Analysis of rabbit articular cartilage repair after chondrocyte implantation using optical coherence tomography

Correlation of Arthroscopic Grading and Optical Coherence Tomography as Markers of Early Repair and Predictors of Later Healing Evident on MRI and Histomorphometric Assessment of Cartilage Defects Implanted with Chondrocytes Overexpressing IGF-I

OBJECTIVE

Injury of articular cartilage is common, and due to the poor intrinsic capabilities of chondrocytes, it can precipitate joint degradation and osteoarthritis (OA). Implantation of autologous chondrocytes into cartilaginous defects has been used to bolster repair. Accurate assessment of the quality of repair tissue remains challenging. This study aimed to investigate the utility of noninvasive imaging modalities, including arthroscopic grading and optical coherence tomography (OCT) for assessment of early cartilage repair (8 weeks), and MRI to determine long-term healing (8 months).

DESIGN

Large (15 mm diameter), full-thickness chondral defects were created on both lateral trochlear ridges of the femur in 24 horses. Defects were implanted with autologous chondrocytes transduced with rAAV5-IGF-I, autologous chondrocytes transduced with rAAV5-GFP, naïve autologous chondrocytes, or autologous fibrin. Healing was evaluated at 8 weeks post-implantation using arthroscopy and OCT, and at 8 months post-implantation using MRI, gross pathology, and histopathology.

RESULTS

OCT and arthroscopic scoring of short-term repair tissue were significantly correlated. Arthroscopy was also correlated with later gross pathology and histopathology of repair tissue at 8 months post-implantation, while OCT was not correlated. MRI was not correlated with any other assessment variable.

CONCLUSIONS

This study indicated that arthroscopic inspection and manual probing to develop an early repair score may be a better predictor of long-term cartilage repair quality following autologous chondrocyte implantation. Furthermore, qualitative MRI may not provide additional discriminatory information when assessing mature repair tissue, at least in this equine model of cartilage repair.

Noninvasive Optical Assessment of Implanted Tissue-Engineered Construct Success In Situ

Quantitative diffuse reflectance spectroscopy (DRS) was developed for label-free, noninvasive, and real-time assessment of implanted tissue-engineered devices manufactured from primary human oral keratinocytes (six batches in two 5-patient cohorts). Constructs were implanted in a murine model for 1 and 3 weeks. DRS evaluated construct success in situ using optical absorption (hemoglobin concentration and oxygenation, attributed to revascularization) and optical scattering (attributed to cellular density and layer thickness). Destructive pre- and postimplantation histology distinguished experimental control from stressed constructs, whereas noninvasive preimplantation measures of keratinocyte glucose consumption and residual glucose in spent culture media did not. In constructs implanted for 1 week, DRS distinguished control due to stressed and compromised from healthy constructs. In constructs implanted for 3 weeks, DRS identified constructs with higher postimplantation success. These results suggest that quantitative DRS is a promising, clinically compatible technology for rapid, noninvasive, and localized tissue assessment to characterize tissue-engineered construct success in vivo. Impact statement Despite the recent advance in tissue engineering and regenerative medicine, there is still a lack of nondestructive tools to longitudinally monitor the implanted tissue-engineered devices. In this study, we demonstrate the potential of quantitative diffuse reflectance spectroscopy as a clinically viable technique for noninvasive, label-free, and rapid characterization of graft success in situ.

Impact-induced cartilage damage assessed using polarisation-sensitive optical coherence tomography

Non-invasive determination of structural changes in articular cartilage immediately after impact and rehydration provides insight into the response and recovery of the soft tissue, as well as provides a potential methodology for clinicians to quantify early degenerative changes. In this study, we use polarisation-sensitive optical coherence tomography (PS-OCT) to examine subtle alterations of the optical properties in healthy and early-stage degenerate articular cartilage immediately after impact loading to identify structurally relevant metrics required for understanding the mechanical factors of osteoarthritic initiation and progression. A custom-designed impact testing rig was used to deliver 0.9 J and 1.4 J impact energies to bovine articular cartilage. A total of 52 (n=26 healthy, n=26 mildly degenerate) cartilage-on-bone samples were imaged before, immediately after, and 3 h after impact. PS-OCT images were analyzed to assess changes relating to surface irregularity, optical attenuation, and birefringence. Mildly degenerate cartilage exhibits a significant change in birefringence following 1.4 J impact energies compared to healthy samples which is believed to be attributable to degenerate cartilage being unable to fully utilise the fluid phase to distribute and dampen the energy. After rehydration, the polarisation-sensitive images appear to 'optically-recover' reducing the reliability of birefringence as an absolute metric. Surface irregularity and optical attenuation encode diagnostically relevant information and may serve as markers to predict the mechanical response of articular cartilage. PS-OCT with its ability to non-invasively image the sub-surface microstructural abnormalities of cartilage presents as an ideal modality for cartilage degeneration assessment and identification of mechanically vulnerable tissue.

Cartilage tissue engineering using injectable functionalized Demineralized Bone Matrix scaffold with glucosamine in PVA carrier, cultured in microbioreactor prior to study in rabbit model

Using 3D model of injectable scaffolds for cartilage tissue engineering is one of the challenges that should be addressed to avoid invasive surgery for treatment. For this purpose, chondrocytes on Demineralized Bone Matrix (DBM) scaffolds functionalized with glucosamine in 20% polyvinyl alcohol (PVA) as a carrier was applied to the micro-bioreactor in-vitro, then the study was continued on in-vivo stage. Scaffold biocompatibility tests were performed and the mechanical and physicochemical properties were studied showing the fact that DBM was functionalized by Glucosamine, scaffold degradation rate was 53% after 720 h and swelling ratio was 2.5 times after 16 h, injectable scaffold demonstrated better mechanical characteristics (P < 0.05) than other concentrations of PVA. Consequently, in-vitro tests, including live-dead imaging resulting in 99% viability after 14 days (P < 0.001), DAPI staining and scanning electron microscope imaging were performed to determine the number and viability of the cells on the scaffold, showing a cells proliferation property of this group compared with the control after 14 days (P < 0.0001), then relative gene expression was evaluated and protein expression was assessed. The overall chondrogenic gene expression improved (P < 0.05) compared to the control (2D culture). Subsequently, the scaffold were loaded with chondrocytes and injected into the cartilage lesion part After 24 weeks of surgery, MRI and immunocytochemistry were performed. Then all outputs proved that the scaffold plus cell group had a significantly higher topological score (P < 0.0001) than other groups compared to normal cartilage. Finally, studies have shown that transplantation of chondrocytes in DBM, polyvinyl alcohol and glucosamine scaffold through one surgical stage improves cartilage lesion and it can be considered as a breakthrough in tissue engineering.

Treatment of Full-Thickness Cartilage Defects with Pedunculated and Free Synovial Grafts: A Comparative Study in an Animal Model

AIMS AND OBJECTIVES

The purpose of this study was to compare the potential effects of pedunculated and free synovial grafts in the repair of full-thickness articular cartilage defects on an animal model with histological and immunohistochemical analysis.

MATERIALS AND METHODS

A comparative study in an animal model was performed with 24 rabbits, divided into two groups. Full-thickness cartilage defects were created bilaterally on the knees of all rabbits. Pedunculated and free synovial grafts were applied to the right knees of Group 1 and Group 2, respectively. Left knees were left as the control group. Six rabbits from each group were randomly selected for euthanasia 4 and 8 weeks postoperatively. All samples were examined histologically with a cartilage scoring system. For immunohistochemical analysis, the degree of collagen 2 staining was determined using a staging system. All data were statistically compared between the study groups with Student's t-test or Mann-Whitney U-test. The correlations between categorical variables were analyzed with Fisher's exact test and Chi-square test.

RESULTS

In Group 1, the mean defect size had significantly decreased at 8 weeks postsurgery. It was also significantly smaller than that of Group 2. Both pedunculated and free synovial grafts had significantly better histological and immunohistochemical outcomes compared with the controls. Contrastingly, the results of comparison between the study groups (Group 1 vs. 2) at the 4th and 8th week were not statistically significant with regard to histological scores and immunohistochemical staining.

CONCLUSION

Synovial tissue, whether pedunculated or free, provided much better cartilage recovery compared with the control. It can be used as a mesenchymal stem cell (MSC) source, and synovium-derived MSCs have the chondrogenic potential for the in vivo treatment of full-thickness cartilage defects.

Changes in viscoelastic properties of articular cartilage in early stage of osteoarthritis, as determined by optical coherence tomography-based strain rate tomography

BACKGROUND

Biomechanical changes in articular cartilage are associated with the onset of osteoarthritis. We developed an optical coherence tomography-based strain rate tomography method: stress relaxation optical coherence straingraphy (SR-OCSA). The purpose of this study was to establish an approach for measuring mechanical properties of articular cartilage using SR-OCSA, and to investigate the distribution of viscoelastic properties of articular cartilage in early osteoarthritis.

METHODS

Anterior cruciate ligament transection surgery was performed on the left knees of 8-9-month-old New Zealand white rabbits. SR-OCSA was used to visualize and measure the viscoelastic properties of articular cartilage via attenuation coefficient of strain rate (ACSR). Using the same conditions as in the SR-OCSA test, an indentation test was conducted, and relaxation time was measured to evaluate the relationship between ACSR and relaxation time.

RESULTS

SR-OCSA could nondestructively detect and visualize changes in the distribution of viscoelastic properties of articular cartilage in early osteoarthritis. SR-OCSA captured significant increases in ACSR in cartilage at 2 weeks after surgery, when a histologically slight osteoarthritis sign was present. As cartilage degeneration progressed, ACSR increased, whereas relaxation time decreased in a time-dependent manner. Moreover, ACSR negatively correlated with relaxation time. In particular, ACSR was elevated around the tidemark and the elevation tended to move as cartilage degeneration progressed.

CONCLUSIONS

SR-OCSA could tomographically and nondestructively detect and visualize changes in the distribution of viscoelastic properties of articular cartilage in early osteoarthritis. The mechanical properties around the tidemark were degraded as cartilage degeneration progressed. Thus, SR-OCSA provides important data needed to understand the biomechanics of early osteoarthritis.

Surgeon Ability to Appropriately Address the Calcified Cartilage Layer: An In Vitro Study of Arthroscopic and Open Techniques

BACKGROUND

Microfracture is a commonly utilized cartilage restoration technique for articular cartilage defects. While the removal of the calcified cartilage layer (CCL) has been shown to be critical with in vivo models, little is known with regard to surgeon reliability to adequately perform the technique.

PURPOSE

To evaluate surgeon reliability in removing the CCL utilizing open and arthroscopic techniques.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eleven cadaveric knees were utilized to create four 12-mm diameter defects in the anterior and posterior medial femoral condyles. Eleven fellowship-trained surgeons were asked to perform the following procedures: remove the CCL open, retain the CCL open, remove the CCL arthroscopically, and retain the CCL arthroscopically. Samples underwent histologic staining and analysis with 3-dimensional micro-computed tomography. The latter was used to calculate the percentage of the CCL that was removed or retained across the entire defect.

RESULTS

When surgeons were asked to retain the CCL arthroscopically, 48% ± 41% (mean ± SD) remained. When surgeons were asked to remove the CCL arthroscopically, 24% ± 35% remained. There was no statistical difference between these groups (P > .05). When the CCL was retained during open preparation, 60% ± 39% remained. During attempts to remove the CCL in an open manner, 19% ± 28% remained. There was a significant difference in the amount of CCL remaining between the open removal and open retaining groups (P = .03). There were no significant differences in the percentage of CCL remaining between the open and arthroscopic preservation groups and between the open and arthroscopic removal groups.

CONCLUSION/CLINICAL RELEVANCE

This study highlights the significant variability in surgeon ability to reliably retain or remove the CCL. However, there appears to be improved ability of surgeons to more reliably remove or retain the CCL in an open fashion as compared with the arthroscopic approach.

3D printed biofunctionalized scaffolds for microfracture repair of cartilage defects

While articular cartilage defects affect millions of people worldwide from adolescents to adults, the repair of articular cartilage defects still remains challenging due to the limited endogenous regeneration of the tissue and poor integration with implants. In this study, we developed a 3D-printed scaffold functionalized with aggrecan that supports the cellular fraction of bone marrow released from microfracture, a widely used clinical procedure, and demonstrated tremendous improvement of regenerated cartilage tissue quality and joint function in a lapine model. Optical coherence tomography (OCT) revealed doubled thickness of the regenerated cartilage tissue in the group treated with our aggrecan functionalized scaffold compared to standard microfracture treatment. H&E staining showed 366 ± 95 chondrocytes present in the unit area of cartilage layer with the support of bioactive scaffold, while conventional microfracture group showed only 112 ± 26 chondrocytes. The expression of type II collagen appeared almost 10 times higher with our approach compared to normal microfracture, indicating the potential to overcome the fibro-cartilage formation associated with the current microfracture approach. The therapeutic effect was also evaluated at joint function level. The mobility was evaluated using a modified Basso, Beattie and Bresnahan (BBB) scale. While the defect control group showed no movement improvement over the course of study, all experimental groups showed a trend of increasing scores over time. The present work developed an effective method to regenerate critical articular defects by combining a 3D-printed therapeutic scaffold with the microfracture surgical procedure. This biofunctionalized acellular scaffold has great potential to be applied as a supplement for traditional microfracture to improve the quality of cartilage regeneration in a cost and labor effective way.

Optical coherence tomography enables accurate measurement of equine cartilage thickness for determination of speed of sound

Background and purpose - Arthroscopic estimation of articular cartilage thickness is important for scoring of lesion severity, and measurement of cartilage speed of sound (SOS)-a sensitive index of changes in cartilage composition. We investigated the accuracy of optical coherence tomography (OCT) in measurements of cartilage thickness and determined SOS by combining OCT thickness and ultrasound (US) time-of-flight (TOF) measurements. Material and methods - Cartilage thickness measurements from OCT and microscopy images of 94 equine osteochondral samples were compared. Then, SOS in cartilage was determined using simultaneous OCT thickness and US TOF measurements. SOS was then compared with the compositional, structural, and mechanical properties of cartilage. Results - Measurements of non-calcified cartilage thickness using OCT and microscopy were significantly correlated (ρ = 0.92; p < 0.001). With calcified cartilage included, the correlation was ρ = 0.85 (p < 0.001). The mean cartilage SOS (1,636 m/s) was in agreement with the literature. However, SOS and the other properties of cartilage lacked any statistically significant correlation. Interpretation - OCT can give an accurate measurement of articular cartilage thickness. Although SOS measurements lacked accuracy in thin equine cartilage, the concept of SOS measurement using OCT appears promising.

Quantitative OCT and MRI biomarkers for the differentiation of cartilage degeneration

OBJECTIVE

To evaluate the usefulness of quantitative parameters obtained by optical coherence tomography (OCT) and magnetic resonance imaging (MRI) in the comprehensive assessment of human articular cartilage degeneration.

MATERIALS AND METHODS

Human osteochondral samples of variable degeneration (n = 45) were obtained from total knee replacements and assessed by MRI sequences measuring T1, T1ρ, T2 and T2* relaxivity and by OCT-based quantification of irregularity (OII, optical irregularity index), homogeneity (OHI, optical homogeneity index]) and attenuation (OAI, optical attenuation index]). Samples were also assessed macroscopically (Outerbridge classification) and histologically (Mankin classification) as grade-0 (Mankin scores 0-4)/grade-I (scores 5-8)/grade-II (scores 9-10)/grade-III (score 11-14). After data normalisation, differences between Mankin grades and correlations between imaging parameters were assessed using ANOVA and Tukey's post-hoc test and Spearman's correlation coefficients, respectively. Sensitivities and specificities in the detection of Mankin grade-0 were calculated.

RESULTS

Significant degeneration-related increases were found for T2 and OII and decreases for OAI, while T1, T1ρ, T2* or OHI did not reveal significant changes in relation to degeneration. A number of significant correlations between imaging parameters and histological (sub)scores were found, in particular for T2 and OII. Sensitivities and specificities in the detection of Mankin grade-0 were highest for OHI/T1 and OII/T1ρ, respectively.

CONCLUSION

Quantitative OCT and MRI techniques seem to complement each other in the comprehensive assessment of cartilage degeneration. Sufficiently large structural and compositional changes in the extracellular matrix may thus be parameterized and quantified, while the detection of early degeneration remains challenging.

Evaluation of three-dimensional chitosan-agarose-gelatin cryogel scaffold for the repair of subchondral cartilage defects: an in vivo study in a rabbit model

In this study, the potential of a chitosan-agarose-gelatin (CAG) cryogel scaffold for the repair of subchondral cartilage defects was explored in female New Zealand white rabbits. Custom-made CAG cryogel scaffold was implanted in a surgically created subchondral defect (diameter of 4 mm, depth of 4 mm) in knee joint of rabbit. The repair of the subchondral defect was evaluated at regular time interval by both macroscopic as well as microscopic examinations. The gross evaluation of the scaffold-implanted site showed integration of the scaffold with the surrounding tissue. Scanning electron microscopy and histological staining of the remnants of implanted cryogel scaffold showed infiltration of the host cells. The repair of the subchondral defect along with well-integrated regenerated cartilage was confirmed by the histology analysis of the joint. Results showed significant cartilage regeneration by the fourth week until eighth week after implantation. Immunohistochemical analysis confirmed that regenerated tissue is hyaline cartilage and absence of hypertrophy marker was reported. In addition, the CAG scaffolds did not elicit any adverse immunological rejection as shown by hematological analysis. Enzyme-linked immunosorbent assay did not show any statistically significant change in the concentration of tumor necrosis factor-α in the serum, and remained in a nontoxic range. Rabbits with a surgically created defect but no scaffold did not show any cartilage regeneration throughout the experiment of 8 weeks. These results demonstrate that CAG cryogel scaffolds promote repair of an osteochondral defect at a load-bearing site in rabbits.

Evaluation of Single-Impact-Induced Cartilage Degeneration by Optical Coherence Tomography

Posttraumatic osteoarthritis constitutes a major cause of disability in our increasingly elderly population. Unfortunately, current imaging modalities are too insensitive to detect early degenerative changes of this disease. Optical coherence tomography (OCT) is a promising nondestructive imaging technique that allows surface and subsurface imaging of cartilage, at near-histological resolution, and is principally applicable in vivo during arthroscopy. Thirty-four macroscopically normal human cartilage-bone samples obtained from total joint replacements were subjected to standardized single impacts in vitro (range: 0.25 J to 0.98 J). 3D OCT measurements of impact area and adjacent tissue were performed prior to impaction, directly after impaction, and 1, 4, and 8 days later. OCT images were assessed qualitatively (DJD classification) and quantitatively using established parameters (OII, Optical Irregularity Index; OHI, Optical Homogeneity Index; OAI, Optical Attenuation Index) and compared to corresponding histological sections. While OAI and OHI scores were not significantly changed in response to low- or moderate-impact energies, high-impact energies significantly increased mean DJD grades (histology and OCT) and OII scores. In conclusion, OCT-based parameterization and quantification are able to reliably detect loss of cartilage surface integrity after high-energy traumatic insults and hold potential to be used for clinical screening of early osteoarthritis.

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 Tukey's or Dunn's 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.

Comparison of optical coherence tomography and histopathology in quantitative assessment of goat talus articular cartilage

BACKGROUND AND PURPOSE

Optical coherence tomography (OCT) is a light-based imaging technique suitable for depiction of thin tissue layers such as articular cartilage. Quantification of results and direct comparison with a reference standard is needed to confirm the role of OCT in cartilage evaluation.

MATERIALS AND METHODS

Goat talus articular cartilage repair was assessed quantitatively with OCT and compared with histopathology using semi-automated analysis software. Osteochondral defects were created centrally in goat tali with subsequent healing over 24 weeks. After sacrifice, the tali were analyzed using OCT and processed into histopathology slides. Cartilage thickness, repair tissue area, and surface roughness were measured. Also, light attenuation coefficient measurements were performed to assess differences in the properties of healthy tissue and repair tissue.

RESULTS

Intra-class correlation coefficients for resemblance between the 2 techniques were 0.95 (p < 0.001) for thickness, 0.73 (p = 0.002) for repair tissue area, and 0.63 (p = 0.015) for surface roughness. Light attenuation differed significantly between healthy cartilage (8.2 (SD 3.9) mm(-1)) and repair tissue (2.8 (SD 1.5) mm(-1)) (p < 0.001).

INTERPRETATION

Compared to histopathology as the standard reference method, OCT is a reproducible technique in quantitative analysis of goat talus articular cartilage, especially when assessing cartilage thickness and to a lesser extent when measuring repair tissue area and surface roughness. Moreover, differences in local light attenuation suggest measurable variation in tissue structure, enhancing the clinical applicability of quantitative measurements from cartilage OCT images.

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.

Arthroscopic optical coherence tomography provides detailed information on articular cartilage lesions in horses

Arthroscopy enables direct inspection of the articular surface, but provides no information on deeper cartilage layers. Optical coherence tomography (OCT), based on measurement of reflection and backscattering of light, is a diagnostic technique used in cardiovascular surgery and ophthalmology. It provides cross-sectional images at resolutions comparable to that of low-power microscopy. The aim of this study was to determine if OCT is feasible for advanced clinical assessment of lesions in equine articular cartilage during diagnostic arthroscopy. Diagnostic arthroscopy of 36 metacarpophalangeal joints was carried out ex vivo. Of these, 18 joints with varying degrees of cartilage damage were selected, wherein OCT arthroscopy was conducted using an OCT catheter (diameter 0.9 mm) inserted through standard instrument portals. Five sites of interest, occasionally supplemented with other locations where defects were encountered, were arthroscopically graded according to the International Cartilage Repair Society (ICRS) classification system. The same sites were evaluated qualitatively (ICRS classification and morphological description of the lesions) and quantitatively (measurement of cartilage thickness) on OCT images. OCT provided high resolution images of cartilage enabling determination of cartilage thickness. Comparing ICRS grades determined by both arthroscopy and OCT revealed poor agreement. Furthermore, OCT visualised a spectrum of lesions, including cavitation, fibrillation, superficial and deep clefts, erosion, ulceration and fragmentation. In addition, with OCT the arthroscopically inaccessible area between the dorsal MC3 and P1 was reachable in some cases. Arthroscopically-guided OCT provided more detailed and quantitative information on the morphology of articular cartilage lesions than conventional arthroscopy. OCT could therefore improve the diagnostic value of arthroscopy in equine orthopaedic surgery.

Cluster analysis of infrared spectra can differentiate intact and repaired articular cartilage

OBJECTIVE

Successful repair of articular cartilage (AC) defects would be a major advantage due to the low ability of AC to heal spontaneously. Sensitive methods to determine changes in AC composition and structure are required to monitor the success of repair. This study evaluates the ability of unsupervised cluster analysis applied to Fourier transform infrared (FTIR) microspectroscopy to discriminate between healthy and repaired AC.

METHODS

Osteochondral lesions (3 mm in depth) were surgically created in patellar grooves of rabbit femurs and were either left to heal spontaneously (n = 6) or surgically repaired with autologous chondrocytes in type II collagen gel (n = 6). After 6 months, tissues were harvested, FTIR microspectroscopy was conducted and Fuzzy c-means (FCM) cluster analysis applied to spectra of pairs of intact and repaired AC samples from each rabbit. Two spectral regions [amide I and carbohydrate (CHO)] were analyzed and the results from the two types of repair were compared.

RESULTS

Two separate regions of repair were detected with FCM. The estimated proteoglycan content (from CHO region) in the repaired AC was significantly lower than that in intact AC. The spontaneously repaired AC was better distinguished from the intact AC than the collagen II gel repaired AC. The most distinct clustering was observed for spontaneously repaired samples using CHO region.

CONCLUSIONS

This study revealed that unsupervised cluster analysis applied to FTIR microspectroscopy can detect subtle differences in infrared spectra between normal and repaired AC. The method may help in evaluation and optimization of future AC repair strategies.

Diagnosis of osteoarthritis: imaging

Osteoarthritis (OA) is a chronic, debilitating joint disease characterized by degenerative changes to the bones, cartilage, menisci, ligaments, and synovial tissue. Imaging modalities such as radiography, magnetic resonance imaging (MRI), optical coherence tomography (OCT), and ultrasound (US) permit visualization of these structures and can evaluate disease onset and progression. Radiography is primarily useful for the assessment of bony structures, while OCT is used for evaluation of articular cartilage and US for ligaments and the synovium. MRI permits visualization of all intraarticular structures and pathologies, though US or OCT may be preferential in some circumstances. As OA is a disease of the whole joint, a combination of imaging techniques may be necessary in order to gain the most comprehensive picture of the disease state. This article is part of a Special Issue entitled "Osteoarthritis".

Comparison of ultrasound and optical coherence tomography techniques for evaluation of integrity of spontaneously repaired horse cartilage

The aim of this study was to compare sensitivity of ultrasound and optical coherence tomography (OCT) techniques for the evaluation of the integrity of spontaneously repaired horse cartilage. Articular surfaces of horse intercarpal joints, featuring both intact tissue and spontaneously healed chondral or osteochondral defects, were imaged ex vivo with arthroscopic ultrasound and laboratory OCT devices. Quantitative ultrasound (integrated reflection coefficient (IRC), apparent integrated backscattering coefficient (AIB) and ultrasound roughness index (URI)) and optical parameters (optical reflection coefficient (ORC), optical roughness index (ORI) and optical backscattering (OBS)) were determined and compared with histological integrity and mechanical properties of the tissue. Spontaneously healed tissue could be quantitatively discerned from the intact tissue with ultrasound and OCT techniques. Furthermore, several significant correlations (p < 0.05) were detected between ultrasound and OCT parameters. Superior resolution of OCT provided a more accurate measurement of cartilage surface roughness, while the ultrasound backscattering from the inner structures of the cartilage matched better with the histological findings. Since the techniques were found to be complementary to each other, dual modality imaging techniques could provide a useful tool for the arthroscopic evaluation of the integrity of articular cartilage.

Early diagnosis to enable early treatment of pre-osteoarthritis

Osteoarthritis is a prevalent and disabling disease affecting an increasingly large swathe of the world population. While clinical osteoarthritis is a late-stage condition for which disease-modifying opportunities are limited, osteoarthritis typically develops over decades, offering a long window of time to potentially alter its course. The etiology of osteoarthritis is multifactorial, showing strong associations with highly modifiable risk factors of mechanical overload, obesity and joint injury. As such, characterization of pre-osteoarthritic disease states will be critical to support a paradigm shift from palliation of late disease towards prevention, through early diagnosis and early treatment of joint injury and degeneration to reduce osteoarthritis risk. Joint trauma accelerates development of osteoarthritis from a known point in time. Human joint injury cohorts therefore provide a unique opportunity for evaluation of pre-osteoarthritic conditions and potential interventions from the earliest stages of degeneration. This review focuses on recent advances in imaging and biochemical biomarkers suitable for characterization of the pre-osteoarthritic joint as well as implications for development of effective early treatment strategies.

Optical coherence tomography for the identification of musculoskeletal structures of the spine: a pilot study

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine requiring in severe cases invasive surgery. Here, we explore the potential of optical coherence tomography (OCT) as a guiding tool for novel fusionless minimally invasive spinal surgeries on an ex vivo porcine model. We show that OCT, despite its limited penetration depth, may be used to precisely locate structures such as growth plate, bone and intervertebral disk using relative attenuation coefficients. We further demonstrate a segmentation algorithm that locates growth plates automatically on en-face OCT reconstructions.

QUANTIFICATION OF CHONDROCYTE MORPHOLOGY BY CONFOCAL ARTHROSCOPY

The purpose of this study was to determine the effectiveness of a novel Laser Scanning Confocal Arthroscope (LSCA) for the morphological quantification of articular cartilage chondrocytes.

Healthy and debrided regions of the knee articular cartilage of six (6) New Zealand White rabbits were imaged during open follow-up surgery. Quantitative morphological analysis of chondrocyte cell populations was performed and compared to known parameters. Optical histology images were compared to conventional histology of similar sites.

Optical histology revealed viable cells in normal hyaline cartilage tissue and enabled the visualization of fibro-cartilage in defect tissue. Morphological analysis was able to characterize the in vivo two-dimensional equivalent-area-diameter of chondrocytes. Significant differences (P<0.05) were seen between the morphology of chondrocytes observed in optical and conventional histology.

This study concludes that the LSCA is capable of illustrating the surface and sub-surface appearance of healthy and defect articular cartilage, thereby providing a non-destructive method for assessing cartilage condition in vivo. In this role the LSCA may find application in the investigation of cartilage pathologies or repair techniques.

HISTOLOGICAL ASSESSMENT OF THE CHONDRAL AND CONNECTIVE TISSUES OF THE KNEE BY CONFOCAL ARTHROSCOPE

Conventional histological assessment of tissue requires the removal of tissue from its physiological environment for pathological processing. In this study we report on the development and application of a laser scanning confocal arthroscope (LSCA) capable of in situ histological assessment by confocal microscopy.

The knee joints of three euthanasied adult Merino sheep were imaged using the LSCA and a combination of fluorescent contrasting agents. LSCA images of various tissues were examined for common histological characteristics.

The confocal histology images from the ovine knee acquired during the course of our study illustrated some of the major histological features of chondral and connective tissues.

Our study demonstrates the efficacy of the LSCA for the histological assessment of the chondral and connective tissues of the ovine knee. The LSCA provides an easy and rapid method for assessing the in situ structure of cartilage, muscle, tendon, ligament, meniscus and synovium in their native and unaltered physiological environment. By obviating the need for mechanical biopsy, the LSCA provides a method for the non-destructive assessment of the chondral and connective tissues of the knee, and may be of great benefit in the investigation of orthopedic diseases or in the assessment of newly emerging cartilage repair techniques.

Arthroscopic optical coherence tomography in diagnosis of early arthritis

Osteoarthritis (OA) is a progressive, debilitating disease that is increasing in prevalence. The pathogenesis of OA is likely multifactorial but ultimately leads to progressive breakdown of collagen matrix and loss of chondrocytes. Current clinical modalities employed to evaluate cartilage health and diagnose osteoarthritis in orthopaedic surgery include, radiography, MRI, and arthroscopy. While these assessment methods can show cartilage fissuring and loss, they are limited in ability to diagnose cartilage injury and degeneration prior breakdown of the articular surface. An improved clinical ability to detect subsurface cartilage pathology is important for development and testing of chondroprotective and chondrorestorative treatments because the pathological changes following surface breakdown are generally considered to be irreversible. Optical Coherence Tomography (OCT), is a novel, non-destructive imaging technology capable of near-real time cross-sectional images of articular cartilage at high resolutions comparable to low power histology. This review discusses a series of bench to bedside studies supporting the potential use of OCT for enhanced clinical diagnosis and staging of early cartilage injury and degeneration. OCT was also found to be useful as a translations research tool to assist in clinical evaluation of novel quantitative MRI technologies for non-invasive evaluation of articular cartilage.

Effects of optical beam angle on quantitative optical coherence tomography (OCT) in normal and surface degenerated bovine articular cartilage

Quantitative measurement of articular cartilage using optical coherence tomography (OCT) is a potential approach for diagnosing the early degeneration of cartilage and assessing the quality of its repair. However, a non-perpendicular angle of the incident optical beam with respect to the tissue surface may cause uncertainty to the quantitative analysis, and therefore, significantly affect the reliability of measurement. This non-perpendicularity was systematically investigated in the current study using bovine articular cartilage with and without mechanical degradation. Ten fresh osteochondral disks were quantitatively measured before and after artificially induced surface degradation by mechanical grinding. The following quantitative OCT parameters were determined with a precise control of the surface inclination up to an angle of 10° using a step of 2°: optical reflection coefficient (ORC), variation of surface reflection (VSR) along the surface profile, optical roughness index (ORI) and optical backscattering (OBS). It was found that non-perpendicularity caused systematic changes to all of the parameters. ORC was the most sensitive and OBS the most insensitive to the inclination angle. At the optimal perpendicular angle, all parameters could detect significant changes after surface degradation (p < 0.01), except OBS (p > 0.05). Nonsignificant change of OBS after surface degradation was expected since OBS reflected properties of the internal cartilage tissue and was not affected by the superficial mechanical degradation. As a conclusion, quantitative OCT parameters are diagnostically potential for characterizing the cartilage degeneration. However, efforts through a better controlled operation or corrections based on computational compensation mechanism should be made to minimize the effects of non-perpendicularity of the incident optical beam when clinical use of quantitative OCT is considered for assessing the articular cartilage.

Terahertz pulsed imaging of knee cartilage

Osteoarthritis (OA) is a common form of arthritis caused by cartilage degeneration. In this paper, we investigate the potential use of terahertz (THz) pulsed imaging to quantitatively measure the early symptoms of OA in an animal model. THz images of excised rabbit femoral condyles were taken. We observe THz waves reflected off different layers within samples and demonstrate that the optical delay between reflections can give a quantitative measure of the thicknesses of particular tissues within cartilage.

Clinical optical coherence tomography of early articular cartilage degeneration in patients with degenerative meniscal tears

OBJECTIVE

Quantitative and nondestructive methods for clinical diagnosis and staging of articular cartilage degeneration are important to the evaluation of potential disease-modifying treatments in osteoarthritis (OA). Optical coherence tomography (OCT) is a novel imaging technology that can generate microscopic-resolution cross-sectional images of articular cartilage in near real-time. This study tested the hypotheses that OCT can be used clinically to identify early cartilage degeneration and that OCT findings correlate with magnetic resonance imaging (MRI) T2 values and arthroscopy results.

METHODS

Patients undergoing arthroscopy for degenerative meniscal tears were recruited under Institutional Review Board-approved protocols. Thirty consecutive subjects completing preoperative 3.0T MRI, arthroscopy, and intraoperative OCT comprised the study group. Qualitative and quantitative OCT results and MRI T2 values were compared with modified Outerbridge cartilage degeneration scores (0-4 scale) assigned at arthroscopy.

RESULTS

Arthroscopic grades showed cartilage abnormality in 23 of the 30 patients. OCT grades were abnormal in 28 of the 30 patients. Both qualitative and quantitative OCT strongly correlated with the arthroscopy results (P = 0.004 and P = 0.0002, respectively, by Kruskal-Wallis test). Neither the superficial nor the deep cartilage T2 values correlated with the arthroscopy results. The quantitative OCT results correlated with the T2 values in the superficial cartilage (Pearson's r = 0.39, P = 0.03).

CONCLUSION

These data show that OCT can be used clinically to provide qualitative and quantitative assessments of early articular cartilage degeneration that strongly correlate with arthroscopy results. The correlation between the quantitative OCT values and T2 values for the superficial cartilage further supports the utility of OCT as a clinical research tool, providing quantifiable microscopic resolution data on the articular cartilage structure. New technologies for nondestructive quantitative assessment of human articular cartilage degeneration may facilitate the development of strategies to delay or prevent the onset of OA.

Quantitative evaluation of spontaneously and surgically repaired rabbit articular cartilage using intra-articular ultrasound method in situ

During the last decade, a major effort has been devoted to developing surgical methods for repairing localized articular cartilage lesions. Despite some promising results no ultimate breakthrough in surgical cartilage repair has been achieved. Improvements in repair techniques would benefit from more sensitive and quantitative methods for long-term follow-up of cartilage healing. In this study, the potential of a new ultrasound technique for detecting the compositional and structural changes in articular cartilage after surgery, using recombinant human type II collagen gel and spontaneous repair was, investigated. Rabbit knee joints containing intact (n = 13) and surgically (n = 8) or spontaneously (n = 5) repaired tissue were imaged in situ at 6 months after the operation using a clinical intravascular high-frequency (40 MHz) ultrasound device. Based on the ultrasound raw data, ultrasound reflection coefficient (R), integrated ultrasound reflection coefficient (IRC), apparent integrated backscattering coefficient (AIB) and ultrasound roughness index (URI) were determined for each sample. URI was significantly higher in both repair groups than in intact cartilage (p < 0.05). The reflection parameters (R and IRC) were significantly lower in surgically repaired cartilage (p < 0.05) than in intact cartilage. Furthermore, AIB was significantly higher in surgically repaired cartilage than in intact tissue (p < 0.05). To conclude, the integrity of the rabbit articular cartilage repair could be quantitatively evaluated with the nondestructive ultrasound approach. In addition, clinically valuable qualitative information on the changes in cartilage integration, structure and composition could be extracted from the ultrasound images. In the present study, the structure and properties of repaired tissue were inferior to native tissue at 6 months after the operation. The applied ultrasound device and probes are FDA approved and, thus, applicable for the quantitative in vivo evaluation of human articular cartilage.

Animal models for cartilage regeneration and repair

Articular cartilage injury and degeneration are leading causes of disability. Animal studies are critically important to developing effective treatments for cartilage injuries. This review focuses on the use of animal models for the study of the repair and regeneration of focal cartilage defects. Animals commonly used in cartilage repair studies include murine, lapine, canine, caprine, porcine, and equine models. There are advantages and disadvantages to each model. Small animal rodent and lapine models are cost effective, easy to house, and useful for pilot and proof-of-concept studies. The availability of transgenic and knockout mice provide opportunities for mechanistic in vivo study. Athymic mice and rats are additionally useful for evaluating the cartilage repair potential of human cells and tissues. Their small joint size, thin cartilage, and greater potential for intrinsic healing than humans, however, limit the translational value of small animal models. Large animal models with thicker articular cartilage permit study of both partial thickness and full thickness chondral repair, as well as osteochondral repair. Joint size and cartilage thickness for canine, caprine, and mini-pig models remain significantly smaller than that of humans. The repair and regeneration of chondral and osteochondral defects of size and volume comparable to that of clinically significant human lesions can be reliably studied primarily in equine models. While larger animals may more closely approximate the human clinical situation, they carry greater logistical, financial, and ethical considerations. A multifactorial analysis of each animal model should be carried out when planning in vivo studies. Ultimately, the scientific goals of the study will be critical in determining the appropriate animal model.

Assessment of depth and degeneration dependences of articular cartilage refractive index using optical coherence tomography in vitro

In this study, optical coherence tomography (OCT) with an axial resolution of 15 mum was used to investigate the depth and degeneration dependences of the refractive index (RI) of articular cartilage collected from bovine patellae in vitro. Eighteen disks of articular cartilage with a diameter of 6.35 mm harvested from different patellae were successfully prepared. Each disk was cut into two halves and three horizontal cartilage slices (n = 18 x 2 x 3) with an approximately equal thickness of 0.5 mm were further prepared from each half disk. The cartilage slices were digested by two different enzymes, collagenase and trypsin, to disturb collagen fibrils and proteoglycans, respectively. The samples were submerged in the physiological saline and tested using OCT before and after the enzyme digestion and the RI for each specimen was calculated. The RI of articular cartilage from the superficial to deep regions was 1.361 +/- 0.032 (mean +/- SD), 1.338 +/- 0.036, and 1.371 +/- 0.041 for normal specimens; 1.357 +/- 0.036, 1.331 +/- 0.030, and 1.392 +/- 0.037 for trypsin digested specimens; and 1.361 +/- 0.032, 1.336 +/- 0.048, and 1.376 +/- 0.043 for those treated by collagenase, respectively. Two-factor repeated measure ANOVA revealed that for all the three groups of specimens, the RI in different depths was significantly different (p < 0.05). However, we found that the trypsin and collagenase treatments did not exert a significant effect on the RI (p > 0.05). The results suggested that the depth dependence of articular cartilage should be taken into account when OCT is used for related measurement.

Characterization of engineered tissue construct mechanical function by magnetic resonance imaging

Non-invasive magnetic resonance imaging (MRI) is a technology that enables the characterization of multiple physical phenomena in living and engineered tissues. The mechanical function of engineered tissues is a primary endpoint for the successful regeneration of many biological tissues, such as articular cartilage, spine and heart. Here we demonstrate the application of MRI to characterize the mechanical function of engineered tissue. Phase contrast-based methods were demonstrated to characterize detailed deformation fields throughout the interior of native and engineered tissue, using an articular cartilage defect model as a study system. MRI techniques revealed that strain fields varied non-uniformly, depending on spatial position. Strains were highest in the tissue constructs compared to surrounding native cartilage. Tissue surface geometry corresponded to strain fields observed within the tissue interior near the surface. Strain fields were further evaluated with respect to the spatial variation in the concentration of glycosaminoglycans ([GAG]), critical proteoglycans in the extracellular matrix of cartilage, as determined by gadolinium-enhanced imaging. [GAG] also varied non-uniformly, depending on spatial position and was lowest in the tissue constructs compared to the surrounding cartilage. The use of multiple MRI techniques to assess tissue mechanical function provides complementary data and suggests that deformation is related to tissue geometry, underlying extracellular matrix constituents and the lack of tissue integration in the model system studied. Specialized and advanced MRI phase contrast-based methods are valuable for the detailed characterization and evaluation of mechanical function of tissue-engineered constructs.

Mechanical effects of surgical procedures on osteochondral grafts elucidated by osmotic loading and real-time ultrasound

Introduction

Osteochondral grafts have become popular for treating small, isolated and full-thickness cartilage lesions. It is recommended that a slightly oversized, rather than an exact-sized, osteochondral plug is transplanted to achieve a tight fit. Consequently, impacting forces are required to insert the osteochondral plug into the recipient site. However, it remains controversial whether these impacting forces affect the biomechanical condition of the grafted articular cartilage. The present study aimed to investigate the mechanical effects of osteochondral plug implantation using osmotic loading and real-time ultrasound.

Methods

A full-thickness cylindrical osteochondral defect (diameter, 3.5 mm; depth, 5 mm) was created in the lateral lower quarter of the patella. Using graft-harvesting instruments, an osteochondral plug (diameter, 3.5 mm as exact-size or 4.5 mm as oversize; depth, 5 mm) was harvested from the lateral upper quarter of the patella and transplanted into the defect. Intact patella was used as a control. The samples were monitored by real-time ultrasound during sequential changes of the bathing solution from 0.15 M to 2 M saline (shrinkage phase) and back to 0.15 M saline (swelling phase). For cartilage sample assessment, three indices were selected, namely the change in amplitude from the cartilage surface (amplitude recovery rate: ARR) and the maximum echo shifts from the cartilage surface and the cartilage-bone interface.

Results

The ARR is closely related to the cartilage surface integrity, while the echo shifts from the cartilage surface and the cartilage-bone interface are closely related to tissue deformation and NaCl diffusion, respectively. The ARR values of the oversized plugs were significantly lower than those of the control and exact-sized plugs. Regarding the maximum echo shifts from the cartilage surface and the cartilage-bone interface, no significant differences were observed among the three groups.

Conclusions

These findings demonstrated that osmotic loading and real-time ultrasound were able to assess the mechanical condition of cartilage plugs after osteochondral grafting. In particular, the ARR was able to detect damage to the superficial collagen network in a non-destructive manner. Therefore, osmotic loading and real-time ultrasound are promising as minimally invasive methods for evaluating cartilage damage in the superficial zone after trauma or impact loading for osteochondral grafting.

Chondrogenesis, joint formation, and articular cartilage regeneration

The repair of joint surface defects remains a clinical challenge, as articular cartilage has a limited healing response. Despite this, articular cartilage does have the capacity to grow and remodel extensively during pre- and post-natal development. As such, the elucidation of developmental mechanisms, particularly those in post-natal animals, may shed valuable light on processes that could be harnessed to develop novel approaches for articular cartilage tissue engineering and/or regeneration to treat injuries or degeneration in adult joints. Much has been learned through mouse genetics regarding the embryonic development of joints. This knowledge, as well as the less extensive available information regarding post-natal joint development is reviewed here and discussed in relation to their possible relevance to future directions in cartilage tissue repair and regeneration.

Preclinical animal models in single site cartilage defect testing: a systematic review

OBJECTIVE

Review the literature for single site cartilage defect research and evaluate the respective strengths and weaknesses of different preclinical animal models.

METHOD

A literature search for animal models evaluating single site cartilage defects was performed. Variables tabulated and analyzed included animal species, age and number, defect depth and diameter and study duration. Cluster analyses were then used to separate animals with only distal femoral defects into similar groups based on defect dimensions. Representative human studies were included allowing comparison of common clinical lesions to animal models. The suitability of each species for single site cartilage defect research and its relevance to clinical human practice is then discussed.

RESULTS

One hundred thirteen studies relating to single site cartilage defects were reviewed. Cluster analysis included 101 studies and placed the murine, laprine, ovine, canine, porcine and caprine models in group 1. Group 2 contained ovine, canine, porcine, caprine and equine models. Group 3 contained only equine models and humans. Species in each group are similar with regard to defect dimensions. Some species occur in multiple groups reflecting utilization of a variety defect sizes. We report and discuss factors to be considered when selecting a preclinical animal model for single site cartilage defect research.

DISCUSSION

Standardization of study design and outcome parameters would help to compare different studies evaluating various novel therapeutic concepts. Comparison to the human clinical counterpart during study design may help increase the predictive value of preclinical research using animal models and improve the process of developing efficacious therapies.

Three Dimensional OCT in the Engineering of Tissue Constructs: A Potentially Powerful Tool for Assessing Optimal Scaffold Structure

Optical Coherence Tomography (OCT) provides detailed, real-time information on the structure and composition of constructs used in tissue engineering. The focus of this work is the OCT three-dimensional assessment of scaffolding architecture and distribution of cells on it. PLGA scaffolds were imaged in two and three-dimensions, both seeded and unseeded with cells. Then two types of scaffolds were reconstructed in three dimensions. Both scaffolding types were examined at three different seeding densities. The importance of three-dimensional assessments was evident, particularly with respect to porosity and identification of asymmetrical cell distribution.

In situ characterization of the degradation of PLGA microspheres in hyaluronic acid hydrogels by optical coherence tomography

The polymeric implant material poly(lactide-co-glycolide) (PLGA) degrades by a process of bulk degradation, which allows it to be used for the controlled release of therapeutic molecules from implants and microspheres. The temporal characterization of PLGA microsphere degradation has been limited by the need to destructively monitor the samples at each time point. In this study, a noninvasive imaging technology, optical coherence tomography (OCT), was utilized to characterize the in situ degradation of PLGA microspheres suspended within photo-crosslinked hyaluronic acid (HA) hydrogels. Microspheres with differing degradation rates were loaded with bovine serum albumin (BSA) as a marker protein, and temporal release of protein was correlated with morphological changes observed during 3-D OCT imaging. As proof-of-principle, a microsphere-loaded hydrogel scaffold was implanted in a modified rat calvarial critical size defect model and imaged using OCT. This animal model presents the opportunity to monitor microsphere degradation over time in living animals.

Novel optical imaging technique to determine the 3-D orientation of collagen fibers in cartilage: variable-incidence angle polarization-sensitive optical coherence tomography

OBJECTIVE

To investigate a novel optical method to determine the three dimensional (3-D) structure of articular cartilage collagen non-destructively.

METHODS

Polarization-sensitive optical coherence tomography was used to determine the apparent optical birefringence of articular cartilage for a number of different illumination directions. A quantitative method based on the theory of light propagation in uniaxial crystalline materials was validated on equine flexor tendon. Qualitative maps of fiber polar and azimuthal orientation at sites on the posterior and anterior segments of the equine third metacarpophalangeal (fetlock) joint were produced, and the azimuthal orientations compared with data from a split-line experiment.

RESULTS

Polar and azimuthal angles of cut flexor tendon broadly agreed with the nominal values but suggested that the accuracy was limited by our method of determining the apparent birefringence. On intact equine fetlock joints we found a non-zero polar tilt that changed in direction at various points along the apex, moving from the sagittal ridge outwards. The azimuthal orientation changes from being parallel to the sagittal ridge in the posterior region to being inclined to the ridge in the anterior region. This broadly agrees with split-line data for the anterior region but differs in the posterior region, possibly reflecting depth-dependent orientation changes.

CONCLUSION

General quantitative agreement was found between our method and histology in validation experiments. Qualitative results for cartilage suggest a complicated 3-D structure that warrants further study. There is potential to develop this approach into a tool that can provide depth-resolved information on collagen orientation in near real-time, non-destructively and in vivo.

Topographical variations in the polarization sensitivity of articular cartilage as determined by polarization-sensitive optical coherence tomography and polarized light microscopy

To understand the influence of topographical variations in collagen fibril orientation of articular cartilage on optical phase images of polarization-sensitive optical coherence tomography (PS-OCT), we use polarized light microscopy (PLM) to quantify the orientation and phase retardation of the collagen architecture in cartilage at the same locations imaged by PS-OCT. The PS-OCT experiments demonstrate that articular cartilage has normal variations in polarization sensitivity at different locations over an intact bovine tibial plateau. Articular cartilage is not polarization sensitive along the vertical axis on the medial edge and central areas of the joint surface, but becomes polarization sensitive on the lateral edge of the tibia. This difference in optical phase retardation, as demonstrated by PS-OCT, is verified by PLM to be caused by differences in collagen fibril orientation at different locations of the tibial plateau. This study demonstrates that normal topographical variations in the collagen architecture of articular cartilage within a joint have a profound influence on the optical phase retardation detected by PS-OCT imaging, and therefore must be understood and mapped for specific joints before PS-OCT imaging can be used for the evaluation of the health status of individual joint surfaces.

Laser scanning confocal arthroscopy of a fresh cadaveric knee joint

OBJECTIVE

Osteoarthritis (OA) inflicts an enormous burden upon sufferers and healthcare systems worldwide. Continuing efforts to elucidate the aetiology of OA have indicated the need for non-destructive methods of in vivo microstructural assessment of articular cartilage (AC). In this study, we describe the first use of a recently developed laser scanning confocal arthroscope (LSCA) to image the cartilage of a fresh frozen cadaveric knee from a patient with OA.

DESIGN

Using an adaptation of the International Cartilage Repair Society (ICRS) joint mapping protocol, the joint was divided into three discrete regions (femoral condyle, patella and tibial plateau) for grading according to the ICRS (Outerbridge) system. The LSCA was used to generate images from each area within the three regions. Following imaging, the joint was sectioned and histology was performed on the corresponding sites with histological grading (modified-Mankin).

RESULTS

Quantitative results of ICRS, LSCA and histological OA assessment were compared using intraclass correlation (ICC) and Pearson correlation analysis. The LSCA enabled visualisation of chondrocyte morphology and cell density, with classical OA changes such as chondrocyte clustering, surface fibrillation and fissure formation evident. Obvious qualitative similarities between LSCA images and histology were observed, with fair to moderate agreement (P<0.05) demonstrated between modalities.

CONCLUSIONS

In this study, we have shown the viability of the LSCA for non-destructive imaging of the microstructure of OA knee cartilage. LSCA technology is potentially a valuable research and clinical tool for the non-destructive assessment of AC microstructure in early to late OA.

Repair of porcine articular cartilage defect with a biphasic osteochondral composite

Autologous chondrocyte implantation (ACI) has been recently used to treat cartilage defects. Partly because of the success of mosaicplasty, a procedure that involves the implantation of native osteochondral plugs, it is of potential significance to consider the application of ACI in the form of biphasic osteochondral composites. To test the clinical applicability of such composite construct, we repaired osteochondral defect with ACI at low cell-seeding density on a biphasic scaffold, and combined graft harvest and implantation in a single surgery. We fabricated a biphasic cylindrical porous plug of DL-poly-lactide-co-glycolide, with its lower body impregnated with beta-tricalcium phosphate as the osseous phase. Osteochondral defects were surgically created at the weight-bearing surface of femoral condyles of Lee-Sung mini-pigs. Autologous chondrocytes isolated from the cartilage were seeded into the upper, chondral phase of the plug, which was inserted by press-fitting to fill the defect. Defects treated with cell-free plugs served as control. Outcome of repair was examined 6 months after surgery. In the osseous phase, the biomaterial retained in the center and cancellous bone formed in the periphery, integrating well with native subchondral bone with extensive remodeling, as depicted on X-ray roentgenography by higher radiolucency. In the chondral phase, collagen type II immunohistochemistry and Safranin O histological staining showed hyaline cartilage regeneration in the experimental group, whereas only fibrous tissue formed in the control group. On the International Cartilage Repair Society Scale, the experimental group had higher mean scores in surface, matrix, cell distribution, and cell viability than control, but was comparable with the control group in subchondral bone and mineralization. Tensile stress-relaxation behavior determined by uni-axial indentation test revealed similar creep property between the surface of the experimental specimen and native cartilage, but not the control specimen. Implanted autologous chondrocytes could survive and could yield hyaline-like cartilage in vivo in the biphasic biomaterial construct. Pre-seeding of osteogenic cells did not appear to be necessary to regenerate subchondral bone.

Confocal arthroscopy-based patient-specific constitutive models of cartilaginous tissues - II: prediction of reaction force history of meniscal cartilage specimens

The theoretical framework developed in a companion paper (Part I) is used to derive estimates of mechanical response of two meniscal cartilage specimens. The previously developed framework consisted of a constitutive model capable of incorporating confocal image-derived tissue microstructural data. In the present paper (Part II) fibre and matrix constitutive parameters are first estimated from mechanical testing of a batch of specimens similar to, but independent from those under consideration. Image analysis techniques which allow estimation of tissue microstructural parameters form confocal images are presented. The constitutive model and image-derived structural parameters are then used to predict the reaction force history of the two meniscal specimens subjected to partially confined compression. The predictions are made on the basis of the specimens' individual structural condition as assessed by confocal microscopy and involve no tuning of material parameters. Although the model does not reproduce all features of the experimental curves, as an unfitted estimate of mechanical response the prediction is quite accurate. In light of the obtained results it is judged that more general non-invasive estimation of tissue mechanical properties is possible using the developed framework.

Clinical diagnosis of potentially treatable early articular cartilage degeneration using optical coherence tomography

A series of bench to operating room studies was conducted to determine whether it is feasible to use optical coherence tomography (OCT) clinically to diagnose potentially reversible early cartilage degeneration. A human cadaver study was performed to confirm the reproducibility of OCT imaging and grading based on identification of changes to cartilage OCT form birefringence using a polarized OCT system approved for clinical use. Segregation of grossly normal appearing human articular cartilage into two groups based on the presence or absence of OCT form birefringence showed that cartilage without OCT form birefringence had reduced ability to increase proteoglycan synthetic activity in response to the anabolic growth factor IGF-1. The bench data further show that IGF-1 insensitivity in cartilage without OCT form birefringence was reversible. To show clinical feasibility, OCT was then used arthroscopically in 19 human subjects. Clinical results confirmed that differences to OCT form birefringence observed in ex vivo study were detectable during arthroscopic surgery. More prevalent loss of cartilage OCT form birefringence was observed in cartilage of human subjects in groups more likely to have cartilage degeneration. This series of integrated bench to bedside studies demonstrates translational feasibility to use OCT for clinical studies on whether human cartilage degeneration can be diagnosed early enough for intervention that may delay or prevent the onset of osteoarthritis.

Confocal arthroscopy-based patient-specific constitutive models of cartilaginous tissues—I: development of a microstructural model

Current development of a laser scanning confocal arthroscope within our school will enable 3D microscopic imaging of joint tissues in vivo. Such an instrument could be useful, for example, in assessing the microstructural condition of the living tissues without physical biopsy. It is envisaged also that linked to a suitable microstructural constitutive formulation, such imaging could allow non-invasive patient-specific estimation of tissue mechanical performance. Such a procedure could have applications in surgical planning and simulation, and assessment of engineered tissue replacements, where tissue biopsy is unacceptable. In this first of two papers the development of a suitable constitutive framework for generating such estimates is reported. A microstructure-based constitutive formulation for cartilaginous tissues is presented. The model extends existing fibre composite-type models and accounts for strain-rate sensitivity of the tissue mechanical response through incorporation of a viscoelastic fibre phase. Importantly, the model is constructed so as to allow direct incorporation of structural data from confocal images. A finite element implementation of the formulation suitable for incorporation within commercial codes is also presented.

Sequential changes in implanted cartilage after autologous osteochondral transplantation: postoperative acoustic properties up to 1 year in an in vivo rabbit model

PURPOSE

For successful autologous osteochondral transplantation, it is important that the cartilage in an implanted plug provide histologic replacement of damaged cartilage with cartilage that is structurally and mechanically normal. The purpose of this study was to investigate whether the press-fit technique reconstructs the normal hyaline cartilage and provides acoustic stiffness equal to that of normal intact cartilage.

METHODS

In 36 rabbits an osteochondral plug, 6 mm in diameter, was removed from the right patellar groove and grafted into a recipient hole, 5 mm in diameter, in the left patellar groove. Specimens at 2, 4, 8, 12, 24, and 52 weeks postoperatively were assessed by macroscopic and histologic observation and by use of an ultrasonic system. The ultrasonic acoustic stiffness, acoustic surface irregularity, and acoustic thickness of the implanted cartilage were examined and compared with normal intact cartilage.

RESULTS

The gross appearance of the implanted cartilage was glossy, maintained good surface smoothness, and survived well throughout the observation period. The cartilage recovered histologic features of hyaline cartilage. The acoustic stiffness decreased up to 12 weeks and then increased at 24 and 52 weeks after surgery. The acoustic stiffness at 8 or 12 weeks was significantly lower (acoustically softer) than that of control cartilage (P < .001). The acoustic stiffness at 52 weeks was equal to that of the control. The difference in acoustic surface irregularity was not significant. The acoustic thickness at 8 weeks was higher (acoustically thicker) than that of the control (P < .01).

CONCLUSIONS

Although the reason acoustically soft cartilage in plugs becomes acoustically stiff and whether the histology of the implanted cartilage had recovered completely remain unclear, the acoustic stiffness recovered to normal control values by 52 weeks postoperatively.

CLINICAL RELEVANCE

Postoperative care for up to 12 weeks should be taken after autologous osteochondral transplantation.

Maturation-dependent change and regional variations in acoustic stiffness of rabbit articular cartilage: an examination of the superficial collagen-rich zone of cartilage

OBJECTIVE

The purpose of the study was to investigate maturation-dependent changes of acoustic (ultrasound) stiffness and other ultrasound features of articular cartilage in healthy rabbit knees.

METHODS

Five groups of rabbits of various ages (3 weeks, 8 weeks, 6 months, 1 year, 2.5 years) consisting of five rabbits per group were examined. Signal intensity (index of stiffness), signal duration (index of surface irregularity) and interval between signals (index of thickness) of the ultrasound reflection from articular cartilage were examined at four sites: posterior lateral femoral condyle, posterior medial femoral condyle, lateral tibial plateau, and medial tibial plateau. The sites were observed macroscopically and microscopically with a light microscope and a polarized light microscope.

RESULTS

At the lateral and medial condyles and the lateral tibial plateau, signal intensity was least in 3-week-old specimens. The intensity increased until 6 months or 1 year of age. At these sites, the signal durations and intervals between signals were least at the ages of 6 months or 1 year. At the medial tibial plateau, the intensity was the least at 2.5 years of age and the interval between signals was least at 3 weeks of age; there was no effect of age on signal duration. Cartilage surfaces of all specimens were smooth and no degenerative changes were macroscopically or microscopically evident. The surface brightness of cartilage under the polarized light microscope was consistent with signal intensity values.

CONCLUSIONS

The response of articular cartilage to ultrasound was maturation-dependent. Acoustic properties differed from mechanical stiffness properties, which were determined using indentation. Ultrasound may detect properties of the surface collagen of the articular cartilage.