Near-infrared (NIR) spectroscopy. A new method for arthroscopic evaluation of low grade degenerated cartilage lesions. Results of a pilot study

Visible and Near-Infrared Spectroscopy Enables Differentiation of Normal and Early Osteoarthritic Human Knee Joint Articular Cartilage

Osteoarthritis degenerates cartilage and impairs joint function. Early intervention opportunities are missed as current diagnostic methods are insensitive to early tissue degeneration. We investigated the capability of visible light-near-infrared spectroscopy (Vis-NIRS) to differentiate normal human cartilage from early osteoarthritic one. Vis-NIRS spectra, biomechanical properties and the state of osteoarthritis (OARSI grade) were quantified from osteochondral samples harvested from different anatomical sites of human cadaver knees. Two support vector machines (SVM) classifiers were developed based on the Vis-NIRS spectra and OARSI scores. The first classifier was designed to distinguish normal (OARSI: 0-1) from general osteoarthritic cartilage (OARSI: 2-5) to check the general suitability of the approach yielding an average accuracy of 75% (AUC = 0.77). Then, the second classifier was designed to distinguish normal from early osteoarthritic cartilage (OARSI: 2-3) yielding an average accuracy of 71% (AUC = 0.73). Important wavelength regions for differentiating normal from early osteoarthritic cartilage were related to collagen organization (wavelength region: 400-600 nm), collagen content (1000-1300 nm) and proteoglycan content (1600-1850 nm). The findings suggest that Vis-NIRS allows objective differentiation of normal and early osteoarthritic tissue, e.g., during arthroscopic repair surgeries.

Nondestructive Evaluation of Mechanical and Histological Properties of the Human Aorta With Near-Infrared Spectroscopy

INTRODUCTION

Ascending aortic dilatation is a well-known risk factor for aortic rupture. Indications for aortic replacement in its dilatation concomitant to other open-heart surgery exist; however, cut-off values based solely on aortic diameter may fail to identify patients with weakened aortic tissue. We introduce near-infrared spectroscopy (NIRS) as a diagnostic tool to nondestructively evaluate the structural and compositional properties of the human ascending aorta during open-heart surgeries. During open-heart surgery, NIRS could provide information regarding tissue viability in situ and thus contribute to the decision of optimal surgical repair.

MATERIALS AND METHODS

Samples were collected from patients with ascending aortic aneurysm (n = 23) undergoing elective aortic reconstruction surgery and from healthy subjects (n = 4). The samples were subjected to spectroscopic measurements, biomechanical testing, and histological analysis. The relationship between the near-infrared spectra and biomechanical and histological properties was investigated by adapting partial least squares regression.

RESULTS

Moderate prediction performance was achieved with biomechanical properties (r = 0.681, normalized root-mean-square error of cross-validation = 17.9%) and histological properties (r = 0.602, normalized root-mean-square error of cross-validation = 22.2%). Especially the performance with parameters describing the aorta's ultimate strength, for example, failure strain (r = 0.658), and elasticity (phase difference, r = 0.875) were promising and could, therefore, provide quantitative information on the rupture sensitivity of the aorta. For the estimation of histological properties, the results with α-smooth muscle actin (r = 0.581), elastin density (r = 0.973), mucoid extracellular matrix accumulation(r = 0.708), and media thickness (r = 0.866) were promising.

CONCLUSIONS

NIRS could be a potential technique for in situ evaluation of biomechanical and histological properties of human aorta and therefore useful in patient-specific treatment planning.

Brillouin-Raman micro-spectroscopy and machine learning techniques to classify osteoarthritic lesions in the human articular cartilage

In this study, Brillouin and Raman micro-Spectroscopy (BRamS) and Machine Learning were used to set-up a new diagnostic tool for Osteoarthritis (OA), potentially extendible to other musculoskeletal diseases. OA is a degenerative pathology, causing the onset of chronic pain due to cartilage disruption. Despite this, it is often diagnosed late and the radiological assessment during the routine examination may fail to recognize the threshold beyond which pharmacological treatment is no longer sufficient and prosthetic replacement is required. Here, femoral head resections of OA-affected patients were analyzed by BRamS, looking for distinctive mechanical and chemical markers of the progressive degeneration degree, and the result was compared to standard assignment via histological staining. The procedure was optimized for diagnostic prediction by using a machine learning algorithm and reducing the time required for measurements, paving the way for possible future in vivo characterization of the articular surface through endoscopic probes during arthroscopy.

In Situ Assessment of Porcine Osteochondral Repair Tissue in the Visible-Near Infrared Spectral Region

Standard assessment of cartilage repair progression by visual arthroscopy can be subjective and may result in suboptimal evaluation. Visible-near infrared (Vis-NIR) fiber optic spectroscopy of joint tissues, including articular cartilage and subchondral bone, provides an objective approach for quantitative assessment of tissue composition. Here, we applied this technique in the 350-2,500 nm spectral region to identify spectral markers of osteochondral tissue during repair with the overarching goal of developing a new approach to monitor repair of cartilage defects in vivo. Full thickness chondral defects were created in Yucatan minipigs using a 5-mm biopsy punch, and microfracture (MFx) was performed as a standard technique to facilitate repair. Tissues were evaluated at 1 month (in adult pigs) and 3 months (in juvenile pigs) post-surgery by spectroscopy and histology. After euthanasia, Vis-NIR spectra were collected in situ from the defect region. Additional spectroscopy experiments were carried out in vitro to aid in spectral interpretation. Osteochondral tissues were dissected from the joint and evaluated using the conventional International Cartilage Repair Society (ICRS) II histological scoring system, which showed lower scores for the 1-month than the 3-month repair tissues. In the visible spectral region, hemoglobin absorbances at 540 and 570 nm were significantly higher in spectra from 1-month repair tissue than 3-month repair tissue, indicating a reduction of blood in the more mature repair tissue. In the NIR region, we observed qualitative differences between the two groups in spectra taken from the defect, but differences did not reach significance. Furthermore, spectral data also indicated that the hydrated environment of the joint tissue may interfere with evaluation of tissue water absorbances in the NIR region. Together, these data provide support for further investigation of the visible spectral region for assessment of longitudinal repair of cartilage defects, which would enable assessment during routine arthroscopy, particularly in a hydrated environment.

Near-Infrared Spectroscopy Enables Arthroscopic Histologic Grading of Human Knee Articular Cartilage

Purpose

To develop the means to estimate cartilage histologic grades and proteoglycan content in ex vivo arthroscopy using near-infrared spectroscopy (NIRS).

Methods

In this experimental study, arthroscopic NIR spectral measurements were performed on both knees of 9 human cadavers, followed by osteochondral block extraction and in vitro measurements: reacquisition of spectra and reference measurements (proteoglycan content, and three histologic scores). A hybrid model, combining principal component analysis and linear mixed-effects model (PCA-LME), was trained for each reference to investigate its relationship with in vitro NIR spectra. The performance of the PCA-LME model was validated with ex vivo spectra before and after the exclusion of outlying spectra. Model performance was evaluated based on Spearman rank correlation (ρ) and root-mean-square error (RMSE).

Results

The PCA-LME models performed well (independent test: average ρ = 0.668, RMSE = 0.892, P < .001) in the prediction of the reference measurements based on in vitro data. The performance on ex vivo arthroscopic data was poorer but improved substantially after outlier exclusion (independent test: average ρ = 0.462 to 0.614, RMSE = 1.078 to 0.950, P = .019 to .008).

Conclusions

NIRS is capable of nondestructive evaluation of cartilage integrity (i.e., histologic scores and proteoglycan content) under similar conditions as in clinical arthroscopy.

Clinical Relevance

There are clear clinical benefits to the accurate assessment of cartilage lesions in arthroscopy. Visual grading is the current standard of care. However, optical techniques, such as NIRS, may provide a more objective assessment of cartilage damage.

Assessment of Ligament Viscoelastic Properties Using Raman Spectroscopy

Injuries to the ligaments of the knee commonly impact vulnerable and physically active individuals. These injuries can lead to the development of degenerative diseases such as post-traumatic osteoarthritis (PTOA). Non-invasive optical modalities, such as infrared and Raman spectroscopy, provide means for quantitative evaluation of knee joint tissues and have been proposed as potential quantitative diagnostic tools for arthroscopy. In this study, we evaluate Raman spectroscopy as a viable tool for estimating functional properties of collateral ligaments. Artificial trauma was induced by anterior cruciate ligament transection (ACLT) in the left or right knee joint of skeletally mature New Zealand rabbits. The corresponding contralateral (CL) samples were extracted from healthy unoperated joints along with a separate group of control (CNTRL) animals. The rabbits were sacrificed at 8 weeks after ACLT. The ligaments were then harvested and measured using Raman spectroscopy. A uniaxial tensile stress-relaxation testing protocol was adopted for determining several biomechanical properties of the samples. Partial least squares (PLS) regression models were then employed to correlate the spectral data with the biomechanical properties. Results show that the capacity of Raman spectroscopy for estimating the biomechanical properties of the ligament samples varies depending on the target property, with prediction error ranging from 15.78% for tissue cross-sectional area to 30.39% for stiffness. The hysteresis under cyclic loading at 2 Hz (RMSE = 6.22%, Normalized RMSE = 22.24%) can be accurately estimated from the Raman data which describes the viscous damping properties of the tissue. We conclude that Raman spectroscopy has the potential for non-destructively estimating ligament biomechanical properties in health and disease, thus enhancing the diagnostic value of optical arthroscopic evaluations of ligament integrity.

Near infrared spectroscopic evaluation of biochemical and crimp properties of knee joint ligaments and patellar tendon

Knee ligaments and tendons play an important role in stabilizing and controlling the motions of the knee. Injuries to the ligaments can lead to abnormal mechanical loading of the other supporting tissues (e.g., cartilage and meniscus) and even osteoarthritis. While the condition of knee ligaments can be examined during arthroscopic repair procedures, the arthroscopic evaluation suffers from subjectivity and poor repeatability. Near infrared spectroscopy (NIRS) is capable of non-destructively quantifying the composition and structure of collagen-rich connective tissues, such as articular cartilage and meniscus. Despite the similarities, NIRS-based evaluation of ligament composition has not been previously attempted. In this study, ligaments and patellar tendon of ten bovine stifle joints were measured with NIRS, followed by chemical and histological reference analysis. The relationship between the reference properties of the tissue and NIR spectra was investigated using partial least squares regression. NIRS was found to be sensitive towards the water (R2_CV = .65) and collagen (R2_CV = .57) contents, while elastin, proteoglycans, and the internal crimp structure remained undetectable. As collagen largely determines the mechanical response of ligaments, we conclude that NIRS demonstrates potential for quantitative evaluation of knee ligaments.

Intraoperative hyperspectral imaging (HSI) as a new diagnostic tool for the detection of cartilage degeneration

To investigate, whether hyperspectral imaging (HSI) is able to reliably differentiate between healthy and damaged cartilage tissue. A prospective diagnostic study was performed including 21 patients undergoing open knee surgery. HSI data were acquired during surgery, and the joint surface's cartilage was assessed according to the ICRS cartilage injury score. The HSI system records light spectra from 500 to 1000 nm and generates several parameters including tissue water index (TWI) and the absorbance at 960 nm and 540 nm. Receiver operating characteristic curves were calculated to assess test parameters for threshold values of HSI. Areas with a cartilage defect ICRS grade ≥ 3 showed a significantly lower TWI (p = 0.026) and higher values for 540 nm (p < 0.001). No difference was seen for 960 nm (p = 0.244). For a threshold of 540 nm > 0.74, a cartilage defect ICRS grade ≥ 3 could be detected with a sensitivity of 0.81 and a specificity of 0.81. TWI was not suitable for cartilage defect detection. HSI can provide reliable parameters to differentiate healthy and damaged cartilage. Our data clearly suggest that the difference in absorbance at 540 nm would be the best parameter to achieve accurate identification of damaged cartilage.

Articular cartilage optical properties in the near-infrared (NIR) spectral range vary with depth and tissue integrity

Optical properties of biological tissues in the NIR spectral range have demonstrated significant potential for in vivo diagnostic applications and are critical parameters for modelling light interaction in biological tissues. This study aims to investigate the optical properties of articular cartilage as a function of tissue depth and integrity. The results suggest consistent wavelength-dependent variation in optical properties between cartilage depth-wise zones, as well as between healthy and degenerated tissue. Also, statistically significant differences (p<0.05) in both optical properties were observed between the different cartilage depth-wise zones and as a result of tissue degeneration. When taken into account, the outcome of this study could enable accurate modelling of light interaction in cartilage matrix and could provide useful diagnostic information on cartilage integrity.

Characterization of connective tissues using near-infrared spectroscopy and imaging

Near-infrared (NIR) spectroscopy is a powerful analytical method for rapid, non-destructive and label-free assessment of biological materials. Compared to mid-infrared spectroscopy, NIR spectroscopy excels in penetration depth, allowing intact biological tissue assessment, albeit at the cost of reduced molecular specificity. Furthermore, it is relatively safe compared to Raman spectroscopy, with no risk of laser-induced photothermal damage. A typical NIR spectroscopy workflow for biological tissue characterization involves sample preparation, spectral acquisition, pre-processing and analysis. The resulting spectrum embeds intrinsic information on the tissue's biomolecular, structural and functional properties. Here we demonstrate the analytical power of NIR spectroscopy for exploratory and diagnostic applications by providing instructions for acquiring NIR spectra, maps and images in biological tissues. By adapting and extending this protocol from the demonstrated application in connective tissues to other biological tissues, we expect that a typical NIR spectroscopic study can be performed by a non-specialist user to characterize biological tissues in basic research or clinical settings. We also describe how to use this protocol for exploratory study on connective tissues, including differentiating among ligament types, non-destructively monitoring changes in matrix formation during engineered cartilage development, mapping articular cartilage proteoglycan content across bovine patella and spectral imaging across the depth-wise zones of articular cartilage and subchondral bone. Depending on acquisition mode and experiment objectives, a typical exploratory study can be completed within 6 h, including sample preparation and data analysis.

Near-Infrared Spectroscopy for Mapping of Human Meniscus Biochemical Constituents

Degenerative changes in meniscus are diagnosed during surgery by means of mechanical testing and visual evaluation. This method is qualitative and highly subjective, providing very little information on the internal state of the meniscus. Thus, there is need for novel quantitative methods that can support decision-making during arthroscopic surgery. In this study, we investigate the potential of near-infrared spectroscopy (NIRS) for mapping the biochemical constituents of human meniscus, including water, uronic acid, and hydroxyproline contents. Partial least squares regression models were developed using data from 115 measurement locations of menisci samples extracted from 7 cadavers and 11 surgery patient donors. Model performance was evaluated using an independent test set consisting of 55 measurement locations within a meniscus sample obtained from a separate cadaver. The correlation coefficient of calibration (ρ_training), test set (ρ_test), and root-mean-squared error of test set (RMSEP) were as follows: water (ρ_training = 0.61, ρ_test = 0.39, and RMSEP = 2.27 percentage points), uronic acid (ρ_training = 0.68, ρ_test = 0.69, and RMSEP = 6.09 basis points), and hydroxyproline (ρ_training = 0.84, ρ_test = 0.58, and error = 0.54 percentage points). In conclusion, the results suggest that NIRS could enable rapid arthroscopic mapping of changes in meniscus biochemical constituents, thus providing means for quantitative assessment of meniscus degeneration.

Non-Destructive Spectroscopic Assessment of High and Low Weight Bearing Articular Cartilage Correlates with Mechanical Properties

OBJECTIVE

Autologous articular cartilage (AC) harvested for repair procedures of high weight bearing (HWB) regions of the femoral condyles is typically obtained from low weight bearing (LWB) regions, in part due to the lack of non-destructive techniques for cartilage composition assessment. Here, we demonstrate that infrared fiber optic spectroscopy can be used to non-destructively evaluate variations in compositional and mechanical properties of AC across LWB and HWB regions.

DESIGN

AC plugs (N = 72) were harvested from the patellofemoral groove of juvenile bovine stifle joints, a LWB region, and femoral condyles, a HWB region. Near-infrared (NIR) and mid-infrared (MIR) fiber optic spectra were collected from plugs, and indentation tests were performed to determine the short-term and equilibrium moduli, followed by gravimetric water and biochemical analysis.

RESULTS

LWB tissues had a significantly greater amount of water determined by NIR and gravimetric assay. The moduli generally increased in tissues from the patellofemoral groove to the condyles, with HWB condyle cartilage having significantly higher moduli. A greater amount of proteoglycan content was also found in HWB tissues, but no differences in collagen content. In addition, NIR-determined water correlated with short-term modulus and proteoglycan content (R = -0.40 and -0.31, respectively), and a multivariate model with NIR data was able to predict short-term modulus within 15% error.

CONCLUSIONS

The properties of tissues from LWB regions differ from HWB tissues and can be determined non-destructively by infrared fiber optic spectroscopy. Clinicians may be able to use this modality to assess AC prior to harvesting osteochondral grafts for focal defect repair.

Arthroscopic Determination of Cartilage Proteoglycan Content and Collagen Network Structure with Near-Infrared Spectroscopy

Conventional arthroscopic evaluation of articular cartilage is subjective and insufficient for assessing early compositional and structural changes during the progression of post-traumatic osteoarthritis. Therefore, in this study, arthroscopic near-infrared (NIR) spectroscopy is introduced, for the first time, for in vivo evaluation of articular cartilage thickness, proteoglycan (PG) content, and collagen orientation angle. NIR spectra were acquired in vivo and in vitro from equine cartilage adjacent to experimental cartilage repair sites. As reference, digital densitometry and polarized light microscopy were used to evaluate superficial and full-thickness PG content and collagen orientation angle. To relate NIR spectra and cartilage properties, ensemble neural networks, each with two different architectures, were trained and evaluated by using Spearman’s correlation analysis (ρ). The ensemble networks enabled accurate predictions for full-thickness reference properties (PG content: ρ_{in vitro, Val}= 0.691, ρ_{in vivo}= 0.676; collagen orientation angle: ρ_{in vitro, Val}= 0.626, ρ_{in vivo}= 0.574) from NIR spectral data. In addition, the networks enabled reliable prediction of PG content in superficial (25%) cartilage (ρ_{in vitro, Val}= 0.650, ρ_{in vivo}= 0.613) and cartilage thickness (ρ_{in vitro, Val}= 0.797, ρ_{in vivo}= 0.596). To conclude, NIR spectroscopy could enhance the detection of initial cartilage degeneration and thus enable demarcation of the boundary between healthy and compromised cartilage tissue during arthroscopic surgery.

Arthroscopic Evaluation of Knee Cartilage Using Optical Reflection Spectroscopy

Articular cartilage is critical for painless and low-friction range of motion; however, disruption of articular cartilage, particularly in the knee joint, is common. Treatment options are based on the size and depth of the chondral defect, as well as involvement of subchondral bone. The gold standard for evaluation of articular cartilage is with arthroscopy, but it is limited by its ability to objectively judge the depth and severity of chondral damage. Optical reflection spectroscopy has been introduced to objectively assess the thickness of cartilage. We present a technique to systematically evaluate the articular cartilage of the knee using BioOptico optical reflection spectroscopy (Arthrex) to better evaluate those with visible chondral and subchondral defects.

Near Infrared Spectroscopic Evaluation of Ligament and Tendon Biomechanical Properties

Knee ligaments and tendons are collagen-rich viscoelastic connective tissues that provide vital mechanical stabilization and support to the knee joint. Deterioration of ligaments has an adverse effect on the health of the knee and can eventually lead to ligament rupture and osteoarthritis. In this study, the feasibility of near infrared spectroscopy (NIRS) was, for the first time, tested for evaluation of ligament and tendon mechanical properties by performing measurements on bovine stifle joint ligament (N = 40) and patellar tendon (N = 10) samples. The mechanical properties of the samples were determined using a uniaxial tensile testing protocol. Partial least squares regression models were then developed to determine if morphological, viscoelastic, and quasi-static properties of the samples could be predicted from the NIR spectra. Best performance of NIRS in predicting mechanical properties was observed for toughness at yield point (median [Formula: see text], median normalized [Formula: see text]), toughness at failure point (median [Formula: see text], median normalized [Formula: see text]), and the ultimate strength of the ligament/tendon (median [Formula: see text], median normalized [Formula: see text]). Thus, we show that NIRS is capable of estimating ligament and tendon biomechanical properties, especially in parameters related to tissue failure. We believe this method could substantially enhance the currently limited arthroscopic evaluation of ligaments and tendons.

Near-Infrared Spectroscopy Predicts Compositional and Mechanical Properties of Hyaluronic Acid-Based Engineered Cartilage Constructs

Hyaluronic acid (HA) has been widely used for cartilage tissue engineering applications. However, the optimal time point to harvest HA-based engineered constructs for cartilage repair is still under investigation. In this study, we investigated the ability of a nondestructive modality, near-infrared spectroscopic (NIR) analysis, to predict compositional and mechanical properties of HA-based engineered cartilage constructs. NIR spectral data were collected from control, unseeded constructs, and twice per week by fiber optic from constructs seeded with chondrocytes during their development over an 8-week period. Constructs were harvested at 2, 4, 6, and 8 weeks, collagen and sulfated glycosaminoglycan content measured using biochemical assays, and the mechanical properties of the constructs evaluated using unconfined compression tests. NIR absorbances associated with the scaffold material, water, and engineered cartilage matrix, were identified. The NIR-determined matrix absorbance plateaued after 4 weeks of culture, which was in agreement with the biochemical assay results. Similarly, the mechanical properties of the constructs also plateaued at 4 weeks. A multivariate partial least square model based on NIR spectral input was developed to predict the moduli of the constructs, which resulted in a prediction error of 10% and R value of 0.88 for predicted versus actual values of dynamic modulus. Furthermore, the maximum increase in moduli was calculated from the first derivative of the curve fit of NIR-predicted and actual moduli values over time, and both occurred at ∼2 weeks. Collectively, these data suggest that NIR spectral data analysis could be an alternative to destructive biochemical and mechanical methods for evaluation of HA-based engineered cartilage construct properties.

Mechanisms of Osteoarthritic Pain. Studies in Humans and Experimental Models

Pain due to osteoarthritis (OA) is one of the most frequent causes of chronic pain. However, the mechanisms of OA pain are poorly understood. This review addresses the mechanisms which are thought to be involved in OA pain, derived from studies on pain mechanisms in humans and in experimental models of OA. Three areas will be considered, namely local processes in the joint associated with OA pain, neuronal mechanisms involved in OA pain, and general factors which influence OA pain. Except the cartilage all structures of the joints are innervated by nociceptors. Although the hallmark of OA is the degradation of the cartilage, OA joints show multiple structural alterations of cartilage, bone and synovial tissue. In particular synovitis and bone marrow lesions have been proposed to determine OA pain whereas the contribution of the other pathologies to pain generation has been studied less. Concerning the peripheral neuronal mechanisms of OA pain, peripheral nociceptive sensitization was shown, and neuropathic mechanisms may be involved at some stages. Structural changes of joint innervation such as local loss and/or sprouting of nerve fibers were shown. In addition, central sensitization, reduction of descending inhibition, descending excitation and cortical atrophies were observed in OA. The combination of different neuronal mechanisms may define the particular pain phenotype in an OA patient. Among mediators involved in OA pain, nerve growth factor (NGF) is in the focus because antibodies against NGF significantly reduce OA pain. Several studies show that neutralization of interleukin-1β and TNF may reduce OA pain. Many patients with OA exhibit comorbidities such as obesity, low grade systemic inflammation and diabetes mellitus. These comorbidities can significantly influence the course of OA, and pain research just began to study the significance of such factors in pain generation. In addition, psychologic and socioeconomic factors may aggravate OA pain, and in some cases genetic factors influencing OA pain were found. Considering the local factors in the joint, the neuronal processes and the comorbidities, a better definition of OA pain phenotypes may become possible. Studies are under way in order to improve OA and OA pain monitoring.

Optimal Regression Method for Near-Infrared Spectroscopic Evaluation of Articular Cartilage

Near-infrared (NIR) spectroscopy has been successful in nondestructive assessment of biological tissue properties, such as stiffness of articular cartilage, and is proposed to be used in clinical arthroscopies. Near-infrared spectroscopic data include absorbance values from a broad wavelength region resulting in a large number of contributing factors. This broad spectrum includes information from potentially noisy variables, which may contribute to errors during regression analysis. We hypothesized that partial least squares regression (PLSR) is an optimal multivariate regression technique and requires application of variable selection methods to further improve the performance of NIR spectroscopy-based prediction of cartilage tissue properties, including instantaneous, equilibrium, and dynamic moduli and cartilage thickness. To test this hypothesis, we conducted for the first time a comparative analysis of multivariate regression techniques, which included principal component regression (PCR), PLSR, ridge regression, least absolute shrinkage and selection operator (Lasso), and least squares version of support vector machines (LS-SVM) on NIR spectral data of equine articular cartilage. Additionally, we evaluated the effect of variable selection methods, including Monte Carlo uninformative variable elimination (MC-UVE), competitive adaptive reweighted sampling (CARS), variable combination population analysis (VCPA), backward interval PLS (BiPLS), genetic algorithm (GA), and jackknife, on the performance of the optimal regression technique. The PLSR technique was found as an optimal regression tool (R²_{Tissue thickness} = 75.6%, R²_{Dynamic modulus} = 64.9%) for cartilage NIR data; variable selection methods simplified the prediction models enabling the use of lesser number of regression components. However, the improvements in model performance with variable selection methods were found to be statistically insignificant. Thus, the PLSR technique is recommended as the regression tool for multivariate analysis for prediction of articular cartilage properties from its NIR spectra.

[Chondral and osteochondral defects : Representation by imaging methods]

Morphological imaging of cartilage at high resolution allows the differentiation of chondral and osteochondral lesions. Nowadays, magnetic resonance imaging is the principal diagnostic tool in the assessment of cartilage structure and composition. Conventional radiography, computed tomography, ultrasound or optical coherence tomography are adjunct diagnostic modalities in the assessment of cartilage pathologies. The present article discusses the up-to-date diagnostic practice of cartilage imaging in terms of its scientific basis and current clinical status, requirements, techniques and image interpretation. Innovations in the field such as functional MRI are discussed as well due to their mid- to long-term clinical perspective.

Characterization of Articular Cartilage Recovery and Its Correlation with Optical Response in the Near-Infrared Spectral Range

OBJECTIVES

In this study, we examine the capacity of a new parameter, based on the recovery response of articular cartilage, to distinguish between healthy and damaged tissues. We also investigate whether or not this new parameter correlates with the near-infrared (NIR) optical response of articular cartilage.

DESIGN

Normal and artificially degenerated (proteoglycan-depleted) bovine cartilage samples were nondestructively probed using NIR spectroscopy. Subsequently they were subjected to a load and unloading protocol, and the recovery response was logged during unloading. The recovery parameter, elastic rebound ( E_R), is based on the strain energy released as the samples underwent instantaneous elastic recovery.

RESULTS

Our results reveal positive relationship between the rebound parameter and cartilage proteoglycan content (normal samples: 2.20 ± 0.10 N mm; proteoglycan-depleted samples: 0.50 ± 0.04 N mm for 1 hour of enzymatic treatment and 0.13 ± 0.02 N mm for 4 hours of enzymatic treatment). In addition, multivariate analysis using partial least squares regression was employed to investigate the relationship between E_R and NIR spectral data. The results reveal significantly high correlation ( R²_cal = 98.35% and R²_val = 79.87%; P < 0.0001), with relatively low error (14%), between the recovery and optical response of cartilage in the combined NIR regions 5,450 to 6,100 cm^-1 and 7,500 to 12,500 cm^-1.

CONCLUSION

We conclude that E_R can indicate the mechanical condition and state of health of articular cartilage. The correlation of E_R with cartilage optical response in the NIR range could facilitate real-time evaluation of the tissue's integrity during arthroscopic surgery and could also provide an important tool for cartilage assessment in tissue engineering and regeneration research.

Ultrasound palpation for fast in-situ quantification of articular cartilage stiffness, thickness and relaxation capacity

Most current cartilage testing devices require the preparation of excised samples and therefore do not allow intra-operative application for diagnostic purposes. The gold standard during open or arthroscopic surgery is still the subjective perception of manual palpation. This work presents a new diagnostic method of ultrasound palpation (USP) to acquire applied stress and strain data during manual palpation of articular cartilage. With the proposed method, we obtain cartilage thickness and stiffness. Moreover, repeated palpations allow the quantification of relaxation effects. USP measurements on elastomer phantoms demonstrated very good repeatability for both, stage-guided (97.2%) and handheld (96.0%) applications. The USP measurements were compared with conventional indentation experiments and revealed very good agreement on elastomer phantoms ([Formula: see text]) and good agreement on porcine cartilage samples ([Formula: see text]). Artificially degenerated cartilage samples showed reduced stiffness, weak capacity to relax after palpation and an increase of stiffness of approximately 50% with each single palpation. Intact cartilage was measured by USP directly at the patella (in situ) and after excision and removal of the subchondral bone (ex situ), leading to stiffness values of [Formula: see text] and [Formula: see text] ([Formula: see text]), respectively. The results demonstrate the potential of the USP system for cartilage testing, its sensitivity to degenerative changes and as a method for quantifying relaxation processes by means of repeated palpations. Furthermore, the differences in the results of in-situ and ex-situ measurements are of general interest, since such comparison has not been reported previously. We point out the limited comparability of ex-situ cartilage with its in-situ biomechanical behavior.

Near Infrared Spectroscopic Mapping of Functional Properties of Equine Articular Cartilage

Mechanical properties of articular cartilage are vital for normal joint function, which can be severely compromised by injuries. Quantitative characterization of cartilage injuries, and evaluation of cartilage stiffness and thickness by means of conventional arthroscopy is poorly reproducible or impossible. In this study, we demonstrate the potential of near infrared (NIR) spectroscopy for predicting and mapping the functional properties of equine articular cartilage at and around lesion sites. Lesion and non-lesion areas of interests (AI, N = 44) of equine joints (N = 5) were divided into grids and NIR spectra were acquired from all grid points (N = 869). Partial least squares (PLS) regression was used to investigate the correlation between the absorbance spectra and thickness, equilibrium modulus, dynamic modulus, and instantaneous modulus at the grid points of 41 AIs. Subsequently, the developed PLS models were validated with spectral data from the grid points of 3 independent AIs. Significant correlations were obtained between spectral data and cartilage thickness (R ² = 70.3%, p < 0.0001), equilibrium modulus (R ² = 67.8%, p < 0.0001), dynamic modulus (R ² = 68.9%, p < 0.0001) and instantaneous modulus (R ² = 41.8%, p < 0.0001). Relatively low errors were observed in the predicted thickness (5.9%) and instantaneous modulus (9.0%) maps. Thus, if well implemented, NIR spectroscopy could enable arthroscopic evaluation and mapping of cartilage functional properties at and around lesion sites.

Near infrared spectroscopic imaging assessment of cartilage composition: Validation with mid infrared imaging spectroscopy

Disease or injury to articular cartilage results in loss of extracellular matrix components which can lead to the development of osteoarthritis (OA). To better understand the process of disease development, there is a need for evaluation of changes in cartilage composition without the requirement of extensive sample preparation. Near infrared (NIR) spectroscopy is a chemical investigative technique based on molecular vibrations that is increasingly used as an assessment tool for studying cartilage composition. However, the assignment of specific molecular vibrations to absorbance bands in the NIR spectrum of cartilage, which arise from overtones and combinations of primary absorbances in the mid infrared (MIR) spectral region, has been challenging. In contrast, MIR spectroscopic assessment of cartilage is well-established, with many studies validating the assignment of specific bands present in MIR spectra to specific molecular vibrations. In the current study, NIR imaging spectroscopic data were obtained for compositional analysis of tissues that served as an in vitro model of OA. MIR spectroscopic data obtained from the identical tissue regions were used as the gold-standard for collagen and proteoglycan (PG) content. MIR spectroscopy in transmittance mode typically requires a much shorter pathlength through the sample (≤10 microns thick) compared to NIR spectroscopy (millimeters). Thus, this study first addressed the linearity of small absorbance bands in the MIR region with increasing tissue thickness, suitable for obtaining a signal in both the MIR and NIR regions. It was found that the linearity of specific, small MIR absorbance bands attributable to the collagen and PG components of cartilage (at 1336 and 856 cm(-1), respectively) are maintained through a thickness of 60 μm, which was also suitable for NIR data collection. MIR and NIR spectral data were then collected from 60 μm thick samples of cartilage degraded with chondroitinase ABC as a model of OA. Partial least squares (PLS) regression using NIR spectra as input predicted the MIR-determined compositional parameters of PG/collagen within 6% of actual values. These results indicate that NIR spectral data can be used to assess molecular changes that occur with cartilage degradation, and further, the data provide a foundation for future clinical studies where NIR fiber optic probes can be used to assess the progression of cartilage degradation.

Nondestructive Techniques to Evaluate the Characteristics and Development of Engineered Cartilage

In this review, methods for evaluating the properties of tissue engineered (TE) cartilage are described. Many of these have been developed for evaluating properties of native and osteoarthritic articular cartilage. However, with the increasing interest in engineering cartilage, specialized methods are needed for nondestructive evaluation of tissue while it is developing and after it is implanted. Such methods are needed, in part, due to the large inter- and intra-donor variability in the performance of the cellular component of the tissue, which remains a barrier to delivering reliable TE cartilage for implantation. Using conventional destructive tests, such variability makes it near-impossible to predict the timing and outcome of the tissue engineering process at the level of a specific piece of engineered tissue and also makes it difficult to assess the impact of changing tissue engineering regimens. While it is clear that the true test of engineered cartilage is its performance after it is implanted, correlation of pre and post implantation properties determined non-destructively in vitro and/or in vivo with performance should lead to predictive methods to improve quality-control and to minimize the chances of implanting inferior tissue.

Optical spectroscopic determination of human meniscus composition

This study investigates the correlation between the composition of human meniscus and its absorption spectrum in the visible (VIS) and near infrared (NIR) spectral range. Meniscus samples (n = 24) were obtained from nonarthritic knees of human cadavers with no history of joint diseases. Specimens (n = 72) were obtained from three distinct sections of the meniscus, namely; anterior, center, posterior. Absorption spectra were acquired from each specimen in the VIS and NIR spectral range (400-1,100 nm). Following spectroscopic probing, the specimens were subjected to biochemical analyses to determine the matrix composition, that is water, hydroxyproline, and uronic acid contents. Multivariate analytical techniques, including principal component analysis (PCA) and partial least squares (PLS) regression, were then used to investigate the correlation between the matrix composition and it spectral response. Our results indicate that the optical absorption of meniscus matrix is related to its composition, and this relationship is optimal in the NIR spectral range (750-1,100 nm). High correlations (R(2) (uronic)  = 86.9%, R(2) (water)  = 83.8%, R(2) (hydroxyproline)  = 81.7%, p < 0.0001) were obtained between the spectral predicted and measured meniscus composition, thus suggesting that spectral data in the NIR range can be utilized for estimating the matrix composition of human meniscus. In conclusion, optical spectroscopy, particularly in the NIR spectral range, is a potential method for evaluating the composition of human meniscus. This presents a promising technique for rapid and nondestructive evaluation of meniscus integrity in real-time during arthroscopic surgery.

Wavelength-dependent penetration depth of near infrared radiation into cartilage

Articular cartilage is a hyaline cartilage that lines the subchondral bone in the diarthrodial joints. Near infrared (NIR) spectroscopy is emerging as a nondestructive modality for the evaluation of cartilage pathology; however, studies regarding the depth of penetration of NIR radiation into cartilage are lacking. The average thickness of human cartilage is about 1-3 mm, and it becomes even thinner as OA progresses. To ensure that spectral data collected is restricted to the tissue of interest, i.e. cartilage in this case, and not from the underlying subchondral bone, it is necessary to determine the depth of penetration of NIR radiation in different wavelength (frequency) regions. In the current study, we establish how the depth of penetration varies throughout the NIR frequency range (4000-10 000 cm(-1)). NIR spectra were collected from cartilage samples of different thicknesses (0.5 mm to 5 mm) with and without polystyrene placed underneath. A separate NIR spectrum of polystyrene was collected as a reference. It was found that the depth of penetration varied from ∼1 mm to 2 mm in the 4000-5100 cm(-1) range, ∼3 mm in the 5100-7000 cm(-1) range, and ∼5 mm in the 7000-9000 cm(-1) frequency range. These findings suggest that the best NIR region to evaluate cartilage with no subchondral bone contribution is in the range of 4000-7000 cm(-1).

Optical absorption spectra of human articular cartilage correlate with biomechanical properties, histological score and biochemical composition

This study investigates the relationship between the optical response of human articular cartilage in the visible (VIS) and near infrared (NIR) spectral range and its matrix properties.Full-thickness osteochondral cores (dia. = 16 mm, n = 50) were extracted from human cadaver knees (N = 13) at four anatomical locations and divided into quadrants. Absorption spectra were acquired in the spectral range 400-1100 nm from one quadrant. Reference biomechanical, biochemical composition, histological, and cartilage thickness measurements were obtained from two other quadrants. A multivariate statistical technique based on partial least squares (PLS) regression was then employed to investigate the correlation between the absorption spectra and tissue properties.Our results demonstrate that cartilage optical response correlates with its function, composition and morphology, as indicated by the significant relationship between spectral predicted and measured biomechanical (79.0%  ⩽  R(2)  ⩽  80.3%, p  <  0.0001), biochemical (65.1%  ⩽  R(2)  ⩽  81.0%, p  < 0.0001), and histological scores ([Formula: see text] = 83.3%, p  < 0.0001) properties. Significant correlation was also obtained with the non-calcified cartilage thickness ([Formula: see text] = 83.2%, p  <  0.0001).We conclude that optical absorption of human cartilage in the VIS and NIR spectral range correlates with the overall tissue properties, thus providing knowledge that could facilitate development of systems for rapid assessment of tissue integrity.

Development of an arthroscopic ultrasound probe for assessment of articular cartilage degeneration

Quantitative assessment of articular cartilage is important for the early diagnosis of osteoarthritis, intra-operation joint tissue evaluation and judgment of repaired cartilage quality. This technique is also applicable to the cartilage if arthroscopic instrument embedding this technique can be developed. In this study, an arthroscopic water-jet ultrasound indentation probe was developed with the help of a small profile intra-articular ultrasound imaging (IAUS) catheter for the intra-articular measurement of cartilage condition. The probe can provide measurement of morphological, acoustical and mechanical properties of articular cartilage. Preliminary tests were conducted on 10 intact porcine knees with the guide of arthroscopy for the evaluation of cartilage degeneration, which was induced by trypsin digestion. Results showed the cartilage stiffness decreased significantly after the digestion (p < 0.001) with the measurement conducted by the developed probe. In summary, an arthroscopic ultrasound probe has been successfully developed and its utility in detecting the cartilage degeneration was demonstrated in this study. Future work includes the improvement of the probe design and studies on measurement of animal or human samples in vivo.

Spatial mapping of proteoglycan content in articular cartilage using near-infrared (NIR) spectroscopy

Diagnosis of articular cartilage pathology in the early disease stages using current clinical diagnostic imaging modalities is challenging, particularly because there is often no visible change in the tissue surface and matrix content, such as proteoglycans (PG). In this study, we propose the use of near infrared (NIR) spectroscopy to spatially map PG content in articular cartilage. The relationship between NIR spectra and reference data (PG content) obtained from histology of normal and artificially induced PG-depleted cartilage samples was investigated using principal component (PC) and partial least squares (PLS) regression analyses. Significant correlation was obtained between both data (R(2) = 91.40%, p<0.0001). The resulting correlation was used to predict PG content from spectra acquired from whole joint sample, this was then employed to spatially map this component of cartilage across the intact sample. We conclude that NIR spectroscopy is a feasible tool for evaluating cartilage contents and mapping their distribution across mammalian joint.

Assessment of hyaline cartilage matrix composition using near infrared spectroscopy

Changes in the composition of the extracellular matrix (ECM) are characteristic of injury or disease in cartilage tissue. Various imaging modalities and biochemical techniques have been used to assess the changes in cartilage tissue but lack adequate sensitivity, or in the case of biochemical techniques, result in destruction of the sample. Fourier transform near infrared (FT-NIR) spectroscopy has shown promise for the study of cartilage composition. In the current study NIR spectroscopy was used to identify the contributions of individual components of cartilage in the NIR spectra by assessment of the major cartilage components, collagen and chondroitin sulfate, in pure component mixtures. The NIR spectra were obtained using homogenous pellets made by dilution with potassium bromide. A partial least squares (PLS) model was calculated to predict composition in bovine cartilage samples. Characteristic absorbance peaks between 4000 and 5000 cm(-1) could be attributed to components of cartilage, i.e. collagen and chondroitin sulfate. Prediction of the amount of collagen and chondroitin sulfate in tissues was possible within 8% (w/dw) of values obtained by gold standard biochemical assessment. These results support the use of NIR spectroscopy for in vitro and in vivo applications to assess matrix composition of cartilage tissues, especially when tissue destruction should be avoided.

The contribution of bone and cartilage to the near-infrared spectrum of osteochondral tissue

Near-infrared (NIR) spectroscopy has been used to assess hyaline cartilage quality in human and animal osteochondral tissues. However, due to the lack of NIR signal from bone phosphate and the relatively deep penetration depth of the radiation, the separate contributions of cartilage and bone to the spectral signatures have not been well defined. The objectives of the current study were (1) to improve the understanding of the contributions of bone and cartilage to NIR spectra acquired from osteochondral tissue and (2) to assess the ability of this nondestructive method to predict cartilage thickness and modified Mankin grade of human tibial plateau articular cartilage. Near-infrared spectra were acquired from samples of bovine bone and cartilage with varying thicknesses and from 22 tibial plateaus harvested from patients undergoing knee replacement surgery. The spectra were recorded from regions of the tibial plateaus with varying degrees of degradation, and the cartilage thickness and modified Mankin grade of these regions were assessed histologically. The spectra from bone and cartilage samples of known thicknesses were investigated to identify spectral regions that were distinct for these two tissues. Univariate and multivariate linear regression methods were used to correlate modified Mankin grade and cartilage thickness with NIR spectral changes. The ratio of the NIR absorbances associated with water at 5270 and 7085 cm(-1) was the best differentiator of cartilage and bone spectra. The NIR prediction models for thickness and Mankin grade calculated using partial least squares regression were more accurate than were univariate-based prediction models, with a root mean square errors of cross-validation of 0.42 mm (for thickness) and 1.3 (for modified Mankin grade). We conclude that NIR spectroscopy may be used to simultaneously assess articular cartilage thickness and modified Mankin grade, based in part on differences in spectral contributions from bone and cartilage.

Near infrared spectroscopic evaluation of water in hyaline cartilage

In diseased conditions of cartilage such as osteoarthritis, there is typically an increase in water content from the average normal of 60-85% to greater than 90%. As cartilage has very little capability for self-repair, methods of early detection of degeneration are required, and assessment of water could prove to be a useful diagnostic method. Current assessment methods are either destructive, time consuming, or have limited sensitivity. Here, we investigated the hypotheses that non-destructive near infrared spectroscopy (NIRS) of articular cartilage can be used to differentiate between free and bound water, and to quantitatively assess water content. The absorbances centered at 5200 and 6890 cm(-1) were attributed to a combination of free and bound water, and to free water only, respectively. The integrated areas of both absorbance bands were found to correlate linearly with the absolute water content (R = 0.87 and 0.86) and with percent water content (R = 0.97 and 0.96) of the tissue. Partial least square models were also successfully developed and were used to predict water content, and percent free water. These data demonstrate that NIRS can be utilized to quantitatively determine water content in articular cartilage, and may aid in early detection of degenerative tissue changes in a laboratory setting, and with additional validations, possibly in a clinical setting.

Manual khalifa therapy in patients with completely ruptured anterior cruciate ligament in the knee: first results from near-infrared spectroscopy

Background:

Manual Khalifa therapy has been practiced in Hallein, Austria, for more than 30 years; however, there are no scientific results available on the topic.

Aims:

The goal of the present study was to investigate possible acute effects of Khalifa therapy on regional oxygen saturation of knee tissues in patients with completely ruptured anterior cruciate ligament.

Materials and Methods:

We investigated 10 male patients (mean age ± standard deviation (SD) 35.9 ± 6.1 year) using a four-channel oximeter. The sensors were applied anterolaterally and anteromedially, beside the patella, on both the injured and the healthy (control) knee.

Results:

The results of the controlled study showed that values of oxygen saturation on the knee with the ruptured ligament were significantly increased (P < 0.001) immediately after Khalifa therapy, whereas the values on the control knee showed insignificant increases. Baselines values of the anterolateral side of the injured knee were significantly (P < 0.001) different from those of the anterolateral side of the control knee. The same effect was present on the anteromedial side; however, with a lower degree of significance (P < 0.05).

Conclusions:

Khalifa therapy was clinically successful in all 10 patients. Further, investigations and analyzes are necessary to explain the underlying mechanism.

Traumatic and degenerative cartilage lesions: arthroscopic differentiation using near-infrared spectroscopy (NIRS)

INTRODUCTION

Cartilage lesions or defects are the most common finding during knee arthroscopy. During arthroscopy, it is often difficult to differentiate between degenerative and traumatic cartilage lesions. The study aimed to determine the impact of near-infrared spectroscopy (NIRS) on the distinction between traumatic and degenerative cartilage lesions in the medial femoral condyle (MFC). It was hypothesized that NIRS as able to distinguish between traumatic and degenerative cartilage lesions.

MATERIALS AND METHODS

Arthroscopic evaluation was performed in six patients who had undergone anterior cruciate ligament (ACL) reconstruction and in six patients who had undergone high tibial osteotomy (HTO). In both groups, a grade III cartilage lesion was present within the MFC. NIRS evaluation was performed with a special probe (arthrospec-one, Arthrospec GmbH, Jena, Germany). NIRS measurements produced semi-quantitative values ranging from 0 (heavily degenerated cartilage) to 100 (completely intact cartilage).

RESULTS

The mean near-infrared-light absorption within the traumatic lesions in the MFC of the ACL group was 71.5 (range 61-80). In the HTO patients, this value was significantly (p < 0.001) lower at 31.7 (range 31-33). The margin of the MFC outside the lesion in the ACL group had the same adsorption as the lesion (p = 0.549).

CONCLUSION

After an injury, cartilage has a normal or nearly normal absorbance on near-infrared-light. Thus, it is possible to distinguish intraoperatively between traumatic and degenerative lesions. In addition, our results demonstrate that evaluating cartilage with NIRS is a dependable method for improving the diagnosis of significant chondral lesions.

Acupressure at the Meridian Acupoint Xiyangguan (GB33) Influences Near-Infrared Spectroscopic Parameters (Regional Oxygen Saturation) in Deeper Tissue of the Knee in Healthy Volunteers

Up to now, it is still unknown whether microcirculation of deeper peripheral tissue (knee) can be modulated by acupuncture or acupressure on a meridian acupoint. The goal of this pilot study was to investigate possible effects of acupressure at the Xiyangguan acupoint (GB33) on the regional oxygen saturation of the deeper knee tissues by near-infrared spectroscopy (NIRS). Twelve healthy volunteers with a mean age of 23.8 ± 1.6 years were investigated. Acupressure stimulation was performed for 5 minutes at the Xiyangguan acupoint. The results of the controlled study showed a significant increase of the values of regional oxygen saturation on the stimulated side of the knee (P = 0.033), whereas the opposite side on the same knee showed insignificant changes. These results may serve as a valuable basis for monitoring a possible therapeutic effect (e.g., after Khalifa therapy) in patients with knee problems.

Fourier-transform infrared spectroscopic imaging of articular cartilage and biomaterials: A review

Fourier transform infrared spectroscopy (FTIR) has the potential to mark up the chemical changes of the materials, as almost all the materials contain their signatures in infrared region. Spectroscopy combined with spatial resolution enables the possibility of characterizing samples up to microscopic level. The emerging development of instrumentation to provide spatial information for infrared (IR) spectroscopy, termed as IR microscopy, provides an opening for newer applications in terms of image analysis, novel data processing tools, etc. Characterization of biomaterials using IR spectroscopy has a trace back to 1950s. The advent of FTIR with imaging capability made characterization possible in cartilage tissue and other biological systems. Extensive analysis of chemical constituents of cartilage and tendon, collagen orientation and polarization property of cartilage using FTIR imaging (FTIRI) has been actively explored during the last two decades. Also, studies using specialized instrumentations like synchrotron FTIR imaging have been attempted to understand the characteristics of biological samples like cartilage. This review covers most of those investigations on cartilage with FTIRI to characterize the same in terms of component characteristics and quantification, collagen orientation, zonal boundary determination, influence of mechanical compression on tissue nature and its correlation to other techniques in last 20 years.

Load-unloading response of intact and artificially degraded articular cartilage correlated with near infrared (NIR) absorption spectra

The conventional mechanical properties of articular cartilage, such as compressive stiffness, have been demonstrated to be limited in their capacity to distinguish intact (visually normal) from degraded cartilage samples. In this paper, we explore the correlation between a new mechanical parameter, namely the reswelling of articular cartilage following unloading from a given compressive load, and the near infrared (NIR) spectrum. The capacity to distinguish mechanically intact from proteoglycan-depleted tissue relative to the "reswelling" characteristic was first established, and the result was subsequently correlated with the NIR spectral data of the respective tissue samples. To achieve this, normal intact and enzymatically degraded samples were subjected to both NIR probing and mechanical compression based on a load-unload-reswelling protocol. The parameter δr, characteristic of the osmotic "reswelling" of the matrix after unloading to a constant small load in the order of the osmotic pressure of cartilage, was obtained for the different sample types. Multivariate statistics was employed to determine the degree of correlation between δr and the NIR absorption spectrum of relevant specimens using Partial Least Squared (PLS) regression. The results show a strong relationship (R(2)=95.89%, p<0.0001) between the spectral data and δr. This correlation of δr with NIR spectral data suggests the potential for determining the reswelling characteristics non-destructively. It was also observed that δr values bear a significant relationship with the cartilage matrix integrity, indicated by its proteoglycan content, and can therefore differentiate between normal and artificially degraded proteoglycan-depleted cartilage samples. It is therefore argued that the reswelling of cartilage, which is both biochemical (osmotic) and mechanical (hydrostatic pressure) in origin, could be a strong candidate for characterizing the tissue, especially in regions surrounding focal cartilage defects in joints.

Infrared fiber optic probe evaluation of degenerative cartilage correlates to histological grading

BACKGROUND

Osteoarthritis (OA), a degenerative cartilage disease, results in alterations of the chemical and structural properties of tissue. Arthroscopic evaluation of full-depth tissue composition is limited and would require tissue harvesting, which is inappropriate in daily routine. Fourier transform infrared (FT-IR) spectroscopy is a modality based on molecular vibrations of matrix components that can be used in conjunction with fiber optics to acquire quantitative compositional data from the cartilage matrix.

PURPOSE

To develop a model based on infrared spectra of articular cartilage to predict the histological Mankin score as an indicator of tissue quality.

STUDY DESIGN

Comparative laboratory study.

METHODS

Infrared fiber optic probe (IFOP) spectra were collected from nearly normal and more degraded regions of tibial plateau articular cartilage harvested during knee arthroplasty (N = 61). Each region was graded using a modified Mankin score. A multivariate partial least squares algorithm using second-derivative spectra was developed to predict the histological modified Mankin score.

RESULTS

The partial least squares model derived from IFOP spectra predicted the modified Mankin score with a prediction error of approximately 1.4, which resulted in approximately 72% of the Mankin-scored tissues being predicted correctly and 96% being predicted within 1 grade of their true score.

CONCLUSION

These data demonstrate that IFOP spectral parameters correlate with histological tissue grade and can be used to provide information on tissue composition.

CLINICAL RELEVANCE

Infrared fiber optic probe studies have significant potential for the evaluation of cartilage tissue quality without the need for tissue harvest. Combined with arthroscopy, IFOP analysis could facilitate the definition of tissue margins in debridement procedures.

Non-destructive evaluation of articular cartilage defects using near-infrared (NIR) spectroscopy in osteoarthritic rat models and its direct relation to Mankin score

OBJECTIVE

The aim of this study was to demonstrate the potential of near-infrared (NIR) spectroscopy for categorizing cartilage degeneration induced in animal models.

METHOD

Three models of osteoarthritic degeneration were induced in laboratory rats via one of the following methods: (1) menisectomy (MSX); (2) anterior cruciate ligament transection (ACLT); and (3) intra-articular injection of mono-ido-acetate (1 mg) (MIA), in the right knee joint, with 12 rats per model group. After 8 weeks, the animals were sacrificed and tibial knee joints were collected. A custom-made near-infrared (NIR) probe of diameter 5 mm was placed on the cartilage surface and spectral data were acquired from each specimen in the wave number range 4,000-12,500 cm(-1). Following spectral data acquisition, the specimens were fixed and Safranin-O staining was performed to assess disease severity based on the Mankin scoring system. Using multivariate statistical analysis based on principal component analysis and partial least squares regression, the spectral data were then related to the Mankin scores of the samples tested.

RESULTS

Mild to severe degenerative cartilage changes were observed in the subject animals. The ACLT models showed mild cartilage degeneration, MSX models moderate, and MIA severe cartilage degenerative changes both morphologically and histologically. Our result demonstrates that NIR spectroscopic information is capable of separating the cartilage samples into different groups relative to the severity of degeneration, with NIR correlating significantly with their Mankin score (R(2) = 88.85%).

CONCLUSION

We conclude that NIR is a viable tool for evaluating articular cartilage health and physical properties such as change in thickness with degeneration.

Clinical outcome of autologous chondrocyte implantation is correlated with infrared spectroscopic imaging-derived parameters

OBJECTIVE

To investigate whether Fourier transform infrared imaging spectroscopy (FT-IRIS), a modality based on molecular vibrations, is a viable alternative to histology and immunohistochemistry (IHC) for assessment of tissue quality and patient clinical outcome.

METHODS

Osteochondral biopsies were obtained from patients (9-65 months post-surgery) who underwent an autologous chondrocyte implantation (ACI) procedure to repair a cartilage defect (N = 14). The repair tissue was evaluated histologically by OsScore grading, for the presence of types I and II collagen by IHC, and for proteoglycan (PG) distribution and collagen quality parameters by FT-IRIS. Patient clinical outcome was assessed by the Lysholm score.

RESULTS

Improvement in Lysholm score occurred in 79% of patients. IHC staining showed the presence of types I and II collagen in all samples, with a greater amount of collagen type II in the deep zone. The amount and location of immunostaining for type II collagen correlated to the FT-IRIS-derived parameters of relative PG content and collagen helical integrity. In addition, the improvement in Lysholm score post-ACI correlated positively with the OsScore, type II collagen (IHC score) and FT-IRIS-determined parameters. Regression models for the relation between improvement in Lysholm score and either OsScore, IHC area score or the FT-IRIS parameters all reached significance (p < 0.01). However, the FT-IRIS model was not significantly improved with inclusion of the OsScore and IHC score parameters.

CONCLUSION

Demonstration of the correlation between FT-IRIS-derived molecular parameters of cartilage repair tissue and patient clinical outcome lays the groundwork for translation of this methodology to the clinical environment to aid in the management of cartilage disorders and their treatment.

Application of near infrared (NIR) spectroscopy for determining the thickness of articular cartilage

The determination of the characteristics of articular cartilage such as thickness, stiffness and swelling, especially in the form that can facilitate real-time decisions and diagnostics is still a matter for research and development. This paper correlates near infrared spectroscopy with mechanically measured cartilage thickness to establish a fast, non-destructive, repeatable and precise protocol for determining this tissue property. Statistical correlation was conducted between the thickness of bovine cartilage specimens (n=97) and regions of their near infrared spectra. Nine regions were established along the full absorption spectrum of each sample and were correlated with the thickness using partial least squares (PLS) regression multivariate analysis. The coefficient of determination (R²) varied between 53 and 93%, with the most predictive region (R²=93.1%, p<0.0001) for cartilage thickness lying in the region (wavenumber) 5350-8850 cm⁻¹. Our results demonstrate that the thickness of articular cartilage can be measured spectroscopically using NIR light. This protocol is potentially beneficial to clinical practice and surgical procedures in the treatment of joint disease such as osteoarthritis.

Reliability in arthroscopic grading of cartilage lesions: results of a prospective blinded study for evaluation of inter-observer reliability

INTRODUCTION AND AIM

Arthroscopy is a well-established method for grading cartilage lesions. This study was undertaken to evaluate the inter-observer variance of grading cartilage lesions in a real life operation.

MATERIALS AND METHODS

Four experienced arthroscopic surgeons used diagnostic arthroscopy, one after the other, to grade cartilage lesions in a total of 16 patients who had undergone knee arthroscopy.

RESULTS

In summary, a total of 14 cartilage areas in 16 patients were graded (n = 224). The Cohens (Fleiss) Kappa Index for multiple investigators was κ = 0.052 in the medial, κ = 0.300 in the central, and κ = 0.107 in the lateral surface of the patella. The indices were κ = 0.292 in the medial, κ = 0.0.255 in the central, and κ = 0.234 in the lateral surface of the trochlea. The inter-observer variance was κ = 0.193 in the MFC mean bearing zone, κ = 0.116 in the margin of the MFC, κ = 0.168 in the mean bearing zone of the TM, and κ = 0.164 in the TM margin. In the lateral compartment, the κ-Index was 0.309 in the LFC mean bearing zone, 0.111 in the margin of the LFC, 0.020 in the mean bearing zone of the TL, and 0.085 in the TL margin.

CONCLUSIONS

The inter-observer reliability of the arthroscopic grading of cartilage lesions is poor. The major problem is the relatively large variability in differentiating between intact cartilage and lesions that consist of the softening of the cartilage and the differentiation between superficial and deep cartilage lesions. In the future, objective measurements should be developed to solve this problem.

How do visual, spectroscopic and biomechanical changes of cartilage correlate in osteoarthritic knee joints?

BACKGROUND

Characteristic changes in cartilage of human knee joints with different degrees of osteoarthritis (OA) have been investigated by visual, biophotonical and biomechanical examination. Knowledge about the cartilage composition and changes during the development of OA is important for diagnostic decisions and understanding the pathogenesis of OA.

METHODS

Thirty two patients with severe knee OA received endoprosthetic replacement. During surgical intervention cartilage specimen were harvested from defined surface areas of the joints. The degree of cartilage defects was classified visually (ICRS Grade: International Cartilage Repair Society), biophotonically (NIRS: near infrared spectroscopy) and biomechanically (Young's Modulus). To characterise links between the investigated parameters the Spearman's rank correlation coefficient was used.

FINDINGS

Significant negative correlations were found between visual macroscopic degree of degeneration (ICRS Grade) and biophotonic characteristics (NIRS) (rho=-0.467) or cartilage stiffness (Young's Modulus) (rho=-0.501). Between NIRS and Young's Modulus significant positive correlation of rho=0.535 was detected.

INTERPRETATION

Visual, biophotonic and biomechanical properties of cartilage reveal strong correlations in all degrees of cartilage defects in patients with severe OA. According to these results, we indicate that an objective, non-invasive and non-destructive measurement of cartilage properties during open and arthroscopic knee surgery is possible by NIRS and provide a novel tool to evaluate disease intervention and treatment.

How valid is the arthroscopic diagnosis of cartilage lesions? Results of an opinion survey among highly experienced arthroscopic surgeons

AIM

In general, arthroscopy is considered the "gold standard" for the evaluation of cartilage lesions. In this multicenter survey, we ascertained the general opinion of surgeons regarding arthroscopic cartilage diagnoses.

METHOD

A total of 301 highly experienced arthroscopists (instructors of the AGA, the German-speaking society of arthroscopy) were contacted in writing with a request to complete the survey.

RESULTS

The data from 105 respondents (34.8% of those contacted) were used for the investigation. In the grading of the cartilage lesions, the Outerbridge classification was most frequently used (n = 87), followed by the ICRS protocol (n = 8) and the Insall score (n = 3). The majority (61%) of the arthroscopic surgeons felt that differentiation between healthy cartilage and low-grade cartilage lesions was simple. For differentiation between grade I and grade II lesions, and for differentiation between grade II and grade III lesions, 41.9 and 51.4%, respectively, thought that there was a "need for improvement". In the case of grade IV lesions, 70.5% of the surgeons thought that the diagnosis was valid. The respondents also judged the utility of incorporating objective measurements (e.g., intraoperative biomechanical tests): 13.3% (n = 14) responded that such measurements would be "very useful" and 61.9% (n = 65) responded that they would be "somewhat useful".

CONCLUSIONS

Among surgeons, arthroscopy was not perceived to be as reliable as a "gold standard" for the diagnosis of cartilage lesions. The majority of experienced arthroscopists felt unsure of the results in general, or at least in some cases. A universal and definitive grading system for lesions appears to be needed. For questionable cases, measurement devices are needed for objective cartilage grading.

Detection and evaluation of initial cartilage pathology in man: A comparison between MRT, arthroscopy and near-infrared spectroscopy (NIR) in their relation to initial knee pain

BACKGROUND AND AIMS

MRI and arthroscopy are important methods in the evaluation of cartilage pathology. But frequently initial changes of cartilage in combination with chronic knee pain cannot be detected by employing these two methods. Better diagnostic tools for the detection of the early stages of osteoarthritis (OA) are required. The objective of this study was to show that near-infrared spectroscopy (NIRS) can be incorporated into routine arthroscopy to improve detection and assessment of the initial cartilage pathology. Furthermore correlations between findings in MRI, arthroscopy and NIRS in patients with initial symptoms of OA have studied.

METHODS

Patients (n=21, 12 women, 9 men, age: 15-59 years, mean 34.19 years) with knee pain lasting for at least half a year without any trauma of the knee in their history were interviewed (body weight, smoking behaviour) and clinically evaluated using the Knee Injury and Osteoarthritis Outcome Score (KOOS). Also serum parameters (cholesterol, lipids) were analysed, conventional X-rays in three directions (evaluated according to Kellgren and Lawrence) and MRI (evaluation of cartilage damage according to the ICRS-score) were performed preoperatively in all patients. During subsequent arthroscopy cartilage damage was evaluated according to the ICRS-score. In addition the spectral reflection of cartilage was investigated in all knees using a special micro-glass-fiber probe in the near-infrared light region (spectral range between 1150 and 1475nm). To characterize relations between the investigated parameters the Spearman's rank correlation coefficient was used. Inter-observer variance was calculated employing the Cohens-Kappa-test.

RESULTS

MRI demonstrated a strong inter-observer variance with no significant correlations to other parameters. The same was observed for arthroscopic findings. Only NIRS showed significant correlations with three out of five KOOS subscores. Within the general parameters only smoking behaviour showed a significant correlation with two of the KOOS-scores. NIRS therefore seemed to be a sensitive diagnostic tool in detection of initial pathology in human cartilage. The additional necessary time for the spectroscopic investigation as part of the routine arthroscopy ranged between 3 and 7min (mean: 4min 18s).

CONCLUSION

Particularly for early-stage cartilage lesions (ICRS 0/I) MRI and arthroscopy have rather low predictive value. The inter-observer variance is very high (Cohens-Kappa<0.4). Correlations found between NIRS and KOOS suggest that NIRS potentially can be used for detection of initial cartilage pathology and may be helpful in the evaluation of the benefit of different medical or surgical interventions at early-stage of articular cartilage damage.

A pilot feasibility study for ultrasound evaluation of living human wrist cartilage: site-specific differences in acoustic properties

PURPOSE

The field of cartilage repair has changed dramatically in the past decade but has not answered the question of how to treat an articular cartilage lesion in the wrist. Indeed, the characteristics of wrist articular cartilage, such as cartilage thickness, hardness, and smoothness, have not been clarified. The purpose of this study was to evaluate and quantify the acoustic properties of wrist articular cartilage quantitatively using a new acoustic probe under arthroscopic observation.

METHODS

We evaluated 10 consecutive patients (9 men, 1 woman) who were examined or treated arthroscopically. The mean age at evaluation was 27 years. In total, 468 points of wrist articular cartilage were investigated using the ultrasonic probe, and the data were transformed into a wavelet map by wavelet transformation. Two parameters, maximum magnitude and echo duration, which are indices of articular cartilage stiffness and macroscopic surface roughness, respectively, were used to evaluate the acoustic properties of wrist cartilage.

RESULTS

The distribution pattern of the acoustic properties was similar to that of previous results for the ankle joint. The mean maximum magnitude and echo duration were 3.41 +/- 1.50 (range, 0.89-7.53) and 1.33 mus +/- 0.30 (range, 0.51-2.17 mus), respectively. For the scaphoid fossa, the maximum magnitude of the radial side was significantly lower than that of the ulnar side, and the echo duration of the radial side was significantly longer than that of the ulnar side.

CONCLUSIONS

A new measurement system using an acoustic probe made it possible to perform a quantitative analysis of wrist articular cartilage, similar to the case for knee and ankle articular cartilage. In addition, site-specific differences in the acoustic properties of the distal radial cartilage were detected in living human wrist cartilage.