Predictors of subacute postoperative pain after total knee arthroplasty: A secondary analysis of two randomized trials.

BACKGROUND: Methods for identifying high-pain responders undergoing total knee arthroplasty remain important to improve individualized pain management. This study aimed at evaluating pre- and perioperative predictors of pain on Days 2-7 after total knee arthroplasty. METHODS: This is a secondary analysis of data from 227 patients participating in two randomized trials. Pain outcomes were mean pain during walking on Days 2-7 and on Days 2, 4 and 7. Multivariable linear and logistic regressions were carried out in two steps. First, only preoperative available variables including demographics, comorbidities, pain catastrophizing scale and preoperative pain were evaluated while controlling for trial intervention and recruitment site. In the second step, perioperative variables and pain during walking 24 h postoperatively were added. RESULTS: The model with only preoperative predictors for mean pain Days 2-7 showed preoperative pain (R-squared 0.097) as the only predictor. In the second model, adding postoperative available variables, only pain 24 h postoperatively (R-squared 0.248) was significant, with a significant main effect of recruitment site. Results for the separate day analysis similarly showed preoperative pain and pain during walking 24 h postoperatively as predictors. The overall best sensitivity (60%) and specificity (74%) for predicting a high-subacute postoperative pain response on Days 2-7 was with cut-off values of VAS 45.5 (out of 100) for pain during walking 24 h postoperatively. CONCLUSIONS: Postoperative pain during walking at 24 h is predictive of subacute postoperative pain on Days 2-7 after total knee arthroplasty, while preoperative pain was only a weak predictor. SIGNIFICANCE STATEMENT: This study investigated factors associated with pain after total knee arthroplasty beyond the immediate postoperative period. The analysis revealed significant associations between preoperative pain levels and, particularly, pain 24 h postoperatively, with subsequent subacute pain the following week. These findings can assist in identifying patients who would benefit from enhanced, individualized analgesic interventions to facilitate postoperative recovery.

Starting Up a Lateral Unicompartmental Knee Arthroplasty Practice - Is Outcome Affected?

INTRODUCTION: In the past, the utilization of lateral unicompartmental knee arthroplasty (UKA) has been limited at national levels, despite the fact that an estimated 10% of patients who have an indication for arthroplasty, present with isolated lateral compartment osteoarthritis (OA). Units dedicated to UKA have reported good outcomes. Identifying patients for the procedure has been less clear, and the procedure has been perceived to be technically more demanding than medial UKA. This may result in a reluctance to start a lateral UKA practice and challenge the early phase. Therefore, this paper aimed to present the outcomes and learning curve when starting up a lateral UKA practice, as this theme remains unelucidated. METHODS: There were 85 primary fixed-bearing lateral UKAs, with a minimum of 1-year follow-up, performed between 2016 and 2022 by two arthroplasty surgeons with existing UKA practices. The indications were primary (n = 79) or post-traumatic (n = 6) osteoarthritis. Patient-reported outcome measures (PROMs) were assessed at 3, 12, and 24 months. A cumulative sum (CUSUM) analysis was used to evaluate surgical duration and the 12-month Oxford Knee Score (OKS). RESULTS: Median (Interquartile range (IQR)) 12-month OKS, Activity and Participation Questionnaire (APQ), and Forgotten Joint Score (FJS) were 43 (37.5 to 46), 78 (42.5 to 98.5), and 72 (55 to 90), respectively. The OKS outcomes did not reveal adverse effects from the learning curve. A performance shift in surgical duration was observed around case 33. Kaplan-Meier implant survival reached 95.4% at 7 years for the endpoint "implant revision," and 93.5% for "implant revision/implant addition." CONCLUSION: Starting up a lateral UKA practice is safe and efficient for surgeons who have prior medial UKA experience, provided strict adherence to indications. While surgical duration indicated a learning curve over approximately 33 cases, PROMs remained stable, suggesting proficient outcomes irrespective of the learning curve.

Acute postoperative pain and catastrophizing in unicompartmental knee arthroplasty: a prospective, observational, single-center, cohort study.

BACKGROUND AND OBJECTIVES: Pain catastrophizing is associated with acute pain after total knee arthroplasty. However, the association between pain catastrophizing and acute pain after unicompartmental knee arthroplasty (UKA) remains unclear. METHODS: We investigated the incidence of predicted high-pain and low-pain responders, based on a preoperative Pain Catastrophizing Scale score >20 or ≤20, respectively, and the acute postoperative pain course in both groups. Patients undergoing UKA were consecutively included in this prospective observational cohort study. Pain at rest and during walking (5 m walk test) was evaluated preoperatively, at 24 hours postoperatively, and on days 2-7 using a pain diary. RESULTS: 125 patients were included, with 101 completing the pain diary. The incidence of predicted high-pain responders was 31% (95% CI 23% to 40%). The incidence of moderate to severe pain during walking at 24 hours postoperatively was 69% (95% CI 52% to 83%) in predicted high-pain responders and 66% (95% CI 55% to 76%) in predicted low-pain responders; OR 1.3 (95% CI 0.5 to 3.1). The incidence of moderate to severe pain at rest 24 hours postoperatively was 49% (95% CI 32% to 65%) in predicted high-pain responders and 28% (95% CI 19% to 39%) in predicted low-pain responders; OR 2.6 (95% CI 1.1 to 6.1; p=0.03). Pain catastrophizing was not associated with increased cumulated pain during walking on days 2-7. CONCLUSIONS: The incidence of predicted high-pain responders in UKA was slightly lower than reported in total knee arthroplasty. Additionally, preoperative pain catastrophizing was not associated with acute postoperative pain during walking.

Psychopharmacological treatment in patients planned for hip or knee replacement.

Psychopharmacological treatment may be an independent risk factor for increased length of stay and readmission after hip and knee replacement. Thus, temporary perioperative discontinuation may be beneficial. However, little is known regarding the treatments, and not all are feasible to discontinue. Therefore, the aim of this study was to describe the treatments in terms of type, dose, duration, indication and initiating physician to assess the feasibility of temporary perioperative discontinuation. We included 482 patients planned for hip or knee replacement in psychopharmacological treatment for psychiatric disorders from 2021 to 2023 at five orthopaedic departments in Denmark. Most patients were treated with antidepressants (89%); most frequently, either selective serotonin reuptake inhibitors (SSRIs; 48%) or serotonin-norepinephrine reuptake inhibitors (SNRIs; 21%). The majority received monotherapy (70%); most frequently, an SSRI (36%) or an SNRI (12%). Most antidepressants were initiated by general practitioners (71%), and the treatments had lasted for more than a year (87%). The doses of SSRIs/SNRIs were moderate, and the most frequent indication for antidepressants was depression (77%). These results imply that temporary perioperative SSRI/SNRI discontinuation may be feasible in hip and knee replacement patients and support a future randomized controlled trial investigating the potential benefits of temporary discontinuation.

Implementation of outpatient hip and knee arthroplasty in a multicenter public healthcare setting.

BACKGROUND AND PURPOSE: Length of hospital stay after hip and knee arthroplasty is about 1 day in Denmark with few patients discharged on the day of surgery. Hence, a protocol for multicenter implementation of discharge on day of surgery has been instituted. We aimed to describe the implementation of outpatient hip and knee arthroplasty in a multicenter public healthcare setting. METHODS: We performed a prospective multicenter study from 7 public hospitals across Denmark. Patients were screened using well-defined in- and exclusion criteria and were discharged on day of surgery when fulfilling functional discharge criteria. The study period was from September 2022 to February 2023 with variable start of implementation. Data from the same centers in a 6-month period before the COVID pandemic from July 2019 to December 2019 was used for baseline control. RESULTS: Of 2,756 primary hip and knee arthroplasties, 37% (95% confidence interval [CI] 35-39) were eligible (range 21-50% in centers) and 52% (range 24-62%) of these were discharged on day of surgery. 21% (CI 20-23) of all patients (eligible and non-eligible) were discharged on day of surgery with a range of 10-31% within centers. This was an additional 15% (CI 13-17, P < 0.001) compared with patients discharged in the control period (6% in 2019). CONCLUSION: We found it possible to perform outpatient hip and knee replacement in 21% of patients in a public healthcare setting, probably to be increased with further center experience.

Postoperative orthostatic intolerance following fast-track unicompartmental knee arthroplasty: incidence and hemodynamics-a prospective observational cohort study.

BACKGROUND: Early postoperative mobilization is essential for early functional recovery but can be inhibited by postoperative orthostatic intolerance (OI). Postoperative OI is common after major surgery, such as total knee arthroplasty (TKA). However, limited data are available after less extensive surgery, such as unicompartmental knee arthroplasty (UKA). We, therefore, investigated the incidence of OI as well as cardiovascular and tissue oxygenation responses during early mobilization after UKA. METHODS: This prospective single-centre observational study included 32 patients undergoing primary UKA. Incidence of OI and cardiovascular and tissue oxygenation responses during mobilization were evaluated preoperatively, at 6 and 24 h after surgery. Perioperative fluid balance, bleeding, surgery duration, postoperative hemoglobin, pain during mobilization and opioid usage were recorded. RESULTS: During mobilization at 6 h after surgery, 4 (14%, 95%CI 4-33%) patients experienced OI; however, no patients terminated the mobilization procedure prematurely. Dizziness and feeling of heat were the most common symptoms. OI was associated with attenuated systolic and mean arterial blood pressure responses in the sitting position (all p < 0.05). At 24 h after surgery, 24 (75%) patients had already been discharged, including three of the four patients with early OI. Only five patients were available for measurements, two of whom experienced OI; one terminated the mobilization procedure due to intolerable symptoms. We observed no statistically significant differences in perioperative fluid balance, bleeding, surgery duration, postoperative hemoglobin, pain, or opioid usage between orthostatic intolerant and tolerant patients. CONCLUSIONS: The incidence of orthostatic intolerance after fast-track unicompartmental knee arthroplasty is low (~ 15%) and is associated with decreased orthostatic pressure responses. Compared to the previously described orthostatic intolerance incidence of ~ 40% following total knee arthroplasty, early orthostatic intolerance is uncommon after unicompartmental knee arthroplasty, suggesting a procedure-specific component. TRIAL REGISTRATION: Prospectively registered at ClinicalTrials.gov; registration number: NCT04195360, registration date: 13.12.2019.

Protocol for a prospective multicentre cohort study to address the question whether diabetes and its management is still a risk factor in fast-track joint arthroplasty.

INTRODUCTION: Perioperative glycaemic control is important. However, the complexity of guidelines for perioperative diabetes management is complicated due to different and novel antihyperglycaemic medications, limited procedure-specific data and lack of data from implemented fast-track regimens which otherwise are known to reduce morbidity and glucose homeostasis disturbances. Consequently, outcome in patients with diabetes mellitus (DM) after surgery and the influence of perioperative diabetes management on postoperative recovery remains poorly understood. METHODS AND ANALYSIS: A prospective observational multicentre study involving 8 arthroplasty centres across Denmark with a documented implemented fast-track programme (median length of hospitalisation (LOS) 1 day). We will collect detailed perioperative data including preoperative haemoglobin A1c and antidiabetic treatment in 1400 unselected consecutive patients with DM undergoing hip and knee arthroplasty from September 2022 to December 2025, enrolled after consent. Follow-up duration is 90 days after surgery. The primary outcome is the proportion of patients with DM with LOS >4 days and 90-day readmission rate after fast-track total hip arthroplasty (THA), total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA). The secondary outcome is the association between perioperative diabetes treatment and LOS >2 days, 90-day readmission rate, other patient demographics and Comprehensive Complication Index for patients with DM after THA/TKA/UKA in a fast-track regimen. ETHICS AND DISSEMINATION: The study will follow the principles of the Declaration of Helsinki and ICH-Good Clinical Practice guideline. Ethical approval was not necessary as this is a non-interventional observational study on current practice. The trial is registered in the Region of Southern Denmark and on ClinicalTrials.gov. The main results and all substudies of this trial will be published in peer-reviewed international medical journals. TRIAL REGISTRATION NUMBER: NCT05613439.

Patient attitudes towards day-case hip and knee arthroplasty.

Aims: This study aimed to investigate patients' attitudes towards day-case hip and knee arthroplasty and to describe patient characteristics associated with different attitudes, with the purpose of providing an insight into the information requirements for patients that surgeons should address when informing patients about day-case surgery. Methods: A total of 5,322 patients scheduled for hip or knee arthroplasty between 2016 and 2022 were included in the study. Preoperatively, patients were asked if they were interested in day-case surgery ('Yes', 'Do not know', 'No'). Patient demographics including age, BMI, sex, and patient-reported outcome measures (PROMs) such as the EuroQol five-dimension three-level questionnaire (EQ-5D-3L) were examined within each attitude group. Additionally, changes in attitude were assessed among patients who had completed the questionnaire in association with prior hip or knee arthroplasty. Results: Of the surveyed patients, 41.8% were interested in day-case surgery (n = 2,222), 20.8% responded 'Do not know' (n = 1,105), and 37.5% were not interested (n = 1,995). Patients who were not interested had a higher mean age ('No', 70.2 years (SD 10.0) vs 'Yes', 65.2 years (SD 10.7)), with a majority being female ('No', 71.9% female (n = 1,434) vs 'Yes', 48.6% female (n = 1,081)). Approximately 20% of patients responded 'Do not know' regardless of age, sex, and PROMs. Patients reporting anxiety/depression based on EQ-5D-3L more frequently answered 'No' (56.9%; 66/116) compared to those not experiencing anxiety/depression (34.9%; 1,356/3,890). Among patients who responded 'Do not know' before their first surgery, over 70% changed their attitude to either 'Yes' (29.9%; 38/127) or 'No' (40.9%; 52/127) at their subsequent surgery. Conclusion: From 2016 to 2022, 58.3% of hip and knee arthroplasty patients expressed uncertainty or no interest in day-case surgery. In connection with current initiatives to increase the number of day-case arthroplasty procedures, there should be a focus on informing patients to address the prevalent negative or uncertain attitude. Further research is needed to investigate what preoperative information patients consider crucial in their decision-making process regarding day-case surgery.

Champions in usage of medial unicompartmental knee arthroplasty : The story behind the Danish success.

Historically, the use of medial unicompartmental knee arthroplasty (mUKA) as treatment for end-stage anteromedial osteoarthritis (AMOA) of the knee was limited by contraindications due to age, weight, and activity level; however, now evidence-based, validated, and less selective criteria are used rendering nearly 50% of end-stage OA patients eligible for mUKA. Recent studies have showcased benefits, such as shorter hospital stays, cost efficiency, and comparable functional outcomes to total knee arthroplasty (TKA). Notably, revision rates have been shown to markedly decrease with increased usage, with an ideal usage of > 30% but an acceptable usage of 20-60%. The usage of unicompartmental knee arthroplasty (UKA) varies among countries, with Denmark achieving a notably higher usage compared to Sweden, the UK, the Netherlands, the USA and Germany. This article investigates potential factors contributing to Denmark having a higher national usage of mUKA, surpassing the recommended threshold of a usage > 20%. We explore the tradition for national alliances and streamlined surgical education as possible explanations of this development. These insights offer valuable perspectives for potentially optimizing surgical approaches and implant choices in the surgical treatment of end-stage AMOA of the knee across diverse healthcare settings, underscoring the impact of collective strategies in advancing knee arthroplasty practices, ultimately benefiting patients.

Minimal important change thresholds change over time after knee and hip arthroplasty.

OBJECTIVES: The minimal important change (MIC) reflects what patients, on average, consider the smallest improvement in a score that is important to them. MIC thresholds may vary across patient populations, interventions used, posttreatment time points and derivation methods. We determine and compare MIC thresholds for the Oxford Knee Score and Oxford Hip Score (OKS/OHS) at 3 months postoperatively to 12- and 24-month thresholds in patients undergoing knee or hip arthroplasty. STUDY DESIGN AND SETTING: This cohort study used data from patients undergoing total knee arthroplasty (TKA), unicompartmental knee arthroplasty (UKA), or total hip arthroplasty (THA) at a public hospital between February 2016 and February 2023. At 3, 12, and 24 months postoperatively, patients responded to the OKS/OHS and a 7-point anchor question determining experienced changes in knee or hip pain and functional limitations. We used the adjusted predictive modeling method that accounts for the proportion improved and the reliability of the anchor question to determine MIC thresholds and their mean differences between time points. RESULTS: Complete data were obtained from 695/957 (73%), 1179/1703 (69%), and 1080/1607 (67%) patients undergoing TKA, 474/610 (78%), 438/603 (73%), and 355/507 (70%) patients undergoing UKA, and 965/1315 (73%), 978/1409 (69%), and 1059/1536 (69%) patients undergoing THA at 3, 12, and 24 months, respectively. The median age ranged from 68 to 70 years and 55% to 60% were females. The proportions improved ranged between 83% and 95%. The OKS/OHS MIC thresholds were 0.1, 4.2, and 5.1 for TKA, 1.8, 5.6, and 3.4 for UKA, and 1.3, 6.1, and 6.0 for THA at 3, 12, and 24 months postoperatively, respectively. The reliability ranged between 0.64 and 0.82, and the MIC values increased between three and 12 months but not between 12 and 24 months. CONCLUSION: Any absence of deterioration in pain and function is considered important at 3 months after knee or hip arthroplasty. Increasing thresholds over time suggest patients raise their standards for what constitutes a minimal important improvement over the first postoperative year. Besides improving our understanding of patients' views on postoperative outcomes, these clinical thresholds may aid in interpreting registry-based treatment outcome evaluations.

The Use of Large Metal Heads in Thin Vitamin E-Doped Cross-Linked Polyethylene Inserts Does Not Increase Polyethylene Wear in Total Hip Arthroplasty: 5-Year Results From a Randomized Controlled Trial.

BACKGROUND: Vitamin E-doped cross-linked polyethylene (VEPE) has encouraged the use of larger heads in thinner liners in total hip arthroplasty (THA). However, there are concerns about wear and mechanical failure of the thin liner, especially when metal heads are used. The aim of this randomized controlled trial was to investigate if the use of a large metal head in thin VEPE liner would increase polyethylene wear compared with a standard 32-mm metal head and to compare periacetabular radiolucencies and patient-reported outcomes in THA. METHODS: There were 96 candidates for uncemented THA who were randomly allocated to either the largest possible metal head (36 to 44 mm) that could be fitted in the thinnest available VEPE liner (intervention group) or a standard 32-mm metal head (control group). The primary outcome was proximal head penetration, measured with a model-based radiostereometric analysis. Secondary outcomes were periacetabular radiolucencies and patient-reported outcomes. The midterm results of the trial at 5 years are presented. RESULTS: The median total proximal head penetration (interquartile range) was -0.04 mm (-0.12 to 0.02) in the intervention group and -0.03 mm (-0.14 to 0.05) in the control group (P = .691). The rates of periacetabular radiolucencies were 1 of 44 and 4 of 42 (P = .197), respectively. Patient-reported hip function and health-related quality of life did not differ between the groups, but participants in the intervention group reported a higher level of activity (median University of California Level of Activity score 7 versus 6, P = .020). There were 5 revisions caused by dislocations (2), periprosthetic fracture (1), stem subsidence (1), or iliopsoas impingement (1). CONCLUSIONS: Large metal heads in thin VEPE liners did not increase liner wear and were not associated with liner failure 5 years after THA.

Half of all hip and knee arthroplasty patients may be potential day-case candidates: a nationwide register study of 166,730 procedures.

BACKGROUND AND PURPOSE: The overall potential pool of day-case candidates on a national level in hip and knee arthroplasty is unknown. We aimed to estimate the proportion of hip and knee arthroplasty patients eligible for day-case surgery based on contemporary widely used criteria and determine whether there has been a change in the proportion of eligible patients over time and, secondarily, to investigate the proportion of eligible patients discharged on the day of surgery. METHODS: Based on data from the Danish National Patient Register, we identified all patients undergoing primary unilateral hip or knee arthroplasty from January 2010 to March 2020. Using a modification of day-case eligibility criteria proposed by a national multicenter collaboration, we sorted patients into either day-case eligible or ineligible. A day-case procedure was defined as discharge on the day of surgery. RESULTS: We included patients comprising a total of 166,730 primary total hip (THA), total knee (TKA), and unicompartmental knee arthroplasty (UKA). 48% (95% confidence interval [CI] 48-49) were eligible for day-case surgery, with a decline from 50% (CI 49-51) in 2010 to 46% (CI 46-47) eligible in 2019. More UKA patients were day-case eligible (55%, CI 54-56) than THA (47%, CI 47-48) and TKA patients (49%, CI 48-49). A maximum of 8.0% (CI 7.4-8.5) of eligible patients were discharged on the day of surgery in 2019. CONCLUSION: 48% of the Danish hip and knee arthroplasty patients were potential day-case candidates, with a small decline in eligibility from 50% in 2010 to 46% in 2019. Day of surgery discharge among day-case eligible patients peaked at 8% in 2019. Thus, the potential for more day-case surgery seems large.

The size of the femoral head does not influence metal ion levels after metal-on-polyethylene total hip arthroplasty: a five-year report from a randomized controlled trial.

Aims: In metal-on-polyethylene (MoP) total hip arthroplasty (THA), large metal femoral heads have been used to increase stability and reduce the risk of dislocation. The increased size of the femoral head can, however, lead to increased taper corrosion, with the release of metal ions and adverse reactions. The aim of this study was to investigate the relationship between the size of the femoral head and the levels of metal ions in the blood in these patients. Methods: A total of 96 patients were enrolled at two centres and randomized to undergo MoP THA using either a 32 mm metal head or a femoral head of between 36 mm and 44 mm in size, being the largest possible to fit the thinnest available polyethylene insert. The levels of metal ions and patient-reported outcome measures (Oxford Hip Score, University of California, Los Angeles Activity Scale) were recorded at two and five years postoperatively. Results: At five years, the median levels of chromium, cobalt, and titanium were 0.5 µg/l (interquartile range (IQR) 0.50 to 0.62), 0.24 µg/l (IQR 0.18 to 0.30), and 1.16 µg/l (IQR 1.0 to 1.68) for the 32 mm group, and 0.5 µg/l (IQR 0.5 to 0.54), 0.23 µg/l (IQR 0.17 to 0.39), and 1.30 µg/l (IQR 1 to 2.05) for the 36 mm to 44 mm group, with no significant difference between the groups (p = 0.825, p = 1.000, p = 0.558). There were increased levels of metal ions at two years postoperatively in seven patients in the 32 mm group, compared with four in the 36 mm to 44 mm group, and at five years postoperatively in six patients in the 32 mm group, compared with seven in the 36 mm to 44 mm group. There was no significant difference in either the OHS (p = 0.665) or UCLA (p = 0.831) scores between patients with or without an increased level of metal ions. Conclusion: In patients who underwent MoP THA, we found no differences in the levels of metal ions five years postoperatively between those with a femoral head of 32 mm and those with a femoral head of between 36 mm and 44 mm, and no corrosion-related revisions. As taper corrosion can start after five years, there remains a need for longer-term studies investigating the relationship between the size of the femoral head size and corrosion in patients undergoing MoP THA.

Spinal anaesthesia versus general anaesthesia (SAGA) on recovery after hip and knee arthroplasty: A study protocol for three randomized, single-blinded, multi-centre, clinical trials.

Mobilisation difficulties, due to muscle weakness, and urinary retention are common reasons for prolonged admission following hip and knee arthroplasty procedures. Whether spinal anaesthesia is detrimental to early mobilisation is controversial. Previous studies have reported differences in post-operative recovery between spinal anaesthesia and general anaesthesia; however, up-to-date comparisons in fast-track setups are needed. Our randomized, single-blinded, multi-centre, clinical trials aim to compare the post-operative recovery after total hip (THA), total knee (TKA), and unicompartmental knee arthroplasties (UKA) respectively when using either spinal anaesthesia (SA) or general anaesthesia (GA) in a fast-track setup. Included patients (74 THA, 74 TKA, and 74 UKA patients) are randomized (1:1) to receive either SA (2 mL 0.5% Bupivacaine) or GA (Induction: Propofol 1.0-2.0 mg/kg iv with Remifentanil 3-5 mcg/kg iv. Infusion: Propofol 3-5 mg/kg/h and Remifentanil 0.5 mcg/kg/min iv). Patients undergo standard primary unilateral hip and knee arthroplasty procedures in an optimized fast-track setup with intraoperative local infiltrative analgesia in TKA and UKA, post-operative multimodal opioid sparing analgesia, immediate mobilisation with full weightbearing, no drains and in-hospital only thromboprophylaxis. Data will be collected on the day of surgery and until patients are discharged. The primary outcome is the ability to be safely mobilised during a 5-m walking test within 6 h of surgery. Secondary outcomes include fulfilment of discharge criteria, post-operative pain, dizziness, and nausea as well as patient reported recovery and opioid related side effects. Data will also be gathered on all hospital contacts within 30-days of surgery. This study will offer insights into advantages and disadvantages of anaesthetic methods used in fast-track arthroplasty surgery.

Does changes in unicompartmental knee arthroplasty practice pattern influence reasons for revision?

Aims: The aim of this study was to describe the pattern of revision indications for unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) and any change to this pattern for UKA patients over the last 20 years, and to investigate potential associations to changes in surgical practice over time. Methods: All primary knee arthroplasty surgeries performed due to primary osteoarthritis and their revisions reported to the Danish Knee Arthroplasty Register from 1997 to 2017 were included. Complex surgeries were excluded. The data was linked to the National Patient Register and the Civil Registration System for comorbidity, mortality, and emigration status. TKAs were propensity score matched 4:1 to UKAs. Revision risks were compared using competing risk Cox proportional hazard regression with a shared γ frailty component. Results: Aseptic loosening (loosening) was the most common revision indication for both UKA (26.7%) and TKA (29.5%). Pain and disease progression accounted for 54.6% of the remaining UKA revisions. Infections and instability accounted for 56.1% of the remaining TKA revision. The incidence of revision due to loosening or pain decreased over the last decade, being the second and third least common indications in 2017. There was a decrease associated with fixation method for pain (hazard ratio (HR) 0.40; 95% confidence interval (CI) 0.17 to 0.94) and loosening (HR 0.29; 95% CI 0.10 to 0.81) for cementless compared to cemented, and units UKA usage for pain (HR 0.67, 95% CI 0.50 to 0.91), and loosening (HR 0.51; 95% CI 0.37 to 0.70) for high usage. Conclusion: The overall revision patterns for UKA and TKA for the last 20 years are comparable to previous published patterns. We found large changes to UKA revision patterns in the last decade, and with the current surgical practice, revision due to pain or loosening are significantly less likely.

Machine-learning vs. logistic regression for preoperative prediction of medical morbidity after fast-track hip and knee arthroplasty-a comparative study.

BACKGROUND: Machine-learning models may improve prediction of length of stay (LOS) and morbidity after surgery. However, few studies include fast-track programs, and most rely on administrative coding with limited follow-up and information on perioperative care. This study investigates potential benefits of a machine-learning model for prediction of postoperative morbidity in fast-track total hip (THA) and knee arthroplasty (TKA). METHODS: Cohort study in consecutive unselected primary THA/TKA between 2014-2017 from seven Danish centers with established fast-track protocols. Preoperative comorbidity and prescribed medication were recorded prospectively and information on length of stay and readmissions was obtained through the Danish National Patient Registry and medical records. We used a machine-learning model (Boosted Decision Trees) based on boosted decision trees with 33 preoperative variables for predicting "medical" morbidity leading to LOS > 4 days or 90-days readmissions and compared to a logistical regression model based on the same variables. We also evaluated two parsimonious models, using the ten most important variables in the full machine-learning and logistic regression models. Data collected between 2014-2016 (n:18,013) was used for model training and data from 2017 (n:3913) was used for testing. Model performances were analyzed using precision, area under receiver operating (AUROC) and precision recall curves (AUPRC), as well as the Mathews Correlation Coefficient. Variable importance was analyzed using Shapley Additive Explanations values. RESULTS: Using a threshold of 20% "risk-patients" (n:782), precision, AUROC and AUPRC were 13.6%, 76.3% and 15.5% vs. 12.4%, 74.7% and 15.6% for the machine-learning and logistic regression model, respectively. The parsimonious machine-learning model performed better than the full logistic regression model. Of the top ten variables, eight were shared between the machine-learning and logistic regression models, but with a considerable age-related variation in importance of specific types of medication. CONCLUSION: A machine-learning model using preoperative characteristics and prescriptions slightly improved identification of patients in high-risk of "medical" complications after fast-track THA and TKA compared to a logistic regression model. Such algorithms could help find a manageable population of patients who may benefit most from intensified perioperative care.

No difference in short-term readmissions following day-case vs. one overnight stay in patients having hip and knee arthroplasty: a nationwide register study of 51,042 procedures from 2010-2020.

BACKGROUND AND PURPOSE: Day-case hip and knee arthroplasty has gained in popularity, but there are conflicting results regarding readmissions. We aimed to investigate differences in 30- and 90-day readmission rates between day-case patients and patients with a single overnight stay following primary total hip arthroplasty (THA), total knee arthroplasty (TKA), and unicompartmental knee arthroplasty (UKA). PATIENTS AND METHODS: We identified day-case (DC) and overnight (ON) THA, TKA, and UKA patients, operated on between 2010 and 2020, from the Danish National Patient Register. Day-case surgery was defined as discharge on the day of surgery. Overnight readmissions within 30 or 90 days of surgery were considered readmissions. We compared readmission rates between DC and ON patients within arthroplasty types using logistic regression adjusted for patient characteristics and year of surgery. We included 29,486 THAs (1,353 DC and 28,133 ON), 15,116 TKAs (617 DC and 14,499 ON), and 6,440 UKAs (1,528 DC and 4,914 ON). RESULTS: The 30-day readmission rates were: DC-THA 4.4% vs. ON-THA 4.4% (adjusted odds-ratio [aOR] 1.2, 95% confidence interval [CI] 0.91-1.6), DC-TKA 4.7% vs. ON-TKA 4.4% (aOR 1.1, CI 0.69-1.5), and DC-UKA 3.0% vs. ON-UKA 3.0% (aOR 1.1, CI 0.78-1.5). Similarly, no significant differences were present between DC and ON THA, TKA, and UKA regarding 90-day readmissions or time to readmission. CONCLUSION: We found no differences in readmission rates between day-case THA, TKA, and UKA patients and patients with a single overnight stay.

Effect of single versus multiple prophylactic antibiotic doses on prosthetic joint infections following primary total hip arthroplasty in patients with osteoarthritis at public and private hospitals in Denmark: protocol for a nationwide cross-over, cluster randomised, non-inferiority trial [The Pro-Hip-Quality Trial].

INTRODUCTION: A feared complication after total hip arthroplasty (THA) is prosthetic joint infection (PJI), associated with high morbidity and mortality. Prophylactic antibiotics can reduce the risk of PJI. However, there is no consensus on the dosages and current recommendations are based on a low evidence level. The objective is to compare the effect of a single versus multiple doses of prophylactic antibiotics administered within 24 hours on PJI. METHODS AND ANALYSIS: The study is designed as a cross-over, cluster randomised, non-inferiority trial. All clinical centres use both antibiotic practices (1 year of each intervention). All Danish orthopaedic surgery departments will be involved: Based on quality databases, 2-year cohorts of approximately 20 000 primary THAs conducted at 39 public and private hospitals, will be included. INCLUSION CRITERIA: age ≥18 years, all indications for THA except patients operated due to acute or sequelae from proximal femoral or pelvic fractures or bone tumour or metastasis. The primary outcome is PJI within 90 days after primary THA. Secondary outcomes include (1) serious adverse events, (2) potential PJI, (3) length of hospitalisation stay, (4) cardiovascular events, (5) hospital-treated infections, (6) community-based antibiotic use, (7) opioid use and (8) use of acetaminophen and non-steroidal anti-inflammatory drugs. All outcome measures will be extracted from national databases. Analyses will be based on the intention-to-treat population. Non-inferiority will be shown if the upper limit of the two-sided 95% CI for the OR is less than 1.32 for the single dose as compared with multiple doses. The results will establish best practice on antibiotic prophylaxis dosages in the future. ETHICS AND DISSEMINATION: This study has been approved by Committees on Health Research Ethics for The Capital Region of Denmark (21069108) and The Danish Medicines Agency (2021091723). All results will be presented in peer-reviewed medical journals and international conferences. TRIAL REGISTRATION NUMBER: NCT05530551.