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Abstract

Total hip arthroplasty (THA) has been associated with excellent functional outcomes and survival rates (Cushner et al., 2010 [1]). Selection of acetabular shell and technique of implantation is an important factor as is the stem for a successful THA. Both cemented all-polyethylene cups and cementless sockets have benefited from improvements in surgical techniques, cup designs, and bearing surfaces. This paper is a review of the current literature that focuses on the options for the acetabular components of a modern total hip replacement, aiming to answer common questions and controversies on this topic.

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... Sculco, 2013;Smith & Smith, 2012), the majority of the existing vibrometry loosening diagnostic literature(Díaz-Pérez et al., 2014; ...
Article
One of the most important human intervention is a total hip replacement (THR), that has the goal of pain relief and performance restoration. From early 1960, THR come a long way and now more than one million patients all around the world every year have THR. Against all these facts, 4‐10% of all THR are failed mostly due to loosening. Precise and fast detection is vital for both surgeons and patients. The diagnosis approaches are generally classified into two groups: conventional non‐imaging and imaging approaches. Imaging approaches are the most widely used because they are most cost‐effective, convenient and available. However, some shortcomings are obvious in the conventional imaging methods of diagnosing prosthesis loosening. Consequently, new techniques have been further developed and recommended based on non‐destructive analysis such as vibrometery, telemetry, and acoustic.
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Aseptic loosening is the most common indication for revision of cementless acetabular cups and often depends on the primary stability achieved following surgery. Cup designs must be capable of achieving primary stability for a wide variety of individuals and surgical conditions to be successful. Typically, pre‐clinical finite element (FE) testing of cups involves assessing the performance in a single patient and under a limited set of idealised conditions. The aim of this study was to assess the effect of patient and surgical parameters on the primary stability of an acetabular cup design in a set of subject‐specific FE models. Interference fit was varied in a representative set of 12 patient‐specific models of the implanted hemipelvis. Linear mixed models showed a significant association with micromotion for interference fit (p < 0.0001), acetabular bone elastic modulus (p < 0.001), native acetabular diameter (p = 0.03), and the interference fit‐elastic modulus interaction (p = 0.01). There were no significant associations between polar gap and any of the parameters considered. The significant interference fit‐elastic modulus interaction suggests increasing the interference fit in patients with low bone quality leads to a greater reduction in micromotion than in patients with higher bone quality. However, the significant association between percentage bone yielding and interference fit (p < 0.0001) suggests a higher periacetabular fracture risk at higher interference fits. This work supports the development of pre‐clinical testing of cup designs for the broad range patients and surgical conditions a cup may face following surgery. This article is protected by copyright. All rights reserved.
Article
Backround: For preclinical statements about the anchoring behavior of prostheses, the primary stability of the prosthesis is of special importance. It was the aim of this study to examine and compare the relevant relative micromotions of three different acetabulum prostheses by introducing three-dimensional torques. Methods: The cups were implanted under standard conditions into an anatomical artificial bone model. Three-dimensional torques were applied to the acetabular cups. Taking into account the resulting frictional moments of two different bearing couples, ceramic-on-ceramic and ceramic-on-polyethylene, the relative micromotions of the cups were recorded as maximum total micromotion, translational and rotational micromotion, and the primary stability values of the three cups were compared. Results: Relative micromotion of all cup models was always significantly smaller with the CoC bearing couples than with the CoP bearing couples (p < 0.001). The rotational micromotion was always lower (p < 0.001) than the translational micromotion, and the rotational as well as the translational micromotions were each always lower than the maximum total micromotion (p < 0.001, p < 0.010). The thinnest-walled cup system always showed the largest relative micromotions. Conclusion: The results of our study can be interpreted as indicating that the low relative micromotions of all cups - irrespective of the use of CoC or CoP bearing couples - are within an acceptable range favoring secondary osseointegration of the implants. Furthermore, we were able to show that the cup wall thickness and the surface quality of the cup systems have an influence on the primary stability and the elastic deformability of the examined cup systems.
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To examine mortality and revision rates among patients with osteoarthritis undergoing hip arthroplasty and to compare these rates between patients undergoing cemented or uncemented procedures and to compare outcomes between men undergoing stemmed total hip replacements and Birmingham hip resurfacing. Cohort study. National Joint Registry. About 275,000 patient records. Hip arthroplasty procedures were linked to the time to any subsequent mortality or revision (implant failure). Flexible parametric survival analysis methods were used to analyse time to mortality and also time to revision. Comparisons between procedure groups were adjusted for age, sex, American Society of Anesthesiologists (ASA) grade, and complexity. As there were large baseline differences in the characteristics of patients receiving cemented, uncemented, or resurfacing procedures, unadjusted comparisons are inappropriate. Multivariable survival analyses identified a higher mortality rate for patients undergoing cemented compared with uncemented total hip replacement (adjusted hazard ratio 1.11, 95% confidence interval 1.07 to 1.16); conversely, there was a lower revision rate with cemented procedures (0.53, 0.50 to 0.57). These translate to small predicted differences in population averaged absolute survival probability at all time points. For example, compared with the uncemented group, at eight years after surgery the predicted probability of death in the cemented group was 0.013 higher (0.007 to 0.019) and the predicted probability of revision was 0.015 lower (0.012 to 0.017). In multivariable analyses restricted to men, there was a higher mortality rate in the cemented group and the uncemented group compared with the Birmingham hip resurfacing group. In terms of revision, the Birmingham hip resurfacings had a similar revision rate to uncemented total hip replacements. Both uncemented total hip replacements and Birmingham hip resurfacings had a higher revision rate than cemented total hip replacements. There is a small but significant increased risk of revision with uncemented rather than cemented total hip replacement, and a small but significant increased risk of death with cemented procedures. It is not known whether these are causal relations or caused by residual confounding. Compared with uncemented and cemented total hip replacements, Birmingham hip resurfacing has a significantly lower risk of death in men of all ages. Previously, only adjusted analyses of hip implant revision rates have been used to recommend and justify use of cheaper cemented total hip implants. Our investigations additionally consider mortality rates and suggest a potentially higher mortality rate with cemented total hip replacements, which merits further investigation.
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This study compared component wear rates and pre-revision blood metal ions levels in two groups of failed metal-on-metal hip arthroplasties: hip resurfacing and modular total hip replacement (THR). There was no significant difference in the median rate of linear wear between the groups for both acetabular (p = 0.4633) and femoral (p = 0.0872) components. There was also no significant difference in the median linear wear rates when failed hip resurfacing and modular THR hips of the same type (ASR and Birmingham hip resurfacing (BHR)) were compared. Unlike other studies of well-functioning hips, there was no significant difference in pre-revision blood metal ion levels between hip resurfacing and modular THR. Edge loading was common in both groups, but more common in the resurfacing group (67%) than in the modular group (57%). However, this was not significant (p = 0.3479). We attribute this difference to retention of the neck in resurfacing of the hip, leading to impingement-type edge loading. This was supported by visual evidence of impingement on the femur. These findings show that failed metal-on-metal hip resurfacing and modular THRs have similar component wear rates and are both associated with raised pre-revision blood levels of metal ions.
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The Kaplan-Meier (KM) method is often used in the analysis of arthroplasty registry data to estimate the probability of revision after a primary procedure. In the presence of a competing risk such as death, KM is known to overestimate the probability of revision. We investigated the degree to which the risk of revision is overestimated in registry data. We compared KM estimates of risk of revision with the cumulative incidence function (CIF), which takes account of death as a competing risk. We considered revision by (1) prosthesis type in subjects aged 75–84 years with fractured neck of femur (FNOF), (2) cement use in monoblock prostheses for FNOF, and (3) age group in patients undergoing total hip arthroplasty (THA) for osteoarthritis (OA). In 5,802 subjects aged 75–84 years with a monoblock prosthesis for FNOF, the estimated risk of revision at 5 years was 6.3% by KM and 4.3% by CIF, a relative difference (RD) of 46%. In 9,821 subjects of all ages receiving an Austin Moore (non-cemented) prosthesis for FNOF, the RD at 5 years was 52% and for 3,116 subjects with a Thompson (cemented) prosthesis, the RD was 79%. In 44,365 subjects with a THA for OA who were less than 70 years old, the RD was just 1.4%; for 47,430 subjects > 70 years of age, the RD was 4.6% at 5 years. The Kaplan-Meier method substantially overestimated the risk of revision compared to estimates using competing risk methods when the risk of death was high. The bias increased with time as the incidence of the competing risk of death increased. Registries should adopt methods of analysis appropriate to the nature of their data.
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Total hip arthroplasty (THA) has been targeted by the United States federal government for cost control because of its high cost and rising incidence in the aging population. The hospital cost for THA during the 1980s was controlled by utilization review and a reduction in the volume of services delivered for each THA. The single largest increase in the cost of THA during the 1980s was the cost of hip implants. The Lahey Clinic Hip Implant Standardization Program was developed to provide objective guidelines for hip implant selection. These guidelines are based on the demands a patient is expected to place on his or her hip prosthesis. Because not every patient requires an expensive high-demand hip prosthesis, the standardization program also has the potential to reduce the hospital cost for hip implants without compromising patient care. Patients are assigned to four demand categories based on five objective criteria: age, weight, expected activity, general health, and bone stock. Selection of the prosthesis in each of the four demand categories is intended to match the implant's capacity with expected patient demand. The standardization program was retrospectively applied to 103 THAs performed during 1991. Analysis of variance demonstrated that patient variables and demand categories were statistically significant groupings. The cost of hip implants would have been reduced by 25.7% with the Lahey Clinic Hip Implant Standardization Program. A prospective outcome study is required to determine the long-term validity of this standardization program.
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Cement fixation of the acetabular cup in total hip arthroplasty (THA) has evolved through multiple generations of cement technology. Whereas cement technology has produced improvements in cemented femoral fixation, the cemented socket still produces inconsistent results. Even with our current knowledge that cemented cups require exposure of cancellous bone, a clean and dry socket, and adequate bony coverage of the cup, surgeons such as myself are unable to control radiolucency at the bone-cement interface. The technical difficulty of cementing the acetabular cup has led to the increasing prevalence of cementless acetabular cups. Although cementless fixation has resulted in increased incidence of osteolysis, the surgical procedure is less technically demanding, and the long-term mechanical fixation results have been more consistent. Given the experiential learning curve that most orthopedic surgeons face with cemented fixation of the acetabular cup component, the role of the cemented socket in THA today is limited.
Article
Highly cross-linked formulations of ultrahigh-molecular-weight polyethylene (XLPE) offer exceptional wear resistance for total joint arthroplasty but are offset with a reduction in postyield and fatigue fracture properties in comparison to conventional ultrahigh-molecular-weight polyethylene (UHMWPE). Oxidation resistance is also an important property for the longevity of total joint replacements (TJRs) as formulations of UHMWPE or XLPE utilizing radiation methods are susceptible to free radical generation and subsequent embrittlement. The balance of oxidation, wear, and fracture properties is an enduring concern for orthopedic polymers used as the bearing surface in total joint arthroplasty. Optimization of material properties is further challenged in designs that make use of locking mechanisms, notches, or other stress concentrations that can render the polymer autoexit eacute framefootchange getusernam insertline JBMB_RV_Review_Article_StyleSheet POLA_Del_Blank_Pg POLA_Shift_Frame PORT_rem_fpg_under removeline tabmini susceptible to fracture due to elevated local stresses. Clinical complications involving impingements, dislocations, or other biomechanical overloads can exacerbate stresses and negate benefits of improved wear resistance provided by XLPE. This work examines trade-offs that factor into the use of XLPE in TJR implants.
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Implant loading can create micromotion at the bone-implant interface. The interfacial strain associated with implant micromotion could contribute to regulating the tissue healing response. Excessive micromotion can lead to fibrous encapsulation and implant loosening. Our objective was to characterize the influence of interfacial strain on bone regeneration around implants in mouse tibiae. A micromotion system was used to create strain under conditions of (1) no initial contact between implant and bone, and (2) a direct bone-implant contact. Pin- and screw-shaped implants were subjected to displacements of 150 μm or 300 μm, 60 cycles/day, for 7 days. Pin-shaped implants placed in 5 animals were subjected to 3 sessions of 150 μm displacement per day, with 60 cycles per session. Control implants in both types of interfaces were stabilized throughout the healing period. Experimental strain analyses, microtomography, image-based displacement mapping, and finite element simulations were used to characterize interfacial strain fields. Calcified tissue sections were prepared and stained with Goldner to evaluate tissue reaction in higher and lower strain regions. In stable implants, bone formation occurred consistently around the implants. In implants subjected to micromotion, bone regeneration was disrupted in areas of high strain concentrations (e.g. > 30%), whereas lower strain values were permissive of bone formation. Increasing implant displacement or number of cycles per day also changed the strain distribution and disturbed bone healing. These results indicate that not only implant micromotion but also the associated interfacial strain field contributes to regulating the interfacial mechanobiology at healing bone-implant interfaces.
Article
The use of cementless acetabular components in total hip arthroplasty has gained popularity over the past decade. Most total hip arthroplasties being performed in North America currently use cementless acetabular components. The objective of this systematic review and meta-analysis was to compare the survivorship and revision rate of cemented and cementless acetabular components utilized in total hip arthroplasty. A primary literature search in PubMed identified 3488 articles, of which 3407 did not meet the inclusion criteria and were excluded. Only English-language articles on either the survivorship or revision rate of primary total hip arthroplasty at a minimum of ten years of follow-up were included. The present study analyzed forty-five articles reporting the long-term outcome of cementless acetabular components, twenty-nine reporting the outcome of cemented acetabular components, and seven comparing cemented and cementless acetabular components. Meta-analysis (with a random-effects model) was performed on the data from the seven comparative studies, and study-level logistic regression analysis (with a quasibinomial model) was performed on the pooled data on the eighty-one included articles to determine a consensus. The studies were weighted according to the number of total hip arthroplasties performed. The meta-analysis did not reveal any effect of the type of acetabular component fixation on either survivorship or revision rate. The regression analysis revealed the estimated odds ratio for survivorship of a cemented acetabular component to be 1.60 (95% confidence interval, 1.32 to 2.40; p = 0.002) when adjustments for factors including age, sex, and mean duration of follow-up were made. The preference for cementless acetabular components on the basis of improved survivorship is not supported by the published evidence. Although concerns regarding aseptic loosening of cemented acetabular components may have led North American surgeons toward the nearly exclusive use of cementless acetabular components, the available literature suggests that the fixation of cemented acetabular components is more reliable than that of cementless components beyond the first postoperative decade.
Article
United Kingdom National Institute for Health and Clinical Excellence guidelines recommend the use of total hip replacement (THR) for displaced intracapsular fractures of the femoral neck in cognitively intact patients, who were independently mobile prior to the injury. This study aimed to analyse the risk factors associated with revision of the implant and mortality following THR, and to quantify risk. National Joint Registry data recording a THR performed for acute fracture of the femoral neck between 2003 and 2010 were analysed. Cox proportional hazards models were used to investigate the extent to which risk of revision was related to specific covariates. Multivariable logistic regression was used to analyse factors affecting peri-operative mortality (< 90 days). A total of 4323 procedures were studied. There were 80 patients who had undergone revision surgery at the time of censoring (five-year revision rate 3.25%, 95% confidence interval 2.44 to 4.07) and 137 patients (3.2%) patients died within 90 days. After adjusting for patient and surgeon characteristics, an increased risk of revision was associated with the use of cementless prostheses compared with cemented (hazard ratio (HR) 1.33, p = 0.021). Revision was independent of bearing surface and head size. The risk of mortality within 90 days was significantly increased with higher American Society of Anesthesiologists (ASA) grade (grade 3: odds ratio (OR) 4.04, p < 0.001; grade 4/5: OR 20.26, p < 0.001; both compared with grades 1/2) and older age (≥ 75 years: OR 1.65, p = 0.025), but reduced over the study period (9% relative risk reduction per year). THR is a good option in patients aged < 75 years and with ASA 1/2. Cementation of the femoral component does not adversely affect peri-operative mortality but improves survival of the implant in the mid-term when compared with cementless femoral components. There are no benefits of using head sizes > 28 mm or bearings other than metal-on-polyethylene. More research is required to determine the benefits of THR over hemiarthroplasty in older patients and those with ASA grades > 2.
Article
Preoperative planning is essential to define anatomy, clarify the operative approach and exposure, and ensure that suitable implants are available.Concerns exist regarding the long-term effectiveness and safety of hip resurfacing arthroplasty for the young dysplastic hip.In light of current evidence, concerns exist regarding the use of metal-on-metal articulations for hip arthroplasty in the young dysplastic hip.The ideal bearing surface is not known, although the longest data available support the use of metal-on-polyethylene.
Article
The cost of healthcare procedures is continuously rising and more emphasis is being placed on increasing the quality and effectiveness of healthcare services. A combined total of 711,000 hip and knee arthroplasties are performed yearly. This figure is expected to increase to 4 million by the year 2030. The American Joint Replacement Registry has been developed to monitor the performance of devices, determine the cost-effectiveness of procedures, and increase patient safety for individuals in need of hip and knee replacement procedures.
Article
Background: THA in patients younger than 30 years presents challenges because of uncertainties regarding the long-term survivorship of prostheses. Alumina-on-alumina bearings, which exhibit little long-term wear, may be a reasonable option but the long-term survivorship is unknown. Questions/purposes: We determined (1) the survival rate of alumina-on-alumina bearings in patients younger than 30 years after a 10-year followup, (2) the incidence of audible hip clicking and squeaking, (3) radiographic evidence of osteolysis, and (4) the effects on pregnancy, childbirth, and career choice. Methods: We retrospectively reviewed 62 patients who had 75 THAs with alumina-on-alumina bearings followed more than 10 years (average, 11.5; range, 10-13.5 years). Mean patient age at the time of surgery was 24 years (range, 18-30 years). All operations were performed using the same cementless implant at a single center. We determined survival, presence of osteolysis, and function (Harris hip score, WOMAC). Results: The 10-year survival rate of alumina-on-alumina bearings in THAs, with revision for any reason as the end point, was 98.9%. Audible hip clicking and squeaking were identified in 10 hips and two hips, respectively. No osteolysis was detected. None of the 11 patients who became pregnant had been affected by their THA during pregnancy or childbirth. Seven of the 14 patients who were unemployed at the time of index surgery stated that their THA affected their job choice. Conclusions: We found a high 10-year survival of cementless alumina-on-alumina bearings in THAs in patients younger than 30 years. Lifetime events such as job choice, pregnancy, and childbirth should be considered when choosing THA for patients younger than 30 years. Level of evidence: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
Article
Different design solutions have been suggested for improvement of the initial stability of cementless acetabular cups, such as adding threads, spikes, or pegs to the hemispherical geometry, the pore structure of the surface; and screw fixation. This experimental study investigated the effect of fins on the initial stability of the acetabular cup. Three designs were studied, with none, 2, and 12 fins, respectively. The cups were press fit into cavities reamed in 2 different polyurethane foams, used to simulate 2 qualities of cancellous bone. Two millimeter press-fit and exact-fit conditions were investigated. The results show that the type of substrate and the interference value are important in determining the initial stability of the cup. The addition of fins on the cup rim enhances in vitro the initial stability, especially in cases of a poor press fit with a good substrate. This preclinical investigation suggests that the use of a cup design with fins may be beneficial in all cases in which press fit of the cup cannot be assured. However, further clinical studies are required to validate in vivo the efficacy of the fins as additional fixation devices.
Article
The purpose of this study was to examine the effects of ceramic femoral head material, size, and implantation periods on the wear of annealed, cross-linked ultra-high molecular weight polyethylene (UHMWPE) (XLPE) in total hip arthroplasty compared to non-cross-linked conventional UHMWPE (CPE). XLPE was fabricated by cross-linking with 60 kGy irradiation and annealing. Femoral heads made from zirconia and alumina ceramics and cobalt-chrome (CoCr) of 22 or 26 mm diameter were used. In this retrospective cohort study, the femoral head penetration into the cup was measured digitally on radiographs of 367 hips with XLPE and 64 hips with CPE. The average follow-up periods were 6.3 and 11.9 years, respectively. Both XLPE creep and wear rates were significantly lower than those of CPE (0.19 mm vs. 0.44 mm, 0.0001 mm/year vs. 0.09 mm/year, respectively). Zirconia displayed increased wear rates compared to alumina in CPE; however, there was no difference among head materials in XLPE (0.0008, 0.00007, and -0.009 mm/year for zirconia, alumina, and CoCr, respectively). Neither head size or implantation period impacted XLPE wear. In contrast to CPE, XLPE displayed low wear rates surpassing the effects of varying femoral head material, size, implantation period, and patient demographics. Further follow-up is required to determine the long-term clinical performance of the annealed XLPE. © 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:2031-2037, 2012.
Article
Knowledge of acetabular anatomy is crucial for cup positioning in total hip replacement. Medial wall thickness of the acetabulum is known to correlate with the degree of developmental dysplasia of the hip (DDH). No data exist about the relationship of routinely used radiographic parameters such as Wiberg's lateral center edge angle (LCE-angle) or Lequesne's acetabular index (AI) with thickness of the medial acetabular wall in the general population. The aim of our study was to clarify the relationship between LCE, AI, and thickness of the medial acetabular wall. Measurements on plain radiographs (LCE and AI) and axial CT scans (quadrilateral plate acetabular distance QPAD) of 1,201 individuals (2,402 hips) were obtained using a PACS imaging program and statistical analyses were performed. The mean thickness of the medial acetabulum bone stock (QPAD) was 1.08 mm (95% CI: 1.05-1.10) with a range of 0.1 to 8.8 mm. For pathological values of either the LCE (<20°) or the AI (>12°) the medial acetabular wall showed to be thicker than in radiological normal hips. The overall correlation between coxometric indices and medial acetabular was weak for LCE (r =-0.21. 95% CI [-0.25, -0.17]) and moderate for AI (r = 0.37, [0.33, 0.41]). We did not find a linear relationship between Wiberg's lateral center edge angle, Lequesne's acetabular index and medial acetabular bone stock in radiological normal hips but medial acetabular wall thickness increases with dysplastic indices.
Article
The Global Orthopaedic Registry (GLORY) has been designed to monitor a broad range of complications and outcomes that occur following total hip arthroplasty (THA) and total knee arthroplasty (TKA). GLORY provides global 'real-world' data, in contrast to the data generated by the controlled conditions of clinical trials. The results to date show an overall incidence of both in-hospital and post-discharge complications of approximately 7% in THA patients and 8% in TKA patients. The most common in-hospital complications in THA patients are fractures (0.6%) and deep-vein thrombosis (DVT) (0.6%), whereas in TKA patients DVT (1.4%) and cardiac events (0.8%) are most common. The most common post-discharge complications in both THA and TKA patients are reoperation due to bleeding, wound necrosis, wound infection, or other causes; and DVT. Bleeding complications were less common than other adverse events in both groups (in-hospital rates of 0.48% and 0.83%, respectively). Functional outcomes improved after surgery in both groups, as expected. Younger patients and patients who had been discharged directly to their homes seemed to have the greatest improvement in functional outcome after surgery.
Article
We reviewed 123 second-generation uncemented total hip replacements performed on 115 patients by a single surgeon between 1993 and 1994. The acetabular component used in all cases was a fully porous-coated threaded hemispheric titanium shell (T-Tap ST) with a calcium ion stearate-free, isostatically compression-moulded polyethylene liner. The titanium femoral component used was a Taperloc with a reduced distal stem. No patient was lost to follow-up. Complete clinical and radiological follow-up was obtained for all 123 hips at a mean of 14 years (12 to 16). One femoral component was revised after a fracture, and three acetabular components for aseptic loosening. No additional femoral or acetabular components were judged loose by radiological criteria. Mild proximal femoral osteolysis was identified in two hips and minor acetabular osteolysis was present in four. The mean rate of penetration of the femoral head was 0.036 mm/year (0.000 to 0.227). These findings suggest that refinements in component design may be associated with excellent long-term fixation in cementless primary total hip replacement.
Article
The socket remains the weakest link of primary total hip arthroplasty (THA). The revision rates of the socket are higher than those of the stem, with aseptic loosening and polyethylene wear being the most frequent indications for revision THA. Both cemented all-polyethylene cups and cementless sockets have benefited from stepwise improvements in surgical techniques and designs. In many countries, cementless sockets have replaced cemented cups during primary THA, with >90% of the acetabular components using a cementless fixation mode. The long-term prospective data of cementless sockets from high-volume centers show excellent and equivalent survivorship to cemented implants, but the insertion technique is easier and quicker. In addition, cementless sockets are more versatile than cemented all-polyethylene cups. With cementless sockets there is a move to increased porosity of the ingrowth surface, tri-bearing options, and enhanced locking mechanisms. There is a role for well-conducted randomized controlled trials to assess these new designs because data from various national registries show that the socket remains the weakest link of primary THA. Factors like sex, age, diagnosis, and bearing couples have a different and significant influence on the intermediate to long-term survivorship of contemporary cemented and cementless THA.
Article
During the past decade, advances in total hip arthroplasty component design have produced implants with reliable clinical results in regard to fixation. The foremost unresolved challenge has been the development of bearing surfaces that can withstand the higher demands of younger and more active patients. New alternative bearings with superior wear characteristics that minimize debris include ceramic-on-ceramic, metal-on-metal, and highly cross-linked polyethylenes in combination with ceramic or metal. Alumina-on-alumina ceramic bearings are extremely hard and scratch resistant and provide superior lubrication and wear resistance compared with other bearing surfaces in clinical use. Survivorship revision for any reason for the alumina ceramic bearings at 10 years was significantly higher compared with metal-on-polyethylene. Bearings currently being studied because of their encouraging wear performance in the laboratory are an alumina matrix (82% alumina, 17% zirconia, 0.3% chromium oxide), zirconium oxide, and ceramic-on-cobalt-chromium.
Article
As part of the 2006 symposium of the French Hip and Knee Society devoted to the dual mobility socket, we report a retrospective multicentric series of 438 first-intention total hip prostheses with a dual mobility socket at a mean 17 years follow-up. The purpose of our report was to ascertain the 15-year survival of this socket and analyze failures. The series included 438 primary replacements. This was a homogeneous multicentric series. The cementless sockets were 80 Novae-1 titanium Serf cups and 358 Novae-1 stainless steel Serf cups. All stems were inserted without cement: 185 Pf((R)) stainless steel screwed Serf stems, 228 PRO titanium screwed Serf stems, and 25 Corail stems. The mobile polyethylene insert was retaining. All of the heads were 22.2-mm chromium-cobalt heads. Degenerative hip disease was the main etiology and mean follow-up was 17 years (range, 12-20). Mean age at implantation was 54.8 years (range, 23-87). The actuarial method with a 95% confidence interval was used to determine the 15-year cup survival rate. At the last follow-up, none of the patients had presented an episode of early or late instability. Analysis of the socket at last follow-up showed 13 aseptic loosenings, 23 intraprosthetic dislocations, and seven replacements of the polyethylene insert for wear. The overall 15-year prosthesis survival rate was 89.2+/-8.7%. The overall 15-year socket survival rate was 96.3+/-3.7%. The fact that, at last follow-up, none of the implants had shown instability confirms the long-term stability of the dual mobility socket. The results in terms of 15-year survival confirm earlier reports. The main cause of failure was cup fixation, which is the weak point of this technique with the initial Novae cup design, which did not have hydroxyapatite coating. The second leading cause was intraprosthetic dislocation, which can be divided into three main categories. The first is intraprosthetic dislocation in a context of pure wear with normal function of the dual mobility socket; the retaining feature of the insert loses its efficacy due to wear. The second category is intraprosthetic dislocation in a context of cup loosening with a third-body effect and increased retention wear, in which case we consider that cup loosening is the primary event leading to rapid secondary wear and subsequent intraprosthetic dislocation. The third category is intraprosthetic dislocation caused by a blockage in a context of fibrosis or impingement involving severe heterotopic ossifications. We had only two femoral failures related to aseptic loosening, most certainly related to use of noncemented implants, which limits the extension of granulomas to the polyethylene. Studying the three series from Saint-Etienne more specifically, where three different configurations were used, it would appear that the titanium cup has a better survival rate and that the titanium used for the thinner necks may be an unfavorable factor for intraprosthetic dislocation.
Article
Total hip arthroplasty (THA) has been targeted by the United States federal government for cost control because of its high cost and rising incidence in the aging population. The hospital cost for THA during the 1980s was controlled by utilization review and a reduction in the volume of services delivered for each THA. The single largest increase in the cost of THA during the 1980s was the cost of hip implants. The Lahey Clinic Hip Implant Standardization Program was developed to provide objective guidelines for hip implant selection. These guidelines are based on the demands a patients is expected to place on his or her hip prosthesis. Because not every patient requires an expensive high-demand hip prosthesis, the standardization program also has the potential to reduce the hospital cost for hip implants without compromising patient care. Patients are assigned to four demand categories based on five objective criteria: age, weight, expected activity, general health, and bone stock. Selection of the prosthesis in each of the four demand categories is intended to match the implant's capacity with expected patient demand. The standardization program was retrospectively applied to 103 THAs performed during 1991. Analysis of variance demonstrated that patient variables and demand categories were statistically significant groupings. The cost of hip implants would have been reduced by 25.7% with the Lahey Clinic Hip Implant Standardization Program. A prospective outcome study is required to determine the long-term validity of this standardization program.
Article
The purpose of our study was to examine the clinical and technical problems associated with reconstruction of the hip in patients who had congenital dysplasia and to offer recommendations for their solution. We reviewed the records on 123 consecutive total hip arthroplasties that had been performed by one of us (M. E. M.), between 1981 and 1986, for the treatment of coxarthrosis due to congenital dysplasia of the hip. A minimum of five years of follow-up was required for inclusion in the study. The study group consisted of seventy patients who had had a total of eighty-seven reconstructions. According to the classification of Crowe et al., eleven hips had type-IV acetabular dysplasia; sixty-five, type-II; and eleven, type-II. Acetabular reconstruction was performed with use of the Müller acetabular roof-reinforcement ring and a polyethylene cup, which was inserted with cement. Autologous graft from the femoral head was used in forty-two hips. Femoral reconstruction was performed with use of the Müller straight-stem component for congenital dysplasia of the hip in eighty hips and with use of a standard Müller straight-stem component in seven hips. At an average of 9.4 years (range, five to fifteen years) postoperatively, the result was described as excellent for sixty hips (69 per cent), as good for twenty-three (26 per cent), as fair for two (2 per cent), and as poor for two. Nine (10 per cent) of the hips had been revised. One revision had been performed because of aseptic loosening of the acetabular component; one, because of aseptic loosening of the femoral component; one, because of aseptic loosening of both components; and six, because of infection. Of the unrevised hips, three had had superior migration of the acetabular component of less than five millimeters, and mild protrusion had developed in one. Two hips had a continuous radiolucent line around the acetabular construct. Two hips had had subsidence of the femoral stem of less than three millimeters; one had a complete, non-progressive radiolucent line at the bone-cement interface; and four had a radiolucent line at the proximal part of the bone-cement interface. Six hips had evidence of endosteal osteolysis. Six hips had grade-III or IV heterotopic ossification according to the system of Brooker et al. These results compare favorably with others in the literature. We recommend restoration of the anatomical hip center with the use of an acetabular roof-reinforcement ring and a polyethylene cup inserted with cement for the reconstruction of a deficient acetabulum. The acetabular reinforcement ring prevents resorption of bone graft and migration of the cup, which are major causes of failure of the cup in patients who have had a reconstruction of a deficient acetabulum. Bone graft should be used medially and superiorly as needed to augment bone stock notably. Cement should not be used to fill acetabular defects as we believe that it contributes to aseptic loosening.
Article
We evaluated 377 patients (428 hips) who had been managed, by a total of fourteen surgeons at twelve clinical sites in the United States and Europe, with a porous-coated press-fit acetabular cup, a hydroxyapatite-coated threaded screw-in cup, or one of two similar designs of hydroxyapatite-coated press-fit cups between April 1987 and November 1992. The same type of hydroxyapatite-coated femoral stem was inserted without cement in all patients. After a minimum duration of follow-up of five years (mean, 7.9 years; range, 5.3 to 9.1 years), one (1 per cent) of the 131 hydroxyapatite-coated threaded cups, two (2 per cent) of the 109 porous-coated press-fit cups, and twenty-one (11 per cent) of the 188 hydroxyapatite-coated press-fit cups had been revised because of aseptic loosening. A common radiographic sign of impending failure of the hydroxyapatite-coated press-fit cups was radiolucency at the interface between the implant and the subchondral bone beneath it. This radiolucency usually was seen initially more than two years after implantation. Radiographic evaluation of the 383 acetabular implants that were in situ at the time of the most recent follow-up showed that 123 (99 per cent) of the 124 hydroxyapatite-coated threaded cups, 101 (98 per cent) of the 103 porous-coated cups, and 139 (89 per cent) of the 156 hydroxyapatite-coated press-fit cups were stable with osseous ingrowth (as indicated by the absence of radiolucency at the interface and the absence of migration within the acetabulum). The probability of revision due to aseptic loosening was significantly greater for the hydroxyapatite-coated press-fit cups than it was for the hydroxyapatite-coated threaded cups or the porous-coated press-fit cups (p < 0.001 for both comparisons). Within the group of patients who had a hydroxyapatite-coated press-fit cup, the probability of revision due to aseptic loosening was significantly greater in association with a young age (p = 0.003), female gender (p = 0.02), the use of a femoral head with a diameter of thirty-two millimeters (p = 0.018), and the use of a thin polyethylene liner (p < 0.001). We found that the hydroxyapatite-coated threaded cups and the porous-coated press-fit cups continued to perform well more than five years after the operation. The hydroxyapatite-coated press-fit cups that were revised probably failed because the fixation interface beneath the cup could not sustain the tensile stresses that were imposed between the cup and the bone by the activity of the patient. Our data suggest that, in the specific biomechanical environment of the acetabulum, physical interlocking between the cup and the supporting bone beneath it may be a prerequisite for long-term stability.
Article
This study examined the clinical results and technical challenges associated with acetabular reconstruction in developmental dysplasia of the hip using the acetabular reinforcement ring with hook. We reviewed 33 consecutive reconstructions performed by a single surgeon. At an average follow-up of 6.7 years, the mean Merle-d'Aubigne score had increased from 7 to 16. Two revisions were performed for aseptic loosening. Of the unrevised hips, 1 was classified as definitely loose and 1 as possibly loose. These results compare favorably with others in the literature. The acetabular reinforcement ring may prevent graft resorption and cup migration, major causes of socket failure in reconstruction of the deficient acetabulum.
Article
Hospital revenues for orthopaedic operations are not keeping pace with inflation or with rising hospital expenses. In an attempt to reduce the hospital cost of orthopaedic operations by reducing the cost of operating-room supplies, we developed a Single Price/Case Price Purchasing Program for implants used in total hip arthroplasty, total knee arthroplasty, and total shoulder arthroplasty as well as for arthroscopic shavers and burrs, interference screws, and bone-suture anchors. The Lahey Clinic asked orthopaedic vendors to supply all instruments, implants, and disposable items related to these selected products for one single price per unit or case. For example, a single price for total hip arthroplasty implants included instruments, acetabular cups, acetabular liners, acetabular screws, femoral stems, femoral heads, and stem centralizers, if required. The hospital implemented the Single Price/ Case Price Purchasing Program with a competitive-bid request for proposal. Surgeons evaluated the responses to the bidding process, and they made final decisions on product selection. The Single Price/Case Price Purchasing Program at the Lahey Clinic was successful in reducing the cost of orthopaedic implants and supplies. In the present article, we could not disclose the specific prices that we agreed to pay our vendors. The specific cost reductions were 32 percent for hip implants with a change of vendor, 23 percent for knee implants without a change of vendor, 25 percent for shoulder implants with a change of vendor, 45 percent for arthroscopic shavers and burrs without a change of vendor, 45 percent for interference screws without a change of vendor, and 23 percent for bone-suture anchors without a change of vendor. The Single Price/Case Price Purchasing Program at the Lahey Clinic allowed the hospital to reduce its cost of orthopaedic operations by lowering the cost of operating-room supplies. This cost reduction is important in a health-care economy in which hospital revenues per unit of service or care are decreasing.
Article
A selection procedure has been developed to identify suitable commercial materials for use in compliant-layer artificial hip joints. Mechanical requirements, notably hardness and strength, as well as biocompatibility, constituted the specification for the compliant layer. Applying these constraints, candidate materials were identified in a broad range of polymeric material classes. Detailed sourcing and literature searching helped to identify materials appropriate to the application, with suitable mechanical and physical properties, as well as a history of successful clinical use. Some likely materials were identified but were prohibited from further consideration by limited commercial availability. Physical and mechanical characterization together with literature data were used to determine the relative ranking of the candidate materials and through a weighted materials property selection procedure the materials of choice were identified. The linear segmented aromatic polyurethanes, Tecothane 1085 and Estane 5714F1, emerged as the preferred materials.
Article
The major failure mode of cemented or noncemented acetabular fixation is osteolysis produced by biologic reaction to polyethylene and metallic debris. A monoblock acetabular noncemented component offers advantages in reducing the failure mechanism of acetabular cups. First, there is no extra-articular back surface polyethylene wear. Second, locking rings that may generate metallic debris are eliminated. Third, screw-holes, which decrease the surface area for ingrowth, are not needed, and pelvic entrance points for wear debris are eliminated. Fourth, an elliptical configuration allows better coaptation of the shell to the dome of the acetabulum. I have implanted >2,400 elliptical monoblock acetabular cups with a short-term follow-up of 6.5 years, with >4 years of follow-up in 840 hips. There have been no mechanical failures requiring revision. Four patients have been revised for recurrent hip instability, and one has been revised for infection. The need to convert to an acetabular component with screw fixation because of poor press-fit is <1%.
Article
Adequate initial fixation is a prerequisite for osseointegration and secondary stability of noncemented cups. Physiologic force transmission between the cup and acetabulum guarantees the best long-term fixation. To study load transfer within the natural hip joint and in the bone-implant interface of 2 different hemispherical noncemented press-fit cups, 10 hips were investigated in an experimental setup simulating single-leg stance. Load distribution and contact area were measured using prescale pressure-sensitive films and digital image analysis. Three dominant locations near the periphery of the acetabulum could be identified. Main load transfer occurs in the cranial region of the acetabulum, where it is buttressed by the iliac bone; the second location is at the posterior-inferior region at the ischial facet, and the third location is at the anterior region, where support is provided by the pubic bone. Peripheral rim contact was present in both cups but not completely circumferential. It showed marked loading at the same 3 locations similar to the natural hip joint. The ilioischial diagonal axis produced the highest press-fit. Peak local forces were found at the ischial and iliac facets. Local forces can be grouped into an iliac, an ischial, and a pubic group contributing 55%, 25%, and 20% to the total hip joint force. Pole contact was not present in the natural hip and with the biradial press-fit cup with flattened pole area but was observed with the pure hemispherical cup. Hence, stable fixation of an acetabular cup is achieved best by a 3-point-like bony support at the iliac, ischial, and pubic bone. The acetabular fovea does not provide functional support of the femoral head or endoprosthetic socket. In revision surgery, remaining peripheral bone stock at the iliac, ischial, and pubic locations allows stable implantation of primary cups.
Article
This study examined the long-term outcome of a single institution's experience with 4,289 primary total hip arthroplasties using hemispheric porous-coated cups. Initial fixation was achieved with spikes (255 AML TriSpike cups), by press-fitting with rim screws (427 Arthropor cups) or by press-fitting the component (83 Harris-Galante, 391 ACS Triloc+, 2,537 Duraloc, and 596 Pinnacle cups). Among 203 revised hips, only 18 cups were found to be loose at the time of revision. Using revision for any reason as an end point, 15-year survivorship was 82.9% +/- 5.6% (95% confidence interval) for spiked components, 71.6% +/- 8.5% for press-fit cups with adjunctive rim screws, and 72.0% +/- 12.6% for press-fit components (P<.001, log rank). Using revision for aseptic loosening as an end point, 15-year survivorship was 94.7% +/- 3.4% for spiked cups, 98.4% +/- 1.9% for press-fit cups with screws and 100% +/- 0.1% for press-fit cups. Despite an increasing incidence of polyethylene wear-related revisions, porous-coated acetabular components have demonstrated excellent long-term fixation.
Article
To evaluate different modes of cementless fixation of hemispherical cups, we operated on 87 hips in 81 patients using 4 different means of cup fixation. The hips were randomly assigned to fixation with press-fit technique only (PF), or with augmentation with screws (S), pegs (P), or hydroxyapatite (HA) coating. The patients were evaluated with radiostereometric analysis (RSA) for cup migration and wear, conventional radiography for osteolysis, and Harris Hip Score for clinical outcome over 5 years. The fixation of the cups did not differ between the groups, but HA showed a tendency to decrease proximal migration. HA-coated cups displayed the best interface with hardly any signs of radiolucent lines, indicating a superior sealing effect of the HA coating. Cups with screws or pegs had more radiolucent lines and osteolytic lesions than the other groups. Radiolucent lines were correlated to higher proximal migration, young age, and female gender (r2=.2). The wear rate of the ethylene oxide-sterilized polyethylene liner was high (0.2 mm/y) but did not differ between the groups. Two cups with a perioperative fracture of the acetabular rim showed large initial migration but stabilized thereafter.
Article
Serial radiographs of a porous tantalum monoblock acetabular cup design were evaluated for cup stability and signs of successful osteointegration. Of 574 primary consecutive total hip replacements in 542 patients performed by 9 surgeons at 7 hospitals, 414 cases were available for minimum 2-year follow-up. Follow-up averaged 33 months and ranged from 24 to 58 months. Postoperative radiographs revealed acetabular gaps in 100 zones in 80 (19%) hips: 29 in zone I, 67 in zone II, and 4 in zone III. At last follow-up, 84 (84%) of the zones with gaps completely filled in, and all 4- and 5-mm gaps filled in. There was no progression of any postoperative gap, no evidence of continuous periacetabular interface radiolucencies, no evidence of lysis, and no revisions for loosening. Although these short-term results are encouraging, further follow-up will be required to assess whether the monoblock design and the low modulus of elasticity of porous tantalum will reduce the incidence of periacetabular stress shielding and occurrence of osteolysis.
Article
The Swedish Hip Register was initiated in 1979. The mission of the register is to improve the outcome of THA. The hypothesis is that feedback of data stimulates participating clinics to reflect and improve. In addition to revision surgery, patient-based outcome measures and radiographic results are included to improve sensitivity. All patients who have a total hip arthroplasty answer a questionnaire preoperatively and again after 1, 6, and 10 years postoperatively. The questionnaire includes the Charnley classification, EQ-5D and visual analog scales concerning pain and overall satisfaction and is used by 31 of 81 units. Average costs for the procedure ($11,000) are obtained from a national database. The mean gain in the EQ-5D index after 1 year for 3900 patients was 0.37, giving a low cost of $3000 per quality adjusted life year. Patient satisfaction and pain amelioration generally was high. The national average 7-year survival (revision as endpoint), has improved from 93.5% (+/- 0.15) to 95.8 (+/- 0.15) between the two periods 1979 to 1991 and 1992 to 2003. National implant registers define the epidemiology of primary and revision surgery. In conjunction with individual subjective patient data and radiography they contribute to development of evidence-based THA surgery.
Article
Instability after primary and revision total hip arthroplasty continues to be problematic for the surgeon. The use of constrained liners, which use a locking mechanism to capture the femoral head, has increased to help manage this problem. Constrained liners, however, present problems with acetabular component loosening, dissociation of the liner/shell interface, failure by breakage, and excessive polyethylene wear. Rather than resort to constrained liners, our approach has been to restore joint stability with large-diameter femoral heads. The advantages are increased range of motion due to more favorable head/neck ratio, increased resistance to dislocation due to increased jump distance, and the avoidance of skirted femoral heads. With the addition of cross-linked polyethylene, the volumetric wear associated with large heads is much decreased and makes this a viable option today.
Article
Unlabelled: There is uncertainty regarding whether and how the subchondral bone plate should be treated during acetabular preparation for cemented cup fixation in a total hip arthroplasty. We hypothesized that removing the bone plate would improve the cement-bone interface without jeopardizing the initial cup stability, and therefore, be advantageous to long-term cup survival. We randomized 50 patients with primary osteoarthritis into two groups, one for removal and one for retention of the subchondral bone plate. The patients were evaluated during 2 years followup using repeated radiostereometric examinations, analyses of radiolucent lines, and clinical followups. Patient scoring was done using the Western Ontario and McMaster Universities Osteoarthritis Index, the Short Form-12, and the Harris hip score. Removal of the subchondral bone plate resulted in a superior cement-bone interface with less development of radiolucent lines. The radiostereometry results showed small migrations in both groups. We found no differences in cup stability between groups, although a difference was observed in rotational behavior with the removal group stabilizing in a slightly vertical position whereas the retention group showed slight but progressive rotation into a more horizontal position. No differences were found during clinical followups. Removing the subchondral bone plate, where possible, improves the cement-bone interface without jeopardizing the stability, implying better long-term cup survival. However, it is a more demanding surgical technique. Level of evidence: Therapeutic study, Level I (high quality randomized controlled trial with statistically significant difference or no statistically significant difference but narrow confidence intervals). See the Guidelines for Authors for a complete description of levels of evidence.
Article
We report a retrospective series of 106 total hip prosthesis with ten years follow-up. The purpose of this study was to analyze survival of cementless dual mobility sockets. The series included 90 consecutive patients with 106 first-intention total hip prosthesis, all with cementless dual mobility sockets. All prosthesis (Novae-1 socket and Profil-1 stem, Serf) were implanted within a 6-month period. The stainless steal socket was coated with alumina and had two short anchorage studs and a superior mooring screw and a polyethylene retentive liner. The stem had a 22.2 mm chromium cobalt head. The main indication for arthroplasty was degenerative joint disease. Mean age at implantation was 56 years (range 23-87). All patients were seen for physical examination and x-rays every two or three years. We noted cup survival at ten years (actuarial method), defining surgical revision for cup replacement due to an aseptic cause as the endpoint. Twelve patients died during the 10-year follow-up and one was lost to follow-up. The Postel-Merle d'Aubligné score improved from 7.1 preoperatively to 15.8 at ten years. There were two isolated acetabular loosenings, two intra-prosthetic dislocations due to advanced wear of the polyethylene insert. The overall survival rate of the socket was 94.6% at ten years. There were no episodes of prosthetic instability in this series. This study demonstrates the good ten-year survival of the dual mobility socket, comparable to that of conventional prostheses. The absence of any case of prosthetic instability in this series confirms the good short-term and long-term stability of the dual mobility socket. Intraprosthetic dislocation, due to loss of the polyethylene retaining ring is the main limitation of this method. The incidence was however low (2% at ten years) and treatment was not a problem. We recommend using the dual-mobility socket as the first-intention implant for patients with a high risk of post-operative instability, but also recommend it for all patients aged over 70 years since instability is the leading cause of surgical revision after this age.
Article
The optimal surface finish on cementless total hip arthroplasty is still a matter of debate. 145 hips in 130 patients with hybrid total hip arthroplasty using a hemispherical, titanium plasma-sprayed cup were followed for an average of 8.5 years. The average age was 63 years, and the average weight was 165 lb. Three hips were revised for polyethylene wear and synovitis/osteolysis. In all 3 cases, the acetabular component remained well fixed. Radiographically, 5 hips had femoral osteolysis, and 5 sockets had osteolysis in zone 2, with 4 in zone 1. There were no cases of progressive lucent lines, and no acetabular components were revised. Plasma-sprayed acetabular components remain durable up to 12 years. Moreover, in cases with wear particle overload and osteolysis, fixation was maintained at revision surgery.
Article
Total hip arthroplasty in dysplastic hips is challenging because of the modified anatomy of the proximal femur and acetabulum. We studied three-dimensional anatomic parameters in 247 dysplastic hips from 218 adult patients using radiographs and computed tomography, and analyzed the consequences for total hip arthroplasty. A cohort of 310 primary osteoarthritic hips was used as a control group. According to the classification of Crowe et al, 78 of the dislocated hips were graded Class I, 26 as Class II, 20 as Class III or IV, and 169 dysplastic hips had no subluxation. Compared with primary osteoarthritis, the intramedullary femoral canal had reduced mediolateral and anteroposterior dimensions. With high grade subluxations the femoral neck shaft angle decreased but with low grades, especially in Class II, the neck shaft angle increased. The proximal femur had more anteversion with individual variations ranging from 1 degrees to 80 degrees. The true acetabulum had a reduced anteroposterior diameter. The large individual morphologic variability across all levels of dysplastic hips suggests the femoral prosthesis cannot be chosen on the basis of the severity of the subluxation alone.
Presidential guest address: the Swedish Hip Registry: increas-ing the sensitivity by patient outcome data. Clinical Ortho-paedics and Related Research
  • H Malchau
  • G Garellick
  • T Eisler
  • J Karrholm
Malchau H, Garellick G, Eisler T, Karrholm J, Herberts P. Presidential guest address: the Swedish Hip Registry: increas-ing the sensitivity by patient outcome data. Clinical Ortho-paedics and Related Research. 2005;441:19.
The American Joint Replacement Registry Orthopaedic Nursing/National Association of Ortho-paedic Nurses
  • Ma Smith
  • Smith
  • Wt
Smith MA, Smith WT. The American Joint Replacement Registry. Orthopaedic Nursing/National Association of Ortho-paedic Nurses. 2012;31(5):296.