The effect of the type of cement on early revision of Charnley total hip prostheses. A review of eight thousand five hundred and seventy-nine primary arthroplasties from the Norwegian Arthroplasty Register

Acrylic bone cements: influence of time and environment on physical properties

Acrylic bone cements are in extensive use in joint replacement surgery. They are weight bearing and load transferring in the bone-cement-prosthesis complex and therefore, inter alia, their mechanical properties are deemed to be crucial for the overall outcome. In spite of adequate preclinical test results according to the current specifications (ISO, ASTM), cements with inferior clinical results have appeared on the market. The aim of this study was to investigate whether it is possible to predict the long term clinical performance of acrylic bone cement on the basis of mechanical in vitro testing. We performed in vitro quasistatic testing of cement after aging in different media and at different temperatures for up to 5 years. Dynamic creep testing and testing of retrieved cement were also performed. Testing under dry conditions, as required in current standards, always gave higher values for mechanical properties than did storage and testing under more physiological conditions. We could demonstrate a continuous increase in mechanical properties when testing in air, while testing in water resulted in a slight decrease in mechanical properties after 1 week and then levelled out. Palacos bone cement showed a higher creep than CMW3G and the retrieved Boneloc specimens showed a higher creep than retrieved Palacos. The strength of a bone cement develops more slowly than the apparent high initial setting rate indicates and there are changes in mechanical properties over a period of five years. The effect of water absorption is important for the physical properties but the mechanical changes caused by physical aging are still present after immersion in water. The established standards are in need of more clinically relevant test methods and their associated requirements need better definition. We recommend that testing of bone cements should be performed after extended aging under simulated physiological conditions. Simple quasistatic and dynamic creep tests seem unable to predict clinical performance of acrylic bone cements when the products under test are chemically very similar. However, such testing might be clinically relevant if the cements exhibit substantial differences.

Comparative finite element analysis of the debonding process in different concepts of cemented hip implants

Damage accumulation in the cement mantle and debonding of the bone-cement interface are basic events that contribute to the long-term failure of cemented hip reconstructions. In this work, a numerical study with these two process coupled is presented. Previously uniform bone-cement interface mechanical properties were only considered. In this work, a new approach assuming nonuniform and random bone-cement interface mechanical properties was applied to investigate its effect on cement degradation. This methodology was also applied to simulate and compare the degradation process of the cement and bone-cement interface in three different concepts of design: Exeter, Charnley, and ABG II stems. Nonuniform and random mechanical properties of the bone-cement interface implied a simulation closer to reality. The predicted results showed that the cement deterioration and bone-cement interface debonding is different for each implant depending on the stem geometry. Lower cement deterioration was obtained for the Charnley stem and lower bone-cement interface debonding was predicted for the Exeter stem, while the highest deterioration (cement and bone-cement interface) was produced for the ABG II stem.

A prospective randomised radiostereometric analysis trial of SmartSet HV and Palacos R bone cements in primary total hip arthroplasty

Background

Introduction of new bone cements into clinical practice should include radiostereometric studies.

Materials and methods

A prospective randomised radiostereometric study was performed, comparing SmartSet HV and Palacos R acrylic bone cements (without antibiotics) using third-generation cementing techniques in primary total hip arthroplasty. Thirty-five patients (36 hips) undergoing Charnley total hip arthroplasty were randomised to receive either of the two cements and were followed with repeated clinical, radiographic and radiostereometric examinations over 24 months. Twenty-seven patients (28 hips) attended 2 years postoperatively.

Results

The mean distal translation observed was −0.15 mm for SmartSet HV and −0.16 mm for Palacos R. The mean rotation around the longitudinal axis was 0.9° for SmartSet HV and 1.2° for Palacos R. The Merle d’Aubigne Postel score was the maximum of 18 points for all patients in both groups.

Conclusions

No statistically significant difference in stem fixation with use of SmartSet HV and Palacos R was found at 2-year follow-up.

Cementless total hip arthroplasty for primary osteoarthritis in patients aged 55 years and older

BACKGROUND

Cemented total hip arthroplasty has been the treatment of choice for elderly patients with osteoarthritis. We analyzed survival rates of the most common cementless designs used in this age group in Finland.

PATIENTS AND METHODS

Inclusion criteria permitted 10,310 replacements (8 designs) performed in patients aged 55 years or older to be selected for evaluation. The risk of revision of each of the 8 implants was compared with that of a group comprising 3 cemented designs as the reference (9,549 replacements). Survival analyses were performed overall and separately for 3 age cohorts: 55-64 years (6,781 replacements), 65-74 years (8,821 replacements), and 75 years or older (4,257 replacements).

RESULTS

In all patients aged 55 years or more, the Bi-Metric stem had a higher survival rate for aseptic loosening at 15 years than the cemented reference group: 96% (95% CI: 94-98) vs. 91% (CI: 90-92). However, the 15-year survival rates of the Bi-Metric/Press-Fit Universal (71% (CI: 67-75)) and the Anatomic Mesh/Harris-Galante II (72% (CI: 67-78)) total hip replacements were lower than that of the reference group (86% (CI: 84-87)). Information was scarce for patients aged 75 years or more.

INTERPRETATION

Cementless proximal porous-coated stems are a good option for elderly patients. Even though biological fixation is a reliable fixation method in THA, polyethylene wear and osteolysis remain a serious problem for cementless cup designs with unplugged screw holes and low-quality liners.

Cross-cultural comparison of patients undergoing ACL reconstruction in the United States and Norway

Data from large prospectively collected anterior cruciate ligament (ACL) cohorts are being utilized to address clinical questions regarding ACL injury demographics and outcomes of ACL reconstruction. These data are affected by patient and injury factors as well as surgical factors associated with the site of data collection. The aim of this article is to compare primary ACL reconstruction data from patient cohorts in the United States and Norway, demonstrating the similarities and differences between two large cohorts. Primary ACL reconstruction data from the Multicenter Orthopaedic Outcomes Network (MOON) in the United States and the Norwegian National Knee Ligament Registry (NKLR) were compared to identify similarities and differences in patient demographics, activity at injury, preoperative Knee injury and Osteoarthritis Outcome Score (KOOS), time to reconstruction, intraarticular pathology, and graft choice. Seven hundred and thirteen patients from the MOON cohort were compared with 4,928 patients from the NKLR. A higher percentage of males (NKLR 57%, MOON 52%; P < 0.01) and increased patient age (NKLR 27 years, MOON 23 years; P\0.001) were noted in the NKLR population. The most common sports associated with injury in the MOON cohort were basketball (20%), soccer (17%), and American football (14%); while soccer (42%), handball (26%), and downhill skiing (10%) were most common in the NKLR. Median time to reconstruction was 2.4 (Interquartile range [IQR] 1.2-7.2) months in the MOON cohort and 7.9 (IQR 4.2-17.8) months in the NKLR cohort (P < 0.001). Both meniscal tears (MOON 65%, NKLR 48%; P < 0.001) and articular cartilage defects (MOON 46%, NKLR 26%; P < 0.001) were more common in the MOON cohort. Hamstring autografts (MOON 44%, NKLR 63%) and patellar tendon autografts (MOON 42%, NKLR 37%) were commonly utilized in both cohorts. Allografts were much more frequently utilized in the MOON cohort (MOON 13%, NKLR 0.04%; P < 0.001). Significant diversity in patient, injury, and surgical factors exist among large prospective cohorts collected in different locations. Surgeons should investigate and consider the characteristics of these cohorts when applying knowledge gleaned from these groups to their own patient populations.

Second-generation uncemented stems: excellent 5-13-year results

INTRODUCTION

The purpose of this study was to prospectively evaluate the 5-13-year results of a cementless total hip arthroplasty with a special focus on the survivorship,occurrence of osteolysis, incidence of intraoperative femoral fractures, thigh pain, and cortical hypertrophy of the femoral stem. The femoral component used in this study was titanium fluted, slotted, symmetrical component that was prepared with intraoperative machining. The proximal third of the stem had hydroxyl-apatite coating and horizontal steps.

METHODS

The clinical and radiographical results of a consecutive series of 157 total hip arthroplasties (124 patients)with this stem were investigated. Minimum follow-up was 5 years. The average age of the patients at the time of surgery was 47 years. Three patients died and ten patients were lost to follow-up, leaving 142 hips for evaluation. The clinical result was evaluated on the basis of the Merled’Aubigné score, complications and thigh pain. A detailed radiographic analysis was performed at each follow-up visit. Kaplan–Meier survivorship analysis was performed to evaluate stem, cup, and bearing survivorship.

RESULTS

The mean follow-up was 8.5 years (range 5-13 years). The average Merle d’Aubigné score improved from 10.5 points preoperatively to 17.4 points postoperatively.The cumulative 10-year survival rate was 99% for the femoral component, 99% for the acetabular component,and 69% for the bearing. Thigh pain was identified in three patients (2%). There was no distal femoral osteolysis.Seventy-nine percent of all the hips had endosteal spot welds around the coated, proximal one-third of the prosthesis.51% had radio dense lines around the distal tip of the prosthesis,and 3% had cortical hypertrophy. One undersized stem and one cup were revised for aseptic loosening, and 25 bearings were exchanged.

CONCLUSIONS

Uncemented, machined, fluted titanium canal-filling femoral components achieve reliable fixation in this young patient population. They have a decreased incidence of activity-related thigh pain, lower rate of intraoperative femur fractures and cortical hypertrophy with comparable bone-ingrowth in comparison to other second generation uncemented femoral components described in literature. Bearing wear and the need for bearing exchange was the only limitation of these constructs.

The contribution of RCTs to quality management and their feasibility in practice

The randomized controlled trial (RCT) is generally accepted as the most reliable method of conducting clinical research. To obtain an unbiased evaluation of the effectiveness of spine surgery, patients should be randomly assigned to either new or standard treatment. The aim of the present article is to provide a short overview of the advantages and challenges of RCTs and to present a summary of the conclusions of the Cochrane Reviews in spine surgery and later published trials in order to evaluate their contribution to quality management and feasibility in practice. From the searches, 130 RCTs were included, 95 from Cochrane Reviews and systematic reviews, and 35 from additional search. No study comparing surgery with sham surgery was identified. The first RCT in spine surgery was published in 1974 and compared debridement and ambulatory treatment in tuberculosis of the spine. The contribution of RCTs in spinal surgery has markedly increased over the last 10 years, which indicates that RCTs are feasible in this field. The results demonstrate missing quality specifications. Despite the number of published trials there is conflicting or limited evidence to support various techniques of instrumentation. The only intervention that receives strong evidence is discectomy for faster relief in carefully selected patients due to lumbar disc prolapse with sciatica. For future trials, authors, referees, and editors are recommended to follow the CONSORT statement. RCTs provide evidence to support clinical opinions before implementation of new techniques, but the individual clinical experience is still important for the doctor who has to face the patient.

Fixation of the cemented stem: clinical relevance of the porosity and thickness of the cement mantle

The aim of this review paper is to define the fixation of the cemented stem. Polymethyl methacrylate, otherwise known as “bone cement”, has been used in the fixation of hip implants since the early 1960s. Sir John Charnley, the pioneer of modern hip replacement, incorporated the use of cement in the development of low frictional torque hip arthroplasty. In this paper, the concepts of femoral stem design and fixation, clinical results, and advances in understanding of the optimal use of cement are reviewed. The purpose of this paper is to help understanding and discussions on the thickness and the porosity of the cement mantle in total hip arthroplasty. Cement does not act as an adhesive, as sometimes thought, but relies on an interlocking fit to provide mechanical stability at the cement–bone interface, while at the prosthesis– cement interface it achieves stability by optimizing the fit of the implant in the cement mantle, such as in a tapered femoral stem.

Does increased bone-cement interface strength have negative consequences for bulk cement integrity? A finite element study

Implant loosening is one of the most important modes of failure of cemented total hip replacement. It may be related to the cement strength, cement-prosthesis interface, cement-bone interface, surgical technique, or stem design. The main purpose of this study is to investigate the effect of bone-cement interface mechanical properties on cement degradation. The computational methodology proposed herein combines a previously developed bone-cement interface damage model and an accumulative damage model for bulk cement. This has been applied to a finite element model of an Exeter cemented hip implant. A higher strength of the bone-cement interface due to a higher amount of interdigitated bone results in faster cement deterioration. Over time, damage both at the bone-cement interface and in the cement mantle worsens. Also, a larger debonded area was predicted proximally, as observed in clinical practice. We conclude that the computational model proposed herein allows a realistic simulation of the bone-cement interface debonding and cement degradation, being a useful tool in the design of this kind of medical devices.

Premixed antibiotic bone cement: an in vitro comparison of antimicrobial efficacy

After Food and Drug Administration (FDA) approval of premixed antibiotic bone cements (polymethylmethacrylate [PMMA]), these products are being used with increasing frequency during revision and primary hip and knee arthroplasties. To date, no studies have compared the antimicrobial efficacy of more than 2 products directly. Using a 7-day modified Kirby-Bauer assay, we assessed the in vitro antibacterial properties of 5 FDA-approved, commercially available antibiotic PMMAs. Significant differences in antimicrobial activity were noted among the antibiotic PMMA products included in this investigation. Antibacterial activity of all products tested was greatest on day 1 and rapidly diminished thereafter. Results of this investigation suggest that the antibacterial efficacies of premixed antibiotic PMMA products are not equivalent.

Efficacy of antibiotic-impregnated cement in total hip replacement

BACKGROUND AND PURPOSE

Antibiotic-impregnated cement is used as a spacer or during re-implantation surgery for the treatment of infected total hip arthroplasties. The routine use of antibiotic-impregnated cement during primary or uninfected revision total hip arthroplasty remains controversial. With this meta-analysis of the published literature, we intended to assess efficacy and safety in the use of antibiotic-impregnated cement for uninfected arthroplasty.

METHODS

Following a detailed literature search, only studies reporting on the outcome of total hip replacement performed with antibiotic cement were included. Strict inclusion criteria were used and studies lacking sufficient sample size or critical data were excluded. 19 studies reporting on 36,033 hip replacements in 35,659 patients met the initial inclusion criteria. The main aim of the meta-analysis was to determine the rate of deep infection with and without the use of antibiotic cement, and to assess the revision rate and the ultimate survivorship of arthroplasty using antibiotic cement.

RESULTS

The rate of deep infection following primary total hip arthroplasty, at 1.2%, was significantly lower when antibiotic cement was used than when cement without antibiotics was used (2.3%). Similarly, the rate of deep infection following revision total hip arthroplasty when a standard combination of cement and antibiotic--or a custom-made combination of cement and antibiotic, depending on the results of culture--was used, was almost half of the rate of deep infection when no antibiotics were present in the cement. Overall, the survivorship was 98% (101 failures in 5,178 hips) for primary arthroplasty and 88% (100 failures in 855 hips) for revision arthroplasty. There were no reported adverse events or complications associated with the use of antibiotic-impregnated cement.

INTERPRETATION

The use of antibiotic-impregnated cement lowered the infection rate by approximately 50% in primary hip arthroplasty. For revisions of previously infected hips, combinations or culture-dependent antibiotics lowered infection rates by approximately 40%.

Alternative acrylic bone cement formulations for cemented arthroplasties: present status, key issues, and future prospects

All the commercially available plain acrylic bone cement brands that are used in cemented arthroplasties are based on poly (methyl methacrylate) and, with a few exceptions, have the same constituents. It is well known that these brands are beset with many drawbacks, such as high maximum exotherm temperature, lack of bioactivity, and volumetric shrinkage upon curing. Furthermore, concerns have been raised about a number of the constituents, such as toxicity of the activator (N,N,dimethyl-p-toluidine) and possible involvement of the radiopacifier (BaSO(4) or ZrO(2) particles) in third-body wear. Thus, over the years, many research efforts have been expended to address these drawbacks, culminating in a large number of alternative formulations, which may be grouped into 16 categories. Although there are a number of reviews of the large literature that now exists on these formulations, each covers only some of the categories and none contains a detailed discussion of the germane issues. The objective of the present work, therefore, was to present a comprehensive and critical review of the whole field. In addition to succinct descriptions of the cements in each category, there are explicative summaries of literature reports, a detailed discussion of several key issues surrounding the potential for use of these cements in cemented arthroplasties, and a presentation of numerous ideas for future studies.

Static shear strength between polished stem and seven commercial acrylic bone cements

The stem-cement interface is one of the most significant sites in cemented total hip replacement and has long been implicated in failure of the whole joint system. However, shear strength at this interface has rarely been compared across a range of commercially available bone cements. The present study seeks to address this issue by carrying out a comparative study. The results indicated that the static shear strength was more dependent on cement type than cement viscosity and volume. However, both cement type and viscosity were contributory factors on porosity and micropore size in the cement surface. There was no significant difference between Simplex P and Simplex P with Tobramycin. Although the bone cements were all hand mixed in this study, the static shear strength was significantly larger than the values recorded by other researchers, and the porosity and micropore size showed much lower values. Bone cement transfer films were detected on the stem surface, typically about 4-10 mum thick. They were considered to be an important factor contributing to high friction at the stem-cement interface after initial debonding.

Development of a national cruciate ligament surgery registry: the Norwegian National Knee Ligament Registry

BACKGROUND

No prospective surveillance system exists for monitoring the outcome of cruciate ligament surgery.

PURPOSE

This article is intended to describe the development and procedures of the Norwegian National Knee Ligament Registry (NKLR), including baseline results from the first 2 years of operation.

STUDY DESIGN

Cohort study (prevalence); Level of evidence, 1.

METHODS

The NKLR was established on June 7, 2004 to collect information prospectively on all cases of cruciate ligament reconstruction surgery in Norway. Information on the details of surgery is gathered through a registration form completed by the surgeon postoperatively, and a validated knee outcome score form is completed by the patients preoperatively and at follow-ups on all patients at 2, 5, and 10 years postoperatively. Hospital compliance was examined in 2005 and 2006.

RESULTS

A total of 2793 primary cruciate ligament reconstruction surgeries were registered by 57 hospitals. This corresponds to an annual population incidence of primary anterior cruciate ligament reconstruction surgeries of 34 per 100,000 citizens (85 per 100 000 citizens in the main at-risk age group of 16-39 years). After 21 months of operation, the NKLR had an overall compliance of 97% when compared with the hospital records.

CONCLUSIONS

A national population-based cruciate ligament registry has been developed, implemented, and maintained in Norway. The registry will each year enroll approximately 1500 primary cruciate ligament reconstruction cases. It is expected that inadequate procedures and devices can be identified, as well as prognostic factors associated with good and poor outcomes, at least for the most frequent categories.

Prosthesis survival after total hip arthroplasty--does surgical approach matter? Analysis of 19,304 Charnley and 6,002 Exeter primary total hip arthroplasties reported to the Norwegian Arthroplasty Register

BACKGROUND AND PURPOSE

Controversies still exist about whether there is any effect of operative approach on survival of hip prostheses. We compared long-term survival of primary total hip arthroplasties in a well-defined study population from a national prospective population-based registry with regard to the three most commonly used surgical approaches.

METHODS

We assessed prosthesis survival according to surgical approach (the lateral with or without trochanteric osteotomy, and the posterolateral) for 19,304 Charnley and 6,002 Exeter total hip arthroplasties performed from 1987 to 2004.

RESULTS

For Charnley total hip arthroplasties, lateral approach with trochanteric osteotomy had a lower probability of revision than lateral approach without trochanteric osteotomy (RR=0.6, 95% CI: 0.5-0.8). The lower revision rate was due to fewer revisions for aseptic loosening and dislocation. The differences had declined in the latest time period (1995-2004). We observed no differences between lateral approach without trochanteric osteotomy and posterolateral approach, except that there were more revisions due to dislocation in the posterolateral approach group (RR=1.9, 95%CI: 1.1-3.2). No statistically significant differences were observed for Exeter total hip arthroplasties.

INTERPRETATION

For Charnley prostheses, the lateral approach with trochanteric osteotomy gave a reduced revision risk compared to the other approaches, which was due to fewer revisions for dislocation, and in the first time period also fewer revisions due to aseptic loosening.

A study of the Elite Plus femoral component using radiostereometric analysis

We performed a three-year radiostereometric analysis (RSA) study of the Elite Plus femoral component on 25 patients undergoing primary total hip replacement. Additional assessments and measurements from standard radiographs were also made. Subsidence of the stem occurred at the cement-stem interface. At 36 months the subsidence of the stem centroid was a mean of 0.30 mm (0.02 to 1.28), and was continuing at a slow rate. At the same time point, internal rotation and posterior migration of the femoral head had ceased. One stem migrated excessively and additional assessments suggested that this was probably due to high patient demand. The failure rate of 4% in our study is consistent with data from arthroplasty registers but contrasts with poor results from another RSA study, and from some clinical studies. We believe that the surgical technique, particularly the use of high-viscosity cement, may have been an important factor contributing to our results.

Brief ultrasonication improves detection of biofilm-formative bacteria around a metal implant

Biofilms are complex microenvironments produced by microorganisms on surfaces. Ultrasonication disrupts biofilms and may make the microorganism or its DNA available for detection. We determined whether ultrasonication could affect our ability to detect bacteria adherent to a metal substrate. A biofilm-formative Staphylococcus aureus strain was used for an in vitro implant infection model (biofilm-formative condition). We used quantitative culture and real time-polymerase chain reaction to determine the influence of different durations of ultrasound on bacterial adherence and viability. Sonication for 1 minute increased the yield of bacteria. Sonication longer than 5 minutes led to fewer bacterial colonies by conventional culture but not by polymerase chain reaction. This suggests short periods of sonication help release bacteria from the metal substrate by disrupting the biofilm, but longer periods of sonication lyse bacteria prohibiting their detection in microbiologic cultures. A relatively short duration of sonication may be desirable for maximizing detection of biofilm-formative bacteria around implants by culture or polymerase chain reaction.

The effect of middle-age body weight and physical activity on the risk of early revision hip arthroplasty: a cohort study of 1,535 individuals

BACKGROUND

Overweight and a high level of physical activity are known risk factors for loosening of a total hip arthroplasty (THA) due to primary osteoarthritis. We wanted to investigate how these factors, together with age and sex, affect the risk of revision surgery.

PATIENTS AND METHODS

We matched data from the Norwegian Arthroplasty Register with information on risk factors collected at a cardiovascular screening. We identified 1,535 primary THAs in the screened cohort (930 cemented implants using well-documented cement). Of the participants included, 969 were female. Mean age at screening was 49 years, at primary THA 63 years, and 69 years at the end of follow-up. We used Cox regression analysis to estimate relative risks (RRs). Event was defined as implant revision due to aseptic loosening of cup, stem or both. Follow-up was time from primary THA to event or censoring.

RESULTS

Men were at greater risk than women of loosening of the femoral stem (RR 2.0, 95% CI 1.3-3.2). Both men and women with upper-quartile body weight were at increased risk of revision due to loosening of the stem (RR 2.5 and 2.7, respectively). Men with a high level of physical activity during leisure time were at increased risk of revision due to loosening of the cup (RR 4.8, 95% CI 1.3-18). In the multivariate model with adjustment for activity, there was little association between age at primary THA and risk of revision due to loosening.

INTERPRETATION

We found that body weight and physical activity recorded long before THA affected the survival of total hip arthroplasties. Controlling for these variables weakened the association between age at primary surgery and aseptic loosening. Men had an increased risk of loosening of the femoral stem, also after controlling for lifestyle factors.

Time dependent mechanical properties of bone cement. Anin vitro study over one year

Changes in mechanical properties of bone cements over time are of clinical importance, but not well documented. Specifications for testing do not address the time factor. This study recorded changes in compressive properties and microstructure of one bone cement stored under simulated physiological conditions (water at 37 degrees C) from 20 min up to 1 year and in dry air at 37 degrees C for comparison. Compressive strength increased within the first week (p < 0.001), decreased at 1 month (p < 0.001), and remained at that level at 1 year. Elastic modulus showed a similar development. Maximum strain values, indicating plastic deformability, increased continuously over 1 year. Microscopy revealed microcracks between the pre-polymer beads and the matrix in specimens tested after 20 min, whereas there were less cracks in 1 year specimens. Increase in strength during the first week is due to polymerization and formation of interpenetrating molecular networks. The subsequent decrease could be due to the plasticizing effect of water uptake, as supported by higher values for dry specimens. It can be speculated that microcracks which could be initiated while reducing an arthroplasty at 15 min, acting as initiators for fatigue fractures in the cement mantle, contribute to cement failure. It is recommended that testing of bone cements should be performed after extended ageing at simulated physiological conditions, for the present cement at least 5 weeks. Results obtained at less than one week could be influenced by ongoing polymerization, as well as microcracks and lower coherence between the prepolymer beads and the matrix.

Palamed G compared with Palacos R with gentamicin in Charnley total hip replacement. A randomised, radiostereometric study of 60 HIPS

We performed a randomised, radiostereometric study comparing two different bone cements, one of which has been sparsely clinically documented. Randomisation of 60 total hip replacements (57 patients) into two groups of 30 was undertaken. All the patients were operated on using a cemented Charnley total hip replacement, the only difference between groups being the bone cement used to secure the femoral component. The two cements used were Palamed G and Palacos R with gentamicin. The patients were followed up with repeated clinical and radiostereometric examinations for two years to assess the micromovement of the femoral component and the clinical outcome. The mean subsidence was 0.18 mm and 0.21 mm, and the mean internal rotation was 1.7 degrees and 2.0 degrees at two years for the Palamed G and Palacos R with gentamicin bone cements, respectively. We found no statistically significant differences between the groups. Micromovement occurred between the femoral component and the cement, while the cement mantle was stable inside the bone. The Harris hip score improved from a mean of 38 points (14 to 54) and 36 (10 to 57) pre-operatively to a mean of 92 (77 to 100) and 91 (63 to 100) at two years in the Palamed G and Palacos R groups, respectively. No differences were found between the groups. Both bone cements provided good initial fixation of the femoral component and good clinical results at two years.

The history and future of radiostereometric analysis

Roentgen stereophotogrammetry allows one to localize the position of an object in space using roentgen rays. For orthopaedic purposes it was developed 35 years ago by Göran Selvik, and since that time many investigators have refined the radiostereometric calculations and evaluative software. Many uses and mathematical algorithms have been developed, and advancements in computer programs and digital radiography continue to expand its capabilities. Despite these advances, improvements in the technical accuracy and type of kinematic analyses possible have been relatively modest. However, radiostereometric analysis is now easier and less time consuming to use, with a resolution in clinical practice almost equal to what could only previously be obtained under ideal laboratory conditions. The ability to measure skeletal and implant movements with high resolution in vivo images was an important progressive step for the orthopaedic community. Radiostereometric analysis has helped develop new fields in clinical orthopaedic research and continues to improve advancements in orthopaedic health care.

Does cement increase the risk of infection in primary total hip arthroplasty? Revision rates in 56,275 cemented and uncemented primary THAs followed for 0-16 years in the Norwegian Arthroplasty Register

INTRODUCTION

The cementation of a total hip prosthesis may cause bone necrosis, either by direct toxicity or by generation of heat during the polymerization process. This necrotic bone may create conditions that encourage the growth of bacteria. We compared the revision rates due to infection in primary uncemented total hip arthroplasties (THAs) with those of cemented THAs with antibiotic-loaded cement and to those of cemented THAs without antibiotic cement.

METHODS

Data from the Norwegian Arthroplasty Register for the period 1987-2003 were used. To have comparable groups, we analyzed only primary THAs performed because of primary osteoarthrosis, and where both the acetabular and the femoral component of the prosthesis were either uncemented or cemented (n = 56,275).

RESULTS

In total, 252 revisions due to infection were reported. Compared to the uncemented THAs (n = 5,259), the risk of revision due to infection for THAs without antibiotic cement (n = 15,802) was increased 1.8 times (CI 1.0-3.1; p = 0.04). No differences could be detected when compared to THAs with antibiotic-loaded cement (n = 35,214) (RR 1.2, CI 0.7-2.0; p = 0.5). The average operating time for uncemented THAs was 15 min less than for cemented THAs.

INTERPRETATION

The risk of revision due to infection was the same for uncemented and for cemented arthroplasties with antibiotic-loaded cement, but higher for cemented arthroplasties without antibiotic cement. Our findings can be explained by reduced resistance to infection caused by the cement, which appears to be neutralized by adding antibiotic to the cement.

Registration completeness in the Norwegian Arthroplasty Register

INTRODUCTION

A high degree of registration completeness is necessary in order to obtain unbiased and accurate register-based study results. We investigated the completeness of registration in the national Norwegian Arthroplasty Register (NAR).

MATERIAL AND METHODS

Registration completeness for the years 1999-2002 was calculated as a percentage, with the number of joint replacements reported to the NAR as numerator and those reported to the Norwegian Patient Register (NPR) as denominator. While the NAR received information directly from the orthopedic surgeons on a voluntary basis, the NPR, which is mandatory, received information from the electronic administrative patient records of the hospitals.

RESULTS

Registration completeness in the NAR was 97% (97% for primary operations; 101% for revisions). Completeness was 98% (97%; 106%) for hip replacements, and for knee replacements it was 99% (99%; 97%). Hip and knee replacements represented 95% of all operations. However, completeness was poorer for less common joint replacements and poorest for ankle implants (82%; 40%) and wrist implants (52%; 14%). In the NAR, completeness of registration of revisions involving only removal of one or more prosthetic parts was lower than for exchange revisions for all types of joint replacement. For hip implants, 76% of the removal revisions (80% of Girdlestone procedures) were reported, and for knee implants the figure was 62%. According to NPR statistics, removal procedures accounted for 9% of all revisions of hip and knee replacements.

INTERPRETATION

In the NAR, registration completeness of hip and knee replacements was high both for primary operations and exchange revisions. For some of the less common joint replacements, completeness was low and may--if not improved--compromise prosthesis survival studies. The lower registration completeness of removal revisions also needs to be improved.

Reducing the risk of deep wound infection in primary joint arthroplasty with antibiotic bone cement

Despite significant advances in intraoperative antimicrobial procedures, deep wound infection remains the most serious complication associated with primary, cemented total joint arthroplasty. A systematic review was conducted to evaluate studies of antibiotic bone cement prophylaxis for reducing the risk of deep wound infection. The literature included 22 articles providing estimates of the prophylactic effectiveness of antibiotic cement. In reducing deep wound infection, antibiotic cement was consistently superior to plain cement, similar to systematic antiobiotics, and independent and additive in effect when combined with other prophylactic measures. Randomized controlled trials in particular had important methodological limitations. However, the collective results nearly unanimously favored prophylactic use of antibiotic cement in primary arthoplasty procedures.

Cement-implant interface gaps explain the poor results of CMW3 for femoral stem fixation: A cadaver study of migration, fatigue and mantle morphology

BACKGROUND

The Norwegian Arthroplasty Register reported that CMW3 cement performed poorly for femoral stem fixation.

METHODS

We implanted collared, satin-finished stems (Ra = 0.35 microm) into cadaver femora using CMW3 and with Simplex as control. Cement mantle function was quantified by stem migration after 300,000 cycles of "stair climbing". Cement cracks and interface gaps were quantified in transverse sections.

RESULTS

The variances of the CMW3 migrations were substantially higher than for the control (p < 0.001): subsidence for CMW3: -32 (SD 42) microm, and for Simplex: -7 (SD 9) microm (p = 0.2); retroversion for CMW3: 0.60 degrees (SD 0.25), and for Simplex: 0.37 degrees (SD 0.04) (p = 0.08). Crack length-densities were similar. CMW3 had significantly more non-apposed stem/cement interface: 52% (SD 17) versus 33% (SD 8) (p = 0.04). Migrations could be predicted by the fraction of non-apposed stem/cement interface (retroversion: R(2)=0.80, p < 0.001; subsidence: R(2) = 0.46, p = 0.02) but not by cement cracks or non-apposed cement-bone interface.

INTERPRETATION

We found that increased stem/cement non-apposition resulted in increased stem migration. Early migration is known to correlate with risk of revision. Thus, the higher stem-revision risk for CMW3 cement reported by the Norwegian Arthroplasty Register may have been due to inferior and variable stem/cement apposition.

VersaBond bone cement prospective randomized study of the clinical properties of a new bone cement in total knee replacement

VersaBond is a newly developed bone cement. To investigate its clinical performance, VersaBond was compared to Palacos R in a prospective randomized study in total knee replacement. Fifty-nine patients (61 knees) undergoing total knee replacement were randomized to either VersaBond or Palacos R bone cement and followed for 24 months using radiostereometric analysis (RSA). Up to 2 years there were no significant differences in clinical performance between the two cements. The mean/median values for implant migration were very similar for the two bone cements, as were the dispersion, and distribution of outliers. Also the proportion "stable" and "continuously migrating" implants was similar between the two cements. The result of this study indicates that VersaBond bone cement will perform at least equally as well as Palacos R in total knee replacement as regards as aseptic loosening.

Cemented or uncemented femoral component in primary total hip replacement? A review from a clinical and radiological perspective

Controversy exists regarding the optimal method of fixation for primary total hip replacement, particularly the femoral component. We performed a systematic literature review to explore whether cemented total hip replacement can achieve better clinical and radiological outcomes. A total of 29 publications were selected using computer-aided and manual searches. A qualitative comparison of results in clinical and radiological changes was then conducted. Most of the literature showed that better short-term clinical and functional outcomes could be obtained from cemented femoral fixation than from uncemented femoral fixation. Results were less clear for the mid-term clinical outcome, though in general, cemented fixation still appeared to show a superior clinical outcome. Radiographic differences are variable and do not seem to correlate with clinical findings. For the short- and mid-term, cemented femoral component is recommended. However, a long-term randomised trial combined with a large cohort study or registry is needed.

The Elite Plus total hip arthroplasty

We prospectively studied 217 patients who underwent 234 Elite Plus total hip arthroplasties. At a mean of 6.4 (SD 0.7) years post-operatively, 39 patients had died and 22 were either lost to follow-up or had no radiographs available. Clinical (Oxford hip score) and radiological assessments were performed on 156 patients (168 hip arthroplasties) who had a mean age of 67.7 (SD 9.7) years at operation.

In the assessed group, 26 of 159 (16.4%) of femoral stems which had not already been revised and 19 of 159 (11.9%) of acetabular cups were definitely loose. In total, 52 of 168 (31%) of hips had either been revised or had definite evidence of loosening of a component. We could not establish any relationship between clinical and radiological outcomes.

Despite the fact that the clinical outcome and rate of revision for the Elite Plus appeared to meet international standards, our findings give us cause for concern. We believe that joint registries should include radiological surveillance in order to provide reliable information about medium-term outcomes for hip prostheses.

Dependency issues in survival analyses of 55,782 primary hip replacements from 47,355 patients

Artificial hip joints are used in only one hip for about 85 per cent of the patients and in both hips (bilateral) for about 15 per cent of the patients. The occurrence of bilateral prostheses and the influence they have in survival analyses of joint arthroplasties are seldom considered. In this study we therefore focus on issues related to bilateral primary hip prostheses, time to revision surgery, and some commonly used statistical methods. We used information from 47,355 patients with 55,782 primary hip prostheses reported to the Norwegian Arthroplasty Register between 1987 and 2000. Due to the large number of diagnoses, fixation techniques for the prostheses, and combination of prostheses brands, we furthermore considered a 'homogeneous' subset of 8703 prostheses from 7930 patients with primary osteoarthritis, and Charnley prosthesis fixed with antibiotic-containing Palacos cement. Kaplan-Meier curves for all prostheses, ignoring that some patients have bilateral prostheses, were compared with Kaplan-Meier curves using only the first inserted prostheses, and with survival curves modified for patients with bilateral prostheses. Cox regression analyses were used to assess explanatory variables and to adjust for confounding factors. The results from the ordinary Cox regression analyses were compared with results from a marginal model, a shared gamma frailty model, and a model using a time dependent covariate to condition on failures in the opposite hip. We found no practical difference between the three calculated survival curves for the hip replacement data. The ordinary Cox-model and the marginal model gave equivalent results. In the shared gamma frailty model estimates for the risk factors were comparable with the former two approaches. The estimated frailty variance was higher when all data were used, even after adjustment for confounding factors. For the 'homogeneous' data the estimated frailty variance was negligible. Using a time dependent covariate to condition on previous revisions in the opposite hip, we found a higher risk of revision for the remaining primary hip prosthesis if the opposite hip had been revised (RR = 3.49, p < 0.0001). There was no difference in risk for revision between right and left hip prostheses. If the time interval between the two primary operations was more than two years, for the full data, the first hip prosthesis had an increased risk of revision compared to prostheses in patients with only one prosthesis (RR = 1.25, p = 0.01). For the 'homogeneous' data no statistically significant difference was found between unilateral and bilateral prostheses. A revision in one hip, for patients with bilateral prostheses, is a risk factor for revision of the other hip. Thus, in analyses of prostheses survival, dependencies between two hip prostheses from one patient should be considered. However, ignoring possible dependencies does not necessarily have an impact on the results on standard risk factors.

Total hip arthroplasty with Boneloc cement: Unsatisfactory results in 163 hips after 9 to 11 years

Boneloc bone cement was introduced in the Netherlands in 1992. Inferior short-term results were reported which led to the withdrawal of Boneloc from clinical use in 1995. However, little is known about the long-term outcome of hip arthroplasties with Boneloc. Between April 1992 and August 1994, Boneloc was used in 163 Mallory-Head primary total hip arthroplasties in 163 patients. Follow-up analysis was performed in 2003. To date, 27 hips (17%) have been revised for aseptic loosening of the femoral component. Median time to revision was 5.5 years. Survival analysis based on revision for aseptic loosening showed 77% cumulative survival at 11 years. With revision for aseptic loosening and/or definite radiological loosening according to Harris as endpoint, cumulative survival was 59% at 11 years. In 27 of 43 patients with definite radiological loosening, a cement fracture was seen at a median of 2.9 years. These results show failure of Boneloc cemented total hip arthroplasties occurring even during the later follow-up. Continuing periodic clinical and radiological examination is recommended. (Hip International 2004; 14: 229-32).

Failures and successes in total hip replacement--why good ideas may not work

The course of development of total hip replacement (THR) is neither harmonious nor linear. Progress and set-backs alternate. Progress in THR manifests itself through reductions in the number and the severity of complications (infection, aseptic loosening, prematurely worn components, etc.). Innovation is the motor of progress. However, today's innovation may well be tomorrow's revision! Progress has been achieved in part through new implant materials and designs that provide improvements in such things as stress distribution in surrounding bone, tissue compatibility and osseointegration, and resistance to both wear and cyclic fatigue. Of at least equal importance, however, are improvements achieved in operative procedures (e.g., cementing technique) and finally, in clinical quality control: more complete documentation of implant and patient variables, establishment of implant registers, and utilization of outcome studies to guide the course of further development. Causes of failure in THR are numerous. However, unexpected side effects of innovations are the most frequent cause. An innovation may solve one problem, but also creates new ones. Problems in innovation which can lead to failures include: over-generalization of expected patient responses, ignoring past experience or assigning wrong causes to encountered problems, and finally, ignoring the dynamic nature of the living system (which can be described as using "necro-" instead of biomechanical thinking). Quality control in both manufacturing and clinical practice has to be improved. The pioneer times have come to an end. Today's patients should have the right to be operated on by a well trained surgeon and to be provided with well tested, well-understood implant materials and devices. Progress in endoprosthetics has led to the present high level of clinical success. Paradoxically, however, success is the greatest obstacle to further progress. This is because the curve of progress as a result of effort expended has turned asymptotic in endoprosthetics, as it does in many endeavors. In such situations the more a product (e.g., surgical implant and procedure, automobile design, computer program) becomes successful, the more efforts (and finances) are needed for further progress. On the other hand, the "scissors"--created by crossing what might be feasible with what resources are available--open widely and can cut sharply. In fact, financial restrictions may force orthopaedic surgeons and the medical device and technology industry to turn to lower technologies in the future. However, whatever new developments in endoprosthetics may bring (be they sophistications or simplifications), we must remain open-minded and not assume things to be facts until there is evidence to support them.

The influence of cement viscosity on the early migration of a tapered polished femoral stem

It is unclear whether it is best to use high-viscosity or low-viscosity cement for fixation of total hip replacement (THR) femoral components. This study examines the influence of cement viscosity on the migration of the Exeter femoral component using roentgen stereophotogrammetric analysis (RSA). Simplex, CMW1 and CMW3 G cements were examined in a total of 46 patients over a 12-month period. The overall pattern of migration for all cohorts was one of subsidence and rotation into valgus. There was no significant difference in any aspect of migration between the groups. In vitro studies demonstrate that low-viscosity cement forms a more stable bone-cement interface. Several groups have examined the in vivo effect of cement viscosity on stem longevity with conflicting results. For a polished, tapered implant that is designed to subside, cement viscosity does not influence the 1-year migration, and it is therefore unlikely to affect long-term outcome.

Fatigue testing and performance of acrylic bone-cement materials: state-of-the-art review

Over the past three decades or so, a very large volume of literature has been generated on the impact of an assortment of variables on the fatigue lifetimes of a large number of acrylic bone-cement formulations. In the present article, this literature is examined critically to reveal areas of agreement, areas of disagreement, as well as a welter of underexplored and unexplored topics. For example, there is unanimity of support for the notion that an increase in the molecular weight of the powder constituents or the fully cured cement leads to an increase in the cement's fatigue life, whereas there is disagreement as to whether vacuum mixing the cement constituents leads to an increase in the fatigue life of the fully cured cement (relative to the hand-mixed counterpart). Among the underexplored topics is systematic study of the effect of test frequency on the fatigue results, whereas determination of the optimal concentration of the antibiotic in an antibiotic-loaded cement is an example of the unexplored topics. It is pointed out that resolving the controversies, addressing the underexplored topics, and filling the lacunae will allow comprehensive evaluations of acrylic bone-cement materials to be made. This enhanced body of knowledge will prove invaluable in the continued use of acrylic bone cement as the anchoring agent in cemented arthroplasties.

Effect of test frequency on the in vitro fatigue life of acrylic bone cement

The goal of the present work was to test the hypothesis that test frequency, f, does not have a statistically significant effect on the in vitro fatigue life of an acrylic bone cement. Uniaxial constant-amplitude tension-compression fatigue tests were conducted on 12 sets of cements, covering three formulations with three very different viscosities, two different methods of mixing the cement constituents, and two values of f (1 and 10 Hz). The test results (number of fatigue stress cycles, N(f)) were analyzed using the linearized form of the three-parameter Weibull equation, allowing the values of the Weibull mean (N(WM)) to be determined for each set. Statistical analysis of the lnN(f) data, together with an examination of the N(WM) estimates, showed support for the hypothesis over the range of f used. The principal use and explanation of the present finding are presented.

No bias of ignored bilaterality when analysing the revision risk of knee prostheses: analysis of a population based sample of 44,590 patients with 55,298 knee prostheses from the national Swedish Knee Arthroplasty Register

BACKGROUND

The current practice of the Swedish Knee Register is not to take into consideration if one or both knees in a patient are subject to surgery when evaluating risk of revision after arthroplasty. Risk calculations are typically done by statistical methods, such as Kaplan-Meier analyses and Cox's proportional hazards models, that are based on the assumption that observed events are independent, and this is rarely appreciated. The purpose of this study was to investigate if ignoring bilateral operations when using these methods biases the results.

METHODS

The bias of not taking bilateral operations into account was investigated by statistically analysing 55 298 prostheses in 44 590 patients, undergoing knee arthroplasty surgery in Sweden during 1985-1999, using traditional proportional hazards analysis, which assumes that all observations are independent, and a shared gamma frailty model, which allows patients to contribute repeated observations.

RESULTS

The effect of neglecting bilateral prostheses is minute, possibly because bilateral prosthesis failure is a rare event.

CONCLUSION

We conclude that the revision risk of knee prostheses in general can be analysed without consideration for subject dependency, at least in study populations with a relatively low proportion of subjects having experienced bilateral revisions.

Fixation of the tibial component using CMW-1 or Palacos bone cement with gentamicin: similar outcome in a randomized radiostereometric study of 51 total knee arthroplasties

We studied CMW-1 bone cement with gentamicin in the laboratory and in a randomized clinical study. Palacos bone cement containing gentamicin was used as the control. In the preclinical evaluation, the CMW cement had slightly less mechanical strength. In the clinical study, 51 patients (51 knees) operated on with total knee arthroplasty were studied for 2 years. We used radiostereometric analysis to measure migration of the tibial components, randomized to fixation with either of the two types of cement. The extent and pattern of migration were similar in both groups, and we found no differences in the number, size and extent of radiolucent lines or clinical outcome. No complications occurred. Our findings suggest a need for more studies of CMW-1 bone cement containing gentamicin in a larger cohort of patients.

Influence of cement viscosity on cement interdigitation and venous fat content under in vivo conditions: a bilateral study of 13 sheep

In a sheep model permitting standardized bilateral, simultaneous cement pressurization, we studied the effect of different cement viscosities on fat and bone marrow intravasation and cement penetration in vivo. High viscosity cement (Palacos) was used on one side and low viscosity cement (Osteopal) on the other. Catheters were inserted into both external iliac veins to collect blood during bilateral simultaneous cement pressurization. After bone preparation and pulsatile lavage, both femora were filled with cement followed by simultaneous cement pressurization. A quantitative fat analysis of the blood collected was done. We used microradiographs to determine cement penetration in a left versus right comparison of both viscosity groups. The low viscosity cement yielded lower rates of cement penetration despite adequate and sustained pressurization. Cement applied at low viscosity state seems to take the path of least resistance into the venous system before more deeper cement penetration can occur. The use of high viscosity cement ran a higher risk of fat embolism, but improved cement interdigitation.

Boneloc bone-cement: experience in hip arthroplasty during a 3-year period

Polymethyl methacrylate (PMMA) bone-cement was introduced in the 1960s for fixation of total hip arthroplasty replacement components. Long-term results of cement fixation for hip and knee arthroplasty have been extremely good. Although the use of PMMA bone-cement has enabled long-term survival of joint arthroplasty implants, there has been concern about aseptic loosening. This concern led to the introduction of Boneloc bone-cement (Biomet, Warsaw, IN) in the early 1990s. It was hoped that with the improved physical and chemical characteristics of Boneloc, there would be less aseptic loosening in the long-term. A clinical trial was conducted to evaluate Boneloc bone-cement in cementing the femoral component of the Bimetric total hip arthroplasty prosthesis in 33 hips in 32 patients. On follow-up, 7 stems (24%) developed definite loosening, and 3 stems (10%) were possibly loose. Of the 7 definite loose stems, 5 (17%) were revised because of increasing pain or progressive loosening. Despite the biologic advantages of Boneloc, this study suggests that the chemicals substituted in Boneloc bone-cement led to an alteration in its mechanical properties. These properties proved to be inferior to conventional PMMA bone-cement. There is possible time-dependent deterioration of mechanical properties leading to early aseptic loosening. The conventional PMMA bone-cement has stood the test of time. Research and experimental studies should continue to improve the mechanical properties of Boneloc before further human trials.

Results with the M. E. Müller cemented, straight-stem total hip prosthesis: a 10-year historical cohort study in 180 women

In 1986, 242 M. E. Muller (MEM) cemented, straight-stem total hip arthroplasty prostheses were implanted in 229 patients; 15 hips (13 patients) were lost to follow-up. Of the remaining 227 implants, 180 were placed in women, and 47 were placed in men (each with mean age, 71 +/- 7.7 years). After 10 years, 66 patients had died, and 152 implants were still in situ. As a result of aseptic loosening, 9 hips were revised (5 femoral and 4 acetabular components); two of these patients had a Girdlestone as a result of postoperative infection. Because 50% of the men died during follow-up, further analysis was performed with the 180 implants in women. The incidence of revision for aseptic loosening was 5.9 per 1,000 implants. The cumulative survival rate after 10 years was 94%. Survival was not influenced significantly by age, indication for operation, or having a contralateral hip prosthesis. The 10-year follow-up results for the MEM straight-stem total hip prosthesis in our hospital are satisfactory despite the probability that the cement mantle produced with this stem is not uniform in thickness.

Early failure of modern cemented stems

In the late 1970s, improved cement technique was introduced in an attempt to address the problem of early cemented stem loosening. Subsequently, numerous centers reported stem survival rates of >95% beyond 10 years. Long-term cemented stem fixation was believed widely to be consistently obtainable in most patients. Despite the widespread clinical success of these early cemented stems, numerous changes were introduced in stem design and cement technique. In more recent years, a surprising number of series of early failures of cemented stems have been reported. Some designs consistently have had a high early failure rate. Others have failed infrequently, but the failures have occurred early and with extensive osteolysis. Numerous causes have been proposed, including poor cement technique, undersized broaches, increased stem offset, decreased stem length, rough surface finish, and circular stem cross-section. Failures often are multifactorial and defy a simple explanation based on a single parameter. Results of cemented stems are more variable than previously appreciated. There are nuances of cemented stem design, cement technique, and patient selection that can lead to early failure and that are not understood completely at present. Given the availability of many cemented designs with proven records of clinical success, new design features should be introduced prudently with extensive premarket testing, limited clinical release, and careful postmarket surveillance.

The Norwegian Arthroplasty Register: 11 years and 73,000 arthroplasties

In 1985, the Norwegian Orthopaedic Association decided to establish a national hip register, and the Norwegian Arthroplasty Register was started in 1987. In January 1994, it was extended to include all artificial joints. The main purpose of the register is to detect inferior results of implants as early as possible. All hospitals participate, and the orthopedic surgeons are supposed to report all primary operations and all revisions. Using the patient's unique national social security number, the revision can be linked to the primary operation, and survival analyses of the implants are done. In general, the survival analyses are performed with the Kaplan-Meier method or using Cox multiple regression analysis with adjustment for possible confounding factors such as age, gender, and diagnosis. Survival probabilities can be calculated for each of the prosthetic components. The end-point in the analyses is revision surgery, and we can assess the rate of revision due to specific causes like aseptic loosening, infection, or dislocation. Not only survival, but also pain, function, and satisfaction have been registered for subgroups of patients. We receive reports about more than 95% of the prosthesis operations. The register has detected inferior implants 3 years after their introduction, and several uncemented prostheses were abandoned during the early 1990s due to our documentation of poor performance. Further, our results also contributed to withdrawal of the Boneloc cement. The register has published papers on economy, prophylactic use of antibiotics, patients' satisfaction and function, mortality, and results for different hospital categories. In the analyses presented here, we have compared the results of primary cemented and uncemented hip prostheses in patients less than 60 years of age, with 0-11 years' follow-up. The uncemented circumferentially porous- or hydroxyapatite (HA)-coated femoral stems had better survival rates than the cemented ones. In young patients, we found that cemented cups had better survival than uncemented porous-coated cups, mainly because of higher rates of revision from wear and osteolysis among the latter. The uncemented HA-coated cups with more than 6 years of follow-up had an increased revision rate, compared to cemented cups due to aseptic loosening as well as wear and osteolysis. We now present new findings about the six commonest cemented acetabular and femoral components. Generally, the results were good, with a prosthesis survival of 95% or better at 10 years, and the differences among the prosthesis brands were small. Since the practice of using undocumented implants has not changed, the register will continue to survey these implants. We plan to assess the mid- and long-term results of implants that have so far had good short-term results.

Effect of mixing method and storage temperature of cement constituents on the fatigue and porosity of acrylic bone cement

The influence of the storage temperature of the cement constituents prior to mixing (21 vs. 4 degrees C) and the mixing method (hand mixing vs. vacuum mixing) on the uniaxial tension-compression fatigue performance and porosity of Palacos R acrylic bone cement was studied. The fatigue results were analyzed using the three-parameter Weibull equation. The fatigue performance was expressed as an index I, which was defined as the product of the Weibull characteristic fatigue life and the square root of the Weibull slope. Statistical analyses of these results show that although the mixing method (for a given storage temperature) exerts a significant influence on the fatigue performance and areal porosity, the effect of storage temperature (for a given mixing method) on either of these parameters is not significant.

Properties of acrylic bone cement: state of the art review

Acrylic bone cement occupies a distinctive place in the hierarchy of synthetic biomaterials, because it is the only material currently used for anchoring the prosthesis to the contiguous bone in a cemented arthroplasty. However, the cement is not without its drawbacks. The main one is the role that it has been postulated to play in the aseptic loosening and, hence, clinical life of the arthroplasty. In turn, this role is directly related to the mechanical properties of the cement, especially the resistance to fracture of the cement in the mantle at the cement-prosthesis interface or the cement-bone interface. The present work is a detailed critical review of the recent literature on the properties of bone cement that are considered germane to its use in the stated application. The relevant properties are identified and a case is made for including each of them. Compilations of the values of these properties, obtained under clearly identified conditions, are presented for the six commercial formulations of bone cement in current popular orthopedic use. The gaps and unresolved questions in the current data base, efforts that should be made to address these issues, and research directions are covered.

A comparison of 2 modern femoral cementing techniques: analysis by cement-bone interface pressure measurements, computerized image analysis, and static mechanical testing

Modern cementing techniques aim to improve microinterlock and to reduce aseptic loosening. The Norwegian and Swedish Arthroplasty Registers have shown an increased risk of revision using reduced-viscosity cement. We have compared 2 modern cementing techniques using retrograde insertion of normal-viscosity and reduced-viscosity cements. Laboratory-simulated arthroplasty was performed in paired human femora. Performance was evaluated by measuring pressures generated during cementation, cement penetration, and shear strength of the prosthesis-cement and bone-cement interfaces. Large differences exist between these 2 modern techniques. Despite no statistical differences between the pressure measurements with the 2 techniques, greater penetration of reduced-viscosity cement was found proximally, with a trend toward increased penetration of the more viscous cement distally. Areas of greater cement penetration with reduced-viscosity cement proximally produced higher values of ultimate shear strength. Both techniques showed a progressive increase in the shear strength as the level of the section progressed toward the tip of the prosthesis. There is a trend with both techniques for the distal fixation to be stronger.

Long-term registration has improved the quality of hip replacement: a review of the Swedish THR Register comparing 160,000 cases

The Swedish Hip Register has defined the epidemiology of total hip replacement in Sweden. Most hip implants are fully cemented. Serious complications and rates of revision have declined significantly despite an increasing number of patients at risk. During the past 5 years, only 8-9% of hip replacements are revisions. Aseptic loosening with or without osteolysis is the major problem and constitutes 71% of the revisions, but the incidence had decreased three times during the past 15 years to less than 3% at 10 years. The effectiveness of the surgical technique is the most important factor for reducing the risk of revision because of aseptic loosening, but choice of implant is also important. In practice, total hip replacement in Sweden has improved, as judged by information from this Register about individualized patient risks, implant safety, and the greater efficacy of surgical and cementing techniques.

Mortality after total hip replacement: 0-10-year follow-up of 39,543 patients in the Norwegian Arthroplasty Register

We have studied the mortality after total hip replacement (THR) of 39,543 patients, having a mean age of 69 years, who were reported to the Norwegian Arthroplasty Register. The median follow-up time was 5.2 (0-10.4) years. 323 of 6201 deaths occurred during the first 60 postoperative days. The patient mortality was compared with the mortality in the Norwegian population, using standardized mortality ratios (SMR). The SMRs were compared and adjusted for age, gender, and other possible confounders in a Cox regression model incorporating the population mortality. We observed a lower mortality in patients with THR than in the Norwegian population (8-year patient mortality was 25%, versus 30% in the corresponding Norwegian population. SMR = 0.81). There was an increased standardized mortality ratio in patients less than 50 years (SMR = 2.50), patients 50-59 years (SMR = 1.16), patients with THR due to rheumatoid arthritis (SMR = 1.48), and patients with femoral neck fracture (SMR = 1.11). The SMR decreased with increasing age at the time of THR surgery. After revision surgery, the SMR was similar to that after the first primary operation, whereas a second primary operation in the opposite hip was associated with a further reduction in the SMR (SMR = 0.65). During the first 60 postoperative days, all patient categories had a higher mortality than the general population (0.8% mortality, SMR = 1.39).

Low-friction arthroplasty with Boneloc bone-cement: outcome at 2 to 4 years

We report the clinical and radiologic outcome of 109 Chamley low-friction arthroplasties implanted with Boneloc bone-cement (Biomet, Bridgend, South Wales, UK) into 104 patients. The mean follow-up was 30 months (range, 2-48 months). There were 72 women (mean age, 71 years) and 32 men (mean age, 72). Cartridge-packed cement was used in 37 cases and vacuum-packed cement in 72 cases. Survivorship analysis based on revision for aseptic loosening showed 79% survival at 4 years. Seventeen (15.5%) hips have been revised for aseptic loosening to date, in which all stems and 4 cups were loose. Extensive femoral osteolysis was always present and resulted in 4 cases of femoral cortical perforation at revision. Survivorship analysis based on revision and radiologic failure showed only 55% survival over the same period. When radiologic loosenings were included as failures, the vacuum-packed cement performed significantly worse than the cartridge-packed cement it replaced. These poor results were consistent with the withdrawal of Boneloc from clinical use in 1995, and we recommend indefinite follow-up for surviving prostheses.