The vast majority of total hip replacements (THR) implanted today enable modularity by means of a tapered junction; based on the Morse taper design introduced for cutting tools in the 19. th. Century . 1. Morse-type tapers at the head-stem junction provide many benefits, key for a successful surgical outcome such as wider component selection and restoration of better biomechanics . 2. However, moving from mono-block to modular designs has not been without its issues. Fluid ingress and motion at the interface has led to a complex multifactorial degradation mechanism better known as fretting-corrosion . 3. Fretting-corrosion products created at the junction are commonly associated with adverse local tissue reactions . 4. . There is a wide variation in the taper junction of THR differing quite significantly from Morse's original design. Performance of the taper junction has been found to vary with different designs . 5,6. However, there is still a lack of common understanding of what design inputs makes a ‘good’
Introduction. Improper seating during head/stem assembly can lead to unintended micromotion between the femoral head and stem taper—resulting in fretting corrosion and implant failure. There is no consensus—either by manufacturers or by the surgical community—on what head/stem taper assembly method maximizes modular junction stability in total hip arthroplasty (THA). A 2018 clinical survey found that orthopedic surgeons prefer applying one strike or three, subsequent strikes when assembling head/stem taper. However, it has been suggested that additional strikes may lead to decreased interference. Additionally, the taper surface finish—micro-grooves—has been shown to affect taper interference and may be influenced by assembly method. Objective. The objective of this study was to employ a novel, micro-grooved finite element (FEA) model of the hip taper interface and assess the role of head/stem assembly method—one vs three strikes—on
Statement of Purpose. Mechanically assisted crevice corrosion of
Introduction:. There has been widespread concern regarding the adverse tissue reactions after metal-on-metal (MoM) total hip replacements (THR). Concerns have also been expressed with mechanical wear from micromotion and fretting corrosion at the head/stem taper junction in total hip replacements. In order to understand the interface mechanism a study was undertaken in order to investigate the effect of surface finish and contact area associated with
Introduction. Mechanically assisted crevice corrosion (MACC) of head-neck
Introduction:. Degradation of
In theory, Finite Element Analysis (FEA) is an attractive method for elucidating the mechanics of modular implant junctions, including variations in materials, designs, and modes of loading. However, the credence of any computational model can only be established through validation using experimental data. In this study we examine the validity of such a simulation validated by comparing values of interface motion predicted using FEA with values measured during experimental simulation of stair-climbing. Two finite element models (FEM) of a modular implant assembly were created for use in this study, consisting of a 36mm CoCr femoral head attached to a TiAlV rod with a 14/12 trunnion. Two head materials were modelled: CoCr alloy (118,706 10-noded tetrahedral elements), and alumina ceramic (124,710 10-noded tetrahedral elements). The quasi-static coefficients of friction (µs) of the CoCr-TiAlV and Ceramic-TiAlV interfaces were calculated from uniaxial assembly (2000N) and dis-assembly experiments performed in a mechanical testing machine (Bionix, MTS). Interface displacements during taper assembly and disassembly were measured using digital image correlation (DIC; Dantec Dynamics). The assembly process was also simulated using the computational model with the friction coefficient set to µs and solved using the Siemens Nastran NX 11.0 Solver. The frictional conditions were then varied iteratively to find the value of µ providing the closest estimate to the experimental value of head displacement during assembly. To validate the FEA model, the relative motion between the head and the trunnion was measured during dynamic loading simulating stair-climbing. Each modular junction was assembled in a drop tower apparatus and then cyclically loaded from 230–4300N at 1 Hz for a total of 2,000 cycles. The applied load was oriented at 25° to the trunnion axis in the frontal plane and 10° in the sagittal plane. The displacement of the head relative to the trunnion during cyclic loading was measured by a three-camera digital image correlation (DIC) system. The same loading conditions were simulated using the FEA model using the optimal value of µ derived from the initial head assembly trials.INTRODUCTION
MATERIALS and METHODS
Introduction. Wear and corrosion between head and stem
Introduction.
Introduction. Corrosion products from
Purpose. In revision hip surgery, Type IIIB femurs have presented the greatest historical challenge to achieving stable fixation and osseous integration. This study evaluated the intermediate term outcome of a
Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990s, and the susceptibility of
The goals of revision total hip on the femoral side are to achieve long term stable fixation, improve quality of life and minimise complications such as intra-operative fracture or dislocation. Ideally these stems will preserve or restore bone stock. Modular titanium stems were first introduced in North America around 2000. They gained popularity as an option for treating Paprosky 3B and 4 defects. Several studies at our institution have compared modular titanium stems with monoblock cobalt chromium stems. The main outcomes of interest were quality of life. We also looked at complications such as intra-operative fracture and post-operative dislocation. We also compared these 2 stems with respect to restoration or preservation of bone stock. In 2 studies we showed that modular titanium stems gave superior functional outcomes as well as decreased complications compared to a match cohort of monoblock cobalt chromium stems. As mentioned, one of the initial reasons for introduction of these stems was to address larger femoral defects where failure rates with monoblock cobalt chromium stems were unacceptably high. We followed a group of 65 patients at 5–10 years post revision with a modular fluted titanium stem. Excellent fixation was obtained with no cases of aseptic loosening. However, there were 5 cases of fracture of the modular junction. Due to concerns of fracture of the modular junction, more recently, at our institution, we have switched to almost 100% monoblock fluted titanium stems. We recently reviewed our first 100 cases of femoral revision with a monoblock stem. Excellent fixation was achieved with no cases of aseptic loosening. Quality of life outcomes were similar to our previous reported series on
Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of
The goals of revision total hip on the femoral side are to achieve long term stable fixation, improve quality of life and minimise complications such as intra-operative fracture or dislocation. Ideally these stems will preserve or restore bone stock. Modular titanium stems were first introduced in North America around 2000. They gained popularity as an option for treating Paprosky 3B and 4 defects. Several studies at our institution have compared the modular titanium stems with monoblock cobalt chromium stems. The main outcomes of interest were quality of life. We also looked at complications such as intra-operative fracture and post-operative dislocation. We also compared these 2 stems with respect to restoration or preservation of bone stock. In 2 studies we showed that modular titanium stems gave superior functional outcomes as well as decreased complications compared to a match cohort of monoblock cobalt chromium stems. As mentioned one of the initial reasons for introduction of these stems was to address larger femoral defects where failure rates with monoblock cobalt chromium stems were unacceptably high. We followed a group of 65 patients at 5–10 years post-revision with a modular fluted titanium stem. Excellent fixation was obtained with no cases of aseptic loosening. However, there were 5 cases of fracture of the modular junction. Due to concerns of fracture of the modular junction more recently at our institution we have switched to almost 100% monoblock fluted titanium stems. We recently reviewed our first 100 cases of femoral revision with monoblock stem. Excellent fixation was achieved with no cases of aseptic loosening. Quality of life outcomes were similar to our previous reported series on
Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of
Corrosion at metal/metal modular interfaces in total hip arthroplasty was first described in the early 1990's, and the susceptibility of
The goals of revision total hip on the femoral side are to achieve long term stable fixation, improve quality of life and minimise complications such as intra-operative fracture or dislocation. Ideally these stems will preserve or restore bone stock. Modular titanium stems were first introduced in North America around 2000. They gained popularity as an option for treating Paprosky 3B and 4 defects. Several studies at our institution have compared the modular titanium stems with monoblock cobalt chromium stems. The main outcomes of interest were quality of life. We also looked at complications such as intra-operative fracture and post-operative dislocation. We also compared these 2 stems with respect to restoration or preservation of bone stock. In two studies we showed that modular titanium stems gave superior functional outcomes as well as decreased complications compared to a matched cohort of monoblock cobalt chromium stems. As mentioned one of the initial reasons for introduction of these stems was to address larger femoral defects where failure rates with monoblock cobalt chromium stems were unacceptably high. We followed a group of 65 patients at 5–10 years post-revision with a modular fluted titanium stem. Excellent fixation was obtained with no cases of aseptic loosening. However, there were 5 cases of fracture of the modular junction. Due to concerns of fracture of the modular junction more recently, at our institution we have switched to almost 100% monoblock fluted titanium stems. We recently reviewed our first 100 cases of femoral revision with monoblock stem. Excellent fixation was achieved with no cases of aseptic loosening. Quality of life outcomes were similar to our previous reported series on
Introduction. The release of metal debris and ions has raised concerns in joint arthroplasty. In THA metal debris and ions can be generated by wear of metal-on-metal bearing surfaces and corrosion at
Periprosthetic fractures in total hip arthroplasty lead to considerable morbidity in terms of loss of component fixation, loss of bone and subsequent functional deficits. We face an epidemic of periprosthetic fractures as the number of cementless implants inserted continues to rise and as the number of revisions continues to increase. The management of periprosthetic fractures requires careful preoperative imaging, planning and templating, the availability of the necessary expertise and equipment, and knowledge of the potential pitfalls so that these can be avoided both intra-operatively and in follow-up. There is a danger that these cases fall between the expertise of the trauma surgeon and that of the revision arthroplasty surgeon. The past decade has afforded us clear treatment algorithms based on fracture location, component fixation and the available bone stock. We still nevertheless face the enduring challenge of an elderly population with a high level of comorbidity who struggle to rehabilitate after such injuries. Perioperative optimisation is critical as we have seen prolonged hospital stays, high rates of systemic complications and a significant short term mortality in this cohort. We have also been presented with new difficult fracture patterns around anatomic cementless stems and in relation to tapered cemented and cementless stems. In many cases, fixation techniques are biomechanically and biologically doomed to fail and intramedullary stability, achieved through complex revision is required. The treatment of unstable peri-prosthetic femur fractures can be technically challenging due to the weak non-supportive bone stock. We have seen an increase in the frequency of Type B3 fractures that require complex reconstruction with