Articular fibrocartilage - Why does hyaline cartilage fail to repair?

Once damaged, articular cartilage has a limited potential to repair. Clinically, a repair tissue is formed, yet, it is often mechanically inferior fibrocartilage. The use of monolayer expanded versus naïve cells may explain one of the biggest discrepancies in mesenchymal stromal/stem cell (MSC) based cartilage regeneration. Namely, studies utilizing monolayer expanded MSCs, as indicated by numerous in vitro studies, report as a main limitation the induction of type X collagen and hypertrophy, a phenotype associated with endochondral bone formation. However, marrow stimulation and transfer studies report a mechanically inferior collagen I/II fibrocartilage as the main outcome. Therefore, this review will highlight the collagen species produced during the different therapeutic approaches. New developments in scaffold design and delivery of therapeutic molecules will be described. Potential future directions towards clinical translation will be discussed. New delivery mechanisms are being developed and they offer new hope in targeted therapeutic delivery.

Development of controlled matrix heterogeneity on a triphasic scaffold for orthopedic interface tissue engineering

Biological fixation of orthopedic soft tissue grafts to bone poses a significant clinical challenge. The clinical success of soft tissue-based grafts for anterior cruciate ligament (ACL) reconstruction is limited by the lack of functional graft integration with subchondral bone. Soft tissues such as the ACL connect to subchondral bone via a complex interface whereby three distinct tissue regions (ligament, fibrocartilage, and bone) work in concert to facilitate load transfer from soft to hard tissue while minimizing stress concentration at the interface. Although a fibrovascular tissue forms at the graft-to-bone interface following surgery, this tissue is nonphysiologic and represents a weak link between the graft and bone. We propose that the re-establishment of the native multi-tissue interface is essential for biological graft fixation. In vivo observations and our in vitro monolayer co-culture results suggest that osteoblast-fibroblast interaction is important for interface regeneration. This study focuses on the design of a triphasic scaffold system mimicking the multi-tissue organization of the native ACL-to-bone interface and the evaluation of osteoblast-fibroblast interactions during three-dimensional co-culture on the triphasic scaffold. We found that the triphasic scaffold supported cell proliferation, migration and phenotypic matrix production while maintaining distinct cellular regions and phase-specific extracellular matrix deposition over time. This triphasic scaffold is designed to guide the eventual reestablishment of an anatomically oriented and mechanically functional fibrocartilage interfacial region directly on biological and synthetic soft tissue grafts. The results of this study demonstrate the feasibility of multi-tissue regeneration on a single scaffold, and the potential of interface tissue engineering to enable the biological fixation of soft tissue grafts to bone.

Repair response of the inner and outer regions of the porcine meniscus in vitro

BACKGROUND

The menisci are essential intra-articular structures that contribute to knee function, and meniscal injury or loss is associated with joint degeneration. Tears of the outer vascularized zone have a greater potential for repair than do tears in the inner avascular region.

OBJECTIVE AND HYPOTHESIS

Develop an in vitro explant model to examine the hypothesis that differences exist in the intrinsic repair response between the outer and inner region of the meniscus.

STUDY DESIGN

Controlled laboratory study.

METHODS

Cylindrical explants were harvested from the outer one third and inner two thirds of medial porcine menisci. To simulate a full-thickness defect, a central core was removed and reinserted immediately. Explants were cultured for 2, 4, or 6 weeks, and meniscal healing was investigated using mechanical testing, histologic analysis, and fluorescence confocal microscopy.

RESULTS

Over the 6-week culture period, meniscal explants exhibited migration of cells into the repair site, followed by increased tissue formation that bridged the interface. The repair strength increased significantly over time, with no differences between the 2 regions.

CONCLUSION

The findings show that explants from the avascular inner zone and vascular outer zone of the meniscus exhibit similar healing potential and repair strength in vitro.

CLINICAL RELEVANCE

These findings support the hypothesis that the regional differences in meniscal repair observed clinically are owed to the additional vascular supply of the outer meniscus rather than intrinsic differences between the extracellular matrix and cells from these 2 areas.

Recent Tissue Engineering Advances for the Treatment of Temporomandibular Joint Disorders

Temporomandibular disorders (TMDs) are among the most common maxillofacial complaints and a major cause of orofacial pain. Although current treatments provide short- and long-term relief, alternative tissue engineering solutions are in great demand. Particularly, the development of strategies, providing long-term resolution of TMD to help patients regain normal function, is a high priority. An absolute prerequisite of tissue engineering is to understand normal structure and function. The current knowledge of anatomical, mechanical, and biochemical characteristics of the temporomandibular joint (TMJ) and associated tissues will be discussed, followed by a brief description of current TMD treatments. The main focus is on recent tissue engineering developments for regenerating TMJ tissue components, with or without a scaffold. The expectation for effectively managing TMD is that tissue engineering will produce biomimetic TMJ tissues that recapitulate the normal structure and function of the TMJ.

Comparative Evaluation of the Book-Type Acellular Bone Scaffold and Fibrocartilage Scaffold for Bone-Tendon Healing

Bone-tendon (B-T) healing is a clinical challenge due to its limited regeneration capability. Fibrocartilage regeneration and bone formation at the healing site are two critical factors for B-T healing. Promoting fibrocartilage regeneration and bone formation by tissue-engineering may be a promising treatment strategy. In this study, we innovatively fabricated two kinds of acellular scaffolds from bone or fibrocartilage tissues, namely the book-type the acellular bone scaffold (BABS) and the book-type acellular fibrocartilage scaffold (BAFS). Histologically, the two scaffolds well preserved the native extracellular matrix (ECM) structure without cellular components. In vitro studies showed BABS is superior in osteogenic inducibility, while BAFS has good chondrogenic inducibility. To comparatively investigate the efficacy on B-T healing, the BABS or BAFS were, respectively, implanted into a rabbit partial patellectomy model. Macroscopically, a regenerated bone-tendon insertion (BTI) was bridging the residual patella and patellar-tendon with no signs of infection and osteoarthritis. Radiologically, more new bone was formed at the healing interface in the BABS group as compared with the BAFS or control (CTL) groups (p < 0.05). Histologically, at postoperative week 16, histological scores were significantly better for regenerated fibrocartilage in the BAFS group or BABS group compared with the CTL group, but the BAFS group showed a significantly larger score than the BABS groups (p < 0.05). Biomechanical evaluation indicated a higher failure load and stiffness were shown in the BAFS group than those in the BABS or CTL groups at week 16 (p < 0.05). This study indicated that the BAFS is a more promising scaffold for B-T healing in comparison with the BABS. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1709-1722, 2019.

Ex vivo effects of corticosteroids on equine deep digital flexor and navicular fibrocartilage explant cell viability

OBJECTIVE

To investigate the effects of triamcinolone acetonide (TA) and methylprednisolone acetate (MPA) on the viability of resident cells within the fibrocartilage on the dorsal surface of the deep digital flexor tendon (FC-DDFT) and fibrocartilage on the flexor surface of the navicular bone (FC-NB) of horses.

SAMPLE

12 to 14 explants of FC-DDFT and of FC-NB from grossly normal forelimbs of 5 cadavers of horses aged 9 to 15 years without evidence of musculoskeletal disease.

PROCEDURES

Explants were incubated with culture medium (control) or TA-supplemented (0.6 or 6 mg/mL) or MPA-supplemented (0.5 or 5 mg/mL) medium for 6 or 24 hours. Explant metabolic activity and percentage of dead cells were assessed with a resazurin-based assay and live-dead cell staining, respectively, at each time point. Drug effects were assessed relative to findings for the respective control group.

RESULTS

Application of TA (at both concentrations) did not significantly change the cell viability of FC-DDFT explants. For FC-NB explants, TA at 6 mg/mL significantly reduced the metabolic activity and increased the percentage of dead cells at both time points. With either MPA concentration, FC-DDFT and FC-NB explants had reduced metabolic activity and an increased percentage of dead cells at 24 hours, whereas only MPA at 5 mg/mL was cytotoxic at the 6-hour time point.

CONCLUSIONS AND CLINICAL RELEVANCE

In ex vivo explants, TA was less cytotoxic to equine FC-DDFT and FC-NB cells, compared with MPA. Further work is warranted to characterize the drugs' transcriptional and translational effects as well as investigate their cytotoxicity at lower concentrations.

Concurrent multi-lineage differentiation of mesenchymal stem cells through spatial presentation of growth factors

Severe tendon and ligament injuries are estimated to affect between 300 000 and 400 000 people annually. Surgical repairs of these injuries often have poor long-term clinical outcomes because of resection of the interfacial tissue-the enthesis-and subsequent stress concentration at the attachment site. A healthy enthesis consists of distinct regions of bone, fibrocartilage, and tendon, each with distinct cell types, extracellular matrix components, and architecture, which are important for tissue function. Tissue engineering, which has been proposed as a potential strategy for replacing this tissue, is currently limited by its inability to differentiate multiple lineages of cells from a single stem cell population within a single engineered construct. In this study, we develop a multi-phasic gelatin methacrylate hydrogel construct system for spatial presentation of proteins, which is then validated for multi-lineage differentiation towards the cell types of the bone-tendon enthesis. This study determines growth factor concentrations for differentiation of mesenchymal stem cells towards osteoblasts, chondrocytes/fibrochondrocytes, and tenocytes, which maintain similar differentiation profiles in 3D hydrogel culture as assessed by qPCR and immunofluorescence staining. Finally, it is shown that this method is able to guide heterogeneous and spatially confined changes in mesenchymal stem cell genes and protein expressions with the tendency to result in osteoblast-, fibrochondrocyte-, and tenocyte-like expression profiles. Overall, we demonstrate the utility of the culture technique for engineering other musculoskeletal tissue interfaces and provide a biochemical approach for recapitulating the bone-tendon enthesis in vitro.

Influence of periostin on the development of fibrocartilage layers of anterior cruciate ligament insertion

BACKGROUND

Periostin (Postn) is thought to play a role in the formation of anterior cruciate ligament (ACL) insertion. However, the influence of Postn on the development of ACL insertion requires further understanding. This study aimed to clarify the influence of Postn on the development of fibrocartilage layers of ACL insertion.

HYPOTHESIS

We hypothesized that Postn would influence the development of fibrocartilage layers of ACL insertion.

MATERIALS AND METHODS

C57BL/6N wild-type (Postn+/+; n=54) and Postn knockout (Postn-/-; n=54) mice were used in this study. Six animals were euthanized at 1 d and 1, 2, 3, 4, 6, 8, 10, and 12 weeks of age in each group. The chondrocyte number, proliferation, apoptosis, safranin O-stained glycosaminoglycan (GAG) area, type II collagen staining area, tidemark length, and insertion width were evaluated.

RESULTS

Chondrocyte proliferation was high up to 2 weeks in Postn+/+, while low at age 1 d; it was, especially lower in Postn-/- than in Postn+/+ at age 1 d and 1 week. Chondrocyte apoptosis was high up to age 8 weeks in Postn+/+ and at 6 weeks in Postn-/-; it was especially higher in Postn-/- than in Postn+/+ at age 1 week. The GAG stained area was thickest for age 1 d to 4 weeks in Postn+/+ and for age 2 to 6 weeks in Postn-/-. The type II collagen staining area in Postn+/+ was thicker than that in Postn-/- at age 6 and 8 weeks. The tidemark length in Postn+/+ was longer than that in Postn-/- from age 8 to 12 weeks. The insertion width in Postn+/+ was longer than that in Postn-/- from age 1 to 3 weeks.

DISCUSSION

Postn decreased cell proliferation in the early postnatal phase and influenced the development of the fibrocartilage layer extracellular matrix of ACL insertion in mice. Postn may contribute to the development of methods for regeneration of the ACL insertion.

LEVEL OF EVIDENCE

V; controlled laboratory study.

Structural and functional heterogeneity of mineralized fibrocartilage at the Achilles tendon-bone insertion

A demanding task of the musculoskeletal system is the attachment of tendon to bone at entheses. This region often presents a thin layer of fibrocartilage (FC), mineralized close to the bone and unmineralized close to the tendon. Mineralized FC deserves increased attention, owing to its crucial anchoring task and involvement in enthesis pathologies. Here, we analyzed mineralized FC and subchondral bone at the Achilles tendon-bone insertion of rats. This location features enthesis FC anchoring tendon to bone and sustaining tensile loads, and periosteal FC facilitating bone-tendon sliding with accompanying compressive and shear forces. Using a correlative multimodal investigation, we evaluated potential specificities in mineral content, fiber organization and mechanical properties of enthesis and periosteal FC. Both tissues had a lower degree of mineralization than subchondral bone, yet used the available mineral very efficiently: for the same local mineral content, they had higher stiffness and hardness than bone. We found that enthesis FC was characterized by highly aligned mineralized collagen fibers even far away from the attachment region, whereas periosteal FC had a rich variety of fiber arrangements. Except for an initial steep spatial gradient between unmineralized and mineralized FC, local mechanical properties were surprisingly uniform inside enthesis FC while a modulation in stiffness, independent from mineral content, was observed in periosteal FC. We interpreted these different structure-property relationships as a demonstration of the high versatility of FC, providing high strength at the insertion (to resist tensile loading) and a gradual compliance at the periosteal surface (to resist contact stresses). STATEMENT OF SIGNIFICANCE: Mineralized fibrocartilage (FC) at entheses facilitates the integration of tendon in bone, two strongly dissimilar tissues. We focus on the structure-function relationships of two types of mineralized FC, enthesis and periosteal, which have clearly distinct mechanical demands. By investigating them with multiple high-resolution methods in a correlative manner, we demonstrate differences in fiber architecture and mechanical properties between the two tissues, indicative of their mechanical roles. Our results are relevant both from a medical viewpoint, targeting a clinically relevant location, as well as from a material science perspective, identifying FC as high-performance versatile composite.

The intervertebral discs' fibrocartilage as a DNA source for genetic identification in severely charred cadavers

Identifying charred human remains poses a challenge to forensic laboratories. High temperature completely incinerates the superficial tissues and partially destroys bones, forcing the forensics to seek an alternative, for bones and teeth, forensic material that should quickly and cheaply deliver DNA of sufficient quantity and quality. We sought, other than rib cartilage, types of cartilages that could serve as a DNA source. DNA was isolated from the fibrous cartilage of a fibrous ring of intervertebral L1-L2 discs sampled from charred cadavers or charred body fragments: 5 victims of car fires, 1 victim of combustion during a residential house gas explosion, and 3 victims of nitroglycerin explosion. DNA was isolated by the column method. DNA quality and concentration were assessed by RT-PCR and multiplex PCR for 23 autosomal and 17 Y chromosome STR loci. STR polymorphism results obtained by capillary electrophoresis served for likelihood ratio (LR) calculations. DNA concentration in relation to the cadaver's age and post-mortem interval (PMI) were analyzed. All samples (n = 9) yielded good-quality DNA in quantities (0.57-17.51 ng/µL for T. Large autosomal sequence) suitable for STR-based amplification. The isolated DNA characterized a low degradation index (0.80-1.99), and we were able to obtain complete genetic profiles. In each of the nine cases, the genotyping results allowed identifying the victims based on comparative material from the immediate family. The results demonstrate the usefulness of human intervertebral disc fibrocartilage as an alternative DNA source for the genetic identification of charred bodies or charred torso fragments.

Single-cell RNA sequencing reveals cellular and molecular heterogeneity in fibrocartilaginous enthesis formation

The attachment site of the rotator cuff (RC) is a classic fibrocartilaginous enthesis, which is the junction between bone and tendon with typical characteristics of a fibrocartilage transition zone. Enthesis development has historically been studied with lineage tracing of individual genes selected a priori, which does not allow for the determination of single-cell landscapes yielding mature cell types and tissues. Here, in together with open-source GSE182997 datasets (three samples) provided by Fang et al., we applied Single-cell RNA sequencing (scRNA-seq) to delineate the comprehensive postnatal RC enthesis growth and the temporal atlas from as early as postnatal day 1 up to postnatal week 8. And, we furtherly performed single-cell spatial transcriptomic sequencing on postnatal day 1 mouse enthesis, in order to deconvolute bone-tendon junction (BTJ) chondrocytes onto spatial spots. In summary, we deciphered the cellular heterogeneity and the molecular dynamics during fibrocartilage differentiation. Combined with current spatial transcriptomic data, our results provide a transcriptional resource that will support future investigations of enthesis development at the mechanistic level and may shed light on the strategies for enhanced RC healing outcomes.

[Labral lesions in femoroacetabular impingement syndrome: evidence-based treatment]

BACKGROUND

The acetabular labrum and the adjacent rim cartilage are the primary targets of primary or secondary degeneration processes in the hip joint. Currently, femoroacetabular impingement syndrome (FAIS) is considered the main mechanical pathology leading to chondrolabral damage. The treatment options for labrum tears range from a debridement/resection, repair to augmentation or transplantation.

AIM

Description of surgical treatment options for pathologic changes of the acetabulare labrum and their results with a focus on FAIS.

MATERIALS AND METHODS

A literature search was performed on https://pubmed.ncbi.nlm.nih.gov using the following key words: hip, labrum, therapy, resection, repair, augmentation, reconstruction.

RESULTS

The different surgical procedures as labrum therapy reduce pain and increase the joint function. Labral repair, augmentation, and reconstruction tend to have better results compared to resection but are associated with a higher rate of postoperative intraarticular adhesions.

DISCUSSION

In addition to reducing pain and improving function, the goal of surgical treatment of labrum lesions should be to maintain the functions of the labrum. The labrum should be preserved, in cases of adequate tissue quality and width. In the setting of resective procedures, the resection should be limited to the unstable parts of the labrum. The results of labral augmentation and reconstruction are promising, allowing these procedures to be considered for patients with ongoing symptoms in the revision situation with labral defects or an insufficient residual labrum.

The role of tendon derived stem/progenitor cells and extracellular matrix components in the bone tendon junction repair

Fibrocartilage enthesis is the junction between bone and tendon with a typical characteristics of fibrocartilage transition zones. The regeneration of this transition zone is the bottleneck for functional restoration of bone tendon junction (BTJ). Biomimetic approaches, especially decellularized extracellular matrix (ECM) materials, are strategies which aim to mimic the components of tissues to the utmost extent, and are becoming popular in BTJ healing because of their ability not only to provide scaffolds to allow cells to attach and migrate, but also to provide a microenvironment to guide stem/progenitor cells lineage-specific differentiation. However, the cellular and molecular mechanisms of those approaches, especially the ECM proteins, remain unclear. For BTJ reconstruction, fibrocartilage regeneration is the key for good integrity of bone and tendon as well as its mechanical recovery, so the components which can guide stem cells to a chondrogenic commitment in biomimetic approaches might well be the key for fibrocartilage regeneration and eventually for the better BTJ healing. In this review, we firstly discuss the importance of cartilage-like formation in the healing process of BTJ. Next, we explore the possibility of tendon-derived stem/progenitor cells as cell sources for BTJ regeneration due to their multi-differentiation potential. Finally, we summarize the role of extracellular matrix components of BTJ in guiding stem cell fate to a chondrogenic commitment, so as to provide cues for understanding the mechanisms of lineage-specific potential of biomimetic approaches as well as to inspire researchers to incorporate unique ECM components that facilitate BTJ repair into design.

[CONDITIONS OF SYNOVIAL MESENCHYMAL STEM CELLS DIFFERENTIATING INTO FIBROCARTILAGE CELLS]

OBJECTIVE

To explore the conditions of synovial derived mesenchymal stem cells (SMSCs) differentiating into the fibrocartilage cells by using the orthogonal experiment.

METHODS

The synovium was harvested from 5 adult New Zealand white rabbits, and SMSCs were separated by adherence method. The flow cytometry and multi-directional differentiation method were used to identify the SMSCs. The conditions were found from the preliminary experiment and literature review. The missing test was carried out to screen the conditions and then 12 conditions were used for the orthogonal experiment, including transforming growth factor β1 (TGF-β1), bone morphogenic protein 2 (BMP-2), dexamethasone (DEX), proline, ascorbic acid (ASA), pyruvic acid, insulin + transferrin + selenious acid pre-mixed solution (ITS), bovin serum albumin (BSA), basic fibroblast growth factor (bFGF), intermittent hydraulic pressure (IHP), bone morphogenic protein 7 (BMP-7), and insulin-like growth factor (IGF). The L60 (212) orthogonal experiment was designed using the SPSS 18.0 with 2 level conditions and the cells were induced to differentiate on the small intestinal submucosa (SIS)-3D scaffold. The CD151+/CD44+ cells were detected with the flow cytometry and then the differentiation rate was recorded. The immumohistochemical staining, cellular morphology, toluidine blue staining, and semi-quantitative RT-PCR examination for the gene expressions of sex determining region Y (SRY)-box 9 gene (Sox9), aggrecan gene (AGN), collagen type I gene (Col I), collagen type II gene (Col II), collagen type IX gene (Col IX) were used for result confirmation. The differentiation rate was calculated as the product of CD151/CD44+ cells and cells with Col I high expression. The grow curve was detected with the DNA abundance using the PicoGreen Assay. The visual observation and the variances analysis among the variable were used to evaluate the result of the orthogonal experiment, 1 level interaction was considered. The q-test and the least significant difference (LDS) were used for the variance analysis with a type III calibration model. The test criteria (a) was 0.05.

RESULTS

The cells were certified as SMSCs, the double-time of the cells was 28 hours. During the differentiation into the fibrocartilage, the volume of the SIS-3D scaffold enlarged double every 5 days. The scaffolds were positively stained by toluidine blue at 14 days. The visual observation showed that high levels of TGF-β1 and BMP-7 were optimum for the differentiation, and BMP-7 showed the interaction with BMP-2. The conditions of DEX, ASA, ITS, transferrin, bFGF showed decreasing promotional function by degrees, and the model showed the perfect relevance. P value was 0.000 according to the variance analysis. The intercept analysis showed different independent variables brought about variant contribution; the TGF-β1, ASA, bFGF, IGF, and BMP-7 were more remarkable, which were similar to the visual observation.

CONCLUSION

In the process of the SMSCs differentiation into the fibrocartilage, the concentrations of TGF-β1, ASA, bFGF, and IGF reasonably can improve the conversion rate of the fibrocartilage cells. The accurate conditions of the reaulatory factor should be explored further.

Comparison study on hyaline cartilage versus fibrocartilage formation in a pig model by using 3D-bioprinted hydrogel and hybrid constructs

Cartilage tissue engineering (CTE) with the help of engineered constructs has shown promise for the regeneration of hyaline cartilage, where fibrocartilage may also be formed due to the biomechanical loading resulting from the host weight and movement. Previous studies have primarily reported on hyaline cartilage formationin vitroand/or in small animals, while leaving the fibrocartilage formation undiscovered. In this paper, we, at the first time, present a comparison study on hyaline cartilage versus fibrocartilage formation in a large animal model of pig by using two constructs (namely hydrogel and hybrid ones) engineered by means of three-dimensional (3D) bioprinting. Both hydrogel and hybrid constructs were printed from the bioink of alginate (2.5%) and ATDC5 cells (chondrogenic cells at a cell density of 5 × 106cells ml-1), with the difference in that in the hybrid construct, there was a polycaprolactone (PCL) strand printed between every two bioink strands, which were strategically designed to shield the force imposed on the cells within the bioink strands. Both hydrogel and hybrid constructs were implanted into the chondral defects created in the articular cartilage of weight-bearing portions of pig stifle joints; the cartilage formation was examined at one- and three-months post-implantation, respectively, by means of Safranin O, Trichrome, immunofluorescent staining, and synchrotron radiation-based (SR) inline phase contrast imaging microcomputed tomography (inline-PCI-CT). Glycosaminoglycan (GAG) and collagen type II (Col II) secretion were used to evaluate the hyaline cartilage formation, while collagen type I (Col I) was used to indicate fibrocartilage given that Col I is low in hyaline cartilage but high in fibrocartilage. Our results revealed that cartilage formation was enhanced over time in both hydrogel and hybrid constructs; particularly, the hydrogel construct exhibited more cartilage formation at both one- and three-months post-implantation, while hybrid constructs tended to have less fibrocartilage formed in a long time period. Also, the result from the inline-PCI-CT revealed that the inline-PCI-CT was able to provide not only the information seen in other histology images, but also high-resolution details of biomaterials and regenerating cartilage. This would represent a significant advance toward the non-invasive assessment of cartilage formation regeneration within large animal models and eventually in human patients.

Meniscal Fibrocartilage Repair Based on Developmental Characteristics: A Proof-of-Concept Study

BACKGROUND

Unlike the adult meniscus, the fetal meniscus possesses robust healing capacity. The dense and stiff matrix of the adult meniscus provides a biophysical barrier for cell migration, which is not present in the fetal meniscus. Inspired by developmental characteristics, modifying the matrix of the adult meniscus into a fetal-like, loose and soft microenvironment holds opportunity to facilitate repair, especially in the avascular zone.

HYPOTHESIS

Modifying the dense and stiff matrix of the adult meniscus into a fetal-like, loose and soft microenvironment could enhance cell migration to the tear interface and subsequent robust healing capacity.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fresh porcine menisci were treated with hyaluronidase or collagenase. The density and arrangement of collagen fibers were assessed. The degradation of proteoglycans and collagen was evaluated histologically. Cell migration within the meniscus or the infiltration of exogenous cells into the meniscus was examined. Dendritic silica nanoparticles with relatively large pores were used to encapsulate hyaluronidase for rapid release. Mesoporous silica nanoparticles with relatively small pores were used to encapsulate transforming growth factor-beta 3 (TGF-β3) for slow release. A total of 24 mature male rabbits were included. A longitudinal vertical tear (0.5 cm in length) was prepared in the avascular zone of the medial meniscus. The tear was repaired with suture, repaired with suture in addition to blank silica nanoparticles, or repaired with suture in addition to silica nanoparticles releasing hyaluronidase and TGF-β3. Animals were sacrificed at 12 months postoperatively. Meniscal repair was evaluated macroscopically and histologically.

RESULTS

The gaps between collagen bundles increased after hyaluronidase treatment, while collagenase treatment resulted in collagen disruption. Proteoglycans degraded after hyaluronidase treatment in a dose-dependent manner, but collagen integrity was maintained. Hyaluronidase treatment enhanced the migration and infiltration of cells within meniscal tissue. Last, the application of fibrin gel and the delivery system of silica nanoparticles encapsulating hyaluronidase and TGF-β3 enhanced meniscal repair responses in an orthotopic longitudinal vertical tear model.

CONCLUSION

The gradient release of hyaluronidase and TGF-β3 removed biophysical barriers for cell migration, creating a fetal-like, loose and soft microenvironment, and enhanced the fibrochondrogenic phenotype of reparative cells, facilitating the synthesis of matrix and tissue integration.

CLINICAL RELEVANCE

Modifying the adult matrix into a fetal-like, loose and soft microenvironment via the local gradient release of hyaluronidase and TGF-β3 enhanced the healing capacity of the meniscus.

Nanofibrous scaffolds for the healing of the fibrocartilaginous enthesis: advances and prospects

With the current developmental advancements in nanotechnology, nanofibrous scaffolds are being widely used. The healing of fibrocartilaginous enthesis is a slow and complex process, and while existing treatments have a certain effect on promoting their healing, these are associated with some limitations. The nanofibrous scaffold has the advantages of easy preparation, wide source of raw materials, easy adjustment, easy modification, can mimic the natural structure and morphology of the fibrocartilaginous enthesis, and has good biocompatibility, which can compensate for existing treatments and be combined with them to promote the repair of fibrocartilaginous enthesis. The nanofibrous scaffold can promote the healing of fibrocartilaginous enthesis by controlling the morphology and ensuring controlled drug release. Hence, the use of nanofibrous scaffold with stimulative response features in the musculoskeletal system has led us to imagine its potential application in fibrocartilaginous enthesis. Therefore, the healing of fibrocartilaginous enthesis based on a nanofibrous scaffold may be a novel therapeutic approach.

Entheseal changes and activity patterns in southern African hunter-gatherer/herders from the Holocene

OBJECTIVES

Activity patterns and lifeways in southern African hunter-gatherer/herders (sAHGH) during the Holocene were dynamic, with subsistence activities and mobility varying through space and time. In this study, spatial and temporal variations in entheseal changes (ECs) are assessed as physical activity markers in sAHGH from the Holocene.

METHODS

The Coimbra method was used to assess fibrocartilaginous ECs in the upper and lower limbs of 118 sAHGH from the Holocene. Descriptive statistics and generalized estimating equations were used to explore the association between ECs, sex, age, ecological biomes, and temporality.

RESULTS

A total of 118 individuals were sampled, comprising 67 males, and 42 females, mostly from the fynbos (59/118), forest (30/118) and succulent karoo biomes (16/118). ECs were identified in 94% of the sample. Interobserver scoring suggests our findings are likely to underrepresent the extent of EC score differences in sAHGH. Findings indicate a complex pattern of physical activity in sAHGH with differences attributable to regional ecology rather than age or sex. More prominent ECs were identified in individuals from the forest biome, relative to the fynbos and succulent karoo biomes. These were consistent with resource search and processing costs, and terrain differences in these ecozones. ECs were only detected temporally relative to the infiltration of pastoralism (at 2000 BP) when the data were stratified by ecological biome.

DISCUSSION

This study provides evidence that regional ecology plays a central role in driving activity patterns regardless of social or cultural organization. Ecological biomes provide a gradient along which the temporal impact of resource limitations on human biology, activity patterns and sociocultural behaviors can be studied.

Divergent chondro/osteogenic transduction laws of fibrocartilage stem cell drive temporomandibular joint osteoarthritis in growing mice

The anterior disc displacement (ADD) leads to temporomandibular joint osteoarthritis (TMJOA) and mandibular growth retardation in adolescents. To investigate the potential functional role of fibrocartilage stem cells (FCSCs) during the process, a surgical ADD-TMJOA mouse model was established. From 1 week after model generation, ADD mice exhibited aggravated mandibular growth retardation with osteoarthritis (OA)-like joint cartilage degeneration, manifesting with impaired chondrogenic differentiation and loss of subchondral bone homeostasis. Lineage tracing using Gli1-CreER+; Tmfl/-mice and Sox9-CreER+;Tmfl/-mice showed that ADD interfered with the chondrogenic capacity of Gli1+ FCSCs as well as osteogenic differentiation of Sox9+ lineage, mainly in the middle zone of TMJ cartilage. Then, a surgically induced disc reposition (DR) mouse model was generated. The inhibited FCSCs capacity was significantly alleviated by DR treatment in ADD mice. And both the ADD mice and adolescent ADD patients had significantly relieved OA phenotype and improved condylar growth after DR treatment. In conclusion, ADD-TMJOA leads to impaired chondrogenic progenitor capacity and osteogenesis differentiation of FCSCs lineage, resulting in cartilage degeneration and loss of subchondral bone homeostasis, finally causing TMJ growth retardation. DR at an early stage could significantly alleviate cartilage degeneration and restore TMJ cartilage growth potential.

Exercise Induced Endothelial Mesenchymal Transition (EndMT) Facilitates Meniscal Fibrocartilage Regeneration

The meniscus is a semilunar wedge-shaped fibrocartilage tissue within the knee joint that is important for withstanding mechanical shock during joint motion. The intrinsic healing capacity of meniscus tissue is very limited, which makes meniscectomy the primary treatment method in the clinic. An effective translational strategy for regenerating the meniscus after total or subtotal meniscectomy, particularly for extensive meniscal lesions or degeneration, is yet to be developed. The present study demonstrates that the endothelial mesenchymal transition (EndMT) contributes to meniscal regeneration. The mechanical stimulus facilitated EndMT by activating TGF-β2 signaling. A handheld bioprinter system to intraoperatively fabricate a porous meniscus scaffold according to the resected meniscus tissue is developed; this can simplify the scaffold fabrication procedure and period. The transplantation of a porous meniscus scaffold combined with a postoperative regular exercise stimulus facilitated the regeneration of anisotropic meniscal fibrocartilaginous tissue and protected the joint cartilage from degeneration in an ovine subtotal meniscectomy model. Single-cell RNA sequencing and immunofluorescence co-staining analyses further confirmed the occurrence of EndMT during meniscal regeneration. EndMT-transformed cells gave rise to fibrochondrocytes, subsequently contributing to meniscal fibrocartilage regeneration. Thus, an efficient translational strategy to facilitate meniscal regeneration is developed.

Histomorphological Investigation of Microfracture Location in a Rabbit Osteochondral Defect Model

BACKGROUND

Microfracture is the most common treatment for cartilage defects of the knee. In microfracture surgery, holes are randomly drilled into the subchondral bone. The effect of the hole's location on its interaction with the cartilage defect site and its influence on the healing process is currently uncertain.

PURPOSE

To investigate the effects of different microfracture locations on healing in a rabbit knee osteochondral defect model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 29 adult New Zealand White rabbits were divided into 5 groups. In the healthy cartilage control group (n = 5), no surgical procedure was performed. Cylindrical full-thickness cartilage defects (5 × 3 mm) were created in the patellar groove of the remaining 24 rabbits. In the defect control group (n = 6), only the defect was created. A microfracture was performed at the 12-o'clock position (group peripheral single; n = 6), centrally (group central; n = 6), and at the 12- and 6-o'clock positions (group peripheral double; n = 6) of the defect. The animals were sacrificed after 8 weeks. Cartilage healing was evaluated by International Cartilage Regeneration & Joint Preservation Society (ICRS) score, modified O'Driscoll score, immunohistochemical analysis (type 1 collagen, type 2 collagen, and aggrecan), and scanning electron microscopy analysis.

RESULTS

In group peripheral double, better cartilage healing was observed in all parameters compared with the other groups (P < .05). Group peripheral double had the greatest amount of filling, with 79% of the defect area filled with fibrocartilage repair tissue. Group peripheral single demonstrated filling of 73% of the defect area, group central 56%, and the defect control group 45%. The ICRS score was significantly higher in group peripheral single compared with group central and the defect control group. Type 2 collagen and aggrecan immunoreactivity were significantly stronger in group central than group peripheral single and the defect control group (P < .05).

CONCLUSION

Microfracture performed at the peripheral margin of the defect had better filling characteristics in a rabbit model. This study suggests that interaction of pluripotent cells released from the microfracture site with the intact cartilage may enhance the quality of the repair tissue.

CLINICAL RELEVANCE

The location of microfracture holes in relation to the peripheral border of the osteochondral defect (to the intact cartilage) is important in both the quality and the quantity of the newly formed repair tissue.