Hidehiko Higaki

Adaptive Multimode Lubrication in Natural Synovial Joints and Artificial Joints

Abstract To examine the lubrication mechanisms in both natural synovial joints and artificial joints with artificial cartilages, pendulum tests of pig shoulder joints and simulator tests of sliding pairs of a stainless steel spherical component and natural articular cartilage or artificial cartilage have been conducted. Firstly, it was shown in pendulum tests of pig shoulder joints that both concentration of hyaluronic acid or viscosity and adsorbed film formation of proteins and phospholipids exerted a significant effect on frictional behaviour in swinging motion immediately after a loading of 100 N. Under a high load of 1 kN, low friction was observed under wide-ranging viscosity conditions, since a high load similar to body weight probably enhanced the squeeze film effect due to improved congruity. Next, frictional behaviour of sliding pairs in knee joint models, consisting of a stainless steel spherical surface and either specimens of pig tibial cartilage or polyvinylalcohol (PVA) hydrogel, was examined during walking in simulator tests. In these tests, the influences of lubricant viscosity and addition of protein on frictional behaviour were evaluated. For both compliant materials, the appropriate addition of γ-globulin to sodium hyaluronate (HA) solution maintained low friction and protected rubbing surfaces under thin film conditions. These phenomena are discussed from the viewpoint of adaptive multimode lubrication.

The lubricating ability of biomembrane models with dipalmitoyl phosphatidylcholine and γ-globulin

Abstract Two kinds of friction tests were conducted to investigate the lubricating effect of the injection of amphiphilies on the osteoarthritic joint. The effects of the addition of Lα-dipalmitoyl phosphatidylcholine (Lα-DPPC) riposomes and γ-globulin in a saline solution of sodium hyaluronate (HA) were evaluated through pendulum friction tests. The frictional characteristics of pig shoulder joints were confirmed to depend on the viscosity of the lubricants only in the physiologically low load condition and in the condition immediately after loading. Detergent (polyoxyethylene p-t-octylphenyl ether) was successfully used to remove adsorbed films from the articular surfaces. The friction coefficient of natural synovial joints was significantly increased in a mode of mixed lubrication with the HA solution of 0.2 g/dl by the treatment of the surface with the detergent. The addition of Lα-DPPC riposomes or y-globulin significantly improved the boundary lubricating ability of the articular surfaces treated with the detergent, depending on the quantity of those additives. It appears that the Lα-DPPC riposomes and γ-globulin can form protective films on the articular surfaces like a biomembrane. Moreover, the reciprocating frictional behaviour in sliding pairs of pig articular cartilages and glass plates was studied in order to elucidate the tribological role of those constituents in the boundary lubricating film on the articular surface. Pig synovial fluid and water solutions of HA were used as lubricants. The synovial fluid had superior lubricating ability compared to the HA solution of equivalent viscosity under a physiologically high load condition. This fact seems to be responsible for the boundary lubricating ability of constituents other than hyaluronic acid. Langmuir-Blodgett (LB) films of Lα-DPPC on the glass plate were kept at a low and stable friction coefficient, depending on the number of film layers. In conditions of mixed films with Lα-DPPC and γ-globulin, the frictional behaviour was improved by increasing the quantity of γ-globulin. A model is proposed in which the effective adsorbed films are composed of proteins, phospholipids and other conjugated constituents on the articular surfaces to be accurate in describing the boundary lubricating mechanism. The mechanism is controlled by hydrophobic groups in those amphiphilies.

Prediction of transient lubricating film thickness in knee prostheses with compliant layers

Abstract The transient lubricating film thickness in knee prostheses using compliant layers has been predicted under simulated walking conditions based upon the elastohydrodynamic lubrication theory. Qualitative agreement has been found between the present theoretical predictions and the experimental measurements using an electric resistance technique reported earlier. It has been shown that the contact geometry plays an important role in the generation of fluid film lubrication in knee prostheses using compliant layers. The maximum lubricating film thickness is predicted for the maximized contact area of a transverse conjunction where the semi-minor contact radius lies in the direction of entraining. The additional advantage of the transverse contact conjunction is that the possibility of lubricant starvation due to small stroke length can be minimized. All these factors, together with the kinematic requirements in the natural knee joint, should be taken into consideration when designing artificial knee joint replacements.

The adaptive multimode lubrication in knee prostheses with compliant layer during walking motion

In the present paper, the lubrication modes in knee prostheses different in geometric design and materials under walking conditions are evaluated on the basis of the experimental results in knee joint simulator tests. The fluid film formation is investigated by applying the electric resistance method for conductive femoral and tibial components. The frictional behaviour also is examined to clarify the tribological severity. To improve the lubricating performance during walking, the design concept of the adaptive multimode lubrication mechanism including weeping, gel film, adsorbed film etc. is proposed to protect articulating surfaces under severe conditions. In this study, frictional behaviour of sliding pair of gelatin gel models lubricated with gelatin solution is observed to investigate the effect of gel film. Furthermore, the application of polyvinylalcohol (PVA) hydrogel as weeping articular surface is evaluated.

The Adaptive Multimode Lubrication in Knee Prostheses with Artificial Cartilage during Walking

The lubricating performance of total knee prosthesis models with compliant layer as artificial cartilage was evaluated and discussed from the viewpoint of adaptive multimode lubrication. The minimum film thickness and inclination of rubbing surface during walking were estimated by numerical analysis based on the plane inclined surface model for polyvinylalcohol (PVA) hydrogel and polyurethane. The numerical results show the effectiveness of softer material on fluid film formation during walking, although surface inclination during swing phase is larger for polyurethane than PVA hydrogel. The actual fluid film formation in knee prostheses during walking was examined by measurement of degree of separation by electric resistance method and frictional force in simulator tests. Under walking condition lubricated with lubricants of appropriate viscosity, considerable elastohydrodynamic film was formed corresponding to numerical analysis. Under thin film conditions lubricated with low viscosity lubricants where significant local direct contact occurred between rubbing surfaces due to breakdown of fluid film, the addition of proteins remarkably decreased friction and suppressed stick-slip for PVA, but increased friction for polyurethane. The addition of phospholipid liposomes had an effect in reducing of friction after repetition of rubbing process in walking motion. The adsorbed film formation of synovia constituents on stainless steel plate was observed by atomic force microscopy.

Three‐dimensional motion analysis of the patellar component in total knee arthroplasty by the image matching method using image correlations

In total knee arthroplasty (TKA), the patella is significantly associated with range of motion and gait performance. Currently, no highly accurate methods are available that can measure the 3D in vivo behavior of the TKA patellar component, as the component is made of x‐ray‐permeable ultra‐high molecular weight polyethylene. Previously, we developed a computer simulation that matches CT scan and unidirectional radiographic images using image correlations, and applied it to kinematic studies of natural and TKA knees. The examination of the measurement accuracy for the patellar bone of a fresh‐frozen pig knee joint yielded a root mean square error of 0.2 mm in translation and 0.2° in rotation. In this study, we recruited four patients who had a TKA and investigated 3D movements of the patellar component during squatting. We could visualize the patellar component using the position of the holes drilled for the component peg, and estimated and visualized the contact points between the patellar and femoral components. The principles and the utility of the simulation method are reported. This analytical method is useful for evaluating the pathologies and post‐surgical conditions of the knee and other joints.

Continuous Sagittal Radiological Evaluation of Stair-Climbing in Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasties Using Image-Matching Techniques

In this study, we evaluated the in vivo kinematics of stair-climbing after posterior stabilized (PS) and cruciate retaining (CR) total knee arthroplasty (TKA) using radiographic-based image-matching techniques. Mid-flexion anteroposterior stability was demonstrated in all knees after CR TKA. However, paradoxical femoral translation at low flexion angles was seen in both designs. The post-cam mechanism did not function after PS TKA. Larger posterior tibial slope in PS TKA was linked to forward sliding of the femur at mid-flexion and unintended anterior tibial post impingement at knee extension. CR TKA is more sagittally stable in mid-flexion during stair climbing and attention must be given to minimize posterior tibial slope when using late cam-post engaging PS TKA designs.

Rotational alignment of the tibial component affects the kinematic rotation of a weight-bearing knee after total knee arthroplasty.

PURPOSE The purpose of this study is to elucidate how the rotational malalignment of prosthesis after total knee arthroplasty affects the rotational kinematics in a weight-bearing condition. METHODS In this study of 18 knees replaced with the posterior stabilizing fixed-bearing system, which has a relatively low-restricting design, rotational angles between the femoral and tibial components and between the femur and tibia during stair climbing were evaluated in vivo in three dimensions using radiologically based image-matching techniques. Rotational alignments of the components were assessed by postoperative CT. The correlations between the rotational alignments and the rotational angles during stair climbing were evaluated. RESULTS Rotational alignment of the tibial component significantly correlated with rotational angles between the components as well as between bones during stair climbing. Rotational malalignment of the tibial component toward internal rotation caused a rotational mismatch of the tibial component toward internal rotation relative to the femoral component in 0° extension and caused a rotational mismatch of the tibia (bone) toward external rotation relative to the femur (bone). The knee in which the tibial component was placed close to the AP axis of the tibia did not show any rotational mismatch between either components or bones. CONCLUSIONS Rotational alignment of the tibial component affects the kinematic rotation of the replaced knee during a weight-bearing condition even though using a low-restricting designed surface, and the AP axis can be a reliable reference in determining rotational alignment for the tibial component.

Biomimetic sealing system with hydrated materials for ocean current or tidal power generation

An all-new sealing system for a rotating shaft, which specializes in excellent separation between water and air, has been developed for installation in an ocean current or tidal power generator. Two seal lips made of a polyvinyl formal (PVF) were attached to a rotating shaft, and an aqueous solution of 3.0 wt% polyethylene glycol (PEG), a non-Newtonian fluid with a molecular weight of 2.0 million, was supplied between two lips for lubrication. Expected lubrication modes between the dynamic seal surfaces were hydration lubrication, soft-elastohydrodynamic lubrication, and weeping lubrication, similar to that observed in a natural synovial joint. Using PVF with a small porous diameter of 8 μm and continuously porous structure promoted hydration lubrication between seal surfaces at the molecular level, and low leakage of water, less than 0.05 ml/h, throughout the experiment. Mean frictional torque was lower than that found in the mechanical and oil seals that are generally used for industrial components. Frictional torque had been stable; the friction was independent of the shaft rotational speed, and the stick-slip friction that might lead to leakage of water was moderated in comparison with the conventional sealing systems.

Influence of Geometry of Conjunction on Elastohydrodynamic Film Formation in Knee Prostheses with Compliant Layer

In most of existing knee prostheses with low geometrical congruity, the sufficient fluid film is unlikely to be formed to prevent a direct contact between femoral and tibial component. The difference in geometry of conjunction of knee prostheses may exert an influence on lubricating film formation. Fluid film formation and frictional behavior in several kinds of knee prostheses with compliant layer different in geometry of conjunction were examined in knee joint simulator tests under walking conditions. The femoral component is the sphere of 30mm radius made of stainless steel. The tibial components were made of conductive silicone rubber layer of 3mm thickness supported by acrylic resin. Four kinds of tibial components were prepared for a different conjunction geometry. Silicone oils were used as lubricants. The geometrical shapes of conjunction are classified into three kinds of shape, i.e., a longitudinally long ellipse, a transversely long ellipse to the sliding direction and a circle. Four kinds of data (tibial axis load, flexion angle, frictional torque and degree of separation) were measured. The data of 25th cycle were evaluated. As a result, the ability of the fluid film formation of the transverse geometry of conjunction was higher than the longitudinal geometry of conjunction.