Aims Although bone cement is the primary mode of fixation in total knee arthroplasty (TKA), cementless fixation is gaining interest as it has the potential of achieving lasting biological fixation. By 3D printing an implant, highly porous structures can be manufactured, promoting osseointegration into the implant to prevent aseptic loosening. This study compares the migration of cementless, 3D-printed TKA to cemented TKA of a similar design up to two years of follow-up using radiostereometric analysis (RSA) known for its ability to predict aseptic loosening. Methods A total of 72 patients were randomized to either cementless 3D-printed or a cemented cruciate retaining TKA. RSA and clinical scores were evaluated at baseline and postoperatively at three, 12, and 24 months. A mixed model was used to analyze the repeated measurements. Results The mean maximum total point motion (MTPM) at three, 12, and 24 months was 0.33 mm (95% confidence interval (CI) 0.25 to 0.42), 0.42 mm (95% CI 0.33 to 0.51), and 0.47 mm (95% CI 0.38 to 0.57) respectively in the cemented group, versus 0.52 mm (95% CI 0.43 to 0.63), 0.62 mm (95% CI 0.52 to 0.73), and 0.64 mm (95% CI 0.53 to 0.75) in the cementless group (p = 0.003). However, using three months as baseline, no difference in mean migration between groups was found (p = 0.497). Three implants in the cemented group showed a > 0.2 mm increase in MTPM between one and two years of follow-up. In the cementless group, one implant was revised due to pain and progressive migration, and one patient had a liner-exchange due to a deep infection. Conclusion The cementless TKA migrated more than the cemented TKA in the first two-year period. This difference was mainly due to a higher initial migration of the cementless TKA in the first three postoperative months after which stabilization was observed in all but one malaligned and early revised TKA. Whether the biological fixation of the cementless implants will result in an increased long-term survivorship requires a longer follow-up. Cite this article: Bone Joint J 2020;102-B(8):1016–1024.
Background and purpose — The all-polyethylene tibial (APT) component, introduced in the early 1970s, was surpassed by metal-backed tibial (MBT) trays as the first choice for total knee arthroplasty (TKA). With improved polyethylene, the modern APT components can reduce costs, and have shown equivalent results in survivorship and early migration of the cruciate-retaining and cruciate-stabilizing designs. This study compares the 2-year migration of a similarly designed APT-posterior stabilized (PS) and a MBT-PS TKA, using radiostereometric analysis (RSA).Patients and methods — 60 patients were randomized to receive either an APT Triathlon PS or an MBT Triathlon PS TKA (Stryker, NJ, USA). Migration measured by RSA and clinical scores were evaluated at baseline and at 3, 12, and 24 months postoperatively. Repeated measurements were analyzed with a linear mixed model and generalized estimating equations.Results — The mean maximum total point movement (MTPM) at 3, 12, and 24 months was 0.41 mm (95% CI 0.33–0.50), 0.57 mm (0.44–0.70), and 0.56 mm (0.42–0.69) respectively in the MBT group and 0.46 mm (0.36–0.57), 0.61 mm (0.49–0.73), and 0.64 mm (0.50–0.77) in the APT group. 2 MBT and 1 APT implant were considered unstable at the 2-year follow-up. The KSS Knee score and KSS Function across 3, 12, and 24 months were comparable in both groups.Interpretation — For an APT-PS designed component, MTPM measured with RSA is comparable to the MBT-PS component after 2 years of follow-up. No differences in complications or clinical outcomes were found.
Background The number of revisions after TKA is expected to rise because of aging populations in many countries and because patients are undergoing TKA at younger ages. Aseptic loosening is a major reason for late revision, which can be predicted by radiostereometric analysis (RSA) of small groups of patients at 2 years of follow-up. RSA is therefore an ideal tool to assess new TKA designs before they are introduced to the market, although not every TKA design has been studied with RSA. If RSA-tested TKA designs have lower 10-year revision rates in national registries than non-RSA-tested TKA designs, RSA testing of all new designs could be advocated. Questions/purposes In this study, we asked: Is there a difference in the all-cause revision rate between non-RSA-tested and RSA-tested TKA designs registered in national knee arthroplasty registries at 5 and 10 years of follow-up? Methods Knee arthroplasty registries were identified through the European Federation of National Associations of Orthopaedics and Traumatology webpage and through a manual internet search. Inclusion criteria were a minimum follow-up duration of 10 years and available revision or survival data per TKA design. Twenty-six registries were identified; seven were included comprising 339 TKA designs, of which 236 designs were classified as RSA-tested and 103 as non-RSA-tested. Six registries were excluded because no report was published. One registry was excluded because no fixation method was mentioned (79 TKA designs). Another registry was excluded because there was no 10-year data available (22 non-RSA-tested designs; 10 RSA-tested designs). Eleven registries were excluded because they did not provide revision rates per design and had not reached 10 years follow-up. The revision rates with their standard errors were extracted per design. We used the data from a recent meta-analysis to identify whether a TKA design was previously tested with RSA. This meta-analysis found 53 RSA studies comprising 70 different TKA designs. The prosthesis model, fixation method and insert type were extracted from these RSA-studies. The design characteristics of the TKA reported in the knee arthroplasty registries were also extracted, and if possible, matched to the TKA designs reported in the RSA-studies. At 5 years of follow-up, 191 TKA designs were identified as non-RSA-tested and 92 were identified as RSA-tested. At 10 years of follow-up, 154 TKA designs and 74 TKA designs were classified as non-RSA-tested and RSA-tested, respectively. A random-effects model using the Metafor Package in R statistics was used to estimate the pooled revision rate at 5 and 10 years of follow-up for both groups. The difference in revision rates between groups at 5 and 10 years of follow-up was estimated by including RSA as a factor in the random-effects model. Results Mean all-cause revision rates at 5 years for non-RSA-tested and RSA-tested implants were 3.6% (95% CI 3.4 to 3.8) and 2.9% (95% CI 2.7 to 3.0), with a mean difference of 0.6% favoring RSA-tested implants (95% CI 0.4 to 0.8; p < 0.001). Mean all-cause revision rates at 10 years for non-RSA-tested and RSA-tested implants were 5.5% (95% CI 5.2 to 5.9) and 4.4% (95% CI 4.1 to 4.7), with a mean difference of 0.9% favoring RSA-tested implants (95% CI 0.4 to 1.3; p < 0.001). Conclusions Although there are exceptions, across registries, TKA designs that have been tested in an RSA setting have a slightly lower (about 1%) mean all-cause revision rate at 5-year and 10-year follow-up than those tested in a non-RSA setting. Acknowledging the inherent limitations of this observational study, a risk difference of 1% could potentially translate into an approximate 20% decrease in revision burden up to 10 years, which may have a profound impact on patient morbidity and health-related costs. Level of Evidence Level III, therapeutic study.
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