Lineage plasticity and cell biology of fibrocartilage and hyaline cartilage: Its significance in cartilage repair and replacement

Cartilage repair is a major goal of modern tissue engineering. To produce novel engineered implants requires a knowledge of the basic biology of the tissues that are to be replaced or reproduced. Hyaline articular cartilage and meniscal fibrocartilage are two tissues that have excited attention because of the frequency with which they are damaged. A basic strategy is to re-engineer these tissues ex vivo by stimulating stem cells to differentiate into the cells of the mature tissue capable of producing an intact functional matrix. In this brief review, the sources of cells for tissue engineering cartilage and the culture conditions that have promoted differentiation are discussed within the context of natural cartilage repair. In particular, the role of cell density, cytokines, load, matrices and oxygen tension are discussed.

The effect of angled osteochondral grafting on contact pressure: a biomechanical study

BACKGROUND

Flush osteochondral plugs can reduce contact pressure compared with an empty defect in the articular cartilage. However, incongruities such as graft angulation have an unknown effect.

HYPOTHESIS

Incongruity of the articular cartilage after osteochondral transplantation affects articular surface contact pressure.

STUDY DESIGN

Controlled laboratory study.

METHODS

An 80-N load was applied with a material testing system for 120 seconds to the femoral condyles of 50 fresh swine knees. Contact pressures were measured using Prescale super low film. Five conditions were tested: (1) intact articular surface; (2) surface with 4.5-mm-diameter circular defect; (3) defect grafted with a flush 4.5-mm-diameter plug from the contralateral condyle; (4) defect grafted with a 30 degrees angled 4.5-mm-diameter plug, with lower edge flush (tip elevated with respect to the adjacent surface); and (5) defect grafted with a 30 degrees plug, with tip flush to the adjacent surface (lower edge sunk). Angled grafts were obtained using a rotational bearing vise aligned with a 30 degrees fixed-angle track. The film was digitally scanned and analyzed, and standard statistical tests were performed.

RESULTS

Mean peak pressures of intact cartilage (8.57 kg/cm2), flush graft (9.81 kg/cm2), and sunk and angled graft (9.15 kg/cm2) were not significantly different (P < .5). The mean pressures for defects (12.01 kg/cm2) and the elevated angled graft (14.50 kg/cm2) were significantly (P < .05) higher than that of intact cartilage.

CLINICAL RELEVANCE

Slightly sunk grafts were still able to reduce elevated contact pressures to normal levels. However, elevated angled grafts increased contact pressure. These results suggest that it is preferable to leave an edge slightly sunk rather than elevated.

Tissue engineered cartilage integration to live and devitalized cartilage: a study by reflectance mode confocal microscopy and standard histology

This study investigated the in vivo formation of engineering cartilage within living or devitalized cartilage discs using reflectance mode confocal microscopy and conventional light microscopy. Pig articular chondrocytes were suspended in fibrin glue and placed between two cartilage discs. Four experimental groups were prepared: in groups 1 and 2, the cell-hydrogel composite was placed between two live or between two devitalized cartilage discs, respectively; in groups 3 and 4, acellular fibrin glue was placed between two live or between two devitalized cartilage discs, respectively. Samples were implanted in the back of nude mice and analyzed after 2, 5, and 8 weeks. Results showed that engineered cartilage seems to grow more homogenously when the cell-seeded gel was placed between devitalized cartilages than when it was placed between live cartilage matrices. Confocal microscopy provides valuable information on the integration of tissue-engineered cartilage with native tissue and could be useful for nondestructive imaging in vivo.

Ingénierie tissulaire du cartilage : état des lieux et perspectives

Lesions of the articular cartilage have a large variety of causes among which traumatic damage, osteoarthritis and osteochondritis dissecans are the most frequent. Returning damaged cartilage in articular joints back to a functionally normal state has been a major challenge for orthopaedic surgeons. This interest results in large part because cartilage defects cannot adequately heal themselves. Current techniques used in orthopaedic practice to repair cartilage give variable and unpredictable results. Bone marrow stimulation techniques such as abrasion arthroplasty, drilling and microfracture produce mostly fibrocartilage. Autologous osteochondral transplant systems (mosaicplasty) have shown encouraging results. Autologous chondrocyte transplantation has led to a hyaline articular cartilage repair but little is known about the predictability and reliability of the procedure. The rapidly emerging field of tissue engineering promises creation of viable substitutes for failing cartilage tissue. Current tissue engineering approaches are mainly focused on the restoration of pathologically altered tissue structure based on the transplantation of cells in combination with supportive matrices and molecules. Among natural and synthetic matrices, collagen and polysaccharidic biomaterials have been extensively used with promising results. Recently, interest has switched to the use of mesenchymal stem cells instead of chondrocytes. Tissue engineering offers the possibility to treat localised cartilage lesions. Genetic engineering techniques using genetically modified chondrocytes offer also the opportunity to treat diffuse cartilage lesions occurring in osteoarthritis or inflammatory joint diseases. Electroporation is specially a reliable and inexpensive technique that shares with electrochemotherapy an ability to target the chondrocytes despite the barrier effect of the extracellular matrix without viral vectors. The authors review recent research achievements and highlight the potential clinical applications of new technologies in the treatment of patients with cartilage injuries.

Transduced bovine articular chondrocytes affect the metabolism of cocultured nucleus pulposus cells in vitro: implications for chondrocyte transplantation into the intervertebral disc

STUDY DESIGN

Biologic study on the effects of coculture of bovine articular chondrocytes transduced ex vivo with genes expressing bone morphogenetic proteins (BMPs) on nucleus pulposus (NP) cells.

OBJECTIVE

To evaluate the effects of bovine articular chondrocytes transduced with adenoviruses expressing various BMPs on proteoglycan and collagen production, and cellular proliferation of NP cells in vitro.

SUMMARY OF BACKGROUND DATA

Matrix synthesis by intervertebral disc cells is promoted by exposing the cells to growth factors or delivering genes that permit sustained expression of growth factors. We propose a novel therapeutic approach involving delivery of autologous chondrocytes, transduced ex vivo with bioactive proteins, to provide both the cells and proteins required to stimulate disc healing.

METHODS

Adult bovine articular chondrocytes were transduced with adenoviruses (Ads) expressing either BMP-2, 4, 5, 7, 10, or 13 and plated as monolayers. Bovine NP cells encapsulated in alginate beads were cocultured, floating in the medium. Proteoglycan and collagen accumulation, and NP cell proliferation were measured after 6 days of coculture. As a positive control, beads were cocultured with articular chondrocytes in the presence of rhBMP-7.

RESULTS

NP cells cocultered with articular chondrocytes transduced with BMPs-2, 4, 7, and 10 accumulated significantly (P < 0.05) more proteoglycan than when cocultured with chondrocytes transduced with AdGFP (control) [AdBMP-2: 23.6%; AdBMP-4: 27.0%; AdBMP-7: 129.1%; AdBMP-10: 102.1% increases respectively]. Collagen accumulation was significantly (P < 0.05) increased by NP cells cocultured with articular chondrocytes transduced with BMPs-2, 4, 5, and 7. [AdBMP-2: 104.6%; AdBMP-4: 40.6%; AdBMP-5: 58.6%; AdBMP-7: 55.5% increases respectively]. NP cells proliferated when cocultured with articular chondrocytes transduced with AdBMP-2 and -7.

CONCLUSIONS

Bovine NP cells are stimulated to produce proteoglycans and collagen when exposed to chondrocytes transduced with genes for various BMPs. If applied to the treatment of disc degeneration, this strategy could provide the disc with not only metabolically active chondrocytes but also promote matrix replenishment by stimulating native NP cells.

Heterogeneous three-dimensional strain fields during unconfined cyclic compression in bovine articular cartilage explants

Articular cartilage provides critical load-bearing and tribological properties to the normal function of diarthrodial joints. The unique properties of cartilage, as well as heterogeneous deformations during mechanical compression, are due to the nonuniform microstructural organization of tissue components such as collagens and proteoglycans. A new cartilage deformation by tag registration (CDTR) technique has been developed by the authors to determine heterogeneous deformations in articular cartilage explants. The technique uses a combination of specialized MRI methods, a custom cyclic loading apparatus, and image processing software. The objective of this study was to use the CDTR technique to document strain patterns throughout the volume of normal bovine articular cartilage explants during cyclic unconfined compression at two physiologically-relevant applied normal stress levels (1.29 and 2.57 MPa). Despite simple uniaxial cyclic compressive loading with a flat, nonporous indenter, strain patterns were heterogeneous. Strains in the thickness direction (E(yy)) were compressive, varied nonlinearly with depth from the articular surface from a maximum magnitude of 11% at the articular surface, and were comparable despite a 2-fold increase in applied normal stress. Strains perpendicular to the thickness direction (E(xx) and E(zz)) were tensile, decreased linearly with depth from the articular surface from a maximum of 7%, and increased in magnitude 2.5-fold with a 2-fold increase in applied normal stress. Shear strains in the transverse plane (E(xz)) were approximately zero while shear strains in the other two planes were much larger and increased in magnitude with depth from the articular surface, reaching maximum magnitudes of 2% at the articular cartilage-subchondral bone interface. In general, strain patterns indicated that cartilage osteochondral explants exhibited depth-dependent nonisotropic behavior during uniaxial cyclic loading. These results are useful in verifying constitutive formulations of articular cartilage during cyclic unconfined compression and in characterizing the micromechanical environment likely experienced by individual chondrocytes throughout the tissue volume.

The autologous osteochondral transplantation of the knee: clinical results, radiographic findings and histological aspects

INTRODUCTION

The osteochondral transplantation (OCT) is a well accepted treatment option for focal cartilage lesions in the knee joint, whereas the fate of the transplanted cartilage is still unclear and the clinical outcome is variable. The purpose of this study was to evaluate the histological character of autologous transplanted cartilage and to correlate technical aspects and the patients' history with the clinical outcome.

MATERIAL AND METHODS

The OCT was performed in 27 patients (median age of 32 (22-43) years) with a focal chondral lesion at the medial femoral condyle. We investigated the clinical outcome after a median follow-up of 13.5 (5-28) months using the Lysholm-score and the integration of the transplanted plugs using an MRI-scoring system. Biopsy specimens from representative patients (n = 8) were evaluated with histological staining and immunohistochemistry.

RESULTS

The median Lysholm-score was 80 (range 45-98). The wide range of the Lysholm-score in clinical outcome did not show significant differences in: follow-up, concomitant injuries, defect size or genesis. The MRI analysis revealed in all cases a regular osseous integration of the subchondral bone, but a failed chondral integration. The congruency of the plugs to the joint surface was often incorrect, however a correlation between the MRI-score and the clinical outcome could not be shown. Histology of the transplanted cartilage revealed small changes in immunohistochemistry after a relatively short-term follow-up, whereas the cartilage has still the typical hyaline character. Often, the surrounding cartilage consists of fibrous and granulation tissue.

CONCLUSION

The congruency of the joint surface can not be restored to the original status, particularly in larger defects with irregular shapes. However, we did not find any aspects which affected the function of the knee joint following OCT. It can be assumed that remaining lesions at the surrounding cartilage could maintain the inflammatory process and therefore maintain the pain and a low knee function. Further investigations are needed to specify the effects of the OCT on the transplanted cartilage and its influence on the later clinical outcome.

Arthroscopic osteochondral autografting

Arthroscopic osteochondral autografting is indicated for unipolar, full thickness articular cartilage lesions between 1 and 2.5 cm in diameter. A stable properly aligned knee is important to a good outcome. This procedure should not be performed in the presence of generalized osteoarthritis. Arthroscopic osteochondral autografting allows the restoration of hyaline articular cartilage with zonal matching of the graft. It is cost-effective, can be performed on an outpatient basis, and results in durable resurfacing with excellent long-term results.

Osteochondral autograft transplantation for osteochondritis dissecans of the capitellum in nonthrowing athletes

In this report, we present the cases of 3 nonthrowing athletes with osteochondritis dissecans of the capitellum. Preoperatively, they complained of elbow pain during rhythmic gymnastics, table tennis, and basketball, respectively. Magnetic resonance imaging showed a completely separated osteochondral fragment or a full-thickness cartilage defect. All 3 patients were treated with transplantation of an osteochondral autograft harvested from the lateral femoral condyle. They returned fully to their sports activities within 6 months of surgery. The continuity of the cartilage layer between the osteochondral graft and the capitellum was shown on magnetic resonance images taken at 12 months postoperatively. We believe that osteochondral autograft transplantation provides successful results for nonthrowing athletes with end-stage osteochondritis dissecans of the capitellum.

Development and remodeling of engineered cartilage-explant composites in vitro and in vivo

OBJECTIVE

Development and remodeling of engineered cartilage-explant composites were studied in vitro and in vivo.

DESIGN

Individual and interactive effects of cell chondrogenic potential (primary or fifth passage bovine calf chondrocytes), scaffold degradation rate (hyaluronan benzyl ester or polyglycolic acid), and adjacent tissue cell activity and architecture (vital trabecular bone (VB), articular cartilage (AC), devitalized bone (DB) or digested cartilage (DC)) were evaluated over 8 weeks in vitro (bioreactor cultures) and in vivo (ectopic implants).

RESULTS

In vitro, significant effects of cell type on construct adhesive strength (P<0.001) and scaffold type on adhesive strength (P<0.001), modulus (P=0.014), glycosaminoglycans (GAG) (P<0.001), and collagen (P=0.039) were observed. Chondrogenesis was best when the scaffold degradation rate matched the extracellular matrix deposition rate. In vivo, adjacent tissue type affected adhesive strength (P<0.001), modulus (P<0.001), and GAG (P<0.001) such that 8-week values obtained for bone (VB and DB) were higher than for cartilage (AC). In the AC/construct group, chondrogenesis appeared attenuated in the region of the construct close to the AC. In contrast, in the VB/construct group, a 500 microm thick zone of mature hyaline-like cartilage formed at the interface, and signs of active remodeling were present in the bone that included osteoclastic and osteoblastic activity and trabecular rebuttressing; these features were not present in the DB group or in vitro.

CONCLUSIONS

Development and remodeling of composites based on engineered cartilage were mediated in vitro by cell chondrogenic potential and scaffold degradation rate, and in vivo by type of adjacent tissue and time.

Fresh ankle osteochondral allograft transplantation for tibiotalar joint arthritis

BACKGROUND

Conventional treatment for tibiotalar joint arthritis relies on arthrodesis or prosthetic arthroplasty. Fresh osteochondral allografting is an alternative procedure to replace diseased articular cartilage.

METHODS

Eleven patients (average age 43 years; range 18 to 65 years) had fresh osteochondral grafting of the tibiotalar joint. The diagnoses were posttraumatic arthritis in seven ankles, osteoarthritis in two, and an osteochondral defect in two. Precise cuts were made using the Agility (DePuy, Warsaw IN) ankle arthroplasty jigs. Bipolar replacements were used in nine ankles and unipolar in two. Results were evaluated using outcome scores, physical examinations, and standing ankle radiographs.

RESULTS

At a minimum followup of 24 (average 33; range 26 to 45) months, six of the 11 ankles had successful grafting procedures. The average AOFAS score preoperatively improved from 55 to 73 postoperatively (p = 0.01). The patients' pain, gait, and walking surface scores were all significantly improved (p < 0.05). Of the five failures three underwent successful repeat allografting and one was revised to a total ankle arthroplasty, and one has had no further surgery. The ankle range of motion arc was 30 degrees or more in six ankles. Additional surgery included five talofibular joint debridements, three repeat graftings, two hardware removals, and one conversion to a prosthetic ankle replacement. There was one intraoperative fibular fracture and one superficial wound infection. The serum of 10 patients tested positive for cytotoxic HLA antibodies postoperatively. Radiographs revealed moderate and severe joint degeneration in six ankles; however, this did not necessarily correlate with a poor outcome. Poor results tended to occur in ankles with a graft-host size mismatch or graft thickness of less than 7 mm.

CONCLUSION

Fresh osteochondral transplantation for tibiotalar joint arthritis is a promising alternative to arthrodesis and prosthetic replacement. Early results demonstrate successful outcomes and good pain relief in over half the patients in this series.

Elimination of rheumatoid synovium in situ using a Fas ligand 'gene scalpel'

Surgical synovectomy to remove the inflammatory synovium can temporarily ameliorate rheumatoid inflammation and delay the progress of joint destruction. An efficient medically induced programmed cell death (apoptosis) in the rheumatoid synovium might play a role similar to synovectomy but without surgical tissue damage. Gene transfer of Fas ligand (FasL) has increased the frequency of apoptotic cells in mouse and rabbit arthritic synovium. In this study, we investigated whether repeated FasL gene transfer could remove human inflammatory synovial tissue in situ and function as a molecular synovectomy. Briefly, specimens of human synovium from joint replacement surgeries and synovectomies of rheumatoid arthritis (RA) patients were grafted subcutaneously into male C.B-17 severe combined immunodeficiency (SCID) mice. Injections of a recombinant FasL adenovirus (Ad-FasL) into the grafted synovial tissue at the dosage of 10(11) particles per mouse were performed every two weeks. Three days after the fifth virus injection, the mice were euthanized by CO2 inhalation and the human synovial tissues were collected, weighed and further examined. Compared to the control adenovirus-LacZ (Ad-LacZ) and phosphate buffered saline (PBS) injected RA synovium, the Ad-FasL injected RA synovium was dramatically reduced in size and weight (P < 0.005). The number of both synoviocytes & mononuclear cells was significantly reduced. Interestingly, an approximate 15-fold increased frequency of apoptotic cells was observed in RA synovium three days after Ad-FasL injection, compared with control tissues. In summary, our in vivo investigation of gene transfer to human synovium in SCID mice suggests that repeated intra-articular gene transfer of an apoptosis inducer, such as FasL, may function as a 'gene scalpel' for molecular synovectomy to arrest inflammatory synovium at an early stage of RA.

Osteochondral autograft transfer of the first metatarsal head: a case report

A case of an osteochondral autograft transfer performed at the head of the first metatarsal for an acute incidence of traumatic osteochondritis dissecans was presented. The donor site for the osteochondral graft was from the medial and plantar aspect of the talar head, which was found to be composed entirely of articular hyaline cartilage, yet was not part of the functional talonavicular articulation. Six months postoperatively, the graft was well seated at the head of the first metatarsal, as confirmed by magnetic resonance imaging, and the graft donor site was asymptomatic. At 12 months' follow-up, the patient had a functional metatarsophalangeal joint range of motion. Details from the case study as well as a review of the literature are presented.

Contact pressures at grafted cartilage lesions in the knee

The use of tissue-engineered cellular constructs is currently under clinical evaluation for the surgical treatment of articular cartilage lesions in the knee. The primary failure mode in such cartilage repair techniques is related to fixation. In addition, the repair tissue is believed to be very fragile in the post-operative period, and unable to support the intra-articular loads. We have developed a laboratory testing protocol in order to quantify the contact pressure distribution that develops on fibrin glue grafts applied to full-thickness cartilage lesions. The contact pressure distribution has been mapped on the contact surface of specimens subject to compression, in three configurations (intact, defect and grafted), at increasing load levels. All the maps show stress concentrations at the rim of the defect and a more uniform stress distribution around the rim after defect grafting. At a contact load of 180 N, the peak contact pressure measured on cartilage is 2.5 MPa. In presence of the graft, the peak pressures on the cartilage area surrounding the defect are reduced by 16%, on average. In contrast, both the mean contact pressure on the graft and the graft's contact area increase. The graft was found to carry around 80% of the total applied contact load, at all load levels tested. Fibrin glue was chosen as a grafting material in our study because it shows material properties very representative of currently-implanted cellular constructs. Thus, the results of this study have quantified aspects of recipient graft sites that may assist in optimising such grafting procedures from a biomechanical point of view.

Impact loading of articular cartilage during transplantation of osteochondral autograft

Surgical reconstruction of articular surfaces by transplantation of osteochondral autografts has shown considerable promise in the treatment of focal articular lesions. During mosaicplasty, each cylindrical osteochondral graft is centred over the recipient hole and delivered by impacting the articular surface. Impact loading of articular cartilage has been associated with structural damage, loss of the viability of chondrocytes and subsequent degeneration of the articular cartilage. We have examined the relationship between single-impact loading and chondrocyte death for the specific confined-compression boundary conditions of mosaicplasty and the effect of repetitive impact loading which occurs during implantation of the graft on the resulting viability of the chondrocytes.

Fresh bovine and porcine femoral condyles were used in this experiment. The percentage of chondrocyte death was found to vary logarithmically with single-impact energy and was predicted more strongly by the mean force of the impact rather than by the number of impacts required during placement of the graft. The significance of these results in regard to the surgical technique and design features of instruments for osteochondral transplantation is discussed.

Treatment Options for Articular Cartilage Defects of the Knee

The treatment of symptomatic articular cartilage defects of the knee has evolved tremendously in the past decade. Previously, there were limited treatment options available to patients who suffered from either partial-thickness or full-thickness cartilage lesions. Because articular cartilage has a limited capacity for healing, patients were often treated symptomatically until they became candidates for osteotomy or total joint replacement. Recently, both reparative and restorative procedures have been developed to address this significant source of morbidity in young active patients. Microfracture is a reparative technique that induces a healing response to occur in an area of articular cartilage damage. Osteochondral autografts and allografts in addition to autologous chondrocyte implantation are restorative techniques aimed at recreating a more normal articular surface. Both types of procedures have been developed to alleviate the symptoms associated with focal chondral defects, as well as limit their potential to progress to a diffuse degenerative arthritis. Treatment can vary depending on both cartilage defect and patient factors. This article summarizes the various treatment options that have recently become available.

A prospective randomized clinical study of mosaic osteochondral autologous transplantation versus microfracture for the treatment of osteochondral defects in the knee joint in young athletes

PURPOSE

The purpose of this study was to compare the outcomes of mosaic-type osteochondral autologous transplantation (OAT) and microfracture (MF) procedures for the treatment of the articular cartilage defects of the knee joint in young active athletes.

TYPE OF STUDY

Prospective randomized clinical study.

METHODS

Between 1998 and 2002, a total of 60 athletes with a mean age of 24.3 years (range, 15 to 40 years) and with a symptomatic lesion of the articular cartilage in the knee were randomized to undergo either an OAT or an MF procedure. Only those athletes playing in competitive sports at regional or national levels were included in the study. Fifty-seven athletes (95%) were available for a follow-up. There were 28 athletes in the OAT group and 29 athletes in the MF group. The mean duration of symptoms was 21.32 +/- 5.57 months and the mean follow-up was 37.1 months (range, 36 to 38 months), and none of the athletes had prior surgical interventions to the affected knee. Patients were evaluated using modified Hospital for Special Surgery (HSS) and International Cartilage Repair Society (ICRS) scores, radiograph, magnetic resonance imaging (MRI), and clinical assessment. An independent observer performed a follow-up examination after 6, 12, 24, and 36 months. At 12.4 months postoperatively, arthroscopy with biopsy for histologic evaluation was carried out. A radiologist and a pathologist, both of whom were blinded to each patient's treatment, did the radiologic and histologic evaluations.

RESULTS

After 37.1 months, both groups had significant clinical improvement (P < .05). According to the modified HSS and ICRS scores, functional and objective assessment showed that 96% had excellent or good results after OAT compared with 52% for the MF procedure (P < .001). At 12, 24, and 36 months after surgery, the HSS and ICRS showed statistically significantly better results in the OAT group (P = .03; P = .006; P = .006). Younger athletes did better in both groups. No serious complications were reported. There was 1 failure in the OAT group and 9 in the MF group. The ICRS Cartilage Repair Assessment for macroscopic evaluation during arthroscopy at 12.4 months showed excellent or good repairs in 84% after OAT and in 57% after MF. Biopsy specimens were obtained from 58% of the patients and histologic evaluation of repair showed better scores (according to ICRS) for the OAT group (P < .05). MRI evaluation showed excellent or good repairs in 94% after OAT compared with 49% after MF. Twenty-six (93%) OAT patients and 15 (52%) MF patients returned to sports activities at the preinjury level at an average of 6.5 months (range, 4 to 8 months). Others showed a decline in sports activity level.

CONCLUSIONS

At an average of 37.1 months (range, 36 to 38 months) follow-up, our prospective, randomized, clinical study in young active athletes under the age of 40 has shown significant superiority of OAT over MF for the repair of articular cartilage defects in the knee. We found that only 52% of MF athletes could return to sports at the preinjury level. Limitations of our study included a small number of athletes and a relatively short (3-year) follow-up. A long-term follow-up is needed to assess the durability of articular cartilage repair using these methods in young active athletes.

LEVEL OF EVIDENCE

Level I, Therapeutic study, randomized controlled trial, significant difference (a).

Intra-articular hyaluronan following autogenous osteochondral grafting of the knee

PURPOSE

The aim of this study was to assess whether intra-articular hyaluronan viscosupplementation after osteochondral grafting (mosaic arthroplasty) of the knee allowed better graft integration and function in a sheep model.

TYPE OF STUDY

Experimental study.

METHODS

Twelve adult sheep underwent a mosaic arthroplasty procedure to a standardized osteochondral defect on the medial femoral condyle. One week after surgery the animals were randomized to receive a course of weekly intra-articular injections for 5 weeks of either sodium-hyaluronate solution 25 mg/2.5 mL (HA group) or of a 2.5 mL buffer solution (control group). Synovial fluid samples were taken preoperatively, preceding each injection, and at 8 and 12 weeks. The animals were euthanized at 12 weeks, the knees dissected out, and biomechanical and histologic assessments were made.

RESULTS

There was no difference in the synovial fluid leukocyte or total protein concentration between the groups, but the hyaluronan concentration was statistically higher in the HA group. Aggregate moduli of the articular surface were statistically higher in the graft articular cartilage in the HA group than in the control group, as were the sulphated glycosaminoglycan levels. Histologic assessment found more articular cartilage flow in the HA group, whereas there was more interstitial tissue present in the interstices between the grafts in the control group.

CONCLUSIONS

Results from this study suggest that hyaluronan viscosupplementation following osteochondral grafting does convey some beneficial effects on graft cartilage in the early postoperative period in an ovine model.

CLINICAL RELEVANCE

This study suggests that, in the early postoperative period, hyaluronan supplementation improves articular cartilage survival after osteochondral grafting.

Autologous osteochondral transplantation for simple cyst in the patella

Treatment options for chondral and osteochondral defects of the patella have been few and results have been inconsistent at best. Autologous osteochondral transplantation presents a new way to revisit these patellar defects. We report the case of a young female softball player with a simple cyst in the patella and an osteochondral defect that serves as the indication for autograft osteochondral transplantation.

Cutting-edge design to improve cell viability in osteochondral grafts

INTRODUCTION

Autologous osteochondral grafting is in widespread use for focal defects of articular cartilage. There is major concern over the nature of the tissue bridging graft elements and graft/recipient cartilage. Chondrocyte viability is thought to be an important determinant of the quality of repair. The aim of the current study was to compare the zone of death for osteochondral grafts harvested with the commercially available Acufex, and an osteotome with a specially designed cutting-edge.

MATERIALS/METHODS

The circular osteotomes were the Acufex 4.5mm MP (Smith & Nephew) and the Lissimore, which has a different cutting-tip geometry and sharpness. These implements were used to harvest osteochondral plugs from macroscopically non-degenerate human lateral condyle explants obtained from the anterior femoral cuts of knee replacement surgery. Confocal laser scanning microscopy with vital staining was used to quantify the zone of marginal chondrocyte death for the entire perimeter of the plugs.

RESULTS

The increase in cartilage plug diameter (reference the osteotome minimal internal diameter) was significantly greater for the Acufex (Mann-Whitney; n=5; P=0.0079), with the diameter (mm) increasing by 0.49+/-0.03 (10.9%), compared with 0.16+/-0.02 (3.3%) for the Lissimore. Osteochondral plugs had a significantly (Mann-Whitney; n=5; P=0.0079) lower mean margin of cell death with the Lissimore osteotome (117.8+/-8.97 microm) than the Acufex MP (315.3+/-5.90 microm).

CONCLUSIONS

Cutting-tip profile is an important factor in determining the extent of marginal death in circular osteochondral grafts. We have designed and assessed an alternative cutting-tip, which caused significantly less marginal death than the commercially available Acufex. We conclude that there is scope for improvement of osteochondral harvest techniques.

Normal and pathological MR findings in osteochondral autografts with longitudinal follow-up

The purpose of this study was to analyze normal and pathological MR findings in osteochondral autograft transfer systems (OATS) of the knee and ankle in the longitudinal follow-up and in relation to the clinical findings. MR imaging was performed in 55 patients (21 females: 34 males; mean age 34.5+/-12.1 years) after OATS procedures in the knee (n=45) and ankle (n=10). MR sequences were obtained with and without intravenous Gd-DTPA administration within the first year post-operatively, in 30 patients within the second and in 13 patients in the third year. One hundred and five OATS cylinders were implanted. MR findings consistent with osteonecroses were detected in eight cylinders (n=6 in the knee and n=2 in the ankle) in six patients; four out of eight were demonstrated during the first year and four/eight in the second year. Edema around and/or in the cylinders was found in 28/55 of the patients within the first year, five/30 in the second year and in two/13 in the third year. No substantial changes in the cartilage signal intensity or the cartilage-cartilage interface were demonstrated in the longitudinal follow-up within the first three years. Clinical and MR findings were not consistently associated in particular in the patients with osteochondral autograft necroses.