Efficiency assessment of follow-up methodology of patients with knee replacement to predict post-surgical functionality: a protocol for randomised control PROKnee trial.

INTRODUCTION: Even when total knee arthroplasty (TKA) is an extended treatment, most patients experience a suboptimal evolution after TKA. The objectives of this study are the following: (1) to determine the effectiveness of two different prosthesis stabilisation systems on the functionality in activities of daily life, and (2) to determine prognostic biomarkers of knee prosthesis function based on radiological information, quantification of cytokines, intra-articular markers and biomechanical functional evaluation to predict successful evolution. METHODS AND ANALYSIS: The PROKnee trial was designed as a randomised controlled patient-blinded trial with two parallel groups that are currently ongoing. The initial recruitment will be 99 patients scheduled for their first TKA, without previous prosthesis interventions in lower limbs, who will be randomly divided into two groups that differed in the stabilisation methodology incorporated in the knee prosthesis: the MEDIAL-pivot group and the CENTRAL-pivot group. The maximum walking speed will be reported as the primary outcome, and the secondary results will be patient-reported questionnaires related to physical status, cognitive and mental state, radiological test, laboratory analysis and biomechanical instrumented functional performance, such as the 6-minute walking test, timed up-and-go test, gait, sit-to-stand, step-over, and ability to step up and down stairs. All the results will be measured 1 week before TKA and at 1.5, 3, 6 and 12 months after surgery. ETHICS AND DISSEMINATION: All procedures were approved by the Ethical Committee for Research with Medicines of the University Clinical Hospital of Valencia on 8 October 2020 (order no. 2020/181). Participants are required to provide informed consent for the study and for the surgical procedure. All the data collected will be treated confidentially since they will be blinded and encrypted. The results from the trial will be published in international peer-reviewed scientific journals, regardless of whether these results are negative or inconclusive. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov Registry (NCT04850300).

Computational assessment of carbon fabric reinforced polymer made prosthetic knee: Mechanics, finite element simulations and experimental evaluation.

A prosthetic knee is designed to replace the functionality of an anatomical knee in transfemoral amputees. The purpose of a prosthetic knee is to restore mobility and compensate amputees for their impairment. In the present research numerical modelling and simulation of a carbon fabric reinforced polymer made polycentric prosthetic knee with four-bar mechanism was performed. Virtual prototyping with computer-aided design and computer-aided engineering software ensured geometric and structural stability of the knee design. The linkage mechanism, instantaneous centre's location and trajectory were investigated using multibody dynamics and analytical formulations. Computational simulations with a non-linear finite element model were employed with joints, contact formulations and an orthotropic material model to predict the displacement, stress formulated and life of the knee prosthesis under static and cyclic loading conditions. Finite element analysis assessed the strength and durability of knee in accordance to standards. Maximum Principal stress of 155 MPa and life expectancy of 3.1 × 106 cycles were determined for the composite knee through numerical simulations ensuring a safe design. Experimental testing was also conducted as per standards and the percentage error was estimated to be 2.52%, thereby establishing the validity of the finite element model deployed. This type of simulation-based approach can be implemented to efficiently and affordably design and prototype a prosthetic knee with desired functioning criteria.

Are Femoral Stems in Primary Total Knee Arthroplasty Cost Effective in High Fracture Risk Patients? A Risk Model and Cost Analysis.

Femoral stemmed total knee arthroplasty (FS TKA) may be used in patients deemed higher risk for periprosthetic fracture (PPF) to reduce PPF risk. However, the cost effectiveness of FS TKA has not been defined. Using a risk modeling analysis, we investigate the cost effectiveness of FS in primary TKA compared with the implant cost of revision to distal femoral replacement (DFR) following PPF. A model of risk categories was created representing patients at increasing fracture risk, ranging from 2.5 to 30%. The number needed to treat (NNT) was calculated for each risk category, which was multiplied by the increased cost of FS TKA and compared with the cost of DFR. The 50th percentile implant pricing data for primary TKA, FS TKA, and DFR were identified and used for the analysis. FS TKA resulted in an increased cost of $2,717.83, compared with the increased implant cost of DFR of $27,222.29. At 50% relative risk reduction with FS TKA, the NNT for risk categories of 2.5, 10, 20, and 30% were 80, 20, 10, and 6.67, respectively. At 20% risk, FS TKA times NNT equaled $27,178.30. A 10% absolute risk reduction in fracture risk obtained with FS TKA is needed to achieve cost neutrality with DFR. FS TKA is not cost effective for low fracture risk patients but may be cost effective for patients with fracture risk more than 20%. Further study is needed to better define the quantifiable risk reduction achieved in using FS TKA and identify high-risk PPF patients.

Direct Hospital Costs per Case of Periprosthetic Hip and Knee Joint Infections in Europe - A Systematic Review.

BACKGROUND: The rise of periprosthetic joint infections (PJIs) due to aging populations is steadily increasing the number of arthroplasties and treatment costs. This study analyzed the direct health care costs of PJI for total hip arthroplasty and total knee arthroplasty (TKA) in Europe. METHODS: The databases PubMed, Scopus, Embase, Cochrane, and Google Scholar were systematically screened for direct costs of PJI in Europe. Publications that defined the joint site and the procedure performed were further analyzed. Mean direct health care costs were calculated for debridement, antibiotics, and implant retention (DAIR), one-stage, and 2-stage revisions for hip and knee PJI, respectively. Costs were adjusted for inflation rates and reported in US-Dollar (USD). RESULTS: Of 1,374 eligible publications, 12 manuscripts were included in the final analysis after an abstract and full-text review. Mean direct costs of $32,933 were identified for all types of revision procedures for knee PJI. The mean direct treatment cost including DAIR for TKA after PJI was $19,476. For 2-stage revisions of TKA, the mean total cost was $37,980. For all types of hip PJI procedures, mean direct hospital costs were $28,904. For hip DAIR, one-stage and 2-stage treatment average costs of $7,120, $44,594, and $42,166 were identified, respectively. CONCLUSIONS: Periprosthetic joint infections are associated with substantial direct health care costs. As detailed reports on the cost of PJI are scarce and of limited quality, more detailed financial data on the cost of PJI treatment are urgently required.

Robotic-assisted TKA is Not Associated With Decreased Odds of Early Revision: An Analysis of the American Joint Replacement Registry.

BACKGROUND: Robotic-assisted TKA continues to see wider clinical use, despite limited knowledge of its impact on patient satisfaction and implant survival. Most studies to date have presented small cohorts and came from single-surgeon or single-center experiences. Therefore, a population-level comparison of revision rates between robotic-assisted and conventional TKA in the registry setting may help arthroplasty surgeons better define whether robotic assistance provides a meaningful advantage compared with the conventional technique. QUESTIONS/PURPOSES: (1) After controlling for confounding variables, such as surgeon, location of surgery, and patient comorbidity profile, were robotic-assisted TKAs less likely than conventional TKAs to result in revision for any reason at 2 years? (2) After again controlling for confounding variables, were robotic-assisted TKAs less likely to result in any specific reasons for revision than the conventional technique at 2 years? METHODS: The American Joint Replacement Registry was used to identify patients 65 years or older who underwent TKA between January 2017 and March 2020 with a minimum of 2 years of follow-up. Patients were limited to age 65 yeas or older to link TKAs to Medicare claims data. Two retrospective cohorts were created: robotic-assisted TKA and conventional TKA. Patient demographic variables included in the analysis were age, gender, BMI, and race. Additional characteristics included the Charlson comorbidity index, anesthesia type, year of the index procedure, and length of stay. A total of 10% (14,216 of 142,550) of TKAs performed during this study period used robotics. Patients with robotic-assisted TKA and those with conventional TKA were similar regarding age (73 ± 6 years versus 73 ± 6 years; p = 0.31) and gender (62% [8736 of 14,126] versus 62% [79,399 of 128,334] women; p = 0.34). A multivariable, mixed-effects logistic regression model was created to analyze the odds of all-cause revision as a factor of robot use, and a logistic regression model was created to investigate specific revision diagnoses. RESULTS: After controlling for potentially confounding variables, such as surgeon, location of surgery, and Charlson comorbidity index, we found no difference between the robotic-assisted and conventional TKAs in terms of the odds of revision at 2 years (OR of robotic-assisted versus conventional TKA 1.0 [95% CI 0.8 to 1.3]; p = 0.92). The reasons for revision of robotic-assisted TKA did not differ from those of conventional TKA, except for an increased odds of instability (OR 1.6 [95% CI 1.0 to 2.4]; p = 0.04) and pain (OR 2.1 [95% CI 1.4 to 3.0]; p < 0.001) in the robotic-assisted cohort. CONCLUSION: In light of these findings, surgeons should not assume that robotic assistance in TKA will lead to improved early implant survival. Our findings do not support an improvement over conventional TKA with robotic assistance with regards to common causes of early revisions such malalignment, malposition, stiffness, pain, and instability, and in some cases, suggest there is a benefit to conventional TKA. Differences in the mid-term and long-term revision risk with conventional versus robotic-assisted TKA remain unknown. Appropriate informed consent around the use of robotic assistance should not imply decreased early revision risk. LEVEL OF EVIDENCE: Level III, therapeutic study.

Validation for the effect of intra-exposure patient motion on the assessment of radiostereometric implant migration in a tibial component phantom study.

BACKGROUND: An increasing number of radiostereometry (RSA) research studies have long-term follow-up implant migration outcomes, which show ascending curves of implant migration with occasionally decreasing migration. After scrutinizing images and RSA scenes related to the alternating curves, we suppose that intra-exposure patient motion may contribute to that. The main purposes of this in vitro study were 1) to identify whether the patient motion in different directions could result in the inaccurate assessment of implant migration, and 2) to figure out which direction(s) accounted for the alternating curves. HYPOTHESIS: It was hypothesized that the assessments of implant migration would be less precise and accurate than they could be when patient motion occurred, and such motion would contribute to the alternating curves of radiostereometric implant migration. MATERIALS AND METHODS: A customized phantom, assembled with a tibial component, was designed for simulating intra-exposure patient motion during follow-up RSA examinations. Two different Roentgen tubes were used as the current standard of radiology departments. Radiographs were acquired in a uniplanar technical arrangement. Two defined protocols were conducted: one is to simulate implant migration outcomes at post-op, the early stage (6months), and the later stage (2 to 10years) ; during the later stage, the other is to mimic patient motion by phantom motion in the medial-lateral (x), distal-proximal (y), and anterior-posterior (z) axes. RESULTS: Phantom motion could result in the inaccurate assessment of implant migration, and translations along the medial-lateral (x) axis were the most influenced by patient motion. Motion along the medial-lateral (x) axis could account for the curves with decreasing migration. DISCUSSION: Our assessments of implant migration may be less precise and accurate than they could be when intra-exposure patient motion occurs. We probably neglect the importance of 100% simultaneous exposures, and the influence of patient motion on RSA accuracy and data reliability, due to the difficulty in detecting patient (micro)motion. Electronically synchronized exposures of two paired Roentgen tubes are 100% simultaneous for image acquisition, and they are thus highly recommended for the assessment of implant migration in RSA. TYPE OF STUDY AND LEVEL OF PROOF: not applicable.

The economic and clinical impact of fast- versus slow-setting cement in primary total knee arthroplasty.

INTRODUCTION: New bone cement products have been developed attempting to shorten their setting time and thus cut down time in the operating room. This study determines whether faster-setting bone cement shortens time in the operating room, and whether the quantity used compromises postoperative TKA outcomes. Additionally, this study looks at cost analyses of the quantity of bone cement used in TKA procedures. MATERIALS AND METHODS: One-hundred and sixty patients at a single institution with primary TKA surgeries between January 2019 and December 2021, and a clinic follow-up of at least one year, were identified. Five cement products used in this time period were identified and categorized by fast- or slow-setting products if their set times were marketed below or above six minutes, respectively. RESULTS: Estimated blood loss was higher in patients receiving fast-setting cements (160.0 vs 126.4 mL; p = 0.0009); however, operative time showed no difference between the cohorts (88.2 vs 89.2 min; p = 0.99). Fewer bags of cement were used for the fast cohort (1.3 vs 1.8 bags; p < 0.0001). The fast group was significantly cheaper on average per patient only when comparing between antibiotic bone cements (p = 0.007). No differences were found in postoperative outcomes between the two groups. CONCLUSIONS: No differences were found in operative times between the fast and slow cemented groups. Fewer bags of faster-setting cement only proved cost saving relative to other antibiotic bone cements studied. Nonetheless, decreased usage of fast cement did not result in any different postoperative outcomes compared to slow cements. LEVEL OF EVIDENCE: III.

A multimodal assessment of cementless tibial baseplate fixation using radiography, radiostereometric analysis, and magnetic resonance imaging.

Fixation in cementless total knee arthroplasty is provided by osseous integration. Radiography, radiostereometric analysis (RSA), and magnetic resonance imaging (MRI) were used simultaneously to investigate fixation. Relationships between RSA-measured implant micromotions and MRI-evaluated osseous integration at the component-bone interface were assessed in 10 patients up to 6 months postoperation. Supine MRI (using multispectral imaging sequences) and RSA exams were performed to evaluate osseous integration and measure longitudinal migration, respectively. Inducible displacement was measured from standing RSA exams. Radiolucent lines were detected on conventional radiographs. Of 10 patients, 6 had fibrous membranes detected on MRI. No fluid or osteolytic interfaces were found, and no components were scored loose. Of 10 patients, 6 had radiolucent lines detected. Average maximum total point motion (MTPM) for longitudinal migration at 6 months was 0.816 mm (range 0.344-1.462 mm). Average MTPM for inducible displacement at 6 months was 1.083 mm (range 0.553-1.780 mm). Fictive points located in fibrous-classified baseplate quadrants had greater longitudinal migration than fictive points located in baseplate quadrants with normal interfaces at 2 weeks (p = 0.031), 6 weeks (p = 0.046), and 3 months (p = 0.047), and greater inducible displacements at 3 months (p = 0.011) and 6 months (p = 0.045). Greater early micromotion may be associated with the presence of fibrous membranes at the component-bone interface. Clinical significance: This multimodal imaging study contributes knowledge of the fixation of modern cementless TKA, supporting the notion that osseous integration is important for optimal implant fixation.

Improved accuracy of implant placement with an imageless handheld robotic system compared to conventional instrumentation in patients undergoing total knee arthroplasty: a prospective randomized controlled trial using CT-based assessment of radiological outcomes.

PURPOSE: Image-free handheld robotic-assisted total knee arthroplasty (RATKA) has shown to achieve desired limb alignment compared to conventional jig-based instrumented total knee arthroplasty (CTKA). The aim of this prospective randomized controlled trial (RCT) was to evaluate the accuracy of a semi-autonomous imageless handheld RATKA compared to CTKA in order to achieve the perioperative planned target alignment of the knee postoperatively. METHODS: Fifty-two patients with knee osteoarthritis were randomized in 1:1 ratio to undergo unilateral CTKA or an imageless handheld RATKA. A full-length lower limb CT-scan was obtained pre- and 6-week postoperative. The primary outcomes were radiologic measurements of achieved target hip-knee-ankle axis (HKA-axis) and implant component position including varus and external rotation and flexion of the femur component, and posterior tibial slope. The proportion of outliers in above radiographic outcomes, defined as > 3° deviation in postoperative CT measurements as compared to perioperative planned target, were also noted. Knee phenotypes were compared with use of the Coronal Plane Alignment of the Knee (CPAK) classification. RESULTS: Baseline conditions were comparable between both groups. The overall proportion and percentage of outliers (n = 38, 24.4% vs n = 9, 5.8%) was statistically significant (p < 0.001) in favor of RATKA. The achieved varus-valgus of the femoral component (varus 1.3° ± 1.7° vs valgus - 0.1° ± 1.9°, p < 0.05) with statistically significant less outliers (0% vs 88.5%, p < 0.01), the achieved HKA-axis (varus 0.4° ± 2.1° vs valgus - 1.2° ± 2.1°, p < 0.05) and the posterior tibial slope (1.4° ± 1.1° vs 3.2° ± 1.8°, p < 0.05) were more accurate with RATKA. The most common postoperative CPAK categories were type II (50% CTKA vs 61.5% RATKA), type I (3.8% CTKA vs 23.1% RATKA) and type V (26.9% CTKA vs 15.4% RATKA). CPAK classification III was only found in CTKA (19.2%). Type VI, VII, VIII, and IX were rare in both populations. CONCLUSIONS: The present trial demonstrates that an imageless handheld RATKA system can be used to accurately perioperatively plan the desired individual component implant positions with less alignment outliers whilst aiming for a constitutional alignment. LEVEL OF EVIDENCE: I.

Tibial bone defect prediction based on preoperative artefact-reduced CT imaging is superior to standard radiograph assessment.

PURPOSE: The purpose of this study was to evaluate the accuracy of preoperative CT-based Anderson Orthopaedic Research Institute (AORI)-grading and to correlate Computed tomography (CT)-based volumetric defect measurements with intraoperative AORI findings. METHODS: 99 patients undergoing revision total knee arthroplasty (rTKA) with preoperative CT-images were identified in an institutional revision registry. CT-image segmentation with 3D-Slicer Software was used to create 3D tibial bone defects which were then graded according to the AORI-classification. The AORI classification categorizes tibial defects into three types: Type I has healthy cortical and cancellous bone near the joint line, Type II involves metaphyseal bone loss affecting one or both condyles, and Type III indicates deficient metaphyseal bone with distal defects and potential damage to the patellar tendon and collateral ligament attachments. These 3D-CT gradings were compared to preoperative X-ray and intraoperative AORI grading. The Friedman test was used to investigate differences between AORI values of each measurement method. Volumetric 3D-bone defect measurements were used to investigate the relationship between AORI classification and volumetric defect size in the three anatomic zones of the tibia. RESULTS: Substantial agreements between preoperative 3D-CT AORI and intraoperative AORI (kappa = 0.663; P < 0.01) and fair agreements between preoperative X-ray AORI and intraoperative AORI grading (kappa = 0.304; P < 0.01) were found. Moderate correlations between volume of remaining bone and intraoperative AORI grading were found in epiphysis (rS = - 0.529; P < 0.001), metaphysis (rS = - 0.557; P < 0.001) and diaphysis (rS = - 0.421; P < 0.001). Small volumetric differences between AORI I vs. AORI II defects and relatively large differences between AORI II and AORI III defects in each zone were detected. CONCLUSION: Tibial bone defect prediction based on preoperative 3D-CT segmentation showed a substantial agreement with intraoperative findings and is superior to standard radiograph assessment. The relatively small difference in defect volume between AORI I, IIa and IIb suggests that updated CT-based classifications might hold benefits for the planning of rTKA. LEVEL OF EVIDENCE: Retrospective Cohort Study; III.

Radiolucent line assessment in cemented stemmed total knee (RISK) arthroplasty: validation of a modernized classification system.

BACKGROUND: This study aims to implement and assess the inter- and intra-reliability of a modernized radiolucency assessment system; the Radiolucency In cemented Stemmed Knee (RISK) arthroplasty classification. Furthermore, we assessed the distribution of regions affected by radiolucency in patients undergoing stemmed cemented total knee arthroplasty. METHODS: Stemmed total knee arthroplasty cases over 7-year period at a single institution were retrospectively identified and reviewed. The RISK classification system identifies five zones in the femur and five zones in the tibia in both the anteroposterior (AP) and lateral planes. Post-operative and follow-up radiographs were scored for radiolucency by four blinded reviewers at two distinct time points four weeks apart. Reliability was assessed using the kappa statistic. A heat map was generated to demonstrate the reported regions of radiolucency. RESULTS: 29 cases (63 radiographs) of stemmed total knee arthroplasty were examined radiographically using the RISK classification system. Intra-reliability (0.83) and Inter-reliability (0.80) scores were both consistent with a strong level of agreement using the kappa scoring system. Radiolucency was more commonly associated with the tibial component (76.6%) compared to the femoral component (23.3%), and the tibial anterior-posterior (AP) region 1 (medial plateau) was the most affected (14.9%). CONCLUSION: The RISK classification system is a reliable assessment tool for evaluating radiolucency around stemmed total knee arthroplasty using defined zones on both AP and lateral radiographs. Zones of radiolucency identified in this study may be relevant to implant survival and corresponded well with zones of fixation, which may help inform future research.

Assessment of patient satisfaction following revision total knee arthroplasty.

BACKGROUND: Patient satisfaction is becoming an increasingly important measure of healthcare quality. Satisfaction following RTKA is poorly described within the literature, resulting in difficulty for clinicians to manage patient expectations and obtain informed consent. METHODS: We investigated postoperative satisfaction of RTKA patients by a single surgeon, using a single prosthesis, at a single institution. Patient satisfaction was assessed using structured telephone assessment questionnaires and review of orthopaedic/hospital records. The effect of patient and surgical characteristics on satisfaction was assessed using correlation coefficients and binary logistic regression in SPSS. RESULTS: Two hundred and two RTKAs were performed in 178 patients between 2004 and 2015 inclusive. One hundred and twenty-four patients (143 RTKAs) were contactable to complete satisfaction assessment. Eighty-five percent of patients were satisfied and would have the RTKA again, 8% were unsure, 7% would not. Mean reported satisfaction on a numerical scale (1-10) was 8.17 (range 1-10), with 74% of patients scoring 8 or above, and 35% of patients scoring 10. The Mahomed Satisfaction Scale outcomes demonstrated a mean score of 87.7. High positive correlation was found between assessment tools. Logistic regression analysis identified factors contributing to satisfaction included ROM, OKS, BMI, and surgical time. CONCLUSION: This cohort demonstrated high patient satisfaction rate following RTKA, utilizing simple and reliable outcome measurement tools. We found a high positive correlation between methods of assessment, and moderate positive correlation between satisfaction and functional outcomes. These results contribute to the understanding of satisfaction in RTKA patients, which may assist in informing patients of expected post-operative outcomes.

Mark-Up Trends in Contemporary Medicare Primary and Revision Total Joint Arthroplasty.

BACKGROUND: Understanding mark-up ratios (MRs), the ratio between a healthcare institution's submitted charge and the Medicare payment received, for high-volume orthopaedic procedures is imperative to inform policy about price transparency and reducing surprise billing. This analysis examined the MRs for primary and revision total hip and knee arthroplasty (THA and TKA) services to Medicare beneficiaries between 2013 and 2019 across healthcare settings and geographic regions. METHODS: A large dataset was queried for all THA and TKA procedures performed by orthopaedic surgeons between 2013 and 2019, using Healthcare Common Procedure Coding System (HCPCS) codes for the most frequently used services. Yearly MRs, service counts, average submitted charges, average allowed payments, and average Medicare payments were analyzed. Trends in MRs were assessed. We evaluated 9 THA HCPCS codes, averaging 159,297 procedures a year provided by a mean of 5,330 surgeons. We evaluated 6 TKA HCPCS codes, averaging 290,244 procedures a year provided by a mean of 7,308 surgeons. RESULTS: For knee arthroplasty procedures, a decrease was noted for HCPCS code 27438 (patellar arthroplasty with prosthesis) over the study period (8.30 to 6.62; P = .016) and HCPCS code 27447 (TKA) had the highest median (interquartile range [IQR]) MR (4.73 [3.64 to 6.30]). For revision knee procedures, the highest median (IQR) MR was for HCPCS code 27488 (removal of knee prosthesis; 6.12 [3.83-8.22]). While no trends were noted for both primary and revision hip arthroplasty, median (IQR) MRs in 2019 for primary hip procedures ranged from 3.83 (hemiarthroplasty) to 5.06 (conversion of previous hip surgery to THA) and HCPCS code 27130 (total hip arthroplasty) had a median (IQR) MR of 4.66 (3.58-6.44). For revision hip procedures, MRs ranged from 3.79 (open treatment of femoral fracture or prosthetic arthroplasty) to 6.10 (revision of THA femoral component). Wisconsin had the highest median MR by state (>9) for primary knee, revision knee, and primary hip procedures. CONCLUSION: The MRs for primary and revision THA and TKA procedures were strikingly high, as compared to nonorthopaedic procedures. These findings represent high levels of excess charges billed, which may pose serious financial burdens to patients and must be taken into consideration in future policy discussions to avoid price inflation.

Timing and Factors Associated With Revision for Infection After Primary Total Knee Arthroplasty Based on American Joint Replacement Registry Data.

BACKGROUND: Infection following total knee arthroplasty (TKA) remains a challenging clinical problem. Using American Joint Replacement Registry data, this study examined factors related to the incidence and timing of infection. METHODS: Primary TKAs performed from January 2012 through December 2018 among patients ≥65 years of age at surgery were queried from the American Joint Replacement Registry and merged with Medicare data to enhance capture of revisions for infection. Multivariate Cox regressions incorporating patient, surgical, and institutional factors were used to produce hazard ratios (HRs) associated with revision for infection and mortality after revision for infection. RESULTS: Among 525,887 TKAs, 2,821 (0.54%) were revised for infection. Men had an increased risk of revision for infection at all-time intervals (≤90 days, HR = 2.06, 95% CI: 1.75-2.43, P < .0001; >90 days to 1 year, HR = 1.90, 95% CI: 1.58-2.28, P < .0001; >1 year, HR = 1.57, 95% CI: 1.37-1.79, P < .0001). TKAs performed for osteoarthritis had an increased risk of revision for infection at ≤90 days (HR = 2.01, 95% CI: 1.45-2.78, P < .0001) but not at later times. Mortality was more likely among patients who had a Charlson Comorbidity Index (CCI) ≥ 5 compared to those who had a CCI ≤ 2 (HR = 3.21, 95% CI: 1.35-7.63, P = .008). Mortality was also more likely among older patients (HR = 1.61 for each decade, 95% CI: 1.04-2.49, P = .03). CONCLUSION: Based on primary TKAs performed in the United States, men were found to have a persistently higher risk of revision for infection, while a diagnosis of osteoarthritis was associated with a significantly higher risk only during the first 90 days after surgery.

Oxidized Zirconium Versus Cobalt Chromium for Primary TKA: No Difference in Midterm Revision Rates From the American Joint Replacement Registry.

BACKGROUND: Cobalt chromium (CoCr) is the most commonly used material in TKA; however, the use of oxidized zirconium (OxZr) implants has increased. The advantages to this material demonstrated in basic science studies have not been borne out in clinical studies to date. QUESTION/PURPOSE: In the setting of the American Joint Replacement Registry (AJRR), how do revision rates differ between CoCr and OxZr after primary TKA? METHODS: The AJRR was accessed for all primary TKAs performed between 2012 and 2020 for osteoarthritis, resulting in 441,605 procedures (68,506 with OxZr and 373,099 with CoCr). The AJRR is the largest joint replacement registry worldwide and collects procedure-specific details, making it ideal for large-scale comparisons of implant materials in the United States. Competing risk survival analyses were used to evaluate the all-cause revision rates of primary TKAs, comparing CoCr and OxZr implants. Data from the Centers for Medicare and Medicaid Services claims from 2012 to 2017 were also cross-referenced to capture additional revisions from other institutions. Revision rates were tabulated and subclassified by indication. Multivariate Cox regression was used to account for confounding variables such as age, gender, region, and hospital size. RESULTS: After controlling for confounding variables, there were no differences between the OxZr and CoCr groups in terms of the rate of all-cause revision at a mean follow-up of 46 ± 23 months and 44 ± 24 months for CoCr and OxZr implants, respectively (hazard ratio 1.055 [95% confidence interval 0.979 to 1.137]; p = 0.16) The univariate analysis demonstrated increased rates of revisions for pain and instability in the OxZr group (p = 0.003 and p < 0.001, respectively). CONCLUSION: These findings suggest there is no difference in all-cause revision between OxZr and CoCr implants in the short-term to mid-term. However, further long-term in vivo studies are needed to monitor the safety and all-cause revision rate of OxZr implants compared with those of CoCr implants. OxZr implants may be favorable in patients who have sensitivity to metal. Despite similar short-term to mid-term all-cause revision rates to CoCr implants, because of the limitations of this study, definitive recommendations for or against the use of OxZr cannot be made. LEVEL OF EVIDENCE: Level III, therapeutic study.

The James A. Rand Young Investigator's Award: Increased Revision Risk With Mobile Bearings in Total Knee Arthroplasty: An Analysis of the American Joint Replacement Registry.

BACKGROUND: Mobile-bearing (MB) total knee arthroplasty (TKA) may reduce wear and improve patellar tracking but may increase revision risk due to tibial component design, balance complexity, and bearing dislocation. We utilized the American Joint Replacement Registry to examine risk of revision with MB compared to fixed-bearing (FB) designs. METHODS: An analysis of primary TKA in patients over 65 years was performed with American Joint Replacement Registry data linked to Centers for Medicare and Medicaid Services data from 2012 to 2019. Analyses compared MB to FB designs with a subanalysis of implants from a single company. We identified 485,024 TKAs, with 452,199 (93.2%) FB-TKAs and 32,825 (6.8%) MB-TKAs. Cox proportional hazards regression modeling was used for all-cause revision and revision for infection, adjusting for sex, age, and competing risk of mortality. Event-free survival curves evaluated time to all-cause revision and revision for infection. RESULTS: MB-TKAs were at an increased risk for all-cause revision: hazard ratio (HR) 1.36 ([95% confidence interval (CI) 1.24-1.49], P < .0001) but not revision for infection: HR 1.06 ([95% CI 0.90-1.25], P = .52). When comparing implants within a single company, MB-TKAs were at an increased risk of all-cause revision: HR 1.55 ([95% CI 1.38-1.73], P < .0001). Event-free survival curves demonstrated increased risk for all-cause revision for MB-TKA across all time points, with a greater magnitude of risk up to 8 years. CONCLUSION: Although survivorship of both designs was outstanding, MB-TKA designs demonstrated increased risk for all-cause revision. Additional investigation is needed to determine if this is related to patient selection factors, surgical technique, bearing, or implant design.

Mid-Term Performance of the First Mass-Produced Three-Dimensional Printed Cementless Tibia in the United States as Reported in the American Joint Replacement Registry.

BACKGROUND: Cementless tibial components have shown improvements in clinical performance compared to predicate designs, though evidence supporting mid-term performance and fixation is scarce. The purpose of this study is to determine the mid-term survivorships, revision rates, and reasons why 3-dimensional printed cementless tibial baseplates (3DTKAs) failed compared to other cementless as well as cemented tibial baseplates reported from the American Joint Replacement Registry (AJRR) data. METHODS: All primary total knee arthroplasty (TKA) cases performed in patients 65 years of age or older within the AJRR from January 2, 2012 through June 30, 2020 were queried. A total of 28,631 3DTKAs were identified from 428 institutions. These were compared to all other "aggregated cementless tibia" (n = 7,577) and "aggregated cemented tibia" (n = 550,133) cases. Centers for Medicare & Medicaid Services data over the same time period were merged with AJRR data to determine survivorship and patient-timed incident revision rates per 1,000 years. Failure reasons were tracked during this study period. RESULTS: At 60 months, Kaplan-Meier implant survivorship was 98.9% (CI 98.7-99.0), 98.3% (CI 97.9-98.6), and 98.4% (CI 98.4-98.5) in the 3DTKA, aggregate cementless, and cemented knee cohorts, respectively (P < .0001). Patient-timed incident revision rates were 3.11 (CI 2.75-3.53), 3.99 (CI 3.34-4.76), and 3.35 (CI 3.28-3.42) for those cohorts, which corresponds to a revision rate of 0.31%, 0.40%, and 0.34% per year. CONCLUSION: In this analysis, 3DTKA had favorable survivorship and lower revision rates compared to aggregate cementless and cemented TKAs implanted from the same national database during the same time period.

Conformity assessment with structural strength requirements of mechanical polycentric prosthetic knee used for amputee rehabilitation.

Prosthetic restoration is an important component of amputee rehabilitation which may be subjected to a static load of nearly five times of amputees' body weight and is continuously administered to cyclic or fatigue loads during its function. This study presents a structural strength analysis of polycentric mechanical prosthetic knee commonly used in National Institutes in India by finite element simulation and its experimental validation. Static and fatigue analyses have been performed to ensure its structural integrity as per the ISO 10328:2006 standard. Accurate dimensioning of knee components have been obtained using coordinate measuring machine and the 3 D CAD model has been generated by CATIA V5 from the 2 D geometry. The model is imported to the ANSYS 20.1 workbench to study stress distribution in the knee for ensuring its safety performance. The selection of reference planes, application of calculated loads, and position of load line have been done as per the ISO test procedure. Static and cyclic loadings of 4130 N and 1230 N are applied at the top and the bottom plate is given with translational constraints to limit its movement in any direction. Results indicate that the prosthetic knee model is moderately strong enough to outstrip the static strength test. However, the calculated strain and predicted fatigue life during the cyclic test suggest that this knee unit has poor fatigue strength. Validation results with an average error percentage of 3.44 and 10 show higher reliability based on previous study results and experimental tests, respectively.

Intraoperative Assessment of Gap Balancing in Total Knee Arthroplasty Using Navigation with Joint Stability Graphs.

The purpose of this study was to assess continuous gaps in the replaced knee throughout the full range of motion (ROM) after total knee arthroplasty (TKA) using a joint stability graph, and to analyze the gap laxity in the mid-flexion range. Ninety-three TKAs were performed using imageless navigation with a joint stability graph. While positioning guides for each respective cut, the surgeon can safely preview the resection's impact for the resulting joint gaps and control the soft tissue balance at the knee flexion of 0° (extension) and 90° (flexion). The gaps between the femoral component and insert were evaluated throughout the full ROM using the joint stability graph. The mechanical axis (MA) and change of joint line height were radiographically evaluated. Posthoc power analyses using a significant α value of 0.05 were performed on the proportion of the mid-flexion instability as a primary outcome to determine whether the sample had sufficient power. The power was determined to be sufficient (100%). The flexion-extension gap differences in each medial and lateral compartment and the mediolateral gap differences in flexion and extension were all ≤3 mm. None of the knees had mid-flexion instability, which is defined by a peak mid-flexion gap that is 3 mm greater than the smaller value of flexion or extension gap. The average MA was well corrected from varus 11.4° to varus 1.0° postoperatively. The proportion of postoperative well-aligned knees (MA ≤ 3°) was 87.1%. The joint line height was well preserved (14.7 vs. 14.8 mm, p = 0.751). The joint stability graph in TKA using the navigation can effectively evaluate the continuous gap throughout the ROM, including the mid-flexion range. Mid-flexion instability was uncommon in primary TKAs with appropriate alignment and proper preservation of the joint line. The Level of evidence for the study is IV.