Deformation Of Articular Cartilage Research Articles

Dynamic Deformation Calculation of Articular Cartilage and Cells Using Resonance-Driven Laser Scanning Microscopy.

The deformation of articular cartilage and its cells at the micro-scale during dynamic activities such as gait has high mechanoregulatory importance. Measuring the cellular geometries during such dynamics has been limited by the rate of microscopic image acquisition. The introduction of resonating mirrors for image rasterization (resonant scanning), rather than the conventional servo control (galvano scanning), has significantly improved the scanning rate by more than 100×. However, the high scanning rate comes at the cost of image quality, thereby posing challenges in image processing. Here, resonance-driven 3-D laser microscopy is used to observe the transient, micro-scale deformation of articular cartilage and its cells under osmotic challenge conditions. Custom image segmentation and deformable registration software were implemented for analysis of the resonance-scanned microscopy data. The software exhibited robust and accurate performance on the osmotic swelling measurements, as well as quantitative validation testing. The resonance-scanning protocol and developed analysis software allow for simultaneous strain calculation of both the local tissue and cells, and are thus a valuable tool for real-time probing of the cell-matrix interactions that are highly relevant in the fields of orthopedic biomechanics, cell mechanobiology, and functional tissue engineering.

ION-INDUCED DEFORMATION OF ARTICULAR CARTILAGE WITH STRAIN-DEPENDENT NONLINEAR PERMEABILITY AND MHD EFFECTS

ION-INDUCED DEFORMATION OF ARTICULAR CARTILAGE WITH STRAIN-DEPENDENT NONLINEAR PERMEABILITY AND MHD EFFECTS

Local deformation of articular cartilage assessed by X-ray phase CT-based digital volume correlation

Local deformation of articular cartilage assessed by X-ray phase CT-based digital volume correlation

Effect of cracks on the local deformations of articular cartilage

Despite significant evidence regarding the increased risk of cartilage degeneration due to traumatic injuries to joints, there is still a lack of understanding of the mechanisms underlying osteoarthritis development following a joint injury. Injuries in knee cartilage are often characterized by lesions or tears. In addition to acute traumatic joint injuries, microscale damages, which may form because of wear, are thought to be a contributing factor in the development of osteoarthritis.While the overall function of a joint may not be affected by the presence of microcracks, we hypothesized that strain magnification in the vicinity of microcracks might be significant. We tested this hypothesis by creating partial cuts in articular cartilages and measuring the strain within 20 µm from the edge of these cuts. Measurements were made in the superficial and middle zones of articular cartilage extract samples. We found that local strain in the vicinity of cuts is magnified by a factor of 1.2–1.6 compared to strains in intact regions for nominal compressions exceeding 5%. For nominal compressions of less than 5%, no strain magnification was detected in the vicinity of the cracks. We concluded that articular cartilage cracks magnify local strains by damaging the structural integrity and decreasing the fluid pressure in the matrix.

Aggrecanase-selective tissue inhibitor of metalloproteinase-3 (TIMP3) protects articular cartilage in a surgical mouse model of osteoarthritis

A key feature of osteoarthritis is the gradual loss of articular cartilage and bone deformation, resulting in the impairment of joint function. The primary cause of cartilage destruction is considered to be the presence of elevated proteases, such as matrix metalloproteinases (MMPs) and a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs). However, clinically tested global MMP inhibitors have low efficacy that may be due to their lack of selectivity. We previously demonstrated in vitro that a variant of tissue inhibitor of metalloproteinase-3 ([-1A]TIMP3) inhibits ADAMTSs but not MMPs. In this study, we tested whether the selectivity of [-1A]TIMP3 is beneficial compared with that of the wild-type TIMP3 in preventing or delaying the onset of the degenerative effects in a mouse model of osteoarthritis. We generated transgenic mice that overexpressed TIMP3 or [-1A]TIMP3 driven by a chondrocyte-specific type II collagen promoter. TIMP3 transgenic mice showed compromised bone integrity as opposed to [-1A]TIMP3 mice. After surgically induced joint instability, TIMP3 overexpression proved to be less protective in cartilage destruction than [-1A]TIMP3 at late stages of OA. The selective inhibition of ADAMTSs provides the possibility of modifying TIMP3 to specifically target a class of cartilage-degrading proteinases and to minimize adverse effects on bone and possibly other tissues.

Research of inflammatory factors and signaling pathways in knee osteoarthritis

Knee osteoarthritis is the most common type of arthritis, which is manifested by the deformation and degeneration of articular cartilage and the discomfort of patients with joint pain, which affects the quality of life of patients and aggravates the medical burden of society. The pathogenesis of knee osteoarthritis is very complex. This paper reviews the inflammatory factors and signal pathways involved in knee osteoarthritis. It is found that most of the inflammatory factors involved are interleukin, such as IL-1 β, IL-6, IL-15, IL-17, IL-18, and tumor necrosis factors, such as TNF-α. These inflammatory factors aggravate knee osteoarthritisby activating corresponding pathways and promoting the release of inflammatory mediators. The inflammatory signaling pathways involved in knee osteoarthritis are complex. Notch pathway, Wnt pathway, SDF-1 / CXCR4 pathway, TLRs pathway, MAPKs pathway, hippo Yap pathway, OPG-RANK-RANKL pathway and TGF-β pathway are all involved in the regulation of knee osteoarthritis, and the pathways related to inflammatory mechanism are mainly MAPKs pathway and TLRs pathway. Different signaling pathways can cause the destruction of articular cartilage, promote the apoptosis of chondrocytes, and finally lead to the further imbalance of homeostasis in the knee joint. At the same time, the activation of signal pathway can promote the release of inflammatory factors, so under the cascade reaction of inflammatory factors and signal pathway, knee osteoarthritis is aggravating.

X-ray phase-contrast dynamic CT for the analysis of local deformation of articular cartilage

X-ray phase-contrast dynamic CT for the analysis of local deformation of articular cartilage

Anterior cruciate ligament transection of rabbits alters composition, structure and biomechanics of articular cartilage and chondrocyte deformation 2 weeks post-surgery in a site-specific manner

Anterior cruciate ligament (ACL) injury often leads to post-traumatic osteoarthritis (OA) and articular cartilage degradation, changing biomechanics of the tissue and chondrocytes, and altering the fixed charged density (FCD) and collagen network. However, changes in these properties are not known at a very early time point after ACL rupture, but recognizing early changes might be crucial for successful intervention. We investigated the effects of ACL transection (ACLT) in rabbits on the site-specific biomechanical properties of articular cartilage and chondrocytes, FCD content and collagen network organization, two weeks post-surgery.Unilateral ACLT was performed in eight rabbits, and femoral condyles, tibial plateaus, femoral grooves and patellae were harvested from experimental and contralateral knee joints. An intact control group was used as a reference. We analyzed chondrocyte morphology under pre- and static loading, cartilage biomechanical properties, FCD content and collagen fibril orientation.ACLT caused FCD loss in the lateral and medial femoral condyle, lateral tibial plateau, femoral groove and patellar cartilage (p < 0.05). Minor changes in the collagen orientation occurred in the femoral groove and lateral and medial femoral condyle cartilage (p < 0.05). Cartilage stiffness was reduced in the lateral and medial femoral condyles, and chondrocyte biomechanics was altered in the lateral femoral condyle and patellar cartilage (p < 0.05).We observed loss of FCD from articular cartilage two weeks after ACLT at several joint locations. These changes may have led to decreased cartilage stiffness and altered cell deformation behavior, especially in the femoral condyles.

Effects of a knee valgus unloader brace on medial femoral articular cartilage deformation following walking in varus-aligned individuals

BackgroundKnee varus alignment may increase loading in the medial tibiofemoral compartment, which can increase strain on the articular cartilage. Knee valgus unloader braces seek to reduce loading through the medial femoral compartment, but their effects on cartilage characteristics during dynamic tasks have not been evaluated. ObjectiveTo determine the effects of a knee valgus unloader brace on medial femoral articular cartilage deformation following a single 5000-step walking protocol in individuals with varus-knee alignment. MethodsTwenty-four healthy individuals (63% female, BMI = 22 ± 3 kg/m2, age = 21 ± 3 years) completed two testing sessions (braced and unbraced) separated by one week. During both sessions, femoral cartilage ultrasound images were acquired prior to and following a 5000-step treadmill walking protocol at self-selected speed. Percent change scores in medial cartilage cross-sectional area (MCCA) were calculated and used as the primary outcome, and compared between the braced and unbraced conditions. ResultsThere was no difference in percent change of MCCA between conditions (braced = −2.77%, unbraced = −3.15%, p = 0.699). Individuals whose cartilage deformed more than a previously established minimal detectable change (MDC ≥ 1.58 mm2) deformed less during the braced condition (braced = −2.94%, unbraced = −6.34%, p = 0.028), compared to individuals who did not deform greater than the MDC (n = 15, braced = −2.67%, unbraced = −1.23%, p = 0.210). ConclusionsThere was no significant difference in MCCA percent change between the braced and unbraced conditions across the entire cohort; yet a valgus unloader braces may serve as a potential intervention strategy for reducing articular cartilage deformation in certain varus-aligned individuals who normally undergo measurable deformation during walking.

Acute Effects of Walking on the Deformation of Femoral Articular Cartilage in Older Adults.

Although discomfort during walking is a common complaint in individuals with knee osteoarthritis (OA), how an acute bout of walking affects femoral cartilage remains unclear. Current literature has suggested that frontal plane knee malalignment (ie, varus and valgus) is associated with the initiation and/or progression of knee OA. However, the association between knee alignment and femoral cartilage deformation after an acute bout of loading has not yet been investigated. This study was aimed to compare the acute effects of walking on femoral cartilage deformation between older adults with and without knee OA. We also examined the association between frontal plane knee alignment and loading-induced femoral cartilage deformation. Ten persons without OA (Kellgren Lawrence grading = 0 or 1; 5 females and 5 males; 55.0 [1.8] years of age; 78.8 [14.1] kg; 1.8 [0.2] m) and 9 persons with OA (Kellgren Lawrence grading ≥2; 4 females and 5 males; 55.6 [4.5] years of age; 97.4 [15.0] kg; 1.7 [0.1] m) participated. Each participant underwent magnetic resonance imaging before and immediately after 30 minutes of fast walking at 3 to 4 miles per hour. To obtain cartilage deformation postwalking, the medial and lateral femoral cartilage of the weight-bearing areas was segmented on participants' magnetic resonance imaging. Cartilage thickness was quantified by computing the average perpendicular distance between opposing voxels defining the edges of the femoral cartilage. Cartilage deformation of the medial and lateral femurs was defined as the percent changes in cartilage thickness after walking. Frontal plane knee alignment was obtained by measuring the angle between the long axes of femur and tibia. Independent t tests were used to compare cartilage deformation between the 2 groups. Pearson correlation coefficients were used to assess the association between cartilage deformation and knee alignment. There was no significant difference in cartilage deformation between the OA and control groups in lateral (P = .69) or medial (P = .87) femur. A significant correlation was found between lateral femoral cartilage deformation and increased knee valgus alignment (r = 0.497; P = .03). No difference was found between medial femoral cartilage deformation and frontal plane knee alignment (r = 273; P = .26). This is the first study comparing the acute effects of walking on femoral cartilage deformation between older adults with and without knee OA. Although there was not a difference in walking-induced femoral cartilage deformation between the OA and control groups, knee valgus was related to lateral femoral cartilage deformation after walking. Our findings suggested that walking exercises may be used safely in older adults without knee malalignment.

Topical Application of Wogonin Provides a Novel Treatment of Knee Osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease characterized by joint pain, decreased functional mobility, and deformation of articular cartilage and consequentially diminishing quality of life. Wogonin (WG), a compound extracted from the Skullcap Baicalensis plant, has been shown to have anti‐inflammatory effects on the Toll‐like Receptor 4 (TLR‐4) inflammatory pathway and antioxidant properties via Nrf2. We have shown that TLR‐4 is a major receptor for pain in OA. In our study, we examined the pain reducing, anti‐inflammatory, and chondroprotective effects of WG when applied as a topical cream (TC). After destabilizing the menisci of mice to induce OA, we examined the severity and progression of OA with and without the topical application of WG. Using a running wheel to track mice activity, we found that mice with WG treatment were statistically more active than mice without WG treatment. OA progression analyzed using Modified Mankin and OARSI scoring showed a significant attenuation of OA severity among mice treated with WG. Immunohistochemistry revealed a significant decrease in protein expression of TGF‐β1, but no significant differences were found among the biomarkers HTRA1, MMP‐13, or BMP‐2, suggesting an alternative pathway of cartilage rescue.Support or Funding InformationBYU Office of Research and Creative WorksThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Macroscopically oriented polymeric soft materials: synthesis and functions

Owing to the similarity to biological tissues, soft materials have attracted increasing attention as components of biological tissues. However, there is a large difference between synthetic soft materials and biological tissues. Most synthetic soft materials are structurally isotropic, whereas some biological tissues have anisotropic structures that continue over a macroscopic size scale. As seen in muscle, blood vessels, articular cartilage, and iridophores, such anisotropic structures often play critical roles in producing their superb functions. Thus, the control of “structural anisotropy” is a key concept for the further exploration of functional soft materials science. Using the magnetic orientation of nanoobjects in a colloidal dispersion and subsequent in situ polymerization, we recently succeeded in developing anisotropic soft materials, in which highly oriented structures (order parameter = > 0.95) extend over a macroscopic size scale (~10 cm). In addition, we demonstrated unprecedented unique functions of the resultant materials, including ultralarge mechanical anisotropy similar to articular cartilage, quick and large deformation similar to muscular tissues, and dynamic structural color modulation similar to the skin of tropical fish. Integration of the related studies on soft materials with anisotropically oriented structures would bring the concepts of artificial organs and soft robotics into reality. Magnetic orientation of nanoscopic objects in dispersions and subsequent in situ polymerization produced anisotropic soft materials, in which highly oriented structures (order parameter = > 0.95) extended over a macroscopic size scale (~10 cm). The resultant materials exhibited unprecedented unique functions that are reminiscent of biological tissues, including ultralarge mechanical anisotropy, similar to articular cartilages, quick and large deformation, similar to muscular tissues, and dynamic structural color modulation, similar to the skin of tropical fish.

Early Deformation of Hip Articular Cartilage Under A High Load Before and After Labral Excision

Background: It has been reported that the function of the labrum is to ensure that an increased surface area encountered the femoral head and spares the cartilage from excessive strain. The purpose of this study was to determine whether early deformation of the hip articular cartilage occurs under high-load conditions in the presence/absence of the labrum. Methods: The hip joints of 4 beagle dogs were retrieved. A continuous static load of 80 Kg was applied for 2.5 hours. Magnetic resonance imaging (MRI) was performed immediately after the loading and at 30, 60, 90, 120, and 150 minutes after the loading. The load was then removed, and the specimens were stored for 14 h to allow the cartilage to recover. The labrum was then carefully removed, and the experiment was performed again. Results: The maximum percentage change in cartilage thickness was 35.3 ± 17.4% when the labrum was intact and 55.7 ± 7.5% after the labrum had been excised (p=0.060). Labral excision resulted in a reduction in cartilage thickness. Cartilage thickness was significantly decreased in the normal and labral excision models immediately after loading (p=0.003 and p=0.022, respectively). Conclusion: The labrum plays a role in dispersing loads equally across the joint cartilage and reduces the load placed on the maximum weight-bearing region of cartilage. Early articular cartilage deformation occurred under high-load conditions both before and after the excision of the labrum.

Shear deformations of human articular cartilage: Certain mechanical anisotropies apparent at large but not small shear strains

Articular cartilage has pronounced through-the-thickness heterogeneity in both ultrastructure and mechanical function. The tissue undergoes a combination of large deformations in vivo, where shear is critical in both failure and chondrocyte death. Yet the microstructure mechanical response of cartilage to multi-axial large shear deformations is unknown. We harvested a total of 42 cartilage specimens from seven matched locations across the lateral femoral condyles and patellofemoral grooves of six human male donors (30.2±8.8yrs old, M±SD). With each specimen we applied a range of quasi-static, multi-axial large (simple) shear displacements both parallel and perpendicular to the local split-line direction (SLD). Shear stresses in cartilage specimens from the patellofemoral grooves were higher, and more energy was dissipated, at all applied strains under loading parallel to the local SLD versus perpendicular, while specimens from the lateral condyles were mechanically anisotropic only under larger strains of 20% and 25%. Cartilage also showed significant intra-donor variability at larger shear strains but no significant inter-donor variability. Overall, shear strain-energy dissipation was almost constant at 5% applied shear strain and increased nonlinearly with increasing shear magnitude. Our results suggest that full understanding of cartilage mechanics requires large-strain analyses to account for nonlinear, anisotropic and location-dependent effects not fully realized at small strains.

In Vivo Dynamic Deformation of Articular Cartilage in Intact Joints Loaded by Controlled Muscular Contractions.

When synovial joints are loaded, the articular cartilage and the cells residing in it deform. Cartilage deformation has been related to structural tissue damage, and cell deformation has been associated with cell signalling and corresponding anabolic and catabolic responses. Despite the acknowledged importance of cartilage and cell deformation, there are no dynamic data on these measures from joints of live animals using muscular load application. Research in this area has typically been done using confined and unconfined loading configurations and indentation testing. These loading conditions can be well controlled and allow for accurate measurements of cartilage and cell deformations, but they have little to do with the contact mechanics occurring in a joint where non-congruent cartilage surfaces with different material and functional properties are pressed against each other by muscular forces. The aim of this study was to measure in vivo, real time articular cartilage deformations for precisely controlled static and dynamic muscular loading conditions in the knees of mice. Fifty and 80% of the maximal knee extensor muscular force (equivalent to approximately 0.4N and 0.6N) produced average peak articular cartilage strains of 10.5±1.0% and 18.3±1.3% (Mean ± SD), respectively, during 8s contractions. A sequence of 15 repeat, isometric muscular contractions (0.5s on, 3.5s off) of 50% and 80% of maximal muscular force produced cartilage strains of 3.0±1.1% and 9.6±1.5% (Mean ± SD) on the femoral condyles of the mouse knee. Cartilage thickness recovery following mechanical compression was highly viscoelastic and took almost 50s following force removal in the static tests.

In vivo articular cartilage deformation: noninvasive quantification of intratissue strain during joint contact in the human knee

The in vivo measurement of articular cartilage deformation is essential to understand how mechanical forces distribute throughout the healthy tissue and change over time in the pathologic joint. Displacements or strain may serve as a functional imaging biomarker for healthy, diseased, and repaired tissues, but unfortunately intratissue cartilage deformation in vivo is largely unknown. Here, we directly quantified for the first time deformation patterns through the thickness of tibiofemoral articular cartilage in healthy human volunteers. Magnetic resonance imaging acquisitions were synchronized with physiologically relevant compressive loading and used to visualize and measure regional displacement and strain of tibiofemoral articular cartilage in a sagittal plane. We found that compression (of 1/2 body weight) applied at the foot produced a sliding, rigid-body displacement at the tibiofemoral cartilage interface, that loading generated subject- and gender-specific and regionally complex patterns of intratissue strains, and that dominant cartilage strains (approaching 12%) were in shear. Maximum principle and shear strain measures in the tibia were correlated with body mass index. Our MRI-based approach may accelerate the development of regenerative therapies for diseased or damaged cartilage, which is currently limited by the lack of reliable in vivo methods for noninvasive assessment of functional changes following treatment.

Effects of aerobic exercise intervention on serum cartilage oligomeric matrix protein levels and lymphocyte dna damage in obese elderly females.

[Purpose] The aim of the reported research was to investigate the effects of regular aerobic exercise on cartilage oligomeric matrix protein and oxidative DNA damage in obese, elderly females. [Subjects and Methods] Sixteen class I obese, elderly females, according to World Health Organization criteria, were randomly and equally assigned to a control group (n=8) or an exercise group (n=8). The exercise group participated in exercise sessions of 60 minutes per day, 3 days per week, for a period of 8 weeks. [Results] After aerobic exercise intervention, weight, body mass index, body fat, waist circumference, and DNA damage (Tail moment) were significantly decreased, compared with baseline values. In contrast, serum cartilage oligomeric matrix protein levels were not significantly different among any groups or time-points. [Conclusion] Regular aerobic exercise may be effective for reducing obesity-induced high DNA damage levels in obese females, without causing the deformation or degradation of lower extremity articular cartilage.

Finite Element Analysis Of Large Deformation Of Articular Cartilage In Upper Ankle Joint Of Occupant In Military Vehicles During Explosion

AbstractThe paper presents the analysis of the load of lower limbs of occupants in the armoured military vehicle, which has been destroyed by detonation of the Improvised Explosive Device (IED) charge under the vehicle. A simplified model of the human lower limb focused on upper ankle joint was developed in order to determine the reaction forces in joints and load in particular segments during the blast load. The model of upper ankle joint, include a tibia and an ankle bone with corresponding articular cartilage, has been developed. An analysis of the stress distribution under the influence of forces applied at different angles to the biomechanical axis of a limb has been performed. We analyzed the case of the lower limb of a sitting man leaning his feet on the floor. It has been shown that during a foot pronation induced by a knee outward deviation, the axial load on the foot causes significantly greater tension in the tibia. At the same time it has been shown that within the medial malleolus, tensile stresses occur on the surface of the bone which may lead to fracture of the medial malleolus. It is a common case of injuries caused by loads on foot of passengers in armored vehicles during a mine or IED load under the vehicle. It was shown that the outward deviation of the knee increases the risk of the foot injury within the ankle joint.

Ratcheting behavior of articular cartilage under cyclic unconfined compression.

The ratcheting deformation of articular cartilage can produce due to the repeated accumulations of compressive strain in cartilage. The aim of this study was to investigate the ratcheting behavior of articular cartilage under cyclic compression. A series of uniaxial cyclic compression tests were conducted for online soaked and unsoaked cartilage samples and the effects of stress variation and stress rate on ratcheting behavior of cartilage were investigated. It is found that the ratcheting strains of online soaked and unsoaked cartilage samples increase rapidly at initial stage and then show the slower increase with cyclic compression going on. On the contrary, the ratcheting strain rate decreases quickly at first and then exhibits a relatively stable and small value. Both the ratcheting strain and ratcheting strain rate increase with stress variation increasing or with stress rate decreasing. Simultaneously, the optimized digital image correlation (DIC) technique was applied to study the ratcheting behavior and Young's modulus of different layers for cartilage under cyclic compression. It is found that the ratcheting behavior of cartilage is dependent on its depth. The ratcheting strain and its rate decrease through the depth of cartilage from surface to deep, whereas the Young's modulus increases.

The Effect of Vigorous Running and Cycling on Novel Markers of Knee Joint Function

To date, no study has been undertaken to compare the effects of running (weight-bearing) and cycling (non-weight bearing) exercise on biomarkers of knee joint loading. PURPOSE: To investigate knee articular cartilage deformation and changes in serum oligomteric matrix protein (COMP) and lubricin in response to vigorous recreational exercise. We tested the hypothesis that the mode of biomechanical loading of the knee joint (weight-bearing versus non-weight bearing) would influence the nature of the responses. METHODS: 11 male runners (age: 40±6 years; weight: 76±8 kg; VO2max: 4.3±0.3 L/min mean±SD) and 11 male cyclists (35±12 years; 75±5 kg; 4.4±0.6 L/min) were investigated. Venous blood samples and supra-patellar ultrasound imaging scans were obtained at baseline rest, immediately after, and 30 minutes after, vigorous exercise (time trial: either 10 km run or 25 km cycle). Knee cartilage thicknesses and serum COMP and lubricin (ELISA) were determined for each time point. Statistical analyses were performed using two-factor repeated measures (group x time) ANOVA. RESULTS: At baseline rest, there were no significant differences between groups for cartilage thicknesses measured at the intercondyle notch, medial condyle and lateral condyle. Vigorous exercise did not result in significant change in any of the cartilage thicknesses for either group. There were no significant differences between runners and cyclists for COMP (runners: 804.1±87.5 ng/ml; cyclists: 693.0±84.7 ng/ml) and lubricin (runners: 104.0±19.8 ng/ml; cyclists: 119.1±23.9 ng/ml) at baseline. For both groups, vigorous exercise was generally accompanied by an increase in both serum COMP (cyclists: 32.1%; p < 0.05; runners: 14.2%; p = 0.14) and lubricin (cyclists: 39.4%; p < 0.05; runners 56.9%; p < 0.05). Following 30 minutes of rest, serum COMP and lubricin decreased towards baseline values in both groups (p < 0.05). CONCLUSIONS: In the absence of ultrasonographic evidence of knee cartilage deformation, responses of lubricin following an acute bout of vigorous exercise is not influenced by the modality of knee joint loading, and may reflect a temporary increase in joint lubrication. However, changes in cartilage metabolism following exercise, as measured by serum COMP, may be dependent on the exercise modality.