Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in the human body after total joint replacement causes serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE is now recognized as one of the major factors restricting the longevity of artificial joints. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. In a previous study (Cho et al., 2016), it was found that roundness (out-of-roundness) of the retrieved UHMWPE acetabular cup liner [Figure 1(a)] had a tendency to increase with increasing roundness of the retrieved metal femoral head [Figure 1(b)]. It appears that roundness of the femoral head contributes to increase of wear of the polyethylene liners. We focused on the roundness of femoral head as a factor influencing the wear of polyethylene liner in
Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE and the polyethylene wear debris generated in the human body after total joint replacement cause serious clinical and biomechanical reactions. Therefore, the wear phenomenon of UHMWPE in total joint replacement is now recognized as one of the major factors restricting the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Materials and Methods. The wear and/or failure characteristics of 33 retrieved UHMWPE acetabular cup liners of hip prostheses were examined in this study. The retrieved liners had an average in vivo duration of 193.8 months (75 to 290 months). Several examples of the retrieved liners are shown in Figure 1. The elasto-plastic contact analyses between metal femoral neck and polyethylene liner and between metal femoral head and polyethylene liner using the finite element method (FEM) were also performed in order to investigate the factors influencing the wear and/or failure mechanism of the polyethylene liner in
Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in knee and hip prostheses after total joint replacement is one of the major restriction factors on the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear of UHMWPE. A number of studies have investigated the factors influencing the wear of UHMWPE acetabular cup liner in
Introduction. After total hip arthroplasty, dislocation is one of the most frequent serious early complications. This occurs in part due to impingement (catching and leverage of the neck-cup on the inlay/cup border). Impingement may also negatively impact long-term outcomes. Materials and Methods. A preliminary model for an optimised hip endoprosthesis system was developed to offer a mechanical solution to avoid impingement and dislocation. A computer-supported range of motion simulation using parameters of cup anteversion and inclination as well as torsion and CCD shaft angle was then performed to localise areas of anterior and posterior impingement of typical acetabular cups. Results. Through isolation of the two main trajectories of motion, and modifications with corresponding gaps to the inlay/cup areas as well as oppositional banking in the abduction/adduction plane, the combination of a snap-fit acetabular cup with reduced cup profile was the result: the “bidirectional total
Introduction. This study reports outcomes of 35 revisions of a recalled metal-on-metal (MOM) monoblock prosthesis performed by a single surgeon. Methods. We prospectively collected data on all patients who underwent revision of a recalled metal-on-metal monoblock prosthesis between 2010 and 2015. Average follow-up was 2.5 years post-revision and 6.9 years post-primary procedure. We evaluated the cohort for age, BMI, gender, existence of medical comorbidities, and post-op complications. We compared pre and post-revision cup abduction angles, anteversion angles, combined angles, cup sizes, and Harris Hip Scores. Cobalt and chromium levels were followed throughout the study period for each patient. Results. Thirty-one patients underwent 35 revisions surgeries for pain, high metal ions, infection, aseptic loosening, failure of ingrowth, leg length discrepancy and/or pseudotumor. Two of these revisions were subsequently re-revised – one for continued pain and one for failure involving multiple dislocations, breakage of screws, and acetabular fracture. The survival rate for our revisions to date is 94.3%. Female patients comprised a majority of revisions (54%) despite comprising a minority (28%) of primary hip replacements using the studied prosthesis. Revised patients were an average of 51.8 years of age with a BMI of 31.07. Demographics are included on Table 1. There were five post-operative complications, including 2 infections, 2 dislocations, and one DVT. Cups were revised from a mean abduction angle of 47.5° in primary hips to 42.3° in revisions. Cups were revised from a mean of 53.4 to 57.8. Cobalt and chromium levels were followed in all patients and showed significant decrease after revision (Graph 1). Cobalt levels decreased from an average of 33.7 to 13.1 ng/mL while Chromium levels decreased from an average of 12.4 to 9.2 ng/mL. Harris Hip Scores increased significantly after revision (45.8 to 72.1). Conclusion. This study presents 35 revisions of a recalled monoblock
Introduction. Total hip arthroplasty in young patients is still associated with high failure rates, especially at the acetabular side. Purpose of this study was to evaluate the long-term results of the Alloclassic cementless Zweymüller total
Ceramic-on-ceramic hip resurfacing offers a bone conserving treatment for more active patients without the potential metal ion risks associated with resurfacing devices. The Biolox Delta ceramic material has over 15 years of clinical history with low wear and good biocompatibility but has been limited previously in total hip replacement to 48mm diameter bearings [1]. Further increasing the diameter for resurfacing bearings and removing the metal shell to allow for direct fixation of the ceramic cup may increase the wear of this material and increase the risk of fracture. Eighteen implants (ReCerf™, MatOrtho, UK; Figure1) were wear tested; six were ⊘40mm (small) and twelve ⊘64mm (large). All small and six large implants were tested under ISO 14242 standard conditions for 5 million cycles (mc) at 30° inclination (45° clinically). The six remaining large implants were tested under microseparation conditions in which rim contact was initiated during heel strike of the gait cycle for 5mc. Cups were orientated at 45° inclination (60° clinically) to allow for separation of the head and cup with a reduced 50N swing phase load and a spring load applied to induce a 0.5mm medial-superior translation of the cup. Wear was determined gravimetrically at 0.5mc, 1mc and every mc after.INTRODUCTION
METHODS
Fluid film lubricating ability of a total
In the present study we describe the clinical results of the Scientific Hip Prosthesis® (SHP). With the goal of smoothening cement-bone interface stress peaks, the SHP was developed using shape optimization algorithms together with finite element modelling techniques. The resulting shape and cement stresses are seen in Figure 1. The introduction of the SHP prosthesis was performed in a stepwise fashion including a RSA study performed by Nivbrant et al1. RSA studies for prosthetic types that are in long-term use are of great value in predicting the survivorship related to the migration rate and pattern for that specific type of prosthesis. If a stem in a patient shows a much higher migration rate than the typical one, the stem may be identified as at high-risk for early loosening. The study of Nivbrant et al1 revealed unexpectedly high migration values and it was stated that the SHP stem was not the preferred stem to use despite the good Harris Hip Score and Pain score at two years follow-up. In the present study the clinical results of a single surgeon study consisting of 171 hips with a follow-up of 5–12 years were evaluated. The mean follow-up was 8.2 years (5.0–12.0). The survival rate was 98.8% at ten years follow-up for aseptic loosening of the stem. The mean Harris Hip Score at 10 year follow-up was 89.2 ± 7.5. This study therefore indicates that a new prosthetic design may function clinically rather well, despite the relatively high migration rates which have been reported. In case of a RSA study with a new prosthesis it may not be so evident what the expected “typical” migration rate or pattern is. So in order to predict early loosening the typical migration rate has to be known. Perhaps typical migration rates can be established using standardized cadaver migration experiments or computer simulation models techniques. Since these standardized tools are currently not available, the prediction of clinical survival of new prosthetic components remains a challenging task and the interpretation of migration rates with new designs should be considered with much caution.
Post op cup anatomical and functional orientation is a key point in THP patients regarding instability and wear. Recently literature has been focused on the consequences of the transition from standing to sitting regarding anteversion, frontal and sagittal inclination. Pelvic incidence (PI) is now considered as a key parameter for the analysis of sagittal balance and sacral slope (SS) orientation. It's influence on THP biomechanics has been suggested. Interestingly, the potential impact of this morphological angle on cup implantation during surgery and the side effects on post op functional orientation have not been studied. Our study explores this topic from a series of standing and sitting post-op EOS images 310 patients (mean age 63,8, mean BMI 30,2) have been included prospectively in our current post-operative EOS protocol. All patients were operated with the same implants and technique using anterior approach in lateral decubitus. According to previous literature, 3 groups were defined: low PI less than 45° (57 cases), high PI if more than 60° (63 cases), and standard PI in 190 other cases.Introduction
Material and methods
After a few years from its introduction, the limits of the THA became evident, mainly due to high rates of mobilization for polyethylene wear and to the release of metal ions from MOM and MOP couplings. Ceramic bearings were thus introduced in surgery to obtain lower levels of friction and wear. These issues have now been well recognized by several studies, which show that ceramic-on-ceramic joint has the lowest wear rate among various articulations and that ceramic particles induce less macrophage reaction and decrease cytokine secretion, allowing to have little periprosthetic osteolysis. After the first results in the late 70′s and early 80′s, the mechanical reliability was improved due to the manufacturers' efforts to reduce the ceramic fragility evolving average grain microstructure and lowering the degree of impurity. Betterment and standardization of production have led to 3rd generation alumina, Biolox Forte in 1994, that achieved a lower incidence of fracture. The purpose of our study has been to assess long-term follow-up results of alumina-on-alumina 3rd generation ceramic total hip cementless arthroplasty performed at our institution from January 1995 to December 2000. We prospectively followed more than 200 patients operated of THA for primary or secondary hip osteoarthritis analyzing clinical and radiographs features. In this period, the total hip replacement were performed by a single surgeon, who is the senior author (A.T.) in our Institution. All patients were clinically examined to confirm the diagnosis and all of them were checked with a standard plain radiographs in two projections and, when necessary, the radiographic examination was completed by CT scans. The same prosthesis was used in all patients, a 3rd generation alumina COC articulation, composed of a hemispherical titanium alloy cup and a 28-mm alumina ceramic femoral head. The modular ceramic head was fixed to a 12/14 taper cone. Proximally plasma-spray hydroxyapatite coated Ti alloy stems completes the implant features. Modular necks were used in retro or anteversion and varus or valgus offset, allowing changes in neck-shaft angle and giving a perfect intraoperative stability. Clinical assessment was performed using the Merle-D'Aubigne and Postel hip score. Each patient was assessed before surgery, after 30 days, afterwards at 4 months and annually after surgery. The mode of femoral component fixation was radiographically classified as bone ingrowth fixation, stable fibrous fixation or unstable fixation, according to the criteria Engh-Bobyn. Osteolysis was evaluated on the femoral side at each Gruen zone. Osteolysis on the acetabular side was evaluated by DeLee and Chanley zone. Our study has concluded that cementless modular hip arthroplasty with 3rd generation ceramic-on-ceramic bearing, with a 13 to 18 years follow-up, shows an excellent survivorship, in particular for the very low volume release of microparticles during friction, which consequently reduction of cytokine release, thus diminishing the risk of periprosthetic osteolysis and loosening of implant components.
This study reports outcomes of primary and revision total hip arthroplasties of a recalled metal-on-metal (MOM) monoblock prosthesis performed by a single surgeon. We performed a retrospective review of all patients who underwent both primary and revision total hip arthroplasties at our institution between 2006 and 2014. Only those patients who underwent primary recalled MOM monoblock prosthesis placement and/or revision of the recalled prosthesis were included. We evaluated revision group versus non-revision group for age, BMI, gender, existence of medical comorbidities, primary cup abduction and anteversion, primary combined angle, post-operative complications, cobalt and chromium ion levels, and Harris Hip Scores. Student t-test was used to compare groups.Introduction
Methods
The objective of this study was to evaluate the intermediate term clinical and radiological results of a new short stem hip implant. In 20 consecutive patients suffering from osteoarthritis with 25 affected hip joints (five cases were bilateral), the clinical and radiological results of 25 hip arthroplasties performed in one hospital between October 2009 and May 2014 through a minimally invasive anterolateral approach using a cementless short stem prosthesis type Aida and a cementless cup type Ecofit with a ceramic on ceramic pairing were evaluated prospectively. The median age of patients at time of surgery was 60 years (range, 42–71 years), 15 male (4 were bilateral) and 5 female patients (one was bilateral) were included in the study. The median clinical follow up was 30 months (range, 2–88 months), and the median radiological follow up was 30 months (range, 2–88 months).Aim
Methods
Mechanical wear and corrosion lead to the release of metal particulate debris and subsequent release of metal ions at the trunnion-taper surface. In order to quantify the amount of volume loss to ultimate locations in the surrounding joint space, finite element analysis of the modular head-stem junction is being carried out. The key purpose being to determine a set of optimum design changes that offer the least material loss at the taper-trunnion junction using optimization algorithms such as the gradient based local search (Sequential Quadratic Programming–SQP) and global search (Non-Dominated Sorting Genetic Algorithm-II–NSGA-II). In a broader sense, the principal goal is to work toward the minimization of wear debris produced in the hip joint, thereby resulting in a longer prosthetic lifetime. A numerical approach that simulates wear in modular hip prostheses with due consideration to the taper-trunnion junction on metal-on-metal contacts is proposed. A quasi-static analysis is performed considering realistic loading stages in the gait cycle, and nonlinear contact analysis is to be employed. The technique incorporates a measured wear rate as an input to the finite element model. The simulation of wear is performed by progressively changing nodal coordinates to simulate the wear loss that occurs during surface interaction. The geometry of the worn surface is updated under gait loading. With a given geometry and gait loading, the linear and volumetric wear increases with the number of gait cycles. The continuous wear propagation is discretized and an approximation scheme known as surrogates is to be developed using Artificial Neural Networks (ANN) to reduce the expensive computational simulations during optimization. The model is employed in the optimization schemes coded in MATLAB and linked to the finite element model developed in ANSYS batch mode. The objective function of the optimization problem is to minimize the volumetric wear at taper-trunnion interface under some constraints. By minimizing the volumetric wear, the chance of failure of modular hip implants is also minimized. The FE model developed to reproduce fretting wear is validated through in vitro wear simulations. The important taper design variables considered to have impact on the fretting corrosion performance include; medial-lateral offset, neck length, taper head diameter, trunnion length and diameter, included angle for the head/neck tapers, angle of mismatch or variation in taper trunnion angle, etc. It is expected from clinical outcomes that increased offset and large taper diameter has serious implications in the fretting corrosion behavior primarily because these variables control the bending stresses and strains along the length of the taper. During cyclic loading of the taper, the higher the strain range, the higher will be the relative micromotion at the point of engagement between the stem and head tapers. This research is carried out with the objective to optimize the effects of these geometrical factors at the mating taper interfaces. The developed models have great potentiality for accurate assessment of wear in a range of metal-on-metal (MoM) hip prostheses at the femoral head taper-trunnion junction while substantially reducing the wear and failure rate of prostheses.
A new conservative hip stem has been designed to address the complex problem of total hip arthroplasty in the younger population. To assess the stability and strain distribution of a new conservative hip stem.Introduction
Objectives
Revision surgery is generally recommended for recurrent dislocation following Total hip arthroplasty (THA). However, dislocation following revision THA continues to remain a problem with further dislocation rates upto 28% quoted in literature. We present early results of one of the largest series in U.K. using dual mobility cemented acetabular cup for recurrent hip dislocation. We retrospectively evaluated 40 patients where revision of hip replacement was performed using cemented dual mobility acetabular prosthesis for recurrent dislocations from March 2006 till August 2009 at our district general hospital by a single surgeon (senior author). The series comprised of 13 men and 27 females with average age of 73.4 years (49-92). The mean follow-up period was 23 months. (36 months –6 months). All the hips that were revised had 3 or more dislocations, some them more than 10 times. The cause of dislocation was multifactorial in majority of cases including acetabular component malpositioning mainly due to loosening and wear. A cemented dual mobility cup was used in all cases. In six cases the femoral stem was also revised.Introduction
Methods
Stress shielding of the proximal femur occurs in stemmed implants. Resurfacing implant does not invade the intramedullary region. We studied the stress patterns in conventional and nonstemmed designs. FE model geometry was based on standard femur from the international Society of Biomechanics Mesh Repository. Loading simulated for one- legged stance with body weight of 826 N. 2 regions were defined, R1 (40 mm from tip of head) and R2 41 mm–150 mm) of the intramedullary part of the stemmed model's interface with bone. 2 different loading conditions bending and torsion were compared for stress and strain. The FE model was solved with ANSYS version 6.1 on a single processor NT station. With conventional implants, stem shields cortical bone from being loaded. In nonstemmed implants, Von Misses stress contours show a similar distribution as intact bone, transferring loads to the cortical shell but with higher stresses and a maximum displacement of 17.39% higher than that of intact bone. 15–23 mm proximal to R2 and around 110 mm, region of the stem tip, there were higher stress and strain concentrations.Methods
Results
Introduction. Advantages of ceramic materials for
Ceramic bearings are widely used in total hip arthroplasty (THR) along with metal and polyethylene bearings. There were several studies in past few years evaluating the advantage of one over the other. The young population with high activity levels has an increased risk of wear debris production at bearing surface and subsequent implant failure. Recently, interest and use of a ceramics with high wear resistance has been growing. Early reports on ceramic on ceramic THR have demonstrated excellent clinical and radiological results. To evaluate clinical, functional and radiological outcomes of cement-less ceramic on ceramic primary total Hip Replacement (THR) in young patients (<50 years age) with diagnosis of avascular necrosis femoral head.BACKGROUND CONTEXT
PURPOSE
Introduction. Hip resurfacing arthoplasty (HRA) is an alternative to total hip arthroplasty (THA), which has increased in the last years, especially in young patients. A suitable positioning of the resurfacing head is important, mainly because it is strongly related with the neck fracture. The goal of this work was to evaluate the influence of the resurfacing head positioning in the load distribution along the femurs’ structures. Materials and methods. Using 3D scan technology, the exterior geometry of a composite femur, used to create the FE models, was obtained. Three resurfacing models were used in three different positions in the frontal plane. A model with a positive offset of +5mm (Resurfacing #1), in neutral position (Resurfacing #2), and with a negative offset of −5mm (Resurfacing #3) was developed. A Birmingham®