Sven Nebelung

Simultaneous anabolic and catabolic responses of human chondrocytes seeded in collagen hydrogels to long-term continuous dynamic compression.

Cartilage repair strategies increasingly focus on the in vitro development of cartilaginous tissues that mimic the biological and mechanical properties of native articular cartilage. However, current approaches still face problems in the reproducible and standardized generation of cartilaginous tissues that are both biomechanically adequate for joint integration and biochemically rich in extracellular matrix constituents. In this regard, the present study investigated whether long-term continuous compressive loading would enhance the mechanical and biological properties of such tissues. Human chondrocytes were harvested from 8 knee joints (n=8) of patients having undergone total knee replacement and seeded into a collagen type I hydrogel at low density of 2×10(5)cells/ml gel. Cell-seeded hydrogels were cut to disks and subjected to mechanical stimulation for 28 days with 10% continuous cyclic compressive loading at a frequency of 0.3 Hz. Histological and histomorphometric evaluation revealed long-term mechanical stimulation to significantly increase collagen type II and proteoglycan staining homogenously throughout the samples as compared to unstimulated controls. Gene expression analyses revealed a significant increase in collagen type II, collagen type I and MMP-13 gene expression under stimulation conditions, while aggrecan gene expression was decreased and no significant changes were observed in the collagen type II/collagen type I mRNA ratio. Mechanical propertywise, the average value of elastic stiffness increased in the stimulated samples. In conclusion, long-term mechanical preconditioning of human chondrocytes seeded in collagen type I hydrogels considerably improves biological and biomechanical properties of the constructs, corroborating the clinical potential of mechanical stimulation in matrix-associated autologous chondrocyte transplantation (MACT) procedures.

Abbreviated Biparametric Prostate MR Imaging in Men with Elevated Prostate-specific Antigen

Purpose To determine the diagnostic accuracy for clinically significant prostate cancer achieved with abbreviated biparametric prostate magnetic resonance (MR) imaging in comparison with full multiparametric contrast material-enhanced prostate MR imaging in men with elevated prostate-specific antigen (PSA) and negative transrectal ultrasonography (US)-guided biopsy findings; to determine the significant cancer detection rate of biparametric versus full multiparametric contrast-enhanced MR imaging and between-reader agreement for interpretation of biparametric MR imaging. Materials and Methods In this institutional review board-approved retrospective review of prospectively acquired data, men with PSA greater than or equal to 3 ng/mL after negative transrectal US-guided biopsy findings underwent state-of-the-art, full multiparametric contrast-enhanced MR imaging at 3.0-T including high-spatial-resolution structural imaging in several planes, diffusion-weighted imaging at 0, 800, 1000, and 1400 mm2/sec, and dynamic contrast-enhanced MR imaging, obtained without endorectal coil within 34 minutes 19 seconds. One of four radiologists with different levels of expertise (1-9 years) first reviewed only a fraction of the full multiparametric contrast-enhanced MR images, consisting of single-plane (axial) structural imaging (T2-weighted turbo spin-echo and diffusion-weighted imaging), acquired within 8 minutes 45 seconds (referred to as biparametric MR imaging), and established a diagnosis according to the Prostate Imaging Reporting and Data System (PI-RADS) version 2; only thereafter, the remaining full multiparametric contrast-enhanced MR images were read. Men with PI-RADS categories 3-5 underwent MR-guided targeted biopsy. Men with PI-RADS categories 1-2 remained in urologic follow-up for at least 2 years, with rebiopsy (transrectal US-guided or transperineal saturation) where appropriate. McNemar test was used to compare diagnostic accuracies. To investigate between-reader agreement, biparametric MR images of 100 patients were read independently by all three radiologists. Results A total of 542 men, aged 64.8 years ± 8.2 (median PSA, 7 ng/mL), were included. Biparametric MR imaging helped detect clinically significant prostate cancer in 138 men. Full multiparametric contrast-enhanced MR imaging allowed detection of one additional clinically significant prostate cancer (a stage pT2a, intermediate-risk cancer with a Gleason score of 3+4) and caused 11 additional false-positive diagnoses. Diagnostic accuracy for detection of clinically significant cancer of biparametric MR imaging (89.1%, 483 of 542) was similar to that of full multiparametric contrast-enhanced MR imaging (87.2%, 473 of 542). Between-reader agreement of biparametric MR imaging interpretation was substantial (κ = 0.81). Conclusion Biparametric MR imaging allows detection of clinically significant prostate cancer missed by transrectal US-guided biopsy. Biparametric prostate MR imaging takes less than 9 minutes examination time, works without contrast agent injection, and offers a diagnostic accuracy and cancer detection rate that are equivalent to those of conventional full multiparametric contrast-enhanced MR imaging protocols.

Morphometric Grading of Osteoarthritis by Optical Coherence Tomography — An Ex Vivo Study

Optical Coherence Tomography (OCT) yields microscopic cross‐sectional images of cartilage in real time and at high resolution. As yet, comprehensive grading of degenerative cartilage changes based on OCT has rarely been performed. This study investigated the potential of quantitative OCT using algorithm‐based image parameters such as irregularity (OII – Optical Irregularity Index), homogeneity (OHI – Optical Homogeneity Index) and attenuation (OAI – Optical Attenuation Index) in the objective grading of cartilage degeneration. Therefore, OCT was used to image and assess 113 human osteochondral samples obtained from total knee replacements. Processing included the analysis of OII (by calculation of the standard deviation with regards to a fitted surface), of OHI (by edge detection of tissue signal changes) and of OAI (by analysis of relative imaging depth). Additionally, samples were subject to macroscopic (Outerbridge grading), biomechanical (elastic stiffness), qualitative OCT and histological evaluation (Modified Mankin grading). Significant correlations were found between all outcome measures. OII and OHI were effective in assessing cartilage surface, integrity and homogeneity, while OAI could discriminate between unmineralized and mineralized cartilage, respectively. Therefore, quantitative OCT holds potential as a diagnostic tool for more reliable, standardized and objective assessment of cartilage tissue properties.

Three-dimensional imaging and analysis of human cartilage degeneration using Optical Coherence Tomography

Optical Coherence Tomography (OCT) is an evolving imaging technology allowing non‐destructive imaging of cartilage tissue at near‐histological resolution. This study investigated the diagnostic value of real time 3‐D OCT in comparison to conventional 2‐D OCT in the comprehensive grading of human cartilage degeneration. Fifty‐three human osteochondral samples were obtained from eight total knee arthroplasties. OCT imaging was performed by either obtaining a single two‐dimensional cross‐sectional image (2‐D OCT) or by collecting 100 consecutive parallel 2‐D OCT images to generate a volumetric data set of 8 × 8 mm (3‐D OCT). OCT images were assessed qualitatively according to a modified version of the DJD classification and quantitatively by algorithm‐based evaluation of surface irregularity, tissue homogeneity, and signal attenuation. Samples were graded according to the Outerbridge classification and statistically analyzed by one‐way ANOVA, Kruskal Wallis and Tukeys or Dunns post‐hoc tests. Overall, the generation of 3‐D volumetric datasets and their multiple reconstructions such as rendering, surface topography, parametric, and cross‐sectional views proved to be of potential diagnostic value. With increasing distance to the mid‐sagittal plane and increasing degeneration, score deviations increased, too. In conclusion, 3‐D imaging of cartilage with image analysis algorithms adds considerable potential diagnostic value to conventional OCT diagnostics.

Bioreactor cultivation and remodelling simulation for cartilage replacement material

For the development of articular cartilage replacement material, it is essential to study the dependence between mechanical stimulation and cell activity in cellular specimens. Bioreactor cultivation is widely used for this purpose, however, it is hardly possible to obtain a quantitative relationship between collagen type II production and applied loading history. For this reason, a bioreactor system is developed, measuring applied forces and number of loading cycles by means of a load cell and a forked light barrier, respectively. Parallel to the experimental study, a numerical model by means of the finite element method is proposed to simulate the evolution of material properties during cyclic stimulation. In this way, a numerical model can be developed for arbitrary deformation cases.

Functional MR Imaging Mapping of Human Articular Cartilage Response to Loading

Purpose To determine if multiparametric magnetic resonance (MR) imaging mapping can be used to quantify the response to loading of histologically intact human knee cartilage. Materials and Methods Institutional review board approval and written informed consent were obtained. Twenty macroscopically intact cartilage-bone samples were obtained from the central lateral femoral condyles in 11 patients undergoing total knee replacement. A clinical 3.0-T MR imaging system was used to generate T1, T1ρ, T2, and T2* maps with inversion recovery, spin-lock multiple gradient-echo, multiple spin-echo, and multiple gradient-echo sequences. Serial mapping was performed at three defined strain levels (strain 0 [δ0], 0%; strain 1 [δ1/2], 19.8% ± 4.6 [standard deviation]; strain 2 [δ1], 39.5% ± 9.3) by using displacement-controlled static indentation loading. The entire sample and specific cartilage zones (superficial zone [SZ], transitional zone [TZ], and deep zone [DZ]) and regions (subpistonal area [SPA] and peripistonal area [PPA]) were defined as regions of interest. Upon log transformation, repeated measures analysis of variance was used to detect groupwise regional and zonal differences. Load-induced relative changes were determined and analyzed by using paired Student t test and Spearman correlation. Biomechanical testing (unconfined compression) and histologic assessment (Mankin score) served as the reference standard. Results All samples were histologically intact. Strain-related decreases were found at the SZ and TZ for T1 and T2*; for T1ρ, increases were seen in all zones; and for T2, increases were seen at the SZ and PPA only. Significant parameter changes in the entire sample depth of SPA versus PPA were found for δ1/2 (T1ρ, 14% ± 12 vs 6% ± 9) and δ1 (T1, -4% ± 5 vs -1% ± 3; T1ρ, 13% ± 12 vs 7% ± 7; T2*, -9% ± 12 vs -2% ± 8). SPA versus PPA changes were significant at the SZ and TZ (T1), TZ and DZ (T1ρ), and SZ (T2*). No significant correlations were found between relative changes and biomechanical or histologic parameters. Conclusion Serial multiparametric MR imaging mapping can be used to evaluate cartilage beyond mere static analysis and may provide the basis for more refined graduation strategies of cartilage degeneration.

Continuous cyclic compressive loading modulates biological and mechanical properties of collagen hydrogels seeded with human chondrocytes.

PURPOSE This study investigated the potential of cyclic compressive loading in the generation of in vitro engineered cartilaginous tissue with the aim of contributing to a better understanding of mechanical preconditioning and its possible role in further optimizing existing matrix-associated cartilage replacement procedures. METHODS Human chondrocytes were harvested from 12 osteoarthritic knee joints and seeded into a type I collagen (col-I) hydrogel at low density (2 × 10(5) cells/ml gel). The cell-seeded hydrogel was condensed and cultivated under continuous cyclic compressive loading (frequency: 0.3 Hz; strain: 10%) for 14 days under standardized conditions. After retrieval, specimens were subject to staining, histomorphometric evaluation, gene expression analysis and biomechanical testing. RESULTS Cellular morphology was altered by both stimulation and control conditions as was staining for collagen II (col-II). Gene expression measurements revealed a significant increase for col-II under either cultivation condition. No significant differences in col-I, aggrecan and MMP-13 gene expression profiles were found. The col-II/col-I mRNA ratio significantly increased under stimulation, whereas the biomechanical properties deteriorated under either cultivation method. CONCLUSIONS Although the effects observed are small, mechanical preconditioning has demonstrated its potential to modulate biological properties of collagen hydrogels seeded with human chondrocytes.

A simplified arthroscopic bone graft transfer technique in chronic glenoid bone deficiency

AbstractIn severe shoulder instability, chronic glenoid bone deficiency is a challenge for arthroscopic shoulder surgeons. This paper presents a new all-arthroscopic technique of iliac crest bone graft transfer for those patients. Transportation through the rotator interval and repositioning into the glenoid defect is achieved by use of a tracking suture, while fixation of the graft is performed by biodegradable or titanium double-helix screws. Overall, the feasibility and reproducibility of this new reconstruction technique in recreating the bony and soft tissue anatomy of the antero-inferior glenoid could be demonstrated. So far, preliminary outcomes of 24 patients operated on using this technique are promising. Level of evidence Case series with no comparison group, Level IV.

Towards Optical Coherence Tomography-based elastographic evaluation of human cartilage.

Optical Coherence Tomography (OCT) is an imaging technique that allows the surface and subsurface evaluation of semitransparent tissues by generating microscopic cross-sectional images in real time, to millimetre depths and at micrometre resolutions. As the differentiation of cartilage degeneration remains diagnostically challenging to standard imaging modalities, an OCT- and MRI-compatible indentation device for the assessment of cartilage functional properties was developed and validated in the present study. After describing the system design and performing its comprehensive validation, macroscopically intact human cartilage samples (n=5) were indented under control of displacement (δ1=202µm; δ2=405µm; δ3=607µm; δ4=810µm) and simultaneous OCT imaging through a transparent indenter piston in direct contact with the sample; thus, 3-D OCT datasets from surface and subsurface areas were obtained. OCT-based evaluation of loading-induced changes included qualitative assessment of image morphology and signal characteristics. For inter-method cross referencing, the device׳s compatibility with MRI as well as qualitative morphology changes under analogous indentation loading conditions were evaluated by a series of T2 weighted gradient echo sequences. Cartilage thickness measurements were performed using the needle-probe technique prior to OCT and MRI imaging, and subsequently referenced to sample thickness as determined by MRI and histology. Dynamic indentation testing was performed to determine Young׳s modulus for biomechanical reference purposes. Distinct differences in sample thickness as well as corresponding strains were found; however, no significant differences in cartilage thickness were found between the used techniques. Qualitative assessment of OCT and MRI images revealed either distinct or absent sample-specific patterns of morphological changes in relation to indentation loading. For OCT, the tissue area underneath the indenter piston could be qualitatively assessed and displayed in multiple reconstructions, while for MRI, T2 signal characteristics indicated the presence of water and related tissue pressurisation within the sample. In conclusion, the present indentation device has been developed, constructed and validated for qualitative assessment of human cartilage and its response to loading by OCT and MRI. Thereby, it may provide the basis for future quantitative approaches that measure loading-induced deformations within the tissue to generate maps of local tissue properties as well as investigate their relation to degeneration.

Optical coherence tomography-based parameterization and quantification of articular cartilage surface integrity

Loss of articular cartilage surface integrity is considered the earliest sign of osteoarthritis; however, its reliable detection has not been established by clinical routine diagnostics. This study comprehensively assesses a set of 11 algorithm-based 2-D Optical Coherence Tomography roughness parameters and investigates their clinical impact. Histology and manual irregularity quantification of 105 human cartilage samples with variable degeneration served as reference. The majority of parameters revealed a close-to-linear correlation with the entire spectrum of degeneration. Surface integrity should therefore be assessed by a combination of parameters to improve current diagnostic accuracy in the determination of cartilage degeneration.