The Current State of Meniscus Replacements.

PURPOSE OF REVIEW: The field of meniscus replacement is changing continuously, with new devices emerging and others disappearing from the market. With the current tendency to preserve the knee joint, meniscus implants may become more relevant than ever. The purpose of this review is to provide an overview of the current state of partial and total meniscus replacements that have been developed beyond the academic phase. The available clinical and pre-clinical data is evaluated, and omissions are identified. RECENT FINDINGS: Recent systematic reviews have shown a lack of homogenous clinical data on the CMI and Actifit meniscal scaffolds, especially regarding long-term performance without concomitant surgical interventions. Clinical studies on the medial total meniscus prostheses NUsurface and Artimis are ongoing, with the NUsurface being several years ahead. New techniques for meniscus replacement are rapidly developing, including the Artimis lateral meniscus prosthesis and the MeniscoFix 3D-printed scaffold. All evaluated clinical studies point towards improved clinical outcomes after implantation of partial and total meniscus replacements. Long-term data on survival and performance is of low quality for CMI and Actifit and is unavailable yet for NUsurface and Artimis. It is of major importance that future research focuses on optimizing fixation methods and identifying the optimal treatment strategy for each patient group. New techniques for total and partial replacement of the medial and lateral meniscus will be followed with interest.

The first-generation anatomical medial meniscus prosthesis led to unsatisfactory results: a first-in-human study.

PURPOSE: The purpose of this first-in-human study was to evaluate the effect of a polycarbonate anatomical meniscus prosthesis system, including the surgical procedure, on knee pain and describe potential adverse events in patients with post-meniscectomy pain syndrome. METHODS: Eleven patients with post-meniscectomy pain syndrome and limited underlying cartilage damage were enrolled in the study. Five received a medial polycarbonate urethane meniscus prosthesis which was clicked onto 2 titanium screws fixated at the native horn attachments on the tibia. The KOOS score was planned to be collected at baseline and at 3, 6, 12 and 24 months following the intervention including radiographs at 6, 12 and 24 months. MRI scans were repeated after 12 and 24 months. RESULTS: The surgical technique to select an appropriately sized implant and correct positioning of the fixation screws and meniscus prosthesis onto the tibia was demonstrated to be feasible and reproducible. Inclusion stopped after 5 patients because of serious adverse device-related events. All patients reported knee joint stiffness and slight effusion in their knee at 6 months follow-up. In 3 patients the implant was removed because of implant failure and in 1 patient the implant was removed because of persistent pain and extension limitation. In none of the patients did the KOOS score improve in the first 6 months after surgery. However, in the patient who still has the implant in situ, PROMs started to improve 1 year after surgery and this improvement continued through 2 years of follow-up. The KOOS Pain, symptoms and ADL were close to the maximal 100 points. KOOS QoL and sport did improve but remained suboptimal. CONCLUSION: This first version of the meniscus prosthesis led to impaired knee function and failed in four out of five patients. The patients where the prosthesis was removed were salvable and the PROMs returned to pre-study levels. The results in the patient where the device is still in place are promising. LEVEL OF EVIDENCE: Level II.

Increased risk for knee replacement surgery after arthroscopic surgery for degenerative meniscal tears: a multi-center longitudinal observational study using data from the osteoarthritis initiative.

OBJECTIVE: The primary objective was to assess whether patients with knee osteoarthritis and whom undergo arthroscopic meniscectomy have an increased risk for future knee replacement surgery. DESIGN: Data used were obtained from the Osteoarthritis Initiative (OAI) study. SETTING: Participants were enrolled, in four clinical centers, between February 2004 and May 2006 and were followed up on an annual basis up to and including 108-months from enrollment. PARTICIPANTS: 4674 participants (58.4% female), aged 45-79, of all ethnic groups, who had, and those who were at high risk for developing, symptomatic knee osteoarthritis were included, of which 3337 (71.4%) were included in the final follow up visit. MAIN OUTCOME MEASURES: Hazard ratio of knee replacement surgery for participants who underwent arthroscopic meniscectomy during follow up compared to propensity score matched participants who did not undergo arthroscopic meniscectomy during follow up. RESULTS: 335 participants underwent arthroscopic meniscectomy during follow up, of which 63 (18.8%) underwent knee replacement surgery in the same knee. Of the 335 propensity score matched participants 38 (11.1%) underwent knee replacement surgery during follow up. Results from the Cox-proportional hazards model demonstrated that the hazard ratio of knee replacement surgery was 3.03 (95% CI (1.67-5.26)) for participants who underwent arthroscopic meniscectomy relative to the propensity score matched participants who did not undergo arthroscopic meniscectomy. CONCLUSIONS: In patients with knee osteoarthritis arthroscopic knee surgery with meniscectomy is associated with a three fold increase in the risk for future knee replacement surgery.

Development of biodegradable hyper-branched tissue adhesives for the repair of meniscus tears.

Meniscus tears are one of the most commonly occurring injuries of the knee joint. Current meniscus repair techniques are challenging and do not bring fully satisfactory results. Tissue adhesives are a promising alternative, since they are easy to apply and cause minimal tissue trauma. In this study, a series of amphiphilic copolymers based on polyethylene glycol, trimethylene carbonate and citric acid were synthesized and subsequently end-functionalized with hexamethylene diisocyanate to form reactive adhesive materials. The shear adhesive strength of the networks to bovine meniscus tissue measured in a lap-shear adhesion test ranged between 20 and 80 kPa, which was better than for fibrin glue (10 kPa). The elastic modulus of the networks depended on composition and was in the same range as that of human meniscus. Cell compatibility was assessed using Alamar Blue staining after incubation of the bovine meniscus cells with different concentrations of the glues for 7 days. Cell viability was not affected after adding up to 3mg of the adhesive/mL of medium. The proposed materials are suitable candidates to be used as resorbable tissue adhesives for meniscus repair. They have excellent mechanical and adhesive properties that can be adjusted by varying the composition of the copolymers. STATEMENT OF SIGNIFICANCE: Meniscal tears often occur and current treatment strategies do not bring fully satisfactory results. Use of biodegradable tissue adhesives would be an interesting option, but currently available adhesives are not suited due to toxicity or poor mechanical properties. Here, we describe the development of novel biodegradable, hyper-branched, adhesive copolymers. These adhesives cure upon contact with water forming flexible networks. Their adhesion to bovine meniscus tissue was significantly better than that of clinically used fibrin glue. The tensile properties of the cured networks were in the same range of values of the human meniscus. When physiologically relevant amounts were added to cells in culture, not toxic effects were observed. Therefore, the proposed materials are interesting resorbable tissue adhesives for meniscus repair.

Anatomical reconstruction of posterolateral corner and combined injuries of the knee.

PURPOSE: The goal of this study was to present a 2- to 5-year prospective follow-up of an anatomical posterolateral corner reconstruction in a series of 16 patients with symptomatic instability and pain complaints of the knee. METHODS: All 16 patients underwent a posterolateral corner reconstruction as described by LaPrade et al. If cruciate ligament ruptures were present and had not been addressed earlier, these were reconstructed as well. Preoperatively and 2-5 years after surgery, multiple subjective knee outcome scores (VAS satisfaction score, Tegner, Lysholm, Noyes score and IKDC subjective knee form) were obtained, and the laxity of the joint was evaluated objectively by using bilateral varus stress radiographs to compare the injured with the uninjured knee. RESULTS: Eleven patients had concomitant ACL or PCL surgery or already had undergone surgery on this cruciate ligament. Mean varus laxity of the injured knee on varus stress radiographs improved significantly from 9.6° (6.6-17.1) to 6.3° (0.3-13.4), p = 0.0011. Post-operative varus laxity did not return to the level of the uninjured knee: 4.4° (1.5-7.7), p = 0.036. VAS satisfaction score, the Tegner, Lysholm, Noyes scores and the IKDC subjective knee form all improved significantly. CONCLUSION: The anatomical reconstruction of the posterolateral corner does provide restoration of the external rotation stability in the majority of patients. However, the varus laxity could not be restored in all patients. Functional knee scores improved significantly, and most reconstructed knees had a laxity of <3° compared with the uninjured knee, but the reconstructed knee did not become as stable as the uninjured knee. The results of this study can assist surgeons and patients to have realistic expectations of this operation. LEVEL OF EVIDENCE: Case series with no comparative group, Level IV.

Functional biomechanical performance of a novel anatomically shaped polycarbonate urethane total meniscus replacement.

PURPOSE: To evaluate the functional biomechanical performance of a novel anatomically shaped, polycarbonate urethane total meniscus implant. METHODS: Five human cadaveric knees were flexed between 0° and 90° under compressive loads mimicking a squat movement. Anteroposterior (AP) laxity tests were performed in 30° and 90° flexion. Meniscal kinematics and knee laxity were quantified using roentgen stereophotogrammetric analysis. Tibial cartilage contact mechanics were determined in 90° flexion. Measurements were repeated for the native medial meniscus, the implant, after total medial meniscectomy and allograft transplantation. RESULTS: The implant and allograft displayed increased posterior and medial displacements compared to the native meniscus, yet no differences were found between the implant and allograft. Meniscal condition did not affect rotational laxity. Compared to the native joint, AP laxity for the implant was increased in 30° flexion, but not in 90°. The implant reduced the mean contact pressure compared to meniscectomy but could not restore contact pressures to native meniscus levels. Compared to the native meniscus, the implant significantly increased the peak pressure, while the contact area was reduced. Contact mechanics of the implant and allograft were never statistically different. CONCLUSIONS: Biomechanical performance was similar for the implant and allograft. However, both meniscal replacements could not restore outcomes to native meniscus levels or sufficiently improve outcomes after meniscectomy. This was presumably caused by the mobility allowed by the suture-only horn fixation. The similarity of implant and allograft performance suggests that the novel implant has the biomechanical potential to serve as an alternative to meniscal allograft transplantation.

Short Term Evaluation of an Anatomically Shaped Polycarbonate Urethane Total Meniscus Replacement in a Goat Model.

PURPOSE: Since the treatment options for symptomatic total meniscectomy patients are still limited, an anatomically shaped, polycarbonate urethane (PCU), total meniscus replacement was developed. This study evaluates the in vivo performance of the implant in a goat model, with a specific focus on the implant location in the joint, geometrical integrity of the implant and the effect of the implant on synovial membrane and articular cartilage histopathological condition. METHODS: The right medial meniscus of seven Saanen goats was replaced by the implant. Sham surgery (transection of the MCL, arthrotomy and MCL suturing) was performed in six animals. The contralateral knee joints of both groups served as control groups. After three months follow-up the following aspects of implant performance were evaluated: implant position, implant deformation and the histopathological condition of the synovium and cartilage. RESULTS: Implant geometry was well maintained during the three month implantation period. No signs of PCU wear were found and the implant did not induce an inflammatory response in the knee joint. In all animals, implant fixation was compromised due to suture breakage, wear or elongation, likely causing the increase in extrusion observed in the implant group. Both the femoral cartilage and tibial cartilage in direct contact with the implant showed increased damage compared to the sham and sham-control groups. CONCLUSION: This study demonstrates that the novel, anatomically shaped PCU total meniscal replacement is biocompatible and resistant to three months of physiological loading. Failure of the fixation sutures may have increased implant mobility, which probably induced implant extrusion and potentially stimulated cartilage degeneration. Evidently, redesigning the fixation method is necessary. Future animal studies should evaluate the improved fixation method and compare implant performance to current treatment standards, such as allografts.

The protective effect of meniscus allograft transplantation on articular cartilage: a systematic review of animal studies.

Despite widespread reporting on clinical results, the effect of meniscus allograft transplantation on the development of osteoarthritis is still unclear. The aim of this study was to systematically review all studies on the effect of meniscus allograft transplantation on articular cartilage in animals. Pubmed and Embase were searched for original articles concerning the effect of meniscus allograft transplantation on articular cartilage compared with both its positive (meniscectomy) and negative (either sham or non-operated) control in healthy animals. Outcome measures related to assessment of damage to articular cartilage were divided in five principal outcome categories. Standardized mean differences (SMD) were calculated and pooled to obtain an overall SMD and 95% confidence interval. 17 articles were identified, representing 14 original animal cohorts with an average timing of data collection of 24 weeks [range 4 weeks; 30 months]. Compared to a negative control, meniscus allograft transplantation caused gross macroscopic (1.45 [0.95; 1.95]), histological (3.43 [2.25; 4.61]) damage to articular cartilage, and osteoarthritic changes on radiographs (3.12 [1.42; 4.82]). Moreover, results on histomorphometrics and cartilage biomechanics are supportive of this detrimental effect on cartilage. On the other hand, meniscus allograft transplantation caused significantly less gross macroscopic (-1.19 [-1.84; -0.54]) and histological (-1.70 [-2.67; -0.74]) damage to articular cartilage when compared to meniscectomy. However, there was no difference in osteoarthritic changes on plain radiographs (0.04 [-0.48; 0.57]), and results on histomorphometrics and biomechanics did neither show a difference in effect between meniscus allograft transplantation and meniscectomy. In conclusion, although meniscus allograft transplantation does not protect articular cartilage from damage, it reduces the extent of it when compared with meniscectomy.

The sensitivity of cartilage contact pressures in the knee joint to the size and shape of an anatomically shaped meniscal implant.

Since meniscal geometry affects the cartilage contact pressures, it is essential to carefully define the geometry of the synthetic meniscal implant that we developed. Recently, six independent modes of size- and shape-related geometry variation were identified through 3D statistical shape modeling (SSM) of the medial meniscus. However, this model did not provide information on the functional importance of these geometry characteristics. Therefore, in this study finite element simulations were performed to determine the influence of anatomically-based meniscal implant size and shape variations on knee cartilage contact pressures. Finite element simulations of the knee joint were performed for a total medial meniscectomy, an allograft, the average implant geometry, six implant sizes and ten shape variations. The geometries of the allograft and all implant variations were based on the meniscus SSM. Cartilage contact pressures and implant tensile strains were evaluated in full extension under 1200N of axial compression. The average implant induced cartilage peak pressures intermediate between the allograft and meniscectomy and also reduced the cartilage area subjected to pressures >5MPa compared to the meniscectomy. The smaller implant sizes resulted in lower cartilage peak pressures and compressive strains than the allograft, yet high implant tensile strains were observed. Shape modes 2, 3 and 6 affected the cartilage contact stresses but to a lesser extent than the size variations. Shape modes 4 and 5 did not result in changes of the cartilage stress levels. The present study indicates that cartilage contact mechanics are more sensitive to implant size than to implant shape. Down-sizing the implant resulted in more favorable contact mechanics, but caused excessive material strains. Further evaluations are necessary to balance cartilage contact pressures and material strains to ensure cartilage protection and longevity of the implant.

Releasing the circumferential fixation of the medial meniscus does not affect its kinematics.

BACKGROUND: Meniscal functioning depends on the fixation between the meniscal horns and the surrounding tissues. It is unknown, however, whether the integration between the outer circumference of the medial meniscus and the knee capsule/medial collateral ligament also influences the biomechanical behavior of the meniscus. Therefore, we aimed to determine whether detaching and resuturing the circumferential fixation of the medial meniscus influence its kinematic pattern. METHODS: Human cadaveric knee joints were flexed (0°-30°-60°-90°) in a knee loading rig, in neutral orientation and under internal and external tibial torques. Roentgen stereophotogrammetric analysis was used to determine the motion of the meniscus in anteroposterior (AP) and mediolateral (ML) directions. Three fixation conditions were evaluated: (I) intact, (II) detached and (III) resutured. RESULTS: Detaching and resuturing the circumferential fixation did not alter the meniscal motion pattern in either the AP or ML direction. Applying an additional internal tibial torque caused the medial meniscus to move slightly anteriorly, and an external torque caused a little posterior translation with respect to the neutral situation. These patterns did not change when the circumferential fixation condition was altered. CONCLUSIONS: This study demonstrated that the motion pattern of the medial meniscus is independent of its fixation to the knee capsule and medial collateral ligament. CLINICAL RELEVANCE: The outcomes of this study can be deployed to design the fixation strategy of a permanent meniscus prosthesis. As peripheral fixation is a complicated step during meniscal replacement, the surgical procedure is considerably simplified when non-resorbable implants do not require circumferential fixation.

3D geometry analysis of the medial meniscus--a statistical shape modeling approach.

The geometry-dependent functioning of the meniscus indicates that detailed knowledge on 3D meniscus geometry and its inter-subject variation is essential to design well functioning anatomically shaped meniscus replacements. Therefore, the aim of this study was to quantify 3D meniscus geometry and to determine whether variation in medial meniscus geometry is size- or shape-driven. Also we performed a cluster analysis to identify distinct morphological groups of medial menisci and assessed whether meniscal geometry is gender-dependent. A statistical shape model was created, containing the meniscus geometries of 35 subjects (20 females, 15 males) that were obtained from MR images. A principal component analysis was performed to determine the most important modes of geometry variation and the characteristic changes per principal component were evaluated. Each meniscus from the original dataset was then reconstructed as a linear combination of principal components. This allowed the comparison of male and female menisci, and a cluster analysis to determine distinct morphological meniscus groups. Of the variation in medial meniscus geometry, 53.8% was found to be due to primarily size-related differences and 29.6% due to shape differences. Shape changes were most prominent in the cross-sectional plane, rather than in the transverse plane. Significant differences between male and female menisci were only found for principal component 1, which predominantly reflected size differences. The cluster analysis resulted in four clusters, yet these clusters represented two statistically different meniscal shapes, as differences between cluster 1, 2 and 4 were only present for principal component 1. This study illustrates that differences in meniscal geometry cannot be explained by scaling only, but that different meniscal shapes can be distinguished. Functional analysis, e.g. through finite element modeling, is required to assess whether these distinct shapes actually influence the biomechanical performance of the meniscus.

Polyurethane scaffold formation via a combination of salt leaching and thermally induced phase separation.

Porous scaffolds have been made from two polyurethanes based on thermally induced phase separation of polymer dissolved in a DMSO/water mixture in combination with salt leaching. It is possible to obtain very porous foams with a very high interconnectivity. A major advantage of this method is that variables like porosity, pore size, and interconnectivity can be independently adjusted with the absence of toxic materials in the production process. The obtained compression moduli were between 200 kPa and 1 MPa with a variation in porosity between 76 and 84%. Currently the biological and medical aspects are under evaluation.

Design, synthesis and properties of a degradable polyurethane scaffold for meniscus regeneration.

Longitudinal lesions in menisci are among the most frequent orthopedic problems of the knee. Repair by simple techniques is only limited to the vascular part of the meniscus. For repair of the avascular part of the meniscus a scaffold, which will assist the body in the formation of new meniscus cell tissue, might be applicable. In this study a biomedical segmented polyurethane with poly(epsilon-caprolactone) as soft segment and 1,4-butanediisocyanate and 1,4-butanediol as uniform hard segments has been synthesised. The material has a micro phase separated morphology and excellent mechanical properties. A porous scaffold was prepared via a combination of liquid-liquid phase separation and salt leaching. The foams prepared combined a very high interconnectivity and porosity with the desired compression modulus. After six months of implantation in the knees of beagles full ingrowth with cells was obtained and it was found that meniscus like tissue had been formed in the scaffold. Moreover, compression behaviour appeared to be comparable to native meniscus tissue.

Tissue engineering of the meniscus.

Meniscus lesions are among the most frequent injuries in orthopaedic practice and they will inevitably lead to degeneration of the knee articular cartilage. The fibro-cartilage-like tissue of the meniscus is notorious for its limited regenerative capacity. Tissue engineering could offer new treatment modalities for repair of meniscus tears and eventually will enable the replacement of a whole meniscus by a tissue-engineered construct. Many questions remain to be answered before the final goal, a tissue-engineered meniscus is available for clinical implementation. These questions are related to the selection of an optimal cell type, the source of the cells, the need to use growth factor(s) and the type of scaffold that can be used for stimulation of differentiation of cells into tissues with optimal phenotypes. Particularly in a loaded, highly complex environment of the knee, optimal mechanical properties of such a scaffold seem to be of utmost importance. With respect to cells, autologous meniscus cells seems the optimal cell source for tissue engineering of meniscus tissue, but their availability is limited. Therefore research should be stimulated to investigate the suitability of other cell sources for the creation of meniscus tissue. Bone marrow stroma cells could be useful since it is well known that they can differentiate into bone and cartilage cells. With respect to growth factors, TGF-beta could be a suitable growth factor to stimulate cells into a fibroblastic phenotype but the problems of TGF-beta introduced into a joint environment should then be solved. Polyurethane scaffolds with optimal mechanical properties and with optimal interconnective macro-porosity have been shown to facilitate ingrowth and differentiation of tissue into fibro-cartilage. However, even these materials cannot prevent cartilage degeneration in animal models. Surface modification and/or seeding of cells into the scaffolds before implantation may offer a solution for this problem in the future.This review focuses on a number of specific questions; what is the status of the development of procedures for lesion healing and how far are we from replacing the entire meniscus by a (tissue-engineered) prosthesis. Subquestions related to the type of scaffold used are: is the degree of tissue ingrowth and differentiation related to the initial mechanical properties and if so, what is the influence of those properties on the subsequent remodelling of the tissue into fibro-cartilage; what is the ideal pore geometry and what is the optimal degradation period to allow biological remodelling of the tissue in the scaffold. Finally, we will finish with our latest results of the effect of tear reconstruction and the insertion of prostheses on articular cartilage degradation.

Presence and mechanism of knee articular cartilage degeneration after meniscal reconstruction in dogs.

OBJECTIVE: Partial meniscectomy is the golden standard for treating a bucket-handle tear in the meniscus of the knee, but it inevitably leads to articular cartilage degeneration. Surgical creation of an access channel between the lesion and the vascularized synovial lining is intended to induce ingrowth of repair tissue and thus avoid degeneration of articular cartilage. DESIGN: The presence and mechanism of cartilage degeneration were evaluated in 24 canine menisci after a longitudinal lesion and access channel had been created in the avascular part of the meniscus. In 12 menisci the channel was implanted with a porous polymer scaffold, while the remaining 12 were left empty. Evaluation was performed using routine histology and antibodies directed against denatured type II collagen (Col2-3/4M). RESULTS: Articular degeneration was apparent in the polymer implant group and the empty channel group. This consisted of fibrillation, loss of chondrocytes and decreased proteoglycan content. Areas of fibrillated cartilage always showed positive labeling with the collagen degradation antibody Col2-3/4M. Collagen degradation was also visible in non-fibrillated areas. The upper zone of the cartilage showed swelling especially in the implant group, with empty cell lacunae and moderate levels of Col2-3/4M antibody labeling. DISCUSSION: This reconstruction technique cannot be considered superior to partial meniscectomy. We propose that degradation of the collagen type II network is a result of cartilage fibrillation and vice versa.

Favorable results of acetabular reconstruction with impacted morsellized bone grafts in patients younger than 50 years: a 10- to 18-year follow-up study of 34 cemented total hip arthroplasties.

We report a long-term review of 41 acetabular reconstructions using impacted morsellized bone grafts and a cemented total hip arthroplasty (THA) in patients younger than 50 (22-49; average 38) years. Reconstruction was performed in 23 primary THA (19 patients) and 18 revision THA (17 patients). 3 patients were lost to follow-up and 3 (4 hips) died within 10 years of surgery; none had a revision. Thus, 34 hips (30 patients) were reviewed with an average follow-up of 13 (10-18) years. In 2 hips, a revision was performed for aseptic loosening of the acetabular component 7 and 11 years after surgery. One additional cup was revised after 12 years during a femoral stem revision due to wear and matching problems, but was well fixed. The survival rate of the acetabular reconstruction technique was 94% (95% CI: 90-98%).

Fibrous dysplasia of bone: management and outcome of 20 cases.

BACKGROUND AND OBJECTIVES: Fibrous dysplasia of bone is difficult to manage because of its variable clinical course with many different methods of treatment reported. Therefore we report on our experience. METHODS: We reviewed a series of 20 patients with 32 lesions included. The average age at the time of diagnosis was 32 years for monostotic disease, 26 years for polyostotic disease, and 3 years for McCune-Albright syndrome. The median follow-up period was 6 years. Functional and radiographic outcomes were scored. RESULTS AND CONCLUSIONS: Monostotic disease mostly presented with a circumscribed lesion and monitoring was often sufficient. Symptomatic circumscribed lesions showed satisfactory outcome when treated with curettage, cryosurgery and bone grafting. Lesions of the extended type were most of all seen in polyostotic disease and eventually needed operative treatment. In case of bony deformity, corrective osteotomies and rigid internal fixation were performed in addition to curettage, cryosurgery, and bone grafting. In polyostotic disease, expected outcomes were good, but in McCune-Albright syndrome, results were uniformly poor. J. Surg. Oncol. 2001;76:157-166.