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.     

Effects of Ultrasound Beam Angle and Surface Roughness on the Quantitative Ultrasound Parameters of Articular Cartilage

High-resolution arthroscopic ultrasound imaging provides a potential quantitative technique for the diagnostics of early osteoarthritis. However, an uncontrolled, nonperpendicular angle of an ultrasound beam or the natural curvature of the cartilage surface may jeopardize the reliability of the ultrasound measurements. We evaluated systematically the effect of inclining an articular surface on the quantitative ultrasound parameters. Visually intact (n = 8) and mechanically degraded (n = 6) osteochondral bovine patella samples and spontaneously fibrillated (n = 1) and spontaneously proteoglycan depleted (n = 1) osteochondral human tibial samples were imaged using a 50-MHz scanning acoustic system. The surface of each sample was adjusted to predetermined inclination angles (0, 2, 5 and 7°) and five ultrasound scan lines along the direction of the inclination were analyzed. For each scan line, reflection coefficient (R), integrated reflection coefficient (IRC) and ultrasound roughness index (URI) were calculated. Nonperpendicularity of the cartilage surface was found to affect R, IRC and URI significantly (p < 0.05). Importantly, all ultrasound parameters were able to distinguish (p < 0.05) the mechanically degraded samples from the intact ones even though the angle of incidence of the ultrasound beam varied between 0 and 5° among the samples. Diagnostically, the present findings are important because the natural curvature of the articular surface varies, and a perfect perpendicularity between the ultrasound beam and the surface of the cartilage may be challenging to achieve in a clinical measurement. (Email: erna.kaleva@uku.fi)     

超声评价不同分期的膝关节软骨退行性变

目的探讨超声诊断膝关节软骨退行性变分期的临床价值。方法超声探查40例患者的41个拟行关节镜手术或关节置换术膝关节，均观察其股骨内髁、股骨外髁、股骨滑车正中沟、滑车内侧斜面和滑车外侧斜面，共计205个关节面。超声结果与手术所见对照。结果超声诊断膝关节软骨退行性变（退变）的敏感性、特异性、准确性分别为64．9％、92．0％、76．5％。但对Ⅰ、Ⅱ期的诊断敏感性（46．7％）远远低于Ⅲ、Ⅳ期（75．7％）。结论超声评价膝关节软骨退变具有一定的敏感性和较高的特异性，可作为诊断该病的重要筛查手段。     

An Ultrasound Biomicroscopic and Water Jet Ultrasound Indentation Method for Detecting the Degenerative Changes of Articular Cartilage in a Rabbit Model of Progressive Osteoarthritis

It is important to assess the early degeneration of articular cartilage associated with osteoarthritis (OA) for early intervention and treatment planning. Previously, we have developed a high frequency ultrasound and water jet indentation method for the morphologic, acoustic and mechanical assessment of articular cartilage, using the enzymatic digestion as a model of osteoarthritic degeneration. No naturally degenerated articular cartilage has been tested with the developed method. In this study, we aimed to determine the usefulness of the developed method for detecting the natural degeneration of articular cartilage in a standard surgical model of OA in rabbits. Forty adult New Zealand white female rabbits were used in this study, which included 30 experimental rabbits undergoing the right anterior cruciate ligament transection surgery and 10 control rabbits. At the 3^rd, 6^th, and 9^th week post-surgery, 10 experimental rabbits were sacrificed, respectively, for assessment of the knee cartilage quality. The cartilage at the medial and lateral femoral condyles and tibial plateaus (four points) was measured by the high frequency ultrasound biomicroscopy, the water jet ultrasound indentation and a contact mechanical indentation test before a histopathologic analysis for grading of degeneration severity. Measured parameters were compared among different groups classified either by post-surgery time or by histopathologic grade. The results showed a general trend of increase for ultrasound roughness index and a general trend of decrease for integrated reflection coefficient, stiffness coefficient from water-jet indentation and Young's modulus (E) from the mechanical indentation with the increase of post-surgery time. Comparisons among groups with different histopathologic grades showed similar trend with the increase of degeneration severity. The water jet ultrasound indentation method was demonstrated to be an effective method to measure the mechanical properties of the articular cartilage and with further development of arthroscopic ultrasound probe; it has the ability to assess the early degeneration of articular cartilage with measurement of morphologic, acoustic and mechanical properties of the cartilage in vivo.     

超声诊断膝关节软骨退行性变的影响因素分析

目的 分析超声诊断膝关节软骨退行性变(退变)的一些影响因素.方法 选择行膝关节镜手术患者36例37个膝关节及关节置换术患者4例4个膝关节,共41个膝关节.术前1周行超声检查,超声诊断结果与关节镜或大体标本肉眼所见结果对比.对超声误诊、漏诊病例进行回顾性分析.结果 本组234处病灶,超声诊断真阳性病灶87处,假阳性病灶8处,假阴性病灶47处,真阴性病灶92处,诊断敏感性、特异性、准确性分别为64.9%、92.0%、76.5%.超声对软骨退变的分期与关节镜分期相关(r=0.703,P<0.01),但有59处病灶(59/234,25.2%)两者分期不符.影响超声诊断准确性的因素主要包括(1)病变部位,(2)病变程度,(3)临床治疗过程,(4)一些与超声成像原理有关的一般性影响因素.结论 超声检测膝关节软骨退变操作较复杂,影响因素也多.正确认识这些因素,有助于更好地理解声像图,避免漏诊误诊.     

Relationships Between Quantitative Pulse-Echo Ultrasound Parameters from the Superficial Zone of the Human Articular Cartilage and Changes in Surface Roughness,Collagen Content or Collagen Orientation Caused by Early Degeneration

We aimed to quantitatively investigate the relationship between amplitude-based pulse-echo ultrasound parameters and early degeneration of the knee articular cartilage. Twenty samples from six human femoral condyles judged as grade 0 or 1 according to International Cartilage Repair Society grading were assessed using a 15-MHz pulsed-ultrasound 3-D scanning system ex vivo. Surface roughness (R_q), average collagen content (A₁) and collagen orientation (A₁₂) in the superficial zone of the cartilage were measured via laser microscopy and Fourier transform infrared imaging spectroscopy. Multiple regression analysis with a linear mixed-effects model (LMM) revealed that a time-domain reflection coefficient at the cartilage surface (R_c) had a significant coefficient of determination with R_q and A₁₂ ($R_{\text{LMMm}}^2=0.79$); however, R_c did not correlate with A₁. Concerning the collagen characteristic in the superficial zone, R_c was found to be a sensitive indicator reflecting collagen disorganization, not collagen content, for the early degeneration samples.     

Quantitative Evaluation of Spontaneously and Surgically Repaired Rabbit Articular Cartilage Using Intra-Articular Ultrasound Method in situ

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

超声对不同部位股骨关节面软骨退行性变的对比研究

目的探讨超声评价不同部位股骨关节面软骨退行性变的优劣。方法超声探查40例患者41个拟行关节镜手术或关节置换术的膝关节，均观察其股骨内髁、股骨外髁、股骨滑车正中沟、滑车内侧斜面和滑车外侧斜面，共计205个关节面。超声结果与手术所见对照。结果超声对滑车关节面病灶的诊断水平远远优于内、外髁，敏感性、特异性、准确性分别为：滑车中央沟76．9％、100％、92．5％；滑车内侧斜面96．0％、85．7％、91．3％；滑车外侧斜面65．2％、95．2％、79．5％；外髁54．5％、100％、70．6％；内髁50．0％、69．2％、54．7％。所有位于外髁负重面偏内侧和内髁负重面近髁间嵴的病灶，超声均未能显示。结论超声对股骨滑车软骨退行性变的诊断水平优于股骨髁，而外髁负重面偏内侧、内髁负重面偏髁间嵴区域是超声的扫查盲区。     

Mitigation of Articular Cartilage Degeneration and Subchondral Bone Sclerosis in Osteoarthritis Progression Using Low-Intensity Ultrasound Stimulation

The purpose of this study was to evaluate the effect of low-intensity ultrasound on articular cartilage and subchondral bone alterations in joints under normal and functional disuse conditions during osteoarthritis (OA) progression. Total of thirty 5-mo-old female Sprague–Dawley rats were randomly assigned to six groups (n?=?5/group): age-matched group, OA group, OA?+?ultrasound (US) group, hindlimb suspension (HLS) group, HLS?+?OA group and HLS?+?OA?+?US group. The surgical anterior cruciate ligament was used to induce OA in the right knee joints. After 2 wk of OA induction, low-intensity ultrasound generated with a 3-MHz transducer with 20% pulse duty cycle and 30 mW/cm² acoustic intensity was delivered to the right knee joints for 20 min a day, 5 d a week for a total of 6 wk. Then, the right tibias were harvested for micro-computed tomography, histologic and mechanical analysis. Micro-computed tomography results indicated that the thickness and sulfated glycosaminoglycan content of cartilage decreased, but the thickness of the subchondral cortical bone plate and the formation of subchondral trabecular bone increased in the OA group under the normal joint use condition. Furthermore, histologic results revealed that chondrocyte density and arrangement in cartilage corrupted and the underlying subchondral bone increased during OA progression. These changes were accompanied by reductions in mechanical parameters in OA cartilage. However, fewer OA symptoms were observed in the HLS?+?OA group under the joint disuse condition. The cartilage degeneration and subchondral bone sclerosis were alleviated in the US treatment group, especially under normal joint use condition. In conclusion, low-intensity ultrasound could improve cartilage degeneration and subchondral sclerosis during OA progression. Also, it could provide a promising strategy for future clinical treatment for OA patients.     

Differences in Acoustic Properties of Intact and Degenerated Human Patellar Cartilage During Compression

Ultrasound indentation measurements have been shown to provide means to assess cartilage integrity and mechanical properties. To determine cartilage stiffness in the ultrasound indentation geometry, cartilage is compressed with an ultrasound transducer to determine the induced strain from the ultrasound signal using the time-of-flight principle. As the ultrasound speed in cartilage has been shown to vary during compression, the assumption of constant speed generates significant errors in the values of mechanical parameters. This variation in ultrasound speed has been investigated in intact cartilage, however, its existence and significance in degenerated tissue is unknown. In the present study, we investigate this issue with both intact and spontaneously degenerated human tissue. To accomplish this aim, we determined ultrasound speed and attenuation in human patellar cartilage (n = 68) during mechanical loading. For reference, cartilage mechanical properties and proteoglycan, collagen and water contents were determined. The acoustic properties were related to the composition and mechanical properties of the samples. Ultrasound speed showed significant, site-dependent variation and it was significantly associated (r = 0.79–0.81, p < 0.01) with the mechanical properties of cartilage. The compression related decrease in ultrasound speed showed statistically significant variation between different stages of degeneration. Error simulations revealed that changes in ultrasound speed during 2% compression could generate errors up to 15% in the values of elastic moduli of samples with early degeneration, if determined with the ultrasound indentation technique. In samples with advanced degeneration, the error was significantly (p < 0.05) smaller being 2% on average. As the compression related variation in ultrasound speed was lower in more degenerated samples, the mechanical parameters could be diagnosed more reliably in tissue showing advanced degeneration. The present results address the need to consider possible uncertainties in mechano-acoustic measurements of articular cartilage and call for methods to correct the effect of variable sound speed during compression. (E-mail: panu.kiviranta@uku.fi)     

膝关节软骨退行性变的声像学表现

目的 探讨膝关节软骨不同时期退行性变（退变）的声像学表现，并设立相应的超声诊断标准。 方法 对行关节镜手术的9个膝关节用超声术中经皮实时观察，对关节置换术的2个膝关节标本（置生理盐水中）进行离体观察。 总结 正常膝关节软骨及软骨Ⅰ～Ⅳ期退变的超声表现。 结果 正常膝关节软骨表现为高-低-高“夹心饼断面”样回声带。膝关节软骨Ⅰ期退变通常改变很不明显。Ⅰ期退变软骨表面毛糙，轻度变薄或局部隆起。Ⅲ期退变软骨局部明显变薄。Ⅳ期退变软骨完全缺失。 结论 膝关节软骨除Ⅰ期退变外，其余各期关节软骨退变在超声上均有特定表现。     

Ultrasound Evaluation of Site-Specific Effect of Simulated Microgravity on Articular Cartilage

Space flight induces acute changes in normal physiology in response to the microgravity environment. Articular cartilage is subjected to high loads under a ground reaction force on Earth. The objectives of this study were to investigate the site dependence of morphological and ultrasonic parameters of articular cartilage and to examine the site-specific responses of articular cartilage to simulated microgravity using ultrasound biomicroscopy (UBM). Six rats underwent tail suspension (simulated microgravity) for four weeks and six other rats were kept under normal Earth gravity as controls. Cartilage thickness, ultrasound roughness index (URI), integrated reflection coefficient (IRC) and integrated backscatter coefficient (IBC) of cartilage tissues, as well as histological degeneration were measured at the femoral head (FH), medial femoral condyle (MFC), lateral femoral condyle (LFC), patello-femoral groove (PFG) and patella (PAT). The results showed site dependence not significant in all UBM parameters except cartilage thickness (p < 0.01) in the control specimens. Only minor changes in articular cartilage were induced by 4-week tail suspension, although there were significant decreases in cartilage thickness at the MFC and PAT (p < 0.05) and a significant increase in URI at the PAT (p < 0.01). This study suggested that the 4-week simulated microgravity had only mild effects on femoral articular cartilage in the rat model. This information is useful for human spaceflight and clinical medicine in improving understanding of the effect of microgravity on articular cartilage. However, the effects of longer duration microgravity experience on articular cartilage need further investigation. (E-mail: rsguoxia@inet.polyu.edu.hk)     

Ultrasound Biomicroscopy Imaging for Monitoring Progressive Trypsin Digestion and Inhibition in Articular Cartilage

This study reports an ultrasound biomicroscopy (UBM) imaging approach to monitor the progressive trypsin-induced depletion of proteoglycan (PG) and its inhibition in articular cartilage. Three fresh, normal bovine patellae were obtained and four full-thickness cartilage-bone specimens were prepared from the lower medial side of each patella. One sample was used as a control and the other three were divided into three groups: Groups A, B and C (n = 3 for each group). After a 40 min 0.25% trypsin digestion, samples from group A were continuously digested in trypsin solution, while those in groups B and C were immersed in physiologic saline and fetal bovine serum (FBS), respectively, for another 280 min. The trypsin penetration front was observed by UBM and M-mode images were acquired using 50 MHz focused ultrasound and custom-developed software. The results show that the 40 min trypsin digestion degraded nearly the whole surface layer of the cartilage tissue. Further digestion in trypsin or residual digestion in saline for 280 min depleted most of the PG content, as observed in groups A and B. The replacement of trypsin with a physiologic saline solution only slightly slowed the digestion process (group B), while trypsin inhibitors in FBS stopped the digestion in approximately 1.5 h (group C). The normalized digestion fractions of the digested tissues were calculated from ultrasound data and histology sections, and then compared between the groups. Without the use of FBS, 80% to 100% of the full thickness was digested, while this number was only approximately 50% when using FBS. Our findings indicate that the UBM imaging system could provide two-dimensional (2-D) visual information for monitoring progressive trypsin-induced PG depletion in articular cartilage. The system also potentially offers a useful tool for preparing cartilage degeneration models with precisely controlled PG depletion. (E-mail: ypzheng@ieee.org)     

Quantitative Assessment of Articular Cartilage with Morphologic,Acoustic and Mechanical Properties Obtained Using High-Frequency Ultrasound

Osteoarthritis (OA) is one of the most common joint diseases among adults, and its early detection is still not possible. In this study, high-frequency ultrasound and ultrasound-assisted mechanical testing systems were used to quantitatively measure the morphologic, acoustic and mechanical properties of normal and enzymatically degraded bovine articular cartilages in vitro. A total of 40 osteochondral cartilage plugs were prepared from 20 bovine patellae (n = 20 × 2) and divided into two groups for collagenase and trypsin digestions, respectively. A high-frequency ultrasound system (center frequency: 40 MHz) was used to analyze the surface integrity (ultrasound roughness index, URI), thickness and acoustic properties of the articular cartilages before and after enzymatic degradations. Acoustic parameters included the integrated reflection coefficient (IRC) from the cartilage surface, reflection from the cartilage-bone interface (AIB_bone), integrated attenuation (IA) and integrated backscatter (IBS) of the internal cartilage tissue. A newly developed ultrasound water jet indentation system was used to assess the mechanical properties of the cartilage samples. The results showed that the URI increased significantly (p < 0.05) after collagenase digestion while no significant change (p > 0.05) was found after trypsin digestion. With regard to acoustic parameters, the IRC decreased significantly (p < 0.05) after collagenase digestion while no significant change (p > 0.05) was found after trypsin digestion. The AIB_bone demonstrated an insignificant change after collagenase digestion (p > 0.05) but a significant decrease after trypsin digestion (p < 0.05). Both enzymatic degradation groups showed insignificant differences (p > 0.05) in the IA but a significant increase (p < 0.05) in the IBS after both enzymatic degradations. The apparent stiffness measured by ultrasound water jet indentation suggested that articular cartilage from both groups became significantly softer (p < 0.05) after the enzymatic degradations. A significant relationship was found to exist between the IRC and URI (p < 0.05). This study showed that high-frequency ultrasound can be a comprehensive tool to quantitatively and systematically analyze the morphologic, acoustic and mechanical properties of articular cartilage in association with its degeneration. (E-mail: ypzheng@ieee.org)     

髌股关节软骨退变的MRI和关节镜对照研究

目的：以关节镜为标准,确定３Ｄ－Ｖｏｌｕｍｅ－ＦＦＦ－Ｔ１ＷＩ对髌股关节软骨退变的诊断价值。方法：４８个人膝关节行关节镜检查及３Ｄ－Ｖｌｏｕｍｅ－ＦＦＦ－Ｔ１ＷＩ矢状位扫描。矢状位图像行多平面重建（ＭＰＲ）处理。ＭＲ图像每个髋股关节分内、外髌骨面、股骨滑车面与关节镜图像逐一对照分析。结果：关节镜下发现１０２个病变软骨面,３Ｄ－Ｖｏｌｕｍｅ－ＦＦＦ－Ｔ１ＷＩ对软骨病变的分级和关切镜分级间有显著正相关性（Ｐ〈０．０１）。结论：３Ｄ－Ｖｏｌｕｍｅ－ＦＦＦ－Ｔ１ＷＩ结合ＭＰＲ评价髌股关节软骨退弯和关节镜评价关节软骨有很好的相关性、互补性。     

超声、X-线平片和MR对膝关节软骨退行性变诊断价值的比较

目的比较超声、X-线平片和MR评价膝关节软骨退行性变（退变）的优劣。 方法选择40例患者41个拟行关节镜手术或关节置换术的膝关节，术前采用超声和X-线平片观察股骨内髁、股骨外髁、股骨滑车正中沟、滑车内侧斜面和滑车外侧斜面，共计205个关节面。其中11个膝关节接受了MR检查，以关节镜或置换术标本所见为对照，比较3种影像学手段对软骨退变的诊断水平。 结果超声、X-线平片和MR诊断膝关节软骨退变的敏感性、特异性、准确性分别为：超声64．9％、92．0％、76．5％；X-线平片46．3％、75．0％、58．5％；MR79．4％、86．2％、82．5％。超声诊断敏感性、准确性低于MR，明显高于X-线平片，而特异性高于MR。 结论超声对膝关节软骨退变的诊断水平低于MR，明显高于X-线平片，可以作为初查手段推广应用。     

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.     

Minimally Invasive Ultrasound Method for Intra-Articular Diagnostics of Cartilage Degeneration

Quantitative ultrasound imaging (QUI) can be used to evaluate the integrity of articular cartilage and for diagnosing the early signs of osteoarthritis (OA). In this study, we applied a minimally invasive ultrasound imaging technique and investigated its ability to detect superficial degeneration of bovine knee articular cartilage. Intact (n = 13), collagenase-digested (n = 6) and mechanically degraded (n = 7) osteochondral samples (dia. = 25 mm) and custom-made phantoms with different degrees of surface roughness (n = 8) were imaged using a high-frequency (40 MHz) QUI system. For each sample and phantom, the ultrasound reflection coefficient (R), integrated reflection coefficient (IRC) and ultrasound roughness index (URI) were determined. Furthermore, to evaluate the clinical applicability of intra-articular ultrasound (IAUS) in diagnostics, one intact bovine knee joint was investigated ex vivo using a simulated arthroscopic approach. Differences in the surface characteristics of the phantoms were detected by monitoring changes in the reflection and surface roughness parameters. Both mechanically- and enzymatically-induced degradation were sensitively diagnosed by decreased (p < 0.05) reflection (R and IRC) at the cartilage surface. Furthermore, mechanical degradation was detected in the increased (p < 0.05) surface roughness (URI). The intra-articular investigation of a bovine knee joint suggested that the IAUS technique may enable minimally invasive, straightforward diagnostics of the degenerative status of the articular surfaces. We conclude that quantitative IAUS imaging can be used for detecting collagen disruption and increased roughness of the articular surface. This quantitative in vivo ultrasound technique could have great clinical value in the diagnostics of joint diseases. (E-mail: tviren@hytti.uku.fi)     

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.