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Purpose It is well-known that revision rates after primary knee arthroplasty vary widely. However, it is uncertain whether hospital revision rates are reliable indicators of general surgical quality as defined by patients. The SPARK study compared primary knee arthroplasty surgery at three high-volume hospitals whose revision rates differed for unknown reasons. Methods This prospective observational study included primary knee arthroplasty patients (total, medial/lateral unicompartmental and patellofemoral) in two low-revision hospitals (Aarhus University Hospital and Aalborg University Hospital Farsø) and one high-revision hospital (Copenhagen University Hospital Herlev-Gentofte). Patients were followed from preoperatively (2016–17) to 1-year postoperatively with patient-reported outcome measures including Oxford Knee Score (OKS), EQ-5D-5L and Copenhagen Knee ROM (range of motion) Scale. The surgical outcomes were compared across hospitals for patients with comparable grades of radiographic knee osteoarthritis and preoperative OKS. Statistical comparisons (parametric and non-parametric) included all three hospitals. Results 97% of the 1452 patients who provided baseline data (89% of those included and 56% of those operated) responded postoperatively (90% at 1 year) . Hospitals’ utilization of unicompartmental knee arthroplasties differed (Aarhus 49%, Aalborg 14%, and Copenhagen 22%, p  < 0.001). 28 patients had revision surgery during the first year (hospital independent, p  = 0.1) and were subsequently excluded. 1-year OKS (39 ± 7) was independent of hospital ( p  = 0.1), even when adjusted for age, sex, Body Mass Index, baseline OKS and osteoarthritis grading. 15% of patients improved less than Minimal Important Change (8 OKS) (Aarhus 19%, Aalborg 13% and Copenhagen 14%, p  = 0.051 unadjusted). Patients with comparable preoperative OKS or osteoarthritis grading had similar 1-year results across hospitals (OKS and willingness to repeat surgery, p  ≥ 0.087) except for the 64 patients with Kellgren–Lawrence grade-4 (Aarhus 4–6 OKS points lower). 86% of patients were satisfied, and 92% were “willing to repeat surgery”, independent of hospital ( p  ≥ 0.1). Hospital revision rates differences diminished during the study period. Conclusions Patients in hospitals with a history of differing revision rates had comparable patient-reported outcomes 1 year after primary knee arthroplasty, supporting that surgical quality should not be evaluated by revision rates alone. Future studies should explore if revision rate variations may depend as much on revision thresholds and indications as on outcomes of primary surgery. Level of evidence Level II (Prospective cohort study).

ObjectivesOrdinal scales provide means for communicating the severity of a condition, but they are affected by cognitive biases, they introduce statistical problems and they sacrifice resolution. Clinicians discern more details than contained in scales, for example, when assessing radiographs, but clinicians’ distinctions are often based on experience-based rules of thumb, that is, heuristics. The objectives of this study are to compare clinicians’ heuristic assessments to ordinal grading, to identify case elements that influence clinicians’ judgements and to present a method for quantifying heuristic assessments.DesignClinicians were presented with 17 207 random pairs from a set of 1087 knee radiographs. For each pair, the radiograph with more severe osteoarthritis was selected. The Bradley-Terry model was used to calculate an osteoarthritis strength parameter for each radiograph. Similarly, strength parameters were determined for 12 morphological features with five additional features being considered either present or absent. All radiographs were also graded according to conventional ordinal systems (Kellgren-Lawrence and Ahlbäck). Relations between clinicians’ judgements and (1) the heuristics-based osteoarthritis strength, (2) conventional ordinal systems and (3) morphological features were investigated.ResultsReceiver operating characteristic analysis showed that the Bradley-Terry model provided a good description of clinicians’ assessments (area under the curve (AUC)=0.97, 95% CI 0.968 to 0.972). Morphological features (AUC=0.90, 95% CI 0.900 to 0.908) provided a superior description of clinicians’ choices compared with conventional ordinal systems (AUC=0.88, 95% CI 0.878 to 0.887 and AUC=0.80, 95% CI 0.796 to 0.809) for Ahlbäck and Kellgren-Lawrence, respectively). The features most strongly associated with osteoarthritis strength were medial joint space width, flattening of the medial femoral and tibial condyles, medial osteophytes and alignment.ConclusionsHeuristics-based assessments give a better distinction than conventional grading systems of knee osteoarthritis. The example presents a general approach to evaluate which features are part of experts’ heuristics. The data suggest that experts discern more details than included in conventional ordinal grading systems. Quantitative heuristic assessments may replace ordinal scales.

Purpose Revision rates following primary knee arthroplasty vary by country, region and hospital. The SPARK study was initiated to compare primary surgery across three Danish regions with consistently different revision rates. The present study investigated whether the variations were associated with differences in the primary patient selection. Methods A prospective observational cohort study included patients scheduled Sep 2016 Dec 2017 for primary knee arthroplasty (total, medial/lateral unicompartmental or patellofemoral) at three high-volume hospitals, representing regions with 2-year cumulative revision rates of 1, 2 and 5%, respectively. Hospitals were compared with respects to patient demographics, preoperative patient-reported outcome measures, motivations for surgery, implant selection, radiological osteoarthritis and the regional incidence of primary surgery. Statistical tests (parametric and non-parametric) comprised all three hospitals. Results Baseline data was provided by 1452 patients (89% of included patients, 56% of available patients). Patients in Copenhagen (Herlev-Gentofte Hospital, high-revision) were older (68.6 ± 9 years) than those in low-revision hospitals (Aarhus 66.6 ± 10 y. and Aalborg (Farsø) 67.3 ± 9 y., p  = 0.002). In Aalborg, patients who had higher Body Mass Index (mean 30.2 kg/m 2 versus 28.2 (Aarhus) and 28.7 kg/m 2 (Copenhagen), p  < 0.001), were more likely to be male (56% versus 45 and 43%, respectively, p  = 0.002), and exhibited fewer anxiety and depression symptoms (EQ-5D-5L) (24% versus 34 and 38%, p  = 0.01). The preoperative Oxford Knee Score (23.3 ± 7), UCLA Activity Scale (4.7 ± 2), range of motion (Copenhagen Knee ROM Scale) and patient motivations were comparable across hospitals but varied with implant type. Radiological classification ≥ 2 was observed in 94% (Kellgren-Lawrence) and 67% (Ahlbäck) and was more frequent in Aarhus (low-revision) ( p  ≤ 0.02), where unicompartmental implants were utilized most (49% versus 14 (Aalborg) and 23% (Copenhagen), p  < 0.001). In the Capital Region (Copenhagen), the incidence of surgery was 15–28% higher ( p  < 0.001). Conclusion Patient-reported outcome measures prior to primary knee arthroplasty were comparable across hospitals with differing revision rates. While radiographic classifications and surgical incidence indicated higher thresholds for primary surgery in one low-revision hospital, most variations in patient and implant selection were contrary to well-known revision risk factors, suggesting that patient selection differences alone were unlikely to be responsible for the observed variation in revision rates across Danish hospitals. Level of evidence II, Prospective cohort study.