Dual Mobility Cups: Effect on Risk of Revision of Primary Total Hip Arthroplasty Due to Osteoarthritis: A Matched Population-Based Study Using the Nordic Arthroplasty Register Association Database.

BACKGROUND: The dual mobility acetabular cup (DMC) was designed to reduce prosthetic instability and has gained popularity for both primary and revision total hip arthroplasty (THA). We compared the risk of revision of primary THA for primary osteoarthritis between patients treated with a DMC and those who received a metal-on-polyethylene (MoP) or ceramic-on-polyethylene (CoP) bearing. METHODS: A search of the Nordic Arthroplasty Register Association (NARA) database identified THAs performed with a DMC during 1995 to 2013. With use of propensity score matching, 2,277 of these patients were matched (1:1), with regard to sex, age, component fixation, and year of surgery, with patients with an MoP or CoP bearing. We estimated the cumulative incidence of revision taking death as a competing risk into consideration and performed competing risk regression with revision or death as end points. RESULTS: There was no difference in the overall risk of revision between the DMC group and the propensity-score-matched MoP/CoP group (adjusted hazard ratio [HR] = 1.18; 95% confidence interval [95% CI] = 0.87 to 1.62). Patients with a DMC bearing had a lower risk of revision due to dislocation (adjusted HR = 0.09; 95% CI = 0.03 to 0.29) but a higher risk of revision caused by infection (adjusted HR = 3.20; 95% CI = 1.49 to 6.85). CONCLUSIONS: There was no difference in overall risk of revision between the DMC and MoP/CoP groups. The DMCs protected against revision due to dislocation but THAs performed with this bearing were more commonly revised because of infection. There may have been a selection bias toward placing DMC implants in patients with greater frailty as the mortality rates were higher in the DMC group than in the age and sex-matched MoP/CoP group. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Better survival of hybrid total knee arthroplasty compared to cemented arthroplasty.

BACKGROUND AND PURPOSE: There have been few comparative studies on total knee replacement (TKR) with cemented tibia and uncemented femur (hybrid TKR). Previous studies have not shown any difference in revision rate between cemented and hybrid fixation, but these studies had few hybrid prostheses. We have evaluated the outcome of hybrid TKR based on data from the Norwegian Arthroplasty Register (NAR). PATIENTS AND METHODS: We compared 4,585 hybrid TKRs to 20,095 cemented TKRs with risk of revision for any cause as the primary endpoint. We included primary TKRs without patella resurfacing that were reported to the NAR during the years 1999-2012. To minimize the possible confounding effect of prosthesis brands, only brands that were used both as hybrids and cemented in more than 200 cases were included. Kaplan-Meier survival analysis and Cox regression analysis were done with adjustment for age, sex, and preoperative diagnosis. To include death as a competing risk, cumulative incidence function estimates were calculated. RESULTS: Estimated survival at 11 years was 94.3% (95% CI: 93.9-94.7) in the cemented TKR group and 96.3% (CI: 95.3-97.3) in the hybrid TKR group. The adjusted Cox regression analysis showed a lower risk of revision in the hybrid group (relative risk = 0.58, CI: 0.48-0.72, p < 0.001). The hybrid group included 3 brands of prostheses: LCS classic, LCS complete, and Profix. Profix hybrid TKR had lower risk of revision than cemented TKR, but the LCS classic and LCS complete did not. Kaplan-Meier estimated survival at 11 years was 96.8% (CI: 95.6-98.0) in the hybrid Profix group and 95.2% (CI: 94.6-95.8) in the cemented Profix group. Mean operating time was 17 min longer in the cemented group. INTERPRETATION: Survivorship of the hybrid TKR at 11 years was better than that for cemented TKR, or the same, depending on the brand of prosthesis. Hybrid fixation appears to be a safe and time-efficient alternative to cemented fixation in total knee replacement surgery.

Increased risk of revision of cementless stemmed total hip arthroplasty with metal-on-metal bearings.

BACKGROUND AND PURPOSE: Data from the national joint registries in Australia and England and Wales have revealed inferior medium-term survivorship for metal-on-metal (MoM) total hip arthroplasty (THA) than for metal-on-polyethylene (MoP) THA. Based on data from the Nordic Arthroplasty Register Association (NARA), we compared the revision risk of cementless stemmed THA with MoM and MoP bearings and we also compared MoM THA to each other. PATIENTS AND METHODS: We identified 32,678 patients who were operated from 2002 through 2010 with cementless stemmed THA with either MoM bearings (11,567 patients, 35%) or MoP bearings (21,111 patients, 65%). The patients were followed until revision, death, emigration, or the end of the study period (December 31, 2011), and median follow-up was 3.6 (interquartile range (IQR): 2.4-4.8) years for MoM bearings and 3.4 (IQR: 2.0-5.8) years for MoP bearings. Multivariable regression in the presence of competing risk of death was used to assess the relative risk (RR) of revision for any reason (with 95% confidence interval (CI)). RESULTS: The cumulative incidence of revision at 8 years of follow-up was 7.0% (CI: 6.0-8.1) for MoM bearings and 5.1% (CI: 4.7-5.6) for MoP bearings. At 6 years of follow-up, the RR of revision for any reason was 1.5 (CI: 1.3-1.7) for MoM bearings compared to MoP bearings. The RR of revision for any reason was higher for the ASR (adjusted RR = 6.4, CI: 5.0-8.1), the Conserve Plus (adjusted RR = 1.7, CI: 1.1-2.5) and "other" acetabular components (adjusted RR = 2.4, CI: 1.5-3.9) than for MoP THA at 6 years of follow-up. INTERPRETATION: At medium-term follow-up, the survivorship for cementless stemmed MoM THA was inferior to that for MoP THA, and metal-related problems may cause higher revision rates for MoM bearings with longer follow-up.

Hip replacement surgery in patients with ankylosing spondylitis.

OBJECTIVES: Although TNF-α inhibitors' striking effect on clinical symptoms have revolutionised the treatment of ankylosing spondylitis (AS), no certain influence on the development of spinal ankylosis and joint destruction has been documented. We wished to investigate whether improved treatment has affected the use of hip arthroplasty surgery. METHODS: Using the Norwegian Arthroplasty Register, we selected hip prosthesis procedures performed in patients with AS in 1988-2010 (n=534), and compared the trend in the number of procedures being performed annually in 1988-2002 versus 2003-2010. Patients with osteoarthritis (OA) (n=95094) were used as a control group. RESULTS: The frequency of hip prosthesis surgery increased significantly in both groups up until 2002. In 2003-2010, although not statistically significant (p=0.087), there was a trend towards a reduced frequency in the AS group when compared with the expected continued increase as was seen among patients with OA. Mean age at surgery increased significantly (p<0.001) from 49.9 years to 56.4 years when comparing patients with AS up until and after 2002. CONCLUSIONS: TNF-α inhibitors were introduced to patients with AS in Norway in 2000-2003, and our findings suggest that they may have altered the prognosis by inhibiting or slowing large joint arthritis and thus reducing the need for hip replacement surgery.

TRIGEN INTERTAN intramedullary nail versus sliding hip screw: a prospective, randomized multicenter study on pain, function, and complications in 684 patients with an intertrochanteric or subtrochanteric fracture and one year of follow-up.

BACKGROUND: Both intramedullary nails and sliding hip screws are used with good results in the treatment of intertrochanteric and subtrochanteric fractures. The aim of our study was to assess whether use of the TRIGEN INTERTAN nail, as compared with a sliding hip screw, resulted in less postoperative pain, improved functional mobility, and reduced surgical complication rates for patients with an intertrochanteric or subtrochanteric fracture. METHODS: In a prospective, randomized multicenter study, 684 elderly patients were treated with the INTERTAN nail or with a sliding hip screw with or without a trochanteric stabilizing plate. The patients were assessed during their hospital stay and at three and twelve months postoperatively. A visual analogue scale (VAS) pain score was recorded at all time points, and functional mobility was assessed with use of the timed Up & Go test. The Harris hip score (HHS) was used to assess hip function more specifically. Quality of life was measured with the EuroQol-5D (EQ-5D). Radiographic findings as well as intraoperative and postoperative complications were recorded and analyzed. RESULTS: Patients treated with an INTERTAN nail had slightly less pain at the time of early postoperative mobilization (VAS score, 48 versus 52; p = 0.042), although this did not influence the length of the hospital stay and there was no difference at three or twelve months. Regardless of the fracture and implant type, functional mobility, hip function, patient satisfaction, and quality-of-life assessments were comparable between the groups at three and twelve months. The numbers of patients with surgical complications were similar for the two groups (twenty-nine in the sliding-hip-screw group and thirty-two in the INTERTAN group, p = 0.67). CONCLUSIONS: INTERTAN nails and sliding hip screws are similar in terms of pain, function, and reoperation rates twelve months after treatment of intertrochanteric and subtrochanteric fractures.

Sliding hip screw versus IM nail in reverse oblique trochanteric and subtrochanteric fractures. A study of 2716 patients in the Norwegian Hip Fracture Register.

BACKGROUND: Intramedullary nailing is commonly recommended as the treatment of choice for transverse/reverse oblique trochanteric (AO/OTA type A3=intertrochanteric) and subtrochanteric fractures. However, only to a limited extent is this approach supported by superior results in well designed clinical trials, and the sliding hip screw (SHS) is still a frequently used implant for these fractures. The aim of the present study was to compare IM nails and SHS in the treatment of transverse/reverse oblique trochanteric and subtrochanteric fractures using data from the Norwegian Hip Fracture Register (NHFR). METHODS: Data on 2716 operations for acute transverse/reverse oblique trochanteric or subtrochanteric fractures were collected from the NHFR from 2005 to 2010. Surgeons reported patient characteristics and details from initial surgery and reoperations, and patients answered questionnaires about pain, satisfaction, and quality of life (EQ-5D) 4, 12, and 36 months postoperatively. Reoperation rates were calculated using Kaplan-Meier analyses. Primary outcome measures were pain (Visual Analogue Scale (VAS)), satisfaction (VAS), quality of life (EQ-5D), and reoperation rates at one year. RESULTS: The treatment groups were similar regarding age, gender, ASA-class, cognitive impairment, and preoperative EQ-5Dindex score. At one year reoperation rates were 6.4% and 3.8% for SHS and IM nails, respectively (p=0.011). Patients treated with SHS also had slightly more pain (VAS 30 vs. 27, p=0.037) and were less satisfied (VAS 31 vs. 36, p=0.003) compared to patients treated with IM nail. There was no statistically significant difference in the EQ-5Dindex score, but the mobility was significantly better for the IM nail group. CONCLUSION: 12 months postoperatively patients with transverse/reverse oblique trochanteric and subtrochanteric fractures operated with a SHS had a higher reoperation rate compared to those operated with an IM nail. Small differences regarding pain, satisfaction, quality of life, and mobility were also in favour of IM nailing. Consequently, a change in our treatment strategy for these fractures could be considered.

Intramedullary nails result in more reoperations than sliding hip screws in two-part intertrochanteric fractures.

BACKGROUND: Sliding hip screws (SHSs) and intramedullary (IM) nails are well-documented implants for simple two-part intertrochanteric fractures; however, there is no consensus regarding which type of implant is better. QUESTIONS/PURPOSES: We asked whether patients with simple two-part intertrochanteric fractures treated with IM nailing had (1) a lower reoperation rate and (2) less pain and better quality of life than patients treated with SHSs. METHODS: We used data from the Norwegian Hip Fracture Register on 7643 operations for simple two-part intertrochanteric fractures (AO/OTA Type A1) treated with an SHS (n=6355) or an IM nail (n=1288) between 2005 and 2010. Kaplan-Meier analysis was used to assess reoperation percentages and a Cox regression model was used to assess the risk of reoperation. Questionnaires regarding pain and quality of life were answered by the patients at 4, 12, and 36 months postoperatively. RESULTS: We found an increased risk of reoperation after IM nailing within 1 postoperative year: 2.4% and 4.2% for SHS and IM nails, respectively. The difference persisted with time: 4.5% and 7.1% at 3 years. We also found minor differences for pain and quality of life which we judged clinically unimportant. CONCLUSIONS: Based on our findings and a critical review of the literature, we suggest an SHS is likely the preferred implant for simple two-part intertrochanteric fractures. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

A randomized study on migration of the Spectron EF and the Charnley flanged 40 cemented femoral components using radiostereometric analysis at 2 years.

BACKGROUND AND PURPOSE: We performed a randomized study to determine the migration patterns of the Spectron EF femoral stem and to compare them with those of the Charnley stem, which is regarded by many as the gold standard for comparison of implants due to its extensive documentation. PATIENTS AND METHODS: 150 patients with a mean age of 70 years were randomized, single-blinded, to receive either a cemented Charnley flanged 40 monoblock, stainless steel, vaquasheen surface femoral stem with a 22.2-mm head (n = 30) or a cemented Spectron EF modular, matte, straight, collared, cobalt-chrome femoral stem with a 28-mm femoral head and a roughened proximal third of the stem (n = 120). The patients were followed with repeated radiostereometric analysis for 2 years to assess migration. RESULTS: At 2 years, stem retroversion was 2.3° and 0.7° (p < 0.001) and posterior translation was 0.44 mm and 0.17 mm (p = 0.002) for the Charnley group (n = 26) and the Spectron EF group (n = 74), respectively. Subsidence was 0.26 mm for the Charnley and 0.20 mm for the Spectron EF (p = 0.5). INTERPRETATION: The Spectron EF femoral stem was more stable than the Charnley flanged 40 stem in our study when evaluated at 2 years. In a report from the Norwegian arthroplasty register, the Spectron EF stem had a higher revision rate due to aseptic loosening beyond 5 years than the Charnley. Initial stability is not invariably related to good long-term results. Our results emphasize the importance of prospective long-term follow-up of prosthetic implants in clinical trials and national registries and a stepwise introduction of implants.

Hip arthroplasty in Norway 1989-2008.

BACKGROUND: Since information on regional variation in the frequency of primary total hip arthroplasty in Norway is scarce, we studied differences by county and regional health authority throughout the last 20 years. MATERIAL AND METHODS: We included 112, 514 primary total hip arthroplasties reported to the Norwegian Arthroplasty Register in the years 1989-2008. Annual gender and age standardized frequencies were calculated, and Poisson regression was used for group comparisons (RR = rate ratio). RESULTS: We observed an increase in hip arthroplasty frequency from 109 operations per 100, 000 inhabitants in the years 1991-1995 to 140 in 2006-2008 (RR = 1.28), and more so for operations performed due to coxarthrosis (RR = 1.46). An increased frequency over time was evident in all five regions and 19 counties. Differences between counties and regions had decreased throughout the study period. In the years 2006-2008, Helse Midt (152 operations) had a statistically significant higher frequency than the other regions except for Helse Sør. The lowest frequencies at county level were found for Finnmark (116 operations) and the highest for Aust-Agder (172). INTERPRETATION: While regional differences have decreased since the early 1990 s, existing differences may in part be due to differing access to surgery, varying indications for surgery, or possibly also genetic or cultural differences.

Failure of total knee arthroplasty with or without patella resurfacing.

BACKGROUND AND PURPOSE: Patella resurfacing during primary total knee arthroplasty (TKA) is disputed and new prosthesis designs have been introduced without documentation of their survival. We assessed the impact on prosthesis survival of patella resurfacing and of prosthesis brand, based on data from the Norwegian Arthroplasty Register. PATIENTS AND METHODS: 5 prosthesis brands in common use with and without patella resurfacing from 1994 through 2009 were included n = 11,887. The median follow-up times were 9 years for patella-resurfaced implants and 7 years for implants without patella resurfacing. For comparison of prosthesis brands, also brands in common use with only one of the two treatment options were included in the study population (n = 25,590). Cox regression analyses were performed with different reasons for revision as endpoints with adjustment for potential confounders. RESULTS: We observed a reduced overall risk of revision for patella resurfaced (PR) TKAs, but the statistical significance was borderline (RR = 0.84, p = 0.05). At 15 years, 92% of PR and 91% of patella non resurfaced (NR) prostheses were still unrevised. However, PR implants had a lower risk of revision due to pain alone (RR = 0.1, p < 0.001), but a higher risk of revision due to loosening of the tibial component (RR = 1.4, p = 0.03) and due to a defective polyethylene insert (RR = 3.2, p < 0.001). At 10 years, the survival for the reference NR brand AGC Universal was 93%. The NR brands Genesis I, Duracon, and Tricon (RR = 1.4-1.7) performed statistically significantly worse than NR AGC Universal, while the NR prostheses e.motion, Profix, and AGC Anatomic (RR = 0.1-0.7), and the PR prostheses NexGen and AGC Universal (RR = 0.4-0.5) performed statistically significantly better. LCS, NexGen, LCS Complete (all NR), and Tricon, Genesis I, LCS, and Kinemax (all PR) showed no differences in this respect from the reference brand. A lower risk of revision (crude) was found for TKAs performed after 2000 as compared to those performed earlier (RR = 0.8, p = 0.001). INTERPRETATION: Although revision risk was similar for PR and NR TKAs, we found important differences in reasons for revision. Our results also indicate that survivorship of TKAs has improved.

Pain and function in patients after primary unicompartmental and total knee arthroplasty.

BACKGROUND: Unicompartmental knee arthroplasty has received renewed interest; however, its short-term advantages over total knee arthroplasty should be weighed against a higher risk of reoperation. Information regarding pain and function after unicompartmental and total knee arthroplasty is therefore needed. METHODS: Patient-reported data regarding pain and function were collected, at least two years postoperatively and by way of postal questionnaire, from 1344 patients who were listed on the Norwegian Arthroplasty Register as having had an unrevised primary total knee arthroplasty (972 patients) or a unicompartmental knee arthroplasty (372 patients) for the treatment of arthritis. Outcomes were assessed (with a score of zero indicating the worst possible outcome and a score of 100 indicating the best possible outcome) with use of the five subscales from the Knee Injury and Osteoarthritis Outcome Score, the scores from visual analog scales regarding degree of pain and satisfaction with the surgery, and the change in index score (from preoperative to postoperative) on the EuroQol-5D health-related quality-of-life instrument. We also used all forty-two questions from the Knee Injury and Osteoarthritis Outcome Score as outcome measures. To be regarded as clinically significant, the differences needed to be eight units for the Knee Injury and Osteoarthritis Outcome Score outcomes, ten units for the pain and satisfaction scales, and 0.4 unit for the detailed Knee Injury and Osteoarthritis Outcome Score questions. RESULTS: Unicompartmental knee implants performed better than total knee implants on the Knee Injury and Osteoarthritis Outcome subscales for "Symptoms" (adjusted mean difference, 2.7; p = 0.04), "Function in Daily Living" (adjusted mean difference, 4.1; p = 0.01), and "Function in Sport and Recreation" (adjusted mean difference, 5.4; p = 0.006). Of the forty-two analyses of the detailed questions, four differences were significant. These differences were in favor of unicompartmental knee arthroplasty, but only the question "Can you bend your knee fully?" reached the level of clinical significance. CONCLUSIONS: We found only small or no differences in pain and function between the scores, at least two years following surgery, of patients who underwent unicompartmental knee arthroplasty and those of patients who underwent total knee arthroplasty; however, patients with unicompartmental knee implants had fewer problems with activities that involved bending the knee.

Does patella resurfacing really matter? Pain and function in 972 patients after primary total knee arthroplasty.

BACKGROUND AND PURPOSE: Resurfacing of the patella during primary total knee arthroplasty (TKA) is often recommended based on higher revision rates in non-resurfaced knees. As many of these revisions are insertions of a patella component due to pain, and since only patients with a non-resurfaced patella have the option of secondary resurfacing, we do not really know whether these patients have more pain and poorer function. The main purpose of the present paper was therefore to assess pain and function at least 2 years after surgery for unrevised primary non-resurfaced and resurfaced TKA, and secondary among prosthesis brands. METHODS: Information needed to calculate subscales from the knee injury and osteoarthritis outcome score (KOOS) was collected in a questionnaire given to 972 osteoarthritis patients with intact primary TKAs that had been reported to the Norwegian Arthroplasty Register. Pain and satisfaction on visual analog scales and improvement in EQ-5D index score DeltaEQ-5D) were also used as outcomes. Outcomes were measured on a scale from 0 to 100 units (worst to best). To estimate differences in mean scores, we used multiple linear regression with adjustment for possible confounders. RESULTS: We did not observe any differences between resurfacing and non-resurfacing in any outcome, with estimated differences of 0.4. There was, however, a tendency of better results for the NexGen implant as compared to the reference brand AGC for symptoms (difference = 4.9, p = 0.05), pain (VAS) (difference = 8.3, p = 0.004), and satisfaction (VAS) (difference = 7.9, p = 0.02). However, none of these differences reached the stated level of minimal perceptible clinical difference. INTERPRETATION: Resurfacing of the patella has no clinical effect on pain and function after TKA. Differences between the brands investigated were small and they were assumed to be of minor importance.

Patient satisfaction, pain, and quality of life 4 months after displaced femoral neck fractures: a comparison of 663 fractures treated with internal fixation and 906 with bipolar hemiarthroplasty reported to the Norwegian Hip Fracture Register.

BACKGROUND: Primary arthroplasty and internal fixation are the two main options for treatment of displaced femoral neck fractures. Despite the fact that there have been several randomized studies, the optimal treatment in the elderly is still controversial. In the present study, based on data from the Norwegian Hip Fracture Register, we compared satisfaction, pain, and quality of life 4 months after surgery in patients over 70 years of age with a displaced femoral neck fracture operated with internal fixation or with a bipolar hemiarthroplasty. PATIENTS AND METHODS: Data on 1,569 fractures in patients over 70 years of age operated with internal fixation (n = 663) or hemiarthroplasty (n = 906) were registered in the hip fracture register. The register also included data on patient satisfaction, pain, and quality of life (EQ-5D) assessed 4 months after surgery using VAS scales and EQ-5D health questionnaires. RESULTS: Patients operated with hemiarthroplasty had less pain (VAS 27 vs. 41), were more satisfied with the result of the operation (VAS 33 vs. 48), and had better EQ-5D index score 4 months postoperatively (0.51 vs. 0.42) than patients who were operated with internal fixation. INTERPRETATION: Our findings suggest that elderly patients with displaced femoral neck fracture should be treated with arthroplasty.

Total hip replacement after femoral neck fractures in elderly patients : results of 8,577 fractures reported to the Norwegian Arthroplasty Register.

BACKGROUND: A total hip arthroplasty (THA) is often used as treatment for failed osteosynthesis of femoral neck fractures and is now also used for acute femoral neck fractures. To investigate the results of THA after femoral neck fractures, we used data from the Norwegian Arthroplasty Register (NAR). PATIENTS AND METHODS: The results of primary total hip replacements in patients with acute femoral neck fractures (n = 487) and sequelae after femoral neck fractures (n = 8,090) were compared to those of total hip replacements in patients with osteoarthrosis (OA) (n = 55,109). The hips were followed for 0-18 years. The Cox multiple regression model was used to construct adjusted survival curves and to adjust for differences in sex, age, and type of cement among the diagnostic groups. Separate analyses were done on the subgroups of patients who were operated with Charnley prostheses. RESULTS: The survival rate of the implants after 5 years was 95% for the patients with acute fractures, 96% for the patients with sequelae after fracture, and 97% for the OA patients. With adjustment for age, sex, and type of cement, the patients with acute fractures had an increased risk of revision compared to the OA patients (RR 1.6, 95% CI: 1.0-2.6; p = 0.05) and the sequelae patients had an increased risk of revision (RR 1.3, 95% CI: 1.2-1.5; p < 0.001). Sequelae hips had higher risk of revision due to dislocation (RR 2.0, 95% CI: 1.6-2.4; p < 0.001) and periprosthetic fracture (RR 2.2, 95% CI: 1.5-3.3; p < 0.001), and lower risk of revision due to loosening of the acetabular component (RR 0.72, 95% CI; 0.57-0.93; p = 0.01) compared to the OA patients. The increased risk of revision was most apparent for the first 6 months after primary operation. INTERPRETATION: THA in fracture patients showed good results, but there was an increased risk of early dislocations and periprosthetic fractures compared to OA patients.

Conversion from failed hemiarthroplasty to total hip arthroplasty: a Norwegian Arthroplasty Register analysis of 595 hips with previous femoral neck fractures.

BACKGROUND AND PURPOSE: Conversion total hip replacement (THR) is a common procedure after failed hemiarthroplasty, but there have been few reports describing the long-term outcome of this procedure. PATIENTS AND METHODS: Between 1987 and 2004, 595 THRs were reported to the Norwegian Arthroplasty Register as conversion THR for failed hemiarthroplasty after a femoral neck fracture in patients aged 60 years and older. 122 operations left the femoral stem intact, whereas 473 were converted with exchange of the femoral stem. RESULTS: We found a lower risk of failure (revision surgery for any reason) for the conversion procedures with stem exchange (RR=0.4; 95% CI: 0.25-0.81) than for the conversion procedures that retained the femoral stem. For the 473 conversion arthroplasties with exchange of the stem, we found no difference in risk of failure compared to all revision stems in the register, either for the complete prosthesis (RR=0.8; CI: 0.50- 1.20) or for the stem (RR=0.9; CI: 0.53-1.59). However, for the 122 conversion procedures in which the femoral stem was retained, we found a significantly increased risk of failure for both the complete prosthesis (RR=4.6; CI: 2.8-7.6) and for the acetabular cup (RR=4.8; CI: 2.3-10) compared to primary hip arthroplasties. INTERPRETATION: Our findings indicate that the seemingly easy operation of implanting an acetabular cup to convert a hemiarthroplasty to a total hip arthroplasty is an uncertain procedure and that the threshold for replacing the stem should be low.

Cost-effectiveness of unicompartmental and total knee arthroplasty in elderly low-demand patients. A Markov decision analysis.

BACKGROUND: Interest in unicompartmental knee arthroplasty has recently increased in the United States, making a firm understanding of the indications for this procedure important. The purpose of this study was to examine the cost-effectiveness of unicompartmental knee arthroplasty compared with total knee arthroplasty in elderly low-demand patients. METHODS: A Markov decision model was used to evaluate the cost-effectiveness of unicompartmental knee arthroplasty as compared with total knee arthroplasty in the elderly population. Transition probabilities were estimated from the Norwegian Arthroplasty Register and the arthroplasty literature, and costs were based on the average Medicare reimbursement for unicompartmental, tricompartmental, and revision knee arthroplasties. Outcomes were measured in quality-adjusted life-years. RESULTS: Our model showed unicompartmental knee arthroplasty to be a cost-effective strategy for this population as long as the annual probability of revision is <4%. The cost of unicompartmental knee arthroplasty must be greater than $13,500 or the cost of total knee arthroplasty must be less than $8500 before total knee arthroplasty becomes more cost-effective. CONCLUSIONS: Our model suggests that, on the basis of currently available cost and outcomes data, unicompartmental knee arthroplasty and total knee arthroplasty have similar cost-effectiveness profiles in the elderly low-demand patient population. However, several important parameters that could alter the cost-effectiveness analysis were identified; these included implant survival rates, costs, perioperative mortality and infection rates, and utility values achieved with each procedure. The thresholds identified in this study may help decision-makers to evaluate the cost-effectiveness of each strategy as further research characterizes the variables associate with unicompartmental and total knee arthroplasties and may be helpful for designing future appropriate clinical trials.

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.