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The aim of this study was to compare the clinical and radiologic outcomes of robot-assisted unicompartmental knee arthroplasty (UKA) to those of conventional UKA in Asian patients. Fifty-five patients underwent robot-assisted UKA and 57 patients underwent conventional UKA were assessed in this study. Preoperative and postoperative range of motion (ROM), American Knee Society (AKS) score, Western Ontario McMaster University Osteoarthritis Index scale score (WOMAC), and patellofemoral (PF) score values were compared between the two groups. The mechanical femorotibial angle (mFTA) and Kennedy zone were also measured. Coronal alignments of the femoral and tibial components and posterior slopes of the tibial component were compared. Additionally, polyethylene (PE) liner thicknesses were compared. There was no significant difference between the two groups regarding postoperative ROM, AKS, WOMAC and PF score. Robot group showed fewer radiologic outliers in terms of mFTA and coronal alignment of tibial and femoral components (p = 0.022, 0.037, 0.003). The two groups showed significantly different PE liner thicknesses (8.4 ± 0.8 versus 8.8 ± 0.9, p = 0.035). Robot group was the only influencing factor for reducing radiologic outlier (postoperative mFTA) in multivariate model (odds ratio: 2.833, p = 0.037). In this study, robot-assisted UKA had many advantages over conventional UKA, such as its ability to achieve precise implant insertion and reduce radiologic outliers. Although the clinical outcomes of robot-assisted UKA over a short-term follow-up period were not significantly different compared to those of conventional UKA, longer follow-up period is needed to determine whether the improved radiologic accuracy of the components in robotic-assisted UKA will lead to better clinical outcomes and improved long-term survival.

Purpose The aim of this study was to investigate the association between pelvic sagittal parameters and acetabular labral tears. Methods Three-hundred and sixty-five patients (449 hips) who underwent magnetic resonance imaging (MRI) or magnetic resonance arthrogram (MRA) for hip pain were enrolled in this study. Pelvic sagittal parameters, including the pelvic incidence, pelvic tilt, and sacral slope, were measured with a standing lumbosacral lateral radiograph. All subjects were divided into two groups according to the presence or absence of radiologic acetabular labral tears and compared. Furthermore, the two groups were divided into subgroups according to whether femoroacetabular impingement (FAI) morphology was present or not and compared. Results Pelvic incidence was greater in the labral tear group than in the non-labral tear group (52.3° ± 8.2° versus 47.1° ± 6.8°, p  < 0.001). After accounting for potentially confounding variables, we found that higher age (odds ratio 1.04, 95% confidence interval [CI] 1.02 to 1.06, p  = 0.001), FAI (odds ratio 15.11, 95% CI 7.43 to 30.75, p  < 0.001), and high pelvic incidence (odds ratio 1.13, 95% CI 1.09 to 1.17, p  < 0.001) were independently associated with acetabular labral tear. When only the patients without FAI (308 hips) were divided into groups with and without acetabular labral tear, we found that higher age (odds ratio 1.03, 95% CI 1.01 to 1.06, p  = 0.008) and high pelvic incidence (odds ratio 1.15, 95% CI 1.11 to 1.19, p  < 0.001) were independently associated with acetabular labral tear. Conclusion Acetabular labral tear is associated with high pelvic incidence with or without FAI morphology. Level of evidence III.

This study aimed to determine the factors related to intraoperative extension gap (EG) in patients who underwent posterior-stabilized total knee arthroplasty (TKA). A total of 106 TKAs in 84 patients were retrospectively reviewed. Only patients who underwent the same method of bone resection were included consecutively. Bilateral popliteal angle (BPA) was used as an indicator of hamstring tightness. EG and extension space angle were measured using an offset type tensor. The associations between patient variables and EG were analyzed using multivariable linear regression and Pearson's correlation coefficients. The average EG was 12.9 ± 2.1 mm, and the average extension space angle was 2.8° ± 3.2°. BPA was greater than flexion contracture in most cases (94.3%), and no difference was found in only six cases (5.7%). According to multivariable linear regression analysis which was conducted after modifying the BPA into a categorical variable by 5°, EG was correlated with BPA (p < 0.001). Pearson’s correlation coefficient between EG and BPA was − 0.674 (p < 0.001). No other factors were significantly correlated with intraoperative EG. The present study found that popliteal angle is a different entity from flexion contracture, and that it is a predictable factor for EG in osteoarthritis patients. Smaller BPAs led to larger EG in patients who underwent the same degree of bone resection.

Purpose The aim of this retrospective study was to compare clinical outcomes of total knee arthroplasty (TKA) with and without patellar resurfacing using the Low Contact Stress (LCS) mobile-bearing prosthesis in 275 osteoarthritic knees (199 patients) after a minimum of 7 years of follow-up. Methods Patients were divided into a patellar retention group (132 knees) and a resurfacing group (143 knees), with median follow-up durations of 7.8 years (range, 7–8.5 years) and 8.5 years (range, 7–10.6 years), respectively. The demographics of the two groups were otherwise matched. The patelloplasty was performed for patellar retention. Patients were evaluated by a blinded, independent observer using Feller’s patellar score, the Knee Society score, patient satisfaction, patellar tilt, and lateral displacement. Results Patellar resurfacing was not superior to retention with respect to any of the measured variables. Eight knees (6.1%) without and 6 (4.2%) with patellar resurfacing had anterior knee pain related to the patellofemoral joint (n.s.). The reoperation rate related to the patellofemoral joint was 0.8% ( n  = 1) in the retention group compared with 2.8% ( n  = 4) in the resurfacing group (n.s.). In the 35 patients who underwent bilateral TKA with patellar resurfacing on only one side, there were no significant differences between the two sides in subjective preference, clinical scores, or functional ability. Conclusions The clinical and radiographic outcomes of TKA with the LCS mobile-bearing prosthesis showed no significant difference between the two groups after a minimum of 7 years of follow-up. The findings in this study suggest that patellar retention with a patelloplasty may be viable as a routine procedure, even in knees with advanced patellofemoral arthritis, if soft tissue balancing and a patella-friendly prosthetic design are properly used. Level of evidence Therapeutic, retrospective, comparative study, Level III.

Being underweight has never been studied in relation to the radiologic and clinical outcomes of total knee arthroplasty (TKA) in elderly patients. The aim of this study was to determine the effect of being underweight on TKA radiological and clinical outcomes and to investigate whether being underweight influences postoperative complications compared to normal body mass index (BMI) in elderly patients. A total of 118 female patients aged 65 years or older with BMI < 25 kg/m who underwent primary TKA were divided into two groups based on BMI: group A: 18.5 kg/m < BMI < 25 kg/m ; group B: BMI < 18.5 kg/m . The radiologic and clinical outcomes were evaluated at follow-up of 6, 12, and 24 months after surgery such as the hip-knee-ankle angle, the American Knee Society (AKS) score, Western Ontario and McMaster University score (WOMAC), and patellofemoral (PF) scale. Moreover, postoperative complications during follow-up were investigated. Preoperative clinical scores did not differ significantly between the two groups. Postoperative WOMAC pain (1.8 ± 1.9 versus 3.4 ± 2.6, p = 0.02), WOMAC function (12.4 ± 8.1 versus 16.5 ± 8.5, p = 0.012) and PF scales (26.1 ± 3.6 versus 23.7 ± 4.1, p = 0.002) were worse in the underweight group at 12 and 24 months after surgery. The frequency of postoperative complications did not differ significantly between groups. In multivariate linear regression analysis, underweight patient group was significantly associated with worse postoperative WOMAC and PF scores (p = 0.002, 0.005). Although postoperative complications of TKA did not differ between groups, underweight patients had worse clinical outcomes of TKA compared to patients with normal BMI in elderly patients. Therefore, care should be taken when performing TKA in elderly underweight patients.

Background Setting bone cutting levels for different joint line orientations of the medial and lateral tibia plateaus in individual patients is not clear. We aimed to evaluate the difference between joint line orientation of the medial and lateral tibia plateaus relative to the horizontal line of mechanical axis of tibia as tibial plateau difference (TPD) for an optimal tibial bone cut in medial unicompartmental knee arthroplasty (UKA) and determine which factors could influence TPD. We aimed to investigate the effect of preoperative TPD on polyethylene liner size in medial UKA. Methods TPD in the coronal plane were measured in 181 female patients (181 knees). To determine the morphology of proximal tibia according to the severity of osteoarthritis, the patients were classified into three groups based on diagnosis and treatment: 80 who underwent robot-assisted medial UKA, 45 who underwent total knee arthroplasty (TKA), and 56 with early-stage osteoarthritis (OA) who had conservative management. Also, we divided the medial UKA group into two groups according to TPD (greater than or less than 5 mm) and compared polyethylene liner sizes. Results No significant difference was observed in TPD ( p  = 0.662), difference between the medial and lateral femoral condyle levels ( p  = 0.54), medial proximal tibial angle ( p  = 0.169), or posterior tibial slope ( p  = 0.466) among the three groups. Increased TPD was significantly associated with increased mechanical femorotibial angle(mFTA) ( p  < 0.01). The medial UKA group was divided into two groups according to TPD greater or less than 5 mm. Thicker polyethylene liners were used for groups with TPD greater than 5 mm (8.5 ± 0.7 mm versus 8.2 ± 0.3 mm, p  = 0.01). Additionally, the proportion of patients using the thinnest polyethylene (8 mm) in each TPD group (greater or less than 5 mm) was higher in patients with TPD less than 5 mm (82.4% versus 58.7%, p  = 0.038). Conclusions Preoperative measurement of TPD is important to help surgeons predict the most appropriate bone cutting level in the coronal plane in primary medial UKA. Tibial bone resection would be likely to be thicker than needed in patients with increased TPD in medial UKA.

Background: The aim of this study was to investigate the relationship between estimated glomerular filtration rate (eGFR) and outcomes of bipolar hemiarthroplasty for femoral neck fracture in elderly patients, and to compare postoperative complications and mortality among groups according to eGFR. Methods: A total of 181 patients who underwent bipolar hemiarthroplasty for displaced femoral neck fracture were divided into three groups according to eGFR. Data were retrospectively analyzed. Group 1 had 96 patients with eGFR greater than or equal to 60 mL/min/1.73 m2; Group 2 had 54 patients with eGFR greater than or equal to 30 mL/min/1.73 m2 and lower than 60 mL/min/1.73 m2; and Group 3 had 31 patients with eGFR lower than 30 mL/min/1.73 m2. Postoperative complications and mortality were compared between groups at a minimum 2-year follow-up. Results: Patients in Group 3 had the longest hospital stay of the three groups (p = 0.001). The rates of medical complications did not differ significantly among groups. However, Group 2 and 3 had higher rates of surgical complications (p = 0.001) and mortality (p = 0.043) than Group 1. Severe renal impairment was associated with increased risk of postoperative complications compared to mild renal impairment (odds ratio (95% confidence interval) = 4.33 (1.32–13.19), p = 0.015). Conclusion: Patients with moderate or severe decreased eGFR associated with chronic kidney disease (CKD) could have higher postoperative complications and mortality after bipolar hemiarthroplasty compared to patients with CKD stage 1 or 2.

Purpose Vitamin D has received considerable attention in recent years owing to the increasing evidence of its importance in muscle function and physical performance. The present study attempted to determine whether patients with low serum vitamin D levels had impairment in early functional outcomes following total knee arthroplasty (TKA). Methods This was a prospective cohort study that included 92 patients. Patients were divided into two groups according to their vitamin D levels as assessed at the preoperative visit: (1) vitamin D-deficient group, serum 25-hydroxyvitamin D 3 (25(OH)D) levels <12 ng/mL; (2) vitamin D non-deficient group, serum 25(OH)D levels ≥12 ng/mL. American Knee Society Score (KSS) and four other performance tests including the alternative step test (AST), six-metre walk test (SMT), sit-to-stand test (STS), and timed up and go test (TUGT) were used for assessment of post-operative function. All assessments were performed one day before and three months after TKA. Results Of the 92 patients included in the study, 87 patients performed all required assessments. The mean post-operative functional KSS was significantly lesser in the vitamin D-deficient group than in the vitamin D non-deficient group (67.2 vs. 73.4, p  = 0.031). The mean values of time taken for post-operative AST (16.6 vs. 14.6 s, p  = 0.033) and SMT (8.8 vs. 7.7 s, p  = 0.012) were significantly longer in the vitamin D-deficient group than in the vitamin D non-deficient group. Post-operative STS and TUGT demonstrated higher values for mean time taken in the vitamin D-deficient group than in the vitamin D non-deficient group, but these were not statistically significant (13.6 vs. 12.4 s, not significant (n.s.); 12.7 vs. 11.7 s, n.s., respectively). Conclusion Early post-operative functional outcomes following TKA appear to be adversely affected by vitamin D deficiency. Level of evidence Prospective cohort study, Level II.

Purpose This study aimed to investigate stress shielding of anatomical tibial components (ATCs) in comparison to conventional symmetric tibial components (STCs) in Korean patients which may be related to medial tibial bone loss. Method 78 knees in 59 patients with ATCs (Persona™) and 74 knees in 58 patients with STCs (NexGen LPS-Flex™) were retrospectively reviewed. Radiographic parameters and clinical outcomes in both groups were compared. Logistic regression analysis was performed to identify risk factors for medial tibial bone loss. Results Medial tibial bone loss was significantly greater in the ATC group (1.6 ± 1.3 mm) than in the STC group (0.4 ± 0.8 mm) ( p  < 0.001). The ATC group showed a shorter distance between the distal metal tip and anteromedial cortex and higher invading into the sclerotic bone lesion (ISBL) than the STC group ( p  = 0.034 and p  = 0.044, respectively). Multiple logistic regression analysis suggested ATC, a shorter distance to the anteromedial cortex, and the presence of ISBL as risk factors for medial tibial bone loss. The odds ratios of medial tibial bone loss according to type of prosthesis, distance to anteromedial cortex, and presence of ISBL were 6.25 (range 2.86–13.63, p  < 0.001), 0.69 (range 0.51–0.93, p  = 0.015), and 3.79 (range 1.56–9.21, p  = 0.003), respectively. Notwithstanding, there was no difference in clinical outcomes between the two groups. Conclusion In Korean patients, ATCs potentially causes greater medial tibial bone loss due to stress shielding than STCs. The design, however, does not yet appear to affect clinical outcomes at mid-term follow-up. Level of evidence Retrospective cohort study, level III.

Purpose This study aimed to investigate the relationship between preoperative femoral axes and femoral implant position and to determine how femoral sagittal axes, including femoral anterior bowing, influence the femoral component position in total knee arthroplasty (TKA). Methods The relationship between femoral axes (femoral anterior bowing, mechanical axis and the anterior cortical line, intramedullary axis) and implant position was compared in 50 conventional and 50 navigated TKAs. Outliers with more than a 3° margin of error in placement of the femoral component compared with the mechanical axis in the sagittal plane were calculated. Results The femoral component flexion angle was 3.1° in the conventional group and 1.6° in the navigation group ( p  < 0.001). Anterior femoral bowing correlated positively with the angle between the mechanical axis and implant ( r  = 0.360, p  = 0.010) in the conventional group and negatively with the angle between the anterior cortical line and flange of the femoral component ( r  = −0.355, p  = 0.010) in navigated TKAs. Incidence of outliers was 48 % (24 patients) in the conventional group compared with 10 % (five patients) in the navigated group ( p  = 0.008). Conclusions Femoral anterior bowing was an influential factor for implant position and could be a risk factor for both femoral implant flexion in conventional TKAs and notching in navigated TKAs. The results of this study should be considered by surgeons when assessing the risk factors for femoral geometry before performing TKAs, as these results may help them to avoid an overly flexed or extended position of the femoral component, which would affect clinical long-term survival. Level of evidence Retrospective comparative study, Level III.