The pharmacokinetics and metabolism of Kö592 in man, dog and rat

Meniscal Allograft versus Synthetic Graft in Treatment Outcomes of Meniscus Repair: A Mini-review and Meta-analysis

Meniscal injuries are highly correlated with osteoarthritis (OA) onset and progression. Although meniscal allograft transplantation (MAT) is a therapeutic option to restore meniscal anatomy, a shortage of donor material and the donor-derived infectious risk may be concerns in clinics. This review summarizes the literature reporting meniscus repair status in preclinical models and clinical practice using allografts or synthetic grafts. The advantages and limitations of biodegradable polymer-based meniscal scaffolds, applied in preclinical studies, are discussed. Then, the long-term treatment outcomes of patients with allografts or commercial synthetic scaffolds are compared. A total of 47 studies are included in our network meta-analysis. Compared with the meniscal allografts, the commercial synthetic products significantly improved clinical treatment outcomes in terms of the Knee Injury and Osteoarthritis Outcome Score (KOOS), Visual Analog Scale (VAS) scores, and Lysholm scores. In addition, development strategies for the next generation of novel synthetic scaffolds are proposed through optimization of structural design and fabrication, and selection of cell sources, external stimuli, and active ingredients. This review may inspire researchers and surgeons to design and fabricate clinic-orientated grafts with improved treatment outcomes.

Fresh Versus Frozen Meniscal Allograft Transplant: Revisit or Redundant? A Systematic Review

BACKGROUND

Fresh-frozen allografts are the current standard in meniscal allograft transplant (MAT) surgery, due to their availability, ease of preservation, and affordability. However, fresh-frozen grafts are associated with several clinical challenges such as graft shrinkage and extrusion, among many others.

PURPOSE

To present the current knowledge on the use of fresh meniscal allografts, presenting whether benefits associated with fresh grafts provide sufficient evidence to support their use in clinical practice.

STUDY DESIGN

Systematic review; Level of evidence, 5.

METHODS

A comprehensive search was conducted with keywords listed below. After an initial screening on title and abstract, full-text articles were assessed with the inclusion criteria.

RESULTS

A total of 78 studies matched the inclusion criteria. Literature and preclinical studies indicated that fresh meniscal allografts are beneficial for maintaining mechanical properties, graft ultrastructure, and matrix metabolism due to the presence of viable cells. Therefore, fresh allografts may address common complications associated with fresh-frozen MAT. To overcome challenges associated with both fresh-frozen and fresh allografts, a group has studied treating fresh-frozen allografts with a cell-based injection therapy.

CONCLUSION

Fresh meniscal allografts pose several challenges including limited availability, demanding preservation procedures, and high costs. Although the role of viable cells within meniscal allografts remains controversial, these cells may be vital for maintaining tissue properties.

Composite Zonal Scaffolds of Collagen I/II for Meniscus Regeneration

The meniscus is divided into three zones according to its vascularity: an external vascularized red-red zone mainly comprising collagen I, a red-white interphase zone mainly comprising collagens I and II, and an internal white-white zone rich in collagen II. Known scaffolds used to treat meniscal injuries do not reflect the chemical composition of the vascular areas of the meniscus. Therefore, in this study, four composite zonal scaffolds (named A, B, C, and D) were developed and characterized; the developed scaffolds exhibited the main chemical components of the external (collagen I), interphase (collagens I/II), and internal (collagen II) zones of the meniscus. Noncomposite scaffolds were also produced (named E), which had the same shape as the composite scaffolds but were entirely made of collagen I. The composite zonal scaffolds were prepared using different concentrations of collagen I and the same concentration of collagen II and were either cross-linked with genipin or not cross-linked. Porous, biodegradable, and hydrophilic scaffolds with an expected chemical composition were obtained. Their pore size was smaller than the size reported for the meniscus substitutes; however, all scaffolds allowed the adhesion and proliferation of human adipose-derived stem cells (hADSCs) and were not cytotoxic. Data from enzymatic degradation and hADSC proliferation assays were considered for choosing the cross-linked composite scaffolds along with the collagen I scaffold and to test if composite zonal scaffolds seeded with hADSC and cultured with differentiation medium produced fibrocartilage-like tissue different from that formed in noncomposite scaffolds. After 21 days of culture, hADSCs seeded on composite scaffolds afforded an extracellular matrix with aggrecan, whereas hADSCs seeded on noncomposite collagen I scaffolds formed a matrix-like fibrocartilage without aggrecan.

Viable Vitreous Grafts of Whole Porcine Menisci for Transplant in the Knee and Temporomandibular Joints

The shortage of suitable donor meniscus grafts from the knee and temporomandibular joint (TMJ) impedes treatments for millions of patients. Vitrification offers a promising solution by transitioning these tissues into a vitreous state at cryogenic temperatures, protecting them from ice crystal damage using high concentrations of cryoprotectant agents (CPAs). However, vitrification's success is hindered for larger tissues (>3 mL) due to challenges in CPA penetration. Dense avascular meniscus tissues require extended CPA exposure for adequate penetration; however, prolonged exposure becomes cytotoxic. Balancing penetration and reducing cell toxicity is required. To overcome this hurdle, a simulation-based optimization approach is developed by combining computational modeling with microcomputed tomography (µCT) imaging to predict 3D CPA distributions within tissues over time accurately. This approach minimizes CPA exposure time, resulting in 85% viability in 4-mL meniscal specimens, 70% in 10-mL whole knee menisci, and 85% in 15-mL whole TMJ menisci (i.e., TMJ disc) post-vitrification, outperforming slow-freezing methods (20%-40%), in a pig model. The extracellular matrix (ECM) structure and biomechanical strength of vitreous tissues remain largely intact. Vitreous meniscus grafts demonstrate clinical-level viability (≥70%), closely resembling the material properties of native tissues, with long-term availability for transplantation. The enhanced vitrification technology opens new possibilities for other avascular grafts.

Sourcing and development of tissue for transplantation in reconstructive surgery: A narrative review

The wealth of allogeneic and xenogeneic tissue products available to plastic and reconstructive surgeons has allowed for the development of novel surgical solutions to challenging clinical problems, often obviating the need to inflict donor site morbidity. Allogeneic tissue used for reconstructive surgery enters the tissue industry through whole body donation or reproductive tissue donation and has been regulated by the FDA as human cells, tissues, and cellular and tissue-based products (HCT/Ps) since 1997. Tissue banks offering allogeneic tissue can also undergo voluntary regulation by the American Association of Tissue Banks (AATB). Tissue prepared for transplantation is sterilized and can be processed into soft tissue or bone allografts for use in surgical reconstruction, whereas non-transplant tissue is prepared for clinical training and drug, medical device, and translational research. Xenogeneic tissue, which is most often derived from porcine or bovine sources, is also commercially available and is subject to strict regulations for animal breeding and screening for infectious diseases. Although xenogeneic products have historically been decellularized for use as non-immunogenic tissue products, recent advances in gene editing have opened the door to xenograft organ transplants into human patients. Herein, we describe an overview of the modern sourcing, regulation, processing, and applications of tissue products relevant to the field of plastic and reconstructive surgery.

Meniscal Allograft Transplants in Skeletally Immature Patients: A Systematic Review of Indications and Outcomes

Meniscal lesions in skeletally immature patients can lead to joint degradation and knee instability. Meniscal allograft transplant (MAT) surgery is a solution to maintain knee stability. There is a lack of consensus on MAT surgery outcomes in pediatric patients. A systematic review was conducted according to the PRISMA guidelines. PubMed, Scopus and EMBASE databases were searched from 1965 to June 2022. Studies were evaluated using the Newcastle-Ottawa Scale (NOS). Three studies were selected, and 58 patients were included (mean age 15.9 years) in total. The lateral meniscus was involved in 82.8% of all MAT surgeries. Post-meniscectomy syndrome and discoid meniscus were the main indications for MAT surgery. All studies reported improved subjective clinical scores and levels of sport after the surgery. The complication rate was 27.5%. Partial meniscectomy, meniscus knot removal, chondral defect treatment and lysis of adhesions were the most frequent procedures performed during reoperation. MAT surgery can improve clinical outcomes in pediatric patients with strictly selected indications. MAT surgery is safe when there are no limb asymmetries or malalignments, but it remains a challenging procedure with a high complication rate. Long-term follow-up is needed for definitive statements on the use of MAT in skeletally immature patients.

Compressive mechanical properties of vitrified porcine menisci are superior to frozen and similar to fresh porcine menisci

The common practice of freezing meniscal allograft tissue is limited due to the formation of damaging ice crystals. Vitrification, which eliminates the formation of damaging ice crystals, may allow the mechanical properties of meniscal allograft tissue to be maintained during storage and long-term preservation. The primary objective of this study was to investigate the differences between fresh, frozen, and vitrified porcine lateral menisci examining compressive mechanical properties in the axial direction. Unconfined compressive stress-relaxation testing was conducted to quantify the mechanical properties of fresh, frozen and vitrified porcine lateral menisci. The compressive mechanical properties investigated were peak and equilibrium stress, secant, instantaneous and equilibrium modulus, percent stress-relaxation, and relaxation time constants from three-term Prony series. Frozen menisci exhibited inferior compressive mechanical properties in comparison with fresh menisci (significant differences in peak and equilibrium stress, and secant, instantaneous and equilibrium modulus) and vitrified menisci (significant differences in peak stress, and secant and instantaneous modulus). Interestingly, fresh and vitrified menisci exhibited comparable compressive mechanical properties (stress, modulus and relaxation parameters). These findings are significant because (1) vitrification was successful in maintaining mechanical properties at values similar to fresh menisci, (2) compressive mechanical properties of fresh menisci were characterized providing a baseline for future research, and (3) freezing affected mechanical properties confirming that freezing should be used with caution in future investigations of meniscal mechanical properties. Vitrification was superior to freezing for preserving compressive mechanical properties of menisci which is an important advance for vitrification as a preservation option for meniscal allograft transplantation.

A decellularized and sterilized human meniscus allograft for off-the-shelf meniscus replacement

PURPOSE

Meniscus tears are one of the most frequent orthopedic knee injuries, which are currently often treated performing meniscectomy. Clinical concerns comprise progressive degeneration of the meniscus tissue, a change in knee biomechanics, and an early onset of osteoarthritis. To overcome these problems, meniscal transplant surgery can be performed. However, adequate meniscal replacements remain to be a great challenge. In this research, we propose the use of a decellularized and sterilized human meniscus allograft as meniscal replacement.

METHODS

Human menisci were subjected to a decellularization protocol combined with sterilization using supercritical carbon dioxide (scCO₂). The decellularization efficiency of human meniscus tissue was evaluated via DNA quantification and Hematoxylin & Eosin (H&E) and DAPI staining. The mechanical properties of native, decellularized, and decellularized + sterilized meniscus tissue were evaluated, and its composition was determined via collagen and glycosaminoglycan (GAG) quantification, and a collagen and GAG stain. Additionally, cytocompatibility was determined in vitro.

RESULTS

Human menisci were decellularized to DNA levels of ~ 20 ng/mg of tissue dry weight. The mechanical properties and composition of human meniscus were not significantly affected by decellularization and sterilization. Histologically, the decellularized and sterilized meniscus tissue had maintained its collagen and glycosaminoglycan structure and distribution. Besides, the processed tissues were not cytotoxic to seeded human dermal fibroblasts in vitro.

CONCLUSIONS

Human meniscus tissue was successfully decellularized, while maintaining biomechanical, structural, and compositional properties, without signs of in vitro cytotoxicity. The ease at which human meniscus tissue can be efficiently decellularized, while maintaining its native properties, paves the way towards clinical use.

Securing Transplanted Meniscal Allografts Using Bone Plugs Results in Lower Risks of Graft Failure and Reoperations: A Meta-analysis

BACKGROUND

Meniscal allograft transplant (MAT) is an important treatment option for young patients with deficient menisci; however, there is a lack of consensus on the optimal method of allograft fixation.

HYPOTHESIS

The various methods of MAT fixation have measurable and significant differences in outcomes.

STUDY DESIGN

Meta-analysis; Level of evidence, 4.

METHODS

A single-arm meta-analysis of studies reporting graft failure, reoperations, and other clinical outcomes after MAT was performed. Studies were stratified by suture-only, bone plug, and bone bridge fixation methods. Proportionate rates of failure and reoperation for each fixation technique were pooled with a mixed-effects model, after which reconstruction of relative risks with confidence intervals was performed using the Katz logarithmic method.

RESULTS

A total of 2604 patients underwent MAT. Weighted mean follow-up was 4.3 years (95% CI, 3.2-5.6 years). During this follow-up period, graft failure rates were 6.2% (95% CI, 3.2%-11.6%) for bone plug fixation, 6.9% (95% CI, 4.5%-10.3%) for suture-only fixation, and 9.3% (95% CI, 6.2%-13.9%) for bone bridge fixation. Transplanted menisci secured using bone plugs displayed a lower risk of failure compared with menisci secured via bone bridges (RR = 0.97; 95% CI, 0.94-0.99; P = .02). Risks of failure were not significantly different when comparing suture fixation to bone bridge (RR = 1.02; 95% CI, 0.99-1.06; P = .12) and bone plugs (RR = 0.99; 95% CI, 0.96-1.02; P = .64). Allografts secured using bone plugs were at a lower risk of requiring reoperations compared with those secured using sutures (RR = 0.91; 95% CI, 0.87-0.95; P < .001), whereas allografts secured using bone bridges had a higher risk of reoperation when compared with those secured using either sutures (RR = 1.28; 95% CI, 1.19-1.38; P < .001) or bone plugs (RR = 1.41; 95% CI, 1.32-1.51; P < .001). Improvements in Lysholm and International Knee Documentation Committee scores were comparable among the different groups.

CONCLUSION

This meta-analysis demonstrates that bone plug fixation of transplanted meniscal allografts carries a lower risk of failure than the bone bridge method and has a lower risk of requiring subsequent operations than both suture-only and bone bridge methods of fixation. This suggests that the technique used in the fixation of a transplanted meniscal allograft is an important factor in the clinical outcomes of patients receiving MATs.

A narrative review of lateral meniscus transplantation with the bridge in slot: technique and outcomes

Objective

This narrative review aims to detail the indications, technique, and published outcomes of the bridge in slot technique for lateral meniscus allograft transplantation (LMAT) and to serve as a concise reference for orthopaedists looking to incorporate this method into their practice.

Background

The menisci are crucial to normal knee function but are commonly injured; partial and subtotal meniscectomy are frequently performed to address meniscal pathology. Following these procedures, a substantial number of patients go on to develop degenerative joint changes accompanied by pain and disability. LMAT is an attractive option for young, active, lateral meniscal-deficient patients who seek pain relief and improved function but who are not yet prepared to undergo arthroplasty. In the properly indicated patient, the bridge in slot technique is a reliable and effective method for LMAT.

Methods

Using a narrative style, this review outlines the indications and preoperative assessment for LMAT, the detailed technical steps for the bridge in slot technique, postoperative considerations, and trends in the surgical outcomes literature. The presented technique is consistent with the senior author's clinical experience and with published literature and the discussed outcomes are elicited from a focused review of recent peer-reviewed sources.

Conclusions

The bridge in slot technique is a reliable and effective method for LMAT and is supported by the literature. This technique may confidently be used in patients with severe lateral meniscal pathology who are not yet candidates for arthroplasty.

Human meniscus allograft augmentation by allogeneic mesenchymal stromal/stem cell injections

Meniscus allograft transplantations (MATs) represent established surgical procedures with proven outcomes. Yet, storage as frozen specimens and limited cellular repopulation may impair graft viability. This proof-of-concept study tests the feasibility of injecting allogeneic mesenchymal stromal/stem cells (MSCs) in meniscus allograft tissue. We investigated the injectable cell quantity, survival rate, migration, and proliferation ability of MSCs up to 28 days of incubation. In this controlled laboratory study, seven fresh-frozen human allografts were injected with human allogeneic MSCs. Cells were labeled and histological characteristics were microscopically imaged up to 28 days. Mock-injected menisci were included as negative controls in each experiment. Toluidine blue staining demonstrated that a 100-µl volume can be injected while retracting and rotating the inserted needle. Immediately after injection, labeled MSCs were distributed throughout the injection channel and eventually migrated into the surrounding tissues. Histological assessment revealed that MSCs cluster in disc-like shapes, parallel to the intrinsic lamination of the meniscus and around the vascular network. Quantification showed that more than 60% of cells were present in horizontally injected grafts and more than 30% were observed in vertically injected samples. On Day 14, cells adopted a spindle-shaped morphology and exhibited proliferative and migratory behaviors. On Day 28, live/dead ratio assessment revealed an approximately 80% cell survival. The study demonstrated the feasibility of injecting doses of MSCs (>0.1 million) in meniscus allograft tissue with active cell proliferation, migration, and robust cell survival.

[Arthroscopic meniscus transplantation without bone blocks]

OBJECTIVE

Replacement of the lateral or medial meniscus with an allogeneic graft.

INDICATIONS

Complete loss of inner or outer meniscus.

CONTRAINDICATIONS

Grade 3 to 4 cartilage damage in the corresponding compartment, uncorrected varus or valgus deformities > 5°, symptomatic instabilities.

SURGICAL TECHNIQUE

Knee joint arthroscopy via the high anterolateral standard portal and checking the indication. Thaw the allogeneic meniscus graft in NaCl at room temperature and incubate in vancomycin solution. Refreshment of the capsule and resection of remnants of the meniscus. Search for the insertion zones on the tibial plateau, debridement, insert a transtibial targeting device and drill target wires in the middle of the insertion zones. Overdrill the target wires with a 4.5 mm drill. Short medial or lateral arthrotomy (approx. 2 cm). Reinforcement of the anterior and posterior horns of the meniscus graft with nonresorbable suture material (e.g. "fiber wire" size 5). Insertion of K‑wires with thread loops into the tibial bone tunnel. The reinforcement threads of the meniscus transplant are drawn into the bone tunnel via the thread loops, and the meniscus transplant is drawn into the joint. Reduction of the meniscus base to the capsule and refixation of the meniscus to the capsule with "inside out" or "all inside" sutures.

POSTOPERATIVE MANAGEMENT

Six weeks partial weight-bearing using a hinged brace, then gradually increased load. Range of motion: 4 weeks 0‑0-60°, then 2 weeks 0‑0-90°, followed by no restrictions.

RESULTS

In our hospital, 15 patients (6 × medial, 9 × lateral) were treated using the described surgical technique. After a minimum period of 1 year (mean = 14.2 months), meniscus extrusion-measured in the MRI-averaged 2.7 mm. The Lysholm score rose from an average of 70.2 (±7.4) to 90.1 points (±10.6). In one case, due to an early reruption, revision with renewed meniscus refixation had to be performed 10 days after the operation. In another case, meniscus resection was performed 6 months after the meniscus transplant due to a reruption. Thrombosis, infection and arthrofibrosis were not observed.

Initial clinical outcomes comparing frozen versus fresh meniscus allograft transplants

BACKGROUND

To evaluate initial clinical outcomes using fresh meniscal allografts with high cell viability at transplantation time and meniscotibial ligament (MTL) reconstruction (Fresh) in comparison to standard fresh-frozen (Frozen) meniscus allograft transplantation (MAT).

METHODS

Patients treated for medial and/or lateral meniscal deficiency using either Fresh or Frozen MAT with minimum of 1-year follow-up were identified from a prospective registry. Patient demographics, prior surgeries, MAT surgery data, complications, revisions, and failures were documented. Functional outcome scores were collected preoperatively, and 6 months and yearly after surgery and radiographic joint space measurements were performed. Treatment cohorts were compared for statistically significant (P < 0.005) differences using t-Tests and Fisher's exact tests.

RESULTS

Twenty-seven patients (14 Fresh, 13 Frozen) met inclusion criteria and showed comparable characteristics. For Fresh MAT + MTL, 10 medial, two lateral, and two medial + lateral MAT were performed. For Frozen MAT, nine medial, and four lateral MAT were performed. There was significantly more improvement in the Fresh cohort compared to the Frozen cohort for VAS pain (P = 0.014), PROMIS Physical Function (P = 0.036) and Single Assessment Numeric Evaluation (P = 0.033) from preoperatively to 2 years postoperatively. Tegner Activity Scale and PROMIS Mobility score showed no significant differences. The International Knee Documentation Committee score revealed a clinically meaningful change for the Fresh group. Radiographic measurements showed no significant differences between groups. There were two Fresh MAT + MTL revisions and one conversion to TKA in each cohort.

CONCLUSIONS

Fresh MAT + MTL is safe and associated with potential advantages with respect to initial pain relief and function compared to standard frozen MAT.

Orthotopic Bone Formation by Streamlined Engineering and Devitalization of Human Hypertrophic Cartilage

Most bones of the human body form and heal through endochondral ossification, whereby hypertrophic cartilage (HyC) is formed and subsequently remodeled into bone. We previously demonstrated that HyC can be engineered from human mesenchymal stromal cells (hMSC), and subsequently devitalized by apoptosis induction. The resulting extracellular matrix (ECM) tissue retained osteoinductive properties, leading to ectopic bone formation. In this study, we aimed at engineering and devitalizing upscaled quantities of HyC ECM within a perfusion bioreactor, followed by in vivo assessment in an orthotopic bone repair model. We hypothesized that the devitalized HyC ECM would outperform a clinical product currently used for bone reconstructive surgery. Human MSC were genetically engineered with a gene cassette enabling apoptosis induction upon addition of an adjuvant. Engineered hMSC were seeded, differentiated, and devitalized within a perfusion bioreactor. The resulting HyC ECM was subsequently implanted in a 10-mm rabbit calvarial defect model, with processed human bone (Maxgraft^®) as control. Human MSC cultured in the perfusion bioreactor generated a homogenous HyC ECM and were efficiently induced towards apoptosis. Following six weeks of in vivo implantation, microcomputed tomography and histological analyses of the defects revealed an increased bone formation in the defects filled with HyC ECM as compared to Maxgraft^®. This work demonstrates the suitability of engineered devitalized HyC ECM as a bone substitute material, with a performance superior to a state-of-the-art commercial graft. Streamlined generation of the devitalized tissue transplant within a perfusion bioreactor is relevant towards standardized and automated manufacturing of a clinical product.

Meniscal Tears: Current Understanding, Diagnosis, and Management

From once being labelled as a functionless remain of leg muscle, extensive scientific investigations in recent decades have described the meniscus as one of the most crucial structures of the knee. The incidence of meniscal injuries is on the rise and can be attributed to the increased participation of youth in sporting activities. MRI continues to be the imaging modality of choice, and surgical management is the mainstay of treatment for meniscal tears. Arthroscopic partial meniscectomy (APM) is currently the most performed orthopedic procedure around the globe. However, recent studies have conclusively shown that outcomes after an APM are no better than the outcomes after a sham/placebo surgery. Meniscal repair is now being touted as a viable and effective alternative. Meniscal repair aims to achieve meniscal healing while completely avoiding the adverse effects of partial meniscectomy. Meniscal repairs have grown in popularity over the past three decades and have proved to be a much more efficient alternative to partial meniscectomy. It is now increasingly recommended to attempt meniscal repair in all repairable tears, especially in young and physically active patients. Partial Meniscal implants have also shown excellent outcomes in long-term studies, but its efficacy in acute settings still requires further research. Research performed on various techniques of meniscal regeneration looks promising, and regenerative medicine appears to be the way forward. This review aims to critically discuss the current understanding of the meniscus, its role in biomechanics of the knee joint, and the current methods used to diagnose and manage meniscal tears.

Mechanical properties of tissue formed in vivo are affected by 3D-bioplotted scaffold microarchitecture and correlate with ECM collagen fiber alignment

Purpose: Musculoskeletal soft tissues possess highly aligned extracellular collagenous networks that provide structure and strength. Such an organization dictates tissue-specific mechanical properties but can be difficult to replicate by engineered biological substitutes. Nanofibrous electrospun scaffolds have demonstrated the ability to control cell-secreted collagen alignment, but concerns exist regarding their scalability for larger and anatomically relevant applications. Additive manufacturing processes, such as melt extrusion-based 3D-Bioplotting, allow fabrication of structurally relevant scaffolds featuring highly controllable porous microarchitectures.Materials and Methods: In this study, we investigate the effects of 3D-bioplotted scaffold design on the compressive elastic modulus of neotissue formed in vivo in a subcutaneous rat model and its correlation with the alignment of ECM collagen fibers. Polycaprolactone scaffolds featuring either 100 or 400 µm interstrand spacing were implanted for 4 or 12 weeks, harvested, cryosectioned, and characterized using atomic-force-microscopy-based force mapping.Results: The compressive elastic modulus of the neotissue formed within the 100 µm design was significantly higher at 4 weeks (p < 0.05), but no differences were observed at 12 weeks. In general, the tissue stiffness was within the same order of magnitude and range of values measured in native musculoskeletal soft tissues including the porcine meniscus and anterior cruciate ligament. Finally, a significant positive correlation was noted between tissue stiffness and the degree of ECM collagen fiber alignment (p < 0.05) resulting from contact guidance provided by scaffold strands.Conclusion: These findings demonstrate the significant effects of 3D-bioplotted scaffold microarchitectures in the organization and sub-tissue-level mechanical properties of ECM in vivo.

Comparison of High-Hydrostatic-Pressure Decellularized Versus Freeze-Thawed Porcine Menisci

The meniscus functions as a load distributor and secondary stabilizer in the knee, and the loss of the meniscus increases the risk of osteoarthritis. Freeze-thawed menisci are used in clinical practice to replace defective menisci; however, the disadvantages of freeze-thawed tissues include disease transmission and immune rejection. In this study, we decellularized menisci using high hydrostatic pressure (HHP) and compared the decellularized menisci with freeze-thawed menisci. Porcine menisci were either pressurized at 1,000 MPa for 10 min and then washed with DNase solution or frozen at -80°C for 2 days and thawed. These menisci then underwent in vitro histological, biochemical, and biomechanical comparisons with native menisci. The HHP-treated and freeze-thawed menisci were also subcutaneously implanted in a pig, and later harvested for histological analysis. The numbers of histologically detected cells were significantly lower and the amount of biochemically detected DNA was approximately 100-fold lower in HHP-treated than in native and freeze-thawed menisci. The compression strength of the HHP-decellularized menisci was decreased after 1 and 50 cycles at 20% strain but was unchanged in the freeze-thawed menisci. After implantation, the numbers of multinucleated giant cells were significantly lower around the HHP-treated menisci than around the freeze-thawed menisci. Recellularization of the HHP-decellularized menisci was confirmed. Thus, although the HHP-decellularized menisci were mechanically inferior to the freeze-thawed meniscus in vitro, they were immunologically superior. Our study is the first to demonstrate the use of HHP for decellularization of the meniscus. © 2019 The Authors. Journal of Orthopaedic Research^® published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2466-2475, 2019.

Biomechanical considerations are crucial for the success of tendon and meniscus allograft integration-a systematic review

PURPOSE

This systematic review intends to give an overview of the current knowledge on how allografts used for the reconstruction of cruciate ligaments and menisci are integrated and specifically perform regarding their biomechanical function.

METHODS

Two reviewers reviewed the PubMed and Central Cochrane library with focus on the biomechanical integration of tendon ligament and meniscus allografts. The literature search was conducted in accordance with the PRISMA statement for reporting systematic reviews and meta-analyses.

RESULTS

The analysed literature on tendon allografts shows that they are more vulnerable to overstretching in the phase of degradation compared to autografts as the revascularization process starts later and takes longer. Therefore, to avoid excessive graft loads, allografts for cruciate ligament replacement should be selected that exhibit much higher failure loads than the native ligaments to counteract the detrimental effect of degradation. Further, placement techniques should be considered that result in a minimum of strain differences during knee joint motion, which is best achieved by near-isometric placement. The most important biomechanical parameters for meniscus allograft transplantation are secure fixation and proper graft sizing. Allograft attachment by bone plugs or by a bone block is superior to circumferential suturing and enables the allograft to restore the chondroprotective biomechanical function. Graft sizing is also of major relevance, because too small grafts are not able to compensate the knee joint incongruity and too large grafts may fail due to extrusion. Only adequate sizing and fixation together can lead to a biomechanically functioning allograft. The objective assessment of the biomechanical quality of allografts in a clinical setting is challenging, but would be highly desirable for monitoring the remodelling and incorporation process.

CONCLUSIONS

Currently, indicators like ap-stability after ACL reconstruction or meniscal extrusion represent only indirect measures for biomechanical graft integration. These parameters are at best clinical indicators of allograft function, but the overall integration properties comprising e.g. fixation and graft stiffness remain unknown. Therefore, future research should e.g. focus on advanced imaging techniques or other non-invasive methods allowing for in vivo assessment of biomechanical allograft properties.

Meniscal allograft transplants and new scaffolding techniques

Clinical management of meniscal injuries has changed radically in recent years. We have moved from the model of systematic tissue removal (meniscectomy) to understanding the need to preserve the tissue.Based on the increased knowledge of the basic science of meniscal functions and their role in joint homeostasis, meniscus preservation and/or repair, whenever indicated and possible, are currently the guidelines for management.However, when repair is no longer possible or when facing the fact of the previous partial, subtotal or total loss of the meniscus, meniscus replacement has proved its clinical value. Nevertheless, meniscectomy remains amongst the most frequent orthopaedic procedures.Meniscus replacement is currently possible by means of meniscal allograft transplantation (MAT) which provides replacement of the whole meniscus with or without bone plugs/slots. Partial replacement has been achieved by means of meniscal scaffolds (mainly collagen or polyurethane-based). Despite the favourable clinical outcomes, it is still debatable whether MAT is capable of preventing progression to osteoarthritis. Moreover, current scaffolds have shown some fundamental limitations, such as the fact that the newly formed tissue may be different from the native fibrocartilage of the meniscus.Regenerative tissue engineering strategies have been used in an attempt to provide a new generation of meniscal implants, either for partial or total replacement. The goal is to provide biomaterials (acellular or cell-seeded constructs) which provide the biomechanical properties but also the biological features to replace the loss of native tissue. Moreover, these approaches include possibilities for patient-specific implants of correct size and shape, as well as advanced strategies combining cells, bioactive agents, hydrogels or gene therapy.Herein, the clinical evidence and tips concerning MAT, currently available meniscus scaffolds and future perspectives are discussed. Cite this article: EFORT Open Rev 2019;4 DOI: 10.1302/2058-5241.4.180103.

Editorial Commentary: Fresh-Frozen Meniscal Allografts-Cold Does Not Always Cause Shrinkage

Meniscal allograft transplantation is an effective treatment for the symptomatic, young, active patient with meniscal deficiency. Modern graft-preservation techniques may reduce clinical sequelae of meniscal shrinkage after transplantation. We prefer fresh-frozen nonirradiated allografts because of easier processing, lower immunogenicity, and lower cost, and on the basis of a 2-decade clinical experience with fresh-frozen meniscal allograft transplantations, we are pleased with our survivorship results.

Two-year follow-up of bone mineral density changes in the knee after meniscal allograft transplantation: Results of an explorative study

BACKGROUND

The potential chondroprotective effect of meniscal allograft transplantation (MAT) is unclear. Subchondral bone mineral density (BMD) and subchondral bone remodeling play important roles in osteoarthritis development. Evaluation of subchondral BMD after MAT might give more insight into the potential chondroprotective effect. The purpose of this study was to determine early BMD changes in the knee after MAT.

METHODS

Twenty-six consecutive patients underwent MAT during 2010-2013. The BMD was measured using dual-energy x-ray absorptiometry (DXA) scan preoperatively, and six months, one and two years postoperatively. Bone mineral density was measured in six regions of interest (ROIs) in the tibia and femur (medial, central, lateral) in both treated and healthy contralateral knees.

RESULTS

The BMD levels of MAT knees did not significantly change during two years of follow-up in almost all ROIs. Bone mineral density was significant higher in nearly all ROIs in MAT knees at almost all follow-ups compared to healthy contralateral knees. In the healthy contralateral knees, BMD slightly, but not statistically, decreased in the first postoperative year, where it normalized to baseline values at two-year follow-up. The BMD levels in all ROIs did not significantly differ between the patients with or without chondropathy at baseline and two-year follow-up.

CONCLUSION

Based on the findings, MAT did not show a significant influence on BMD in the first two postoperative years. Longer follow-up is necessary to prove the potential chondroprotective effect of MAT using BMD measurements.

The effects of graft shrinkage and extrusion on early clinical outcomes after meniscal allograft transplantation

BACKGROUND

Graft shrinkage or radial extrusion is a reported complication after meniscus allograft transplantation (MAT). Whether shrinkage or extrusion progress after surgery and whether they are associated with the clinical outcome of MAT remain debatable. In this study, graft shrinkage and extrusion were measured in the coronal and sagittal planes using serial postoperative magnetic resonance imaging (MRI). The purpose of this study was to evaluate if graft shrinkage or extrusion is correlated to the clinical outcome of MAT.

METHODS

MRIs acquired at 3 and 12 months postoperatively in 30 patients (21 men and 9 women) who underwent MAT (6 medial and 24 lateral menisci) from 2010 to 2016 were analyzed. Two orthopedic surgeons and two musculoskeletal specialized radiologists each performed the MRI measurements. Allograft shrinkage was measured by the width and thickness of the graft at the coronal and sagittal planes. To determine the graft extrusion, distances between the proximal tibia cartilage margin and the extruded graft margin were measured in both coronal (either lateral or medial) and sagittal (both anterior and posterior) plane and relative percentage of extrusion (RPE) were calculated. Subjective International Knee Documentation Committee (IKDC) scores at 12 months were evaluated as a clinical outcome measurement, and correlations between shrinkage or extrusion of allograft and IKDC score were analyzed.

RESULTS

In the coronal plane, radial RPE averaged 43.6% at postoperative 3 months, but there was no significant progression of extrusion at 12 months (average 42.0%) (P = 0.728). In the sagittal plane, there were no significant progressions of anterior and posterior RPE (P = 0.487 and 0.166, respectively) between postoperative 3 and 12 months. Shrinkage was calculated by multiplying the width and height of the three sections and summing these values. There was no significant progression of shrinkage between postoperative 3 and 12 months (P = 0.150). RPE in the radial (R = 0.147, P = 0.525), anterior (R = 0.249, P = 0.264), and posterior (R = 0.230, P = 0.315) directions and shrinkage (R = 0.176, P = 0.435) were not correlated to IKDC score at postoperative 12 months.

CONCLUSIONS

In the coronal and sagittal planes, extrusion and shrinkage did not progress from 3 months to 1 year. Extrusion and shrinkage had no correlation with early clinical outcomes. This finding suggests that graft extrusion or shrinkage may be not a great concern especially in early postoperative period of MAT, and multiple, serial MRI may be not necessary.

[Indication and limitations of meniscus replacement]

BACKGROUND

Meniscal lesions are among the most important musculoskeletal disorders and are the most common indication for knee joint arthroplasty. However, the structural integrity and function is rarely retained, and a loss of tissue results. Thus, there is a huge demand for meniscal replacement options.

CURRENT PROCEDURES

Autografts were used in the past but did not fulfill expectations. Meniscus allografts have been developed to be a viable treatment option. However, availability is limited and evidence of a long-term chondroprotective effect scarce. Artificial scaffolds made from either collagen or PCU foam are available, which aid the regeneration of meniscal tissue and are rather intended as a partial replacement with an intact peripheral rim. Those implants thus have a limited spectrum of indication. While they seem to be symptomatically effective, it remains unclear whether they can reduce secondary cartilage damage. Newer developments aim at a permanent replacement of lost meniscal tissue.

LIMITATIONS

In summary, there is currently no meniscal replacement available for a broad range of indications and with a solid scientific foundation. Prophylactic use should be limited to cases with a high chance of progression to osteoarthritis, like a lateral total meniscectomy. Otherwise meniscal replacement should be considered in younger, symptomatic patients with mild to moderate secondary changes. Potential causes of the initial meniscal injury like instability or deformities should be carefully assessed and addressed. In many cases, osteotomy might be a viable alternative to meniscus replacement.

Radiation sterilization of tissue allografts: A review

Tissue substitutes are required in a number of clinical conditions for treatment of injured and diseased tissues. Tissues like bone, skin, amniotic membrane and soft tissues obtained from human donor can be used for repair or reconstruction of the injured part of the body. Allograft tissues from human donor provide an excellent alternative to autografts. However, major concern with the use of allografts is the risk of infectious disease transmission. Therefore, tissue allografts should be sterilized to make them safe for clinical use. Gamma radiation has several advantages and is the most suitable method for sterilization of biological tissues. This review summarizes the use of gamma irradiation technology as an effective method for sterilization of biological tissues and ensuring safety of tissue allografts.

Macroscopic and histological evaluations of meniscal allograft transplantation using gamma irradiated meniscus: a comparative in vivo animal study

BACKGROUND

Many studies suggest that the gamma irradiation decreases allograft strength in a dose-dependent manner. However, no study has demonstrated that this decrease in strength translates into higher failure rate in meniscal allograft transplantation (MAT). The aim of this study was to investigate the effects of gamma irradiation on macroscopic and histological alterations of transplanted meniscal tissue and joint cartilage after MAT.

METHODS

Medial total meniscectomies were performed on the right knees of 60 New Zealand white rabbits. All meniscal allografts were divided into three groups (20 in each group) and then sterilized with 0 Mrad, 1.5 Mrad, or 2.5 Mrad of gamma irradiation. For each group, 5 menisci were randomly chosen for scanning electron microscopic (SEM) analysis and the remaining 15 were prepared for MAT surgeries. Forty-five right knees received MAT surgeries (0 Mrad group, 1.5 Mrad group, 2.5 Mrad group, 15 in each group), whereas the remaining 15 only received medial meniscectomy (Meni group). The left knees of the Meni group were chosen as the Sham group (n = 15). All the rabbits were sacrificed at week 24 postoperatively. Cartilage of the medial compartment of each group was evaluated macroscopically using the International Cartilage Repair Society (ICRS) score and then histologically using the Mankin score based on the Masson Trichrome staining.

RESULTS

The SEM analysis confirmed that the meniscal collagen fibers would be significantly damaged as the dose of gamma irradiation increased. At week 24, the overall scores of macroscopic evaluations of the transplanted meniscal tissue showed no significant differences among the three groups receiving MAT surgeries, except for 2 in the 2.5 Mrad group presented partial radial tears at midbody. The ICRS scores and the Mankin scores showed the lowest in the Sham group and the highest in the Meni group (P < 0.05). For the three groups receiving MAT surgeries, the 2.5 Mrad group showed significant higher ICRS scores and Mankin scores than both the 0 Mrad group and the 1.5 Mrad group (P < 0.05). Whereas the 1.5 Mrad group presented similar results to the 0 Mrad group concerning both the ICRS scores and the Mankin scores.

CONCLUSIONS

The current in vivo animal study proved that although the meniscal collagen fibers were damaged after gamma irradiation, the failure rate of MAT surgeries might not significantly increase if the irradiation dose was <1.5 Mrad for New Zealand white rabbits.

Bone morphogenetic protein-2 and vascular endothelial growth factor in bone tissue regeneration: new insight and perspectives

The study of bone tissue regeneration in orthopaedic diseases has stimulated great interest among bone tissue engineering specialists and orthopaedic surgeons. Combinations of biomaterials, growth factors and stem cells for repairing bone have been much studied and researched, yet remain a challenge for both scientists and clinicians pursuing regenerative medicine. The purpose of this review was to elucidate the role of sequential release of bone morphogenetic protein-2 and vascular endothelial growth factor in producing better outcomes in the field of bone tissue regeneration.

X-ray microtomography-based measurements of meniscal allografts

BACKGROUND

X-ray microcomputed tomography (XMT) is a technique widely used to image hard and soft tissues. Meniscal allografts as collagen structures can be imaged and analyzed using XMT. The aim of this study was to present an XMT scanning protocol that can be used to obtain the 3D geometry of menisci. It was further applied to compare two methods of meniscal allograft measurement: traditional (based on manual measurement) and novel (based on digital measurement of 3D models of menisci obtained with use of XMT scanner).

HYPOTHESIS

The XMT-based menisci measurement is a reliable method for assessing the geometry of a meniscal allograft by measuring the basic meniscal dimensions known from traditional protocol.

MATERIALS AND METHODS

Thirteen dissected menisci were measured according the same principles traditionally applied in a tissue bank. Next, the same specimens were scanned by a laboratory scanner in the XMT Lab. The images were processed to obtain a 3D mesh. 3D models of allograft geometry were then measured using a novel protocol enhanced by computer software. Then, both measurements were compared using statistical tests.

RESULTS

The results showed significant differences (P<0.05) between the lengths of the medial and lateral menisci measured in the tissue bank and the XMT Lab. Also, medial meniscal widths were significantly different (P<0.05).

DISCUSSION

Differences in meniscal lengths may result from difficulties in dissected meniscus measurements in tissue banks, and may be related to the elastic structure of the dissected meniscus. Errors may also be caused by the lack of highlighted landmarks on the meniscal surface in this study.

CONCLUSION

The XMT may be a good technique for assessing meniscal dimensions without actually touching the specimen.