Medial meniscus replacement by a fat pad autograft. An experimental study in sheep

Autologous semitendinosus meniscus graft significantly improves knee joint kinematics and the tibiofemoral contact after complete lateral meniscectomy

PURPOSE

The purpose of this study was to investigate the potential of a doubled semitendinosus (ST) and a single gracilis tendon (GT) lateral meniscus autograft to restore the knee joint kinematics and tibiofemoral contact after total lateral meniscectomy (LMM).

METHODS

Fourteen human knee joints were tested intact, after LMM and after ST and GT meniscus autograft treatment under an axial load of 200 N during full range of motion (0°-120°) and four randomised loading situations: without external moments, external rotation, valgus stress and a combination of external rotation and valgus stress using a knee joint simulator. Non-parametric statistical analyses were performed on joint kinematics and on the tibiofemoral contact mechanics.

RESULTS

LMM led to significant rotational instability of the knee joints (p < 0.02), which was significantly improved after ST autograft application (p < 0.04), except for knee joint flexions > 60°. The GT autograft failed to restore the joint kinematics. LMM significantly increased the tibiofemoral contact pressure (p < 0.03), while decreasing the contact area (p < 0.05). The ST autograft was able to restore the contact mechanics after LMM (p < 0.02), while the GT replacement displayed only an improvement trend.

CONCLUSION

The doubled ST lateral meniscus autograft improved the knee joint kinematics significantly and restored the tibiofemoral contact mechanics almost comparable to the native situation. Thus, from a biomechanical point of view, ST meniscus autografts might be a potential treatment alternative for patients who are indicated for meniscus allograft transplantation.

Advances in the Mechanisms Affecting Meniscal Avascular Zone Repair and Therapies

Injuries to menisci are the most common disease among knee joint-related morbidities and cover a widespread population ranging from children and the general population to the old and athletes. Repair of the injuries in the meniscal avascular zone remains a significant challenge due to the limited intrinsic healing capacity compared to the peripheral vascularized zone. The current surgical strategies for avascular zone injuries remain insufficient to prevent the development of cartilage degeneration and the ultimate emergence of osteoarthritis (OA). Due to the drawbacks of current surgical methods, the research interest has been transferred toward facilitating meniscal avascular zone repair, where it is expected to maintain meniscal tissue integrity, prevent secondary cartilage degeneration and improve knee joint function, which is consistent with the current prevailing management idea to maintain the integrity of meniscal tissue whenever possible. Biological augmentations have emerged as an alternative to current surgical methods for meniscal avascular zone repair. However, understanding the specific biological mechanisms that affect meniscal avascular zone repair is critical for the development of novel and comprehensive biological augmentations. For this reason, this review firstly summarized the current surgical techniques, including meniscectomies and meniscal substitution. We then discuss the state-of-the-art biological mechanisms, including vascularization, inflammation, extracellular matrix degradation and cellular component that were associated with meniscal avascular zone healing and the advances in therapeutic strategies. Finally, perspectives for the future biological augmentations for meniscal avascular zone injuries will be given.

Preparation and Characterization of an Optimized Meniscal Extracellular Matrix Scaffold for Meniscus Transplantation

Many studies have sought to construct a substitute to partially replace irreparably damaged meniscus. Only the meniscus allograft has been used in clinical practice as a useful substitute, and there are concerns about its longevity and inherent limitations, including availability of donor tissue and possibility of disease transmission. To overcome these limitations, we developed an acellular xenograft from whole porcine meniscus. Samples were treated with 2% Triton X-100 for 10 days and 2% sodium dodecyl sulfate for 6 days. The DNA content of extracellular matrix (ECM) scaffolds was significantly decreased compared with that of normal porcine menisci (p < 0.001). Histological analysis confirmed the maintenance of ECM integrity and anisotropic architecture in the absence of nuclei. Biochemical and biomechanical assays of the scaffolds indicated the preservation of collagen (p = 0.806), glycosaminoglycan (p = 0.188), and biomechanical properties (elastic modulus and transition stress). The scaffolds possessed good biocompatibility and supported bone marrow mesenchymal stem cells (BMSCs) proliferation for 2 weeks in vitro, with excellent region-specific recellularization in vivo. The novel scaffold has potential value for application in recellularization and transplantation strategies.

Meniscal substitution, a developing and long-awaited demand

The menisci represent indispensable intraarticular components of a well-functioning knee joint. Sports activities, traumatic incidents, or simply degenerative conditions can cause meniscal injuries, which often require surgical intervention. Efforts in biomechanical and clinical research have led to the recommendation of a meniscus-preserving rather than a meniscus-resecting treatment approach. Nevertheless, partial or even total meniscal resection is sometimes inevitable. In such circumstances, techniques of meniscal substitution are required. Autologous, allogenic, and artificial meniscal substitutes are available which have evolved in recent years. Basic anatomical and biomechanical knowledge, clinical application, radiological and clinical outcomes as well as future perspectives of meniscal substitutes are presented in this article. A comprehensive knowledge of the different approaches to meniscal substitution is required in order to integrate these evolving techniques in daily clinical practice to prevent the devastating effects of lost meniscal tissue.

Materials and structures used in meniscus repair and regeneration: a review

Meniscus is a vital functional unit in knee joint. It acts as a lubricating structure, a nutrient transporting structure, as well as shock absorber during jumping, twisting and running and offers stability within the knee joint. It helps in load distribution, in bearing the tensile hoop stresses and balancing by providing a cushion effect between hard surfaces of two bones. Meniscus may be injured in sports, dancing, accident or any over stressed condition. Any meniscal lesion can lead to a gradual development of osteoarthritis or erosion of bone contact surface due to disturbed load and contact stress distribution caused by injury/pain. Once injured, the possibilities of self-repair are rare in avascular region of meniscus, due to lack of blood supply in avascular region. Meniscus has vascular and avascular regions in structure. Majority of the meniscus parts turn avascular with increase in age.

Purpose of this review is to highlight advances in meniscus repair with special focus on tissue engineering using textile/fiber based scaffolds, as well as the recent technical advances in scaffolds for meniscus recon- struction/ regeneration treatment.

Ultrasound anatomy of the normal stifle in the sheep

Though the ovine stifle is commonly used as a model in research, there is no description of its anatomy at ultrasonography (US). The objective of this study was to provide reference US images of the ovine stifle that are relevant in musculoskeletal research. Four pairs of hindlimbs were scanned, whilst four other pairs were frozen and cut in different planes to compare gross anatomy to US scans. In another pair, the synovial compartments of the stifle were injected and scanned. This study demonstrated that US could be used to assess the ovine stifle. Several structures of clinical interest could be identified with cranial, lateral and medial approaches, such as (a) the tendons of m. quadriceps femoris, m. gluteobiceps, m. popliteus, (b) the common tendon of m. peroneus tertius-extensor longus digitorum-extensor digiti III proprius, (c) the patellar ligament, (d) the medial and lateral collateral ligaments, (e) the cranial horn and middle segment of medial and lateral meniscus, and (f) the synovial recesses. However, the caudal approach was not successful to identify caudal anatomical structures of the joint, due to the muscular mass, that is the caudal aspects of the articular surfaces of the femoral and tibial condyles, the caudal horns of the menisci and the supracondylar synovial recesses. In addition, US remained challenging to assess the internal structures such as cruciate ligaments and articular surfaces. The feasibility of US needs to be tested in vivo.

Native tissue-based strategies for meniscus repair and regeneration

Meniscus injuries appear to be becoming increasingly common and pose a challenge for orthopedic surgeons. However, there is no curative approach for dealing with defects in the inner meniscus region due to its avascular nature. Numerous strategies have been applied to regenerate and repair meniscus defects and native tissue-based strategies have received much attention. Native tissue usually has good biocompatibility, excellent mechanical properties and a suitable microenvironment for cellular growth, adhesion, redifferentiation, extracellular matrix deposition and remodeling. Classically, native tissue-based strategies for meniscus repair and regeneration are divided into autogenous and heterogeneous tissue transplantation. Autogenous tissue transplantation is performed more widely than heterogeneous tissue transplantation because there is no immunological rejection and the success rates are higher. This review first discusses the native meniscus structure and function and then focuses on the use of the autogenous tissue for meniscus repair and regeneration. Finally, it summarizes the advantages and disadvantages of heterogeneous tissue transplantation. We hope that this review provides some suggestions for the future design of meniscus repair and regeneration strategies.

Meniscal transplantation: state of the art

Meniscal resection is the most common surgical procedure in orthopaedics. When a large meniscal loss becomes clinically relevant, meniscal allograft transplantation (MAT) is a feasible option. However, although this technique has evolved since the ‘80s, there are still several controversial issues related to MAT. Most importantly, its chondroprotective effect is still not completely proven. Its relatively high complication and reoperation rate is another reason for this procedure not yet being universally accepted. Despite its controversial chondroprotective effect, nevertheless, MAT has become a successful treatment for pain localised in a previously meniscectomised knee, in terms of pain relief and knee function. We conducted a careful review of the literature, highlighting the most relevant studies in various aspects of this procedure. Precise indications, how it behaves biomechanically, surgical techniques, return to sport and future perspectives are among the most relevant topics that have been included in this state-of-the-art review.

A new method for meniscus repair using type I collagen scaffold and infrapatellar fat pad

AIM

The aim of this study was to investigate a new method for meniscal repair by combinative transplantation with type I collagen scaffold and infrapatellar fat pad.

METHODS

Two-mm cylindrical defects at the anterior part of bilateral medial menisci were prepared in nine Japanese white rabbits. The 18 knees were equally divided into three groups: I, no treatment; II, collagen scaffold transplantation; and III, collagen scaffold and infrapatellar fat pad transplantation. Another three rabbits (six knees) underwent sham surgery and served as controls. Rabbits were sacrificed at eight weeks after transplantation. Surface area of the medial meniscus was evaluated using macrophotographs. Ishida score for meniscal regeneration was used for assessment. To evaluate the composition of regenerated tissue, immunohistochemistry was analyzed with anti-type I and anti-type II collagen antibodies, and anti-Ki67 antibody. To investigate the effects of collagen scaffold on human meniscus, cells were isolated from human meniscus and infrapatellar fat pad, and cultured with collagen scaffold for three weeks. After that, gene expression was evaluated by using quantitative real-time polymerase chain reaction.

RESULTS

In group I, the meniscus shrank anterior to posterior, and the surface area was significantly less than that of normal meniscus. However, the surface area was maintained in group III. Ishida score and Ki67-positive cell ratio in group III were significantly higher than that in any other group, and staining with type I and type II collagen was similar to that of the control. Expression of matrix metalloproteinase was significantly lower in cocultures of collagen scaffold, meniscus cell, and infrapatellar fat pad cell than in monocultured meniscus cell, and expression of interleukin-1β was not increased.

CONCLUSION

This new method for meniscal repair by combinative transplantation with type I collagen scaffold and infrapatellar fat pad showed meniscal regeneration and potential for suppressing inflammation.

PLDLA/PCL-T Scaffold for Meniscus Tissue Engineering

The inability of the avascular region of the meniscus to regenerate has led to the use of tissue engineering to treat meniscal injuries. The aim of this study was to evaluate the ability of fibrochondrocytes preseeded on PLDLA/PCL-T [poly(L-co-D,L-lactic acid)/poly(caprolactone-triol)] scaffolds to stimulate regeneration of the whole meniscus. Porous PLDLA/PCL-T (90/10) scaffolds were obtained by solvent casting and particulate leaching. Compressive modulus of 9.5±1.0 MPa and maximum stress of 4.7±0.9 MPa were evaluated. Fibrochondrocytes from rabbit menisci were isolated, seeded directly on the scaffolds, and cultured for 21 days. New Zealand rabbits underwent total meniscectomy, after which implants consisting of cell-free scaffolds or cell-seeded scaffolds were introduced into the medial knee meniscus; the negative control group consisted of rabbits that received no implant. Macroscopic and histological evaluations of the neomeniscus were performed 12 and 24 weeks after implantation. The polymer scaffold implants adapted well to surrounding tissues, without apparent rejection, infection, or chronic inflammatory response. Fibrocartilaginous tissue with mature collagen fibers was observed predominantly in implants with seeded scaffolds compared to cell-free implants after 24 weeks. Similar results were not observed in the control group. Articular cartilage was preserved in the polymeric implants and showed higher chondrocyte cell number than the control group. These findings show that the PLDLA/PCL-T 90/10 scaffold has potential for orthopedic applications since this material allowed the formation of fibrocartilaginous tissue, a structure of crucial importance for repairing injuries to joints, including replacement of the meniscus and the protection of articular cartilage from degeneration.

Meniscus reconstruction: today's achievements and premises for the future

Injuries of the meniscus remain a burden for the development of premature cartilage degeneration and osteoarthritis. This review surveys all treatment options and focuses on the recent development of tissue engineering. Tissue engineering of the meniscus means a successful combination of cells, scaffolds and specific stimuli. Each element of the combination can be subject to variation. Studies investigating the optimum meniscus implant and previous steps in producing these implants are presented in this article. A comprehensive search of the English and German literature was performed in PubMed to retrieve appropriate manuscripts for review. Based on the literatures, autografts and allografts can delay the progress of osteoarthritis for a restricted time period, but several concerns persist. The biomechanical properties of the native meniscus are not copied entirely by the current existing autografts. Congruence, fixation, biocompatibility and potential infection will always remain as limitations for the users of allografts. Long-term results are still not available for meniscus prosthesis and even though it permits fast recovery, several aspects are questionable: bioincompatibility and a lack of cellular adhesion are likely to compromise their long-term fate. Currently, there is no ideal implant generated by means of tissue engineering. However, meniscus tissue engineering is a fast developing field, which promises to develop an implant that mimics histological and biomechanical properties of the native meniscus. At present several cell sources and scaffolds have been used successfully to grow 3-dimensional constructs. In future, optimal implants have to be developed using growth factors, modified scaffolds and stimuli that support cellular proliferation and differentiation to regenerate the native meniscus more closely.

Expanded human meniscus-derived cells in 3-D polymer-hyaluronan scaffolds for meniscus repair

Treatment options for lesions of the avascular region of the meniscus using regenerative medicine approaches based on resorbable scaffolds are rare. Recent approaches using scaffold-based techniques for tissue regeneration known from cartilage repair may be a promising treatment option for meniscal tears. The aim of the study was the investigation of meniscus matrix formation of in vitro expanded human meniscus-derived cells in a three-dimensional (3-D) bioresorbable polymer graft for meniscal repair approaches. Cultivation of the human meniscus cells was performed in a resorbable scaffold material made of polyglycolic acid (PGA) and hyaluronic acid, stabilized with fibrin glue. Cell viability and distribution of human meniscus cells in PGA-hyaluronan scaffolds were evaluated by fluorescein diacetate and propidium iodide staining. Verification of typical meniscal extracellular matrix molecules like type I and type III collagen was performed histologically, immunohistochemically and by gene expression analysis. In results, 3-D scaffold-based meniscus cultures showed high cell viability over an observational period of 21 days in PGA-hyaluronan scaffolds. On the protein level, type I collagen and proteoglycans were evident. Gene expression analysis confirmed the re-expression of meniscus-specific markers in PGA-hyaluronan scaffolds. This study demonstrated that in vitro expanded human meniscus cells allow for formation of meniscal matrix components when cultured in 3-D PGA-hyaluronan scaffolds stabilized with fibrin. These results encourage scaffold-based approaches for the treatment of meniscal lesions.

A study of the anatomy and injection techniques of the ovine stifle by positive contrast arthrography, computed tomography arthrography and gross anatomical dissection

Although ovine stifle models are commonly used to study osteoarthritis, meniscal pathology and cruciate ligament injuries and repair, there is little information about the anatomy of the joint or techniques for synovial injections. The objectives of this study were to improve anatomical knowledge of the synovial cavities of the ovine knee and to compare intra-articular injection techniques. Synovial cavities of 24 cadaver hind limbs from 12 adult sheep were investigated by intra-articular resin, positive-contrast arthrography, computed tomography (CT) arthrography and gross anatomical dissection. Communication between femoro-patellar, medial femoro-tibial and lateral femoro-tibial compartments occurred in all cases. The knee joint should be considered as one synovial structure with three communicating compartments. Several unreported features were observed, including a communication between the medial femoro-tibial and lateral femoro-tibial compartments and a latero-caudal recess of the lateral femoro-tibial compartment. No intermeniscal ligament was identified. CT was able to define many anatomical features of the stifle, including the anatomy of the tendinous synovial recess on the lateral aspect of the proximal tibia under the combined tendon of the peroneus tertius, extensor longus digitorum and extensor digiti III proprius. An approach for intra-articular injection into this recess (the subtendinous technique) was assessed and compared with the retropatellar and paraligamentous techniques. All three injection procedures were equally successful, but the subtendinous technique appeared to be most appropriate for synoviocentesis and for injections in therapeutic research protocols with less risk of damaging the articular cartilage.

Chondroprotective effects of a polycarbonate-urethane meniscal implant: histopathological results in a sheep model

PURPOSE

injury or loss of the meniscus generally leads to degenerative osteoarthritic changes in the knee joint. However, few surgical options exist for meniscal replacement. The goal of this study was to examine the ability of a non-degradable, anatomically shaped artificial meniscal implant, composed of Kevlar-reinforced polycarbonate-urethane (PCU), to prevent progressive cartilage degeneration following complete meniscectomy.

METHODS

the artificial meniscus was implanted in the knees of mature female sheep following total medial meniscectomy, and the animals were killed at 3- and 6-months post-surgery. Macroscopic analysis and semi-quantitative histological analysis were performed on the cartilage of the operated knee and unoperated contralateral control joint.

RESULTS

the PCU implants remained well secured throughout the experimental period and showed no signs of wear or changes in structural or material properties. Histological analysis showed relatively mild cartilage degeneration that was dominated by loss of proteoglycan content and cartilage structure. However, the total osteoarthritis score did not significantly differ between the control and operated knees, and there were no differences in the severity of degenerative changes between 3 and 6 months post-surgery.

CONCLUSION

current findings provide preliminary evidence for the ability of an artificial PCU meniscal implant to delay or prevent osteoarthritic changes in knee joint following complete medial meniscectomy.

Changes in articular cartilage after meniscectomy and meniscus replacement using a biodegradable porous polymer implant

PURPOSE

To evaluate the long-term effects of implantation of a biodegradable polymer meniscus implant on articular cartilage degeneration and compare this to articular cartilage degeneration after meniscectomy.

METHODS

Porous polymer polycaprolacton-based polyurethane meniscus implants were implanted for 6 or 24 months in the lateral compartment of Beagle dog knees. Contralateral knees were meniscectomized, or left intact and served as controls. Articular cartilage degeneration was evaluated in detail using India ink staining, routine histology, immunochemistry for denatured (Col2-¾M) and cleaved (Col2-¾C(short)) type II collagen, Mankin's grading system, and cartilage thickness measurements.

RESULTS

Histologically, fibrillation and substantial immunohistochemical staining for both denatured and cleaved type II collagen were found in all three treatment groups. The cartilage of the three groups showed identical degradation patterns. In the 24 months implant group, degradation appeared to be more severe when compared to the 6 months implant group and meniscectomy group. Significantly more cartilage damage (India ink staining, Mankin's grading system, and cartilage thickness measurements) was found in the 24 months implant group compared to the 6 months implant group and meniscectomy group.

CONCLUSION

Degradation of the cartilage matrix was the result of both mechanical overloading as well as localized cell-mediated degradation. The degeneration patterns were highly variable between animals. Clinical application of a porous polymer implant for total meniscus replacement is not supported by this study.

Meniscal tears

The menisci are two semilunar-shaped fibrocartilagenous structures, which are interposed between the femoral condyles and tibial plateaux. They have an important role in knee function. Long-term follow-up studies showed that virtually all meniscectomized knees develop arthritic changes with time. The meniscus has functions in load bearing, load transmission, shock absorption, joint stability, joint lubrication, and joint congruity. Because of these functions, meniscal tissue should be preserved whenever possible. A well-trained surgeon can safely rely on clinical examination for diagnosing meniscal injuries. History and clinical examination are at least as accurate as magnetic resonance imaging in the skilled orthopedic surgeon’s hand. When meniscal repair is not possible, partial resection of the meniscus is indicated. Meniscal repair has evolved from open to arthroscopic techniques, which include the inside-out and outside-in suture repairs and the all-inside techniques. Meniscal transplantation is generally accepted as a management alternative option for selected symptomatic patients with previous complete or near-complete meniscectomy.

Generation and characterization of a human acellular meniscus scaffold for tissue engineering

Meniscus tears are frequent indications for arthroscopic evaluation which can result in partial or total meniscectomy. Allografts or synthetic meniscus scaffolds have been used with varying success to prevent early degenerative joint disease in these cases. Problems related to reduced initial and long-term stability, as well as immunological reactions prevent widespread clinical use so far. Therefore, the aim of this study was to develop a new construct for tissue engineering of the human meniscus based on an acellular meniscus allograft. Human menisci (n = 16) were collected and acellularized using the detergent sodium dodecyl sulfate as the main ingredient or left untreated as control group. These acellularized menisci were characterized biomechanically using a repetitive ball indentation test (Stiffness N/mm, residual force N, relative compression force N) and by histological (hematoxylin-eosin, phase-contrast) as well as immunohistochemical (collagen I, II, VI) investigation. The processed menisci histologically appeared cell-free and had biomechanical properties similar to the intact meniscus samples (p > 0.05). The collagen fiber arrangement was not altered, according to phase-contrast microscopy and immunohistochemical labeling. The removal of the immunogenic cell components combined with the preservation of the mechanically relevant parts of the extracellular matrix could make these scaffolds ideal implants for future tissue engineering of the meniscus.

What tissue bankers should know about the use of allograft meniscus in orthopaedics

The menisci of the knee are two crescent shaped cartilage shock absorbers sitting between the femur and the tibia, which act as load sharers and shock absorbers. Loss of a meniscus leads to a significant increase in the risk of developing arthritis in the knee. Replacement of a missing meniscus with allograft tissue can reduce symptoms and may potentially reduce the risk of future arthritis. Meniscal allograft transplantation is a complex surgical procedure with many outstanding issues, including 'what techniques should be used for processing and storing grafts?', 'how should the allografts be sized?' and 'what surgical implantation techniques might be most appropriate?' Further clinical research is needed and close collaboration between the users (surgeons) and the suppliers (tissue banks) is essential. This review explores the above subject in detail.

The effects of lateral meniscal allograft transplantation techniques on tibio-femoral contact pressures

This paper reports a series of comparative tests in vitro, that examined how meniscectomy and meniscal allografting affected tibio-femoral joint contact pressure. Knees were loaded in axial compression and pressure maps obtained from the lateral compartment using Fuji Prescale film inserted below the meniscus. This was repeated after meniscectomy, and then after meniscal allografting with fixation by a bone plug for the insertional ligaments, plus sutures. Finally, the pressure, when the allograft was secured by sutures alone, was measured. The peak pressure rose significantly after meniscectomy, and then was reduced significantly by both allograft methods so that it was not significantly different to normal. Allografts fixed by sutures only allowed slightly higher contact pressure than when they had bone fixation. This study suggests that meniscal allografting should have a chondroprotective effect and that there is a small advantage from adding bony fixation to suture fixation.

The influence of nonanatomical insertion and incongruence of meniscal transplants on the articular cartilage in an ovine model

BACKGROUND

Adequate size matching and anatomically correct positioning must be recognized as essential factors influencing the outcome of meniscal transplantation.

HYPOTHESIS

Nonanatomical insertion and incongruence of meniscal transplants has an influence on the development of degenerative changes.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten female sheep were used for this animal study. Both knees (N = 20) were divided into 3 groups, subjected to either meniscectomy (group I; n = 10), to a medial meniscal autograft transplantation with a nonanatomical insertion of the anterior and posterior horn (group II; n = 5), or a meniscal autograft transplantation from the opposite knee as an incongruent meniscal autograft (group III; n = 5). After 6 months, radiographic (Fairbank's criteria), macroscopic (Jackson score), and histological evaluation by light microscopy (Mankin score) and scanning electron microscopy of the articular cartilage was performed.

RESULTS

All applied evaluation methods demonstrated that nonanatomical insertion of meniscal transplants resulted in the highest amount of degenerative cartilage changes. The histological assessment even revealed a significantly enlarged cartilage damage for the non-anatomic-positioned meniscal transplants in relation to the meniscectomized knees. Furthermore, the incongruent meniscal transplants demonstrated a significantly better cartilage situation than nonanatomically inserted meniscal transplants.

CONCLUSION

The histological evaluation demonstrated clearly that a nonanatomically inserted meniscal transplant leads to degenerative cartilage changes that are worse than that after meniscectomy.

CLINICAL RELEVANCE

Precise anatomic positioning is mandatory for the potential chondroprotective effect of meniscal transplants.

In vitro analysis of an allogenic scaffold for tissue-engineered meniscus replacement

Scaffolds play a key role in the field of tissue engineering. Particularly for meniscus replacement, optimal scaffold properties are critical. The aim of our study was to develop a novel scaffold for replacement of meniscal tissue by means of tissue engineering. Emphasis was put on biomechanical properties comparable to native meniscus, nonimmunogenecity, and the possibility of seeding cells into and cultivating them within the scaffold (nontoxicity). For this purpose, native ovine menisci were treated in vitro in a self-developed enzymatic process. Complete cell removal was achieved and shown both histologically and electron microscopically (n = 15). Immunohistochemical reaction (MHC 1/MHC 2) was positive for native ovine meniscus and negative for the scaffold. Compared to native meniscus (25.8 N/mm) stiffness of the scaffold was significantly increased (30.2 N/mm, p < 0.05, n = 10). We determined the compression (%) of the native meniscus and the scaffold under a load of 7 N. The compression was 23% for native meniscus and 29% for the scaffold (p < 0.05, n = 10). Residual force of the scaffold was significantly lower (5.2 N vs. 4.9 N, p < 0.05, n = 10). Autologous fibrochondrocytes were needle injected and successfully cultivated within the scaffolds over a period of 4 weeks (n = 10). To our knowledge, this study is the first to remove cells and immunogenetic proteins (MHC 1/MHC 2) completely out of native meniscus and preserve important biomechanical properties. Also, injected cells could be successfully cultivated within the scaffold. Further in vitro and in vivo animal studies are necessary to establish optimal cell sources, sterilization, and seeding techniques. Cell differentiation, matrix production, in vivo remodeling of the construct, and possible immunological reactions after implantation are subject of further studies.

New algorithm for selecting meniscal allografts that best match the size and shape of the damaged meniscus

Procedures used by tissue banks in selecting meniscal allografts that will best restore normal contact pressure at the time of surgical implantation into a recipient's knee should be improved. Our objective was to develop regression equations that use dimensions measured from magnetic resonance (MR) images of the contralateral knee to predict values of important meniscal parameters of the injured knee. Another objective was to incorporate these equations into an algorithm for selecting allografts that best match the size and shape of the damaged meniscus (either medial or lateral). In each of 10 knee specimens, four transverse and six cross-sectional parameters of the medial and lateral menisci were quantified from measurements obtained using a laser-based, noncontacting, 3-D coordinate digitizing system. In each of 10 contralateral knee specimens, six transverse and 24 cross-sectional (i.e., perpendicular to transverse plane) dimensions were measured for the medial and lateral menisci from MR images of each knee specimen. Simple linear regression equations related these 10 parameters to each of 38 predictor variables determined from magnetic resonance imaging (MRI) dimensions and the best regression equation for each parameter was identified. Requiring only 9 of the 30 dimensions as predictor variables, the best regression equations predicted 8 of 10 and 10 of 10 medial and lateral menisci parameters, respectively, with R2 values>0.500. The algorithm for selecting meniscal allografts involves: collecting an inventory of meniscal allografts and determining the 10 meniscus parameter values for all allografts in the inventory; measuring the dimensions as required from MRI scans of the uninjured knee; using the dimensions as inputs to the regression equations to predict values of meniscal parameters; and selecting the meniscal allograft from the inventory that best matches the predicted values of meniscal parameters. Selecting meniscal allografts using our new algorithm may enable allografts to better meet the clinical objectives of meniscal transplantation, which are to reduce pain in some patients following meniscal resection and to inhibit the degeneration of the articular cartilage.

Meniscal replacement in dogs. Tissue regeneration in two different materials with similar properties

In earlier studies, meniscal replacement with a porous polymer implant led to regeneration of neo-meniscal tissue. To evaluate the influence of the chemical properties on the tissue regeneration in the implant, in the present study, the meniscus in the dog's knee was replaced with either an aromatic 4,4-diphenylmethanediisocyanate based polyesterurethane implant (Estane) (n = 6) or with an aliphatic 1,4-butanediisocyanate based polyesterurethane implant (PCLPU) (n = 6). After 6 months, the knee joints were resected and the tissue behavior in the two different prostheses was evaluated microscopically. In both prostheses, a meniscus-like distribution of the tissue phenotype was found with collagen type I in the peripheral fibrous zones and collagen type II in the central, more cartilaginous zones. The compression-stress behavior of the implant-tissue construct remained in between the stiffness of the polymer material and that of the native meniscus. The PCLPU implant seemed to provoke less synovial tissue reaction. After meniscectomy solely, in 5 out of 6 cases, a meniscus-like regenerate was formed. Furthermore, the articular cartilage degeneration after placing a PCLPU implant did also not exceed the degeneration after the Estane implant or after meniscectomy. The differences between these two implants did not seem to influence the tissue regeneration in the implant. However, PCLPU seemed to evoke less tissue reaction and, therefore, is thought to be less or even nontoxic as compared with the Estane implant. Therefore, for studies in the future, the authors prefer the PCLPU prostheses for replacement of the meniscus.

Second generation of meniscus transplantation: in-vivo study with tissue engineered meniscus replacement

INTRODUCTION

The options available after meniscus loss offer only limited chances for a long-term success. In the following experimental study, we investigated the effect of meniscus tissue engineering on properties of the collagen meniscus implant (CMI).

METHODS

Autologous fibrochondrocytes, obtained per biopsy from adult Merino sheep (n=25), were released from the matrix, cultured in-vitro and seeded into CMI scaffolds (n=10, group 1). Following a 3-week in-vitro culture, the tissue engineered menisci were used for autologous transplantation. Macroscopical and histological evaluation were performed in comparison with non-seeded CMI controls (n=10, group 2) and with meniscus-resected controls (n=5, group 3) after 3 weeks (each 1 animal group 1 and 2) and 3 months.

RESULTS

The lameness score did not show any difference between the groups. Meniscus tissue was found in seven knee joints (group 1), in five knee joints (group 2) and in two knee joints (group 3). The size of the transplants reduced from 25.9+/-4.5 to 20.1+/-10.8 mm (group 1) and from 25.9+/-1.5 to 14.4+/-12.5 mm (group 2). Histologically, enhanced vascularisation, accelerated scaffold re-modelling, higher content of extra-cellular matrix and lower cell number were noted in the pre-seeded menisci in comparison with non-seeded controls. Dense high-cellular fibrous scar tissue was found in two of five cases in the resection control group.

CONCLUSION

Tissue engineering of meniscus with autologous fibrochondrocytes demonstrates a macroscopic and histological improvement of the transplants. However, further development of the methods, especially of the scaffold and of the cell-seeding procedure must prove the feasibility of this procedure for human applications.

Replacement of the knee meniscus by a porous polymer implant: a study in dogs

BACKGROUND

Meniscectomy will lead to articular cartilage degeneration in the long term. Therefore, the authors developed an implant to replace the native meniscus.

HYPOTHESIS

The porous polymer meniscus implant develops into a neomeniscus and protects the cartilage from degeneration.

STUDY DESIGN

Controlled laboratory study.

METHODS

In a dog model, a porous polymer scaffold with optimal properties for tissue infiltration and regeneration of a neomeniscus was implanted and compared with total meniscectomy. The tissue infiltration and redifferentiation in the scaffold, the stiffness of the scaffold, and the articular cartilage degeneration were evaluated.

RESULTS

Three months after implantation, the implant was completely filled with fibrovascular tissue. After 6 months, the central areas of the implant contained cartilage-like tissue with abundant collagen type II and proteoglycans in their matrix. The foreign-body reaction remained limited to a few giant cells in the implant. The compression modulus of the implant-tissue construct still differed significantly from that of the native meniscus, even at 6 months. Cartilage degeneration was observed both in the meniscectomy group and in the implant group.

CONCLUSION

The improved properties of these polymer implants resulted in a faster tissue infiltration and in phenotypical differentiation into tissue resembling that of the native meniscus. However, the material characteristics of the implant need to be improved to prevent degeneration of the articular cartilage.

CLINICAL RELEVANCE

The porous polymer implant developed into a polymer-tissue construct that resembled the native meniscus, and with improved gliding characteristics, this prosthesis might be a promising implant for the replacement of the meniscus.

Articular cartilage degeneration after frozen meniscus and Achilles tendon allograft transplantation: experimental study in sheep

PURPOSE

The purpose of this study was to analyze cartilage degeneration in knees after total medial meniscectomy, transplantation of fresh-frozen meniscus allograft, and Achilles tendon allograft.

TYPE OF STUDY

Experimental study.

METHODS

We have studied the articular cartilage in the medial compartment of the left knees in 32 sheep aged 5 to 6 months, with 8 animals in each group. The study was performed after meniscectomy (group I), transplantation of fresh-frozen meniscus allograft (group II), use of fresh-frozen Achilles tendon allograft (group III), and in a control group (group IV). For the histologic study, all samples were stained with Masson's trichrome and Safranine-O. Mankin's score was applied to grade the histologic damage to the articular cartilage.

RESULTS

The group with the greatest number of degenerative changes was group III, followed by groups I and II. The percentage of thickness of cartilage detected by Safranine-O stain was found to be significantly different in both tibia and femur between the control group and the other 3 groups, but not among groups I, II, and III. The immunoreactivity of the articular surfaces in tibia and femur showed notable differences in all the groups. Collagen X was present in the degenerative hypertrophic chondrocytes in the damaged articular surfaces.

CONCLUSIONS

Meniscal replacement with meniscal and Achilles tendon allografts provides partial protection against articular damage after a meniscectomy.

The current state of meniscal allograft transplantation and replacement

This review details current efforts to transplant or to replace a meniscus. Different substitutes for meniscal transplantation or replacement have been used with varying experimental and clinical success. Meniscal transplantation emerges as a useful option for selected patients with a stable knee and appropriate alignment. Some long-term studies of meniscal transplantation prove that cartilage protection is possible. Clear convincing evidence that meniscal transplantation or replacement restores the normal function of the knee joint has not been shown. In keeping with the multiple functions and anatomy of the meniscus experience of meniscal transplantation has shown that many aspects have to be considered to achieve successful results. This offers many possibilities for further scientific investigations.

Meniscal substitutes--animal experience

Animal studies have shown that meniscus allografts and tendon autografts generally heal to the capsule, are revascularized and repopulated with host cells. In animals, neither meniscal allografts nor tendon or fat autografts gain the properties of a normal meniscus. Meniscus allografts and tendon autografts are promising as both seem to offer some protection to the cartilage of the tibial plateau. There is no evidence that meniscal transplantation can prevent cartilage degenerative changes, and the long-term effect of meniscal transplantation on articular cartilage remains unknown. Whether cellular repopulation of the meniscal allograft is sufficient to restore its biomechanical properties is unknown. Collagen scaffolds and tissue engineered grafts are still under investigation, showing promising results especially for the former. Viable meniscal allografts should be implanted within 1 to 2 weeks after harvesting, as the production of proteoglycans decreases after 2 weeks.

Future research in meniscal replacement

To study the remodelling process after meniscus replacement and to learn how to control it will be a key topic for future research. Not enough is known about the importance of precision in meniscal fixation and how to make the insertions as strong as in the normal meniscus. Methods to measure load-distribution, mechanical properties of the graft and status of the cartilage should be developed. A number of different auto- and allografts have been shown to heal and revascularize, but whether the grafts are functioning is not known. Meniscal scaffolds, which can be used for replacement of partial meniscal loss, need to be tested. Scaffolds and tissue engineering will be the subject of intensive research in the future.

Meniscal regeneration or meniscal transplantation?

Owing to the initial necrosis to which any freely transplanted biological graft is subjected, meniscus transplantation is based on similar principles to meniscal regeneration. Both methods rely on repopulation of extrinsic cells of the graft. In the former procedure a biological matrix (meniscus, tendon, fatpad) is used as graft (scaffold), whereas in meniscal regeneration commercially available resorbable or non-resorbable scaffolds are implanted. However, the cellular (re)population and (re)vitalization process is deleterious rather than beneficial for the function of the graft as the remodelling of the tissue leads to shrinkage and narrowing of the implant. In addition, improper fixation and subsequent elongation of the anterior and posterior bony attachments leads to peripheral graft dislocation, loss of the load distribution function, and subsequently to cartilage degeneration. Hence, meniscus transplantation or regeneration faces two major problems: 1) remodelling of graft to inferior tissue properties after allograft transplantation, or lacking establishment of normal tissue properties after use of biological matrixes other than the meniscus (fatpad, tendon), or commercially available matrixes; 2) improper fixation with elongation of the anterior and posterior attachments. Furthermore, use of allografts incorporates the risk for disease transmission. Today we are unable to control these problems, and therefore the concept of meniscal replacement does not work yet. Further research is necessary to control remodelling and improve fixation to make this procedure a successful one in the future.

The menisci of the knee joint. Anatomical and functional characteristics, and a rationale for clinical treatment

The menisci and their insertions into bone (entheses) represent a functional unit. Thanks to their firm entheses, the menisci are able to distribute loads and therefore reduce the stresses on the tibia, a function which is regarded essential for cartilage protection and prevention of osteoarthrosis. The tissue of the hypocellular meniscal body consists mainly of water and a dense elaborate type I collagen network with a predominantly circumferential alignment. The content of different collagens, proteoglycans and nonproteoglycan proteins shows significant regional variations probably reflecting functional adaptation. The meniscal horns are attached via meniscal insertional ligaments mainly to tibial bone. At the enthesis, the fibres of the insertional ligaments attach to bone via uncalcified and calcified fibrocartilages. This anatomical configuration of gradual transition from soft to hard tissue, which is identical to other ligament entheses, is certainly essential for normal mechanical function and probably protects this vulnerable transition between 2 biomechanically different tissues from failure. Clinical treatment of meniscal tears needs to be based on these special anatomical and functional characteristics. Partial meniscectomy will preserve some of the load distribution function of the meniscus only when the meniscal body enthesis entity is preserved. Repair of peripheral longitudinal tears will heal and probably preserve the load distribution function of the meniscus, whereas radial tears through the whole meniscal periphery or more central and complex tears may be induced to heal, but probably do not preserve the load distribution function. There is no proof that replacement of the meniscus with an allograft can reestablish some of the important meniscal functions, and thereby prevent or reduce the development of osteoarthrosis which is common after meniscectomy. After implantation, major problems are the remodelling of the graft to inferior structural, biochemical and mechanical properties and its insufficient fixation to bone which fails to duplicate a normal anatomical configuration and therefore a functional meniscal enthesis.