Correlation of cartilage stiffness to thickness and level of degeneration using a handheld indentation probe

Functional Assessment of Human Articular Cartilage Using Second Harmonic Generation (SHG) Imaging: A Feasibility Study

Many arthroscopic tools developed for knee joint assessment are contact-based, which is challenging for in vivo application in narrow joint spaces. Second harmonic generation (SHG) laser imaging is a non-invasive and non-contact method, thus presenting an attractive alternative. However, the association between SHG-based measures and cartilage quality has not been established systematically. Here, we investigated the feasibility of using image-based measures derived from SHG microscopy for objective evaluation of cartilage quality as assessed by mechanical testing. Human tibial plateaus harvested from nine patients were used. Cartilage mechanical properties were determined using indentation stiffness (Einst) and streaming potential-based quantitative parameters (QP). The correspondence of the cartilage electromechanical properties (Einst and QP) and the image-based measures derived from SHG imaging, tissue thickness and cell viability were evaluated using correlation and logistic regression analyses. The SHG-related parameters included the newly developed volumetric fraction of organised collagenous network (Φcol) and the coefficient of variation of the SHG intensity (CVSHG). We found that Φcol correlated strongly with Einst and QP (ρ = 0.97 and - 0.89, respectively). CVSHG also correlated, albeit weakly, with QP and Einst, (|ρ| = 0.52-0.58). Einst and Φcol were the most sensitive predictors of cartilage quality whereas CVSHG only showed moderate sensitivity. Cell viability and tissue thickness, often used as measures of cartilage health, predicted the cartilage quality poorly. We present a simple, objective, yet effective image-based approach for assessment of cartilage quality. Φcol correlated strongly with electromechanical properties of cartilage and could fuel the continuous development of SHG-based arthroscopy.

Detecting early osteoarthritis through changes in biomechanical properties - A review of recent advances in indentation technologies in a clinical arthroscopic setup

Osteoarthritis (OA) is a degenerative joint disease currently affecting half of all women and one-third of all men aged over 65 and it is predicted to even increase in the next decades. In the variety of causes leading to OA, the first common denominator are changes in the extracellular matrix of the cartilage. In later stages, OA affects the whole joint spreading to higher levels of tissue architecture causing irreversible functional and structural damage. To date, the diagnosis of OA is only formulated in the late stages of the disease. This is also, where most present therapies apply. Since a precise diagnosis is a prerequisite for targeted therapy, tools to diagnose early OA, monitor its progression, and accurately stage the disease are wanted. This review article focuses on recent advances in indentation technologies to diagnose early OA through describing biomechanical cartilage characteristics. We provide an overview of microindentation instruments, indentation-type Atomic Force Microscopy, ultrasound, and water-jet ultrasound indentation, Optical Coherence Tomography-based air-jet indentation, as well as fiber Bragg grating.

A Useful Combination of Quantitative Ultrashort Echo Time MR Imaging and a Probing Device for Biomechanical Evaluation of Articular Cartilage

In this study, we combined quantitative ultrashort echo time (UTE) magnetic resonance (MR) imaging and an investigation by a probing device with tri-axial force sensor to seek correlations with mechanical properties of human patellar cartilage for in situ evaluation of biomechanical properties. Cartilage blocks (15 × 20 × 5 mm³) were dissected from the patella of six donors; 5 mm square regions of interest from the cartilage blocks were imaged using UTE-MR imaging sequences (T2* and magnetization transfer ratio (MTR)), and mechanical properties were measured using a micro indentation device. Then, the vertical reaction force on the cartilage surface was measured while push-probing forward 3 mm with the probing device at a 30° tilt to the horizontal plane. The results showed a positive correlation between stiffness/elastic modulus and each predictor variable (UTE-T2* (r = 0.240 and 0.255, respectively, UTE-MTR (r = 0.378 and 0.379, respectively), and probing device force (r = 0.426 and 0.423, respectively). Furthermore, multiple linear regression analysis showed the combination of the three predictors had stronger correlation (adjusted r² = 0.314 (stiffness), 0.323 (elastic), respectively). Our results demonstrate the potential for these non- and less- invasive methods for in situ evaluation of the mechanical properties of cartilage tissue.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part I: Large animals

BACKGROUND

The human knee is a complex joint, and affected by a variety of articular cartilage disorders. Large animal models are critical to model the complex disease mechanisms affecting a functional joint. Species-dependent differences highly affect the results of a pre-clinical study and need to be considered, necessitating specific knowledge not only of macroscopic and microscopic anatomical and pathological aspects, but also characteristics of their individual gait and joint movements.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major translational large animal species, comprising dogs, (mini)pigs, sheep, goats, and horses in comparison with humans. Specific characteristics of each species, including kinematical gait parameters are provided. Considering these multifactorial dimensions will allow to select the appropriate model for answering the research questions in a clinically relevant fashion.

A Novel Bioreactor System Capable of Simulating the In Vivo Conditions of Synovial Joints

Any significant in vitro evaluation of cartilage tissue engineering and cartilage repair strategies has to be performed under the harsh conditions encountered in vivo within synovial joints. To this end, we have developed a novel automated physiological robot reactor system (PRRS) that is capable of recapitulating complex physiological motions and load patterns within an environment similar to that found in the human knee. The PRRS consists of a mechanical stimulation unit (MSU) and an automatic sample changer (ASC) within an environment control box in which the humidity, temperature, and gas composition are tightly regulated. The MSU has three linear (orthogonal) axes and one rotational degree of freedom (around the z-axis). The ASC provides space for up to 24 samples, which can be allocated to individual stimulation patterns. Cell-seeded scaffolds and ex vivo tissue culture systems were established to demonstrate the applicability of the PRRS to the investigation of the effect of load and environmental conditions on engineering and maintenance of articular cartilage in vitro. The bioreactor is a flexible system that has the potential to be applied for culturing connective tissues other than cartilage, such as bone and intervertebral disc tissue, even though the mechanical and environmental parameters are very different.

Comparative anatomy and morphology of the knee in translational models for articular cartilage disorders. Part II: Small animals

BACKGROUND

Small animal models are critical to model the complex disease mechanisms affecting a functional joint leading to articular cartilage disorders. They are advantageous for several reasons and significantly contributed to the understanding of the mechanisms of cartilage diseases among which osteoarthritis.

METHODS

Literature search in Pubmed.

RESULTS AND DISCUSSION

This narrative review summarizes the most relevant anatomical structural and functional characteristics of the knee (stifle) joints of the major small animal species, including mice, rats, guinea pigs, and rabbits compared with humans. Specific characteristics of each species, including kinematical gait parameters are provided and compared with the human situation. When placed in a proper context respecting their challenges and limitations, small animal models are important and appropriate models for articular cartilage disorders.

Discrimination between healthy and degenerated bovine articular cartilage with a fiber Bragg grating based microindenter

OBJECTIVE

In this study we aim to show that an optical fiber Bragg grating-based microindentation system, which has the potential to be deployed arthroscopically, can differentiate between healthy and degenerated articular cartilage, which represents an important challenge in minimally-invasive surgery.

DESIGN

Twenty bovine osteochondral cylinders, extracted from the patellar groove of ten 24 months old animals were subjected to stepwise in vitro stress-relaxation indentation measurements. The indentation procedure comprised 15 indentation steps of 20 μm each, reaching a total depth of 300 μm. Ten samples remained untreated and served as a control group for healthy cartilage. A second group of ten samples was treated for 12 h with an aqueous trypsin solution (concentration 2.5%) to deplete the proteoglycans. For both groups and all indentation depths deeper than 100 μm, the step response functions of a two elements Maxwell-Wiechert model fitted well to the measured relaxation curves.

RESULTS

The standard deviations of the identified stiffness parameters within each group were much smaller than the difference of the average stiffness values between both groups. Based on the measured stiffness values, the system was capable to discriminate between healthy and degenerated cartilage with a high level of significance (p < 0.001). The experimental results are also discussed in terms of the biomechanical changes of cartilage under the action of trypsin.

CONCLUSION

The fiber Bragg grating microindentation system showed the capability to differentiate intact and proteoglycan depleted cartilage with high significance.

Quantitative MRI of Human Cartilage In Vivo: Relationships with Arthroscopic Indentation Stiffness and Defect Severity

Objective To investigate the association of cartilage defect severity, as determined by the International Cartilage Repair Society (ICRS) grading with indentation stiffness and T2 relaxation time of magnetic resonance imaging (MRI), a biomarker for the integrity of articular cartilage. Design Twenty-one patients scheduled for arthroscopic were included in the study. Prior to arthroscopy, subjects underwent quantitative MRI of articular cartilage, namely T2 relaxation time mapping at 1.5 T. Within 2 months, subjects underwent arthroscopy, which also included ICRS grading and measurement of arthroscopic indentation stiffness. Arthroscopic evaluations and T2 mapping at anterior, central, and posterior medial and lateral femoral condyles were correlated using a colocalization scheme. Differences in Young's modulus, as derived by indentation tests, and T2 times between ICRS grades were analyzed using Mann-Whitney's U or Kruskal-Wallis H tests. The correlation between modulus and T2 times was analyzed using Spearman's rank correlation coefficients. Results Modulus and T2 showed significant topographical variation. In the anterior region of interest (ROI) on the medial condyle the modulus showed a negative association with ICRS grade ( P = 0.040) and the T2 times were longer in ICRS grade 2 compared with grades 0 and 1 ( P = 0.047). Similar, but nonsignificant associations were found in the central ROI on the medial condyle. No significant correlations were observed between the indentation modulus and T2 times. Conclusions Cartilage degeneration is identified both with mechanical indentation and T2 mapping in MRI. However, in this study, indentation stiffness and T2 relaxation time in vivo, were not associated.

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.

Biomechanical Characterization of Human Soft Tissues Using Indentation and Tensile Testing

Regenerative medicine aims to engineer materials to replace or restore damaged or diseased organs. The mechanical properties of such materials should mimic the human tissues they are aiming to replace; to provide the required anatomical shape, the materials must be able to sustain the mechanical forces they will experience when implanted at the defect site. Although the mechanical properties of tissue-engineered scaffolds are of great importance, many human tissues that undergo restoration with engineered materials have not been fully biomechanically characterized. Several compressive and tensile protocols are reported for evaluating materials, but with large variability it is difficult to compare results between studies. Further complicating the studies is the often destructive nature of mechanical testing. Whilst an understanding of tissue failure is important, it is also important to have knowledge of the elastic and viscoelastic properties under more physiological loading conditions. This report aims to provide a minimally destructive protocol to evaluate the compressive and tensile properties of human soft tissues. As examples of this technique, the tensile testing of skin and the compressive testing of cartilage are described. These protocols can also be directly applied to synthetic materials to ensure that the mechanical properties are similar to the native tissue. Protocols to assess the mechanical properties of human native tissue will allow a benchmark by which to create suitable tissue-engineered substitutes.

Animal Models for Evaluation of Bone Implants and Devices

Bone implants and devices are a rapidly growing field within biomedical research, and implants have the potential to significantly improve human and animal health. Animal models play a key role in initial product development and are important components of nonclinical data included in applications for regulatory approval. Pathologists are increasingly being asked to evaluate these models at the initial developmental and nonclinical biocompatibility testing stages, and it is important to understand the relative merits and deficiencies of various species when evaluating a new material or device. This article summarizes characteristics of the most commonly used species in studies of bone implant materials, including detailed information about the relevance of a particular model to human bone physiology and pathology. Species reviewed include mice, rats, rabbits, guinea pigs, dogs, sheep, goats, and nonhuman primates. Ultimately, a comprehensive understanding of the benefits and limitations of different model species will aid in rigorously evaluating a novel bone implant material or device.

In vitro and in vivo evaluation of doxycycline-chondroitin sulfate/PCLmicrospheres for intraarticular treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease, which has no complete treatment with medication yet. Intraarticular hyaluronan (HA) injection can decrease pain and modify the natural course of OA. This study was designed to provide long term delivery of an MMP (matrix-metalloproteinase) inhibitor agent-doxycycline, together with matrix regenerative agent-chondroitin sulfate for treating OA which progress with matrix degenerations. Doxycycline (D) and doxycycline-chondroitin sulfate (D-CS) loaded poly-ɛ-caprolactone (PCL) microspheres (MS) were prepared as intraarticular delivery systems. Bio-effectiveness of developed microspheres was first evaluated with three-dimensional in vitro model of OA where both MS showed significant reduction in MMP-13 levels compared to untreated OA-chondrocytes at 15 and 24 days. Significant decrease was observed in GAG release into the media for both D MS and D-CS MS treated groups at 15 and 24 days. Second, the microspheres were injected to rabbit knee in hyaluronan (HA) to evaluate the effectiveness of the treatment. Radiographic scores of D MS and D-CS MS groups improved after 8 weeks when compared to OA group. Mankin-Pitzker histological scores similarly showed improvement with D MS and D-CSMS groups when compared to OA group. Ex vivo hardness tests of cartilages demonstrated superior hardness values with both doses of D-CSMS compared to OA group. D MS showed promising improvement of OA in histology results. Although, both MS groups had similar effects on cells in the in vitro model, D-CSMS had a positive contribution on all in vivo treatment outcomes and showed potential as a new strategy for treatment when applied to OA knee joints.

Biomarkers affected by impact velocity and maximum strain of cartilage during injury

Osteoarthritis is one of the most common, debilitating, musculoskeletal diseases; 12% associated with traumatic injury resulting in post-traumatic osteoarthritis (PTOA). Our objective was to develop a single impact model with cartilage "injury level" defined in terms of controlled combinations of strain rate to a maximum strain (both independent of cartilage load resistance) to study their sensitivity to articular cartilage cell viability and potential PTOA biomarkers. A servo-hydraulic test machine was used to measure canine humeral head cartilage explant thickness under repeatable pressure, then subject it (except sham and controls) to a single impact having controlled constant velocity V=1 or 100mm/s (strain rate 1.82 or 182/s) to maximum strain ε=10%, 30%, or 50%. Thereafter, explants were cultured in media for twelve days, with media changed at day 1, 2, 3, 6, 9, 12. Explant thickness was measured at day 0 (pre-injury), 6 and 12 (post-injury). Cell viability, and tissue collagen and glycosaminoglycan (GAG) were analyzed immediately post-injury and day 12. Culture media were tested for biomarkers: GAG, collagen II, chondroitin sulfate-846, nitric oxide, and prostaglandin E2 (PGE2). Detrimental effects on cell viability, and release of GAG and PGE2 to the media were primarily strain-dependent, (PGE2 being more prolonged and sensitive at lower strains). The cartilage injury model appears to be useful (possibly superior) for investigating the relationship between impact severity of injury and the onset of PTOA, specifically for discovery of biomarkers to evaluate the risk of developing clinical PTOA, and to compare effective treatments for arthritis prevention.

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 3rd, 6th, and 9th 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.

[Possibilities for the biomechanical characterization of cartilage: a brief update]

The quantitative description of the biomechanical function of diarthrodial joint cartilage is a particularly challenging task due to the unique load bearing, load distribution and tribological properties of the tissue,which have their origin in the unique structure and biochemical composition. In the course of recent decades,different material models and testing methods have been published which claim to meet this challenge in one way or another. The goal of this paper is to provide an overview of the basic principles involved in the most important of these material models and testing methods. The relationship between the material models and the relevant testing methods will be illustrated in a comprehensible manner. As practical use of these methods is also associated with the amount of time required to perform them, particular attention will be paid to experimental approaches requiring only one test modality to be performed.

One-step surgical procedure for the treatment of osteochondral defects with adipose-derived stem cells in a caprine knee defect: a pilot study

Regenerative therapies offer attractive alternatives for the treatment of osteochondral defects. Adipose-derived stromal vascular fraction (SVF) cells allow the development of one-step surgical procedures by their abundant availability and high frequency. In this pilot study we evaluated the in vivo safety, feasibility, and efficacy of this concept using scaffolds seeded with freshly isolated (SVF) or cultured adipose stem cells (ASCs), and compared these to their acellular counterparts. Osteochondral defects were created in medial condyles and trochlear grooves in knees of eight goats. Defects were filled with acellular collagen I/III scaffolds or scaffolds seeded with SVF cells or cultured ASCs. Osteochondral regeneration was evaluated after 1 and 4 months by macroscopy, immunohistochemistry, biomechanical analysis, microCT analysis, and biochemistry. After 1 month, no adverse effects were noted. Microscopic, but not macroscopic evaluation showed considerable yet not significant differences, with cell-loaded constructs showing more extensive regeneration. After 4 months, acellular constructs displayed increased regeneration, however, to a lesser degree than cell-treated constructs. The latter exhibited more extensive collagen type II, hyaline-like cartilage, and higher elastic moduli, and their glycosaminoglycan content in the cartilaginous layer better approached native tissue values. Moreover, their defect regions contained higher levels of regenerated, mature subchondral bone with more intense collagen type I staining. SVF cells tended to perform best on all parameters. In summary, this pilot study demonstrated the preclinical safety and feasibility of a one-step surgical procedure for osteochondral defect regeneration. Similar regeneration was found between freshly isolated SVF cells and cultured ASCs. Larger studies with longer follow-up are required to substantiate these findings.

ARE TIBIOFEMORAL COMPRESSIVE LOADS TRANSFERRED ONLY VIA CONTACT MECHANISMS?

The tibiofemoral joint is known to bear compressive loads of several body-weights during daily activities. These forces are known to be transferred through the joint via compression of the tibial and femoral surfaces against one another. The menisci are also known to enhance this process by increasing the contact area and decreasing contact stress. However, calculations presented in this paper suggest that the load-bearing capacity of contact mechanisms is seemingly several times smaller than tibiofemoral joint loads. This suggests that probably one or more non-contact load-bearing mechanism(s) exist, and share the load with the already known contact mechanisms.

Correlation of dynamic impact testing, histopathology and visual macroscopic assessment in human osteoarthritic cartilage

OBJECTIVE

Improved staging of cartilage degeneration is required, particularly during the early stages. We correlated mechanical properties with histological and macroscopic findings.

METHODS

One hundred and twenty cartilage samples were obtained during total knee arthroplasty. Two adjacent plugs were harvested--one for histological classification and one for macroscopic and biomechanical purposes. Dynamic impact testing was performed; normal stress, dissipated energy (∆E), tangent modulus and stiffness were evaluated.

RESULTS

Samples were classified according to six categories of the ICRS histological scale. Mechanical characteristics revealing significant differences between the groups (p < 0.01) were specific damping and related absolute ∆E. A significant correlation was found between the macroscopic score and specific damping, as well as absolute and relative ∆E (p < 0.01). A strong relation was revealed between relative ∆E and cartilage thickness (p < 0.001; R (2) = 0.69).

CONCLUSIONS

Only ∆E correlated with the condition of the cartilage--the value increased with decreasing quality-and is the most suitable characteristic. This change appears substantial in initial stages of cartilage deterioration.

Histopathology atlas of animal model systems - overview of guiding principles

Animal model systems represent an important adjunct and surrogate for studies of osteoarthritis (OA) in humans. They provide a means to study OA pathophysiology as well as aid in the development of therapeutic agents and biological markers for diagnosing and prognosing the disease. Thus, it is of great importance for the OA scientific community, both in academic as well as industrial research, to standardize scoring systems for evaluating the OA disease process and to make results between different studies comparable. The task of the histopathology initiative of OARSI was to achieve a consensus of scoring systems for the most important species used in OA animal model research (dog, guinea pig, horse, mouse, rabbit, rat, and sheep/goat), which are presented in the various chapters in this special volume of Osteoarthritis & Cartilage together with extra chapters on basic methodology (histochemistry, statistics, morphometry), the specific terminology and a general discussion of animal models in OA research. Standardized definitions are suggested for basic but essential terms such as "grading" and "staging" in order to promote their consistent use and thereby promote improved understanding and data interpretation across all model systems. Thus, this introductory chapter presents an overview of the guiding principles for assessment of important OA animal model systems. Use of such systems, independently or in conjunction with other systems in parallel, should facilitate comparability of results across animal model studies.

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=20x2) 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.

Sequential alterations in magnetic resonance imaging findings after autologous osteochondral mosaicplasty for young athletes with osteochondritis dissecans of the humeral capitellum

BACKGROUND

The goal of osteochondral mosaicplasty (mosaicplasty) against osteochondritis dissecans of the humeral capitellum (capitellar OCD) is to allow patients to return to their sports activities without functional disturbance of the affected elbow. Consequently, the rehabilitation protocol and the interval before returning to sports activities must be established. Although surgeons need this type of data for establishing sequential alterations of grafts in the elbow, no such data have been published.

HYPOTHESIS

The findings of magnetic resonance imaging (MRI) improve with increasing time after mosaicplasty for capitellar OCD.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Ten young male athletes with advanced lesions of capitellar OCD, treated with mosaicplasties, underwent MRI scans at 3, 6, and 12 months, postoperatively. The surgical technique involved obtaining small-sized cylindrical osteochondral grafts from the lateral periphery of the femoral condyle at the level of the patellofemoral joint and transplanting them to the capitellar lesion. The MRI findings were semiquantitatively assessed according to the scoring system of Henderson et al (4, normal; 16, no repair).

RESULTS

At 12 months, all patients returned to their competitive level of sports without any disturbances of the operated elbow. Fluid surrounding the graft was found in all patients at 3 months and 4 patients at 6 months. The grafts were all well seated within the recipient sites, with no MRI evidence of graft loosening at 12 months. The overall MRI scores significantly improved from 3 to 12 months.

CONCLUSION

The MRI findings indicate that the graft incorporation to the surrounding tissues occurs around or after 6 months, postoperatively. This finding suggests that rehabilitation precautions be taken for up to 6 months after mosaicplasty for young athletes with capitellar OCD.

Evaluation of bone-tendon junction healing using water jet ultrasound indentation method

The re-establishment of bone-tendon junction (BTJ) tissues with the junction, characterized as a unique transitional fibrocartilage zone, is involved in many trauma and reconstructive surgeries. Experimental and clinical findings have shown that a direct BTJ repair requires a long period of immobilization, which may be associated with a postoperative weak knee. Therefore, it is necessary to evaluate the morphologic and mechanical properties of BTJ tissues in situ to better understand the healing process for the purpose of reducing the adverse effects of immobilization. We previously reported a noncontact ultrasound water jet indentation system for measuring and mapping tissue mechanical properties. The key idea was to utilize a water jet as an indenter as well as the coupling medium for high-frequency ultrasound. In this article, we used ultrasound water jet indentation to evaluate the BTJ healing process. The system's capability of measuring the material elastic modulus was first validated using tissue-mimicking phantoms. Then it was employed to assess the healing of the BTJ tissues after partial patellectomy over time on twelve 18-week-old female New Zealand White rabbits. It was found that in comparison with the normal control samples, the elastic modulus of the fibrocartilage of the postoperative samples was significantly smaller, while its thickness increased significantly. Among the postoperative sample groups, the elastic modulus of the fibrocartilage of the samples harvested at week 18 was significantly higher than those harvested at week 6 and week 12, which was even comparable with the value of the control samples at the same sacrifice time. The results suggested that the noncontact ultrasound water jet indentation system provided a nondestructive way to evaluate the material properties of small animal tissues in situ and thus had the ability to evaluate the healing process of BTJ.

Comparison of single-phase isotropic elastic and fibril-reinforced poroelastic models for indentation of rabbit articular cartilage

Classically, single-phase isotropic elastic (IE) model has been used for in situ or in vivo indentation analysis of articular cartilage. The model significantly simplifies cartilage structure and properties. In this study, we apply a fibril-reinforced poroelastic (FRPE) model for indentation to extract more detailed information on cartilage properties. Specifically, we compare the information from short-term (instantaneous) and long-term (equilibrium) indentations, as described here by IE and FRPE models. Femoral and tibial cartilage from rabbit (age 0-18 months) knees (n=14) were tested using a plane-ended indenter (diameter=0.544 mm). Stepwise creep tests were conducted to equilibrium. Single-phase IE solution for indentation was used to derive instantaneous modulus and equilibrium (Young's) modulus for the samples. The classical and modified Hayes' solutions were used to derive values for the indentation moduli. In the FRPE model, the indentation behavior was sample-specifically described with three material parameters, i.e. fibril network modulus, non-fibrillar matrix modulus and permeability. The instantaneous and fibril network modulus, and the equilibrium Young's modulus and non-fibrillar matrix modulus showed significant (p<0.01) linear correlations of R(2)=0.516 and 0.940, respectively (Hayes' solution) and R(2)=0.531 and 0.960, respectively (the modified Hayes' solution). No significant correlations were found between the non-fibrillar matrix modulus and instantaneous moduli or between the fibril network modulus and the equilibrium moduli. These results indicate that the instantaneous indentation modulus (IE model) provides information on tensile stiffness of collagen fibrils in cartilage while the equilibrium modulus (IE model) is a significant measure for stiffness of PG matrix. Thereby, this study highlights the feasibility of a simple indentation analysis.

Noncontact evaluation of articular cartilage degeneration using a novel ultrasound water jet indentation system

We previously reported a noncontact ultrasound water jet indentation system for measuring and mapping tissue mechanical properties. The key idea was to utilize a water jet as an indenter as well as the coupling medium for high-frequency ultrasound. In this paper, the system was employed to assess articular cartilage degeneration, using stiffness ratio as an indicator of the mechanical properties of samples. Both the mechanical and acoustical properties of intact and degenerated bovine patellar articular cartilage (n = 8) were obtained in situ. It was found that the stiffness ratio was reduced by 44 +/- 17% after the articular cartilage was treated by 0.25% trypsin at 37 degrees C for 4 h while no significant difference in thickness was observed between the intact and degenerated samples. A significant decrease of 36 +/- 20% in the peak-to-peak amplitude of ultrasound echoes reflected from the cartilage surface was also found for the cartilage samples treated by trypsin. The results also showed that the stiffness obtained with the new method highly correlated with that measured using a standard mechanical testing protocol. A good reproducibility of the measurements was demonstrated. The present results showed that the ultrasound water jet indentation system may provide a potential tool for the non-destructive evaluation of articular cartilage degeneration by simultaneously obtaining mechanical properties, acoustical properties, and thickness data.

Indentation diagnostics of cartilage degeneration

OBJECTIVE

Mechanical indentation and ultrasound (US) indentation instruments have been introduced for quantitative assessment of cartilage properties in vivo. In this study, we compared capabilities of these instruments to determine properties of healthy and spontaneously degenerated human patellar cartilage in situ and to diagnose the early stages of osteoarthritis (OA).

DESIGN

Six anatomical sites were localized from human patellae (N=14). By determining the force by which the tissue resists constant deformation (F(IND)), a mechanical indentation instrument was used to measure the compressive dynamic stiffness of cartilage. Further, the dynamic modulus (E(US)) and the US reflection coefficient of cartilage surface (R(US)) were measured with an US indentation instrument. For reference, Young's modulus and dynamic modulus were determined from cartilage disks using unconfined compression geometry. Proteoglycan and collagen contents of samples were analyzed microscopically. The samples were divided into three categories (healthy, early degeneration, and advanced degeneration) based on the Osteoarthritis Research Society International (OARSI) OA-grading.

RESULTS

Parameters R(US), E(US) and F(IND) were significantly associated with the histological, compositional and mechanical properties of cartilage (|r|=0.28-0.72, n=73-75, P<0.05). Particularly, R(US) was able to discern degeneration of the samples with high sensitivity (0.77) and specificity (0.98). All parameters, except R(US,) showed statistically significant site-dependent variation in healthy cartilage.

CONCLUSIONS

US reflection measurement shows potential for diagnostics of early OA as no site-matched reference values are needed. In addition, the high linear correlations between indentation and reference measurements suggest that these arthroscopic indentation instruments can be used for quantitative evaluation of cartilage mechanical properties, e.g., after cartilage repair surgery.

Dynamic biomechanics correlate with histopathology in human tibial cartilage: a preliminary study

Improved staging of cartilage degeneration is required, particularly during early stages when minimal surface damage is visible arthroscopically. Degradation of articular cartilage extracellular matrix, resulting from degenerative changes associated with osteoarthritis, can influence its functional properties. Cartilage mechanical properties therefore may provide a quantitative method for monitoring degenerative change in this tissue. We determined whether dynamic mechanical properties of cartilage (effective shear modulus and phase lag) measured with a handheld indenter correlated with histopathology scores, proteoglycan, and collagen content or expression of chondrocyte-specific (aggrecan, collagen II) or dedifferentiation (collagen I and III) genes in human osteoarthritic cartilage with International Cartilage Repair Society scores of 0 to 1. We observed an association between the histopathologic stage of cartilage disease and dynamic shear modulus and phase lag. In contrast, there generally was a poor relationship between cartilage biomechanical properties and biochemistry with the only noteworthy correlation being between shear modulus and collagen. Phase lag but not shear modulus correlated with gene expression. These data support the potential of dynamic indentation for assessing the stage of cartilage degeneration in tissue with minimal gross surface damage.

Uncertainties in indentation testing of articular cartilage: a fibril-reinforced poroviscoelastic study

Indentation testing provides a quantitative technique to evaluate mechanical characteristics of articular cartilage in situ and in vivo. Traditionally, analytical solutions proposed by Hayes et al. [Hayes WC, Keer LM, Herrmann G, Mockros LF. A mathematical analysis for indentation tests of articular cartilage. J Biomech 1972;5(5):541-51] have been applied for the analysis of indentation measurements, and due to their practicality, they have been used for clinical diagnostics. Using this approach, the elastic modulus is derived based on scaling factors which depend on cartilage thickness, indenter radius and Poisson's ratio, and the cartilage model is assumed isotropic and homogeneous, thereby greatly simplifying the true tissue characteristics. The aim was to investigate the validity of previous model assumptions for indentation testing. Fibril-reinforced poroviscoelastic cartilage (FRPVE) model including realistic tissue characteristics was used to simulate indentation tests. The effects of cartilage inhomogeneity, anisotropy, and indentation velocity on the indentation response were evaluated, and scaling factors from the FRPVE analysis were derived. Subsequently, the validity of scaling factors obtained using the traditional and the FRPVE analyses was studied by calculating indentation moduli for bovine cartilage samples, and comparing these values to those obtained experimentally in unconfined compression testing. Collagen architecture and compression velocity had significant effects on the indentation response. Isotropic elastic analysis gave significantly higher (30-107%) Young's moduli for indentation compared to unconfined compression testing. Modification of Hayes' scaling factors by accounting for cartilage inhomogeneity and anisotropy improved the agreement of Young's moduli obtained for the two test configurations by 14-28%. These results emphasize the importance of realistic cartilage structure and mechanical properties in the indentation analysis. Although it is not possible to fully describe tissue inhomogeneity and anisotropy with just the Young's modulus and Poisson's ratio, accounting for inhomogeneity and anisotropy in these two parameters may help to improve the in vivo characterization of tissue using arthroscopic indentation testing.

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

BACKGROUND

Arthroscopy is a highly sensitive method of evaluating high-grade cartilage lesions but the detection of low-grade lesions is often is unreliable. Objective measurements are required. A novel NIRS (near-infrared-spectroscopy) device for detection of low-grade cartilage defects was evaluated in a preliminary clinical study.

METHODS

In 12 patients who had undergone arthroscopy, the cartilage lesions within the medial knee compartment were classified according to the ICRS protocol. With a NIR spectrometer system and an optical probe, similar in design to a hook used for routine arthroscopy, the optical properties of cartilage were measured during arthroscopy.

RESULTS

The mean ratio of 2 NIR absorption bands of intact cartilage 3.8 (range 2.3 to 8.7).was significantly lower than that of cartilage with grade 1 lesions (12.8, range 4.8 to 19.6) and grade 2 lesions (13.4, range 10.4 to 15.4).No differences were observed between grade 1 and grade 2 lesions.

CONCLUSION

NIRS can be used to distinguish between ICRS grade 1 lesions and healthy cartilage during arthroscopic surgeries. The results of this clinical study demonstrate the potential of NIRS to objectify classical arthroscopic grading systems.

Microindentation test for assessing the mechanical properties of cartilaginous tissues

Mechanical properties of the fresh control, frozen, and vitrified cartilaginous (cartilage and meniscus) samples were measured by microindentation. Indentation depth, elastic modulus, and indentation yield strength were obtained from the microindentation loading curves. Indentation deformation behavior was studied using Hertz contact model. The stress distribution of cartilaginous tissues under indentation loading was analyzed by finite element technique. It was found that fresh tissue shows the lowest indentation depth and the highest elastic modulus and indentation yield strength, followed by vitrified and frozen tissues. The vitrified tissue shows slightly lower but comparable mechanical properties with control tissue. The vitrification technique used in this study can preserve live cells with superior mechanical properties that make it an ideal technique for use in orthopedic and other biomedical applications. The microindentation tests and corresponding analysis methods used in this study offer a simple way to evaluate the mechanical properties of cartilaginous tissues. It suits small sample sizes and it may be used for other biological tissues.

A review on the mechanical quality of articular cartilage - implications for the diagnosis of osteoarthritis

The functional behaviour of articular cartilage in diarthrodial joints is determined by its morphological and biomechanical properties. Whereas morphological changes are mainly detectable in the progressed stages of osteoarthritis, biomechanical properties seem to be more sensitive to early degenerative variations since they are determined by the biochemical composition and structural arrangement of the extracellular matrix. The objective of this paper is to review studies focussing on variations in the mechanical compressive properties during the early pre-osteoarthritic stage. The aim is to quantify the requirements to detect the early cartilage degeneration in pre-osteoarthritis based on the mechanical parameters and to create an updated basis for a better understanding of inherent relationships between characteristic parameters in articular cartilage. Correlations between mechanical and biochemical parameters as well as magnetic resonance, ultrasonic, histological and structural parameters were observed. In early osteoarthritis, static moduli decrease below 80% of healthy controls and dynamic moduli below 30% of controls. To identify osteoarthritic changes of articular cartilage based on static or dynamic mechanical parameters in an early stage of the disease progression the accuracy of a mechanical testing method has to be adequate to detect changes of 10% in cartilage stiffness.

Arthroscopic evaluation of cartilage degeneration using indentation testing--influence of indenter geometry

BACKGROUND

It has been suggested that the early onset of cartilage degeneration might be detected with a handheld indentation probe during knee arthroscopy, prior to any visible change on the articular surface. Collagen degradation has been considered as the first sign of cartilage degeneration. Therefore, it is important to consider the collagen network as a distinct constituent in the study of arthroscopic evaluation of cartilage degeneration.

METHODS

The tip of an arthroscopic probe (indenter) was modeled as rigid and in contact with a cartilage/bone disk of sufficiently large radius to simulate an indentation in a joint. A fibril-reinforced model of cartilage, including streaming potentials and distinct constitutive laws for the proteoglycan matrix and collagen network, was used to determine the contact mechanics of indenter and cartilage. The finite element package ABAQUS was employed to obtain numerical solutions.

FINDINGS

A spherical indenter produces a relatively uniform deformation in cartilage, but can easily slide on the articular surface. In contrast, a cylindrical indenter produces great deformation gradients for quick compression rates, but does not slide as easily on the articular surface as the spherical indenter. Small porous and large solid indenters should be used to evaluate the properties of the proteoglycan matrix and collagen network, respectively, in order to minimize or maximize the fluid pressure in the corresponding case. When the collagen network is substantially degraded, the gradients of fluid pressure and deformation are greatly reduced regardless of indenter geometry.

INTERPRETATION

The indenter geometry including its porosity is important to the material safety of articular cartilage in indentation and precise evaluation of cartilage degeneration.

Electromechanical response of articular cartilage in indentation--considerations on the determination of cartilage properties during arthroscopy

A finite element formulation of streaming potentials in articular cartilage was incorporated into a fibril-reinforced model using the commercial software ABAQUS. This model was subsequently used to simulate interactions between an arthroscopic probe and articular cartilage in a knee joint. Fibril reinforcement was found to account for large fluid pressure at considerable strain rates, as has been observed in un-confined compression. Furthermore, specific electromechanical responses were associated with specific changes in tissue properties that occur with cartilage degeneration. For example, the strong strain-rate dependence of the load response was only observed when the collagen network was intact. Therefore, it is possible to use data measured during arthroscopy to evaluate the degree of cartilage degeneration and the source causing changed properties. However, practical problems, such as the difficulty of controlling the speed of the hand-held probe, may greatly reduce the reliability of such evaluations. The fibril-reinforced electromechanical model revealed that high-speed transient responses were associated with the collagen network, and equilibrium response was primarily determined by proteoglycan matrix. The results presented here may be useful in the application of arthroscopic tools for evaluating cartilage degeneration, for the proper interpretation of data, and for the optimization of data collection during arthroscopy.

Analysis of stored osteochondral allografts at the time of surgical implantation

BACKGROUND

To date, the morphological, biochemical, and biomechanical characteristics of articular cartilage in osteochondral allografts that have been stored have not been fully described.

HYPOTHESIS

Osteochondral allografts procured and stored commercially for a standard period as determined by tissue banking protocol will have compromised chondrocyte viability but preserved extracellular matrix quality.

STUDY DESIGN

Controlled laboratory study.

METHODS

Unused cartilage from 16 consecutive osteochondral allografts was sampled during surgery after tissue bank processing and storage. Ten grafts were examined for cell viability and viable cell density using confocal microscopy, proteoglycan synthesis via 35SO4 uptake, and glycosaminoglycan content and compared with fresh cadaveric articular cartilage. Biomechanical assessment was performed on the 6 remaining grafts by measuring the indentation stiffness of the cartilage.

RESULTS

The mean storage time for the transplanted specimens was 20.3 +/- 2.9 days. Chondrocyte viability, viable cell density, and 35SO4 uptake were significantly lower in allografts at implantation when compared to fresh, unstored controls, whereas matrix characteristics, specifically glycosaminoglycan content and biomechanical measures, were unchanged. In addition, chondrocyte viability in the stored allografts was preferentially decreased in the superficial zone of cartilage.

CONCLUSION

Human osteochondral allografts stored for a standard period (approximately 3 weeks) before implantation undergo decreases in cell viability, especially in the critically important superficial zone, as well as in cell density and metabolic activity, whereas matrix and biomechanical characteristics appear conserved. The exact clinical significance of these findings, however, is unknown, as there are no prospective studies examining clinical outcomes using grafts stored for extended periods.

CLINICAL RELEVANCE

Surgeons who perform this procedure should understand the cartilage characteristics of the graft after 21 days of commercial storage in serum-free media.

Novel ultrasonic evaluation of tissue-engineered cartilage for large osteochondral defects--non-invasive judgment of tissue-engineered cartilage

Although numerous methods for regenerating articular cartilage have been investigated, the regenerated tissue showed various histological findings from hyaline-like cartilage to fibrous tissue. Without biopsy, we are unable to know whether the cartilage regeneration method was histologically successful or not. We developed a new ultrasonic evaluation system for articular cartilage using the maximum magnitude (MM) from ultrasonic analysis. The purpose of this study was to investigate the usefulness of ultrasonic judgment of the cartilage regeneration procedure. Using our system we quantitatively evaluated tissue-engineered cartilage in rabbit cartilage defects. The specimens were retrospectively divided into two groups on the basis of histological findings and investigated whether significant differences in ultrasonic analysis could be found between the two (group H: hyaline-like cartilage group, successful; group F: fibrous tissue group, failure). In the ultrasonic findings, the MM was 1.11+/-0.32 in group H and 0.65+/-0.18 in group F and these differences were significant (P=0.00061). Our results suggest that the ultrasonic evaluation system used in the present study is capable of judging the success or failure of cartilage regeneration procedures, and therefore, it could be a valuable tool arthroscopic diagnosis of cartilage regeneration.

Differential acoustic properties of early cartilage lesions in living human knee and ankle joints

OBJECTIVE

Although numerous studies have been performed to determine whether there are histologic, biochemical, biomechanical, and metabolic differences between knee and ankle cartilage, none have investigated the presence of such differences in living human cartilage. We previously developed an ultrasonic evaluation system for articular cartilage that analyzes the A-mode echogram using wavelet transformation. The current study was undertaken to determine whether the acoustic properties of living human cartilage differ between knee and ankle joints.

METHODS

Twenty-eight patients were subjected to ultrasonic evaluation under arthroscopy. After arthroscopic grading, the cartilage was measured using an ultrasonic probe. Two quantitative parameters were used, i.e., the maximum magnitude and the echo duration at the 95% interval of the maximum magnitude.

RESULTS

In intact cartilage, the maximum magnitude and echo duration did not differ between the knee and the ankle. In lesional cartilage, in contrast, the maximum magnitude was higher, and the echo duration was shorter, in the ankle than in the knee. These differences were statistically significant.

CONCLUSION

Ultrasound findings could be used to judge the degree of early cartilage degeneration in vivo on the basis of objective data such as the maximum magnitude and echo duration. Because we were unable to quantitatively analyze the biochemical and biomechanical properties of the cartilage in this study, our biochemical and biomechanical findings are based only on qualitative assessment. Nevertheless, the results indicate that this ultrasonic evaluation system may be useful for elucidating the processes of articular cartilage degeneration in osteoarthritis.