Recent reports implicate fretting corrosion at the head-stem taper junction as a potential cause of failure of some large diameter metal-on-metal (MOM) devices. Fretting observed at modular junctions is thought to be a type of ‘mechanically assisted’ corrosion phenomenon, initiated by mechanical factors that lead to an increase in contact stresses and micromotions at the taper interface. These may include: intra-operative taper assembly, taper contamination by debris or body fluids, patient weight and ‘toggling’ of the head or increased frictional torque in a poorly functioning bearing. We adopted a finite element approach to model the head-taper junction, to analyze the contact mechanics at the taper interface. We investigated the effect of assembly force and angle on contact pressures and micromotions, during loads commonly used to test hip implants. Models of the Biomet Type-1 taper, a 60 mm head and a taper adaptor were created. These models were meshed with a mesh size based on a mesh density convergence study. Internal mesh coarsening was applied to reduce computational cost. Elastic-plastic material properties based on tensile tests were assigned to all titanium components. The contact conditions used in the FE analyses were validated against push-on and pull-off experiments, resulting in a coefficient of friction of 0.5. To analyze micromotions at the taper-adaptor connection, the models were loaded with 2300N (ISO 7206-4) and 5340N (ISO 7206-6), after being assembled with 2-4-15 kN, axially and under a 30º angle. This ISO standard is commonly used to determine endurance properties of stemmed femoral components. Micromotions and contact pressures were analyzed by scoring them to an average micromotion and average contact pressure for the surface area in contact.Introduction
Materials and methods
Recent reports have implicated fretting corrosion at the head-stem taper junction as a potential cause of failure of some large diameter metal-on-metal (MOM) devices. While it has been suggested that larger MOM heads, may induce greater frictional torques at the taper connection, the exact mechanisms underlying fretting corrosion remain poorly understood. It is likely that the onset of the corrosion process is caused by mechanical factors, such as contact stresses and micromotions occurring at the interface. These stresses and micromotions depend on the fixation of the head onto the stem and may be affected by blood, fat, bone debris or other contaminations. The fixation of the head is achieved intraoperatively through impaction. To further study this phenomenon, we adopted a finite element approach in which we modeled the head-taper junction fixation mechanics. In this model, we analyzed the effect of impaction force on the micromotions occurring at the head-stem interface. We created a model of a BIOMET Type-1 taper and an adapter that is typically used for larger heads. Titanium alloy material properties were assigned to both components, and frictional contact (μ = 0.5) was simulated between the adapter and the taper. To ensure that the model accurately represented the contact mechanics, we first simulated experiments in which the head was assembled on the taper in a load-controlled manner, at different load (4 and 15 kN), after which it was disassembled axially. The disassembly loads predicted by the FEA simulations were then compared to the experimental values. After ensuring a correct prediction of the disassembly loads, we used various impaction loads (2, 4, and 15 kN) to assemble the taper, after which a 2.3 kN load (ISO 7206-4) was applied to the adapter/taper assembly. This loading regime is commonly used to determine endurance properties of stemmed femoral components. Under these loading conditions, we then analyzed the contact stresses and micromotions, and the effect of impaction load on these quantities.Introduction
Materials and methods
These days, total hip arthroplasties (THA) are more implanted in young patients. Due to the expected lifespan of a THA and the life expectancy of young patients, a future revision is inevitable. Indirectly increasing the number of revisions in these patients. Therefore we evaluated the results of revision THA in patients under the age of 60 years. However, we used a unique protocol in which we used in all cases of acetabular and/or femoral bone deficiencies reconstruction with bone impaction grafting. To determine the mid- to longterm results of cemented revision total hip arthroplasties in patients under the age of 60, all clinical data and radiographs were analyzed of patients operated between 1992 and 2005. Patients with multiple previous revisions were also included. Only cemented components were used. During this period 146 consecutive revision total hip arthroplasties were implanted in 129 patients. This included 124 cup and 106 stem revisions. The average age at index surgery was 47 years. No case was lost. Mean follow-up was 7.6 (range, 2.0–16.7) years.Background
Methods
Total hip arthroplasties in younger patients often requires revision because these patients frequently have acetabular deficiencies, which hamper proper implantation of the cup essential for good long-term prosthesis survival. For 30 years, we have used a biological acetabular-reconstruction technique with bone-impaction grafting in all patients <50 years with an acetabular deficiency at surgery, always in combination with a cemented total hip implant. We evaluated all 150 consecutive patients (177 hips) < 50 years with an acetabular reconstruction by bone-impaction grafting surgically-treated from 1978–2004 at our clinic. Mean follow-up was 10.3 (range, 2.0–28.3) years with no patient lost to follow-up. Mean index surgery age was 38.1 (range, 16–49) years. Clinical, radiological, and statistical analysis of all patients was performed.Introduction
Methods
Surgeons always must take into account that a primary total hip arthroplasty (THA) in a young patient will be revised in the future, this because of the long life expectancy of young THA patients and the limited durability of prosthetic implants in these patients. Therefore we would like to accentuate the revisability of a primary THA in this specific and high demanding patient population. 343 consecutive THA in 267 patients under the age of 50 years were evaluated. We also assessed the results of the revised THA (n=53) within the same population. Clinical, radiographical and survival of primary and revision THA were evaluated.Background
Methods
Especially in young patients, total hip implants with proven long-term follow-up data should be used. Despite this, almost all patients under 30 years old will face a revision of their hip prosthesis during their life time because of their life expectancy. Therefore, all the used implants should be revisable with reliable outcome. Although, several studies have evaluated the outcome of different THA implants in patients under 30, only few report the long term follow-up of 10 years or more. None of them present the outcome of the revised total hips. We retrospectively reviewed prospectively collected data of 48 consecutive patients (69 hips), all received a cemented implant and in case of acetabular bone stock deficiency (29 hips), a reconstruction with bone impaction grafting (BIG) was performed. Mean age at surgery was 24.6 years (range, 16.0–29.0 years). Two patients were lost to follow-up. As far as we know, no revisions are performed in these two patients and their data are included in the study up to their last radiographic control. All failed hips were revised with again cemented implants and, if needed, bone impaction grafting. For the primary THA Kaplan-Meier survival curves at 10- and 15-year endpoint revision for any reason and revision for aseptic loosening were calculated. Separate survival rates at 10- and 15- year were calculated for the BIG group versus the non-BIG group. The outcome of the revised hips was studied and reported with re-revision as the endpoint.Introduction
Methods
