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Autosomal recessive juvenile parkinsonism (AR-JP) is a hereditary neurodegenerative disorder characterized by levodopa-responsive parkinsonism with onset before age 40 years and a slowly progressive course. Families with this condition have been described predominantly in Japanese population, occasionally under different names including an autosomal recessive early-onset parkinsonism with diurnal fluctuation (AR-EPDF) or a familial form of juvenile parkinsonism. Recently, the causative gene for AR-JP was mapped on chromosome 6q25.2-q27, and subsequently a novel gene ‘parkin’ was identified by means of positional cloning. In this manuscript, we review the clinical, pathological and genetical aspects of AR-JP. It would not only promise to provide important insights into the molecular mechanisms of selective degeneration of dopaminergic neurons in AR-JP, but also bring insights into the mechanisms of degeneration of these neurons in Parkinson's disease.

As sliding surfaces in an all-ceramic joint prosthesis generally conform well to keep contact stress low, an end-face friction apparatus is used to investigate the tribological characteristics between nominally flat surfaces. Friction and wear of ceramic specimens were measured with distilled water, hyaluronic acid solutions, and bovine serum. In a water environment, friction and wear of silicon nitride is particularly high due to tribochemical reaction. Zirconia surfaces become very rough during sliding. It is found that alumina and zirconia have excellent tribological properties for the next generation of hip prostheses.

It is difficult to measure the displacement of the menisci under external forces by the radiographic method using markers because the movement may be smaller than the detecting limit. A device with a flexible needle attached to a journal of a miniature linear bearing is developed to investigate the meniscal functions which depend on the mobility. The needle tip is fixed to the target point in the meniscus and the axial displacement is measured with a laser sensor. According to the test, the lower limit for detection was 10 μm, the error due to non-linearity was less than 5 per cent and the reactive force was less than 0.15 N in the operating range of ± mm. Displacement vectors were determined at four points in a pair of menisci in a porcine knee subjected to external forces. This accurate method will lead to further investigation into the mechanical function of the menisci.

Ultra high molecular weight polyethylene (UHMWPE) has been used in artificial joints for a few decades, and wear of UHMWPE has been one of the main problems. Though many other materials have been tested over the years, the best clinical results are still achieved with UHMWPE. This makes the study of UHMWPE, especially in relation to artificial joints, very important. Frequently, more severe wear can be observed in artificial knee joints than in artificial hip joints especially when the flaking-like wear occurs. This flaking-like wear can lead to significant destruction of the artificial knee joint. Macroscopically, artificial knee joints have combinational movements of rolling and sliding in order to simulate the motion of the normal knee joint. The components of motion are separated to make study easier. Fatigue tests of UHMWPE under the rolling contact condition were performed in this study. Three ceramic spheres were rolled over the UHMWPE specimen using 37 degrees C distilled water as a lubricant. The UHMWPE specimen was observed by the scanning acoustic tomography, microscopy, and SEM. Some subsurface defects could be observed by SAT even before experiments. Although the apparent wear is not observed on the surface, there was an increase in the number of observable subsurface cracks in the UHMWPE specimen. This shows that cracks occur under the surface after a 10(7) rolling contact loading, which is very close to the cyclic loading and unloading with very little friction compared to the sliding contact.

Many efforts have been made to improve the low stiffness of air bearing due to compressibility. This paper presents methods to improve the stiffness of an air thrust bearing by control technology, which is composed of a feedback loop and a controller with operating elements. Three methods were tested and compared. The criteria were the amplitude of shaft displacement caused by changing load, the stability of bearing and the limitation of variable restrictor. In conclusion, the bearing with changing load feedback loop has the best performance.

This paper reviews some of the recent trends in lubrication of natural and artificial joints focusing the functions of synovial fluid. While elasto-hydrodynamic lubrication is the major mechanism in human joints, they operate with adaptive multimode lubrication. Though the effect of cartilage porosity is small in fluid film lubrication condition, fluid may be pressed out from the cartilage to the gap in mixed lubrication region and it lubricates cartilage effectively. Cushion form joint proved to result better lubrication condition. However, it needs the assistance of supplemental lubrications at startup.

To improve the frictional characteristics of a biomaterial, the mechanical performance of a lubricated surface was studied. In vitro friction tests showed that the coefficient of dynamic friction of the lubricated surface was about 0.01 against rabbit bladder and the coefficient of static friction increased with the preload period. The efficacy of a lubricated cystoscope was evaluated by an in vivo test simulating cystoscope operation. The maximal and the total resistance force on the cystoscope model were found to decrease with the surface lubrication. Histological study revealed that urethral damage caused by rubbing with the cystoscope model was reduced by this lubrication technique. Presumably, prolonged retention of water on the lubricated surface region prevented tissue adhesion to the foreign material. © 1994 John Wiley & Sons, Inc.

Deformation behavior of trabecular architecture (cancellous structure) was visualized using an ultrahigh-speed video recording camera during both static and impact compression tests of subchondral cancellous bone at nominal strain rates from 0.008 to 25 s−1. The mechanical energy-absorbing mechanisms of cancellous bone could be roughly classified into two types: viscoelastic hysteresis and release of elastic energy from microfractures of the trabeculae. The energy-absorbing ability of degenerated cancellous bone was approximately 50% that of normal bone. The osteoarthritic process results in a change in the cancellous structures such that a pronounced fabric direction is not evident. In the case of normal cancellous bone, the structural stiffness of the bone was maintained by each trabecula functioning as a long column in the cancellous structure. It was confirmed visually that, for the in vitro case, aseptic loosening of the prosthesis was caused by a decrease in the cancellous bone stock or reduction in the energy-absorbing abihty of the joints. Thus, the energy-absorbing properties of subchondral cancellous bone were dependent on the morphology and deformability of the cancellous structure.

Pullout friction and cross-sectional relaxation tests were conducted to quantitatively evaluate the handling characteristics of braided suture. The excellent handling of silk suture could be explained in terms of a large difference between static and dynamic pullout resistances. The difference in the resistance was closely correlated to the slope of the cross-sectional relaxation versus time logarithmic plot. It was therefore concluded that the cross-sectional stress-relaxation plays an important role in the handling performance of braided sutures.

This paper presents the experimental results of compression and sliding tests and discusses the relationship between the lubrication conditions and deformation of the cartilage in a synovial joint. The compression test simulating fluid lubrication conditions resulted in no cartilage deformation. Creep deformation was detected only in the test which simulated direct contact conditions. Friction and deformation were measured with a thrust collar apparatus. It was found that water, which exudes from the cartilage under direct contact, lubricates and suppresses the increase in friction. It was also determined that, as the creep deformation accompanying water exudation is related to the contact pressure, the deformation rate of the cartilage is a good index of the lubrication condition.

The establish criteria for characterizing synthetic sutures, the handling characteristics of silk suture were analyzed. The characteristics that distinguish silk suture from other braided suture materials are its good “knot security” and relatively low “tiedown resistance.” Analytic consideration of knot security suggests that not only superficial friction but also resistance force produced by cross-sectional deformity of braided threads plays an important role in silk's superior performance. Results of a “pullout friction test,” developed to quantitatively evaluate resistance produced by surface friction and cross-sectional deformity suggest that the superiority of silk thread can be explained in terms of high static withdrawal resistance under low loads and relatively low dynamic withdrawal resistance under high loads. © 1993 John Wiley & Sons, Inc.

A model for squeeze film effect in a hip joint is presented. Gap flow. Flow in the cartilage, solid contact of the cartilage are considered. The result shows that most of applied load is supported hydrodynamically by synovial fluid, while contact arises in a short time. The contact pressure is kept low by fluid exuding from the cartilage to the gap.

A femoral head of quartz glass was attached to a hip joint simulator to observe the contact region. The area of contact changes for an ultra high molecular weight polyethylene (UHMWPE) socket. Squeeze film effect, which reduces friction at heel strike, diminishes during step phase. Frictional torque is lower for a compliant socket of silicon rubber. However, if extremely compliant socket (E=1.7 MPa) is used, friction which was low at the start of walking increases and becomes even higher than the case with UHMWPE socket. This transition is late with more viscous fluid.