Similar QALY gain in primary and revision knee arthroplasty: A cost analysis and Markov model.

PURPOSE: The aim of this study is to investigate the cost-effectiveness of revision total knee arthroplasty compared to primary total knee arthroplasty in terms of cost-per-quality-adjusted life year (QALY). METHODS: Data were retrieved for all primary and revision total knee replacement (TKA) procedures performed at a tertiary Swiss hospital between 2006 and 2019. A Markov model was created to evaluate revision risk and we calculated lifetime QALY gain and lifetime procedure costs through individual EuroQol 5 dimension (EQ-5D) scores, hospital costs, national life expectancy tables and standard discounting processes. Cost-per-QALY gain was calculated for primary and revision procedures. RESULTS: EQ-5D data were available for 1343 primary and 103 revision procedures. Significant QALY gains were seen following surgery in all cases. Similar, but significantly more QALYs were gained following primary TKA (PTKA) (5.67 ± 3.98) than following revision TKA (RTKA) (4.67 ± 4.20). Cost-per-QALY was €4686 for PTKA and €10,364 for RTKA. The highest average cost-per-QALY was seen in two-stage RTKA (€12,292), followed by one-stage RTKA (€8982). CONCLUSION: RTKA results in a similar QALY gain as PTKA. The costs of achieving health gain are two to three times higher in RTKA, but both procedures are highly cost-effective. LEVEL OF EVIDENCE: Economic level II.

Sex-Specific Implant Fixation Can Reduce Revision Rates in Total Hip Arthroplasty: Evidence From the Swiss National Joint Registry.

BACKGROUND: Patient's sex is considered a risk factor for revision following primary total hip arthroplasty (THA), but sex-specific treatment guidelines are lacking. The purpose was to assess sex-specificity of risk factors for periprosthetic femoral fractures (PFFs) and aseptic stem loosening (ASL) in a nationwide register study. METHODS: All uncemented and hybrid THAs for hip osteoarthritis registered in the Swiss National Joint Registry were considered. 86,423 THAs were analyzed. Comparable THA subsets for both sexes were obtained through propensity score matching (1:1). A sex-specific analysis of risk factors for early PFF or ASL was performed using recursive partitioning analyses. RESULTS: In women, PFFs were most significantly associated with uncemented THA fixation (P < .0001) and age (P < .01, threshold: 70.5 years). The ASLs were solely associated with patient age of <65 years (P = .023). In men, PFFs were associated exclusively with an American Society of Anesthesiologists (ASA) score >2 (P = .026). The ASLs were not correlated to any of the potential risk factors analyzed. A mathematical simulation indicated that avoiding uncemented THA fixation in women ≥70.5 years of age decreased the number of revisions within the observational period by 21% in this subset and by 4.9% in the entire patient population. CONCLUSION: Uncemented THA should be avoided in women >70.5 years due to the increased risk of early PFF, while the mode of stem fixation did not influence revision risk in men. A sex-specific regimen for THA fixation has the potential to markedly reduce early THA revision rates.

Revision total knee arthroplasty results in financial deficits within the Swiss healthcare system.

PURPOSE: Revision total knee arthroplasty (RTKA) results in high costs with inadequately low reimbursement in different healthcare systems. Therefore, a financial analysis was performed comparing costs and reimbursements of primary total knee arthroplasty (PTKA) versus RTKA using financial and total knee arthroplasty-register data from a large tertiary hospital, the Cantonal Hospital of St. Gallen (KSSG), Switzerland. METHODS: All PTKA and RTKA performed between January 2012 and September 2019 at the KSSG were included. Financial and TKA-register data for each case were collected, including detailed cost allocation, reimbursement, patients' insurance status, type and indication for surgery and length of hospital stay. RTKA was further subdivided in one-stage and two-stage RTKA. Direct hospital costs were analyzed and compared to reimbursement in both groups. Cost-coverage ratios were calculated. RESULTS: 730 PTKA and 106 RTKA were included. The RTKA group contained 66 one-stage and 40 two-stage RTKA. Cost-coverage ratio for PTKA and RTKA showed to be 110.9% and 81.3%, respectively. Cost-coverage ratio was lower for two-stage RTKA than for one-stage RTKA with 74.1% and 92.3%, respectively. CONCLUSION: RTKA leads to financial deficits especially for tertiary hospitals within the Swiss healthcare system. Restructuring of the reimbursements for PTKA and RTKA should be considered in favor of RTKA. Otherwise, tertiary hospitals will face a growing financial burden with the constantly increasing annual number of RTKA procedures, predominantly performed in this type of hospitals. LEVEL OF EVIDENCE: III.

Differences in case mix and outcomes between Swiss and Scottish total knee arthroplasty patients.

PURPOSE: The clinical benefits of total knee arthroplasty (TKA) are well defined, but little attention has been paid to the cross-cultural variation. The objective of this study was to compare case mix and outcomes following TKA in Swiss and Scottish patients. METHODS: Data from local registries at a Swiss and a Scottish orthopaedic hospital were extracted to evaluate: (A) age, sex, body mass index (BMI), self-reported health status (EQ-5D), and joint awareness (Forgotten Joint Score-12 (FJS-12)) at pre-surgery, (B) improvement in EQ-5D and FJS-12 scores from pre-surgery to 1 year, and (C) patient satisfaction at 1 year. RESULTS: Data from 2075 Swiss and 994 Scottish TKA patients were available from the local registries. Swiss and Scottish patients differed in age (69.3 vs 68.8 years, p = 0.046), sex ratio (62.9% vs 56.9% women, p = 0.002) and BMI (29.6 vs 30.9, p < 0.001). At pre-surgery, FJS-12 scores were comparable (Swiss 12.1 vs Scottish 10.9, n.s.), but EQ-5D scores were better in Swiss patients (0.52 vs 0.40, p < 0.001). Post-operative improvement was greater in Switzerland for the FJS-12 (+ 55.1 vs + 32.2, p < 0.001), but not for the EQ-5D (+ 0.31 vs + 0.29, n.s.). The satisfaction rate was similar in both groups (88.3% vs 89.6%, n.s.). CONCLUSION: Subtle cross-cultural variation was evident in TKA case-mix factors between the two countries. Satisfaction and improvement in health status were similar, while improvement in joint-specific outcome was notably greater in Switzerland. Understanding cross-cultural variability of the outcome has important implications when interpreting study and registry data from other countries and when counselling a patient in daily practice. LEVEL OF EVIDENCE: Retrospective cohort, Level III.

Normative Values for the Forgotten Joint Score-12 for the US General Population.

BACKGROUND: The Forgotten Joint Score-12 (FJS-12) is a patient-reported outcome questionnaire of joint awareness in patients with hip and knee pathologies. To improve interpretability of values derived from this measure, we collected normative values for the US general population. METHODS: A sample of 2000 participants, representative of US general population, was sought via an online panel. Quota sampling was used to obtain age-specific and sex-specific groups of 200 participants each. The FJS-12 is a 12-item questionnaire assessing the ability to forget the hip or knee joint during activities of daily living. To match US national census data from 2010, raking was used for determining data weights. RESULTS: Normative data for the FJS-12 could be established based on a data set from 2017 respondents (50.1% men; mean age, 54.0 years; 66.3% white/Caucasian). Median FJS-12 scores in the total sample were 75.0 points for knees and 87.5 points for hips. In the age-specific and sex-specific groups, the lowest median score for knees was 54.2 points (men aged 18-39 years) and the highest median was 97.0 (men aged above 70 years). Similarly, median scores for hips were lowest in men aged 18-39 years (60.9 points) and highest in men aged above 70 years (100 points). CONCLUSION: Normative values have been established for the FJS-12 for hips and knees in US general population. Age-specific and sex-specific differences require relying on normative values from the respective groups when interpreting FJS-12 data.

Clinical and radiological outcome at mean follow-up of 11 years after hip arthroscopy.

INTRODUCTION: The use of hip arthroscopy (HA) has substantially increased over the last decade. However, while the benefits of HA after 1 year in patients with femoroacetabular impingement (FAI) are well documented, long-term data on the progression of osteoarthritis (OA) or patient-reported outcomes (PROMs) are lacking. OBJECTIVES: To evaluate long-term clinical and radiological outcomes after HA. MATERIALS AND METHODS: Preoperative clinical records, operative notes, and radiographs from all patients who underwent HA at our hospital between 1998 and 2006 were reviewed. Exclusion criteria were previous hip surgery or diagnostic HA. Primary endpoints were subsequent total hip arthroplasty (THA) or other hip surgery. Secondary endpoints were OA progression and PROMs. RESULTS: HA was performed in 92 consecutive patients from 1998 to 2006. Indications for HA were FAI, labral lesions, early OA, and focal osteochondral defects. Mean follow-up was 11.2 years (SD 2.5, range 7.9-16). Data from 43 patients were available for analysis; 38 patients were excluded, and 11 were lost to follow-up. 20 patients had subsequent hip surgery, of which 11 patients required THA. 33 patients (77%) stated that they would undergo HA again under the same circumstances. Longitudinal radiological analysis showed no significant OA progression in patients without THA. The Forgotten Joint Score-12 was the only PROM to significantly differ between patients who had no further surgery and patients who had undergone revision (p = 0.037). CONCLUSION: There was no significant OA progression on plain radiography at an average of 11 years post-HA. Sound indication criteria is essential, as 45% of patients required subsequent surgery.

Treatment Success Following Joint Arthroplasty: Defining Thresholds for the Oxford Hip and Knee Scores.

BACKGROUND: Patient-reported outcome scores are the mainstay method for quantifying success following arthroplasty. However, it is unclear when a "successful outcome" is achieved. We calculated threshold values for the Oxford Hip and Knee Score (OHS and OKS) representing achievement of a successful treatment at 12-month follow-up. METHODS: Questionnaires were administered to patients undergoing total hip (THA) or knee (TKA) arthroplasty before and 12 months after surgery alongside questions assessing key aspects of treatment success. A composite success criterion was used to perform receiver operator characteristic analysis. Thresholds providing maximum sensitivity and specificity were determined for the total sample and subgroups defined by presurgery scores. RESULTS: Data were available for 3203 THA and 2742 TKA patients. Applying the composite treatment success criterion, 67.3% of the TKA and 77.6% of the THA sample reported treatment success. Accuracy for predicting treatment success was high for the OHS and OKS (both areas under the curve, 0.87). For the OHS, a threshold value of 37.5 points showed highest sensitivity and specificity in the total sample, while for the OKS the optimal threshold was 32.5 points. Depending on presurgery scores, optimal thresholds varied between 32.5 and 38.5 for the OHS and 28.5 and 36.5 for the OKS. CONCLUSION: This is the first study to apply a composite "success" anchor to the OHS and OKS to evaluate outcome following total joint arthroplasty. Notably fewer patients report a "successful outcome" using a composite outcome threshold than report being "satisfied."

Joint awareness after ACL reconstruction: patient-reported outcomes measured with the Forgotten Joint Score-12.

PURPOSE: To measure joint awareness in patients who have undergone anterior cruciate ligament (ACL) reconstruction and to investigate medium- and long-term results of the procedure. METHODS: All patients who had undergone ACL reconstruction with the same arthroscopic surgical technique at our institution between 2011 and 2014 (medium-term follow-up group (Group I)) or between 2000 and 2005 (long-term follow-up group (Group II)) were considered for inclusion in the study. A group of healthy controls were recruited to obtain reference values for the FJS-12 (Forgotten Joint Score-12). Propensity score matching was applied to improve comparability of patients and healthy controls in terms of sex and age. RESULTS: Fifty-eight patients of the Group I (mean follow-up 31.5 (SD13.4) months, range 12-54), 57 patients of the Group II (mean follow-up 139 (SD15.2) months, range 120-179), and the healthy control samples (100 individuals) were analysed. Significantly lower FJS-12 was found in both groups (Group I: 71.6 and Group II: 70.1), compared to the two matched control groups (88.1 and 90.0). CONCLUSIONS: The concept of joint awareness was successfully applied to evaluate medium- and long-term results of ACL reconstruction. The clinical relevance of this study is that it extends the construct of joint awareness as a patient-reported outcome parameter to ACL reconstruction surgery. LEVEL OF EVIDENCE: Level III.

Impact of Comorbidities on Outcome After Total Hip Arthroplasty.

BACKGROUND: Patient-reported outcome scores gain increasing importance in quantifying clinical success and procedure remuneration. Our aim was to evaluate the impact of comorbidity on joint-specific outcome and general health in patients undergoing elective total hip arthroplasty (THA). METHODS: Longitudinal data on THA procedures were used to evaluate the association between comorbidity and surgical outcome in terms of joint-specific measures and general health (Forgotten Joint Score-12 [FJS-12], Oxford Hip Score [OHS], and Short Form-12) at 1-year follow-up. Comorbidities comprised the Charlson comorbidity index (CCI), low back pain (LBP), pain from other joints (POJ), and body mass index. RESULTS: We analyzed data from 251 THA patients (age: 67.7 ± 11.8 years; 58.2% female). Most common conditions were POJ (75.9%), LBP (55.1%), connective tissue disease (12.1%), and diabetes (5.6%). With regard to postoperative improvement, we did not find statistically significant differences between patients with or without CCI comorbidities (FJS-12, +38.7 vs +43.2, P = .370; OHS, +15.6 vs +17.9, P = .100) or POJ (FJS-12, +39.9 vs +45.1, P = .325; OHS, +17.3 vs +16.6, P = .645). Patients with LBP showed less improvement on the FJS-12 than those without LBP (+35.6 vs +49.1; P = .002), whereas no difference was found for the OHS (+17.9 vs +16.5; P = .266). CONCLUSION: Patients with comorbid conditions report lower preoperative and postoperative outcome scores compared with patients with no such conditions; however, there was no statistically significant association of CCI comorbidities and POJ with postoperative improvement in joint-specific outcomes. LBP was found to have a negative impact on postoperative improvement in terms of joint awareness.

Factors Predicting the Forgotten Joint Score After Total Knee Arthroplasty.

BACKGROUND: We recently developed the forgotten joint score 12 (FJS-12), a tool to assess joint awareness in everyday life. It is unknown whether patient factors predicting the outcome of the FJS-12 after total knee arthroplasty (TKA) exist. METHODS: Five hundred forty cases of TKA were analyzed. Objective clinical results were obtained for range of motion, stability, and alignment. Patient-reported outcome was assessed using the FJS-12. Baseline data and complications were recorded. Cluster analysis based on FJS-12, postoperative flexion, and age resulted in 3 groups: poor outcome (88 patients), good outcome (340 patients), and excellent outcome (118 patients). The characteristics of "poor" compared to "excellent" clusters were studied more closely using bivariate comparative tests and logistic regression. RESULTS: We could find that male patients around 63 years with a lower body mass index were most likely to be allocated to the cluster "excellent" (defined as high FJS-12 and high postoperative flexion). Preoperative extension and flexion, stability, varus/valgus alignment, surgery prior TKA, or comorbidities were not predictive for the FJS-12 at 1 year follow-up. CONCLUSION: We identified 3 preoperative patient-related factors that may predict the FJS-12 after TKA: body mass index, age, and gender. These findings can be used to guide decision-making and important preoperative discussions on expectations after TKA.

Plate Positioning in Periprosthetic or Interprosthetic Femur Fractures With Stable Implants-A Biomechanical Study.

BACKGROUND: Angular stable plate fixation is a widely accepted treatment option for interprosthetic or periprosthetic femoral fractures with stable implants. This biomechanical study tries to establish a safe distance of the plate from the tip of a femoral prosthesis. METHODS: A total of 38 composite femurs were reamed to an inner diameter of 23 mm to create an osteoporotic bone model. A Weber hip stem was cemented into each and a distal femoral NCB plate applied with the distance to the stem varying from 8 cm apart to 6 cm overlap in 2-cm steps. Each specimen was tested in cyclic axial loading (400 N-1500 N) and then cyclic torsion (0.6 Nm-50 Nm). Peak strain on the femur around the tip of the plate was measured with a 3D image correlation system and averaged over 26 cycles (excluding the first 3 and the last cycles). Finally, each femur was axially loaded to failure. RESULTS: Strain increased with decreasing overlap or gap. Seven specimens failed early between 2-cm overlap and 2-cm gap. Results were divided into a far group with a distance of >4 cm and a close group of <4 cm. Strain was significantly higher in the close group for axial (P < .001) and torsional (P < .001) loading. Failure load was significantly lower in the close group (P = .002). CONCLUSION: A minimal gap and/or overlap of at least 6 cm is recommended in osteoporotic bone to avoid stress risers.

Lateral subvastus approach with tibial tubercle osteotomy for primary total knee arthroplasty: clinical outcome and complications compared to medial parapatellar approach.

PURPOSE: The lateral subvastus approach (LSVA) with tibial tubercle osteotomy (TTO) is an alternative approach for total knee arthroplasty (TKA) in selected patients. The aim of this study was to compare clinical outcomes between LSV and medial parapatellar approaches for primary TKA and to investigate incidence of complications related to TTO. METHODS: A total of 580 patients with primary TKA, meeting the inclusion criteria, were treated at our hospital from February 2006 until February 2013. All patients' data were included in the local arthroplasty register and were followed up 12 months postoperatively. The data set contains: demographic data, the WOMAC score, the KSS as well as knee flexion and complications related to tibial tubercle osteotomy. RESULTS: The clinical outcome after TKA using the LSVA combined with TTO was comparable with those using the medial standard approach 1 year postoperatively. Four patients (3.8 %) needed a revision due to complications related to tubercle osteotomy. CONCLUSIONS: The LSVA is thus a viable alternative in cases of primary TKA if technical difficulties with the medial approach are anticipated. Applying precise surgical technique, the LSVA seems to be a safe and reproducible procedure.

Comparison of preoperative continuation and discontinuation of aspirin in patients undergoing total hip or knee arthroplasty.

INTRODUCTION: Preoperative discontinuation of aspirin (acetylsalicylic acid) can reduce bleeding risk but may increase the risk of perioperative cardiovascular events. MATERIALS AND METHODS: We retrospectively assessed the impact of preoperative continuation versus discontinuation of aspirin compared with a control group in a cohort of 739 consecutive patients undergoing total hip (THA) (n = 396) or knee arthroplasty (TKA) (n = 343) at a tertiary hospital. Bleeding risk, local complications, orthopaedic outcome, and cardiac and cerebral complications were assessed. RESULTS: Four hundred and sixty-five patients did not receive antithrombotic or full-dose anticoagulant medication, 175 patients were taking low-dose aspirin, 99 vitamin K antagonists, clopidogrel, or a combination of these drugs. Of the patients taking aspirin, 139 discontinued and 36 continued aspirin. Blood loss and local bleeding complications were comparable in these two groups. TKA patients who continued aspirin more frequently showed marked knee swelling after 1 week than those discontinuing aspirin (35.1 vs. 81.3 %; p = 0.001). However, orthopaedic outcome did not differ significantly between the two groups. There was a trend towards an increased risk of cardiac complications in patients who discontinued aspirin (6.5 vs. 0.0 %; p = 0.107). CONCLUSIONS: Continuation or discontinuation of aspirin did not show a statistically significant difference in the risk of relevant perioperative bleeding complications in our study. Continuation of aspirin was associated with a transitory increase in knee swelling, but had no effect on orthopaedic outcome. Continuation of aspirin may be associated with a favourable perioperative cardiac outcome. Our data support perioperative continuation of aspirin intake in patients undergoing THA or TKA.

Development of an item list to assess the forgotten joint concept in shoulder patients.

BACKGROUND: To generate an item list for the assessment of joint awareness in shoulder patients and to collect patient feedback on the comprehensibility of the items and the forgotten joint concept. METHODS: Item content was generated on the basis of literature search and expert ratings following a stepwise refinement procedure, including final evaluation by an international expert board (n = 12) including members with various professional backgrounds. Items were translated from English to German and evaluated in 30 German-speaking shoulder patients in Switzerland and 30 shoulder patients in the UK. RESULTS: Literature search identified 45 questionnaires covering 805 issues potentially relevant for the assessment of joint awareness. Stepwise item selection resulted in 97 items to be evaluated by the international expert board leaving 70 items for collecting patient feedback. The majority of patients indicated that the introductory text explaining the forgotten joint concept was easy or very easy to understand (79.3%) and that the items were clear (91.4%). CONCLUSION: We developed a list of 70 questions for the assessment of joint awareness in shoulder patients and obtained positive patient feedback for these. In a next step, we will administer the items to a large international patient sample to obtain data for psychometric analysis and development of a measurement model, which is the basis for creation of computer-adaptive assessments or static short-forms.

WOMAC, EQ-5D and Knee Society Score Thresholds for Treatment Success After Total Knee Arthroplasty.

Our study aimed at developing clinical thresholds (cut-off scores) for the Western Ontario and McMaster Universities (WOMAC) osteoarthritis index, EQ-5D and Knee Society Score for discriminating between patients with and without treatment success following total knee arthroplasty (TKA). We performed a retrospective analysis of 1055 patients 2 months after TKA and 765 patients 1 year after TKA. We considered treatment successful if the patient reported high levels of satisfaction and pain relief, functional increase, and a willingness to undergo the same procedure again. Based on this criterion we identified cut-off scores that will facilitate interpretation of the WOMAC, the EQ-5D and the KSS in TKA patients.

Can plate osteosynthesis of periprosthethic femoral fractures cause cement mantle failure around a stable hip stem? A biomechanical analysis.

Periprosthetic femoral fractures (PFF) are a serious complication after total hip arthroplasty. Plate fixation with screws perforating the cement mantle is a common treatment option. The study objective was to investigate hip stem stability and cement mantle integrity under dynamic loading. A cemented hip stem was implanted in 17 composite femur models. Nine bone models were osteotomised just distal to the stem and fixed with a polyaxial locking plate the other eight constructs served as the control group. All specimens were tested in a bi-axial material testing machine (100000 cycles). There were no statistically significant differences in axial nor in medial (varus) stem migration. No cement cracks were detected in both groups. Plate fixation of a PFF with a stable, cemented prosthesis did not lead to cement mantle failure in this in vitro study.

Association of psychological status and patient-reported physical outcome measures in joint arthroplasty: a lack of divergent validity.

BACKGROUND: Patient-reported outcome measures have become a well-recognised part of outcome assessment in orthopaedic surgery. These questionnaires claim to measure joint-specific dimensions like pain, function in activities of daily living, joint awareness or stiffness. Interference of the patient's psychological status with these orthopaedic questionnaires however may make accurate interpretation difficult. METHODS: We recruited 356 patients after unilateral, primary THA or TKA and performed a postal survey including the Brief Symptom Inventory (psychological distress measure), the Catastrophising Scale (from the Coping Strategies Questionnaire), the WOMAC score (Western Ontario and McMaster Universities Osteoarthritis Index) and the Forgotten Joint Score--12 (FJS-12). Associations between the different questionnaires were determined calculating Pearson correlation coefficients. Two multiple linear regression models were used to investigate the impact of socio-demographic variables, clinical variables and of the psychological scales (BSI and Catastrophising Scale) separately for the WOMAC score and the FJS-12. RESULTS: WOMAC-Total score showed strong correlation to Catastrophising (r = 0.79), BSI-Somatisation (r = 0.63) and BSI-GSI (r = 0.54). The FJS-12 demonstrated modest to strong correlation with Catastrophising (r = -0.60), BSI-Somatisation (r = -0.49) and the BSI-GSI (Global Severity Index) (r = -0.44). BSI-GSI and Catastrophising explained 54.3% of variance in a multivariate regression model for the WOMAC score. The same two scales explained 30.0% of variance for the FJS-12. CONCLUSIONS: There is a strong relationship between psychological status and orthopaedic outcome. The scale names of orthopaedic outcome measures suggest to measure specific dimensions like pain, stiffness, function or joint awareness. In fact they largely include patient's psychological status indicating poor divergent validity.

Development of a computer-adaptive version of the forgotten joint score.

Patient-reported outcomes (PROs) are an important endpoint in orthopedics providing comprehensive information about patients' perspectives on treatment outcome. Computer-adaptive test (CAT) measures are an advanced method for assessing PROs using item sets that are tailored to the individual patient. This provides increased measurement precision and reduces the number of items. We developed a CAT version of the Forgotten Joint Score (FJS), a measure of joint awareness in everyday life. CAT development was based on FJS data from 580 patients after THA or TKA (808 assessments). The CAT version reduced the number of items by half at comparable measurement precision. In a feasibility study we administered the newly developed CAT measure on tablet PCs and found that patients actually preferred electronic questionnaires over paper-pencil questionnaires.

Digital TKA Alignment Training with a New Digital Simulation Tool (Knee-CAT) Improves Process Quality, Efficiency, and Confidence.

Individual alignment techniques have been introduced to restore patients' unique anatomical variations during total knee arthroplasty. The transition from conventional mechanical alignment to individualised approaches, with the assistance of computer and/or robotic technologies, is challenging. The objective of this study was to develop a digital training platform with real patient data to educate and simulate various modern alignment philosophies. The aim was to evaluate the training effect of the tool by measuring the process quality and efficiency, as well as the post-training surgeon's confidence with new alignment philosophies. Based on 1000 data sets, a web-based interactive TKA computer navigation simulator (Knee-CAT) was developed. Quantitative decisions on bone cuts were linked to the extension and flexion gap values. Eleven different alignment workflows were introduced. A fully automatic evaluation system for each workflow, with a comparison function for all workflows, was implemented to increase the learning effect. The results of 40 surgeons with different experience levels using the platform were assessed. Initial data were analysed regarding process quality and efficiency and compared after two training courses. Process quality measured by the percentage of correct decisions was increased by the two training courses from 45% to 87.5%. The main reasons for failure were wrong decisions on the joint line, tibia slope, femoral rotation, and gap balancing. Efficiency was obtained with a reduction in time spent per exercise from 4 min 28 s to 2 min 35 s (42%) after the training courses. All volunteers rated the training tool as helpful or extremely helpful for learning new alignment philosophies. Separating the learning experience from OR performance was mentioned as one of the main advantages. A novel digital simulation tool for the case-based learning of various alignment philosophies in TKA surgery was developed and introduced. The simulation tool, together with the training courses, improved surgeon confidence and their ability to learn new alignment techniques in a stress-free out-of-theatre environment and to become more time efficient in making correct alignment decisions.

The "forgotten joint" as the ultimate goal in joint arthroplasty: validation of a new patient-reported outcome measure.

With improving patient outcome after joint arthroplasty, new assessment tools with increased discriminatory power especially in well-performing patients are desirable. The goal of the present study was to develop and validate a new score ("Forgotten Joint Score," or FJS) introducing a new aspect of patient-reported outcome: the patient's ability to forget the artificial joint in everyday life. After a pilot study, the FJS was validated and showed high internal consistency (Cronbach α = .95). Ceiling effects were considerably lower for the FJS (9.2%) compared with the Western Ontario and McMaster Universities subscales (16.7%-46.7%). Known-group comparisons proved the FJS to be highly discriminative in a validation sample of 243 patients. The FJS not only reflects differences between "good" and "bad" but also between "good," "very good," and "excellent" outcomes. This concise score is appealing for its more adequate measurement range and because it measures the new, promising concept of the "forgotten joint."