including T2 mapping demonstrates reformation of the subchondral lamina, resorption of the graft and a similar signal from neo-cartilage as that of adjacent native cartilage. TruFit plugs offer an exciting novel solution for cartilage repair in the knee with advantages of low morbidity and rapid recovery without the need for prolonged non-weight bearing. The implant may be suitable for small lesions only and further prospective study is required to establish long-term outcome

Summary Statement. Hypoxia enhances chondrocyte phenotype of cells migrating from cartilage fragments, thus supporting the use of chondral fragment as a potential cell source for one-stage cartilage repair. Introduction. Minced cartilage fragments are a viable cell source for one stage cartilage repair, as shown in both in preclinical and clinical studies. However, the joint microenvironment, in which the repair process takes place, is hypoxic and no evidences are present in literature regarding the behaviour of cartilage fragments in a hypoxic environment. Aim of the study is to verify if hypoxia could influence chondrocyte outgrowth from cartilage fragments into a Hyaluronic-Acid/fibrin scaffold and evaluate its effects on migrating chondrocyte behaviour, compared to normoxic condition. This could be significant in the perspective of a wide clinical application of human chondral fragments for single stage repair. Materials and methods. Constructs were prepared with minced cartilage fragments harvested from the trochlear region of 20 human young donors during ACL reconstruction, loaded onto a non-woven esterified Hyaluronic-Acid-derivative felt (Hyaff-11) and retained with a coating of fibrin glue (Tisseel). Constructs were cultured either in normoxic or in hypoxic (10% O. 2. ) condition. The growth medium contained DMEM-high-glucose (4500mg/l)with 10% fetal-bovine-serum. After 1 month, construct sections were stained with haematoxylin/eosin and Safranin-O and examined for cell counting. Expression of chondrocyte markers (SOX9, collagen-II, collagen-I), hypoxic markers(HIFs) and proliferative markers (beta-catenin, PCNA) was assessed using immunofluorescence. Results. Migrating cells predominantly showed a spindle-like shape when close to the fragments and a more roundish shape when embedded into the scaffold. A slight decrease in chondrocyte migration and proliferation was observed in hypoxic cultures, albeit not statistically significant. Conversely, an increase in the expression of SOX9, beta-catenin, HIFs, collagen-II (p<0.05) in migrating chondrocytes from hypoxic cultures was shown by immunofluorescence. Discussion/Conclusion. Hypoxia seems to improve the chondrocyte phenotype/behaviour of cell outgrowing from cartilage fragments onto a HA/fibrin scaffold. Moreover, hypoxic condition did not hamper the ability and the mechanisms by which chondrocytes migrate from cartilage fragments and proliferate into the surrounding environment. This is clinically relevant in order to validate one-step repair techniques by means of human cartilage fragments loaded into composite scaffolds