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Purpose Research has shown that a cemented mobile-bearing component has a favorable effect on the bone mineral density (BMD) of the distal femur at 2 years after total knee arthroplasty (TKA). This study was performed to determine whether the advantage on BMD of a cemented mobile-bearing TKA over a conventional cemented fixed-bearing TKA changes with time. This report is an update of a matched cohort study initiated in 2004 and for which the 2-year results have been published. Methods Twenty-eight knees that were treated with a fixed-bearing posterior stabilized (PS) prosthesis and 28 matched knees from a database of 76 knees that were treated with a mobile-bearing PS prosthesis in the same period were investigated. All knees underwent dual-energy X-ray absorptiometry (DEXA) scans around the femoral component preoperatively, 2 weeks postoperatively, 5 years postoperatively, and annually thereafter. Eighteen knees with a cemented mobile-bearing PS prosthesis and 20 knees with a cemented fixed-bearing PS prosthesis were investigated for more than 6 years. The mean follow-up period was 11 years. Results The range of motion, Knee Society Score, BMD of the lumbar spine, and follow-up period were not significantly different preoperatively and postoperatively in the two groups. In the fixed-bearing group, the BMD of the anterior part of the femoral condyle decreased postoperatively. In the mobile-bearing group, the BMD of the posterior part of the femoral condyle increased postoperatively. The postoperative change in the BMD at 5 years and the latest follow-up period was statistically significant in the two groups. Conclusions This DEXA study revealed that a cemented mobile-bearing component had a favorable effect on the BMD of the distal femur after TKA even at a mean of 11 years postoperatively. Level of evidence Therapeutic study, level II, prospective comparative study.

Purpose This study aimed to identify factors associated with rotational mismatch after total knee arthroplasty (TKA) using fixed-bearing posterior stabilized prosthesis and to evaluate the impact of the rotational mismatch on clinical outcomes. Methods This retrospective cohort study included 159 cases that underwent TKA. Whole-leg computed tomography images were obtained 2 weeks after TKA, with three-dimensional measures of alignment. Rotational alignment of the femoral and tibial components and rotational mismatch between components and between the femur and tibia bones were evaluated. The new Knee Society Score (KSS) was obtained at the final outpatient visit, which was defined as the final follow-up timepoint. Predictive factors were identified for rotational mismatch of the lower extremity and poor new KSS. Results The mean follow-up period was 42 ± 16 months. Rotational mismatch ≥ 10° between bones was identified in 56 cases (35%), with a mean mismatch angle of 5.0° ± 9.1° of external rotation of the tibia relative to the femur. Rotational mismatch ≥ 10° between components was identified in three cases (2%; mean 0.3° ± 3.6° of internal tibial rotation). A multivariate regression analysis showed that component malrotation was predictive of post-operative rotational mismatch between bones ( p  < 0.01) and rotational mismatch ≥ 10° associated with poor new KSS (odds ratio 4.22; p  < 0.01). Conclusion Malrotation of the fixed-bearing posterior stabilized TKA causes a rotational mismatch between the femur and tibia bones. Excessive rotational mismatch between bones greater than 10° is a risk factor for poor postoperative functional outcome. Precise component positioning is essential for improving TKA outcomes. Level of evidence III

Purpose The accuracy of patient-specific instrumentation (PSI) in total knee arthroplasty (TKA) is still controversial, especially in the tibial prosthesis. It was hypothesized that the design modification of PSI improved the tibial prosthetic alignment and reduced the associated complications. The aim of this study was to compare the accuracy of a conventional PSI with that of a newly designed PSI for total knee arthroplasty (TKA) using a new three-dimensional (3D) measurement method. Methods Thirty TKAs each using the conventional and newly designed PSIs were studied. The postoperative 3D-computed tomography (3D CT) image was superimposed on the preoperative 3D CT plan. The absolute differences in the tibial prosthetic alignment between the preoperative and postoperative 3D CT images were directly measured in the coronal, sagittal, and axial planes. Knees in which the difference in the prosthetic alignment was > 3° were considered deviations. Results The new PSI showed less mean absolute differences and lower rate of deviations than the conventional PSI in the coronal and axial planes ( p  = 0.045 and p  = 0.004, respectively). The deviations (> 3°) of the tibial prosthesis using the conventional PSI were 27, 30, and 63% and of those using the new PSI were 0, 20, and 20% in the coronal, sagittal, and axial planes, respectively. Conclusions This is the first report to evaluate the effect of improvement in PSI design on the postoperative alignment using 3D method, and it clearly showed that the modification significantly improved the accuracy of alignment and reduced the deviations. Level of evidence Therapeutic study, case–control study, Level III.

The acetabular component orientation in total hip arthroplasty is of critical importance to clinical results. Although navigation systems and surgical robots have been introduced, most surgeons still use acetabular component alignment guides. This study aimed to compare the accuracy between modern acetabular component alignment guides for the lateral position and those for the supine position. Thirteen alignment guides for the lateral position and 10 for the supine position were investigated. All the lateral position alignment guides indicated cup alignment in operative definition, and the supine position alignment guides indicated cup alignment in radiographic definition. For lateral position alignment guides, the anteversion actually indicated by the alignment guide itself was smaller than that indicated by the manufacturer by a mean of 6° (maximum, 9°), and the inclination actually indicated by alignment guides themselves was larger than that by the manufacturer ( p  < 0.01) by a mean of 2° (maximum, 4°). For supine position alignment guides, the inclination and anteversion indicated by the alignment guide itself were identical with those indicated by the manufacturer. The current study showed that the angles actually indicated and those stated by manufacturers were not identical for lateral position alignment guides.

The objective of this study was to assess radiolucent lines (RLLs) and to determine their effect on clinical outcomes of the newly introduced cementless mobile-bearing total knee arthroplasty (TKA) system. This was prospective, multicentre study. Seventy-eight patients with knee osteoarthritis who underwent primary TKA were enrolled. Patient-reported outcome measures (PROMs) and radiographic assessments were evaluated at preoperative baseline and at 6 weeks, 1 year, and 2 years after surgery. KOOS, PKIP, 2011KSS, EQ-5D-3L and SKO improved from preoperative baseline to all postoperative timepoints, with no loosening of components. No RLLs were detected at 6 weeks after surgery. However, RLLs ≥ 1 mm developed in 2.8% of the patients for the femur and 9.7% for the tibia at 1 year after surgery, and values were 5.7% and 10.9%, respectively, at 2 years after surgery. RLL incidence was not correlated with PROMs. Age, sex, body mass index, range of motion knee flexion, posterior cruciate ligament treatment and β angle did not impact the occurrence of RLLs. There were no intraoperative complications, revisions or reoperations. This TKA system improved PROMs and showed less incidence of RLLs compared to the previous reported TKA without implant-related complications.

IntroductionIt is preferable to reduce postoperative excessive rotational mismatch between the femur and tibia that causes poor clinical results following total knee arthroplasty (TKA). The aim of this study is to compare postoperative rotational mismatches and clinical outcomes with mobile- and fixed-bearing prostheses.Materials and methodsThis study classified 190 TKAs into two groups equally by propensity score matching: mobile-bearing group (n = 95) and fixed-bearing group (n = 95). Computed tomography images of the whole leg were taken at 2 weeks postoperatively. The component alignments, rotational mismatches between the femur and tibia, and rotations among components were measured three-dimensionally. The knee range of motion, New Knee Society Score (KSS) subjective sores, and Forgotten Joint Score (FJS-12) were assessed at the final follow-up.ResultsRotational mismatch between the femur and tibia was significantly less in the mobile- (− 0.8° ± 7.3°) than in the fixed-bearing (3.3° ± 8.5°, p < 0.001) group. New KSS functional activity score was significantly poorer in patients with excessive rotational mismatch (61.3 ± 21.4) than in those without it (49.5 ± 20.6, p = 0.02). Comparing mobile-bearing prosthesis, the use of fixed-bearing prosthesis was a risk factor for postoperative excessive rotational mismatch (odds ratio: 2.32, p = 0.03).ConclusionWhen compared to a fixed-bearing prosthesis, TKA using a mobile-bearing prosthesis could suppress the postoperative rotational mismatch between the femur and tibia that causes poor subjective functional activity score. However, since this study was conducted for PS-TKA, the results might not be applicable to other models.

IntroductionIt is clinically important to analyze the initial contact state between an implant and femoral cortical bone as it affects clinical outcomes, such as stress shielding, stem subsidence, thigh pain, and patient-reported outcomes after total hip arthroplasty. Whether the initial contact state of a double-tapered fully hydroxyapatite (HA)-coated stem is achieved with the preserved cancellous or cortical bone remains to be established. This study aimed to compare the contact area with the femoral cortical bone between a double-tapered fully HA-coated stem (HA group) and a tapered wedge cementless stem (TW group) using three-dimensional computed tomography (3DCT)-based templating software.Materials and methodsForty-seven total hip arthroplasties in the HA and TW groups each were retrospectively analyzed. The contact area between the implant and femoral cortical bone in the whole stem and at each Gruen zone was measured using density mapping with 3DCT-based templating software.ResultsThe demographic data were not significantly different between the two groups. The contact area in the whole stem area was lower in the HA group (HA 5.4 ± 1.8% vs. TW 9.0 ± 4.8%, p < 0.01). The HA group had a lower contact area in zone 2 (HA 6.7 ± 6.5% vs. TW 15.6 ± 10.8%, p < 0.01) and zone 6 (HA 1.8 ± 3.5% vs. TW 6.3 ± 3.6%, p < 0.01) than the TW group. The implant type (β = 0.41, p < 0.01) and stem coronal alignment (β = − 0.29, p < 0.01) were significant predictors of the contact area in the whole stem area in a multiple regression analysis (adjusted R2 = 0.27, p < 0.01).ConclusionThe contact area of the double-tapered fully HA-coated stem was significantly lower than that of the tapered wedge cementless stem.

IntroductionThe medial pivot total knee arthroplasty (TKA) has good patients’ satisfaction; however, there is likely the restriction of postoperative knee flexion. The 2nd generation medial pivot TKA prosthesis was designed to improve postoperative knee flexion. This study aimed to compare the clinical outcomes and patient satisfaction between the 2nd generation and 1st generation medial pivot TKA prostheses.Materials and methodsWe conducted a retrospective study of 472 consecutive TKAs, performed using either the 2nd generation (EVOLUTION™), having smaller posterior femoral condyle and asymmetrical tibial tray, or 1st generation (ADVANCE™) prosthesis. The use of each system was historically determined. Patient age, sex and body mass index were matched between the two groups, with 157 cases ultimately included in each group. Measured clinical outcomes included: knee range of motion, the Knee Society Score, the rate of re-operation, and radiological parameters. Patient satisfaction was evaluated using the 12-item Forgotten Joint Score (FJS-12).ResultsThe average follow-up period was 5.0 (3.7–6.3) years for the 2nd generation group and 8.7 (6.1–12.8) years for the 1st generation group (p < 0.01). The postoperative knee flexion range was 127° (80°–140°) for the 2nd generation and 118° (90°–135°) for the 1st generation at final follow-up (p < 0.01). On multivariate regression analysis, use of the 2nd generation prosthesis predicted greater postoperative knee flexion. The average FJS-12 score was 64 (0–100) for the 2nd generation and mean 57 (0–100) for the 1st generation (p < 0.01). Other clinical outcomes were similar between the two groups.ConclusionsCompared to the 1st generation, the 2nd generation medial pivot prosthesis provides greater postoperative knee flexion and patient satisfaction.

Purpose Two-dimensional (2D) and three-dimensional (3D) measurements of prosthetic alignment and “outliers” after total knee arthroplasty (TKA) might not necessarily be comparable. The aim of this study was to compare the use of 2D and 3D measurements in the identification of prosthetic alignment and outliers after TKA. Methods This cross-sectional study included 159 consecutive TKAs. All patients underwent plain radiography, fluoroscopy-guided radiography, and computed tomography after TKA. The same baseline was used for 2D and 3D measurements. The reliability of prosthetic alignment and outlier identification (> 3° from neutral alignment) was compared between the 2D and 3D measurements. Results The mean prosthetic alignment and rate of outliers were not significantly different the between 2D and 3D measurements. The inter- and intra-observer reliabilities were higher for the 3D measurements than for the 2D measurements. The agreement between 2D and 3D measurements in outlier identification was poor, except for femoral coronal alignment. Cohen’s κ coefficients were 0.19 in femoral sagittal (poor), 0.02 in tibial coronal (poor), and 0.10 in tibial sagittal (poor) on plain radiography. The values were 0.23 in tibial coronal (poor) and 0.002 in tibial sagittal (poor) on fluoroscopy-guided radiography. Conclusions The agreement between 2D and 3D measurements in the identification of outliers was poor, even on fluoroscopy-guided radiography. Since 2D measurements have an inherent risk of misidentifying alignment outliers, this finding is clinically relevant. To properly analyze the correlation between outliers and clinical results, such as longevity, patient satisfaction, and patient-reported outcome, 3D measurements for prosthetic alignment are desirable. Level of evidence III.

PurposeLeg length discrepancy (LLD) after total hip arthroplasty (THA) prevents functional recovery and reduces patient satisfaction. We investigated impact of changes in patient-perceived LLD on patient satisfaction and walking ability.Methodsone hundred and forty-nine patients with unilateral hip osteoarthritis undergoing THA from 2014 to 2017, (125 women, 24 men; average age, 68.5 years) with an objective LLD < 1 cm were included. Outcome measures included the patient-perceived LLD, Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index, 10-m walking speed, and affected leg loading rate, assessed preoperatively and at 3 weeks, 3 months, and 1 year postoperatively.ResultsThe absolute patient-perceived LLD (mean ± SD) (the number of patients with perceived LLD > 5 mm) were 6.4 ± 9.6 mm [88 patients (59%)] preoperatively; and 2.2 ± 4.0 mm [48 (32%); p < 0.001], 0.7 ± 2.3 mm [17 (11%); p < 0.001], and 0.4 ± 1.6 mm [10 (7%); p = 0.095] at 3 weeks, 3 months, and 1 year postoperatively, respectively. All outcome measures improved over time. One year postoperatively, a weak positive correlation between the patient-perceived LLD and WOMAC or 10-m walking speed (r = 0.24, 0.23, respectively) was found. The risk of patient-perceived LLD persisting > 1 year postoperatively was 5.5-fold higher in patients who exhibited it at 3 months and those with a WOMAC score > 10 at 3 months postoperatively, using multivariate logistic regression.ConclusionAchieving a post-THA objective LLD < 1 cm significantly reduced the patient-perceived LLD up to 3 months postoperatively. The residual patient-perceived LLD at 1 year postoperatively was predicted from the WOMAC score or the presence of patient-perceived LLD at 3 months after THA.Level of evidenceTherapeutic level IV.