Arthroscopic Ultrasound Assessment of Articular Cartilage in the Human Knee Joint: A Potential Diagnostic Method

Application of an indentation sensor for the arthroscopic measurement of articular cartilage stiffness

Direct measurement of cartilage stiffness provides useful clinical information and enables us to develop treatment strategies for patients. We applied an indentation sensor to evaluate cartilage stiffness under arthroscopic control. The purpose of this study was to validate the arthroscopic indentation sensor using cadaver knees and to measure cartilage stiffness in clinical cases. The stiffness of a material with known properties was measured at thicknesses from 2 mm to 10 mm with a 2-mm interval. This was repeated three times at each thickness to evaluate repeatability. The articular cartilage stiffness of the medial and lateral femoral condyles of five human cadaveric knees was measured. The sensor was inclined from 0° to 20° with 1° intervals. The stiffness value at each degree of inclination was compared to evaluate the acceptable measuring angle. Additionally, articular cartilage stiffness was measured in 23 adolescent and 11 adult patients under arthroscopy. Young's moduli of the material were 1.15-1.24 (mean 1.20) MPa. Inter-class correlation coefficients in repeated measurements using the material were 0.83-0.99. There were no differences in the cartilage stiffness between the medial and lateral femoral condyles of the cadaver knees. All condyles showed a nonlinear relationship between force and displacement. The force decreased in all condyles when the tip of the sensor system was tilted. The range of error was < 97.1% within 5° inclination. There was a moderate negative correlation between age and cartilage stiffness in adolescent patients, and a moderate positive correlation in adult patients. Since the sensor system is manually held during measurement, the validity and repeatability to assess material properties of the cartilage may be inaccurate. This study has proven that the instrument can measure the stiffness of joint cartilage reliably and is a useful clinical tool under arthroscopic control.

Quantifying Region-Specific Elastic Properties of Distal Femoral Articular Cartilage: A Shear-Wave Elastography Study

Knee osteoarthritis is a disease with the degeneration of articular cartilage as its main feature. Cartilage thickness cannot become a single index to evaluate cartilage degeneration, so it is essential to also evaluate the stiffness. The purposes were as follows: (1) to examine test-retest reliabilities of the elastic modulus measurement in distal femoral articular cartilage (FAC) and compare the changes in specific-regional of distal FAC, (2) to explore the difference in distal FAC stiffness and thickness between the dominant and nondominant sides, and (3) to examine the correlation between the elastic properties of cartilage and the thickness of cartilage. Twenty healthy participants were recruited. The stiffness of distal FAC at the lateral femoral condyle (LFC), medial femoral condyle (MFC), and intercondylar notch (IN) was quantified using shear-wave elastography (SWE). Intra- and interrater reliabilities were excellent for measuring the stiffness of distal FAC (ICC: 0.83-0.98). About a 50% increase in the stiffness of LFC (40.78 kPa) was found when compared with IN (21.82 kPa) and MFC (18.34 kPa). No significant difference was found between the dominant and nondominant sides in distal FAC stiffness and thickness. There was no correlation between the stiffness and thickness of the distal FAC. In conclusion, SWE can quantify the stiffness of the distal FAC.

Comparison Between Arthroscopic and Histological International Cartilage Repair Society Scoring Systems in Porcine Cartilage Repair Model

OBJECTIVE

The arthroscopic and histological International Cartilage Repair Society (ICRS) scores are designed to evaluate cartilage repair quality. Arthroscopic ICRS score can give a maximum score of 12 and the histological score can give values between 0% and 100% for each of its 14 subscores. This study compares these methods in an animal cartilage repair model. This study hypothesizes that there is a significant correlation between these methods.

DESIGN

A chondral defect was made in the medial femoral condyle of 18 pigs. Five weeks later, 9 pigs were treated with a novel recombinant human type III collagen/polylactide scaffold and 9 were left untreated to heal spontaneously. After 4 months, the medial condyles were evaluated with a simulated arthroscopy using the ICRS scoring system followed by a histological ICRS scoring.

RESULTS

This porcine cartilage repair model produced repaired cartilage tissue ranging from good to poor repair tissue quality. The mean arthroscopic ICRS total score was 6.8 (SD = 2.2). Histological ICRS overall assessment subscore was 38.2 (SD = 31.1) and histological ICRS average points were 60.5 (SD = 19.5). Arthroscopic ICRS compared with histological ICRS average points or its overall assessment subscore showed moderate correlation (r = 0.49 and r = 0.50, respectively). The interrater reliability with the intraclass correlation coefficients for arthroscopic ICRS total scores, histological ICRS overall assessment subscore, and ICRS average points showed moderate to excellent reliability.

CONCLUSIONS

Arthroscopic and histological ICRS scoring methods for repaired articular cartilage show a moderate correlation in the animal cartilage repair model.

Ultrasound-Based Quantification of Cartilage Damage After In Vivo Articulation With Metal Implants

OBJECTIVE

This study aims to evaluate the applicability of the ultrasound roughness index (URI) for quantitative assessment of cartilage quality ex vivo (post-mortem), after 6 months of in vivo articulation with a Focal Knee Resurfacing Implant (FKRI).

DESIGN

Goats received a metal FKRI (n = 8) or sham surgery (n = 8) in the medial femoral condyles. After 6 months animals were sacrificed, tibial plateaus were stained with Indian ink, and macroscopic scoring of the plateaus was performed based on the ink staining. The URI was calculated from high-frequency ultrasound images at several sections, covering both areas that articulated with the implant and non-articulating areas. Cartilage quality at the most damaged medial location was evaluated with a Modified Mankin Score (MMS).

RESULTS

The URI was significantly higher in the FKRI-articulating than in the sham plateaus at medial articulating sections, but not at sections that were not in direct contact with the implant, for example, under the meniscus. The mean macroscopic score and MMS were significantly higher in the FKRI-articulating group than in the sham group (P=0.035, P<0.001, respectively). Correlation coefficients between URI and macroscopic score were significant in medial areas that articulated with the implant. A significant correlation between URI and MMS was found at the most damaged medial location (ρ=0.72,P=0.0024).

CONCLUSIONS

This study demonstrates the potential of URI to evaluate cartilage roughness and altered surface morphology after in vivo articulation with a metal FKRI, rendering it a promising future tool for quantitative follow-up assessment of cartilage quality.

Biomechanical Changes of Repair Tissue after Autologous Chondrocyte Implantation at Long-Term Follow-Up

Objective. This study aims to describe biomechanical maturation process of repair tissue after cartilage repair with autologous chondrocyte implantation (ACI) at long-term follow-up. Design. After ACI, 40 patients underwent altogether 60 arthroscopic biomechanical measurements of the repair tissue at various time points during an up to 11-year follow-up period. Of these patients, 30 patients had full-thickness cartilage lesions and 10 had an osteochondritis dissecans (OCD) defect. The mean lesion area was 6.5 cm² (SD 3.2). A relative indentation stiffness value for each individually measured lesion was calculated as a ratio of repair tissue and surrounding cartilage indentation value to enable interindividual comparison. Results. Repair tissue stiffness improved during approximately 5 years after surgery. Most of the increase in stiffness occurred during the first 2 years. The curvilinear correlation between relative stiffness values and the follow-up time was 0.31 (95% CI 0.07-0.52), P = 0.017. The interindividual variation of the stiffness was high. Lesion properties or demographic factors showed no significant correlation to biomechanical outcome. The overall postoperative average relative stiffness was 0.75 (SD 0.47). Conclusions. Our clinical study describes a biomechanical maturation process of cartilage repair that may continue even longer than expected. A substantial increase in tissue stiffness proceeds for the first two years postoperatively. Minor progression proceeds for even longer. In some repairs, the biomechanical result was equal to native cartilage, suggesting hyaline-type repair. The variation in biomechanical results suggests substantial inconsistency in the structural outcome following ACI.

Arthroscopic International Cartilage Repair Society Classification System Has Only Moderate Reliability in a Porcine Cartilage Repair Model

BACKGROUND

The International Cartilage Repair Society (ICRS) score was designed for arthroscopic use to evaluate the quality of cartilage repair.

PURPOSE

To evaluate the reliability of the ICRS scoring system using an animal cartilage repair model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A chondral defect with an area of 1.5 cm² was made in the medial femoral condyle of 18 domestic pigs. Five weeks later, 9 pigs were treated using a novel recombinant human type III collagen/polylactide scaffold, and 9 were left to heal spontaneously. After 4 months, the pigs were sacrificed, then 3 arthroscopic surgeons evaluated the medial femoral condyles via video-recorded simulated arthroscopy using the ICRS scoring system. The surgeons repeated the evaluation twice within a 9-month period using their recorded arthroscopy.

RESULTS

The porcine cartilage repair model produced cartilage repair tissue of poor to good quality. The mean ICRS total scores for all observations were 6.6 (SD, 2.6) in arthroscopy, 5.9 (SD, 2.7) in the first reevaluation, and 6.2 (SD, 2.8) in the second reevaluation. The interrater reliability with the intraclass correlation coefficient (ICC) for the ICRS total scores (ICC, 0.46-0.60) and for each individual subscore (ICC, 0.26-0.71) showed poor to moderate reliability. The intrarater reliability with the ICC also showed poor to moderate reliability for ICRS total scores (ICC, 0.52-0.59) and for each individual subscore (ICC, 0.29-0.58). A modified Bland-Altman plot for the initial arthroscopy and for the 2 reevaluations showed an evident disagreement among the observers.

CONCLUSION

In an animal cartilage repair model, the ICRS scoring system seems to have poor to moderate reliability.

CLINICAL RELEVANCE

Arthroscopic assessment of cartilage repair using the ICRS scoring method has limited reliability. We need more objective methods with acceptable reliability to evaluate cartilage repair outcomes.

In-Vitro Detection of Small Isolated Cartilage Defects: Intravascular Ultrasound Vs. Optical Coherence Tomography

This experimental work focused on the sensor selection for the development of a needle-like instrument to treat small isolated cartilage defects with hydrogels. The aim was to identify the most accurate and sensitive imaging method to determine the location and size of defects compared to a gold standard (µCT). Only intravascular ultrasound imaging (IVUS) vs. optical coherent tomography (OCT) were looked at, as they fulfilled the criteria for integration in the needle design. An in-vitro study was conducted on six human cadaveric tali that were dissected and submerged in saline. To simulate the natural appearance of cartilage defects, three types of defects were created via a standardised protocol: osteochondral defects (OCD), chondral defects (CD) and cartilage surface fibrillation (CSF), all sized between 0.1 and 3 mm in diameter. The detection rate by two observers for all diameters of OCD were 80, 92 and 100% with IVUS, OCT and µCT, for CD these were 60, 83 and 97%, and for CSF 0, 29 and 24%. Both IVUS and OCT can detect the presence of OCD and CD accurately if they are larger than 2 mm in diameter, and OCT can detect fibrillated cartilage defects larger than 3 mm in diameter. A significant difference between OCT–µCT and IVUS–µCT was found for the diameter error (p = 0.004) and insertion depth error (p = 0.002), indicating that OCT gives values closer to reference µCT. The OCT imaging technique is more sensitive to various types and sizes of defects and has a smaller diameter, and is therefore preferred for the intended application.

The role of ultrasonography in the diagnosis of anterior cruciate ligament injury: A systematic review and meta-analysis

To evaluate the value of ultrasonography in the diagnosis of anterior cruciate ligament injury (ACL injury) by conducting a systematic review and meta-analysis. A literature search was carried out in the Cochrane Library, Embase, Pubmed databases and included studies prior to April 2017. Based on inclusion and exclusion criteria, studies evaluating ultrasound to diagnose ACL injury were selected. MRI, arthroscopy and clinical-follow were considered the reference standards. The diagnostic accuracy of ultrasound was assessed using a combination of sensitivity, specificity, likelihood ratio (LR), post-test probability, diagnostic odds ratio (DOR) and by summarizing the area under the receiver operating characteristic (SROC) curve. A total of 4 studies involving 246 patients were eventually included in the analysis. In these four studies, the combined sensitivity, specificity, positive likelihood ratio, negative likelihood ratio, post-test probability and DOR were 90.0% (95% CI: 77-96), 97% (95% CI: 90-99), 31.08 (95% CI: 8.75-110.41), 0.11 (95% CI: 0.05-0.24), 89% (3%) and 288.81 (95% CI: 78.51-1062.48), respectively. The area under the SROC curve was 0.98 (95% CI: 0.97-0.99). Our meta-analysis showed that ultrasound can play an important role in the diagnosis of ACL injury. Because of its high sensitivity, high specificity and high diagnostic ability, ultrasound should be a part of the standard diagnostic work-up of an ACL injury.

Ultrasound Arthroscopy of Hip in Treatment of Osteochondritis Dissecans

An ultrasound arthroscopy (UA) technique is a promising tool for the evaluation of the articular cartilage during arthroscopic examination. However, the applicability of UA for the evaluation of the hip joint is unknown. We describe a UA assessment of a patient with osteochondritis dissecans at the femoral head. An ultrasound catheter designed for intravascular imaging was inserted into the hip joint by use of conventional arthroscopic portals, and the cartilage surfaces of the femoral head and acetabulum were investigated with ultrasound. UA provided essential quantitative information on the integrity of the articular cartilage and the condition of the subchondral plate not assessable with conventional arthroscopy. Furthermore, the UA technique provided the possibility to monitor arthroscopy-assisted retrograde drilling and bone transplantation in the hip joint.

Regular chondrocyte spacing is a potential cause for coherent ultrasound backscatter in human articular cartilage

The potential of quantitative ultrasound (QUS) to assess the regular cellular spacing in the superficial cartilage zones was investigated experimentally and numerically. Nine osteochondral samples, extracted from two human cadaver knee joints, were measured using a 50-MHz ultrasound scanning device and evaluated using Mankin score. Simulated backscattered power spectra from models with an idealized cell alignment exhibited a pronounced frequency peak. From the peak, cell spacing in the range between 15 and 40 μm between cell layers was detected with an average error of 0.2 μm. The mean QUS-based cell spacing was 28.3 ± 5.3 μm. Strong correlation (R²= 0.59, p ≤ 0.001) between spacing estimates from light microscopy (LM) and QUS was found for samples with Mankin score ≤3. For higher scores, QUS-based spacing was significantly higher (p ≤ 0.05) compared to LM-based spacing. QUS-based spacing estimates together with other QUS parameters may serve as future biomarkers for detecting early signs of osteoarthrosis.

In Vivo Evaluation of the Potential of High-Frequency Ultrasound for Arthroscopic Examination of the Shoulder Joint

OBJECTIVE

Accurate arthroscopic evaluation of cartilage lesions could significantly improve the outcome of repair surgery. In this study, we investigated for the first time the potential of intra-articular ultrasound as an arthroscopic tool for grading cartilage defects in the human shoulder joint in vivo and compared the outcome to results from arthroscopic evaluation and magnetic resonance imaging findings.

DESIGN

A total of 26 sites from 9 patients undergoing routine shoulder arthroscopy were quantitatively evaluated with a clinical intravascular (40MHz) ultrasound imaging system, using the regular arthroscopy portals. Reflection coefficient (R), integrated reflection coefficient (IRC), apparent integrated backscattering (AIB), and ultrasound roughness index (URI) were calculated, and high-resolution ultrasound images were obtained per site. Each site was visually graded according to the International Cartilage Repair Society (ICRS) system. "Ultrasound scores" corresponding to the ICRS system were determined from the ultrasound images. Magnetic resonance imaging was conducted and cartilage integrity at each site was classified into 5 grades (0 = normal, 4 = severely abnormal) by a radiologist.

RESULTS

R and IRC were lower at sites with damaged cartilage surface (P = 0.033 and P = 0.043, respectively) and correlated with arthroscopic ICRS grades (r s = -0.444, P = 0.023 and r s = -0.426, P = 0.03, respectively). Arthroscopic ICRS grades and ultrasound scores were significantly correlated (rs = 0.472, P = 0.015), but no significant correlation was found between magnetic resonance imaging data and other parameters.

CONCLUSION

The results suggest that ultrasound arthroscopy could facilitate quantitative clinical appraisal of articular cartilage integrity in the shoulder joint and provide information on cartilage lesion depth and severity for quantitative diagnostics in surgery.

Finite difference time domain model of ultrasound propagation in agarose scaffold containing collagen or chondrocytes

Measurement of ultrasound backscattering is a promising diagnostic technique for arthroscopic evaluation of articular cartilage. However, contribution of collagen and chondrocytes on ultrasound backscattering and speed of sound in cartilage is not fully understood and is experimentally difficult to study. Agarose hydrogels have been used in tissue engineering applications of cartilage. Therefore, the aim of this study was to simulate the propagation of high frequency ultrasound (40 MHz) in agarose scaffolds with varying concentrations of chondrocytes (1 to 32 × 10(6) cells/ml) and collagen (1.56-200 mg/ml) using transversely isotropic two-dimensional finite difference time domain method (FDTD). Backscatter and speed of sound were evaluated from the simulated pulse-echo and through transmission measurements, respectively. Ultrasound backscatter increased with increasing collagen and chondrocyte concentrations. Furthermore, speed of sound increased with increasing collagen concentration. However, this was not observed with increasing chondrocyte concentrations. The present study suggests that the FDTD method may have some applicability in simulations of ultrasound scattering and propagation in constructs containing collagen and chondrocytes. Findings of this study indicate the significant role of collagen and chondrocytes as ultrasound scatterers and can aid in development of modeling approaches for understanding how cartilage architecture affects to the propagation of high frequency ultrasound.

High-Resolution Methods for Diagnosing Cartilage Damage In Vivo

Advances in current clinical modalities, including magnetic resonance imaging and computed tomography, allow for earlier diagnoses of cartilage damage that could mitigate progression to osteoarthritis. However, current imaging modalities do not detect submicrometer damage. Developments in in vivo or arthroscopic techniques, including optical coherence tomography, ultrasonography, bioelectricity including streaming potential measurement, noninvasive electroarthrography, and multiphoton microscopy can detect damage at an earlier time point, but they are limited by a lack of penetration and the ability to assess an entire joint. This article reviews current advancements in clinical and developing modalities that can aid in the early diagnosis of cartilage injury and facilitate studies of interventional therapeutics.

Diagnosis of Knee Osteochondral Lesions With Ultrasound Imaging

Evaluation of articular cartilage and subchondral bone is essential in the diagnosis of joint diseases and injuries. Interobserver and intraobserver reproducibilities of arthroscopic grading are only poor to moderate. Thus, for quantitative and objective evaluation of cartilage and subchondral bone, ultrasound arthroscopy (UA) has been introduced to clarify this dilemma. Assessment of the clinical feasibility of high-frequency ultrasonography (US) during 6 knee arthroscopies was conducted, and the surgical technique is presented. US imaging was conducted with a flexible 9-MHz US catheter inserted into the joint through conventional portals. US and arthroscopy videos were synchronously recorded, and US parameters for cartilage and subchondral bone characteristics were measured. Arthroscopy and US imaging were combined to perform cartilage grading. UA produced quantitative data on lesion size, as well as cartilage quality, and showed subchondral bone changes. Visualization of an osteochondritis dissecans lesion not detected by conventional arthroscopy and US-guided retrograde drilling were possible with UA. To conclude, UA proved to be clinically feasible and aided in the diagnosis when assessing knee osteochondral lesions.

Ultrasound Backscattering Is Anisotropic in Bovine Articular Cartilage

Collagen, proteoglycans and chondrocytes can contribute to ultrasound scattering in articular cartilage. However, anisotropy of ultrasound scattering in cartilage is not fully characterized. We investigate this using a clinical intravascular ultrasound device with ultrasound frequencies of 9 and 40 MHz. Osteochondral samples were obtained from intact bovine patellas, and cartilage was imaged in two perpendicular directions: through articular and lateral surfaces. At both frequencies, ultrasound backscattering was higher (p < 0.05) when measured through the lateral surface of cartilage. In addition, the composition and structure of articular cartilage were investigated with multiple reference methods involving light microscopy, digital densitometry, polarized light microscopy and Fourier infrared imaging. Reference methods indicated that acoustic anisotropy of ultrasound scattering arises mainly from non-uniform distribution of chondrocytes and anisotropic orientation of collagen fibers. To conclude, ultrasound backscattering in articular cartilage was found to be anisotropic and dependent on the frequency in use.

A new method for evaluating the degeneration of articular cartilage using pulse-echo ultrasound

This paper presents a novel nondestructive ultrasonic technique for measuring the sound speed and acoustic impedance of articular cartilage using the pulsed Vz,t technique. Vz,t data include a series of pulsed ultrasonic echoes collected using different distances between the ultrasonic transducer and the specimen. The 2D Fourier transform is applied to the Vz,t data to reconstruct the 2D reflection spectrum Rθ,ω. To obtain the reflection coefficient of articular cartilage, the Vz,t data from a reference specimen with a well-known reflection coefficient are obtained to eliminate the dependence on the general system transfer function. The ultrasound-derived aggregate modulus (Ha) is computed based on the measured reflection coefficient and the sound speed. In the experiment, 32 cartilage-bone samples were prepared from bovine articular cartilage, and 16 samples were digested using 0.25% trypsin solution. The sound speed and Ha of these cartilage samples were evaluated before and after degeneration. The magnitude of the sound speed decreased with trypsin digestion (from 1663 ± 5.6 m/s to 1613 ± 5.3 m/s). Moreover, the Young's modulus in the corresponding degenerative state was measured and was correlated with the ultrasound-derived aggregate modulus. The ultrasound-derived aggregate modulus was determined to be highly correlated with the Young's modulus (n = 16, r>0.895, p<0.003, Pearson correlation test for each measurement). The results demonstrate the effectiveness of using the proposed method to assess the changes in sound speed and the ultrasound-derived aggregate modulus of cartilage after degeneration.

Ultrasound arthroscopy of human knee cartilage and subchondral bone in vivo

Arthroscopic ultrasound imaging enables quantitative evaluation of articular cartilage. However, the potential of this technique for evaluation of subchondral bone has not been investigated in vivo. In this study, we address this issue in clinical arthroscopy of the human knee (n = 11) by determining quantitative ultrasound (9 MHz) reflection and backscattering parameters for cartilage and subchondral bone. Furthermore, in each knee, seven anatomical sites were graded using the International Cartilage Repair Society (ICRS) system based on (i) conventional arthroscopy and (ii) ultrasound images acquired in arthroscopy with a miniature transducer. Ultrasound enabled visualization of articular cartilage and subchondral bone. ICRS grades based on ultrasound images were higher (p < 0.05) than those based on conventional arthroscopy. The higher ultrasound-based ICRS grades were expected as ultrasound reveals additional information on, for example, the relative depth of the lesion. In line with previous literature, ultrasound reflection and scattering in cartilage varied significantly (p < 0.05) along the ICRS scale. However, no significant correlation between ultrasound parameters and structure or density of subchondral bone could be demonstrated. To conclude, arthroscopic ultrasound imaging had a significant effect on clinical grading of cartilage, and it was found to provide quantitative information on cartilage. The lack of correlation between the ultrasound parameters and bone properties may be related to lesser bone change or excessive attenuation in overlying cartilage and insufficient power of the applied miniature transducer.

Collagen and chondrocyte concentrations control ultrasound scattering in agarose scaffolds

Ultrasound imaging has been proposed for diagnostics of osteoarthritis and cartilage injuries in vivo. However, the specific contribution of chondrocytes and collagen to ultrasound scattering in articular cartilage has not been systematically studied. We investigated the role of these tissue structures by measuring ultrasound scattering in agarose scaffolds with varying collagen and chondrocyte concentrations. Ultrasound catheters with center frequencies of 9 MHz (7.1-11.0 MHz, -6 dB) and 40 MHz (30.1-45.3 MHz, -6 dB) were applied using an intravascular ultrasound device. Ultrasound backscattering quantified in a region of interest starting right below sample surface differed significantly (p < 0.05) with the concentrations of collagen and chondrocytes. An ultrasound frequency of 40 MHz, as compared with 9 MHz, was more sensitive to variations in collagen and chondrocyte concentrations. The present findings may improve diagnostic interpretation of arthroscopic ultrasound imaging and provide information necessary for development of models describing ultrasound propagation within cartilage.

Identification of cartilage injury using quantitative multiphoton microscopy

OBJECTIVE

Cartilage injury can lead to post-traumatic osteoarthritis (PTOA). Immediate post-trauma cellular and structural changes are not widely understood. Furthermore, current cellular-resolution cartilage imaging techniques require sectioning of cartilage and/or use of dyes not suitable for patient imaging. In this study, we used multiphoton microscopy (MPM) data with FDA-approved sodium fluorescein to identify and evaluate the pattern of chondrocyte death after traumatic injury.

METHOD

Mature equine distal metacarpal or metatarsal osteochondral blocks (OCBs) were injured by 30 MPa compressive loading delivered over 1 s. Injured and control sites were imaged unfixed and in situ 1 h post-injury with sodium fluorescein using rasterized z-scanning. MPM data was quantified in MATLAB, reconstructed in 3-D, and projected in 2-D to determine the damage pattern.

RESULTS

MPM images (600 per sample) were reconstructed and analyzed for cell death. The overall distribution of cell death appeared to cluster into circular (n = 7) or elliptical (n = 4) patterns (p = 0.006). Dead cells were prevalent near cracks in the matrix, with only 26.3% (SE = 5.0%, p < 0.0001) of chondrocytes near cracks being viable.

CONCLUSION

This study demonstrates the first application of MPM for evaluating cellular-scale cartilage injury in situ in live tissue, with clinical potential for detecting early cartilage damage. With this technique, we were able to uniquely observe two death patterns resulting from the same compressive loading, which may be related to local variability in matrix structure. These results also demonstrate proof-of-concept MPM diagnostic use in detecting subtle and early cartilage damage not detectable in any other way.

Application of optical coherence tomography enhances reproducibility of arthroscopic evaluation of equine joints

BACKGROUND

Arthroscopy is widely used in various equine joints for diagnostic and surgical purposes. However, accuracy of defining the extent of cartilage lesions and reproducibility in grading of lesions are not optimal. Therefore, there is a need for new, more quantitative arthroscopic methods. Arthroscopic optical coherence tomography (OCT) imaging is a promising tool introduced for quantitative detection of cartilage degeneration and scoring of the severity of chondral lesions. The aim of this study was to evaluate the inter-investigator agreement and inter-method agreement in grading cartilage lesions by means of conventional arthroscopy and with OCT technique. For this aim, 41 cartilage lesions based on findings in conventional and OCT arthroscopy in 14 equine joints were imaged, blind coded and independently ICRS (International Cartilage Repair Society) scored by three surgeons and one PhD-student.

RESULTS

The intra- and inter-investigator percentages of agreement by means of OCT (68.9% and 43.9%, respectively) were higher than those based on conventional arthroscopic imaging (56.7% and 31.7%, respectively). The intra-investigator Kappa coefficients were 0.709 and 0.565 for OCT and arthroscopy, respectively. Inter-investigator Kappa coefficients were 0.538 and 0.408 for OCT and arthroscopy, respectively.

CONCLUSIONS

OCT can enhance reproducibility of arthroscopic evaluation of equine joints.

3-D high-frequency ultrasound backscatter analysis of human articular cartilage

High-frequency ultrasound is a promising method for non-invasive characterization of cartilage degeneration. Surface reflection and integrated spectral parameters are often used. In the work described here, human cartilage samples with varying degrees of degeneration were measured using a 40-MHz transducer. Backscatter signals originating from the superficial and transitional zones of cartilage were analyzed using amplitude, spectral and envelope statistical parameters and related to degenerative changes of the matrix given by the Mankin score. The results indicate an increased sensitivity of spectral slope and envelope statistical parameters to early matrix degeneration compared with conventional amplitude parameters. Furthermore, moderate correlations of chondrocyte number with backscatter amplitude and envelope statistics were observed, suggesting that at high frequencies, cells are one important scattering source in cartilage. An application of spectral and envelope statistical parameters to intra-articular ultrasound arthroscopy is conceivable and could improve the diagnostic potential of these examinations. Future studies are necessary to clarify the contributions of chondrocytes, extracellular matrix and collagen content to ultrasound backscatter to further improve the diagnostic potential of ultrasound for cartilage assessment.

Arthroscopic ultrasound technique for simultaneous quantitative assessment of articular cartilage and subchondral bone: an in vitro and in vivo feasibility study

Traditional arthroscopic examination is subjective and poorly reproducible. Recently, we introduced an arthroscopic ultrasound method for quantitative diagnostics of cartilage lesions. Here we describe our investigation of the feasibility of ultrasound arthroscopy for simultaneous measurements of articular cartilage and subchondral bone. Human osteochondral samples (n = 13) were imaged using a clinical 9-MHz ultrasound system. Ultrasound reflection coefficients (R, IRC), the ultrasound roughness index (URI) and the apparent integrated backscattering coefficient (AIB) were determined for both tissues. Mechanical testing, histologic analyses and micro-scale computed tomography imaging were the reference methods. Ultrasound arthroscopies were conducted on two patients. The ultrasound reflection coefficient correlated with the Mankin score and Young's modulus of cartilage (|r| > 0.56, p < 0.05). Ultrasound parameters (R, IRC, AIB) for subchondral bone correlated with the bone surface/volume ratio (|r| > 0.70, p < 0.05) and trabecular thickness (|r| > 0.59, p < 0.05). Furthermore, R and subchondral bone mineral density were significantly correlated (|r| > 0.65, p < 0.05). Arthroscopic ultrasound examination provided diagnostically valuable information on cartilage and subchondral bone in vivo.

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.

3-d high-frequency ultrasound improves the estimation of surface properties in degenerated cartilage

High-frequency ultrasound (US) surface parameters are well known to be sensitive to degenerative changes in cartilage tissue, but estimates deteriorate if the sample is inclined. We propose 3-D US to precisely estimate the local surface and inclination. For this purpose, the most common ultrasonic surface parameters ultrasound roughness index and integrated reflection coefficient were extended to 2-D surface measurements. Tissue-mimicking phantoms and human cartilage samples with varying degrees of degeneration were measured using a 40-MHz transducer. Characteristic inclination dependencies of the parameters aided in the distinction between specular reflected or backscattered signal origins and allowed a restriction to suitable local inclinations. In the application to cartilage, comparisons with histologic grading (structural Mankin-score) depicted a statistically significant (p < 0.05) increase of US roughness index for scores larger than 0 and decrease of integrated reflection coefficient for scores larger than 1. The presented findings will increase the reliability of ultrasonic surface parameters and can in principal be applied in vivo.

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.

Ultrasonic evaluation of acute impact injury of articular cartilage in vitro

OBJECTIVE

The aim of the study was to investigate whether high frequency ultrasound technique, originally designed for arthroscopic use can be utilized to detect traumatic cartilage injuries.

METHODS

A total of four intact osteochondral plugs were prepared from eight patellas for parallel comparison (total of 32 plugs). The plugs were injured by dropping an impactor on them from heights of 2.5 cm, 5.0 cm, 10.0 cm and 15.0 cm (corresponding to impact energies of 0.12, 0.25 0.50 and 0.74 J, respectively), in a custom made dropping tower. The samples were imaged with a high frequency (40 MHz) ultrasound device before and after the injury. Reflection coefficient (R), integrated reflection coefficient (IRC), apparent integrated backscattering (AIB) and ultrasound roughness index (URI) were determined for each sample.

RESULTS

Injuries invisible to the naked eye could be sensitively detected via the decreased values of the ultrasound reflection parameters (P < 0.05). Furthermore, a decreasing trend was detected in the values of R and IRC as the momentum of the impactor increased. The values of AIB were significantly lower for samples injured by dropping the impactor on the cartilage from heights of 2.5 cm and 15 cm but the URI values were similar in intact and injured cartilage. Histological analysis of the cartilage samples revealed that the injured cartilage exhibited depletion of the cartilage surface proteoglycans but the structure of collagen network was almost normal.

CONCLUSIONS

Quantitative ultrasound imaging enables the detection of minor visually non-detectable cartilage injuries. As the present technique is feasible for arthroscopic use it might have clinical value in the evaluation of cartilage lesions during arthroscopy e.g., after tear of the anterior cruciate ligament.

Diagnostic performance of knee ultrasonography for detecting degenerative changes of articular cartilage

OBJECTIVE

To investigate the diagnostic performance of non-invasive knee ultrasonography (US) to detect degenerative changes of articular cartilage using arthroscopic grading as the gold standard.

DESIGN

Forty adult patients referred to a knee arthroscopy because of knee pain were randomly selected for the study. Before the arthroscopy, knee US was performed and cartilage surfaces at medial and lateral femoral condyles as well as at intercondylar notch area (sulcus) were semi-quantitatively graded from US. Ultrasonographic grading was compared with the arthroscopic Noyes' grading for cartilage degeneration.

RESULTS

Sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic odds ratio for detecting arthroscopic cartilage changes in US varied between 52 and 83%, 50-100%, 88-100%, 24-46%, and 5.0-13.0, respectively, depending on the site. Correlation of severity of cartilage changes (grades) between US and arthroscopy varied from insignificant to significant depending on the site: at the sulcus area the correlation was highest (r(s)=0.593, P<0.001), at the medial condyle also significant (r(s)=0.465, P=0.003), and at the lateral condyle non-significant (r(s)=0.262, P=0.103). The sum of cartilage grades in all three sites of the femoral cartilage between US and arthroscopy had the highest correlation (r(s)=0.655, P<0.001).

CONCLUSIONS

Positive finding in US is a strong indicator of arthroscopic degenerative changes of cartilage, but negative finding does not rule out degenerative changes. Non-invasive knee US is a promising technique for screening of degenerative changes of articular cartilage, e.g., during osteoarthritis.