Commercial Products for Osteochondral Tissue Repair and Regeneration.

The osteochondral tissue represents a complex structure composed of four interconnected structures, namely hyaline cartilage, a thin layer of calcified cartilage, subchondral bone, and cancellous bone. Due to the several difficulties associated with its repair and regeneration, researchers have developed several studies aiming to restore the native tissue, some of which had led to tissue-engineered commercial products. In this sense, this chapter discusses the good manufacturing practices, regulatory medical conditions and challenges on clinical translations that should be fulfilled regarding the safety and efficacy of the new commercialized products. Furthermore, we review the current osteochondral products that are currently being marketed and applied in the clinical setting, emphasizing the advantages and difficulties of each one.

Is there a role for stem cells in treating articular injury?

Articular cartilage is a specialized tissue with a high prevalence of injuries. The complex architecture of articular cartilage means that injuries are difficult to treat. The sequelae of such injuries include post-traumatic osteoarthritis. Current treatments include microfracture, microdrilling, osteochondral transplantation and matrix autologous chondral implantation. However, current surgical therapies have a number of disadvantages. Mesenchymal stem cells have been suggested as a potential alternative therapy, with a theoretical ability to regenerate articular cartilage. Research, although positive, is mainly limited to case series, in which the follow up is short to medium term. Stem cells may hold the answer to the age-old problem of articular cartilage injury but more robust evidence is required.

Comparative efficacy of cartilage repair procedures in the knee: a network meta-analysis.

PURPOSE: While numerous randomized controlled trials have compared surgical treatments for cartilage defects of the knee, the comparative efficacy of these treatments is still poorly understood. The goal of this network meta-analysis was to synthesize these randomized data into a comprehensive model allowing pairwise comparisons of all treatment options and treatment rankings based on multiple measures of efficacy. We hypothesized that advanced chondral procedures would have improved outcomes when compared to microfracture. METHODS: The MEDLINE, COCHRANE and EMBASE databases were searched systematically up to January 2015. The primary outcome was re-operation measured at 2, 5 and 10 years. Secondary outcomes included Tegner and Lysholm scores, the presence of hyaline cartilage on post-operative biopsy and graft hypertrophy. A random-effects network meta-analysis was performed, and the results are presented as odds ratios and mean differences with 95 % CIs. We ranked the comparative effects of all treatments with surface under the cumulative ranking probabilities. RESULTS: Nineteen RCT from 15 separate cohorts including 855 patients were eligible for inclusion. No differences were seen in re-operation rates at 2 years. At 5 years osteochondral autografts (OC Auto) had a lower re-operation rate than microfracture (OR 0.03, 95 % CI 0.00-0.49), and at 10 years OC Auto had a lower re-operation rate than microfracture (OR 0.34, 95 % CI 0.12-0.92), but a higher re-operation rate than second-generation ACI (OR 5.81, 95 % CI 2.33-14.47). No significant differences in Tegner or Lysholm scores were seen at 2 years. Functional outcome data at 5 and 10 years were not available. Hyaline repair tissue was more common with OC Auto (OR 16.13, 95 % CI 2.80-92.91) and 2nd generation ACI (OR 7.69, 95 % CI 1.17-50) than microfracture, though the clinical significance of this is unknown. Second-generation ACI (OR 0.12, 95 % CI 0.02-0.59) and MACI (OR 0.13, 95 % CI 0.03-0.59) had significantly lower rates of graft hypertrophy than first-generation ACI. Second-generation ACI, OC Auto and MACI were the highest ranked treatments (in order) when all outcome measures were included. CONCLUSIONS: Microfracture and advanced cartilage repair techniques have similar re-operation rates and functional outcomes at 2 years. However, advanced repair techniques provide higher-quality repair tissue and might afford lower re-operation rates at 5 and 10 years. LEVEL OF EVIDENCE: Meta-analysis studies, Level I.

Autologous tissue transplantations for osteochondral repair.

Articular cartilage forms the articulating surface of synovial joints. Along with the synovial fluid it facilitates near frictionless movement in healthy joints. Injuries to articular cartilage in the knee are frequent and can lead to severe osteoarthritis, which is expected to affect 25% of the adult population by 2030. Hyaline cartilage does not regenerate spontaneously when injured and the current clinical treatment methods suffer from high cost and relatively high failure rates. This calls for new treatment methods to be developed. The backbone of developing new treatment methods for cartilage injuries is a reliable, cost-effective, clinically relevant large animal model. Study 1 aimed at developing such a model. We hypothesized that in the Göttingen minipig, the repair response of a selection of treatment methods would be similar to what is found in a clinical setting, and that two defects per knee, rather than one, could be applied without affecting the repair outcome. We found that the outcomes of the applied treatments were consistent with the outcomes in clinical studies. Furthermore, the use of two defects per knee did not have any significant effect on the repair response. The Göttingen minipig model was easy to handle, cost-effective, and provided a predictable repair response. Based on this study the use of two defects per knee in male Göttingen minipigs is recommended. The model has been implemented as the standard animal model for cartilage research at the Orthopedic Research Laboratory, Aarhus University Hospital. Synthetic osteochondral scaffolds represent an off-the-shelf, one-step treatment method, and preliminary clinical results have been promising. However, MRI investigations have shown issues related to subchondral healing. In study 2 we aimed at evaluating the osteochondral repair in 10 patients treated with the MaioRegen synthetic scaffold. Of the ten patients, two patients were re-operated due to treatment failure. CT imaging revealed that none of the eight remaining patients had complete regeneration of the subchondral bone. At 2.5 years, 6/8 patients had no or very limited (< 10%) bone formation in the defects and 2/8 had 50-75% bone formation in the treated defect. MRI showed no improvement at either one or 2.5 years compared with baseline. Clinical outcome scores were improved at 2.5 years. These results raise serious concerns about the biological repair potential of the MaioRegen scaffold. The use of the MaioRegen scaffold has been discontinued in Denmark as a result of this study. An alternative treatment approach for osteochondral lesions is combined transplantation of autologous bone graft and cartilage fragments, embedded in fibrin glue. In study 3 we investigated the early biological and clinical outcome of autologous dual-tissue transplantation (ADTT). ADTT is a combined autologous bone and cartilage chips transplantation for treatment of osteochondral injuries. It is easily applicable and bypasses the need for costly cell culturing or synthetic materials. After one year, all eight patients had significant improvements on MRI, CT and all clinical outcome scores. This study establishes ADTT as a promising, low-cost, treatment option for osteochondral injuries in the knee. To investigate the role of the implanted cartilage chips, we tested the isolated effect of the chips in the newly developed Göttingen minipig model. In study 4 we compared ADTT with autologous bone graft alone. The hypothesis was that the presence of cartilage chips would improve the quality of the repair tissue. Twelve Göttingen minipigs were included, and follow-up time was six and 12 months. Follow-up consisted of histomorphometry, immunohistochemistry, semi-quantitative scoring and CT. There was significantly more hyaline cartilage in the ADTT group compared with the autologous bone graft group at both six and 12 months. At both six and 12 months there were significantly more fibrocartilage in the ADTT group compared with the ABG group. The presence of cartilage chips in an osteochondral defect facilitated the formation of fibrocartilage as opposed to fibrous tissue at both six and 12 months. This study substantiates the chondrogenic role of cartilage chips in osteochondral defects, but questions the widely accepted repair mechanism involved in cartilage chip treatment methods. Further studies on the repair mechanism(s) involved are needed to improve the clinical application of autologous cartilage chips.

Evaluation of the Early In Vivo Response of a Functionally Graded Macroporous Scaffold in an Osteochondral Defect in a Rabbit Model.

Cartilage tissue engineering is a multifactorial problem requiring a wide range of material property requirements from provision of biological cues to facilitation of mechanical support in load-bearing diarthrodial joints. The study aim was to design, fabricate and characterize a template to promote endogenous cell recruitment for enhanced cartilage repair. A polylactic acid poly-ε-caprolactone (PLCL) support structure was fabricated using laser micromachining technology and thermal crimping to create a functionally-graded open pore network scaffold with a compressive modulus of 9.98 ± 1.41 MPa and a compressive stress at 50% strain of 8.59 ± 1.35 MPa. In parallel, rabbit mesenchymal stem cells were isolated and their growth characteristics, morphology and multipotency confirmed. Sterilization had no effect on construct chemical structure and cellular compatibility was confirmed. After four weeks implantation in an osteochondral defect in a rabbit model to assess biocompatibility, there was no evidence of inflammation or giant cells. Moreover, acellular constructs performed better than cell-seeded constructs with endogenous progenitor cells homing through microtunnels, differentiating to form neo-cartilage and strengthening integration with native tissue. These results suggest, albeit at an early stage of repair, that by modulating the architecture of a macroporous scaffold, pre-seeding with MSCs is not necessary for hyaline cartilage repair.

Intra-articular administration of hyaluronic acid increases the volume of the hyaline cartilage regenerated in a large osteochondral defect by implantation of a double-network gel.

Implantation of PAMPS/PDMAAm double-network (DN) gel can induce hyaline cartilage regeneration in the osteochondral defect. However, it is a problem that the volume of the regenerated cartilage tissue is gradually reduced at 12 weeks. This study investigated whether intra-articular administration of hyaluronic acid (HA) increases the volume of the cartilage regenerated with the DN gel at 12 weeks. A total of 48 rabbits were used in this study. A cylindrical osteochondral defect created in the bilateral femoral trochlea was treated with DN gel (Group DN) or left without any implantation (Group C). In both Groups, we injected 1.0 mL of HA in the left knee, and 1.0 mL of saline solution in the right knee. Quantitative histological evaluations were performed at 2, 4, and 12 weeks, and PCR analysis was performed at 2 and 4 weeks after surgery. In Group DN, the proteoglycan-rich area was significantly greater in the HA-injected knees than in the saline-injected knees at 12 weeks (P = 0.0247), and expression of type 2 collagen, aggrecan, and Sox9 mRNAs was significantly greater in the HA-injected knees than in the saline-injected knees at 2 weeks (P = 0.0475, P = 0.0257, P = 0.0222, respectively). The intra-articular administration of HA significantly enhanced these gene expression at 2 weeks and significantly increased the volume of the hyaline cartilage regenerated by implantation of a DN gel at 12 weeks. This information is important to develop an additional method to increase the volume of the hyaline cartilage tissue in a potential cartilage regeneration strategy using the DN gel.

Subchondral chitosan/blood implant-guided bone plate resorption and woven bone repair is coupled to hyaline cartilage regeneration from microdrill holes in aged rabbit knees.

OBJECTIVE: Little is known of how to routinely elicit hyaline cartilage repair tissue in middle-aged patients. We tested the hypothesis that in skeletally aged rabbit knees, microdrill holes can be stimulated to remodel the bone plate and induce a more integrated, voluminous and hyaline cartilage repair tissue when treated by subchondral chitosan/blood implants. DESIGN: New Zealand White rabbits (13 or 32 months old, N = 7) received two 1.5 mm diameter, 2 mm depth drill holes in each knee, either left to bleed as surgical controls or press-fit with a 10 kDa (distal hole: 10K) or 40 kDa (proximal hole: 40K) chitosan/blood implant with fluorescent chitosan tracer. Post-operative knee effusion was documented. Repair tissues at day 0 (N = 1) and day 70 post-surgery (N = 6) were analyzed by micro-computed tomography, and by histological scoring and histomorphometry (SafO, Col-2, and Col-1) at day 70. RESULTS: All chitosan implants were completely cleared after 70 days, without increasing transient post-operative knee effusion compared to controls. Proximal control holes had worse osteochondral repair than distal holes. Both implant formulations induced bone remodeling and improved lateral integration of the bone plate at the hole edge. The 40K implant inhibited further bone repair inside 50% of the proximal holes, while the 10K implant specifically induced a "wound bloom" reaction, characterized by decreased bone plate density in a limited zone beyond the initial hole edge, and increased woven bone (WB) plate repair inside the initial hole (P = 0.016), which was accompanied by a more voluminous and hyaline cartilage repair (P < 0.05 vs control defects). CONCLUSION: In a challenging aged rabbit model, bone marrow-derived hyaline cartilage repair can be promoted by treating acute drill holes with a biodegradable subchondral implant that elicits bone plate resorption followed by anabolic WB repair within a 70-day repair period.

Evaluación del cartílago articular mediante técnicas de dignóstico por la imagen / Assessment of joint cartilage using image diagnostic techniques

Se presenta un breve descripción del cartílago hialino, su composición y ultraestructura. Posteriormente, se ofrece una breve revisión del papel de las técnicas de imagen en la evaluación de esta patología. Las secuencias de pulso son las más útiles para la evaluación morfológica de las lesiones cartilaginosas mediante resonancia magnética (RM), presentamos las imágenes que se pueden observar en los intervalos de pre y post-quirúrgicos (AU)

This article briefl y reviews the composition of the hyaline cartilage and its ultrastructure. Subsequently, we offer a brief review of the role of imaging techniques in the assessment of this pathology. These include the most useful pulse sequences for the morphological assessment of cartilaginous injuries using MRI, as well as how these injuries appear in the images, at pre and post-surgical intervals (AU)

Influence of the gel thickness on in vivo hyaline cartilage regeneration induced by double-network gel implanted at the bottom of a large osteochondral defect: short-term results.

BACKGROUND: A double-network (DN) gel, which is composed of poly(2-acrylamido-2-methylpropanesulfonic acid) and poly(N,N'-dimethyl acrylamide), can induce hyaline cartilage regeneration in vivo in a large osteochondral defect. The purpose of this study was to clarify the influence of the thickness of the implanted DN gel on the induction ability of hyaline cartilage regeneration. METHODS: Thirty-eight mature rabbits were used in this study. We created an osteochondral defect having a diameter of 4.3-mm in the patellofemoral joint. The knees were randomly divided into 4 groups (Group I: 0.5-mm thick gel, Group II: 1.0-mm thick gel, Group III: 5.0-mm thick gel, and Group IV: untreated control). Animals in each group were further divided into 3 sub-groups depending on the gel implant position (2.0-, 3.0-, or 4.0-mm depth from the articular surface) in the defect. The regenerated tissues were evaluated with the Wayne's gross and histological grading scales and real time PCR analysis of the cartilage marker genes at 4 weeks. RESULTS: According to the total Wayne's score, when the depth of the final vacant space was set at 2.0 mm, the scores in Groups I, II, and III were significantly greater than that Group IV (p<0.05), although there were no significant differences between Groups I and IV at a 3.0-mm deep vacant space. The expression levels of type-2 collagen in Groups II and III were significantly higher (p<0.05) than that in Group IV. CONCLUSIONS: The 1.0-mm thick DN gel sheet had the same ability to induce hyaline cartilage regeneration as the 5.0-mm thick DN gel plug. However, the induction ability of the 0.5-mm thick sheet was significantly lower when compared with the 1.0-mm thick gel sheet. The 1.0-mm DN gel sheet is a promising device to establish a cell-free cartilage regeneration strategy that minimizes bone loss from the gel implantation.

A primer in cartilage repair.

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.

Cartilage defect regeneration by ex vivo engineered autologous microtissue--preliminary results.

We analysed the improvement of cartilage defect regeneration by the use of microspheres of autologous chondrocytes. Autologous chondrocytes from minipigs were cultured using the microsphere technology. Cartilage defects were surgically introduced to tibia-femoral joints. Tissue constructs were then implanted into defect sites. Histological, immunohistological and transmission electron microscopic analyses were performed. Histological and ultrastructural investigations of chondrospheres revealed a cartilage-like tissue formation, indicated by phenotypically differentiated chondrocyte-like cells surrounded by de novo synthesised chondrogenic extracellular matrix. Clinical inspection of defects demonstrated nearly complete cartilage regeneration in the microtissue treated defect sites, whereas controls exhibited irregular fibrous tissue formation. In vitro-expanded articular chondrocytes are able to form a microtissue capable of repairing cartilage defects in vivo, improving regeneration of cartilage defects.

Effectiveness and limitations of autologous osteochondral grafting for the treatment of articular cartilage defects in the knee.

PURPOSE: To evaluate the effectiveness and limitations of autologous osteochondral grafting for the treatment of articular cartilage defects in the knee. METHODS: The subjects were 40 patients who had undergone autologous osteochondral grafting. Fifteen knees had cartilage defects combined with anterior cruciate ligament tears (ACL group), 15 knees had cartilage defects combined with osteoarthritis (OA group), and 10 knees had cartilage defects combined with osteochondral dissecans (OCD group). From one to five osteochondral pegs were harvested from the less-weight-bearing periphery of the articular surface of the femoral condyle and grafted to cartilage defects. The clinical results were assessed based on the Lysholm score and radiographic and magnetic resonance imaging (MRI) image assessment. RESULTS: The median follow-up duration was 24 months (range from 12 to 41 months). The mean Lysholm score following treatment was improved in all groups. The patients who had cartilage defects combined with OA had a significantly poorer prognosis than did those with cartilage defects combined with ACL or OCD. In the OA group, advanced stage and an alignment abnormality were correlated with poor prognosis. Advanced age was correlated with poor prognosis. Other parameters showed no significant difference in prognosis. CONCLUSION: Autologous osteochondral grafting was found to be an effective technique for treating relatively young patients who had cartilage defects combined with ACL injury or OCD, but this technique showed limited results in treating cartilage defects based on advanced patient age and degenerative changes in the cartilage. LEVEL OF EVIDENCE: Diagnostic studies-investigating a diagnostic test, Level III.

Induction of spontaneous hyaline cartilage regeneration using a double-network gel: efficacy of a novel therapeutic strategy for an articular cartilage defect.

BACKGROUND: A double-network (DN) gel, which was composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) and poly-(N,N'-dimetyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. PURPOSE: To establish the efficacy of a therapeutic strategy for an articular cartilage defect using a DN gel. STUDY DESIGN: Controlled laboratory study. METHODS: A 4.3-mm-diameter osteochondral defect was created in rabbit trochlea. A DN gel plug was implanted into the defect of the right knee so that a defect 2 mm in depth remained after surgery. An untreated defect of the left knee provided control data. The osteochondral defects created were examined by histological and immunohistochemical evaluations, surface assessment using confocal laser scanning microscopy, and real-time polymerase chain reaction (PCR) analysis at 4 and 12 weeks. Samples were quantitatively evaluated with 2 scoring systems reported by Wayne et al and O'Driscoll et al. RESULTS: The DN gel-implanted defect was filled with a sufficient volume of the hyaline cartilage tissue rich in proteoglycan and type 2 collagen. Quantitative evaluation using the grading scales revealed a significantly higher score in the DN gel-implanted defects compared with the untreated control at each period (P < .0001). The mean relative values of type 2 collagen mRNAs in the regenerated tissue were obviously higher in the DN gel-implanted defect than in the untreated control at each period. The mean surface roughness of the untreated control was significantly higher than the normal cartilage at 12 weeks (P = .0106), while there was no statistical difference between the DN gel-implanted and normal knees. CONCLUSION: This study using the mature rabbit femoral trochlea osteochondral defect model demonstrated that DN gel implantation is an effective treatment to induce cartilage regeneration in vivo without any cultured cells or mammalian-derived scaffolds. CLINICAL RELEVANCE: This study has prompted us to develop a potential innovative strategy to repair cartilage lesions in the field of joint surgery.

A pseudo-elastic effective material property representation of the costal cartilage for use in finite element models of the whole human body.

OBJECTIVE: Injury-predictive finite element (FE) models of the chest must reproduce the structural coupling behavior of the costal cartilage accurately. Gross heterogeneities (the perichondrium and calcifications) may cause models developed based on local material properties to erroneously predict the structural behavior of cartilage segments. This study sought to determine the pseudo-elastic effective material properties required to reproduce the structural behavior of the costal cartilage under loading similar to what might occur in a frontal automobile collision. METHODS: Twenty-eight segments of cadaveric costal cartilage were subjected to cantilever-like, dynamic loading. Three limited-mesh FE models were then developed for each specimen, having element sizes of 10 mm (typical of current whole-body FE models), 3 mm, and 2 mm. The cartilage was represented as a homogeneous, isotropic, linear elastic material. The elastic moduli of the cartilage models were optimized to fit the anterior-posterior (x-axis) force versus displacement responses observed in the experiments. For a subset of specimens, additional model validation tests were performed under a second boundary condition. RESULTS: The pseudo-elastic effective moduli ranged from 4.8 to 49 MPa, with an average and standard deviation of 22 ± 13.6 MPa. The models were limited in their ability to reproduce the lateral (y-axis) force responses observed in the experiments. The prediction of the x-axis and y-axis forces in the second boundary condition varied. Neither the effective moduli nor the model fit were significantly affected (Student's t-test, p < 0.05) by the model mesh density. The average pseudo-elastic effective moduli were significantly (p < 0.05) greater than local costal cartilage modulus values reported in the literature. CONCLUSIONS: These results are consistent with the presence of stiffening heterogeneities within the costal cartilage structure. These effective modulus values may provide guidance for the representation of the costal cartilage in whole-body FE models where these heterogeneities cannot be modeled distinctly.

Hip injuries in athletes.

Hip injuries are common in athletes, and there is an extensive differential diagnosis of potential causes. This article reviews the anatomy of the hip, and discusses the imaging findings of hip pathology in athletes including skeletal, intraarticular, and extra-articular abnormalities. The role of radiography, computed tomography (CT), magnetic resonance (MR) imaging, MR arthrography, CT arthrography, and sonography in evaluating each condition is discussed.

Repair of full-thickness articular cartilage defects using injectable type II collagen gel embedded with cultured chondrocytes in a rabbit model.

BACKGROUND: Recently, tissue-engineered chondrocyte transplantation has been tried to treat full-thickness cartilage defects. We developed an injectable type II collagen gel scaffold by chemically reacting type II collagen with polyethylene glycol crosslinker. This type II collagen was prepared from the nasal septa of cattle. In the present study, chondrocytes embedded in type II collagen gel were injected into rabbit full-thickness cartilage defects without a periosteal graft, and the feasibility for clinical application of the gel was evaluated. METHODS: Chondrocytes were isolated from 1-kg New Zealand white rabbits. A full-thickness articular cartilage defect (5 mm diameter, 4 mm depth) was created on the patellar groove of the femur of 16 male 3-kg New Zealand white rabbits. A type II collagen solution of mixed chondrocytes at a density of 1 x 10(7) cells/ml was injected and transplanted into the defect in the right knee. The controls were the defect only in the left knee. At 4, 8, 12, and 24 weeks after operation, four cases from each group were evaluated macroscopically and histologically. RESULTS: After injection into the cartilage defect, the gel bonded to the adjacent cartilage and bone within several minutes. Macroscopic examination revealed that the surface of the transplanted area was smooth and exhibited similar coloration and good integration with the surrounding cartilage at 12 and 24 weeks after transplantation. Histological examination at 8 weeks revealed favorable hyaline cartilage regeneration with good chondrocyte morphology. At 12 and 24 weeks, reparative cartilage remained rich in type II collagen. According to O'Driscoll histological scores, significant differences between the transplanted and control groups were apparent at 12 and 24 weeks. Immunohistochemical staining indicated sufficient type II collagen synthesis in regenerated cartilage 8 weeks after transplantation, and it was maintained until 24 weeks. CONCLUSIONS: These results indicate that type II collagen gel is suitable for injection into cartilage defects without any covering of a graft and offers a useful scaffold during chondrocyte transplantation.

Hyaline cartilage regeneration using mixed human chondrocytes and transforming growth factor-beta1- producing chondrocytes.

The purpose of this study was to investigate the efficacy of cartilage regeneration when using a mixture of transforming growth factor-beta1 (TGF-beta1)-producing human chondrocytes (hChon-TGF-beta1) and primary human chondrocytes (hChon) ("mixed cells"), compared with either hChon-TGF-beta1 or hChon cells alone. Specifically, mixed cells or hChon cells were first injected intradermally into the backs of immune-deficient nude mice to test the feasibility of cartilage formation in vivo. Both the mixed cells and the hChon-TGF-beta1 cells alone induced cartilage formation in nude mice, whereas hChon cells alone did not. To further test the efficacy of the cells in generating cartilage, an artificially induced partial thickness defect of the femoral condyle of a rabbit knee joint was loaded with hChon-TGF-beta1 cells with or without mixing additional untransduced hChon cells, and hyaline cartilage regeneration was observed at 4 or 6 weeks. The efficiency of complete filling of the defect and the quality of tissue generated after implanting were evaluated on the basis of a histological grading system modified from O'Driscoll et al. (J. Bone Joint Surg. 70A, 595, 1988). Significantly, mixed cells (14.2 +/- 0.9) produced significantly better results than hChon-TGF-beta1 (9.0 +/- 1.7) or hChon (8.0 +/- 1.8) cells alone. Histological and immunohistochemical staining of the newly repaired tissues produced after treatment with either mixed cells or hChon-TGF-beta1 cells alone showed hyaline cartilage- like characteristics. These results suggest that the implantation of mixed cells may be a clinically efficient method of regenerating hyaline articular cartilage.