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. Author manuscript; available in PMC: 2011 Mar 1.
Published in final edited form as: Osteoarthritis Cartilage. 2009 Nov 23;18(3):464–471. doi: 10.1016/j.joca.2009.11.008

Cartilage Shear Kinematics During Tibio-Femoral Articulation: Effect of Acute Joint Injury & Tribosupplementation on Synovial Fluid Lubrication

Benjamin L Wong 1, Seung Hyun Chris Kim 1, Jennifer M Antonacci 1, C Wayne McIlwraith 2, Robert L Sah 1,¥
PMCID: PMC2905237  NIHMSID: NIHMS161669  PMID: 20004636

Abstract

Objective

To determine the effects of acute injury and tribosupplementation by hyaluronan (HA) on synovial fluid (SF) modulation of cartilage shear during tibio-femoral articulation.

Methods

Human osteochondral blocks from the lateral femoral condyle (LFC) and tibial plateau (LTP) were apposed, compressed 13%, and subjected to sliding under video microscopy. Tests were conducted with equine SF from normal joints (NL-SF), SF from acutely injured joints (AI-SF), and AI-SF to which HA was added (AI-SF+HA). Local and overall shear strain (Exz) and the lateral displacement (Δx) at which Exz reached 50% of peak values (Δx1/2) were determined.

Results

During articulation, LFC and LTP cartilage Exz increased with Δx and peaked when surfaces slid, with peak Exz being maintained during sliding. With AI-SF as lubricant, surface and overall Δx1/2 were ~40% and ~20% higher, respectively than values with NL-SF and AI-SF+HA as lubricant. Also, peak Exz was markedly higher with AI-SF as lubricant than with NL-SF as lubricant, both near the surface (~80%) and overall (50–200%). Following HA supplementation to AI-SF, Exz was reduced from values with AI-SF alone by 30–50% near the surface and 20–30% overall. Magnitudes of surface and overall Exz were markedly (~50–80%) higher in LTP cartilage than LFC cartilage for all lubricants.

Conclusion

Acute injury impairs SF function, elevating cartilage Exz markedly during tibio-femoral articulation; such elevated Exz may contribute to post-injury associated cartilage degeneration. Since HA partially restores the function of AI-SF, as indicated by Exz, tribosupplements may be beneficial in restoring cartilage mechanobiology.

Keywords: synovial fluid, lubrication, hyaluronan, acute injury, cartilage mechanics, shear deformation

INTRODUCTION

Within the knee joint, articular cartilage lining the femoral condyle articulates against articular cartilage of the tibial plateau that is uncovered by meniscus (Figure 1A) to facilitate diarthrodial joint movement1. Following various physical activities such as knee bending, impact loading, and running, cartilage compresses ~3–20%2-4, with compression typically being higher in cartilage from the tibial plateau than the femoral condyle3,4. Under such magnitudes of physiologic compression, tibio-femoral cartilage compression and shear are depth-varying, being highest near the surface and decreasing monotonically with increasing depth, and greater in tibial cartilage than femoral cartilage5. However, the shear kinematics as well as the effects of synovial fluid lubrication remains to be elucidated for physiologically-apposed cartilage surfaces. Such characterization would further the understanding of cartilage contact mechanics during joint loading and motion by elucidating the boundary conditions at the interface and the intra-tissue shear deformation within physiologically articulating femoral and tibial cartilage surfaces.

Figure 1.

Figure 1

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Schematic of (A) knee joint movements at multiple scales and (B) of experimental setup and loading protocol for micro-shear testing.

In healthy joints, synovial fluid (SF) is present between articulating cartilage surfaces, functioning as an effective boundary lubricant. Two major constituents of SF identified to lubricate the articular surface are hyaluronan (HA)6 and proteoglycan 4 (PRG4)7,8. In a configuration to reveal boundary lubrication effects, the surface interactions, as indicated by friction9 and shear deformation10,11 of articulating cartilage, are reduced by SF relative to phosphate buffered saline (PBS). The SF lubricant molecules, HA and PRG4, contribute, independently and in combination, to reduce articulating cartilage friction under boundary lubrication conditions12. Thus, altered lubricant molecule concentrations may diminish the boundary lubrication function of SF and cause elevated tissue shear, predisposing cartilage to accelerated wear and degradation.

Following acute injury, the friction-reducing function of SF is compromised13-15, possibly due, in part, to reduced HA concentration. The HA concentration in SF of acutely injured equine joints was decreased from normal (~0.3mg/ml to 0.2mg/ml), while PRG4 and SAPL concentrations were increased16. When SF was tested between articulating cartilage surfaces to reveal boundary mode lubrication, friction was markedly higher with SF from acutely injured joints (AI-SF) than that from contra-lateral normal joints (NL-SF). When AI-SF was augmented with HA (AI-SF+HA), friction coefficient was reduced towards normal values, suggesting lowered HA concentrations reduced SF function. Such alterations in the friction-reducing function of SF following acute injury may alter the normal mechanobiology of articulating cartilage since tissue shear deformation markedly regulates lubricant and matrix metabolism17-19.

Femoral and tibial human articular cartilage exhibit shear deformation and interaction during tibio-femoral cartilage articulation5, as revealed by video microscopy20 to track the displacement of fluorescently-labeled cells21. With this experimental approach, osteochondral samples from the tibia and femoral condyle were compressed with the cartilage surfaces in apposition and subjected to lateral shearing motion to mimic the biomechanics of tibio-femoral joint articulation (Figure 1B). Resultant compressive and shear strains of cartilage were determined locally and overall, with resolution of small magnitudes (~1%) of strain. Using such a configuration, biomechanical microscale analysis can be used to assess the effects of synovial fluid lubrication on local and overall shear deformation of femoral and tibial cartilage during tibio-femoral cartilage articulation.

The hypothesis of this study was that during tibio-femoral articulation, cartilage lubrication by AI-SF elevates tissue shear deformation, while lubrication by AI-SF with augmented HA reduces shear deformation toward normal magnitudes. To test this hypothesis, the objectives of this study were to determine, during tibio-femoral cartilage articulation, (1) the effects of acute injury on SF lubricant function and (2) the ability of HA addition to AI-SF to enhance lubricant function, with lubricant function assessed as peak cartilage shear deformation during sliding motion.

MATERIALS AND METHODS

Sample isolation and preparation

Six osteochondral cores, each with a 10 mm diameter, were isolated, one from each anterior lateral femoral condyle (LFC) of six fresh cadaveric human male (n=3) and female (n=3) donors (mean ± SEM age of 46 ± 1.5 yrs). In addition, six osteochondral blocks (each with a chondral surface area of ~1 cm2) were harvested from the region of the donor-matched lateral tibial plateau (LTP) not covered by the meniscus. LFC cores with grossly normal surfaces (modified Outerbridge grade of 122) were selected, while all donor-matched LTP blocks displayed mild surface fibrillation and were modified Outerbridge grades of 2–322. The harvested specimens were immersed in phosphate buffered saline (PBS) containing proteinase inhibitors (PI)23 and stored at −70°C until use.

The osteochondral specimens were thawed and further processed on the day of testing. The LFC core and LTP block were each trimmed using a low-speed saw with a 0.3mm thick diamond edge blade (Isomet™, Buehler, Lake Bluff, IL) to yield one ~rectangular block for biomechanical testing. Each rectangular block had a cartilage surface area of ~3×8mm2 and a total thickness of ~1cm. Blocks were created such that their 8mm lengths were parallel to the direction of articulation in the joint from which they were isolated from (Figure 1A). Samples consisted of one LFC and one donor-matched LTP block and were each rinsed with PBS+PI overnight to prior to mechanical testing12.

From macroscopic images5 thickness measurements of the present samples were made at three separate locations and averaged to yield a full cartilage thickness measurement. For the LTP samples, cartilage thickness (2.88 ± 0.53mm, mean ± SEM, n=6 blocks) was somewhat thicker than the cartilage thickness of the LFC samples (2.20 ± 0.15mm). In addition, the LFC and LTP samples used in this study were characterized by histopathology5. LFC cartilage was normal, while LTP cartilage exhibited typical features of very mild degeneration. Both LFC and LTP cartilage exhibited normal cellularity and an absence of cell cloning. LTP cartilage exhibited mild surface irregularity, occasional transverse clefts, and mildly-reduced glycosaminoglycan staining.

Lubricants

Soon after an acute injury (within 3 weeks), synovial fluid (SF) was aspirated from joints of six mature (2–4yr old) horses (with IACUC approval) during arthroscopic surgery by one of the authors (CWM). SF was aspirated from the injured joint (AI-SF) as well as the contralateral uninjured joint (NL-SF) which showed no clinical signs of injury. Collected samples were cleared of cells and debris by centrifugation (3,000g, 30min) and resultant supernatants were frozen at −70°C until mechanical testing.

The synovial fluid samples were characterized for boundary lubrication properties of lubricant molecules, confirming NL-SF and AI-SF were characteristic of SF from normal and acutely injured joints, respectively. For lubricant samples used in this study, coefficient of kinetic friction was 0.040 ± 0.003 for AI-SF and 0.022 ± 0.001 for NL-SF. Levels of HA were lower in AI-SF (0.19 ± 0.05 mg/ml) than NL-SF (0.31 ± 0.11 mg/ml) samples, while proteoglycan 4 concentrations were higher in AI-SF (90.9 ± 90.4 μg/ml) than NL-SF lubricants (17.6 ± 5.3 μg/ml), differences that are distinctive of synovial response to injury. Lubricant samples used in this study were (1) SF from the contralateral non-injured joint (NL-SF), (2) SF from the injured joint (AI-SF), and (3) AI-SF to which hyaluronan (HA) was added (AI-SF+HA). For AI-SF+HA lubricant samples, high molecular weight (800kDa) HA (SUPARTZ®, Seikagaku Corporation, Tokyo, Japan) was added to AI-SF to create a final concentration of supplemented HA to be 1mg/ml. All lubricant samples in the present study had PI added prior to mechanical testing.

Experimental Design

To assess the effect of acute injury on SF function in terms of cartilage shear deformation, lubricants were tested on cartilage samples in microshear tests described below. In particular, each of the lubricant samples (AI-SF, AI-SF+HA, NL-SF) from one equine animal were paired and tested sequentially between cartilage tissue from one human donor to reduce donor-donor variability of lubricant and tissue. Prior to mechanical testing, cartilage was completely immersed in ~0.5ml of test lubricant containing PI and 20μg/ml propidium iodide to fluorescently highlight cell nuclei at 4°C for 12–16h. Subsequently, AI-SF, AI-SF+HA, and then NL-SF were tested sequentially in microscale shear tests. In between lubricant bathing and mechanical testing, cartilage samples were rinsed, allowed to reswell, and reincubated in PBS+PI for ~4h at 4°C.

Microscale shear testing

Samples were tested for effects of lubricant on cartilage shear as described previously5. Briefly, each LFC and LTP pair were apposed in a custom bi-axial loading chamber mounted onto an epi-fluorescence microscope for digital video imaging (Figure 1B)24. The chamber secured the LFC block at the bone and allowed in-plane movement of the apposing mobile LTP block with orthogonally positioned plungers interfaced with either a micrometer (for axial displacement; Model 262RL; Starrett Co., Athol, MA) or motion-controller (for lateral displacement; Model MFN25PP; Newport, Irvine, CA). Subsequently, an axial displacement was applied (~40μm/s) to the bone portion of the LFC sample to induce 13% compression (1-Λz, where Λz is the stretch ratio25) of the overall (i.e. LFC and LTP) cartilage thickness determined from gross images. Samples were then allowed to stress relax for 1h which was confirmed to be sufficient to reach an approximate equilibrium stress for the current sample geometries10.

Following axial compression, cartilage deformation was assessed separately in the LFC and LTP tissue during shear loading as previously described5. Three sets of applied lateral displacements (Δx), each consisting of +1mm and then −1mm (returning to initial position) was applied to the bone portion of the LFC block (Figure 1B) to induce relative lateral motion. The first set of sliding motion was for preconditioning9, while tissue motions during the second and third set were recorded for analysis of LTP and LFC cartilage, respectively. Before and during the application of lateral displacements, sequential fluorescence (Nikon G-2A filter) images were taken separately for LFC and LTP cartilage at increments of 33μm to capture the shear deformation and sliding during tibio-femoral cartilage articulation. Resultant images with a field of view of ~3×2mm2 encompassed the entire cartilage thickness of the LFC (or LTP) and a partial view of the apposing surface. The same regions of tissue were imaged and analyzed for each of the three lubricant conditions.

Data collection and calculations

Digital fluorescence images from microscale tests were analyzed as described previously10,21 to determine the depth-varying and overall shear deformation in cartilage. Briefly, an evenly distributed set of cell nuclei (~250cells/mm2) was selected to serve as fiducial markers and tracked by maximizing cross-correlation of regions surrounding each marker to the preceding, and then initial frames. For each recorded image, local affine mappings of nuclei were used to calculate the displacement of uniformly-spaced (10 pixel) mesh points in the region of interest (~1mm × full thickness) during deformation. Subsequently, displacement gradients were determined by finite difference approximation, from which, Lagrangian shear strains (Exz) relative to the compressed cartilage thickness at compressive equilibrium were determined for both LFC and LTP cartilage during lateral shearing26.

Local and overall Exz as well as measurements to assess the rates at which Exz reached their peaks were determined separately for LFC and LTP samples. For each image frame, Exz of the LFC and LTP were each consolidated by averaging Exz at the same normalized depth (0, surface and 1, tidemark) and then interpolating Exz linearly at every 0.05 times the normalized tissue thickness near the articular surface (i.e. 0 to 0.3) and 0.1 for remaining regions of the tissue depth (i.e. 0.3 to 1). Surface Exz was defined as that occurring at the top 5% of the cartilage thickness, while overall Exz was determined as half the lateral tissue displacement near the articular surface normalized to the compressed cartilage thickness. Surface and overall Exz determined at Δx increments of 0.1mm (Δx ranging between 0 to 0.8mm) were used to determine the Δx when surface and overall Exz reached 50% of their peak values (Δx1/2).

Statistical analysis

Data are reported as mean ± standard error of the mean (SEM), unless noted otherwise. Repeated measures ANOVA was used to determine the effects of joint location (LFC, LTP) and lubricant (AI-SF, AI-SF+HA, NL-SF) on local and overall Exz. To account for sample variances being approximately proportional to the amplitude of the data, Δx1/2 data were log transformed prior to analysis. Planned comparisons (AI-SF versus NL-SF, AI-SF+HA versus NL-SF, and AI-SF versus AI-SF+HA) were made between lubricant groups for a given joint location. Systat 10.2.05 (Systat Software, Richmond, CA) and Microsoft Office Excel 2003 (Microsoft Corporation, Redmond, WA) were used to perform all statistical analyses.

RESULTS

Shear deformation kinematics

Similar to previous qualitative10 and quantitative11 descriptions of cartilage-on-cartilage articulation, tibio-femoral cartilage articulation resulted in a sequence of four main events for all experimental conditions during shear loading. Qualitatively at compressive equilibrium, (1) LFC and LTP surfaces adhered and began to move laterally in unison to initiate Exz in both apposing tissues near the onset of Δx. (2) With increasing Δx, LFC and LTP Exz increased while surfaces remained adhered. (3) Eventually with sufficient Δx, LFC and LTP Exz reached a peak just as their respective surfaces detached and slid relative to each other. (4) With additional Δx, cartilage Exz in both LFC and LTP tissues maintained their steady-state peak.

During shear loading, cartilage Exz, near the articular surface and overall, increased markedly with Δx and was significantly higher for LTP than LFC cartilage (p<0.05). For both LFC and LTP cartilage and for all lubricant conditions, Exz near the surface and overall increased markedly (p<0.001) with increasing Δx, eventually reaching a maximum that was maintained even as Δx continued to increase (Figure 2). These quantitative trends were consistent with the qualitative observations described above. When AI-SF was used as the lubricant, the resultant Exz near the articular surface of LFC samples reached a peak value during articulation that was higher than that when samples were tested with AI-SF+HA and NL-SF as lubricants (Figure 2A). Analogously, overall Exz of LFC cartilage also reached a higher peak magnitude for AI-SF as lubricant than AI-SF+HA and NL-SF as lubricants (Figure 2C). Typically, Exz near the surface and overall of LFC samples reached peak values that were highest, 2nd highest, and lowest during articulation with AI-SF, AI-SF+HA, and NL-SF, respectively, as lubricant. Similar trends in LTP Exz during tibio-femoral articulation were found; however, the Exz magnitudes of LTP cartilage were markedly higher near the articular surface (p<0.01) and overall (p<0.05) than those of the LFC samples (Figure 2B,D). For all cases, Exz reached a steady-state peak at a Δx of 0.8 mm. Thus, effects of lubrication on tissue Exz were further compared at this point as described below (Peak shear deformation).

Figure 2.

Figure 2

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Surface (A,B) and overall (C,D) shear strain (Exz) versus applied lateral displacement (Δx) for (A,C) the lateral femoral condyle (LFC) and (B,D) tibial plateau (LTP) cartilage tested with acutely injured SF (AI-SF), acutely injured SF supplemented with HA (AI-SF+HA), and contra-lateral normal SF (NL-SF).

The rate at which surface and overall Exz reached their peak values during articulation, as indicated by Δx1/2, were significantly dependent upon lubricant. Near the articular surface, Δx1/2 was markedly affected by lubricant (p<0.05), tending to be higher with AI-SF (70–80%, p=0.13) and AI-SF+HA (20–60%, p=0.07) as lubricant than with NL-SF (Figure 3A). Overall, Δx1/2 was also markedly affected by lubricant (p<0.05), being 65–80% higher (p<0.05) with AI-SF as lubricant than with NL-SF as lubricant (Figure 3B). However, with AI-SF+HA as lubricant, overall Δx1/2 was similar to that with NL-SF as lubricant (p=0.7). Differences in Δx1/2 near the surface (p=0.5) and overall (p=0.10) were not statistically significant between LFC and LTP cartilage for all cases (Figure 3).

Figure 3.

Figure 3

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Effect of acute injury lubrication on Δx at 50% peak (Δx1/2) (A) surface and (B) overall shear strain for lateral femoral condyle (LFC) and tibial plateau (LTP) samples.

Peak shear deformation

When tibio-femoral surfaces were sliding and Exz was at a peak, lateral tissue displacements and deformation were depth-varying, being highest near the articular surface and lowest (almost negligible) near the tidemark for LFC and LTP cartilage (Figure 4A-C). For LTP cartilage, the maximum lateral displacement when tibio-femoral surfaces were lubricated with NL-SF (76 ± 48 μm) increased when lubricated with AI-SF (to 193 ± 63 μm, p<0.05), but not significantly when lubricated with AI-SF+HA (143 ± 48 μm, p=0.06). For LFC cartilage, trends were similar but not statistically significant with the maximum lateral displacement when tibio-femoral surfaces were lubricated with NL-SF (31 ± 11 μm) increased when lubricated with AI-1 SF (to 48 ± 13 μm, p=0.4) and AI-SF+HA (to 41 ± 6 μm , p=0.7). Differences in shear deformation between LFC and LTP cartilage were also apparent, with shear deformation of LFC (Figure 4A-C; top images) cartilage being much lower than LTP shear deformation (Figure 4A-C; bottom images) during tibio-femoral articulation.

Figure 4.

Figure 4

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A-C, Representative micrographs with superimposed colormaps of shear strain taken of apposing LFC (top images) to LTP (bottom images) samples after achieving maximum shear strain with NL-SF (A), AI-SF (B), and AI-SF+HA (C) as lubricants. Cell nuclei tracking method was used to determine maps of shear strain (color maps, A-C). Dashed lines (- -) encompass the analyzed regions on the undeformed images, while strain map boundaries encompass the corresponding deformed states. D, Local shear strain (Exz) averaged depth-wise versus normalized tissue depth for LFC (top graph) and LTP (bottom graph) samples. Values are mean ± SEM.

Peak Exz varied with tissue depth, lubricant, and joint location (Figure 4D). With tissue depth, Exz markedly (p<0.001) decreased monotonically with increasing depth from the articular surface for all experimental conditions. There was an interactive effect between lubricant and tissue depth (p<0.001) on LFC and LTP Exz, as indicated by the differences in Exz between lubricant conditions being greatest near the surface and lowest (almost indistinguishable) in the deeper regions. A similar interactive effect between cartilage location and depth on Exz was also evident (p<0.001) for all lubricant cases, with LTP Exz being markedly higher in magnitude than LFC Exz near the surface and being similarly low to LFC Exz near the tidemark.

Depending on the joint location from which cartilage samples were isolated, peak Exz near the surface and overall were affected by lubrication. Near the surface and overall, interactive effects between joint location and lubrication on Exz were marked (p<0.05). In the LTP, peak Exz increased markedly and significantly with acute injury lubricant and reduced towards normal with HA supplementation. LTP cartilage Exz near the surface and overall were 0.2 and 0.02, respectively, when tibio-femoral surfaces were lubricated with NL-SF, and increased markedly (p<0.05) to 0.37 and 0.05, respectively, when surfaces were lubricated with AI-SF (Figure 5A,B). When AI-SF was supplemented with HA (AI-SF+HA), surface and overall Exz of LTP cartilage were reduced (p<0.05) to 0.26 and 0.03, respectively, during tibio-femoral articulation, and the resultant Exz were statistically indistinguishable (p=0.3–0.5) from that with NL-SF as lubricant. In contrast, in the LFC, while surface and overall Exz tended to be lowest for NL-SF, highest for AI-SF, and 2nd highest for AI-SF+HA surface lubricants, differences in peak Exz were relatively small (<0.01) and not statistically significant near the surface (p=0.2) and overall (p=0.25).

Figure 5.

Figure 5

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Effect of acute injury lubrication (NL-SF, AI-SF, or AI-SF+HA) on (A) peak surface and (B) overall shear strain for both lateral femoral condyle (LFC) and tibial plateau (LTP) samples.

DISCUSSION

The present results indicate that synovial fluid function, as reflected by intra-tissue cartilage shear deformation during tibio-femoral cartilage articulation, is impaired by acute injury, while tribosupplementation with HA partially restores SF function. As in a previous study11, tibio-femoral cartilage articulation involved four sequential events: adherence, adherence and shear deformation, surface detachment as shear deformation peaks, and sliding with maintenance of peak shear (Figures 2,6A). When samples were lubricated with AI-SF, surface and overall Δx1/2 increased to ~1.8-fold, indicating surfaces detached (Figure 6B, III) at greater Δx magnitudes than when NL-SF was used as a lubricant (Figures 3,6B). Concomitantly peak cartilage Exz, near the surface and overall, increased ~1.6 to 2.9-fold when samples were lubricated with AI-SF compared to NL-SF (Figure 4). When AI-SF was supplemented with HA (AI-SF+HA), surface and overall Δx1/2 were reduced; concomitantly, Exz near the surface and overall were reduced with AI-SF+HA as lubricant compared to AISF. Magnitudes of Exz were consistently greater in LTP cartilage than LFC cartilage for all experimental cases, being ~7- and ~3-fold greater near the surface and overall, respectively.

Figure 6.

Figure 6

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(A) Schematic of the four sequential events ((I) adherence, (II) adherence and deformation, (III) detachment, and (IV) sliding) that occurs during tibio-femoral cartilage articulation and (B) representative shear strain (Exz) versus applied lateral displacement (Δx) diagrams with markers indicating where detachment (III) occurs for each lubricant condition.

The present study addresses the biomechanical environment (i.e. compression and sliding) of articulating tibio-femoral cartilage during normal joint loading. Osteochondral samples were taken from the lateral femoral condyle and donor-matched tibial plateau, whose surfaces anatomically articulate against one another within the joint27. Such regions are load-bearing, and tibio-femoral cartilage undergoes a wide range of compression amplitude (3–20%)2-4 and sliding velocity (0–0.1 m/s) during normal activities (estimated from refs 28 and 29). The loading parameters of present study mimic relatively high compression (13%) and low sliding velocity (0.1mm/s) corresponding to the contralateral toe-off and heel rise phases of gait28, when surface interaction is likely to be high. In addition, anatomically articulating cartilage surfaces (femoral versus tibial cartilage) were analyzed.

Furthermore, the role of equine SF lubricant component of the boundary condition of human cartilage articulation was analyzed in the present study. Articular cartilage surfaces were lubricated with SF from the contra-lateral normal (NL-SF) and acutely injured (AI-SF) joint to mimic normal and injured lubrication conditions during loading. Samples were also tested with AI-SF supplemented with HA (AI-SF+HA) to analyze a tribosupplementation type of therapy30. HA was added to AI-SF to bring the total supplemented HA concentration to be ~1mg/ml and so that final levels of HA would be within the range (0.3–1.3mg/ml)31-34 reported in normal equine SF. Whether other tribosupplements, such as PRG4 or LUB-1, the engineered variant of PRG4,35 have similar effects, remains to be established. In addition, equine SF was tested for lubrication of human articular cartilage since SF lubrication of articular cartilage appears to be largely species independent. Normal bovine SF reduces boundary mode friction between bovine cartilage surfaces9 and human cartilage Exz10 compared to saline. Since the shear-reducing function of equine SF was preserved in this study compared to that of saline5, the lubricating function of equine SF appears to be species independent. This is consistent with findings that equine SF lubricates bovine cartilage, as indicated by boundary-mode friction, just as well as bovine SF16.

The elevation in Exz with AI-SF as lubricant is consistent with the increased friction found between surfaces lubricated with SF from acutely injured joints. Friction coefficient increases with AI-SF as lubricant compared to NL-SF for both cartilage-on-cartilage16 and latex-on-glass14 boundary-mode friction tests. Assuming cartilage material properties (i.e., compressive and shear modulus) are maintained with the uses of AI-SF and NL-SF, higher friction would be predicted to result in an elevation of tissue Exz. Such elevated tissue Exz may contribute to the cartilage wear and degeneration associated with impaired SF function14,36.

The molecular mechanisms and consequences of tribosupplementation of AI-SF by HA remains to be fully established. Tribosupplementation by HA alone may not fully restore SF function following acute injury since the resultant Exz was generally higher (~0–98%) when samples were tested with AI-SF+HA than NL-SF as lubricant Other identified (i.e. PRG47,8 and SAPL37) and unidentified lubricant molecules may be necessary for supplementation to fully restore SF function following acute injury. Furthermore, changes in lubricant molecule structure may occur following acute injury, as found in arthritis38, and alter the ability of the molecules to function. The benefit of tribosupplementation (AI-13SF+HA), associated with reduction of Exz by ~20–50% compared to lubricant conditions without HA supplementation (AI-SF) (Figure 4), appear to have beneficial consequences in animal models of arthritis35.

The greater shear deformation in cartilage from the tibia than the femoral condyle is consistent with previous studies on in vitro tibio-femoral cartilage shear deformation. Analogous to the current study, osteochondral samples from the tibial plateau and femoral condyle were previously tested mechanically with articular surfaces in apposition, but with PBS as lubricant5. Resultant cartilage Exz near the surface and overall were higher in tibial cartilage than femoral cartilage, consistent with variation in Exz between LFC and LTP samples for the lubricants tested in the present study. Such differences in shear deformation between LFC and LTP cartilage reflect cartilage from femoral condyles being stiffer in shear than the cartilage from the tibial plateau5.

The present study provides insight into the effects of acute injury on SF function and the ability of tribosupplementation to restore SF lubricant function, as indicated by cartilage mechanics, during tibio-femoral joint articulation. Reduced SF function, as indicated by increased friction, is positively associated with cartilage wear in mice joints36, suggesting altered SF function contributes to cartilage degeneration. Excessive Exz that results from impaired SF function may damage cells and matrix, analogous to excessive compression39-42, and contribute to post-injury cartilage degeneration and wear. Tribosupplementation of biomechanically deficient SF may also be beneficial by restoring cartilage mechanobiology.

ACKNOWLEDGMENTS

We thank the many residents and staff at Dr. Lotz’s Laboratory at the Scripps Research Institute for harvesting and providing the human tissue used in this study.

This work was supported by NIH and Howard Hughes Medical Institute through the Professors Program Award to UCSD for Dr. Robert L. Sah.

Footnotes

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CONFLICT OF INTEREST

The authors have no conflicts of interest to report.

REFERENCES

  • 1.Mow VC, Huiskes R. Basic Orthopaedic Biomechanics and Mechano-Biology. 3rd Edition Lippincott Williams & Wilkins; Philadelphia: 2005. [Google Scholar]
  • 2.Van de Velde SK, Bingham JT, Gill TJ, Li G. Analysis of tibiofemoral cartilage deformation in the posterior cruciate ligament-deficient knee. J Bone Joint Surg Am. 2009;91:167–175. doi: 10.2106/JBJS.H.00177. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Eckstein F, Hudelmaier M, Putz R. The effects of exercise on human articular cartilage. J Anat. 2006;208:491–512. doi: 10.1111/j.1469-7580.2006.00546.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Kersting UG, Stubendorff JJ, Schmidt MC, Bruggemann GP. Changes in knee cartilage volume and serum COMP concentration after running exercise. Osteoarthritis Cartilage. 2005;13:925–934. doi: 10.1016/j.joca.2005.06.005. [DOI] [PubMed] [Google Scholar]
  • 5.Wong BL, Sah RL. Cartilage mechanicals during tibio-femoral articulation: local and overall compressive and shear deformation and properties. J Biomech. 2009 doi: 10.1016/j.jbiomech.2010.02.035. Submitted. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 6.Noyori K, Takagi T, Jasin HE. Characterization of the macromolecular components of the articular cartilage surface. Rheumatol Int. 1998;18:71–77. doi: 10.1007/s002960050060. [DOI] [PubMed] [Google Scholar]
  • 7.Schumacher BL, Block JA, Schmid TM, Aydelotte MB, Kuettner KE. A novel proteoglycan synthesized and secreted by chondrocytes of the superficial zone of articular cartilage. Arch Biochem Biophys. 1994;311:144–152. doi: 10.1006/abbi.1994.1219. [DOI] [PubMed] [Google Scholar]
  • 8.Jay GD. Lubricin and surfacing of articular joints. Curr Opin Orthop. 2004;15:355–359. [Google Scholar]
  • 9.Schmidt TA, Sah RL. Effect of synovial fluid on boundary lubrication of articular cartilage. Osteoarthritis Cartilage. 2007;15:35–47. doi: 10.1016/j.joca.2006.06.005. [DOI] [PubMed] [Google Scholar]
  • 10.Wong BL, Bae WC, Chun J, Gratz KR, Sah RL. Biomechanics of cartilage articulation: effects of lubrication and degeneration on shear deformation. Arthritis Rheum. 2008;58:2065–2074. doi: 10.1002/art.23548. [DOI] [PubMed] [Google Scholar]
  • 11.Wong BL, Bae WC, Gratz KR, Sah RL. Shear deformation kinematics during cartilage articulation: effect of lubrication, degeneration, and stress relaxation. Mol Cell Biomech. 2008;5:197–206. [PMC free article] [PubMed] [Google Scholar]
  • 12.Schmidt TA, Gastelum NS, Nguyen QT, Schumacher BL, Sah RL. Boundary lubrication of articular cartilage: role of synovial fluid constituents. Arthritis Rheum. 2007;56:882–891. doi: 10.1002/art.22446. [DOI] [PubMed] [Google Scholar]
  • 13.Jay GD, Elsaid KA, Zack J, Robinson K, Trespalacios F, Cha CJ, et al. Lubricating ability of aspirated synovial fluid from emergency department patients with knee joint synovitis. J Rheumatol. 2004;31:557–564. [PubMed] [Google Scholar]
  • 14.Elsaid KA, Jay GD, Warman ML, Rhee DK, Chichester CO. Association of articular cartilage degradation and loss of boundary-lubricating ability of synovial fluid following injury and inflammatory arthritis. Arthritis Rheum. 2005;52:1746–1755. doi: 10.1002/art.21038. [DOI] [PubMed] [Google Scholar]
  • 15.Teeple E, Elsaid KA, Fleming BC, Jay GD, Aslani K, Crisco JJ, et al. Coefficients of friction, lubricin, and cartilage damage in the anterior cruciate ligament-deficient guinea pig knee. J Orthop Res. 2007 doi: 10.1002/jor.20492. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 16.Antonacci JM, Ballard BL, Schumacher BL, Sah RL. Role of hyaluronan in bovine synovial fluid in the boundary lubricating of articular cartilage. Trans Orthop Res Soc. 2008;33:625. [Google Scholar]
  • 17.Jin M, Frank EH, Quinn TM, Hunziker EB, Grodzinsky AJ. Tissue shear deformation stimulates proteoglycan and protein biosynthesis in bovine cartilage explants. Arch Biochem Biophys. 2001;395:41–48. doi: 10.1006/abbi.2001.2543. [DOI] [PubMed] [Google Scholar]
  • 18.Nugent GE, Aneloski NM, Schmidt TA, Schumacher BL, Voegtline MS, Sah RL. Dynamic shear stimulation of bovine cartilage biosynthesis of proteoglycan 4 (PRG4) Arthritis Rheum. 2006;54:1888–1896. doi: 10.1002/art.21831. [DOI] [PubMed] [Google Scholar]
  • 19.Sah RL, Grodzinsky AJ, Plaas AHK, Sandy JD. Effects of static and dynamic compression on matrix metabolism in cartilage explants. In: Kuettner KE, Schleyerbach R, Peyron JG, Hascall VC, editors. Articular Cartilage and Osteoarthritis. Raven Press; New York: 1992. pp. 373–392. [Google Scholar]
  • 20.Schinagl RM, Ting MK, Price JH, Sah RL. Video microscopy to quantitate the inhomogeneous equilibrium strain within articular cartilage during confined compression. Ann Biomed Eng. 1996;24:500–512. doi: 10.1007/BF02648112. [DOI] [PubMed] [Google Scholar]
  • 21.Gratz KR, Sah RL. Experimental measurement and quantification of frictional contact between biological surfaces experiencing large deformation and slip. J Biomech. 2008;41:1333–1340. doi: 10.1016/j.jbiomech.2008.01.006. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Yamada K, Healey R, Amiel D, Lotz M, Coutts R. Subchondral bone of the human knee joint in aging and osteoarthritis. Osteoarthritis Cartilage. 2002;10:360–369. doi: 10.1053/joca.2002.0525. [DOI] [PubMed] [Google Scholar]
  • 23.Frank EH, Grodzinsky AJ, Koob TJ, Eyre DR. Streaming potentials: a sensitive index of enzymatic degradation in articular cartilage. J Orthop Res. 1987;5:497–508. doi: 10.1002/jor.1100050405. [DOI] [PubMed] [Google Scholar]
  • 24.Schinagl RM, Gurskis D, Chen AC, Sah RL. Depth-dependent confined compression modulus of full-thickness bovine articular cartilage. J Orthop Res. 1997;15:499–506. doi: 10.1002/jor.1100150404. [DOI] [PubMed] [Google Scholar]
  • 25.Fung YC. Biomechanics: Mechanical Properties of Living Tissues. 2nd Edition Springer-Verlag; New York: 1993. [Google Scholar]
  • 26.Fung YC. A First Course in Continuum Mechanics. 2nd Edition Prentice-Hall; Englewood Cliffs: 1977. [Google Scholar]
  • 27.Mow VC, Hayes WC. Basic Orthopaedic Biomechanics. Raven Press; New York: 1997. p. 514. [Google Scholar]
  • 28.Whittle M. Gait Analysis: An Introduction. 3rd Edition Butterworth-Heinemann; Oxford; Boston: 2002. [Google Scholar]
  • 29.Shelburne KB, Torry MR, Pandy MG. Muscle, ligament, and joint-contact forces at the knee during walking. Med Sci Sports Exerc. 2005;37:1948–1956. doi: 10.1249/01.mss.0000180404.86078.ff. [DOI] [PubMed] [Google Scholar]
  • 30.Brockmeier SF, Shaffer BS. Viscosupplementation therapy for osteoarthritis. Sports Med Arthrosc. 2006;14:155–162. doi: 10.1097/00132585-200609000-00007. [DOI] [PubMed] [Google Scholar]
  • 31.Rowley G, Antonas KN, Hilbert BJ. Quantitation of hyaluronic acid in equine synovia. Am J Vet Res. 1982;43:1096–1099. [PubMed] [Google Scholar]
  • 32.Saari H, Konttinen YT, Tulamo RM, Antti-Poika I, Honkanen V. Concentration and degree of polymerization of hyaluronate in equine synovial fluid. Am J Vet Res. 1989;50:2060–2063. [PubMed] [Google Scholar]
  • 33.Tulamo RM. Comparison of high-performance liquid chromatography with a radiometric assay for determination of the effect of intra-articular administration of corticosteroid and saline solution on synovial fluid hyaluronate concentration in horses. Am J Vet Res. 1991;52:1940–1944. [PubMed] [Google Scholar]
  • 34.Palmer JL, Bertone AL, McClain H. Assessment of glycosaminoglycan concentration in equine synovial fluid as a marker of joint disease. Can J Vet Res. 1995;59:205–212. [PMC free article] [PubMed] [Google Scholar]
  • 35.Flannery CR, Zollner R, Corcoran C, Jones AR, Root A, Rivera-Bermudez MA, et al. Prevention of cartilage degeneration in a rat model of osteoarthritis by intraarticular treatment with recombinant lubricin. Arthritis Rheum. 2009;60:840–847. doi: 10.1002/art.24304. [DOI] [PubMed] [Google Scholar]
  • 36.Jay GD, Torres JR, Rhee DK, Helminen HJ, Hytinnen MM, Cha CJ, et al. Association between friction and wear in diarthrodial joints lacking lubricin. Arthritis Rheum. 2007;56:3662–3669. doi: 10.1002/art.22974. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 37.Sarma AV, Powell GL, LaBerge M. Phospholipid composition of articular cartilage boundary lubricant. J Orthop Res. 2001;19:671–676. doi: 10.1016/S0736-0266(00)00064-4. [DOI] [PubMed] [Google Scholar]
  • 38.Dahl LB, Dahl IM, Engstrom-Laurent A, Granath K. Concentration and molecular weight of sodium hyaluronate in synovial fluid from patients with rheumatoid arthritis and other arthropathies. Ann Rheum Dis. 1985;44:817–822. doi: 10.1136/ard.44.12.817. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 39.Loening A, Levenston M, James I, Nuttal M, Hung H, Gowen M, et al. Injurious mechanical compression of bovine articular cartilage induces chondrocyte apoptosis. Arch Biochem Biophys. 2000;381:205–212. doi: 10.1006/abbi.2000.1988. [DOI] [PubMed] [Google Scholar]
  • 40.Thibault M, Poole AR, Buschmann MD. Cyclic compression of cartilage/bone explants in vitro leads to physical weakening, mechanical breakdown of collagen and release of matrix fragments. J Orthop Res. 2002;20:1265–1273. doi: 10.1016/S0736-0266(02)00070-0. [DOI] [PubMed] [Google Scholar]
  • 41.Chen C-T, Bhargava M, Lin PM, Torzilli PA. Time, stress, and location dependent chondrocyte death and collagen damage in cyclically loaded articular cartilage. J Orthop Res. 2003;21:888–898. doi: 10.1016/S0736-0266(03)00050-0. [DOI] [PubMed] [Google Scholar]
  • 42.Patwari P, Gaschen V, James IE, Berger E, Blake SM, Lark MW, et al. Ultrastructural quantification of cell death after injurious compression of bovine calf articular cartilage. Osteoarthritis Cartilage. 2004;12:245–252. doi: 10.1016/j.joca.2003.11.004. [DOI] [PMC free article] [PubMed] [Google Scholar]

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