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PURPOSE: This study aimed to compare bone mineral density (BMD) changes around the femoral component after total hip arthroplasty (THA) in a fully hydroxyapatite-coated stem (CORAIL) and in a tapered-wedge stem (Taperloc complete) and identify predictors of BMD changes. METHODS: This retrospective study compared 43 hips in the CORAIL group and 40 hips in the Taperloc group. The relative changes in BMD at 2 years after THA measured using dual-energy X-ray absorptiometry and the three-dimensional quantified contact states of the stem with the femoral cortical bone were assessed. Predictors of the relative change in the BMD around the proximal part of the stem were examined using multiple regression analysis. RESULTS: The decrease in BMD in Gruen zone 7 was significantly less in the CORAIL group than in the Taperloc group (P = 0.02). In the CORAIL group, the contact area in any zone was not a significant predictor of the relative changes in BMD. The contact area between the Taperloc stem and the femoral cortical bone in zones 2 and 6 was a positive predictor of the relative changes in BMD in zones 1 (P = 0.02 and P = 0.04, respectively) and 2 (P = 0.008 and P = 0.004, respectively). CONCLUSION: The CORAIL stem suppressed the postoperative BMD loss around the stem, irrespective of the contact state. The Taperloc complete stem required contact with the proximal femoral metaphysis to suppress the postoperative BMD loss around the stem.

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Riveting is the most important method of joining sheet metal and is widely used in the assembly of aircraft components. The perpendicularity error of the holes is unavoidable during automatic drilling and riveting, which has a significant impact on the quality of the assembly. In this paper, the effects of hole perpendicularity error and squeeze force on the interference fit size, interface contact state, microstructure morphology, fatigue life, and fracture form of riveted joints were investigated experimentally. The results show that the interference fit size increases with a greater tilt angle. When the tilt angle is 0°, the rivet shank is in close contact with the inner and outer sheets, and there is no obvious gap at the interface between the rivet and the sheets. As the tilt angle increases to 2° and 4°, a gap appears at the interface of regions 1, 2, and 3, while the rivet shank at region 4 is in close contact with the outer sheet. The fatigue life decreases when the tilt angle increases from 0° to 4°. For the same tilt angle, the fatigue life of riveted joints with a 0° tilt direction is higher than that of riveted joints with a 180° tilt direction. Increasing the squeeze force can to some extent reduce the adverse effect of the tilt angle on the fatigue life. The hole perpendicularity error does not affect the failure form, while the squeeze force has a significant effect on the failure form of the specimens. RESEARCH HIGHLIGHTS: The fatigue life of riveted joints decreases as the tilt angle increases. The size of the interfacial gap increases with increasing tilt angle. Higher fatigue life at 0° tilt direction than at 180° tilt direction. Increasing the squeeze force can somewhat reduce the negative effect of tilt angle on fatigue life.

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INTRODUCTION: It is clinically important to analyze the initial contact state between an implant and femoral cortical bone as it affects clinical outcomes, such as stress shielding, stem subsidence, thigh pain, and patient-reported outcomes after total hip arthroplasty. Whether the initial contact state of a double-tapered fully hydroxyapatite (HA)-coated stem is achieved with the preserved cancellous or cortical bone remains to be established. This study aimed to compare the contact area with the femoral cortical bone between a double-tapered fully HA-coated stem (HA group) and a tapered wedge cementless stem (TW group) using three-dimensional computed tomography (3DCT)-based templating software. MATERIALS AND METHODS: Forty-seven total hip arthroplasties in the HA and TW groups each were retrospectively analyzed. The contact area between the implant and femoral cortical bone in the whole stem and at each Gruen zone was measured using density mapping with 3DCT-based templating software. RESULTS: The demographic data were not significantly different between the two groups. The contact area in the whole stem area was lower in the HA group (HA 5.4 ± 1.8% vs. TW 9.0 ± 4.8%, p < 0.01). The HA group had a lower contact area in zone 2 (HA 6.7 ± 6.5% vs. TW 15.6 ± 10.8%, p < 0.01) and zone 6 (HA 1.8 ± 3.5% vs. TW 6.3 ± 3.6%, p < 0.01) than the TW group. The implant type (ß = 0.41, p < 0.01) and stem coronal alignment (ß = - 0.29, p < 0.01) were significant predictors of the contact area in the whole stem area in a multiple regression analysis (adjusted R2 = 0.27, p < 0.01). CONCLUSION: The contact area of the double-tapered fully HA-coated stem was significantly lower than that of the tapered wedge cementless stem.

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The relationship between clutch thermodynamic characteristics and contact states of friction components is explored numerically and experimentally. The clutch thermodynamic numerical model is developed with consideration of the contact state and oil film between friction pairs. The clutch bench test is conducted to verify the variation of the clutch thermodynamic characteristics from the uniform contact (UCS) to the intermittent contact (ICS). The results show that the oil film decreases gradually with increasing temperature; the lubrication state finally changes from hydrodynamic lubrication to dry friction, where the friction coefficient shows an increasing trend before a decrease. Thus, the friction torque in UCS gradually increases after the applied pressure stabilizes. When the contact state changes to ICS, the contact pressure increases suddenly and the oil film decreases rapidly in the local contact area, bringing about a sharp increase in friction torque; subsequently, the circumferential and radial temperature differences of friction components expand dramatically. However, if the contact zone is already in the dry friction state, friction torque declines directly, resulting in clutch failure. The conclusions can potentially be used for online monitoring and fault diagnosis of the clutch.

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Inspired by the sliding behavior of gecko feet during climbing, the contribution of the shear effect to the self-cleaning performance of a bio-inspired micropillar-arrayed surface is studied through a load-shear-pull contact process. It is found that self-cleaning efficiency can be enhanced significantly by shear. The efficiency also depends on microparticle size. For the case of relatively large and small microparticles, self-cleaning efficiency increases first and then almost keeps a constant with the increase of shear distance at different preloads. For medium microparticles, shear can effectively improve self-cleaning efficiency only when the preload is small. The mechanical mechanism under such enhancement is mainly due to the varying contact states between microparticles and micropillars with the shear distance. When the shear distance is large enough, the final self-cleaning efficiency is not sensitive to shear distance anymore because the contact state reaches dynamic equilibrium. Based on such a self-cleaning mechanism of large microparticles, a simple and effective manipulator that can efficiently transfer solid particles is further proposed.

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BACKGROUND: Despite the increasing use of short cementless stems in total hip arthroplasty, their potential benefits have yet to be confirmed. We evaluated the cortical contact state of short and conventional stems in different femoral canal types and stem positions using a CT-based 3-dimensional templating software. METHODS: We reviewed 153 hips in 153 patients, grouped according to femoral canal type-normal (68), champagne-flute (41), and stove-pipe canal (44). We investigated the influence of stem position on the contact state by evaluating three situations of stem anteversion (original anteversion, +5°anteverted, and +5°retroverted), three stem positions, neutral +2°extended, and +2°flexed positions using Taperloc Complete MicroplastyⓇ stem. FINDINGS: The contact values of all zones between both stems in all canal types exhibited no significant differences. The values in zones 1, 2, 6, and 7 of both stems in 5° retroverted and anteverted, 2° extended and flexed positions were not significantly different compared to those of the neutral position. However, the values in zones 3, 4, and 5 of both stems were significantly greater compared to those of the neutral position in 2° extended and flexed positions; these values were also significantly larger in all canal types for the conventional stem. INTERPRETATION: We demonstrated that the short and conventional stems can achieve the same proximal cortical contact in any femoral canal, regardless of the stem position. However, extended and flexed stem positions increase the distal contact, especially in conventional stems. Furthermore, the distal contact increases for the retroverted stem insertions.

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This paper investigates the pre-pressure's influence on the key performance of a traveling wave ultrasonic motor (TRUM) using simulations and experimental tests. An analytical model accompanied with power dissipation is built, and an electric cylinder is first adopted in regulating the pre-pressure rapidly, flexibly and accurately. Both results provide several new features for exploring the function of pre-pressure. It turns out that the proportion of driving zone within the contact region declines as the pre-pressure increases, while a lower power dissipation and slower temperature rise can be achieved when the driving zones and the braking zones are in balance. Moreover, the shrinking speed fluctuations with the increasing pre-pressures are verified by the periodic-varying axial pressure. Finally, stalling torque, maximum efficiency, temperature rise and speed variance are all integrated to form a novel optimization criterion, which achieves a slower temperature rise and lower stationary error between 260 and 320 N. The practical speed control errors demonstrate that the proportion of residual error declines from 2.88% to 0.75% when the pre-pressure is changed from 150 to 300 N, which serves as one of the pieces of evidence of the criterion's effectiveness.

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BACKGROUND: The transtrochanteric rotational osteotomy is a common osteotomy for osteonecrosis of the femoral head, although the results of conversion total hip arthroplasty after the osteotomy are controversial. We evaluated how deformities in the proximal femur after the osteotomy affect hip impingement and the contact state of the stem in total hip arthroplasty. METHODS: We retrospectively reviewed 35 hips (24 men) that had undergone the transtrochanteric rotational osteotomy for osteonecrosis of the femoral head (TRO-group) and compared them with 31 contralateral, unoperated hips (Primary group). The distance between the anterior and posterior greater trochanter at the cutting point of the femur, defined as the greater trochanter width and the contact area of the femoral implant surface with cortical bone were measured by CT-based three-dimensional templating software. We also calculated the hip range of motion in conversion total hip arthroplasty and analyzed the correlations between the greater trochanter width and the range of motion. FINDINGS: The number of bony-impingement cases was significantly greater, and the range of motion in flexion, internal rotation and external rotation was significantly less in TRO-group. There was a significant negative correlation between the greater trochanter width and range of motion of internal rotation. There were no significant differences between two groups in percentages of femoral-implant contact area. INTERPRETATIONS: The femoral implant fixation appears to be satisfactorily fixed in all zones in conversion total hip arthroplasty. However, the greater attention should be paid to minimizing bony impingement, especially on the anterior side, in conversion total hip arthroplasty.

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BACKGROUND: It would be ideal if surgeons could precisely confirm whether the planned femoral component achieves the best fit and fill of implant and femur. However, the cortico-cancellous interfaces can be difficult to standardize using plain radiography, and therefore, determining the contact state is a subjective decision by the examiner. Few reports have described the use of CT-based three-dimensional templating software to quantify the contact state of stem and femur in detail. The purpose of this study was to use three-dimensional templating software to quantify the implant-femur contact state and develop a technique to analyze the initial fixation pattern of a cementless femoral stem. METHODS: We conducted a retrospective review of 55 hips in 53 patients using a short proximal fit-and-fill anatomical stem (APS Natural-Hip™ System). All femurs were examined by density mapping which can visualize and digitize the contact state. We evaluated the contact state of implant and femur by using density mapping. RESULTS: The varus group (cases that had changed varus 2° by 3 months after surgery) consisted of 11 hips. The varus group showed no significant difference with regard to cortical contact in the proximal medial portion (Gruen 7), but the contact area in the distal portion (Gruen 3 and Gruen 5) was significantly lower than that of non-varus group. Density mapping showed that the stem only has to be press-fit to the medial calcar, but also must fill the distal portion of the implant in order to achieve the ideal contact state. CONCLUSIONS: Our results indicated that quantifying the contact state of implant and femur by using density mapping is a useful technique to accurately analyze the fixation pattern of a cementless femoral stem.

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