Transient elastohydrodynamic lubrication analysis of a novel metal-on-metal hip prosthesis with a non-spherical femoral bearing surface

Effective lubrication performance of metal-on-metal hip implants only requires optimum conformity within the main loaded area, while it is advantageous to increase the clearance in the equatorial region. Such a varying clearance can be achieved by using non-spherical bearing surfaces for either acetabular or femoral components. An elastohydrodynamic lubrication model of a novel metal-on-metal hip prosthesis using a non-spherical femoral bearing surface against a spherical cup was solved under loading and motion conditions specified by ISO standard. A full numerical methodology of considering the geometric variation in the rotating non-spherical head in elastohydrodynamic lubrication solution was presented, which is applicable to all non-spherical head designs. The lubrication performance of a hip prosthesis using a specific non-spherical femoral head, Alpharabola, was analysed and compared with those of spherical bearing surfaces and a non-spherical Alpharabola cup investigated in previous studies. The sensitivity of the lubrication performance to the anteversion angle of the Alpharabola head was also investigated. Results showed that the non-spherical head introduced a large squeeze-film action and also led to a large variation in clearance within the loaded area. With the same equatorial clearance, the lubrication performance of the metal-on-metal hip prosthesis using an Alpharabola head was better than that of the conventional spherical bearings but worse than that of the metal-on-metal hip prosthesis using an Alpharabola cup. The reduction in the lubrication performance caused by the initial anteversion angle of the non-spherical head was small, compared with the improvement resulted from the non-spherical geometry

Clinical treatment of femoral head using Thompson hip prosthesis

Background: Hip prosthesis is a successful surgical technique the treatment of hip joint fracture. Thompson hip prosthesis is commonly used treatment of femoral head fracture. It is designed for non-union of fracture neck of femur when there is no neck available.Methods: In this retrospective study, examined the results of patients with Thompson hip prosthesis (cemented and uncemented). This examination has been done from August 2014 to February 2016. 50 Patients were enrolled in this study with mean age of 70 years in which the ratio of number of females more than the number of males. AO classification was used to categorize the hip fracture type. Patient physical fitness was obtained through visual analog scale. Thompson hip prosthesis has been used to treatment of femoral head fracture, manufactured at Auxein Medical Pvt. Ltd., Sonipat, Haryana, India.Results: Patients were follow-up on six week and three-month after discharge from hospital. 90% patients have excellent or pain-free results. There is no implant related complication has been found such as Loosening, prosthesis related size. The overall performance of hip prosthesis was very good.Conclusions: Present guideline strongly favor of hip prosthesis. After clinical study, we can conclude that the Thompson hip prosthesis is the best technique to treatment of femoral head fracture. Thompson is also a quick, simple, palliative solution to early mobility

Pembersih bilah kipas siling

Kebanyakan rumah pada kebiasaannya mempunyai kipas siling tidak kira samada rumah moden atau tradisional. Kipas siling merupakan sejenis kipas yang digantung pada bahagian atas rumah untuk mengitar udara melalui bilah-bilah kipas berputar (Norfarahanim Mohd@Ramli, 2007). Ia berfungsi untuk menyerakkan udara di sekeliling kawasan secara lebih menyeluruh namun ia tidak mengubah suhu bilik secara langsung. Lazimnya, bilah akan berputar pada arah lawan jam untuk menolak udara sejuk turun ke bawah. Apabila menghampiri lantai, angin yang terhasil akan terserak ke semua arah dan udara panas akan naik ke atas secara semulajadi untuk menggantikan udara sejuk yang telah ditolak kebawah

Fracture simulation for zirconia toughened alumina microstructure

Purpose - The purpose of this paper is to describe finite element modelling for fracture and fatigue behaviour of zirconia toughened alumina microstructures. Design/methodology/approach - A two-dimensional finite element model is developed with an actual $Al{_2}O{_3}$ - 10 vol% $ZrO{_2}$ microstructure. A bilinear, time-independent cohesive zone law is implemented for describing fracture behaviour of grain boundaries. Simulation conditions are similar to those found at contact between a head and a cup of hip prosthesis. Residual stresses arisen from the mismatch of thermal coefficient between grains are determined. Then, effects of a micro-void and contact stress magnitude are investigated with models containing residual stresses. For the purpose of simulating fatigue behaviour, cyclic loadings are applied to the models. Findings - Results show that crack density is gradually increased with increasing magnitude of contact stress or number of fatigue cycles. It is also identified that a micro-void brings about the increase of crack density rate. Social implications - This paper is the first step for predicting the lifetime of ceramic implants. The social implications would appear in the next few years about health issues. Originality/value - This proposed finite element method allows describing fracture and fatigue behaviours of alumina-zirconia microstructures for hip prosthesis, provided that a microstructure image is available

Finite Element analysis of stress state in the cement of total hip prosthesis with elastomeric stress barrier

In the total hip prosthesis, according to different positions of the patient, there are a variety of loads acting on femoral head which generate stress concentration in the cement called polymethylmethacrylat (PMMA) and consequently in the interfaces stem/cement/bone. This load transfer can provoke loosening of the implant from the femoral bone. This paper focused on optimal stress distribution in the total hip prosthesis and devoted to the development of a redesigned prosthesis type in order to minimize stress concentration in the cement. This study investigated the effect of elastomeric stress barrier incorporated between the stem and femoral head using 3D-finite element analysis. This proposed implant provoked lower load transfer in the cement due to the elastomeric effect as stress absorber.  However, the proposed model provided an acceptable solution for load transfer reduction to the cement. This investigation permitted to increase the service life of the total hip prosthesis avoiding the loosening

Complications of Resection Arthroplasty in Two-Stage Revision for the Treatment of Periprosthetic Hip Joint Infection

Little data is available regarding complications associated with resection arthroplasty in the treatment of hip periprosthetic joint infection (PJI). We assessed complications during and after two-stage revision using resection arthroplasty. In this retrospective study, 93 patients undergoing resection arthroplasty for hip PJI were included. Patients were assigned to a prosthesis-free interval of ≤10 weeks (group 1; 49 patients) or >10 weeks (group 2; 44 patients). The complication rates between groups were compared using the chi-squared test. The revision-free and infection-free survival was estimated using a Kaplan-Meier survival analysis. Seventy-one patients (76%) experienced at least one local complication (overall 146 complications). Common complications were blood loss during reimplantation (n = 25) or during explantation (n = 23), persistent infection (n = 16), leg length discrepancy (n = 13) and reinfection (n = 9). Patients in group 1 experienced less complications after reimplantation (p = 0.012). With increasing severity of acetabular bone defects, higher incidence of complications (p = 0.008), periprosthetic bone fractures (p = 0.05) and blood loss (p = 0.039) was observed. The infection-free survival rate at 24 months was 93.9% in group 1 and 85.9% in group 2. The indication for resection arthroplasty needs to be evaluated carefully, considering the high rate of complications and reduced mobility, particularly if longer prosthesis-free intervals are used