Shigeaki Moriyama

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.

Evaluation of Dynamic Instability of the Dysplastic Hip with Use of Triaxial Accelerometry

BACKGROUND Dysfunction of the hip secondary to dysplasia is a complex problem that includes excessive stresses on the articular cartilage, dynamic hip instability, and muscular fatigue, eventually leading to degenerative arthritis if left uncorrected. Mechanical stress on the dysplastic hip has been widely described, but dynamic instability requires further evaluation. The purpose of this study was to investigate dynamic instability of the dysplastic hip with use of triaxial accelerometry. METHODS We evaluated forty-eight hips of twenty-four patients with unilateral hip dysplasia (a center-edge angle of <25 degrees ). All contralateral hips were disease-free with normal radiographic findings. An accelerometer was used to record triaxial acceleration while the patient was walking (x-axis: superoinferior direction, y-axis: anteroposterior direction, and z-axis: mediolateral direction). Sensors were attached to the skin, with adhesive tape, over the greater trochanter and the anterior superior iliac spine bilaterally. The time of heel-strike was confirmed visually and by superoinferior acceleration. The averages of the peak values of the middle three gait cycles were used for data analysis. The overall magnitude of acceleration was calculated to evaluate hip instability. The overall magnitudes of acceleration of the dysplastic and contralateral, normal hips were compared with the radiographic data. RESULTS The three directions of acceleration were the same in all cases. The overall magnitude of acceleration of the dysplastic hips was significantly larger than that of the contralateral, normal hips (p < 0.0001). There was a negative correlation between the overall magnitude of acceleration and both the center-edge angle and the acetabular head index, and there was a positive correlation between the overall magnitude of acceleration and both the acetabular roof angle and the Sharp angle. CONCLUSIONS Hip instability is increased in proportion to the degree of dysplasia. Triaxial accelerometry is helpful in the evaluation of dynamic instability of the dysplastic hip. The center-edge angle can be used as an indicator of hip instability.

Periacetabular osteotomy reduces the dynamic instability of dysplastic hips

We compared the dynamic instability of 25 dysplastic hips in 25 patients using triaxial accelerometry before and one year after periacetabular osteotomy. We also evaluated the hips clinically using the Harris hip score and assessed acetabular orientation by radiography before surgery and after one year. The mean overall magnitude of acceleration was significantly reduced from 2.30 m/s(2) (sd 0.57) before operation to 1.55 m/s(2) (sd 0.31) afterwards. The mean Harris hip score improved from 78.08 (47 to 96) to 95.36 points (88 to 100). The radiographic parameters all showed significant improvements. This study suggests that periacetabular osteotomy provides pain relief, improves acetabular cover and reduces the dynamic instability in patients with dysplastic hips.

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.

Modified pubic osteotomy for medialization of the femoral head in periacetabular osteotomy: A retrospective study of 144 hips

Background and purpose Medial displacement of the femoral head reduces the force transmitted across the hip joint. Since 2005, we have performed a modified Ganzs osteotomy with curved periacetabular osteotomy (CPO) to obtain medialization of the femoral head. The modification involves cutting of the pubis at 30 degrees to the horizontal line. Here, we examined whether this modified CPO procedure medialized the femoral head more than the conventional CPO procedure. Patients and methods 69 patients (mean age 37 years, 72 hips) treated with the modified CPO procedure (the M group) were compared with 68 patients (mean age 38 years, 72 hips) previously treated with conventional CPO (the C group). All patients were operated because of dysplastic hips. We used radiographic measurements from anteroposterior radiographs. The magnitude of the resultant hip force normalized with respect to the body weight (R/WB) and hip contact joint stress (Pmax/ WB) was calculated in all cases. Results The average lateral center‐edge (CE) angle, acetabular roof obliquity (ARO), and acetabulum‐head index (AHI) improved in both groups. The CE angle, ARO, and AHI were similar in the 2 groups before and after surgery. Medialization of the femoral head was larger in the M group than in the C group (p < 0.001). The average value of the resultant hip force decreased from 3.2 to 2.9 in the M group and remained unchanged, at 3.1, in the C group. In addition, the average value of the peak contact stress decreased more in the M group (from 9.4 kPa/N to 3.4 kPa/N) than in the C group (from 9.1 kPa/N to 4.3 kPa/N). Interpretation In dysplastic hips, the modified CPO reduces the contact hip stress more than the conventional CPO because of better medialization of the femoral head.

Three lateral osteotomy designs for bilateral sagittal split osteotomy: biomechanical evaluation with three-dimensional finite element analysis

BackgroundThe location of the lateral osteotomy cut during bilateral sagittal split osteotomy (BSSO) varies according to the surgeons preference, and no consensus has been reached regarding the ideal location from the perspective of biomechanics. The purpose of this study was to evaluate the mechanical behavior of the mandible and screw-miniplate system among three lateral osteotomy designs for BSSO by using three-dimensional (3-D) finite element analysis (FEA).MethodsThe Trauner-Obwegeser (TO), Obwegeser (Ob), and Obwegeser-Dal Pont (OD) methods were used for BSSO. In all the FEA simulations, the distal segments were advanced by 5 mm. Each model was fixed by using miniplates. These were applied at four different locations, including along Champys lines, to give 12 different FEA miniplate fixation methods. We examined these models under two different loads.ResultsThe magnitudes of tooth displacement, the maximum bone stress in the vicinity of the screws, and the maximum stress on the screw-miniplate system were less in the OD method than in the Ob and TO methods at all the miniplate locations. In addition, Champys lines models were less than those at the other miniplate locations.ConclusionsThe OD method allows greater mechanical stability of the mandible than the other two techniques. Further, miniplates placed along Champys lines provide greater mechanical advantage than those placed at other locations.

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.

A New Fatigue Testing Machine for Investigating the Behavior of Small Shear-Mode Fatigue Cracks

The investigation of the behavior of small shear-mode fatigue cracks in the high-cycle fatigue regime is essential to understand the mechanism of rolling-contact fatigue failures, such as flaking in bearings and shelling in rails, from the fracture mechanics point of view. The stable growth of a shear-mode fatigue crack was achieved by applying static compression to a specimen in a cyclic torsion fatigue test. This loading condition is usually obtained by a combined tension-torsion testing machine with a servo-hydraulic control system. In this study, a new testing machine was developed and found to be superior to the servo-hydraulic testing machine in terms of price, operation/maintenance costs, operating speed, and installation volume. For substantiation and demonstration purposes, a shear-mode fatigue crack growth test with a bearing steel was also carried out using both the new and the conventional servo-hydraulic testing machines. The experiments revealed that under the same loading conditions, nonpropagating shear-mode cracks of similar size and geometry could be obtained by the respective testing machines. Thus, it was concluded that the new testing machine has equivalent capabilities to the servo-hydraulic testing machine in performing shear-mode fatigue crack growth tests.

Teleconferences on thoracoscopic surgery using an academic network between Asian institutions

Internet teleconferences using an advanced academic network are now quite common in the medical field. However, such conferences are still not particularly common in the area of pulmonary surgery. Here, we report the practical lessons learned from participating in international teleconferences on video‐assisted thoracic surgery. Between November 2007 and February 2010, teleconferences with high‐definition live video feeds were held five times between Fukuoka University Hospital and other institutions across the Asia‐Pacific region. For these teleconferences, a digital video transport system, connected with the high‐performance network of the Asia‐Pacific Advanced Network, was used to establish communication. In all conferences, discussions were conducted without difficulty. No surgeries were performed live; a video presentation of the recorded surgery was sufficient. Though technical assistance is required to connect and communicate with other professionals, international teleconferences are a worthwhile and intellectually stimulating activity.

Mechanical Property of Porous Titanium Produced by Spark Plasma Sintering

Titanium has widely been used as a biomaterial because of its excellent corrosion resistance and biocompatibility. However, problems with respect to biological reaction and fitness of elastic modulus for human bone or tooth have yet to be solved. Porous titanium is expected to be a promising material to solve these problems. The aim of this study is to clarify the effect of the porous structure of this material on the biomechanical compatibility. The spherical pure titanium powder, with an average particle size of 100 µm, was sintered by spark plasma sintering. The sintered porous titanium compacts had a porosity of 33 %. The specimens were machined from the sintered compacts for the evaluation of the mechanical properties. The elastic modulus indicated a value close to human bone, while the tensile and compressive strengths showed lower values than those of human bone.