Lubrication of human joints

Advances in viscosupplementation and tribosupplementation for early-stage osteoarthritis therapy

Joint kinematic instability, arising from congenital or acquired musculoskeletal pathoanatomy or from imbalances in anabolism and catabolism induced by pathophysiological factors, leads to deterioration of the composition, structure and function of cartilage and, ultimately, progression to osteoarthritis (OA). Alongside articular cartilage degeneration, synovial fluid lubricity decreases in OA owing to a reduction in the concentration and molecular weight of hyaluronic acid and surface-active mucinous glycoproteins that form a lubricating film over the articulating joint surfaces. Minimizing friction between articulating joint surfaces by lubrication is fundamental for decreasing hyaline cartilage wear and for maintaining the function of synovial joints. Augmentation with highly viscous supplements (that is, viscosupplementation) offers one approach to re-establishing the rheological and tribological properties of synovial fluid in OA. However, this approach has varied clinical outcomes owing to limited intra-articular residence time and ineffective mechanisms of chondroprotection. This Review discusses normal hyaline cartilage function and lubrication and examines the advantages and disadvantages of various strategies for restoring normal joint lubrication. These strategies include contemporary viscosupplements that contain antioxidants, anti-inflammatory drugs or platelet-rich plasma and new synthetic synovial fluid additives and cartilage matrix enhancers. Advanced biomimetic tribosupplements offer promise for mitigating cartilage wear, restoring joint function and, ultimately, improving patient care.

Synovial Extracellular Vesicles: Structure and Role in Synovial Fluid Tribological Performances

The quality of the lubricant between cartilaginous joint surfaces impacts the joint’s mechanistic properties. In this study, we define the biochemical, ultrastructural, and tribological signatures of synovial fluids (SF) from patients with degenerative (osteoarthritis-OA) or inflammatory (rheumatoid arthritis-RA) joint pathologies in comparison with SF from healthy subjects. Phospholipid (PL) concentration in SF increased in pathological contexts, but the proportion PL relative to the overall lipids decreased. Subtle changes in PL chain composition were attributed to the inflammatory state. Transmission electron microscopy showed the occurrence of large multilamellar synovial extracellular vesicles (EV) filled with glycoprotein gel in healthy subjects. Synovial extracellular vesicle structure was altered in SF from OA and RA patients. RA samples systematically showed lower viscosity than healthy samples under a hydrodynamic lubricating regimen whereas OA samples showed higher viscosity. In turn, under a boundary regimen, cartilage surfaces in both pathological situations showed high wear and friction coefficients. Thus, we found a difference in the biochemical, tribological, and ultrastructural properties of synovial fluid in healthy people and patients with osteoarthritis and arthritis of the joints, and that large, multilamellar vesicles are essential for good boundary lubrication by ensuring a ball-bearing effect and limiting the destruction of lipid layers at the cartilage surface.

The Effect of Synovial Fluid Composition, Speed and Load on Frictional Behaviour of Articular Cartilage

Articular cartilage ensures smooth motion of natural synovial joints operating at very low friction. However, the number of patients suffering from joint diseases, usually associated with cartilage degradation, continuously increases. Therefore, an understanding of cartilage tribological behaviour is of great interest in order to minimize its degradation, preserving the reliable function of the joints. The aim of the present study is to provide a comprehensive comparison of frictional behaviour of articular cartilage, focusing on the effect of synovial fluid composition (i), speed (ii), and load (iii). The experiments were realized using a pin-on-plate tribometer with reciprocating motion. The articular cartilage pin was loaded against smooth glass plate while the tests consisted of loading and unloading phases in order to enable cartilage rehydration. Various model fluids containing albumin, γ-globulin, hyaluronic acid, and phospholipids were prepared in two different concentrations simulating physiologic and osteoarthritic synovial fluid. Two different speeds, 5 mm/s and 10 mm/s were applied, and the tests were carried out under 5 N and 10 N. It was found that protein-based solutions exhibit almost no difference in friction coefficient, independently of the concentration of the constituents. However, the behaviour is considerably changed when adding hyaluronic acid and phospholipids. Especially when interacting with γ-globulin, friction coefficient decreased substantially. In general, an important role of the interaction of fluid constituents was observed. On the other hand, a limited effect of speed was detected for most of the model fluids. Finally, it was shown that elevated load leads to lower friction, which corresponds well with previous observations. Further study should concentrate on specific explored phenomena focusing on the detailed statistical evaluation.

Therapeutic effects of intra-articular ultra-purified low endotoxin alginate administration on an experimental canine osteoarthritis model

OBJECTIVE

This study aimed to elucidate the therapeutic effects of intra-articular administration of ultra-purified low endotoxin alginate (UPLE-alginate) on osteoarthritis (OA) using a canine anterior cruciate ligament transection (ACLT) model.

DESIGN

We used 20 beagle dogs. ACLT was performed on the left knee of each dog and a sham operation was performed on the right knee as a control. All animals were randomly divided into the control (saline) and therapeutic (UPLE-alginate) groups. Animals in the control and therapeutic groups received weekly injections with 0.7 mL normal saline or 0.7 mL 0.5% UPLE-alginate, respectively, from 0 to 3 weeks after ACLT or sham operation. At 9 weeks after ACLT, the knee joints of all animals were observed using arthroscopy. All animals were euthanized at 14 weeks after ACLT and evaluated using morphologic assessment, histologic assessment, and biomechanical testing.

RESULTS

Arthroscopic findings showed intact cartilage surface in both groups. Morphologic findings in the therapeutic group showed milder degeneration compared with those of the control group, but there were no significant differences between groups. Histologic scores of the medial femoral condyle (MFC) and lateral femoral condyle (LFC) were better in the therapeutic group than the control group (MFC: p = 0.009, LFC: p = 0.009). Joint lubrication did not differ significantly between groups.

CONCLUSION

Intra-articular administration of UPLE-alginate in the early stage of OA slowed disease progression in canines. UPLE-alginate may have potential as a therapeutic agent for OA patients and reduce the number of patients who need to undergo total joint arthroplasty.

Chondroprotective effects of high-molecular-weight cross-linked hyaluronic acid in a rabbit knee osteoarthritis model

OBJECTIVES

We hypothesized that high-molecular-weight (MW) cross-linked (CL) hyaluronic acid (HA) improves joint lubrication and has an enhanced chondroprotective effect. We examined the histopathological changes and friction coefficients in osteoarthritic knee joints after injecting high-MW CL HA.

DESIGN

A bilateral anterior cruciate ligament transection (ACLT) model in 20 Japanese white rabbits was used. From week 5 after transection, low-MW HA (0.8 × 10(6) Da; HA80) or high-MW CL HA (6 × 10(6) Da; HA600) was injected weekly into 10 right knee for 3 weeks; normal saline (NS) was injected into the 10 left knee. A sham operation was undertaken to exclude spontaneous osteoarthritis (OA) in five knees. Results were evaluated with macroscopy, histopathology (Kikuchi's score), biomechanical testing, and rheological assessment of the joint fluid viscoelasticity. Statistical analysis was performed using one-way analysis of variance with a 95% confidence interval (CI) (P < 0.05).

RESULTS

The macroscopic findings showed severely damaged cartilage in 30% of the NS group and 20% of the HA80 and HA600 groups and intact cartilage in 100% of the sham group. The histological scores and friction coefficients of the HA600 group were significantly lower than those of the NS group (P = 0.007 and P = 0.002, respectively). Viscoelasticity measurements of the joint fluid showed no significant differences between the three treatment groups.

CONCLUSION

High-MW CL HA exerts potential chondroprotective effects and produces superior friction coefficients. Our results suggest that HA600 delays the progression of OA effectively and improves joint lubrication significantly.

Therapeutic Effects of Intra-Articular Ultrapurified Low Endotoxin Alginate Administration on Experimental Osteoarthritis in Rabbits

OBJECTIVE

We have developed an ultrapurified low endotoxin alginate (UPLE alginate), which can drastically reduce endotoxin levels. Our purposes were to examine the effects of UPLE alginate administration on osteoarthritis (OA) progression and to determine the adequate molecular weight of the UPLE alginate for therapeutic effects.

DESIGN

To induce knee OA, 35 Japanese White rabbits underwent anterior cruciate ligament transection. Intra-articular injections of 0.3 mL solution of each material were started at 4 weeks postoperatively for a total of 5 weekly injections. Seventy knees were divided into the following groups: AL430 (430 kDa molecular weight UPLE alginate), AL1000 (1,000 kDa), AL1700 (1,700 kDa), HA (hyaluronan), and NS (normal saline). At 9 weeks postoperatively, all knees were assessed macroscopically, histologically, and mechanically.

RESULTS

Macroscopically, the UPLE alginate groups exhibited milder cartilage degradation compared to that of the NS and HA groups. Histological findings of the UPLE alginate groups showed an obvious reduction in the severity of OA. The histological scores of Kikuchi et al. were superior in the alginate treatment groups compared to the NS group. The friction coefficient of the AL1000 group was significantly lower than that of the NS and HA groups.

CONCLUSION

This study indicates that our UPLE alginates, especially AL1000, have promising potential as an effective agent in preventing OA progression.

The role of interstitial fluid pressurization in articular cartilage lubrication

Over the last two decades, considerable progress has been reported in the field of cartilage mechanics that impacts our understanding of the role of interstitial fluid pressurization on cartilage lubrication. Theoretical and experimental studies have demonstrated that the interstitial fluid of cartilage pressurizes considerably under loading, potentially supporting most of the applied load under various transient or steady-state conditions. The fraction of the total load supported by fluid pressurization has been called the fluid load support. Experimental studies have demonstrated that the friction coefficient of cartilage correlates negatively with this variable, achieving remarkably low values when the fluid load support is greatest. A theoretical framework that embodies this relationship has been validated against experiments, predicting and explaining various outcomes, and demonstrating that a low friction coefficient can be maintained for prolonged loading durations under normal physiological function. This paper reviews salient aspects of this topic, as well as its implications for improving our understanding of boundary lubrication by molecular species in synovial fluid and the cartilage superficial zone. Effects of cartilage degeneration on its frictional response are also reviewed.

Compressive properties of cartilage-like tissues repaired in vivo with scaffold-free, tissue engineered constructs

BACKGROUND

It is crucial to develop an effective methodology for restoring adequate compressive properties to osteoarthritic cartilage. We have developed a scaffold-free tissue engineered construct cultured from synovium-derived mesenchymal stem cells. However, the compressive properties of cartilage-like tissues repaired with the construct have not been fully determined.

METHODS

Synovium-derived mesenchymal stem cells were cultured in Dulbecco's modified Eagle's medium to produce the tissue engineered construct. Implantation of the construct into cylindrically-shaped partial defects in femoral cartilage in an experimental porcine model was performed. Six months after implantation, cartilage-like tissues repaired with the construct were subjected to static and cyclic compression tests using a micro-unconfined compression test apparatus developed in our laboratory.

FINDINGS

The developed apparatus was validated in preliminary examinations. The repaired tissues exhibited rate-dependent viscoelastic properties; the compressive modulus was slightly lower than that of normal cartilage at a rate of 4 microm/s, while no difference was observed at a rate of 100 microm/s. In contrast, the repaired tissue without the construct exhibited rate-independent, non-viscoelastic properties. In the cyclic compression test, however, the compressive strain was significantly larger in both repaired tissues as compared with normal cartilage.

INTERPRETATION

Although the quasi-static compressive properties of the repaired tissue with the construct, indicating rate-dependent and viscoelastic behaviors, are comparable to normal cartilage, the cyclic compressive strain increases more rapidly than in normal cartilage. It is suggested that the differences between the tissues and normal cartilage are attributable to the increased permeability of the extracellular matrix.

Biphasic surface amorphous layer lubrication of articular cartilage

The biphasic nature of articular cartilage has been acknowledged for some time and is known to play an important role in many of the biomechanical functions performed by this unique tissue. From the lubrication point of view however, a simple biphasic model is unable to account for the extremely low friction coefficients that have been recorded experimentally, particularly during start-up. In addition, research over the last decade has indicated the presence of a surface amorphous layer on top of articular cartilage. Here, we present results from a finite element model of articular cartilage that includes a thin, soft, biphasic surface amorphous layer (BSAL). The results of this study show that a thin BSAL, with lower elastic modulus, dramatically altered the load sharing between the solid and liquid phases of articular cartilage, particularly in the near-surface regions of the underlying bulk cartilage and within the surface amorphous layer itself where the fluid load support exceeded 85%. By transferring the load from the solid phase to the fluid phase, the biphasic surface layer improves lubrication and reduces friction, whilst also protecting the underlying cartilage surface by 'shielding' the solid phase from elevated stresses. The increase in lubrication effectiveness is shown to be greatest during short duration loading scenarios, such as shock loads.

Mechanical effects of the intraarticular administration of high molecular weight hyaluronic acid plus phospholipid on synovial joint lubrication and prevention of articular cartilage degeneration in experimental osteoarthritis

OBJECTIVE

To examine in vivo the effects of a mixture of high molecular weight hyaluronic acid (HA) plus phospholipids on joint lubrication and articular cartilage degeneration.

METHODS

Experimental osteoarthritis (OA) of the right knee was induced by anterior cruciate and medial collateral ligament transection in 40 rabbits. The animals were subjected to 8 consecutive weekly intraarticular administrations of high molecular weight HA (the HA200 group), conventional molecular weight HA (the HA80 group), or high molecular weight HA plus L-delta dipalmitoyl phosphatidylcholine liposomes (the PHA group) and were killed 1 week after the final injection. The remaining transected right knees (the OA group) and randomly selected nontransected contralateral left knees (the control group) were collected simultaneously. Each group (n = 10) was divided into 2 equal subgroups, one of which was evaluated histologically while the other was subjected to a lubricating ability test using a pendulum friction tester.

RESULTS

The injected knees had a tendency to demonstrate less damage to the articular cartilage compared with the OA group, and the histologic findings in all groups except for the PHA group differed significantly from the control group. There was a significant difference in the mean +/- SD friction coefficient between the control group (0.0100 +/- 0.00300) and the OA (0.0206 +/- 0.00649), HA200 (0.0190 +/- 0.00427), and HA80 (0.0177 +/- 0.00712) groups (P < 0.05 for each comparison), but not between the control group and the PHA group (0.0150 +/- 0.00330) (P = 0.15).

CONCLUSION

To our knowledge, this is the first in vivo study to examine whether intraarticular injections of phospholipids influence joint lubrication by acting as a boundary lubricant, thus protecting articular cartilage from degenerative changes.