Early revision among 12,179 hip prostheses. A comparison of 10 different brands reported to the Norwegian Arthroplasty Register, 1987-1993

Restoring global offset and lower limb length with a 3 offset option double-tapered stem

Background

A proper restoration of hip biomechanics is fundamental to achieve satisfactory outcomes after total hip arthroplasty (THA). A global hip offset (GO) postoperatively reduction of more than 5 mm was known to impair hip functionality after THA. This study aimed to verify the restoration of the GO radiographic parameter after primary THA by the use of a cementless femoral stem available in three different offset options without length changing.

Methods

From a consecutive series of 201 patients (201 hips) underwent primary cementless THA in our center with a minimum 3-year follow up, 80 patients (80 hips) were available for complete radiographic evaluation for GO and limb length (LL) and clinical evaluation with Harris hip score (HHS). All patients received the same femoral stem with three different offset options (option A with – 5 mm offset, option B and option C with + 5 mm offset, constant for each sizes) without changing stem length.

Results

Mean GO significantly increased by + 3 mm (P < 0.05) and mean LL significantly decreased by + 5 mm (P < 0.05) after surgery, meaning that postoperatively the limb length of the operated side increased by + 5 mm. HHS significantly improved from 56.3 points preoperatively to 95.8 postoperatively (P < 0.001). Offset option A was used in 1 hip (1%), B in 59 hips (74%) and C in 20 hips (25%).

Conclusions

The femur is lateralized with a mean of + 5 mm after surgery than, the native anatomy, whatever type of stem was used. Thus, the use of this 3-offset options femoral stem is effective in restoring the native biomechanical hip parameters as GO, even if 2 offset options were considered sufficient to restore GO.

Advantages and limitations of national arthroplasty registries. The need for multicenter registries: the Rempro-SBQ

While the value of national arthroplasty registries (NAR) for quality improvement in total hip arthroplasty (THA) has already been widely reported, some methodological limitations associated with observational epidemiological studies that may interfere with the assessment of safety and efficacy of prosthetic implants have recently been described in the literature.

Among the main limitations of NAR, the need for at least 80% compliance of all health institutions covered by the registry is emphasized; completeness equal or greater than 90% of all THA performed; restricted data collection; use of revision surgery as the sole criterion for outcome; and the inability of establishing a definite causal link with prosthetic dysfunction.

The present article evaluates the advantages and limitations of NAR, in the light of current knowledge, which point to the need for a broader data collection and the use of more structured criteria for defining outcomes.

In this scenario, the authors describe of idealization, conceptual and operational structure, and the project of implantation and implementation of a multicenter registry model, called Rempro-SBQ, which includes healthcare institutions already linked to the Brazilian Hip Society (Sociedade Brasileira de Quadril [SBQ]). This partnership enables the collection of more reliable and comprehensive data at a higher hierarchical level, with a significant reduction in maintenance and financing costs. The quality improvement actions supported by SBQ may enhance its effectiveness and stimulate greater adherence for collecting, storing, interpreting, and disseminating information (feedback).

Stable Fixation of a Cementless, Proximally Coated, Double Wedged, Double Tapered Femoral Stem in Total Hip Arthroplasty: A 5-Year Radiostereometric Analysis

BACKGROUND

The objective of this 5-year prospective study of 51 hips was to assess migration of a cementless tapered femoral stem using radiostereometric analysis (RSA), plain radiographs (radiolucencies), and patient-reported outcome measures (PROMs).

METHODS

Forty-seven patients (51 hips) agreed to participate in this prospective RSA study. All patients received a Taperloc stem. Tantalum beads were inserted into the femoral bone surrounding the stem to measure migration using RSA. RSA films, plain radiograph, and PROM follow-up were obtained immediately after surgery, 6 months, 1, 2, 3, and 5 years after surgery.

RESULTS

The median (interquartile range) subsidence was 0.03 mm (-0.23 to 0.06) at 5 years, with no significant differences over time. Four outlier stems had >1.5 mm of subsidence by 1 year. No stem showed radiolucencies in more than 3 zones during the 5 years. All PROMs remained favorable at 5 years, suggesting an excellent outcome. There were no stems revised for mechanical loosening; 1 stem was revised for an infection.

CONCLUSION

After initial settling, the cementless tapered femoral stems in our series were stable. The 4 outlier stems with >1.5 mm of subsidence by 1 year remain stable at 5 years. RSA was the most sensitive method of detection for stems at greater risk for potential future failure. This report adds contributions to the positive results associated with this type of fixation. The results at 5 years showed excellent midterm survivorship in this cohort with a cementless tapered femoral component.

Early subsidence of shape-closed hip arthroplasty stems is associated with late revision. A systematic review and meta-analysis of 24 RSA studies and 56 survival studies

BACKGROUND AND PURPOSE

Few studies have addressed the association between early migration of femoral stems and late aseptic revision in total hip arthroplasty. We performed a meta-regression analysis on 2 parallel systematic reviews and meta-analyses to determine the association between early migration and late aseptic revision of femoral stems.

PATIENTS AND METHODS

Of the 2 reviews, one covered early migration data obtained from radiostereometric analysis (RSA) studies and the other covered long-term aseptic revision rates obtained from survival studies with endpoint revision for aseptic loosening. Stems were stratified according to the design concept: cemented shape-closed, cemented force-closed, and uncemented. A weighted regression model was used to assess the association between early migration and late aseptic revision, and to correct for confounders. Thresholds for acceptable and unacceptable migration were determined in accordance with the national joint registries (≤ 5% revision at 10 years) and the NICE criteria (≤ 10% revision at 10 years).

RESULTS

24 studies (731 stems) were included in the RSA review and 56 studies (20,599 stems) were included in the survival analysis review. Combining both reviews for the 3 design concepts showed that for every 0.1-mm increase in 2-year subsidence, as measured with RSA, there was a 4% increase in revision rate for the shape-closed stem designs. This association remained after correction for age, sex, diagnosis, hospital type, continent, and study quality. The threshold for acceptable migration of shape-closed designs was defined at 0.15 mm; stems subsiding less than 0.15 mm in 2 years had revision rates of less than 5% at 10 years, while stems exceeding 0.15 mm subsidence had revision rates of more than 5%.

INTERPRETATION

There was a clinically relevant association between early subsidence of shape-closed femoral stems and late revision for aseptic loosening. This association can be used to assess the safety of shape-closed stem designs. The published research is not sufficient to allow us to make any conclusions regarding such an association for the force-closed and uncemented stems.

Randomized comparison between the cemented Scientific Hip Prosthesis and Omnifit: 2-year DEXA and minimum 10-year clinical follow-up

Radiostereometry (RSA) of the cemented Scientific Hip Prosthesis (SHP) reported excessive migration and predicted high failure rates. In a prospective randomized clinical trial we compared minimum 10 years results of the SHP (n=38) with the Omnifit-stem (n=37). Two-year bone remodelling, compared with dual energy x-ray absorptiometry and assessed in regions of interest A-D based on the 7 Gruen zones, showed better periprosthetic bone preservation around the SHP in all but one regions (P<.05). At 10 years Harris Hip Score was better for the SHP (P=.0001) but Oxford Hip Score was the same (P=.79). There were no revisions in either group, but radiographic loosening was definite in 1 SHP and 1 Omnifit. Based on earlier RSA studies, the rough surface finish of the SHP was expected to cause cement abrasion, osteolysis and inferior survival. However our clinical and remodelling results could not confirm these expectations, suggesting that the link of early migration and mid-term clinical results is not sufficiently clear for the SHP.

Coordinating retrieval and register studies improves postmarket surveillance

BACKGROUND

The relative risk of revision of the Titan(®) femoral stem due to aseptic loosening increased after 2000; however, the reasons for this have not been established. A retrieval analysis was initiated with the aim of delineating the failure mechanism.

QUESTIONS/PURPOSES

We asked whether aseptic loosening in stems after 2000 was associated with (1) appearance of osteolytic lesions, (2) wear particle exposure, (3) stem damage, or (4) changes to the implant or surgical instrumentation.

METHODS

Femoral stems, cement, tissue, and radiographs were collected from 28 patients. We assessed the development of osteolytic lesions in 17 patients. Exposure to wear particles was quantified in 18 patients. Stem damage was assessed in 15 patients. We observed differences in the implants by examination of 24 retrieved stems. Information concerning changes to instrumentation was requested from the manufacturer.

RESULTS

We found osteolysis in all patients receiving implants after 2000, which was associated with a median dose of cement and stem particles of 14,726/mm(2). Abrasion covered 59% of the surface of stems implanted from 1999. We identified geometric changes to the stem, the percent weight of aluminum in the stem's oxide layer decreased from 25% to 14% after 1997 and the rasp used to prepare the femoral cavity changed to a broach in 1999.

CONCLUSIONS

Stems implanted from 2000 failed through osteolysis induced by particles released from the cement and implant. Changes to implant geometry, surface oxide layer, and surgical tools occurred in the same time frame as the reduction in survivorship.

The cement mantle of femoral hip implants is more influenced by stem-broach sizing than by shape: an in vitro CT analysis of straight Charnley-Kerboul and anatomic Lubinus SPII stems

INTRODUCTION

Both, the stem shape and the implantation technique could influence the quality of the cement mantle surrounding femoral hip implants. We investigated which of these two factors is most important for the stem-cement-bone construct.

METHODS

We compared morphological data of 22 straight Charnley-Kerboul and 18 anatomic Lubinus SPII plastic replicas implanted line-to-line with the broach or one size undersized in paired cadaver femora. Specimens were CT scanned and assessed with validated segmentation software.

RESULTS

According to a general linear model, the canal-filling capacity of the stem, the cement thickness, the amount of thin and deficient cement and cortical support to areas of weak cement, were exclusively related to the implantation technique. The anatomic shape of Lubinus stems did not improve centralization or alignment.

CONCLUSION

Stem shape was the most obvious difference between Lubinus SPII and Chanrley-Kerboul implants. However, comparing both, stem-broach sizing was the most important determining factor for the cemented stem construct.

A prospective study of hip revision surgery using the Exeter long-stem prosthesis: function, subsidence, and complications for 57 patients

Background

The long-stem Exeter femoral component is commonly used in revision hip surgery. Subsidence of the femoral stem in primary hip arthroplasty has been studied extensively, but much less is known about its significance in revision surgery. This prospective study examined the relationship between radiological subsidence, Western Ontario and McMaster (WOMAC) osteoarthritis index pain score, patient satisfaction and complication rates for the long-stem Exeter hip prosthesis.

Materials and methods

Data was prospectively collected for a single-surgeon series of 96 patients undergoing revision surgery with a mean follow-up period of 36 months. Pre- and post-operative clinical evaluation was carried out using the validated WOMAC osteoarthritis index. Radiographic evaluation was carried out on magnification-adjusted digital radiographic images.

Results

Data from 57 patients were analysed. The mean rate of subsidence recorded was 0.43 mm/year, with a mean total subsidence of 0.79 mm [95% confidence interval (CI) 0.57–1.01] at 36.3 months. There was no correlation between subsidence and post-operative WOMAC score, complication rate or patient satisfaction. There was a statistically significant reduction between pre-operative and post-operative WOMAC scores, with means of 33.5 and 10.7, respectively (P < 0.001), and high patient satisfaction.

Conclusion

Our subsidence rates for long-stem revision femoral components are lower than the published data but demonstrate the same plateau. Radiographic subsidence does not appear to relate to functional outcome or complication rates in our data.

18 years of results with cemented primary hip prostheses in the Norwegian Arthroplasty Register: concerns about some newer implants

BACKGROUND AND PURPOSE

Few studies have compared the long-term survival of cemented primary total hip arthroplasties (THAs), and several prostheses have been used without adequate knowledge of their endurance. We studied long-term outcome based on data in the Norwegian Arthroplasty Register.

PATIENTS AND METHODS

The 10 most used prosthesis brands in 62,305 primary Palacos or Simplex cemented THAs reported to the Register from 1987 through 2007 were included. Survival analyses with revision as endpoint (for any cause or for aseptic loosening) were performed using Kaplan-Meier and multiple Cox regression with time-dependent covariates. Revision rate ratios (RRs) were estimated for the follow-up intervals: 0-5, 6-10, and > 10 years.

RESULTS

5 prosthesis brands (cup/stem combinations) (Charnley, Exeter, Titan, Spectron/ITH, Link IP/Lubinus SP; n = 24,728) were investigated with 0-20 year follow-up (inserted 1987-1997). After 18 years, 11% (95% CI: 10.6-12.1) were revised for any cause and 8.4% (7.7-9.1) for aseptic loosening. Beyond 10 years of follow-up, the Charnley cup had a lower revision rate due to aseptic loosening than Exeter (RR = 1.8) and Spectron (RR = 2.4) cups. For stems, beyond 10 years we did not find statistically significant differences comparing Charnley with Titan, ITH, and SP stems, but the Exeter stem had better results (RR = 05). 10 prosthesis brands (9 cups in combination with 6 stems; n = 37,577) were investigated with 0-10 years of follow-up (inserted from 1998 through 2007). The Charnley cup had a lower revision rate due to aseptic loosening than all cups except the IP. Beyond 5 years follow-up, the Reflection All-Poly cup had a 14 times higher revision rate. For stems, beyond 5 years the Spectron-EF (RR = 6.1) and Titan (RR = 5.5) stems had higher revision rates due to aseptic loosening than Charnley. The analyses also showed a marked improvement in Charnley results between the periods 1987-1997 and 1998-2007.

INTERPRETATION

We observed clinically important differences between cemented prosthesis brands and identified inferior results for previously largely undocumented prostheses, including the commonly used prosthesis combination Reflection All-Poly/ Spectron-EF. The results were, however, satisfactory according to international standards.

257 ankle arthroplasties performed in Norway between 1994 and 2005

BACKGROUND AND PURPOSE

There have been few reports on the long-term outcome of ankle replacements. The Norwegian Arthroplasty Register has been registering ankle replacements since 1994, but no analysis of these data has been published to date. Here we report data on the use of total ankle replacements and the revision rate in the Norwegian population over a 12-year period.

METHODS

We used the Norwegian Arthroplasty Register to find ankle arthroplasties performed between 1994 and 2005. Patient demographics, diagnoses, brands of prosthesis, revisions, and time trends were investigated.

RESULTS

There were 257 primary ankle replacements, 32 of which were cemented TPR prostheses and 212 of which were cementless STAR prostheses. The overall 5- year and 10-year survival was 89% and 76%, respectively. Prosthesis survival was the same for the cementless STAR prosthesis and the cemented TPR prosthesis. There was no significant influence of age, sex, type of prosthesis, diagnosis, or year of operation on the risk of revision. The incidence of ankle replacements due to osteoarthritis, but not due to inflammatory arthritis, increased over the years.

INTERPRETATION

The revision rate was acceptable compared to other studies of ankle arthroplasties, but high compared to total knee and hip arthroplasties. The overall incidence of ankle replacements increased during the study period.

Unicondylar knee replacement for primary osteoarthritis: a prospective follow-up study of 1,819 patients from the Finnish Arthroplasty Register

BACKGROUND

The choice and use of unicondylar knee arthroplasty (UKA) has gone through a nation wide resurgence at the start of the 21st century in Finland. We evaluated the population-based survival of UKA in patients with primary osteoarthritis (OA) in Finland, and the factors affecting their survival.

METHOD

The Finnish Arthroplasty Register was established in 1980. During the years 1985-2003, 1,928 primary UKAs were recorded in the register; 1,819 of these were performed for primary OA. Of these 1,819 UKAs, we selected for further analysis implants that had been used in more than 100 operations during the study period. The survival rates of UKAs were analyzed using Kaplan-Meier analysis and the Cox regression model.

RESULTS

Analysis of the whole study period showed that UKAs had a 73% (95% CI: 70-76) survival rate at 10 years, with revision for any reason as the end point. Those patients who received the Oxford menisceal bearing unicondylar (n = 1145) had a survival rate of 81% (95% CI: 72-89) at 10 years. The group that received the Miller-Galante II unicondylar (n = 330) had a 79% survival rate (95% CI: 71-87) at 10 years, whereas the Duracon (n = 196) had a survival rate of 78% (95% CI: 72-84) and the PCA (n = 146) had a survival rate of 53% (95% CI: 45-60) at 10 years. The number of UKA operations in Finland has increased markedly in recent years. At the time of operation, the mean age of the patients was 65 (38-91) years. Younger patients (<or= 65 years of age) were found to have a 1.5-fold (95% CI: 1.1-2.0; p = 0.04) increased risk of revision compared to older patients (< 65 years).

INTERPRETATION

UKA is a viable option for the treatment of unicompartmental osteoarthritis of the knee. However, patients should be made aware of the lower survival of the UKAs compared with total knee arthroplasties.

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.

Statistical analysis of failure times in total joint replacement

Time to revision is an important criterion describing the quality of implants in total joint surgery. Estimates of failure probabilities are required to inform a patient about the risk of suffering a reoperation. Also, regression models are used for comparing different prosthesis designs. Typically, patients dying before a revision are considered as censored for time to prosthesis failure. We argue that this technique is inadequate for estimation of failure probabilities and insufficient for comparison of different designs. We propose a new approach based on a competing risk model to account for concurrent mortality. We describe differences in the estimation of failure probabilities and in the interpretation of regression models for implant failure. Additionally, we introduce a random effects term in the regression model to account for potential dependencies in the failure times of bilaterally treated patients. The new approach is illustrated with fictitious data and data from an observational study conducted at a specialized hospital in Switzerland.

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.

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).

Increased migration of the SHP prosthesis: radiostereometric comparison with the Lubinus SP2 design in 40 cases

40 patients with primary arthrosis were randomized to receive either a cemented SHP (Scientific Hip Prosthesis) or Lubinus SP2 prosthesis. At 2 years radiostereometric measurements showed increased proximal migration (0.4/0.2 mm; p = 0.02) and more proximal wear (0.3/0.1 mm, p = 0.01) of the SHP socket. The SHP stem also subsided (-O.6/-0.1 mm, p<0.001) and rotated more into retroversion (2.6/0.3 degrees ) than did the SP2 design. This subsidence mainly occurred inside the cement mantle in 17 of 18 cases (13 SHP, 4 SP2), where this type of motion could be measured. The changes in bone mineral density evaluated with DEXA and the clinical results did not differ between the 2 groups. The subsidence of the SHP stem is the most pronounced so far recorded with radiostereometry in stems without a completely polished surface. This subsidence and the rotational instability imply a substantial risk of abrasive wear and increased stresses in the cement mantle.

The effect of hospital-type and operating volume on the survival of hip replacements. A review of 39,505 primary total hip replacements reported to the Norwegian Arthroplasty Register, 1988-1996

We investigated associations between the survival of total hip replacements (THRs), type of hospital and annual number of THRs per hospital. The study was based on 39,505 primary THRs reported to the Norwegian Arthroplasty Register from 45 local (n 20,756), 15 central (n 12,455) and 10 university hospitals (n 6,294) during 1988-1996. The annual number of THRs was highest at central and university hospitals, both of which are training hospitals. University hospitals were further characterized by the lowest mean annual number of THRs performed per surgeon. For cemented THRs, with adjustment for gender, age, diagnosis, surgical procedure, and annual hospital volume, the revision rates at central and university hospitals were 0.8 (95% confidence interval: 0.67-0.95) and 1.2 (CI: 1.02-1.47) times that of local hospitals, respectively. A high annual number of cemented THRs per hospital was not associated with lower revision rates. In uncemented THRs, survival results were similar in central and local hospitals, whereas the adjusted revision rate at university hospitals was 1.6 (CI: 1.13-2.19) times that of local hospitals. The adjusted 6.5 year revision probability was 12% in hospitals performing < or = 10 uncemented THRs per year (n 606), 8% in hospitals performing from 18-28 operations (n 1,378) and 5% in hospitals performing > 84 operations (n 526).

Migration, stem shape, and surface finish in cemented total hip arthroplasty

In many recent publications it was suggested that the amount of early subsidence of a femoral stem in total hip arthroplasty is indicative for later revision. In this article it is argued that stems can be designed according to alternative objectives, resulting in different shapes and surface roughness, each producing its own characteristic postoperative subsidence pattern. It was investigated whether these inherent subsidence patterns can be estimated in preclinical testing. For that purpose two stems, both without a collar, relying on cement fixation only, were compared regarding their stress transfer, migration, and induced micromotion behavior. Finite element analysis, cyclic bench testing of substitute bone reconstructions, and clinical radiostereophotogrammetric analysis were applied. The stems investigated were the Exeter, which is assumed to be a force closed fixation design, relying on subsidence under load as a method of maintaining stability, and the SHP, as a shape closed fixation design, meant to be contained by the cement mantle. Both designs were true to their design concepts in the analyses, in the sense that migrations and micromotions of the Exeter stems far exceeded those of the SHP stems. It was found that preclinical studies such as finite element analysis or bench tests give reasonable indications of in vivo postoperative behavior. It is concluded that early clinical migration values should be considered relative to stem shape and surface finish, when prediction of later revision probability is the issue.

Fixation and metal release from the Tifit femoral stem prosthesis. 5-year follow-up of 64 cases

We stratified the fixation of the femoral component in 64 hips with degenerative joint disease into 3 groups, cemented (C), proximal hydroxyapatite coating (HA) or proximal porous coating (P). All implants had the same basic design and were made of TiAIV alloy. The migration of the implants was assessed by radiostereometry. After 5 years, the mean subsidences in the cemented and porous-coated groups were 0.16 and 0.31 mm, whereas the HA-coated implants displayed a mean proximal migration of 0.1 mm. 7 stems (2 C, 1 HA, 4 P) showed a continuous subsidence (> 0.25 mm) between the 2- and 5-year follow-up. 1 porous-coated stem was revised after the 2-year follow-up, because of pain and implant failure (previously reported) and 1 cemented stem was revised after 5 years because of pain and osteolysis. In a subset of patients, all with a femoral head made of aluminum oxide, the levels of metal were determined using atomic adsorption spectrometry. Subsidence of the stem between the 2- and 5-year follow-up was associated with increased levels of aluminum in the blood at 2 years. Generation of metallic particles from abrasive wear of the stem followed by third body abrasion of the ceramic femoral head could be one explanation of this finding. 5 hips which had shown high levels of titanium and aluminum in joint fluid at the 2-year follow-up displayed increased subsidence and developed proximal radiolucencies or osteolysis at the 5-year follow up. One of these was the cemented hip which was subsequently revised.

Exeter and charnley arthroplasties with Boneloc or high viscosity cement. Comparison of 1,127 arthroplasties followed for 5 years in the Norwegian Arthroplasty Register

During the years 1991-1994, the Norwegian Arthroplasty Register recorded 1,324 primary hip arthroplasties implanted with the Boneloc cement. We have compared the survival until revision due to aseptic loosening for charnley (n 955) and Exeter (n 172) prostheses. The Boneloc cemented hips were also compared with high viscosity cemented hips implanted during the same period. In the Boneloc cemented group, the estimated probability of survival at 4.5 years of a Charnley femoral component was 74% and for an Exeter femoral component 97% (p < 0.0001). Using a Cox regression model with adjustment for age, gender, type of cement, systemic antibiotic and stratified for diagnosis, an 8 times higher risk of revision was found in Boneloc cemented Charnley femoral components than in Exeter femoral components (p < 0.0001). For the acetabular components, the difference between the Charnley and Exeter components with Boneloc cement was not statistically significant. In both the Charnley and the Exeter prostheses, the high viscosity cemented components had significantly better survival than the Boneloc cemented components. The Cox regression model showed that a Boneloc cemented Charnley femoral component had a 14 times higher risk of revision than a high viscosity cemented component (p < 0.0001), and for Exeter femoral components a 7 times higher revision risk was found in the Boneloc cemented components (p = 0.003). Our results confirm the previously reported inferior results of Charnley prostheses implanted with Boneloc cement and inferior results of Boneloc cemented Exeter prostheses as well, but less pronounced than for Charnley prostheses.

Patient-related risk factors for early revision of total hip replacements. A population register-based case-control study of 674 revised hips

In this population register-based, matched case-control study, we assessed patient-related factors and early risk of revision after total hip replacement (THR). Information was obtained via a mall survey among patients reported to the Norwegian Arthroplasty Register during the period 1987-1993. The study included 674 revised hips, as cases, and 1,343 hips with a primary operation only, as controls. Completed questionnaires were received from 81% of the 2,017 individual cases and controls. We identified a set of patient-related factors associated with poor THR prognosis. Increasing weight was a risk factor among male patients older than 67 years who were more than 1.77 m tall (p = 0.01). Smoking had no overall effect, but former heavy smokers had an increased risk of 2.8 compared to never-smokers. Alcohol intake was associated with an increased risk of dislocation. Revision due to infection was commoner among patients taking anti-diabetic drugs (OR = 14) than among patients taking no medication. An increased overall revision risk was found among patients using systemic steroids (OR = 2.8) or local pulmonary steroids (OR = 6.0). The risk also increased in male patients performing regular exercise before the primary operation (OR = 2.6), and in female patients of working-age doing heavy work (OR = 1.9).

The economic impact of failures in total hip replacement surgery: 28,997 cases from the Norwegian Arthroplasty Register, 1987-1993

The Norwegian Arthroplasty Register was established in 1987. Until January 1994, approximately 200 different implant combinations had been used in total hip replacements (THR) in Norway. About 5,500 THR were performed each year in this period with a total cost of 70 million USD per year. We analyzed the economic consequences related to the use of some inferior primary hip arthroplasties in this period. As the reference arthroplasty, we chose the most commonly used prosthesis in Norway, i.e., the Charnley prosthesis fixed with high viscosity cement containing antibiotic and with systemic antibiotic prophylaxis (n 4,970). We compared this reference group to all other primary THR registered in the same time period (n 24,027), and to the following sub-groups of primary THR: 1) uncemented Ti-Fit/ Bio-Fit (acetabulum/femur) combination (n 173), 2) uncemented Coxa/Femora combination (n 153), 3) THR with low-viscosity cement (n 1,807) and 4) THR with Boneloc cement (n 1,250). We estimated the number of additional revisions compared to the reference arthroplasty after a follow-up of 3-5 years in the different groups, with adjustment for age, sex and diagnosis. The direct extra revision costs were calculated. Compared to the reference arthroplasty, the group of all other primary THR gave an extra revision cost estimated at about 1.7 million USD per year. About 1,000 uncemented Bio-Fit femoral prostheses have been applied in Norway, including those implanted before the registration started (1985-1987). The extra revision costs the first postoperative years for these 1,000 prostheses amount to about 0.7 million USD per year. Corresponding figures in the Coxa/ Femora group were 0.08 million USD, in the group with low-viscosity cement, 0.3 million USD and in the Boneloc group, 0.4 million USD per year.