Comprehensive analysis of translational osteochondral repair: Focus on the histological assessment

Subchondral bone: An emerging target for the treatment of articular surface lesions of the knee

Purpose

When dealing with the health status of the knee articular surface, the entire osteochondral unit has gained increasing attention, and in particular the subchondral bone, which plays a key role in the integrity of the osteochondral unit. The aim of this article was to discuss the current evidence on the role of the subchondral bone.

Methods

Experts from different geographical regions were involved in performing a review on highly discussed topics about the subchondral bone, ranging from its etiopathogenetic role in joint degeneration processes to its prognostic role in chondral and osteochondral defects, up to treatment strategies to address both the subchondral bone and the articular surface.

Discussion

Subchondral bone has a central role both from an aetiologic point of view and as a diagnostic tool, and its status was found to be relevant also as a prognostic factor in the follow-up of chondral treatment. Finally, the recognition of its importance in the natural history of these lesions led to consider subchondral bone as a treatment target, with the development of osteochondral scaffolds and procedures to specifically address osteochondral lesions.

Conclusion

Subchondral bone plays a central role in articular surface lesions from different points of view. Several aspects still need to be understood, but a growing interest in subchondral bone is to be expected in the upcoming future towards the optimization of joint preservation strategies.

Level of Evidence

Level V, expert opinion.

Modulation of early osteoarthritis by tibiofemoral re-alignment in sheep

OBJECTIVE

To investigate whether tibiofemoral alignment influences early knee osteoarthritis (OA). We hypothesized that varus overload exacerbates early degenerative osteochondral changes, and that valgus underload diminishes early OA.

METHOD

Normal, over- and underload were induced by altering alignment via high tibial osteotomy in adult sheep (n = 8 each). Simultaneously, OA was induced by partial medial anterior meniscectomy. At 6 weeks postoperatively, OA was examined in five individual subregions of the medial tibial plateau using Kellgren-Lawrence grading, quantification of macroscopic OA, semiquantitative histopathological OA and immunohistochemical type-II collagen, ADAMTS-5, and MMP-13 scoring, biochemical determination of DNA and proteoglycan contents, and micro-computed tomographic evaluation of the subchondral bone.

RESULTS

Multivariate analyses revealed that OA cartilaginous changes had a temporal priority over subchondral bone changes. Underload inhibited early cartilage degeneration in a characteristic topographic pattern (P ≥ 0.0983 vs. normal), in particular below the meniscal damage, avoided alterations of the subarticular spongiosa (P ≥ 0.162 vs. normal), and prevented the disturbance of otherwise normal osteochondral correlations. Overload induced early alterations of the subchondral bone plate microstructure towards osteopenia, including significantly decreased percent bone volume and increased bone surface-to-volume ratio (all P ≤ 0.0359 vs. normal).

CONCLUSION

The data provide high-resolution evidence that tibiofemoral alignment modulates early OA induced by a medial meniscus injury in adult sheep. Since underload inhibits early OA, these data also support the clinical value of strategies to reduce the load in an affected knee compartment to possibly decelerate structural OA progression.

The role of autologous bone grafting in matrix-associated autologous chondrocyte implantation at the knee: Results from the German Cartilage Registry (KnorpelRegister DGOU)

PURPOSE

To investigate whether concomitant autologous bone grafting adversely affects clinical outcome and graft survival after matrix-associated autologous chondrocyte implantation (M-ACI).

METHODS

The present study examines registry data of patients who underwent M-ACI with or without autologous bone grafting for large-sized chondral or osteochondral defects. Propensity score matching was performed to exclude potential confounders. A total of 215 patients with similar baseline characteristics were identified. Clinical outcome was assessed at the time of surgery and at 6, 12, 24, 36 and 60 months using the Knee Injury and Osteoarthritis Outcome Score (KOOS). KOOS change, clinical response rate, KOOS subcomponents and failure rate were determined.

RESULTS

Patients treated with M-ACI and autologous bone grafting achieved comparable clinical outcomes compared with M-ACI alone. At 24 months postoperatively, the patient-reported outcome (PRO) of patients treated with M-ACI and autologous bone grafting was even significantly better as measured by KOOS (74.9 ± 18.8 vs. 79.2 ± 15.4; p = 0.043). However, the difference did not exceed the minimal clinically important difference (MCID). In patients with M-ACI and autologous bone grafting, a greater change in KOOS relative to baseline was observed at 6 (9.3 ± 14.7 vs. 15.0 ± 14.7; p = 0.004) and 12 months (12.6 ± 17.2 vs. 17.7 ± 14.6; p = 0.035). Overall, a high clinical response rate was observed in both groups at 24 months (75.8% vs. 82.0%; p = n.s.). The estimated survival at the endpoint of reoperation for any reason was 82.1% (SD 2.8) at 8.4 years for isolated M-ACI and 88.7% (SD 2.4) at 8.2 years for M-ACI with autologous bone grafting (p = 0.039).

CONCLUSIONS

Even in the challenging cohort of large osteochondral defects, the additional treatment with autologous bone grafting leads to remarkably good clinical outcomes in patients treated with M-ACI. In fact, they tend to benefit more from surgery, have lower revision rates and achieve clinical response rates earlier. Subchondral bone management is critical to the success of M-ACI and should be addressed in the treatment of borderline defects.

LEVEL OF EVIDENCE

Level III.

Correlation of the Histological ICRS II Score and the 3D MOCART Score for the Analysis of Aged Osteochondral Regenerates in a Large Animal Model

OBJECTIVE

Reliable outcome measures are essential to predict the success of cartilage repair techniques. Histology is probably the gold standard, but magnetic resonance imaging (MRI) has the potential to decrease the need for invasive histological biopsies. The 3D magnetic resonance observation of cartilage repair tissue (MOCART) score is a reliable yet elaborate tool. Moreover, literature is controversial concerning the correlation of histology and MRI.

DESIGN

To test the applicability of the International Cartilage Regeneration and Joint Preservation Society (ICRS) II and MOCART 3D score for the evaluation of aged osteochondral regenerates in a large animal model, and to identify correlating histological and MRI parameters. Osteochondral defects in medial femoral condyles of n = 12 adult sheep were reconstructed with biodegradable bilayer implants. About 19.5 months postoperation, n = 10 joints were analyzed with MRI (3D MOCART score). Histological samples were analyzed using the ICRS II score; both pre- and post-training. The intraclass correlation coefficient, the inter-rater reliability, and the 95% confidence interval were calculated. Matching histological and MRI parameters were tested for correlation.

RESULTS

We found a statistically significant correlation of all histological parameters. MRI parameters reflecting "overall" assessments had very strong inter-rater correlations. Statistically significant strong correlations were found for the MRI parameters defect filling, cartilage interface, bone interface, and surface. For defect overall (MRI) and overall assessment (ICRS II), we found a significant yet mild correlation.

CONCLUSIONS

The ICRS II and the 3D MOCART score are applicable to aged osteochondral regenerates. Prior training on the scoring systems is essential. Select MRI and histological parameters correlate; however, the only statistically significant correlation was found for overall assessment.

Axial alignment is a critical regulator of knee osteoarthritis

Although osteoarthritis (OA), a leading cause of disability, has been associated with joint malalignment, scientific translational evidence for this link is lacking. In a clinical case study, we provide evidence of osteochondral recovery upon unloading symptomatic isolated medial tibiofemoral knee OA associated with varus malalignment. By mapping response correlations at high resolution, we identify spatially complex degenerative changes in cartilage after overloading in a clinically relevant ovine model. We further report that unloading diminishes OA cartilage degeneration and alterations of critical parameters of the subchondral bone plate in a similar topographic fashion. Last, therapeutic unloading shifted the articular cartilage and subchondral bone phenotype to normal and restored several physiological correlations disturbed in neutral and varus OA, suggesting a protective effect on the integrity of the entire osteochondral unit. Collectively, these findings identify modifiable trajectories with considerable translational potential to reduce the burden of human OA.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Spatial organization of biochemical cues in 3D-printed scaffolds to guide osteochondral tissue engineering

Functional repair of osteochondral (OC) tissue remains challenging because the transition from bone to cartilage presents gradients in biochemical and physical properties necessary for joint function. Osteochondral regeneration requires strategies that restore the spatial composition and organization found in the native tissue. Several biomaterial approaches have been developed to guide chondrogenic and osteogenic differentiation of human mesenchymal stem cells (hMSCs). These strategies can be combined with 3D printing, which has emerged as a useful tool to produce tunable, continuous scaffolds functionalized with bioactive cues. However, functionalization often includes one or more post-fabrication processing steps, which can lead to unwanted side effects and often produce biomaterials with homogeneously distributed chemistries. To address these challenges, surface functionalization can be achieved in a single step by solvent-cast 3D printing peptide-functionalized polymers. Peptide-poly(caprolactone) (PCL) conjugates were synthesized bearing hyaluronic acid (HA)-binding (HAbind-PCL) or mineralizing (E3-PCL) peptides, which have been shown to promote hMSC chondrogenesis or osteogenesis, respectively. This 3D printing strategy enables unprecedented control of surface peptide presentation and spatial organization within a continuous construct. Scaffolds presenting both cartilage-promoting and bone-promoting peptides had a synergistic effect that enhanced hMSC chondrogenic and osteogenic differentiation in the absence of differentiation factors compared to scaffolds without peptides or only one peptide. Furthermore, multi-peptide organization significantly influenced hMSC response. Scaffolds presenting HAbind and E3 peptides in discrete opposing zones promoted hMSC osteogenic behavior. In contrast, presenting both peptides homogeneously throughout the scaffolds drove hMSC differentiation towards a mixed population of articular and hypertrophic chondrocytes. These significant results indicated that hMSC behavior was driven by dual-peptide presentation and organization. The downstream potential of this platform is the ability to fabricate biomaterials with spatially controlled biochemical cues to guide functional tissue regeneration without the need for differentiation factors.

Resilience to height loss of articular cartilage of osteoarthritic stifle joints of old pigs, compared with healthy cartilage from young pigs in a tribological pin-on-plate exposure, revealing similar friction forces

Introduction

We saw a lack of data on the biomechanical behavior of degenerated articular cartilage (OA) compared with that of healthy cartilage, even though the susceptibility to wear and tear of articular cartilage plays a key role in the progression of osteoarthritis (OA). Therefore, we performed a comparison between naturally occurring OA and healthy cartilage from pigs, before and after tribological stress.

Aim

The aim of the study was to compare OA-cartilage with healthy cartilage and to analyze the resilience to tribological shear stress, which will be measured as height loss (HL), and to friction forces of the cartilage layers. The findings will be substantiated in macro- and microscopical evaluations before and after tribological exposure.

Methods

We assessed stifle joints of fifteen old and sixteen young pigs from the local abattoir radiologically, macroscopically and histologically to determine possible OA alterations. We put pins from the femoral part of the joints and plates from the corresponding tibial plateaus in a pin-on-plate tribometer under stress for about two hours with about 1108 reciprocating cycles under a pressure of approximately 1 MPa. As a surrogate criterion of wear and tear, the HL was recorded in the tribometer. The heights of the cartilage layers measured before and after the tribological exposure were compared histologically. The condition of the cartilage before and after the tribological exposure was analyzed both macroscopically with an adapted ICRS score and microscopically according to Little et al. (2010). We assessed the friction forces acting between the surfaces of the cartilage pair–specimens.

Results

Articular cartilage taken from old pigs showed significant degenerative changes compared to that taken from the young animals. The macroscopic and microscopic scores showed strong alterations of the cartilage after the tribological exposure. There was a noticeable HL of the cartilage specimens after the first 100 to 300 cycles. The HL after tribological exposure was lower in the group of the old animals with 0.52 mm ± 0.23 mm than in the group of the young animals with 0.86 mm ± 0.26 mm (p < 0.0001). The data for the HL was validated by the histological height measurements with 0.50 mm ± 0.82 mm for the old and 0.79 mm ±0.53 mm for the young animals (p = 0.133). The friction forces measured at the cartilage of the old animals were 2.25 N ± 1.15 N and 1.89 N ± 1.45 N of the young animals (p = 0.3225).

Conclusion

Unlike articular cartilage from young pigs, articular cartilage from old pigs showed OA alterations. Tribological shear stress exposure revealed that OA cartilage showed less HL than healthy articular cartilage. Tribological stress exposure in a pin–on–plate tribometer seemed to be an appropriate way to analyze the mechanical stability of articular cartilage, and the applied protocol could reveal weaknesses of the assessed cartilage tissue. Friction and HL seemed to be independent parameters when degenerated and healthy articular cartilage were assessed under tribological exposure in a pin–on- plate tribometer.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part II: Small animals

BACKGROUND

Small animal models are critical to model the complex disease mechanisms affecting a functional joint leading to articular cartilage disorders. They are advantageous for several reasons and significantly contributed to the understanding of the mechanisms of cartilage diseases among which osteoarthritis.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major small animal species, including mice, rats, guinea pigs, and rabbits compared with humans. Specific characteristics of each species, including kinematical gait parameters are provided and compared with the human situation. When placed in a proper context respecting their challenges and limitations, small animal models are important and appropriate models for articular cartilage disorders.

Topographic modeling of early human osteoarthritis in sheep

Articular cartilage damage occurring during early osteoarthritis (OA) is a key event marking the development of the disease. Here, we modeled early human OA by gathering detailed spatiotemporal data from surgically induced knee OA development in sheep. We identified a specific topographical pattern of osteochondral changes instructed by a defined meniscal injury, showing that both cartilage and subchondral bone degeneration are initiated from the region adjacent to the damage. Alterations of the subarticular spongiosa arising locally and progressing globally disturbed the correlations of cartilage with subchondral bone seen at homeostasis and were indicative of disease progression. We validated our quantitative findings against human OA, showing a similar pattern of early OA correlating with regions of meniscal loss and an analogous late critical disturbance within the entire osteochondral unit. This translational model system can be used to elucidate mechanisms of OA development and provides a roadmap for investigating regenerative therapies.

Small-Diameter Subchondral Drilling Improves DNA and Proteoglycan Content of the Cartilaginous Repair Tissue in a Large Animal Model of a Full-Thickness Chondral Defect

This study quantified changes in the DNA content and extracellular matrix composition of both the cartilaginous repair tissue and the adjacent cartilage in a large animal model of a chondral defect treated by subchondral drilling. Content of DNA, proteoglycans, and Type II and Type I collagen, as well as their different ratios were assessed at 6 months in vivo after treatment of full-thickness cartilage defects in the femoral trochlea of adult sheep with six subchondral drill holes, each of either 1.0 mm or 1.8 mm in diameter by biochemical analyses of the repair tissue and the adjacent cartilage and compared with the original cartilage. Only subchondral drilling which were 1.0 mm in diameter significantly increased both DNA and proteoglycan content of the repair tissue compared to the original cartilage. DNA content correlated with the proteoglycan and Type II collagen content within the repair tissue. Significantly higher amounts of Type I collagen within the repair tissue and significantly increased DNA, proteoglycan, and Type I collagen content in the adjacent cartilage were identified. These translational data support the use of small-diameter bone-cutting devices for marrow stimulation. Signs of early degeneration were present within the cartilaginous repair tissue and the adjacent cartilage.

T1ρ, T2 mapping, and EPIC-µCT Imaging in a Canine Model of Knee Osteochondral Injury

The dog is the most commonly used large animal model for the study of osteoarthritis. Optimizing methods for assessing cartilage health would prove useful in reducing the number of dogs needed for a valid study of osteoarthritis and cartilage repair. Twelve beagles had critical-sized osteochondral defects created in the medial femoral condyle of both knees. Eight dogs had T1ρ and T2 magnetic resonance imaging (MRI) performed approximately 6 months after defect creation. Following MRI evaluations, all 12 dogs were humanely euthanatized and cartilage samples were obtained from the medial and lateral femoral condyles, medial and lateral tibial plateaus, trochlear groove, and patella for proteoglycan and collagen quantification. Equilibrium partitioning of an ionic contrast (EPIC)-µCT was then performed followed by the histologic assessment of the knees. Correlations between T1ρ, T2, EPIC-µCT and proteoglycan, collagen, and histology scores were assessed using a multivariate analysis accounting for correlations from samples within the same knee and in the same dog. Pearson's correlation coefficients were calculated to assess the strength of significant relationships. Correlations between µCT values and biochemical or histologic assessment were weak to moderately strong (0.09-0.41; p < 0.0001-0.66). There was a weak correlation between the T2 values and cartilage proteoglycan (-0.32; p = 0.04). The correlation between T1ρ values and cartilage proteoglycan were moderately strong (-0.38; p < 0.05) while the strongest correlation was between the T1ρ values and histological assessment of cartilage with a correlation coefficient of 0.58 (p < 0.0001). These data suggest that T1ρ shows promise for possible utility in the translational study of cartilage health and warrants further development in this species. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:368-377, 2020.

Thermosensitive Hydrogel Based on PEO-PPO-PEO Poloxamers for a Controlled In Situ Release of Recombinant Adeno-Associated Viral Vectors for Effective Gene Therapy of Cartilage Defects

Advanced biomaterial-guided delivery of gene vectors is an emerging and highly attractive therapeutic solution for targeted articular cartilage repair, allowing for a controlled and minimally invasive delivery of gene vectors in a spatiotemporally precise manner, reducing intra-articular vector spread and possible loss of the therapeutic gene product. As far as it is known, the very first successful in vivo application of such a biomaterial-guided delivery of a potent gene vector in an orthotopic large animal model of cartilage damage is reported here. In detail, an injectable and thermosensitive hydrogel based on poly(ethylene oxide) (PEO)-poly(propylene oxide) (PPO)-PEO poloxamers, capable of controlled release of a therapeutic recombinant adeno-associated virus (rAAV) vector overexpressing the chondrogenic sox9 transcription factor in full-thickness chondral defects, is applied in a clinically relevant minipig model in vivo. These comprehensive analyses of the entire osteochondral unit with multiple standardized evaluation methods indicate that rAAV-FLAG-hsox9/PEO-PPO-PEO hydrogel-augmented microfracture significantly improves cartilage repair with a collagen fiber orientation more similar to the normal cartilage and protects the subchondral bone plate from early bone loss.

Bone block augmentation from the iliac crest for treatment of deep osteochondral defects of the knee resembles biomechanical properties of the subchondral bone

PURPOSE

Bone block augmentation from the iliac crest can be used for reconstruction of the osteochondral unit to restore the underlying subchondral bone upon restoration of the cartilaginous layer via matrix-induced chondrocyte transplantation. To critically understand the successful restoration of the defect, biomechanical and histological analysis of the implanted bone blocks is required. The aim of the study was to analyse the ability of the bone block technique to restore huge bone defects by mimicking the physiological subchondral zone.

METHODS

The experiments were performed using lateral femoral condyles and iliac crest bone grafts from the same cadavers (n = 6) preserved using the Thiel method. CT scans were made to evaluate bone pathology. Bone mineral density of all specimens was evaluated in the femoral head prior to testing. A series of tests were conducted for each pair of specimens. A static compression test was performed using an electro dynamic testing machine with maximal strength and failure behavior analyzed. Biomechanical tests were performed in the medial-lateral direction for iliac crest and for femoral condyles with and without removal of the cartilage layer. Histological analysis was performed on decalcified specimens for comparison of the condyle at lesion site and the graft.

RESULTS

No significant difference in failure load could be found for iliac crest (53.3-180.5 N) and femoral condyle samples upon cartilage removal (38.5-175.1 N) (n.s.). The femoral condyles with an intact cartilage layer showed significantly higher loads (118.3-260.4N) compared to the other groups indicating that native or regenerated cartilage can further increase the failure load (p < 0.05). Bone mineral density significantly influenced failure load in all study groups (p < 0.05). Histological similarity of the cancellous bone in the femoral condyle and in the iliac crest was observed. However, within the subchondral zone, there was a higher density of sponge like organized trabeculae in the bone samples from the iliac crest. Tide mark was only detected at the osteochondral interface in femoral condyles.

CONCLUSION

This study demonstrated that, bone blocks derived from the iliac crest allow a biomechanical appropriate and stable restoration of huge bony defects by resembling the subchondral zone of the femoral condyle. Therefore, bone augmentation from the iliac crest combined with matrix-induced autologous chondrocyte transplantation seems to be a reasonable method to treat these challenging injuries.

Effects of TGF-β Overexpression via rAAV Gene Transfer on the Early Repair Processes in an Osteochondral Defect Model in Minipigs

BACKGROUND

Application of the chondrogenic transforming growth factor beta (TGF-β) is an attractive approach to enhance the intrinsic biological activities in damaged articular cartilage, especially when using direct gene transfer strategies based on the clinically relevant recombinant adeno-associated viral (rAAV) vectors.

PURPOSE

To evaluate the ability of an rAAV-TGF-β construct to modulate the early repair processes in sites of focal cartilage injury in minipigs in vivo relative to control (reporter lacZ gene) vector treatment.

STUDY DESIGN

Controlled laboratory study.

METHODS

Direct administration of the candidate rAAV-human TGF-β (hTGF-β) vector was performed in osteochondral defects created in the knee joint of adult minipigs for macroscopic, histological, immunohistochemical, histomorphometric, and micro-computed tomography analyses after 4 weeks relative to control (rAAV- lacZ) gene transfer.

RESULTS

Successful overexpression of TGF-β via rAAV at this time point and in the conditions applied here triggered the cellular and metabolic activities within the lesions relative to lacZ gene transfer but, at the same time, led to a noticeable production of type I and X collagen without further buildup on the subchondral bone.

CONCLUSION

Gene therapy via direct, local rAAV-hTGF-β injection stimulates the early reparative activities in focal cartilage lesions in vivo.

CLINICAL RELEVANCE

Local delivery of therapeutic (TGF-β) rAAV vectors in focal defects may provide new, off-the-shelf treatments for cartilage repair in patients in the near future.

Three-dimensional visualization and pathologic characteristics of cartilage and subchondral bone changes in the lumbar facet joint of an ovariectomized mouse model

BACKGROUND CONTEXT

Low back pain (LBP) is more prevalent among postmenopausal women than men. Ovariectomy (OVX) is an established animal model that mimics the estrogen deficiency of postmenopausal women. Little is known about the three-dimensional (3D) morphologic properties of cartilage and subchondral bone changes in the lumbar facet joint (LFJ) of an OVX mouse model.

PURPOSE

The purpose of this study was to characterize the 3D morphologic change of cartilage and subchondral bone in the LFJ of an OVX mouse model.

STUDY DESIGN

Three-dimensional visualization and a histologic study on degenerative changes in cartilage and subchondral bone in the LFJ of an OVX mouse model were conducted.

MATERIALS AND METHODS

Ovariectomy is performed to mimic postmenopausal changes in adult female mice. We present an imaging tool for 3D visualization of the pathologic characteristics of cartilage and subchondral bone changes LFJ degradation using propagation-based phase-contrast computed tomography (PPCT). The samples were further dissected, fixed, and stained for histologic examination.

RESULTS

Propagation-based phase-contrast computed tomography imaging provides a 3D visualization of altered cartilage with a simultaneous high detail of the subchondral bone abnormalities in an OVX LFJ model. A quantitative analysis demonstrated that the cartilage volume, the surface area, and thickness were decreased in the OVX group compared with the control group (p<.05). Meanwhile, these decreases were accompanied by an obvious destruction of the subchondral bone surface and a loss of trabecular bone in the OVX group (p<.05). The delineation of the 3D pathologic changes in the PPCT imaging was confirmed by a histopathologic method with Safranin-O staining. Tartrate-resistant acid phosphatase staining revealed an increased number of osteoclasts in the subchondral bone of the OVX mice compared with that of the control group.

CONCLUSIONS

These results demonstrated that a mouse model of OVX-induced LFJ osteoarthritis (OA)-like changes was successfully established and showed a good resemblance to the human OA pathology. Propagation-based phase-contrast computed tomography has great potential to becomea powerful 3D imaging method to comprehensively characterize LFJ OA and to effectively monitor therapeutics. Moreover, degenerative LFJ possesses a severe morphologic change in the subchondral bone, may be the source of postmenopausal LBP, and has the potential to be a novel therapeutic target for LBP treatment.

Stem Cells for Cartilage Repair: Preclinical Studies and Insights in Translational Animal Models and Outcome Measures

Due to the restricted intrinsic capacity of resident chondrocytes to regenerate the lost cartilage postinjury, stem cell-based therapies have been proposed as a novel therapeutic approach for cartilage repair. Moreover, stem cell-based therapies using mesenchymal stem cells (MSCs) or induced pluripotent stem cells (iPSCs) have been used successfully in preclinical and clinical settings. Despite these promising reports, the exact mechanisms underlying stem cell-mediated cartilage repair remain uncertain. Stem cells can contribute to cartilage repair via chondrogenic differentiation, via immunomodulation, or by the production of paracrine factors and extracellular vesicles. But before novel cell-based therapies for cartilage repair can be introduced into the clinic, rigorous testing in preclinical animal models is required. Preclinical models used in regenerative cartilage studies include murine, lapine, caprine, ovine, porcine, canine, and equine models, each associated with its specific advantages and limitations. This review presents a summary of recent in vitro data and from in vivo preclinical studies justifying the use of MSCs and iPSCs in cartilage tissue engineering. Moreover, the advantages and disadvantages of utilizing small and large animals will be discussed, while also describing suitable outcome measures for evaluating cartilage repair.

Reliable landmarks for precise topographical analyses of pathological structural changes of the ovine tibial plateau in 2-D and 3-D subspaces

Selecting identical topographical locations to analyse pathological structural changes of the osteochondral unit in translational models remains difficult. The specific aim of the study was to provide objectively defined reference points on the ovine tibial plateau based on 2-D sections of micro-CT images useful for reproducible sample harvesting and as standardized landmarks for landmark-based 3-D image registration. We propose 5 reference points, 11 reference lines and 12 subregions that are detectable macroscopically and on 2-D micro-CT sections. Their value was confirmed applying landmark-based rigid and affine 3-D registration methods. Intra- and interobserver comparison showed high reliabilities, and constant positions (standard errors < 1%). Spatial patterns of the thicknesses of the articular cartilage and subchondral bone plate were revealed by measurements in 96 individual points of the tibial plateau. As a case study, pathological phenomena 6 months following OA induction in vivo such as osteophytes and areas of OA development were mapped to the individual subregions. These new reference points and subregions are directly identifiable on tibial plateau specimens or macroscopic images, enabling a precise topographical location of pathological structural changes of the osteochondral unit in both 2-D and 3-D subspaces in a region-appropriate fashion relevant for translational investigations.

WITHDRAWN: 3D visualization and pathological characteristics of cartilage and subchondral bone changes in the lumbar facet joint of an Ovariectomized mouse model

The Publisher regrets that this article is an accidental duplication of an article that has already been published, http://dx.doi.org/10.1016/j.spinee.2017.11.009. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal.

Macroscopic cartilage repair scoring of defect fill, integration and total points correlate with corresponding items in histological scoring systems - a study in adult sheep

OBJECTIVE

To correlate osteochondral repair assessed by validated macroscopic scoring systems with established semiquantitative histological analyses in an ovine model and to test the hypothesis that important macroscopic individual categories correlate with their corresponding histological counterparts.

METHODS

In the weight-bearing portion of medial femoral condyles (n = 38) of 19 female adult Merino sheep (age 2-4 years; weight 70 ± 20 kg) full-thickness chondral defects were created (size 4 × 8 mm; International Cartilage Repair Society (ICRS) grade 3C) and treated with Pridie drilling. After sacrifice, 1520 blinded macroscopic observations from three observers at 2-3 time points including five different macroscopic scoring systems demonstrating all grades of cartilage repair where correlated with corresponding categories from 418 blinded histological sections.

RESULTS

Categories "defect fill" and "total points" of different macroscopic scoring systems correlated well with their histological counterparts from the Wakitani and Sellers scores (all P ≤ 0.001). "Integration" was assessed in both histological scoring systems and in the macroscopic ICRS, Oswestry and Jung scores. Here, a significant relationship always existed (0.020 ≤ P ≤ 0.049), except for Wakitani and Oswestry (P = 0.054). No relationship was observed for the "surface" between histology and macroscopy (all P > 0.05).

CONCLUSIONS

Major individual morphological categories "defect fill" and "integration", and "total points" of macroscopic scoring systems correlate with their corresponding categories in elementary and complex histological scoring systems. Thus, macroscopy allows to precisely predict key histological aspects of articular cartilage repair, underlining the specific value of macroscopic scoring for examining cartilage repair.

Early loss of subchondral bone following microfracture is counteracted by bone marrow aspirate in a translational model of osteochondral repair

Microfracture of cartilage defects may induce alterations of the subchondral bone in the mid- and long-term, yet very little is known about their onset. Possibly, these changes may be avoided by an enhanced microfracture technique with additional application of bone marrow aspirate. In this study, full-thickness chondral defects in the knee joints of minipigs were either treated with (1) debridement down to the subchondral bone plate alone, (2) debridement with microfracture, or (3) microfracture with additional application of bone marrow aspirate. At 4 weeks after microfracture, the loss of subchondral bone below the defects largely exceeded the original microfracture holes. Of note, a significant increase of osteoclast density was identified in defects treated with microfracture alone compared with debridement only. Both changes were significantly counteracted by the adjunct treatment with bone marrow. Debridement and microfracture without or with bone marrow were equivalent regarding the early cartilage repair. These data suggest that microfracture induced a substantial early resorption of the subchondral bone and also highlight the potential value of bone marrow aspirate as an adjunct to counteract these alterations. Clinical studies are warranted to further elucidate early events of osteochondral repair and the effect of enhanced microfracture techniques.

Osteoarthritis in the Knee Joints of Göttingen Minipigs after Resection of the Anterior Cruciate Ligament? Missing Correlation of MRI, Gene and Protein Expression with Histological Scoring

Introduction

The Göttingen Minipig (GM) is used as large animal model in articular cartilage research. The aim of the study was to introduce osteoarthritis (OA) in the GM by resecting the anterior cruciate ligament (ACLR) according to Pond and Nuki, verified by histological and magnetic resonance imaging (MRI) scoring as well as analysis of gene and protein expression.

Materials and Methods

The eight included skeletally mature female GM were assessed after ACLR in the left and a sham operation in the right knee, which served as control. 26 weeks after surgery the knee joints were scanned using a 3-Tesla high-field MR tomography unit with a 3 T CP Large Flex Coil. Standard proton-density weighted fat saturated sequences in coronal and sagittal direction with a slice thickness of 3 mm were used. The MRI scans were assessed by two radiologists according to a modified WORMS-score, the X-rays of the knee joints by two evaluators. Osteochondral plugs with a diameter of 4mm were taken for histological examination from either the main loading zone or the macroscopic most degenerated parts of the tibia plateau or condyle respectively. The histological sections were blinded and scored by three experts according to Little et al. Gene expression analysis was performed from surrounding cartilage. Expression of adamts4, adamts5, acan, col1A1, col2, il-1ß, mmp1, mmp3, mmp13, vegf was determined by qRT-PCR. Immunohistochemical staining (IH) of Col I and II was performed. IH was scored using a 4 point grading (0—no staining; 3-intense staining).

Results and Discussion

Similar signs of OA were evident both in ACLR and sham operated knee joints with the histological scoring result of the ACLR joints with 6.48 ± 5.67 points and the sham joints with 6.86 ± 5.84 points (p = 0.7953) The MRI scoring yielded 0.34 ± 0.89 points for the ACLR and 0.03 ± 0.17 for the sham knee joints. There was no correlation between the histological and MRI scores (r = 0.10021). The gene expression profiles as well as the immunohistochemical findings showed no significant differences between ACLR and sham knee joints. In conclusion, both knee joints showed histological signs of OA after 26 weeks irrespective of whether the ACL was resected or not. As MRI results did not match the histological findings, MRI was obviously unsuitable to diagnose the OA in GM. The analysis of the expression patterns of the 10 genes could not shed light on the question, whether sham operation also induced cartilage erosion or if the degeneration was spontaneous. The modified Pond-Nuki model may be used with reservation in the adult minipig to induce an isolated osteoarthritis.