Evaluation of the Lubricating Effect of Hyaluronic Acid on Contact Lenses Using a Pendulum-Type Friction Tester Under Mimicking Physiological Conditions.

OBJECTIVE: To evaluate the lubricating effect of hyaluronic acid (HA) on soft contact lenses (SCLs) measured using a pendulum-type friction tester. METHODS: We measured the coefficient of friction (CoF) of narafilcon A, delefilcon A, and etafilcon A with polyvinylpyrrolidone (PVP), daily disposable SCL material, using a modified pendulum-type friction tester. Sample SCLs were set on an acrylic plastic half-ball and placed into the polyethylene terephthalate hemisphere cup filled with 0.4 mL of test lubricants that included saline and 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% (wt/vol) HA (molecular weight, 850 kDa). The viscosities of saline and HA were measured using an Ubbelohde viscometer. RESULTS: The CoF of the SCL under a low concentration (0.05%) of HA was the lowest and significantly lower than saline in narafilcon A and delefilcon A (P<0.05, Steel multiple comparison test). Under higher HA concentrations (0.3%, 0.4%, and 0.5%), the CoF was significantly higher than that of saline (P<0.01, Steel' multiple comparison test) in all three SCLs. There were no significant differences of CoF among three SCLs in saline and all concentrations of HA. The HA viscosities increased exponentially with the concentration (Y=1.2829e9.286X). CONCLUSION: The viscosity of a high concentration of HA may increase the friction of SCLs, which may have a deleterious effect on the ocular surface.

Should we use cortical bone screws for cortical bone trajectory?

OBJECT: In 2009, Santoni et al. reported cortical bone trajectory (CBT) as a method of inserting pedicle screws to obtain more solid fixation, and proposed the use of cortical trajectory screws with a more closely placed thread (cortical screws) for CBT. Since the entry trajectory in CBT differs from that in the traditional trajectory, it is unclear whether the increased strength derives from the specific trajectory or the shape of the screw thread in contact with the cortical bone. Whether the use of cortical screws is always required with CBT thus remains unclear. The authors therefore investigated the relationship between screw entry trajectory and screw thread characteristics and pullout strength in animal experiments. METHODS: Lumbar vertebrae (L1-L4) from 4-month-old female pigs were randomly assigned to one of 4 groups, with cancellous screws or cortical screws inserted via the traditional trajectory or CBT. For pullout strength testing, the screw was pulled out vertically against the direction of insertion. Rod pullout testing (toggle testing) was also performed, and the peak breaking strength was measured. RESULTS: The maximum pullout strength was significantly greater for CBT using cortical screws than for the traditional trajectory using cancellous screws. Pullout strength tended to be higher when cortical screws were used in both CBT and the traditional trajectory, although the difference was not significant. Toggle testing showed no significant differences among the 4 groups. CONCLUSIONS: The specific unconventional trajectory seemed to have a major impact on the increased strength obtained with CBT.

Comparison of internal fixations for distal clavicular fractures based on loading tests and finite element analyses.

It is difficult to apply strong and stable internal fixation to a fracture of the distal end of the clavicle because it is unstable, the distal clavicle fragment is small, and the fractured region is near the acromioclavicular joint. In this study, to identify a superior internal fixation method for unstable distal clavicular fracture, we compared three types of internal fixation (tension band wiring, scorpion, and LCP clavicle hook plate). Firstly, loading tests were performed, in which fixations were evaluated using bending stiffness and torsional stiffness as indices, followed by finite element analysis to evaluate fixability using the stress and strain as indices. The bending and torsional stiffness were significantly higher in the artificial clavicles fixed with the two types of plate than in that fixed by tension band wiring (P < 0.05). No marked stress concentration on the clavicle was noted in the scorpion because the arm plate did not interfere with the acromioclavicular joint, suggesting that favorable shoulder joint function can be achieved. The stability of fixation with the LCP clavicle hook plate and the scorpion was similar, and plate fixations were stronger than fixation by tension band wiring.

Correlation between the bone mineral density and stress on femur around a Duetto SI stem.

In cementless stem fixation, BMD reduction around the stem is of concern because it may cause loosening. This BMD reduction is assumed to be caused by stem implantation-induced alteration of the physiological feedback system, which may cause stress shielding and result in loosening, but the causal relationship has not been clarified. In this study, using a Duetto SI stem, we investigated the correlation between the postoperative BMD around the stem and stress. In patients who underwent their first THA at the orthopedic department of our university, the BMD was measured using DEXA, and FEA was performed with an equivalent time course. Time-course changes in the BMD, von Mises stress, and triaxial stress in Gruen zones 1 through 7 were calculated from those measured at 2 weeks and 5 months after surgery. The BMD and von Mises stress showed a bidirectional correlation when Gruen's classification was plotted on the horizontal axis. An increase in stress loaded on bone was assumed to be a factor increasing the BMD. The Duetto SI stem was fixed on the distal side, suggesting its stable fixation. BMD measurement and FEA were useful for quantification of the bone dynamics around the stem from an early phase.

Hammering sound frequency analysis and prevention of intraoperative periprosthetic fractures during total hip arthroplasty.

Adequate fixation at the time of cementless stem implantation depends on the operator's experience. An objective evaluation method to determine whether the stem has been appropriately implanted may be helpful. We studied the relationship between the hammering sound frequency during stem implantation and internal stress in a femoral model, and evaluated the possible usefulness of hammering sound frequency analysis for preventing intraoperative fracture. Three types of cementless stem (BiCONTACT®, SL-PLUS®, and AI-Hip®) were used. Surgeons performed stem insertion using a procedure similar to that employed in a routine operation. Stress was estimated by finite element analysis, the hammering force was measured, and frequency analysis of hammering sound data obtained using a microphone. Finite element analysis showed a decrease in the hammering sound frequency with an increase in the estimated maximum stress. When a decrease in frequency was observed, adequate hammering had occurred, and the continuation of hammering risked fracture. Based on the relationship between stress and frequency, the evaluation of changes in frequency may be useful for preventing the development of intraoperative fractures. Using our method, when a decrease in frequency is observed, the hammering force should be reduced. Hammering sound frequency analysis may allow the prediction of bone fractures that can be visually confirmed, and may be a useful objective evaluation method for the prevention of intraoperative periprosthetic fractures during stem insertion.

Hammering force during cementless total hip arthroplasty and risk of microfracture.

During cementless stem fixation, impaction of the stem is occasionally complicated by bony injuries. Small fractures not visible to the eye during surgery or on post-operative radiographs may remain undetected, and the incidence of such injuries may be underestimated. Employing the same techniques as those employed during total hip arthroplasty, we implanted cementless stems into artificial femora, with equivalent mechanical characteristics to living femora. The hammering force applied to the femur and the displacement of the stem and femur were measured using a load sensor and imaging, respectively. The von Mises stress generated in the femur during cementless stem press-fixation was also measured using finite element analysis. Average hammering force under these conditions (9.25 kN) was sufficient to cause damage to the artificial femur. The first two of eight hammer strikes caused most displacement of the stem. The von Mises stresses generated by the first and second hammer strikes were 31 and 68 MPa, respectively. Applying a high average hammering force to the stem after displacement has ceased probably contributes to the generation of intraoperative fractures during cementless stem fixation. Given that two strikes appeared to be sufficient, we believe that hammering force should be reduced to a micro-adjustment level after the second hit.

Cryoprotective effect of low-molecular-weight hyaluronan on human dermal fibroblast monolayers.

The purpose of this study was to assess the availability of low-molecular-weight (low-MW) hyaluronan (HA) as a cryoprotectant for cellular cryopreservation. To clarify whether low-MW HA is cryoprotective, we evaluated the effect of HA concentration (0-5% w/w) in a cryoprotectant solution on cell membrane integrity after freeze-thaw. A test sample was created using human dermal fibroblast monolayers incubated in a culture dish for 24 h (37 degrees C, 5% CO2). Sodium hyaluronate (MW 3 x 10(4)-5 x 10(4)) dissolved in medium served as the cryoprotectant solution. Samples were immersed in the solution for 2 h at 0-4 degrees C. They were frozen at a cooling rate of 3 degrees C/min from 4 to -80 degrees C, cooled further to below -185 degrees C, and then thawed. Cell membrane integrity after thawing was evaluated using a trypan blue exclusion assay. The sample and freezing procedures were repeated in subsequent experiments, while the conditions of the solution immersion with respect to the sample varied. Next, to clarify whether the cryoprotective action of HA is intra- or extracellular, we performed three experiments. The first studied the dependence of membrane integrity after freeze-thaw on preliminary incubation time (0.75-24 h at 37 degrees C) with a sample immersed in the solution (5% w/w HA). In the second, membrane integrity of thawed samples that were initially frozen in a medium instead of solution, by removing extracellular HA following a preliminary 6-h incubation period, were evaluated. Thirdly, we investigated cellular uptake of fluorescein isothiocyanate-labeled HA (MW 10(5), 1% w/w) after a preliminary 6-h incubation period under fluorescent microscopy (without freeze-thaw). The results show that HA had a cryoprotective effect, and that this cryoprotective action was intracellular. Therefore, low- MW HA proves to be a promising cellular cryoprotectant.

Initial fixation of a finite element model of an AI-Hip cementless stem evaluated by micromotion and stress.

BACKGROUND: This study investigated issues related to initial stability after stem fixation. Finite element models of the AI-Hip cementless stem were constructed for computer simulation. METHODS: Analysis was performed after implantation of two types of cementless hip stem for clinical use; and micromotion and stress were then calculated. Boundary and initial conditions were (1) rigid contact of the distal end of the model femur with a rigid base; (2) a stepping load of 1800 N was applied to the proximal top of the stem; (3) a load of 1440 N was pulled from the greater trochanter of the femur as muscle force; (4) a torsion load of 18.9 Nm was applied to the proximal femur as the intrarotation. RESULTS: Relative micromotion of the AI-Hip cementless stem showed a value as low as that of a conventional stem. The calculated von Mises stress was below the level that would cause destruction of the femur and stem. CONCLUSIONS: Based on the relative micromotion and von Mises stress level, the AI-Hip cementless stem showed initial stability. The present experimental results should be compared with those obtained in clinical practice.

Hyperlipidemia and hyperinsulinemia in the spontaneous osteoarthritis mouse model, STR/Ort.

Recent studies have focused on the association between primary osteoarthritis and dyslipidemia. STR/Ort mice have unique characteristics including osteoarthritis and hyperlipidemia, and may be a useful model for investigating the effect of dyslipidemia on the underlying mechanism of primary osteoarthritis. However, little is known about the hyperlipidemic properties of STR/Ort mice. In this study we investigated hyperlipidemia and lipotoxicity in STR/Ort mice. STR/Ort mice have human hyperlipidemic patient-like symptoms such as hypercholesteremia, hypertriglyceridemia, hyperinsulinemia, insulin resistance, dysregulation of NEFA, and low serum adiponectin. Excess triglyceride accumulation in the liver of STR/Ort mice was not observed even when they exhibited hyperinsulinemia. This information may be useful for researchers investigating lipid metabolism and primary osteoarthritis using STR/Ort mice.

Finite element analysis of the effect of proximal interlocking on primary fixation of the Intra-Medullary Cruciate stem.

BACKGROUND: The primary fixation of cementless hip prostheses is related to the shape of the stem. When there is a complication of loading in the rotational direction, the mechanical fixation of a hip stem is considered to provide good primary fixation. The purpose of this study was to evaluate whether the Intra-Medullary Cruciate stem with a characteristic fixation method, which was developed by a group at Kitasato University, contributes to primary fixation by finite element analysis. METHODS: Analysis was performed at a friction coefficient of 0.1 with automatic contact, under the restriction of the distal femoral end. The following three loading conditions were applied: (1) step loading of the joint resultant force in the region around the hip stem; (2) loading in the rotational direction, simulating torsion; and (3) loading of the femoral head equivalent to that during walking. Displacement of an Intra-Medullary Cruciate stem and a reference stem along the x-, y-, and z-axes and rotational direction was calculated by simulation, and the stress distributed on the stem and femur was determined. RESULTS: Relative displacement along the z-axis of distal parts, which is a clinical problem with hip prosthesis stems, was lower for the Intra-Medullary Cruciate stem than for the reference stem. Displacement of the stem along the z-axis direction was low, indicating a low risk of sinking. The interlocking mechanism, which is a characteristic of the Intra-Medullary Cruciate stem, functioned to suppress its displacement, indicating that the locking method of this stem contributed to its stability. Because no stress concentration was detected in certain regions, it was thought that there are no risks of breakage of the Intra-Medullary Cruciate stem and femur. CONCLUSIONS: It was suggested that effective fixation of the Intra-Medullary Cruciate stem can be achieved because its displacement is lower than that of the reference stem and displacement of the stress level is appropriate for primary fixation.

Rotational stability based on displacements obtained by simulation and measurement when torsion loading is applied to hip stems.

BACKGROUND: The rotational stability of cementless hip prostheses corresponds to the design of the fixation parts. The appropriate design of a femoral stem is important for secure primary fixation. The relative displacement of the bone and stems in the rotational direction should be used to evaluate the initial fixability and stability of stems. This article addresses the issue of the fixation method of hip stems and their rotational stability. METHODS: Specimens comprised four kinds of hip prosthesis. Rotational displacement that reproduced a torsion moment was analyzed and measured. Various finite element models (FEMs) of the four femoral stems were constructed for computer simulation. The measurement models consisted of an artificial femur and real stems used clinically. Common conditions of analyses and measurements were as follows: (1) a torsion load of 18.9 Nm was applied to the proximal femur as the intrarotation; (2) a stepping load of 1800 N was applied to the proximal tip of the stem; and (3) rigid contact existed between the distal end of the model femur and the rigid base. RESULTS: It was found that the relative rotational displacement obtained by FEMs was 0.21 mm for the Intra-Medullary Cruciate stem, 0.10 mm for the VerSys stem, 0.67 mm for the PerFix SV stem, and 0.03 mm for the Duetto SI stem. The relative rotational displacement obtained by the laser sensor was 0.37 mm for the Intra-Medullary Cruciate stem, 0.25 mm for the VerSys stem, 1.87 mm for the PerFix SV stem, and 0.17 mm in the Duetto SI stem. CONCLUSIONS: Judging from rotational displacement values obtained by the two approaches, three types of stem (Intra-Medullary Cruciate stem, VerSys stem, Duetto SI stem) provided rotational stability.

Investigation of the influence of cell density of human fibroblasts cryopreserved inside collagen sponges at various cooling rates.

The influence of cell density of cells cryopreserved inside a collagen matrix at various cooling rates was investigated. Human fibroblasts were three-dimensionally cultured for 2 days in a collagen sponge (20 mm in diameter and 1 mm in thickness) as an extracellular matrix to imitate biological tissue (artificial tissue). Different cell densities for the artificial tissue were used, from 10(5) to 10(7) cells/cm(3). Four artificial tissues were first stacked in a test chamber, frozen at a cooling rate of 0.3 to 50 degrees C/min in a solution of Dulbecco's Modified Eagle Medium, 20% fetal bovine serum and 10% dimethylsulfoxide, kept frozen below -185 degrees C for 2 hours, and then finally thawed. Membrane integrity of fibroblasts using a trypan blue exclusion assay was evaluated as an index for post-thaw cellular viability. Results show that with increasing cell density, the post-thaw membrane integrity decreased. Therefore, in the cryopreservation of biological tissue, it seems high cell density is one factor which causes a decline in viability.

Assessments of different kinds of stems by experiments and FEM analysis: appropriate stress distribution on a hip prosthesis.

BACKGROUND: It is now recognized that initial stability is essential for avoidance of thigh pain in hip replacement. The initial stability corresponds to an optimal stress distribution of cementless orthopedic implants. Although the relationship between the contour and stress at the fixation site has been analyzed, guidelines on stem design have not been established. METHODS: Finite element models of three currently-used stems were constructed for a computer simulation. Contact stress at the fixation site of a joint prosthesis was analyzed by an explicit three-dimensional finite element method. The stress immediately after applying load using a film or sensor which can measure contact stress was observed. The situation of the initial fixation about the specific part which becomes important clinically based on the results was clarified. FINDINGS: We introduced fluctuation area as a measure to evaluate the primary fixation of femoral stems. It was found that the stress distribution on the PerFix SV stem fluctuated with a slight disturbance. On the Intra-Medullary Cruciate stem, the high stress areas were distributed on the proximal area and under the pin. The high stress area on the VerSys stem were spread on the medial side. INTERPRETATION: This study highlights the mechanical instability of the fixation site of joint prostheses, and thus suggests that the general idea that unconditionally recommends a larger area for the fixation site of joint prostheses should be revised.

Assessment of the fixation stiffness of some femoral stems of different designs.

BACKGROUND: Appropriate contour design of a femoral stem is important for the secure primary fixation. Although the relationship between the contour and stress or micro-motion at the fixation site has been analyzed, guidelines on stem design have not been established. METHODS: Different kinds of finite element models of three femoral stems were constructed for computer simulation. These models had the contour designs that head for the tight mechanical fixation by the different ways, respectively. Boundary and initial conditions were (i) rigid contact of the distal end of the model femur with the rigid base. (ii) Stepping load of 800 N or 1800 N was applied to the proximal top of the stem. (iii) Stepping load of 640 N or 1440 N was pulled from the greater trochanter of the femur as muscle force. The ratio of displacement to the vertical load, which was defined as fixation stiffness, was calculated. FINDINGS: The mean displacement of the intra-medullary cruciate stem was 27.6 nm. For the VerSys stem with sharp fins, the mean displacement was 32.9 nm. For the PerFix SV stem with a flange, the mean displacement was 52.8 nm. Vertical fixation stiffness estimated on the intra-medullary cruciate stem, the VerSys stem, and the PerFix SV stem was 461, 264, and 313 MN/mm, respectively. INTERPRETATION: Contour design of a femoral stem is important for achieving secure fixation, which prevents loosening. We introduce fixation stiffness as a measure to theoretically evaluate the primary fixation of femoral stems.

Development of heating method by microwave for sterilization of bone allografts.

The purpose of this study was to develop a disinfection method using a microwave apparatus to treat large bone allografts. Heating of a bone allograft is an effective method for the disinfection of bacteria or inactivation of viruses. However, the size of the bone we can treat is limited, and following the popular method of using a bathtub is a lengthy process. The experimental system described here was designed using a microwave oven, an optical-fiber thermometer, and a power regulator. Large and small specimens, a femoral head, and a metatarsal were harvested from a bovine femur. The influence of size and the electrical or thermal characteristics of the specimens were assessed regarding temperature distribution after microwave irradiation. The effects of humidity or hot-air supply were also assessed. The average temperature of the bovine femoral head became 80 degrees C throughout the 15 min of microwave irradiation, although the temperature in the metatarsal did not attain uniformity. Microwave irradiation with a hot-air supply realized a uniform distribution of temperature at 83.0 degrees +/- 0.4 degrees C in the metatarsal within 15 min. Use of microwave irradiation enables quick heating for disinfection of large allograft bones when a hot-air supply was used as well.

Appropriate radial clearance of ceramic-on-ceramic total hip prostheses to realize squeeze-film lubrication.

OBJECTIVE: Estimation of appropriate radial clearance of ceramic-on-ceramic total hip prostheses to realize squeeze-film lubrication. BACKGROUND: Some clinical results show that severe wear occurs at ceramic-on-ceramic interfaces of total hip prostheses if the design parameters are improper. Appropriate design is required to realize the optimum lubrication of joint prostheses. DESIGN: Squeeze-film thickness of total hip prostheses with different radial clearances was numerically estimated under the physiological conditions of normal walking. METHODS: The changes in the fluid film thickness between ceramic balls and a ceramic cups with radial clearances of various values from 10 to 80 microm were numerically estimated under the assumption of normal walking conditions by means of elastohydrodynamic squeeze-film lubrication theory including the three-dimensional theory of elasticity. RESULTS: The minimum film thickness remained over 0.02 microm during a few walking steps with a radial clearance under 20 microm and a head diameter of 28 mm. On the other hand, the fluid film was squeezed out during a few steps when the radial clearance was greater than 30 microm. CONCLUSIONS: Squeeze-film lubrication can be realized in a ceramic-on-ceramic total hip prosthesis if the radial clearance is smaller than 20 microm on a head of 28 mm diameter. RELEVANCE: Fluid film lubrication is necessary to prevent the severe wear of ceramic joint prostheses. The present investigation shows which radial clearance of ceramic-on-ceramic hip prostheses is appropriate for squeeze-film lubrication under physiological conditions in daily action.