Improved repair of chondral and osteochondral defects in the ovine trochlea compared with the medial condyle

Associations between topographic location and articular cartilage repair in preclinical animal models are unknown. Based on clinical investigations, we hypothesized that lesions in the ovine femoral condyle repair better than in the trochlea. Full‐thickness chondral and osteochondral defects were simultaneously established in the weightbearing area of the medial femoral condyle and the lateral trochlear facet in sheep, with chondral defects subjected to subchondral drilling. After 6 months in vivo, cartilage repair and osteoarthritis development was evaluated by macroscopic, histological, immunohistochemical, and biochemical analyses. Macroscopic and histological articular cartilage repair and type‐II collagen immunoreactivity were better in the femoral trochlea, regardless of the defect type. Location‐independently, osteochondral defects induced more osteoarthritic degeneration of the adjacent cartilage than drilled chondral lesions. DNA and proteoglycan contents of chondral defects were higher in the condyle, reflecting physiological topographical differences. The results indicate that topographic location dictates the structural patterns and biochemical composition of the repair tissue in sheep. These findings suggest that repair of cartilage defects at different anatomical sites of the ovine stifle joint needs to be assessed independently and that the sheep trochlea exhibits cartilage repair patterns reflective of the human medial femoral condyle. © 2013 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 31:1772–1779, 2013     

Xeno-implantation of pig chondrocytes into rabbit to treat localized articular cartilage defects: an animal model

Articular cartilage has only a limited ability to regenerate. The transplantation of autologous chondrocytes is currently used to treat focal defects in human articular cartilage, although use of organs, tissues, or cells from different species is being investigated as an alternative treatment. The object of this study was to use xeno-transplantation of cultured pig chondrocytes for the repair of rabbit chondral defects, and to analyze the significance of tissue rejection in this animal model. Partial chondral defects, including removal of cartilage tissue and a part of the subchondral bone, were created in the lateral femoral condyles of 30 adult New Zealand White rabbits. A periosteal flap was sutured to the native cartilage with the cambium layer facing the defect. As a control, culture medium was injected into the defect void of one group of rabbits while in a treatment group, chondrocytes, isolated from normal femoral pig cartilage, were injected into the defect void. All rabbits were killed by 24 weeks. Macroscopic changes of the cartilage were analyzed using Mankin's score. The distal femoral portion was studied histologically using hematoxylin and eosin, alcian blue, toluidine blue, and Mason's trichrome. Pig cells and pig genetic material were detected in the neo-synthesized tissue by immunohistochemical detection of SLA-II-DQ and polymerase chain reaction analysis of the gene SLA-II-DQB. The synovial membrane was studied histologically by hematoxylin and eosin staining. In the control group, on average, less than 25 percent of the chondral defect was filled. The repair tissue had an irregular surface with few cells similar to chondrocytes or fibroblasts and a minimal formation of extracellular matrix. In the treatment group, the chondral defect was approximately 90 percent filled with good integration between the neo-synthesized cartilage and the native cartilage. The repair tissue had a smooth surface with cells similar to chondrocytes and a hyaline-like extracellular matrix. The neo-synthesized cartilage was morphologically similar to hyaline cartilage. Importantly, there were no signs of graft-vs.-host rejections or infiltration by immune cells. In the neo-synthesized tissue, pig genetic material was detected in 27 +/- 5 percent of all cells. These cells containing pig genetic material were distributed throughout the neo-synthesized cartilage. We conclude that the xeno-transplantation of chondrocytes could be an alternative method for the repair of articular cartilage defects.     

Marrow stimulation and chondrocyte transplantation using a collagen matrix for cartilage repair

OBJECTIVE: The purpose of the study was to determine whether the implantation of a scaffold would facilitate cartilage repair after microfracture in sheep over a period of 12 months. Furthermore, we investigated the effect of additional autologous cell augmentation of the implanted constructs. METHODS: Two chondral defects were produced in the medial femoral condyle of sheep without penetrating the subchondral bone. Twenty-seven sheep were divided into the following groups: seven served as untreated controls (Group 1), microfracture was created in 20 animals, seven of them without further treatment (Group 2), in six sheep the defects were additionally covered with a porcine collagen matrix (Group 3), and in seven animals the matrix was augmented with cultured autologous chondrocytes (Group 4). After 4 (11 sheep) and 12 months (16 sheep), the filling of the defects, tissue types, and semiquantitative scores were determined. RESULTS: The untreated defects revealed the least amount of defect fill. Defects treated with microfractures achieved better defect fill, while the additional use of the matrix did not increase the defect fill. The largest quantity of reparative tissue was found in the cell-augmented group. Semiquantitative scores were best in the cell-augmented group. CONCLUSION: Microfracture treatment was observed to enhance the healing response. The implantation of a cell-seeded matrix further improved the outcome. The implantation of a collagen matrix alone did not enhance repair. Autologous cell implantation appears to be a very important aspect of the tissue engineering approach to cartilage defects.     

Treatment of chondral lesions in advanced osteochondritis dissecans: a comparative study of the efficacy of chondrocytes, mesenchymal stem cells, periosteal graft, and mosaicplasty (osteochondral autograft) in animal models

Management of chondral lesions in osteochondritis dissecans remains a challenge. This study investigated the efficacy of periosteal graft, osteochondroidal autograft, autologous chondrocyte and mesenchymal stem cell transplants in the treatment of chondral lesions in animal models. Full-thickness articular cartilage defects were created in the weight-bearing surface of the medial femoral condyle in 20-week-old NZW rabbits. A total of 56 knees were randomly divided into four groups as follows: group 1, transfer of cultured chondrocytes; group 2, transfer of cultured mesenchymal stem cells; group 3, repair by periosteal graft; and group 4, mosaicplasty. All of the contralateral knees served as control. Gross, histologic, and biomechanical examinations at 36 weeks after the operation showed that the cultured chondrocytes and mesenchymal stem cells had comparable enhancing effects on the repair of chondral defects in advanced osteochondritis dissecans, whereas mosaicplasty did well initially and periosteal graft did less favorably.     

Effects of a cultured autologous chondrocyte-seeded type II collagen scaffold on the healing of a chondral defect in a canine model.

Using a previously established canine model for repair of articular cartilage defects, this study evaluated the 15-week healing of chondral defects (i.e., to the tidemark) implanted with an autologous articular chondrocyte-seeded type II collagen scaffold that had been cultured in vitro for four weeks prior to implantation. The amount and composition of the reparative tissue were compared to results from our prior studies using the same animal model in which the following groups were analyzed: defects implanted with autologous chondrocyte-seeded collagen scaffolds that had been cultured in vitro for approximately 12 h prior to implantation, defects implanted with autologous chondrocytes alone, and untreated defects. Chondrocytes, isolated from articular cartilage harvested from the left knee joint of six adult canines, were expanded in number in monolayer for three weeks, seeded into porous type II collagen scaffolds, cultured for an additional four weeks in vitro and then implanted into chondral defects in the trochlear groove of the right knee joints. The percentages of specific tissue types filling the defects were evaluated histomorphometrically and certain mechanical properties of the repair tissue were determined. The reparative tissue filled 88+/-6% (mean+/-SEM; range 70-100%) of the cross-sectional area of the original defect, with hyaline cartilage accounting for 42+/-10% (range 7-67%) of defect area. These values were greater than those reported previously for untreated defects and defects implanted with a type II collagen scaffold seeded with autologous chondrocytes within 12 h prior to implantation. Most striking, was the decreased amount of fibrous tissue filling the defects in the current study, 5+/-5% (range 0-26%) as compared to previous treatments. Despite this improvement, indentation testing of the repair tissue formed in this study revealed that the compressive stiffness of the repair tissue was well below (20-fold lower stiffness) that of native articular cartilage.     

Value of autologous chondrocyte transplantation in the reconstruction of experimental cartilage defects. Part I. Extent of defect, macroscopic appearance of reconstructed articular surface and microscopic analysis of predominant tissue]

Articular cartilage defect is one of the main reasons of osteoarthritis. Currently, tissue engineering techniques are the methods concerning better cartilage reconstruction. The aim of this part of the study was macroscopic evaluation of degree of defect feeling, macroscopic appearance of repair tissue and microscopic analysis of predominant tissue after autologous chondrocytes transplantation. Repair of partial thickness cartilage defect on distal part of femur was evaluated (25 adolescent rabbits). Procedures were performed in II groups: I--autologous chondrocytes transplantation under periosteal flap, II--periosteal graft. Chondrocytes were isolated from the cartilage specimens by enzymatic digestion and cultured in vitro. The regenerates were inspected 4, 8 and 12 weeks after the operation. Macroscopic analysis in group I, in most cases revealed filling of the defect with tissue resembling surrounding cartilage. In group II the defect was partially filled, and there was many fissures and cracks in all regenerates. In microscopic analysis in group I, after 4 and 8 weeks following the transplantation the tissue similar to juvenile hyaline cartilage predominated. After 12 weeks it resembled mature hyaline cartilage. In group II, in all cases fibrous cartilage was observed after 4, 8, 12 weeks. Obtained results indicate, that macroscopic and microscopic characteristics of repair tissue after autologous chondrocytes transplantation more closely resembled hyaline cartilage, than in periosteal graft group. 12 weeks after autologous chondrocytes transplantation the repair tissue reached maturity, and demonstrated microscopic characteristics of hyaline-like cartilage. The method of autologous chondrocytes transplantation provides potential for clinical application.     

The fate of osteochondral grafts after autologous osteochondral transplantation: a one-year follow-up study in a minipig model

Introduction  Because articular cartilage shows little intrinsic capacity of spontaneous regeneration, a variety of treatment options are currently at use to repair cartilage damage. One of these is the autologous osteochondral transplantation (AOT). The aim of the present work was to study the histological changes during the progress of 1 year after AOT in the knee joint. Materials and methods  Twelve Minipigs underwent an AOT on the medial femoral condyles of both knees using cooled diamond studded trephines with a diameter of the grafts of 4.6 mm. Three animals were sacrificed at each 2, 8, 26 and 52 weeks after the operation. The condyles were analyzed histologically and immunohistologically for collagen types I and II. Results  A successful bony incorporation was observed in all specimens. The transplant demonstrated an increasingly stable integration of the chondral matrix into the cartilage of the surrounding femoral condyle. At 52 weeks after the operations 5 of 6 condyles showed a chondral integration at least at one side of the graft. Immunohistologically all specimens showed physiological staining characteristics up to 52 weeks after operation. The quality of the chondral part of the graft showed a wide range of variations, ranging from vital tissue resembling native cartilage after 52 weeks, to severe degenerative signs beginning 2 weeks after operation and ending at 52 weeks with deep fissures fragmenting the cartilage and the complete loss of vital cells. Conclusion  The press-fit technique allows a stable bony incorporation. A chondral integration of the graft seems to occur, provided that a close contact between the interfaces can be achieved. Present results demonstrate a vital cartilagenous transplant for up to 52 weeks. However, some specimens showed in part severe degenerative signs. A possible explanation is an insufficient cooling of the trephines in relation to the small diameter of the grafts used in the minipig model. The collagen network seems not to be affected for up to 52 weeks. Klaus Baumbach, Jan-Philipp Petersen contributed equally to this work.     

Integration of periosteum covered autogenous bone grafts with and without autologous chondrocytes. An animal experiment using the Göttinger minipig

Autologous osteochondral transplantation has the major disadvantage of significant damage to a healthy joint surface at the donor site.The purpose of this study was to examine the effect of autogenous chondrocytes injected into the periosteum of autologous bone grafts in order to provide an alternative method for cartilagerepair. A total of 22 Göttinger minipigs were operated twice on both knees.The first operation served for cartilage biopsy for the chondrocyte culture.During the second operation an osteochondral defect was created in the medial facet of the trochlear groove.The defect was treated differently with an autologous cortico-cancellous bone cylinder,harvested from the proximal tibia.Group A: untreated defect (control);B: bone-graft;C: bone-graft covered with periosteum; D: bone-graft with periosteum and injected autologous chondrocytes.The animals were killed after 6,12,26 and 52weeks.The regenerated areas were evaluated macroscopically, tested biomechanically (long-term specimens; indentation-test) and a histological, blind evaluation was carried out according to a semi-quantitative scoring system. The periosteum covered bone cylinders in Groups C and D showed good repair of the bone and cartilage defect.The repaired tissue consisted predominantly of fibrocartilage with the partial formation of hyalin like tissue.The regenerated areas were integrated with the adjacent cartilage and were biomechanically superior when compared with the other groups. The additional injection of chondrocytes did not produce significantly better results. Our findings suggest that the transplantation of periosteum-covered bone cylinders may provide an alternative method for treating chondral and osteochondral defects and can be recommended for filling large donor site defects in joint surgery.The additional transplantation of chondrocytes does not seem to be justified.     

Intraarticular location predicts cartilage filling and subchondral bone changes in a chondral defect

Background and purpose The natural history of, and predictive factors for outcome of cartilage restoration in chondral defects are poorly understood. We investigated the natural history of cartilage filling subchondral bone changes, comparing defects at two locations in the rabbit knee.

Animals and methods In New Zealand rabbits aged 22 weeks, a 4-mm pure chondral defect (ICRS grade 3b) was created in the patella of one knee and in the medial femoral condyle of the other. A stereo microscope was used to optimize the preparation of the defects. The animals were killed 12, 24, and 36 weeks after surgery. Defect filling and the density of subchondral mineralized tissue was estimated using Analysis Pro software on micrographed histological sections.

Results The mean filling of the patellar defects was more than twice that of the medial femoral condylar defects at 24 and 36 weeks of follow-up. There was a statistically significant increase in filling from 24 to 36 weeks after surgery at both locations.

The density of subchondral mineralized tissue beneath the defects subsided with time in the patellas, in contrast to the density in the medial femoral condyles, which remained unchanged.

Interpretation The intraarticular location is a predictive factor for spontaneous filling and subchondral bone changes of chondral defects corresponding to ICRS grade 3b. Disregarding location, the spontaneous filling increased with long-term follow-up. This should be considered when evaluating aspects of cartilage restoration.     

Orderly osteochondral regeneration in a sheep model using a novel nano‐composite multilayered biomaterial

The objective of this article was to investigate the safety and regenerative potential of a newly developed biomimetic scaffold when applied to osteochondral defects in an animal model. A new multilayer gradient nano‐composite scaffold was obtained by nucleating collagen fibrils with hydroxyapatite nanoparticles. In the femoral condyles of 12 sheep, 24 osteochondral lesions were created. Animals were randomized into three treatment groups: scaffold alone, scaffold colonized in vitro with autologous chondrocytes and empty defects. Six months after surgery, the animals were sacrificed and the lesions were histologically evaluated. Histologic and gross evaluation of specimens showed good integration of the chondral surface in all groups except for the control group. Significantly better bone regeneration was observed both in the group receiving the scaffold alone and in the group with scaffold loaded with autologous chondrocytes. No difference in cartilage surface reconstruction and osteochondral defect filling was noted between cell‐seeded and cell‐free groups. In the control group, no bone or cartilage defect healing occurred, and the defects were filled with fibrous tissue. Quantitative macroscopic and histological score evaluations confirmed the qualitative trends observed. The results of the present study showed that this novel osteochondral scaffold is safe and easy to use, and may represent a suitable matrix to direct and coordinate the process of bone and hyaline‐like cartilage regeneration. The comparable regeneration process observed with or without autologous chondrocytes suggests that the main mode of action of the scaffold is based on the recruitment of local cells. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:116–124, 2010     

Pig chondrocyte xenoimplants for human chondral defect repair: an in vitro model

The objective of this study was to evaluate the use of cultured porcine chondrocyte xenotransplantation for the repair of human chondral defects. Two-millimeter-diameter defects were drilled into explants of femoral cartilage from healthy adult donors. No cells were implanted in the chondral defects of the control group, while pig chondrocytes from normal femoral cartilage were deposited into the treated chondral defects. Cartilage explants were cultured for 4, 8, and 12 weeks. Tissue sections were processed for standard histologic staining and immunostaining with monoclonal antibodies against types I and II collagen, chondroitin-4-sulfate, chondroitin-6-sulfate, keratan sulfate, and integrin subunit beta1. The porcine origin of chondrocytes was confirmed using a specific pig monoclonal anti-CD46. Repair was only observed in the cell-treated defects. Mono- or bilayers of cells were detected after 4 culture weeks on the bottom of the defects, while after 8-12 weeks a repair tissue filled near 30-40 percent of the defect. At 8 weeks, the newly synthesized tissue was composed of a fibrous mesh including some cells. However, at 12 weeks it showed a hypercellular hyaline-like region. This hypercellular region showed excellent bonding with the native cartilage, cells were located in numerous lacunae, and a high content of proteoglycans as indicated by an intense toluidine blue stain was observed. The repaired tissue showed positive immunostaining for both type I and II collagen, as well as chondroitin-4-sulfate, chondroitin-6-sulfate, keratan sulfate, and integrin subunit beta1. Positive staining for porcine anti-CD46 was localized exclusively in the neo-synthesized tissue. We conclude that xenotransplantation of pig chondrocytes can repair, in an in vitro model, defects in human articular cartilage.     

Reconstruction of Articular Cartilage Defects with Free Periosteal Grafts: An Experimental Study

The chondrogenic potential of free autogenous periosteal grafts was studied histologically in 6-month-old rabbits. The grafts were taken from the tibia and transplanted to 7 × 14 mm large artificial defects of the femoral articular cartilage. The results revealed that the defects were repaired and filled after 4 weeks with a hyaline-like cartilage which was histologically similar to the cartilage adjacent to the transplant. The tissue maintained this morphology after 1 year of observation. In control animals where no periosteum was transplanted to the defect, no real cartilage was found. The tissue which partially filled the defect was a variable mixture of fibrous tissue and fibrocartilage.     

Chitosan-glycerol phosphate/blood implants increase cell recruitment, transient vascularization and subchondral bone remodeling in drilled cartilage defects

OBJECTIVE: Marrow-stimulation techniques are used by surgeons to repair cartilage lesions although consistent regeneration of hyaline cartilage is rare. We have shown previously that autologous blood can be mixed with a polymer solution containing chitosan in a glycerol phosphate (GP) buffer (chitosan-GP), and that implantation of this polymer/blood composite onto marrow-stimulated chondral defects in rabbit and sheep leads to the synthesis of more chondral repair tissue with greater hyaline character compared to marrow-stimulation alone. In the current study, we examined the modulation of cell recruitment and repair tissue characteristics at early post-surgical time points (from day 1 to 56) in a rabbit model to elucidate potential mechanisms behind this improved repair outcome. DESIGN: Thirty-three skeletally mature New Zealand White rabbits underwent bilateral arthrotomies, with each trochlea receiving a cartilage defect (3.5 mm x 4.5mm) bearing four microdrill holes (0.9 mm diameter, approximately 4 mm deep) into the subchondral bone. One defect per rabbit was treated with a chitosan-GP/blood implant, while the other defect was left as a microdrilled control. Repair tissues were stained by histochemistry, for collagen types I, II, and X by immunohistochemistry and analyzed using quantitative stereological tools. RESULTS: Histological analyses demonstrated that control defects followed a typical healing sequence observed previously in marrow-stimulation animal models while chitosan-GP/blood implants led to three significant modifications in the healing sequence at early stages: (1) increased inflammatory and marrow-derived stromal cell recruitment to the microdrill holes, (2) increased vascularization of the provisional repair tissue in the microdrill holes, and (3) increased intramembranous bone formation and subchondral bone remodeling (BR). CONCLUSIONS: These results suggest that the greater levels of provisional tissue vascularization and BR activity are main factors supporting improved cartilage repair when chitosan-GP/blood implants are applied to marrow-stimulated cartilage lesions.     

Articular Cartilage Repair in the Knee Joint with Autologous Chondrocytes and Periosteal Graft

Objective Repair of articular cartilage defects of knee to restore a pain-free joint function. Indications Full-thickness chondral or osteochondral posttraumatic lesions and osteochondritis dissecans defects that have not been successfully repaired with methods such as debridement, drilling, and microfracturing. Contraindications Osteoarthritis. Rheumatoid arthritis. Surgical Technique During arthroscopy, the cartilage lesion is evaluated, and cartilage slices weighing 200-300 mg are harvested from the upper medial femoral condyle, a minor load bearing area. The chondrocytes are isolated enzymatically and grown in culture to increase the cell number during approximately 2 weeks. During the second operation, an arthrotomy is performed through a medial or lateral parapatellar approach. The defect is carefully debrided. A periosteal patch is obtained from proximal tibia, placed over the defect and sutured to the surrounding cartilage. The suture line is sealed with fibrin glue, and the chondrocytes are injected into the defect under the patch. Results Recently, Peterson has presented results in 213 patients with a follow-up between 2-10 years. He reported good to excellent results in 90% of 57 patients with single femoral condyle lesions, in 84% of 32 patients with osteochondritis dissecans and in 74% of 27 patients with femoral condyle lesions in combination with anterior cruciate ligament reconstruction. In 32 patients the patella was grafted and 22 improved, in twelve patients the trochlea was grafted and seven improved. and in 53 patients multiple lesions were grafted and 42 improved. Second-look arthroscopies were performed in 46 patients, 26 of them were biopsied; the transplanted tissues showed a hyaline-like appearance in 21 patients (80%).     

Treatment of a full-thickness articular cartilage defect in the femoral condyle of an athlete with autologous bone-marrow stromal cells

OBJECTIVES: Human bone-marrow stromal cells are believed to be multipotent even in adults. This study assessed the effectiveness of autologous bone-marrow stromal cells, which were embedded within a collagen scaffold, to repair a full-thickness articular cartilage defect in the medial femoral condyle of an athlete. PATIENT AND METHODS: A 31-year-old male judo player suffering from pain in the right knee was reviewed. A 20 x 30-mm full-thickness cartilage defect (International Cartilage Repair Society classification (ICRS) grade IV) was revealed in the weight-bearing area of the medial femoral condyle. With the informed consent of the patient, the defect was treated with autologous bone-marrow stromal cells. Bone marrow was aspirated from the iliac crest of the patient 4 weeks before surgery. After removing the erythrocytes, the remaining cells were expanded in culture. Adherent cells were collected and embedded within a collagen gel, which was transferred to the articular cartilage defect in the medial femoral condyle. The implant was covered with an autologous periosteal flap. RESULTS: Seven months after surgery, arthroscopy revealed the defect to be covered with smooth tissues. Histologically, the defect was filled with a hyaline-like type of cartilage tissue which stained positively with Safranin-O. One year after surgery, the clinical symptoms had improved significantly. The patient had reattained his previous activity level and experienced neither pain nor other complications. CONCLUSIONS: Our findings indicate that the transplantation of autologous bone-marrow stromal cells can promote the repair of large focal articular cartilage defects in young, active patients.     

Effects of hyaluronan on periosteal grafts for large full-thickness defects in rabbit articular cartilage

We studied the effects of hyaluronan (HA) on chondrogenesis in periosteal grafts in rabbit knees to elucidate the effects of this agent in the repair of articular cartilage. Large full-thickness defects of the articular cartilage were created in the anteromedial part of the femoral articular surface of bilateral knee joints. Periosteal grafts were then harvested and sutured onto the defects. HA was injected in the right knee immediately after the operation and then once a week for 4 weeks (HA group). The same volume of saline was injected in the left knee in the control group. The animals were killed 2, 5, 8, and 12 weeks after the operation. Macroscopic and histological findings of the regenerated tissue were evaluated with a semiquantitative histological grading system. The total histological scores of the HA group were better than those in the control group at each time examination point. At 12 weeks, in particular, the scores for surface regularity and integration to adjacent articular cartilage were significantly better in the HA group than in the control group (P < 0.05). No significant differences were observed between the two groups in regard to the area healed (%). HA may have beneficial effects on the repair of large full-thickness defects of the articular cartilage with autologous periosteal grafts. Received for publication on Feb. 18, 1998; accepted on Oct. 20, 1998     

Chitosan-glycerol phosphate/blood implants improve hyaline cartilage repair in ovine microfracture defects

BACKGROUND: Microfracture is a surgical procedure that is used to treat focal articular cartilage defects. Although joint function improves following microfracture, the procedure elicits incomplete repair. As blood clot formation in the microfracture defect is an essential initiating event in microfracture therapy, we hypothesized that the repair would be improved if the microfracture defect were filled with a blood clot that was stabilized by the incorporation of a thrombogenic and adhesive polymer, specifically, chitosan. The objectives of the present study were to evaluate (1) blood clot adhesion in fresh microfracture defects and (2) the quality of the repair, at six months postoperatively, of microfracture defects that had been treated with or without chitosan-glycerol phosphate/blood clot implants, using a sheep model. METHODS: In eighteen sheep, two 1-cm2 full-thickness chondral defects were created in the distal part of the femur and treated with microfracture; one defect was made in the medial femoral condyle, and the other defect was made in the trochlea. In four sheep, microfracture defects were created bilaterally; the microfracture defects in one knee received no further treatment, and the microfracture defects in the contralateral knee were filled with chitosan-glycerol phosphate/autologous whole blood and the implants were allowed to solidify. Fresh defects in these four sheep were collected at one hour postoperatively to compare the retention of the chitosan-glycerol phosphate/blood clot with that of the normal clot and to define the histologic characteristics of these fresh defects. In the other fourteen sheep, microfracture defects were made in only one knee and either were left untreated (control group; six sheep) or were treated with chitosan-glycerol phosphate/blood implant (treatment group; eight sheep), and the quality of repair was assessed histologically, histomorphometrically, and biochemically at six months postoperatively. RESULTS: In the defects that were examined one hour postoperatively, chitosan-glycerol phosphate/blood clots showed increased adhesion to the walls of the defects as compared with the blood clots in the untreated microfracture defects. After histological processing, all blood clots in the control microfracture defects had been lost, whereas chitosanglycerol phosphate/blood clot adhered to and was partly retained on the surfaces of the defect. At six months, defects that had been treated with chitosan-glycerol phosphate/blood were filled with significantly more hyaline repair tissue (p < 0.05) compared with control defects. Repair tissue from medial femoral condyle defects that had been treated with chitosan-glycerol phosphate/blood contained more cells and more collagen compared with control defects and showed complete restoration of glycosaminoglycan levels. CONCLUSIONS: Solidification of a chitosan-glycerol phosphate/blood implant in microfracture defects improved cartilage repair compared with microfracture alone by increasing the amount of tissue and improving its biochemical composition and cellular organization.     

Articular cartilage defects in a rabbit model, retention rate of periosteal flap cover

BACKGROUND: A periosteal flap is frequently used in procedures involving repair of articular cartilage defects. Hypertrophy of the repair tissue, probably from a retained periosteum, is a clinical problem but not much is known about this issue. The objective of the present experimental study was to investigate the retention rate of periosteal flaps with respect to various postoperative mobilization regimes and the introduction of bone marrow elements underneath the flap. METHOD: We created a chondral lesion (diameter 4 mm) in both patellas of 18 New Zealand white rabbits. The subchondral bone was left intact in one knee. In the other, the bone plate was perforated, allowing bone marrow elements to enter the defect. All defects were covered with a periosteal flap, sutured and glued to the rim of the cartilage defect. Postoperatively, the rabbits were allocated to one of three groups: A. rehabilitation in cages for 4 days, then killed; B. rehabilitation in cages for 7 days, then free activity on the floor of a 10 m2 room until the end of the second week, then killed; C. rehabilitation in cages for 2 weeks, then killed. RESULTS: 16 of 23 periosteal flaps became detached within 2 weeks (one knee was excluded because of clinical signs of infection), with no difference in the retention rate with respect to mobilization regime or established access to bone marrow elements in the defect. The periosteum still served as a cover of the defect in 10 of 12 knees at day 4. This figure decreased to 7 of 23 knees at day 14. CONCLUSION: Our study is the first to document the retention rate of periosteal flaps in a rabbit model. The low retention rate observed may explain why periosteal hypertrophy is not reported in experimental studies where the periosteal flap is sutured to the cartilage rim.     

Critical‐size defect induces unicompartmental osteoarthritis in a stable ovine knee

Animal models simulating osteoarthritis are frequently associated with irreversible changes in biomechanics. Although these models successfully induce osteoarthritis, results of experimental repair procedures are impaired by biomechanical problems. The aim of this study was to define the critical size of a chondral lesion to induce unicompartmental osteoarthritis in a stable joint. Sixteen sheep were randomly divided into four treatment groups. A cartilage defect (7‐ or 14‐mm diameter) was created in the weight‐bearing zone of the medial femoral condyle. The sheep were mobilized for 6 or 12 weeks. Osteoarthritis was determined by gross assessment, India ink staining, histology (Mankin score), and analysis of COMP in the serum. In the 6‐week group, only minor osteoarthritis was registered for either defect size. After 12 weeks, the 14‐mm defect induced minor osteoarthritis at the femoral condyle and caused significant degenerative changes at the tibial articular cartilage and the meniscus. The 7‐mm defect created focal unicompartmental osteoarthritis at the medial femoral condyle and minor degenerative changes at the corresponding tibia. A 7‐mm full‐thickness chondral defect with a weight‐bearing regimen of 12 weeks induced local osteoarthritis at the medial compartment in an otherwise stable joint as aimed. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 30:214–220, 2012     

Morphological evaluation of fascia lata tissue implantation for chondral defects in the knee joint of sheep under active motion and load]

Experiments carried out on 64 knees of 32 Lein sheep with superficial and deep chondral defects of the patella and femoral condyles covered by autogenic fascia lata grafts indicate that under active motion and load the grafted tissue after 6 weeks is thinner, fragile and lustreless. Quantitative and qualitative deterioration of collagen fibers, almost complete atrophy of elastic fibers and increase in number of cells and vessels is observed under microscope. After 9 weeks remodeling of the fascia occurs which thickens and increases in number of fascicular collagen fibres, after 12 weeks the foci of neochondrogenesis can be found. After 26 weeks a new hyaline like cartilage is generated surrounded by connective tissue containing fascicular collagen and elastic fibers. At this point remodeling is not yet completed.