Short-term evaluation of collagen meniscus implants by MRI and morphological analysis

Meniscectomy can lead to degenerative joint changes in the knee. Collagen meniscus implantation is a tissue engineering technique designed to stimulate regeneration of meniscal tissue in case of irreparable tears or previous meniscectomy. The implant is composed of type I collagen derived from bovine Achilles tendon and enriched with glycosaminoglycans. Previous clinical trials demonstrated satisfactory medium-term results in patients who received a collagen meniscus implant (CMI). In this study, CMI structure was analysed by light microscopy and scanning electronic microscopy (SEM). The same morphological studies were performed on two implant biopsies, obtained from two patients who underwent a second arthroscopic look six months after implantation. The evolution of the implant was also investigated by magnetic resonance imaging, 6 and 12 months postoperatively. CMI presented a multilamellar structure, with inner lacunae allowing tissue ingrowth. The lamellae were made of collagen fibrils, randomly oriented and preserving the typical 64-nm period. At second arthroscopic look, the implant appeared in continuity to the native residual meniscus and parameniscus, and showed good consistency and stability at probing. The biopsy specimens demonstrated invasion of the scaffold by connective tissue and blood vessels. The newly synthesised collagen fibrils were clearly distinguishable from the scaffold ones. No phagocytomacrophagic cells nor inflammatory reactions were observed inside the implant. MRI findings confirmed CMI biocompatibility and highlighted the evolution of the integration process with time. The data achieved in this study support the hypothesis that CMI stimulates regeneration of meniscal-like tissue, which could prevent the development of degenerative changes after meniscectomy. Received: 30 August 2002, Accepted: 2 September 2002 Correspondence to: M. Ronga     

Meniscus pathology, osteoarthritis and the treatment controversy

The menisci are internal structures that are of central importance for a healthy knee joint; they have a key role in the structural progression of knee osteoarthritis (OA), and the risk of the disease dramatically increases if they are damaged by injury or degenerative processes. Meniscus damage might be considered a signifying feature of incipient OA in middle-aged and elderly people. As approximately every third knee of people in these groups has a damaged meniscus, tears are common incidental findings of knee MRI. However, as most tears do not cause symptoms, careful clinical evaluation is required to determine if a damaged meniscus is likely to directly impact a patient's symptoms. Conservative management of patients with knee pain and a degenerative meniscal tear should be considered as a first-line therapy before surgical treatment is contemplated. Patients with mechanical interference of joint movements, such as painful catching or locking, might need surgical treatment with meniscal repair if possible. In a subset of patients, meniscal resection might relieve pain and other symptoms that potentially originate directly from the torn meniscus. However, the possibility of an increased risk of OA if functional meniscal tissue is removed cannot be overlooked.     

Pull-out suture in posterior root avulsion fracture of the medial meniscus: 2 cases

The menisci are key structures in the complex biomechanics of the knee joint, and are fundamentally important in shock absorption to attenuate axial loads on the articular surfaces of the opposing femur and tibia [1]. The menisci have secondary roles in knee joint stability, proprioception, joint lubrication, and stress distribution. During weight bearing, the menisci bear, distribute, and contain hoop stress by the circumferential orientation of the collagen fibers [2]. Loss of the bony attachments of the posterior horn of the medial meniscus can lead to extrusion of the meniscus [3]. With extrusion, the medial meniscus loses its ability to absorb hoop stress, resulting in a biomechanical equivalent somewhere between the intact knee and a complete meniscectomy [4]. The literature has suggested that meniscal ossicles could arise from multiple causes, including trauma, metaplastic ossification [5], or a sesamoid bone [6]. Irrespective of cause, there has been no agreement regarding treatment of these meniscal ossicles. We performed pull-out sutures for medial meniscus posterior horn root avulsions to restore the normal anatomy and biomechanical function of the meniscus and report results from 2 cases.     

Evaluation of electrosurgical meniscectomy in rabbits

Recently, electrosurgical cutting instruments utilizing radiofrequency energy have been designed as arthroscopic devices for cutting meniscal tissue. This study attempted to determine the in vivo gross and microscopic effects of radiofrequency energy on meniscal tissue in rabbits. Twelve adult New Zealand white rabbits (48 menisci) underwent bilateral knee arthrotomies. Ten rabbits (40 menisci) underwent partial meniscectomies in which one half of each meniscus in the longitudinal plane was removed with the electrosurgical generator. Two control rabbits underwent arthrotomy without resection of meniscal tissue. At specific time intervals, the rabbits were killed, and the menisci were removed. The gross specimens were photographed, and microscopic sections of each meniscus were fixed and stained. Specimens were evaluated to determine the cellular and vascular response to the electrosurgical cut edge of each meniscus. The microscopic specimens revealed that the radiofrequency cutting instruments produced a small degree of direct thermal damage to the cut meniscus. A tissue response producing a hypercellular dense collagen matrix was present for approximately 3 months. The spontaneous repair of tissue was complete by 6 months, and the histologic 6-month specimens could not be distinguished from the 6-month control specimens except with respect to the overall width of the specimens.     

Cellular repopulation of deep-frozen meniscal autografts: An experimental study in the dog

This study evaluated the cellular repopulation of deep-frozen meniscal autografts. Medial menisci of adult dogs were excised, deep-frozen in liquid nitrogen (-196 degrees C) for 10 min, and orthotopically reimplanted into the joint. Deep-freezing was found to effectively kill all the cells within the meniscus as determined by the absence of Na(2)35SO4 incorporation. Following orthotopic replacement within the knee joint, menisci were repopulated with cells that seemed to originate from the adjacent synovium. These cells migrated over the surface of the meniscus and began to invade the deeper layers of the tissue. However, even after 6 months, the central core of the meniscus remained acellular. While the new cells appeared to modulate into cells that are similar in appearance to meniscal fibrochondrocytes, the exact phenotypic expression of these newly differentiated cells has yet to be determined. Histological alterations, as manifested by a loss of normal orientation of the collagen architecture of the superficial layers of the meniscus; was evident at 6 months and suggests that a remodeling phenomenon may be associated with the cellular repopulation. While biomaterial studies have not been carried out on these specimens, the morphologic alterations observed in the collagen orientation would suggest a possible alteration in the material properties of the repopulated meniscus. The clinical implication of this study is that the structural remodeling associated with the cellular repopulation of deep-frozen meniscal allografts may make the transplanted meniscus more susceptible to injury.     

Meniscectomy

To review the meniscus from a historical perspective especially on surgical management and general guidelines for arthroscopic meniscectomy procedures for various types of meniscal tears. We searched MEDLINE and PubMed for the years of 1980-2010 using the terms meniscus, meniscal repair, menisectomy, and arthroscopy. Orthopedic surgeons frequently encounter patients with pain or functional impairment of the knee joint and repair or resection of the injured meniscus is one of the most common orthopedic operative procedures. The object of meniscal surgery is to reduce pain, restore functional meniscus and prevent the development of degenerative osteoarthritis in the involved knee. Historically, total meniscectomy was a common procedure performed for meniscus tear symptoms. However, it has been reported that total meniscectomy has deleterious effects on the knee. In the past, the menisci were thought as a functionless remnant tissue. Currently, it is known that the meniscus is an important structure for knee joint function. Menisci provide several vital functions including mechanical support, localized pressure distribution, and lubrication to the knee joint. It is widely accepted that the function of the meniscus can be preserved through minimal excision. An arthroscopic partial meniscectomy preserving more of the meniscus is preferred over total meniscectomy. In recent decades, this shift toward arthroscopic partial meniscectomy has led to the development of new surgical techniques.     

Tissue-engineered meniscal constructs

The medial and lateral menisci play important roles in knee biomechanics, kinematics, and stability. Unfortunately, these structures are prone to damage and, because of a tenuous blood supply, have great difficulty healing. Many interventions have been proposed for treatment of damaged meniscal tissue, but most surgical options are fraught with difficulties, from continued osteoarthritic degeneration to potential for disease transmission. The field of tissue engineering has made wide inroads into constructing meniscal tissue. Investigations involving collagenous tissue, meniscal fibrochondrocytes, chondrocytes, synthetic scaffolds, and gene therapy have all been reported in the literature. Despite these advances, however, more work needs to be done, including incorporating concepts and applications from other engineering disciplines, to potentiate the possibility of a tissue-engineered meniscus that approximates native tissue. In particular, the histologic, morphologic, and biomechanical properties of tissue-engineered meniscal constructs must be better understood to facilitate this goal.     

Tissue-engineered meniscal constructs.

The medial and lateral menisci play important roles in knee biomechanics, kinematics, and stability. Unfortunately, these structures are prone to damage and, because of a tenuous blood supply, have great difficulty healing. Many interventions have been proposed for treatment of damaged meniscal tissue, but most surgical options are fraught with difficulties, from continued osteoarthritic degeneration to potential for disease transmission. The field of tissue engineering has made wide inroads into constructing meniscal tissue. Investigations involving collagenous tissue, meniscal fibrochondrocytes, chondrocytes, synthetic scaffolds, and gene therapy have all been reported in the literature. Despite these advances, however, more work needs to be done, including incorporating concepts and applications from other engineering disciplines, to potentiate the possibility of a tissue-engineered meniscus that approximates native tissue. In particular, the histologic, morphologic, and biomechanical properties of tissue-engineered meniscal constructs must be better understood to facilitate this goal.     

Use of roentgenography and magnetic resonance imaging to predict meniscal geometry determined with a three-dimensional coordinate digitizing system.

To evaluate and improve on the procedures used by a tissue bank in selecting donor menisci for transplantation, this study was designed to fulfill four objectives: (a) define and quantify a set of independent parameters for describing the geometry of the medial and lateral menisci, (b) determine how well the sizing protocol of the tissue bank (i.e., two transverse roentgenographic measurements obtained from the injured knee or six transverse magnetic resonance imaging measurements obtained from the contralateral knee) predicts the four standard transverse parameters of the menisci, (c) determine if including one additional transverse roentgenographic measurement for each compartment improves the ability of roentgenograms to predict transverse meniscal parameters, and (d) determine if five magnetic resonance imaging measurements at three different meniscal cross sections of the contralateral knee predict the 15 standard cross-sectional parameters of the meniscus in the injured knee. A laser-based, noncontacting three-dimensional coordinate digitizing system was used to determine surface coordinates from which menisci were reconstructed in a computer. For each reconstructed meniscus, four parameters in the transverse plane and five cross-sectional parameters in each of three regions (i.e., anterior, middle, and posterior) were defined, yielding a set of 19 standard parameters to describe the geometry. Through a correlation analysis, these standard parameters were shown to be largely unrelated to one another, thus confirming that the parameters form an independent set describing the three-dimensional geometry of the menisci. The two roentgenographic measurements were poor predictors of transverse standard meniscal parameters, predicting only one of four standard parameters for the medial meniscus and none of four standard parameters for the lateral meniscus with coefficients of determination greater than or equal to 0.5. Including one additional roentgenographic measurement to the tissue bank protocol increased the number of standard transverse parameters predicted to three of four for the medial meniscus and two of four for the lateral meniscus. Magnetic resonance imaging was better than roentgenography for predicting the three-dimensional meniscal geometry. The transverse measurements from magnetic resonance imaging predicted three of four standard transverse parameters for the medial meniscus and all four for the lateral meniscus. With the addition of the cross-sectional measurements by magnetic resonance imaging, seven of 15 standard cross-sectional parameters were predicted for both the medial and lateral menisci. Assuming that a successful clinical outcome depends on how well an allograft matches the size and shape of the original meniscus, magnetic resonance imaging rather than roentgenography should be used for allograft size-matching by tissue banks.     

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.     

Treatment of meniscal injury: a current concept review

Meniscal injury is one of the most common injuries to the knee. The menisci are important for normal knee function. And loss of a meniscus increases the risk of subsequent development of degenerative changes in the knee. Now there are different techniques available for meniscal injury. These techniques include expectant treatment, meniscectomy, meniscal repair, meniscal replacement, and meniscal tissue engineering. Expectant treatment is the appropriate treatment for minor tears of the menisci. Meniscectomy being favored at the beginning is now obsolete. Meniscus repair has become a standard procedure. Meniscal replacement and tissue engineering are used to deal with considerable meniscal injuries. The purpose of this paper is to provide current knowledge regarding the anatomy and function of the menisci, incidence,aetiology, symptoms, signs, investigations and treatments of meniscal injury.     

Feasibility of a self‐assembling peptide hydrogel scaffold for meniscal defect: An in vivo study in a rabbit model

The inner avascular zone of the meniscus has limited healing capacity as the area is poorly vascularized. Although peptide hydrogels have been reported to regenerate bone and cartilage, their effect on meniscus regeneration remains unknown. We tested whether the self‐assembling peptide hydrogel scaffold KI24RGDS stays in the meniscal lesion and facilitates meniscal repair and regeneration in an induced rabbit meniscal defect model. Full‐thickness (2.0 mm diameter) cylindrical defects were introduced into the inner avascular zones of the anterior portions of the medial menisci of rabbit knees (n = 40). Right knee defects were left empty (control group) while the left knee defects were transplanted with peptide hydrogel (KI24RGDS group). Macroscopic meniscus scores were significantly higher in the KI24RGDS group than in the control group at 2, 4, and 8 weeks after surgery. Histological examinations including quantitative and qualitative scores indicated that compared with the control group, the reparative tissue in the meniscus was significantly enhanced in the KI24RGDS group at 2, 4, 8, and 12 weeks after surgery. Immunohistochemical staining showed that the reparative tissue induced by KI24RGDS at 12 weeks postimplantation was positive for Type I and II collagen. KI24RGDS is highly biocompatible and biodegradable, with strong stiffness, and a three dimensional structure mimicking native extracellular matrix and RGDS sequences that enhance cell adhesion and proliferation. This in vivo study demonstrated that KI24RGDS remained in the meniscal lesion and facilitated the repair and regeneration in a rabbit meniscal defect model.     

The usefulness of MRI in evaluating menisci after meniscus repair.

We reviewed magnetic resonance imaging (MRI) scans of 15 asymptomatic patients at 6 months to 1 year following meniscal repair procedures. All of the patients were found to have persistent MRI signals in the region of the repair. Nine of the 17 meniscal repairs in the 15 patients had persistent grade 3 signals. Arthrograms were performed on six patients (eight meniscal repairs). Seven of these postoperative menisci showed grade 3 signals on MRI. Only one meniscus was shown to have a complete tear by arthrogram. There were no false negative scans. The overall accuracy, defined as the percentage of postoperative menisci correctly diagnosed by MRI, was 38% (3/8). MRI is a useful preoperative diagnostic study following knee injury. This report demonstrates, however, that present MRI modalities are unable to distinguish between scar tissue of healed meniscal repairs and meniscal tears. Therefore, it is not a useful diagnostic tool in evaluating reinjury following successful meniscal repair.     

Stage-based treatment by partial meniscectomy, meniscal refixation and transplantation

Clinical and experimental studies have demonstrated that the meniscus is important for normal knee function. Loss of meniscus results in abnormal load transmission across the knee and may lead to degenerative joint disease. Preservation of meniscal tissue is therefore important. About 10 % of all meniscal tears are repairable. The most successful repairs occur in younger patients who have an acute, vertical tear in the vascular portion of the meniscus. Currently, arthroscopic meniscal repair procedures include the inside-out, the outside-in and the all-inside technique. Vertical suture techniques are superior to horizontally placed sutures. From a biomechanical point of view, 2-0 to 1 sutures are recommended for suture repair. Various meniscus implants are also available for meniscal repair. The initial fixation strength of the implants is lower compared to vertical sutures. A combination of suture techniques and implants might be a treatment option in posterior meniscal lesions. The collagen meniscus implant has been designed to support tissue ingrowth after segmental medial meniscectomy. Although fibrocartilage matrix formation has been shown, long-term clinical follow-ups are still required. Meniscal allograft transplantation may be indicated in limited situations. Younger patients with meniscal deficiency due to previous meniscectomy who have only early arthrosis, normal axial alignment, and a stable knee may currently considered appropriate candidates for meniscal transplantation.     

In vitro culture of meniscal tissue

The importance of the fibrocartilaginous menisci to the proper biomechanical function of the knee joint has been increasingly appreciated over the past 30 years. Meniscectomy is not the innocuous procedure it was once considered. Consequently, emphasis is now being placed on ways of repairing injured menisci in situ. To attain this goal, it is important to investigate the biology of the cells that synthesize and maintain the tissue that is to be repaired. In vitro culture techniques have aided in the understanding of how the cells of the meniscus (fibrochondrocytes) function and what is required to stimulate them to carry out the biologic functions they were designed to perform. In vitro culture of meniscal tissues may become an experimental tool for elucidating the requirements for meniscal repair and restoration of normal joint function after meniscal injury.     

Survival analysis of human meniscal transplantations

We describe a prospective survival analysis of 63 consecutive meniscal allografts transplanted into 57 patients. The lateral meniscus was transplanted in 34, the medial meniscus in 17, and both menisci (combined) in the same knee in six. For survival analysis we used persistent pain or mechanical damage as clinical criteria of failure. A total of 13 allografts failed (5 lateral, 7 medial, 1 medial and lateral). A significant negative correlation (p = 0.003) was found between rupture of the anterior cruciate ligament (ACL) and successful meniscal transplantation. A significant difference (p = 0.004) in the clinical results was found between lateral and medial meniscal transplants. The cumulative survival rate of the lateral, medial and combined allografts in the same knee, based on the life-table method and the Kaplan-Meier calculation, was 76%, 50% and 67%, respectively. The survival of medial meniscal allografts may improve when reconstruction of the ACL is carried out at the same time as meniscal transplantation in an ACL-deficient knee.     

Material properties and structure-function relationships in the menisci

The menisci serve several important biomechanical functions in the knee. They distribute stresses over a broad area of articular cartilage, absorb shocks during dynamic loading, and probably assist in joint lubrication. These functions enhance the ability of articular cartilage to provide a smooth, near-frictionless articulation and to distribute loads evenly to the underlying bone of the femur and tibia. In addition, the menisci provide stability to the injured knee when the cruciate ligaments or other primary stabilizers are deficient. The ability to perform these mechanical functions is based on the intrinsic material properties of the menisci as well as their gross anatomic structure and attachments. The material properties of the menisci are determined by their biochemical composition and, perhaps more important, by the organization and interactions of the major tissue constituents: water, proteoglycan, and collagen. Interactions among the important constituents of the fibrocartilage matrix cause meniscal tissue to behave as a fiber-reinforced, porous, permeable composite material similar to articular cartilage, in which frictional drag caused by fluid flow governs its response to dynamic loading. The menisci are one-half as stiff in compression and dissipate more energy under dynamic loading than articular cartilage. Energy dissipation, or shock absorption, by the menisci is the result of high frictional drag caused by low permeability of the matrix, which is about one-sixth as permeable as articular cartilage. The dynamic shear modulus of meniscal tissue is only one-fourth to one-sixth as great as that of articular cartilage. The coarse, circumferential Type I collagen fiber bundles of the meniscus give the tissue great tensile stiffness (range, 100-300 megapascals) and strength. The highly oriented collagen ultrastructure of the menisci makes the tissue anisotropic in tension, compression, and shear and appears to dominate its behavior under all loading conditions.     

Advances in arthroscopic surgery

Removal of the whole meniscus from the knee has been shown to be associated with a high incidence of degenerative change. The degeneration is proportional to the amount of meniscus removed. After meniscal injury, retention of the meniscus in part (partial meniscectomy) or in whole (meniscal suture) is preferable. Replacement of a previously removed meniscus (meniscal transplantation) may be feasible in the future. Fifty patients had arthroscopic partial meniscectomies performed alternately by standard mechanical techniques or by electrosurgical techniques. The latter group was found to have less pain and swelling. Another 46 patients had meniscal sutures performed on one or more menisci. Twenty-one of these patients had a follow-up arthroscopy for recurrence of symptoms and only one meniscus had not healed. Another single patient had a meniscal transplant, and a follow-up arthroscopy six months after surgery revealed the meniscus to be largely intact.     

Discoid meniscus

The discoid meniscus is an uncommon but not remote meniscal anomaly. Watanabe classified discoid menisci into three types: complete, incomplete, and Wrisberg-ligament type. These menisci vary in size, shape, presence of a posterior meniscal attachment, and mode of presentation.The complete and incomplete types are usually incidental arthroscopic findings unless they present with symptoms of an associated meniscal tear. The Wrisberg variant presents with the snapping knee syndrome, with visible, and often audible dunking with flexion and extension of the knee. The complete and incomplete types should be left alone unless there is an associated meniscal tear, in which case a saucerization procedure should be performed. The Wrisberg variant should have attachment of its hypermobile posterior horn.