To determine the risk of total knee replacement (TKR) for primary osteoarthritis (OA) associated with overweight/obesity in the Australian population. This population-based study analyzed 191,723 cases of TKR collected by the Australian Orthopaedic Association National Joint Registry and population data from the Australian Bureau of Statistics. The time-trend change in incidence of TKR relating to BMI was assessed between 2015-2018. The influence of obesity on the incidence of TKR in different age and gender groups was determined. The population attributable fraction (PAF) was then calculated to estimate the effect of obesity reduction on TKR incidence. The greatest increase in incidence of TKR was seen in patients from obese class III. The incidence rate ratio for having a TKR for obesity class III was 28.683 at those aged 18-54 years but was 2.029 at those aged >75 years. Females in obesity class III were 1.7 times more likely to undergo TKR compared to similarly classified males. The PAFs of TKR associated with overweight or obesity was 35%, estimating 12,156 cases of TKR attributable to obesity in 2018. The proportion of TKRs could be reduced by 20% if overweight and obese population move down one category. Obesity has resulted in a significant increase in the incidence of TKR in the youngest population in Australia. The impact of obesity is greatest in the young and the female population. Effective strategies to reduce the national obese population could potentially reduce 35% of the TKR, with over 10,000 cases being avoided

To determine risk factors of infection in total knee arthroplasty. This descriptive study was conducted in the Department of Orthopedics for a duration of three years from January 2016 to January 2019. All patients undergoing primary total knee replacement were included in the study. Exclusion criteria were all patients operated in another hospital and revision total knee replacement. All patients were followed up at 2, 4, 8, 12 and 24 weeks post-operatively. Signs of inflammation and inflammatory markers such as total leukocyte count (TLC), C-reactive protein (CRP) and ESR were measured. Risk factors like age, body mass index (BMI), ASA, co-morbid conditions were also noted. A total of 78 patients underwent primary unilateral Total Knee Replacement (TKR) during the study period. Of these, 30 (34.09%) were male and 48 (61.54%) female patients. Mean age of patients was 68.32 ± 8.54 years. Average BMI 25.89 Kg/m2 .Osteoarthritis was the pre-dominant cause of total knee replacement (94.87%). Among co-morbid factors 33.33% were diabetic, 28.20% having ischemic heart disease and 12.82% with chronic lung disease. Upon anaesthesia fitness pre-operatively, 91.02% patients had an American society of anaesthesiologist score (ASA) between 0–2 while 07 (8.97%) between 3- 5. Average duration of surgery was 85.62± 4.11 minutes. 6.41% cases got infected. In majority of the infected cases (60%), Staphylococcus aureus was the infective organism. Diabetes Mellitus (p=0.01) and Obesity (p=0.02) had a significant relation to post-operative infection. Pre-operative risk evaluation and prevention strategies along with early recognition of infection and control can greatly reduce the risk of joint infection post-TKR which will not only improve the mobility of patient but also its morbidity and mortality as well. Key Words:. C-reactive protein (CRP), Erythrocyte Sedimentation Rate (ESR), Staphylococcus aureus, Total Knee Arthroplasty (TKA)

Introduction. Knee arthroplasty (KA), encompassing Total Knee Replacement (TKR) and Unicompartmental Knee Replacement (UKR), is one of the most common orthopedic procedures, aimed at alleviating severe knee arthritis. Postoperative KA management, especially radiographic imaging, remains a substantial financial burden and lacks standardised protocols for its clinical utility during follow-up. Method. In this retrospective multicentre cohort study, data were analysed from January 2014 to March 2020 for adult patients undergoing primary KA at Imperial NHS Trust. Patients were followed over a five-year period. Four machine learning models were developed to evaluate if post-operative X-ray frequency can predict revision surgery. The best-performing model was used to assess the risk of revision surgery associated with different number of X-rays. Result. The study assessed 289 knees with a 2.4% revision rate. The revision group had more X-rays on average than the primary group. The best performing model was Logistic Regression (LR), which indicated that each additional X-ray raised the revision risk by 52% (p<0.001). Notably, having four or more X-rays was linked to a three-fold increase in risk of revision (OR=3.02; p<0.001). Our results align with the literature that immediate post-operative X-rays have limited utility, making the 2nd post-operative X-ray of highest importance in understanding the patient's trajectory. These insights can enhance management by improving risk stratification for patients at higher revision surgery risk. Despite LR being the best-performing model, it is limited by the dataset's significant class imbalance. Conclusion. X-ray frequency can independently predict revision surgery. This study provides insights that can guide surgeons in evidence-based post-operative decision-making. To use those findings and influence post-operative management, future studies should build on this predictive model by incorporating a more robust dataset, surgical indications, and X-ray findings. This will allow early identification of high-risk patients, allowing for personalised post-operative recommendations

Total knee replacement (TKR) design aims to restore normal kinematics with emphasis on flexion range. The survivorship of a TKR is dependent on the kinematics in six-degrees-of-freedom (6-DoF). Stepping up, such as stair ascent is a kinematically demanding activity after TKR. The debate about design choice has not yet been informed by 6-DoF in vivo kinematics. This prospective randomised controlled trial (RCT) compared kneeling kinematics in three TKR designs. 68 participants were randomised to receive either cruciate retaining (CR-FB), rotating platform (CR-RP) or posterior stabilised (PS-FB) prostheses. Image quality was sufficient for 49 of these patients to be included in the final analysis following a minimum 1-year follow-up. Patients completed a step-up task while being imaged using single-plane fluoroscopy. Femoral and tibial computer-aided design (CAD) models for each of the TKR designs were registered to the fluoroscopic images using bespoke software OrthoVis to generate six-degree-of-freedom kinematics. Differences in kinematics between designs were compared as a function of flexion. There were no differences in terminal extension between the groups. The CR-FB was further posterior and the CR-RP was more externally rotated at terminal extension compared to the other designs. Furthermore, the CR-FB designs was more posteriorly positioned at each flexion angle compared to both other designs. Additionally, the CR-RP design had more external femoral rotation throughout flexion when compared with both fixed bearing designs. However, there were no differences in total rotation for either step-up or down. Visually, it appears there was substantial variability between participants in each group, indicating unique patient-specific movement patterns. While use of a specific implant design does influence some kinematic parameters, the overall patterns are similar. Furthermore, there is high variability indicating patient-specific kinematic patterns. At a group level, none of these designs appear to provide markedly different step-up kinematic patterns. This is important for patient expectations following surgery. Future work should aim to better understand the unique patient variability

Stiffness is reported in up to 16% of patients after total knee replacement (TKR). 1. Treatment of stiffness after TKR remains a challenge. Manipulation under anaesthesia (MUA) accounts for between 6%-36% of readmissions following TKR. 2,3. The outcomes of MUA remain variable/unpredictable. Post-operative CPM is used as an adjuvant to MUA, potentially offering improved ROM, however, remains the subject of debate. We report a retrospective study comparing MUA with and without post-operative CPM. In our institution patients undergoing MUA to receive CPM post-operatively. Owing to the COVID-19 pandemic hospital admissions were limited. During this period MUA procedures were undertaken without CPM. Two cohorts were included: 1) MUA + post-operative CPM 2) Daycase MUA. Patients’ demographics, pre-manipulation ROM, post-MUA ROM, and ROM at final follow-up were recorded. Between 2017-2022 126 patients underwent MUA and were admitted for CPM and 42 had daycase MUA. The median Age was 66.5 and 64% were female. 57% had extension deficit (>5. o. ), 70% had flexion deficit (< 90. o. ), and 37% had both. The mean Pre-operative ROM was 72.3. o. (SD:18.3. o. ) vs. 68.5. o. (19.0. o. ), ROM at MUA was 95.5. o. (SD:20.7. o. ) vs 108.3. o. (SD:14.1. o. ) [p< 0.01], and at final follow-up 87.4. o. (SD:21.9. o. ) vs. 92.1. o. (SD:18.2. o. ) for daycase and CPM groups respectively. At final follow-up for the daycase and CPM groups respectively 10% vs. 7% improved, 29% vs. 13% maintained, and 57% vs. 79% regressed from the ROM achieved at MUA. The mean percentage of ROM gained at MUA maintained at final follow-up was 92%(SD:17) and 85%(SD:14)[p=0.03] for daycase and CPM groups respectively. There was no significant difference in ROM achieved at final follow-up despite the significantly greater improvement in ROM achieved at MUA for the CPM group. The CPM group lost a greater ROM after MUA (15% vs. 8%). We conclude that post-operative CPM does not improve ROM achieved after MUA

Abstract. Introduction. Component mal-positioning in total hip replacement (THR) and total knee replacement (TKR) can increase the risk of revision for various reasons. Compared to conventional surgery, relatively improved accuracy of implant positioning can be achieved using computer assisted technologies including navigation, patient-specific jigs, and robotic systems. However, it is not known whether application of these technologies has improved prosthesis survival in the real-world. This study aimed to compare risk of revision for all-causes following primary THR and TKR, and revision for dislocation following primary THR performed using computer assisted technologies compared to conventional technique. Methods. We performed an observational study using National Joint Registry data. All adult patients undergoing primary THR and TKR for osteoarthritis between 01/04/2003 to 31/12/2020 were eligible. Patients who received metal-on-metal bearing THR were excluded. We generated propensity score weights, using Sturmer weight trimming, based on: age, gender, ASA grade, side, operation funding, year of surgery, approach, and fixation. Specific additional variables included position and bearing for THR and patellar resurfacing for TKR. For THR, effective sample sizes and duration of follow up for conventional versus computer-guided and robotic-assisted analyses were 9,379 and 10,600 procedures, and approximately 18 and 4 years, respectively. For TKR, effective sample sizes and durations of follow up for conventional versus computer-guided, patient-specific jigs, and robotic-assisted groups were 92,579 procedures over 18 years, 11,665 procedures over 8 years, and 644 procedures over 3 years, respectively. Outcomes were assessed using Kaplan-Meier analysis and expressed using hazard ratios (HR) and 95% confidence intervals (CI). Results. For THR, analysis comparing computer-guided versus conventional technique demonstrated HR of 0.771 (95%CI 0.573–1.036) p=0.085, and 0.594 (95%CI 0.297–1.190) p=0.142, for revision for all-causes and dislocation, respectively. When comparing robotic-assisted versus conventional technique, HR for revision for all-causes was 0.480 (95%CI 0.067 –3.452) p=0.466. For TKR, compared to conventional surgery, HR for all-cause revision for procedures performed using computer guidance and patient-specific jigs were 0.967 (95% CI 0.888–1.052) p=0.430, and 0.937 (95% CI 0.708–1.241) p=0.65, respectively. HR for analysis comparing robotic-assisted versus conventional technique was 2.0940 (0.2423, 18.0995) p = 0.50. Conclusions. This is the largest study investigating this topic utilising propensity score analysis methods. We did not find a statistically significant difference in revision for all-causes and dislocation although these analyses are underpowered to detect smaller differences in effect size between groups. Additional comparison for revision for dislocation between robotic-assisted versus conventionally performed THR was not performed as this is a subset of revision for all-causes and wide confidence intervals were already observed for that analysis. It is also important to mention this NJR analysis study is of an observational study design which has inherent limitations. Nonetheless, this is the most feasible study design to answer this research question requiring use of a large data set due to revision being a rare outcome. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Abstract. Objectives. Stiffness is reported in 4%–16% of patients after having undergone total knee replacement (TKR). Limitation to range of motion (ROM) can limit a patient's ability to undertake activities of daily living with a knee flexion of 83. o. , 93. o. , and 106. o. required to walk up stairs, sit on a chair, and tie one's shoelaces respectively. The treatment of stiffness after TKR remains a challenge. Many treatment options are described for treating the stiff TKR. In addition to physiotherapy the most employed of these is manipulation under anaesthesia (MUA). MUA accounts for up to 36% of readmissions following TKR. Though frequently undertaken the outcomes of MUA remain variable and unpredictable. CPM as an adjuvant therapy to MUA remains the subject of debate. Combining the use of CPM after MUA in theory adds the potential benefits of CPM to those of MUA potentially offering greater improvements in ROM. This paper reports a retrospective study comparing patients who underwent MUA with and without post-operative CPM. Methods. Standard practice in our institution is for patients undergoing MUA for stiff TKR to receive CPM for between 12–24hours post-operatively. Owing to the COVID-19 pandemic hospital admissions were limited. During this period several MUA procedures were undertaken without subsequent inpatient CPM. We retrospectively identified two cohorts of patients treated for stiff TKR: group 1) MUA + post-operative CPM 2) Daycase MUA. All patients had undergone initial physiotherapy to try and improve their ROM prior to proceeding to MUA. In addition to patients’ demographics pre-manipulation ROM, post-MUA ROM, and ROM at final follow-up were recorded for each patient. Results. In total 168 patients who had undergone MUA between 2017–2022 were identified with a median Age of 66.5 years and 64% female. 57% had extension deficit (>5. o. ), 70% had flexion deficit (< 90. o. ), and 37% had both. 42 had daycase MUA without CPM and the remaining 126 were admitted for post-operative CPM. The mean Pre-operative ROM was 72.3. o. (SD:18.3. o. ) and 68.5. o. (19.0. o. ) for the daycase and CPM groups respectively. The mean ROM recorded at MUA was 95.5. o. (SD:20.7. o. ) and 108.3. o. (SD:14.1. o. ) [p<0.01] and at final follow-up was 87.4o (SD:21.9o) and 92.1o (SD:18.2o) for daycase and CPM groups respectively. At final follow-up for the daycase and CPM groups respectively 10% vs. 7% improved, 29% vs. 13% maintained, and 57% vs. 79% regressed from the ROM achieved at MUA. The mean percentage of ROM gained at MUA maintained at final follow-up was 92% (SD:17%) and 85% (SD:14%) [p=0.03] for daycase and CPM groups respectively. Conclusion. Overall, there was no significant difference in ROM achieved at final follow-up despite the significantly greater improvement in ROM achieved at MUA for the CPM group. Analysis of the percentage ROM gained at MUA maintained at follow up showed that most patients regressed from ROM achieved at MUA in both groups with those in the CPM only maintaining 85% as opposed to 92% in the daycase patients. It is our observation that post-operative CPM does not improve ROM achieved after MUA as compared to MUA alone. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Abstract. Objectives. Exploring the relationship of gait function pre and post total knee replacement (TKR) in two groups of patients. Methods. Three-dimensional gait analysis was performed at Cardiff University, UK, and Karolinska University Hospital, Sweden, on 29 and 25 non-pathological (NP) volunteers, and 39 and 28 patients with end-stage knee osteoarthritis (OA), respectively. Patients were assessed pre and one-year post-TKR. Data reduction was performed via Principal Component (PC) analysis on twenty-four kinematic and kinetic waveforms in both NP and pre/post-TKR. Cardiff's and Karolinska's cohorts were analysed separately. The Cardiff Classifier, a classification system based on the Dempster-Shafer theory, was trained with the first 3 PCs of each variable for each cohort. The Classifier classifies each participant by assigning them a belief in NP, belief in OA (BOA) and belief in uncertainty, based on their biomechanical features. The correlation between patient's BOA values (range: 0–1, 0 indicates null BOA and 1 high BOA) pre and post-TKR was tested through Spearman's correlation coefficient in each cohort. The related-samples Wilcoxon signed-rank test (α=0.05) determined the significant changes in BOA in each cohort of patients. The Mann-Whitney U test (α=0.05) was run to explore differences between the patients’ cohorts. Results. There were no significant differences between patients’ cohorts in median age (p=0.096), height (p=0.673), weight (p=0.064) or KOOS sub-scores pre or post-TKR (p-value ranged 0.069 to 0.955) but Cardiff's patients had a significantly higher BMI (p=0.047). There was a significant, median decrease of 0.12 and 0.19 in the BOA pre to post TKR (p<0.001) in Cardiff's and Karolinska's patients, respectively. There was a statistically significant, strong positive correlation between the BOA pre and post-TKR (Cardiff:r. s. =0.706, p<0.001; Karolinska:r. s. =0.669, p<0.001). Conclusions. In two distinct cohorts of patients, having a more compromised gait function in end-stage knee OA was correlated with poorer gait function post-TKR

Introduction and Objective. Kinesiophobia, the fear of physical movement and activity related to injury vulnerability, has been linked to sub-optimal outcomes following total knee replacement (TKR). This systematic review has two aims: to define the relationship between kinesiophobia and functional outcomes, pain and range of motion following TKR, and to evaluate published treatments for kinesiophobia following TKR. Materials and Methods. A primary search was performed in March 2020. English-language studies recruiting adult primary TKR patients, using the Tampa Scale of Kinesiophobia (TSK) were included. Study quality was assessed using the Newcastle Ottawa Scale for cohort or case control studies, and the Cochrane Collaboration Risk of Bias tool for randomised controlled trials. Results. All thirteen included papers (82 identified) showed adequately low risk of methodological bias. TSK1 (activity avoidance) correlated with WOMAC functional score at 12 months in three studies (r=0.20 p<0.05, R=0.317 p=0.001, and correlation coefficient 0.197 p=0.005). TSK score significantly correlated with mean active range of motion (ROM) at six months (105.33 (SD=12.34) vs 85.53 (SD=14.77) p=0.000) post-operation. Three post-operative interventions improved TSK score vs control following TKR: a home-based functional exercise programme (TSK −14.30 (SD=0.80) vs −2.10 (SD=0.80) p<0.001)), an outpatient CBT programme (TSK 27.76 (SD=4.56) vs 36.54 (SD=3.58), and video-based psychological treatment (TSK 24 (SD=5) vs 29 (SD=5) p<0.01). Conclusions. Kinesiophobia negatively affects functional outcomes up until one year post-operatively, while active ROM is reduced up to six months post procedure. Post-operative functional and psychological interventions can improve kinesiophobia following TKR

Abstract. Background. Whilst the literature abounds with patient reported outcomes following total knee replacement (TKR) there is a paucity of literature covering objective functional outcomes. Awareness of objective functional outcomes following TKR is key to the consent process and relating it to pre-operative function enables a tailored approach to consent. Objectives. Identify trends in a range of functional outcomes prior to and following TKR up to one year post-operatively. Methods. We prospectively gathered data from 82 patients undergoing TKR, examining over 20 functional measures preoperatively and postoperatively at 6 weeks, 3, 6 and 12 months. Our functional lab incorporated validated assessments and assessments selected by surgeons & physiotherapists seen to be critical to outcomes following TKR, such as: kneeling ability, 6 minute walking distance, time to ascend/descend stairs, quadricep moment strength, single stance difficulty, ability to walk on an uneven surface, “Time to get up and go”, upslope/downslope speed. Results. Our results demonstrated that if a patient was able to kneel preoperatively they had an 82.5% chance of being able to kneel postoperatively; if they could not kneel preoperatively this dropped to only 50% but overall over two-thirds of patients were able to kneel at 1 year postoperatively. Other selected results include: 49% increase in 6-minute walking distance, 45% reduction in time to ascend then descend stairs, over 50% increase in quadriceps moment strength, over 40% increase in both upslope/downslope speed and over 70% reduction in difficulty walking on an uneven surface. Conclusions. With these results we can not only discuss specific functional outcomes following TKR but also relate these to preoperative functional level, enabling a more tailored, detailed and robust consent process. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Background. The current average tariff of a total knee replacement (TKR) is £5500. The approximate cost of each knee prosthesis is £2500. Therefore, length of patient stay (LOS) and the cost of patient rehabilitation influence the total costs significantly. Previous studies have shown a mean LOS of between 5 and 9.4 days for patients undergoing primary unilateral TKR but none looked at the factors influencing length of stay following bilateral primary total knee replacements (BTKR) at the same sitting. Objectives. To identify significant factors that influence the LOS following BTKR at the same sitting in a single centre in the UK. Methods. This was a retrospective single-centre study performed at the Princess Royal Hospital which performed a total of 25 BTKR. Surgical and patient factors that may influence LOS were recorded and analysed. Results. The mean LOS was 10 days with a median of 9 days. 64% were discharged within 10 days. Those staying longer were classified as long stayers. Being a female (0.65, p< 0.05), having a higher Charlson index (0.68, p< 0.05) and having a post-operative blood transfusion (0.59, p< 0.05) were the only significant factors that influenced LOS. Post-operative acute kidney injury (AKI), underlying diagnosis such as rheumatoid arthritis, BMI, age, worse pre-operative oxford knee scores and type of implant did not influence LOS. Conclusion. Factors influencing LOS following BTKR shown in our study seems to be the same as those influencing unilateral TKRs as identified in the literature. This should be taken into consideration when comparing unilateral versus bilateral TKR results as well as when planning a local arthroplasty service

Abstract. Objectives. Exploring the association of objective lower limb function pre and post total knee replacement (TKR). Methods. 3D gait analysis was performed on 28 non-pathological participants (NP) and 40 patients with advanced knee osteoarthritis (OA) before and approximately one year after TKR. For NP and OA patients pre/post-TKR, 12 waveforms on kinetic and kinematic variables of the operative side were chosen to perform data reduction through Principal Component (PC) Analysis. The Cardiff Classifier, a classification system based on Dempster-Shafer theory, was trained with the first 3 PCs of each variable. The 18 highest-ranking PCs classifying the biomechanical features of each participant as Belief in Healthy, Belief in OA (BOA) or Belief in Uncertainty were used to quantify biomechanical changes pre- to post-TKR. The correlation between patients’ BOA values (range: 0 to 1, 0 indicates null BOA and 1 high BOA) pre- and post-TKR was tested through Spearman's correlation coefficient. Wilcoxon matched-pair test (α<0.05) determined the significance of the change in BOA. Results. NP (57% women) had a mean age of 38 (SD=18.13), mean height and weight of 1.70 m (SD=0.09) and 68 Kg (SD=15.24), respectively. Their mean BOA was 0.05 (SD=0.08), in line with inclusion criteria. OA patients (38% women) had a mean age of 68.5 (SD=7.59), mean height and weight of 1.68 m (SD=0.10) and 92.6 Kg (SD=21.22), respectively. Their mean pre-TKR BOA was 0.81 (SD=0.18), falling to 0.64 (SD=0.26) post-TKR. The change in BOA (0.16, SD=0.19) pre- to post-TKR was significant (p=0.000). BOAs pre- and post-TKR were non-normally distributed therefore, a Spearman's rank-order correlation was run, revealing a positive, statistically significant (p=0.000), strong correlation (r. S. =0.657) between BOA pre- and post-TKR. Conclusions. This study found that worse objective pre-operative lower limb function in people with advanced knee OA was strongly correlated with poorer one-year post-TKR function (r. S. =0.657, p<0.01). Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Background. Post-operative acute kidney injury is significant complication following surgery. Patients who develop AKI have an increased risk for progression into chronic kidney disease, end-stage renal failure and increased mortality risk. The patient outcomes following total knee replacement (TKR), who develop AKI has been a topic of interest in recent years as it may have patient and medicolegal implications. Nevertheless, there are no studies looking at the incidence, risk factors and outcomes of AKI following bilateral TKRs at the same sitting. Objectives. To determine the incidence, risk factors and outcomes of post-operative AKI following bilateral TKRs surgery at the same sitting. Methods. This was a retrospective single-centre study performed at the Princess Royal Hospital, which performed a total of 25 BTKR. The incidence, Surgical and patient risk factors were recorded and analysed. Results. The incidence of AKI as defined by NICE guidelines following bilateral TKRs was 20%. 16% (4 patients) had stage 1 and 4% (1 patient) had stage 2 AKI. The mean change in Creatinine between pre- and post-operative blood tests was +19μmol/L. There was a strong significant correlation between CKD and AKI (r=0.75, P<0.05). Furthermore, a moderate correlation was found between higher BMI and pre-operative Charlson index and AKI. AKI did not have an effect on the length of inpatient stay with the mean inpatient length of stay for patients who had an AKI of 10 days compared to 11days for those who did not. All AKIs were resolved within 72 hours. There were no associated mortalities with AKI. Conclusion. The incidence of AKI following bilateral TKR was 20%. Pre-operative chronic kidney disease as well as having a higher BMI were identified as risk factors for developing AKI. Pre-operative CKD optimisation and careful adequate hydration intra-operatively should be considered in these patients. AKI was not associated with an increased length of stay or mortality in our study

In the UK and USA in 2016 more than 263,000 primary knee replacements were performed. Around 20% of patients report chronic post-surgical pain (CPSP) at three or more months after total knee replacement (TKR). A large proportion of adults with all types of chronic musculoskeletal pain do not use services for a number of reasons, despite being in constant or daily pain. Given the high prevalence of CPSP, there is potentially a large hidden population with an unexpressed need for care, experiencing ongoing pain and disability; understanding why they do not use health services may herald further insight into why many remain dissatisfied with knee replacement surgery. The aim of this study is to understand why some people with CPSP after TKR do not access services or make little use of healthcare. We conducted face-to-face in-depth interviews with 34 patients from 2 high-volume orthopaedic hospitals in England, to investigate their experience of long-term pain after knee replacement; their knowledge and understanding of CPSP; and their decisions about consulting for CPSP. The sample size was based on achievement of saturation and participants provided written informed consent. Interviews were transcribed and analysed using an inductive thematic approach with double coding for rigor. Ethical approval for the study was granted by the West Midlands Solihull Research Ethics Committee (15/WM/0469). A core theme within the analysis suggests that participants do not seek healthcare because they believe that nothing further can be done, either by themselves or by healthcare professionals. Surgeons' satisfaction with the knee surgery and reassurances that pain would improve, left patients feeling uncertain about whether to re-consult, and some assumed that further consultation could lead to further surgery or medication, which they wish to avoid. Some participants' comorbidities took precedence over their knee pain when seeking healthcare. Others felt they had received their “share” of healthcare resources and that others were more deserving of treatment. People's descriptions of pain varied, from dull, or aching to shooting pains. Many described their pain as “discomfort” rather than pain. The majority described pain that was better than their pre-surgical pain, though others described pain that was worse, which they believed to be nerve damage. Many expressed disappointment in the outcome of their TKR. Expectations of pain varied, where most had expected some post-surgical pain, others underestimated it, and some had expected to be completely pain free following their TKR. Our analysis suggests that the reasons that some people with CPSP after TKR do not consult are varied and complex, spanning psychosocial, structural, moral, and organisational domains. There was an overriding sense that further consultation would be futile or may lead to unwanted treatment. Results suggest that improved information for patients about CPSP and appropriate post-surgical healthcare services may help patients and clinicians to manage this condition more effectively

Objectives. To define Patient Acceptable Symptom State (PASS) thresholds for the Oxford hip score (OHS) and Oxford knee score (OKS) at mid-term follow-up. Methods. In a prospective multicentre cohort study, OHS and OKS were collected at a mean follow-up of three years (1.5 to 6.0), combined with a numeric rating scale (NRS) for satisfaction and an external validation question assessing the patient’s willingness to undergo surgery again. A total of 550 patients underwent total hip replacement (THR) and 367 underwent total knee replacement (TKR). Results. Receiver operating characteristic (ROC) curves identified a PASS threshold of 42 for the OHS after THR and 37 for the OKS after TKR. THR patients with an OHS ≥ 42 and TKR patients with an OKS ≥ 37 had a higher NRS for satisfaction and a greater likelihood of being willing to undergo surgery again. Conclusions. PASS thresholds appear larger at mid-term follow-up than at six months after surgery. With- out external validation, we would advise against using these PASS thresholds as absolute thresholds in defining whether or not a patient has attained an acceptable symptom state after THR or TKR. Cite this article: Bone Joint Res 2014;3:7–13

Summary Statement. Wear of total knee replacement (TKR) is a clinical concern. This study demonstrated low-conformity moderately cross-linked-polyethylene fixed bearing TKRs showed lower volumetric wear than conventional-polyethylene curved fixed bearing TKRs highlighting potential improvement in TKR performance through design and material selection. Introduction. Wear of total knee replacement (TKR) continues to be a significant factor in the clinical performance of the implants. Historically, failure due to delamination and fatigue directed implant design towards more conforming implants to reduce contact stress. However, the new generations of more oxidatively-stable polyethylene have improved the long-term mechanical properties of the material, and therefore allowed more flexibility in the bearing design. The purpose of this study was to investigate the effect of insert conformity and material on the wear performance of a fixed bearing total knee replacement through experimental simulation. Methods. The wear of TKR bearings were investigated using a physiological six station Prosim knee wear simulator (Simulator Solutions, UK). Six samples of each test configuration (Sigma CR fixed bearing knees (DePuy Synthes, UK) were studied, and compared with previously reported data, tested under identical conditions (1, 2). The central axis of the implant was offset from the aligned axes of applied load and tibial rotation to replicate a right knee. High kinematics, under anterior-posterior displacement control was used for this study (3). The lubricant was 25% (v/v) calf serum supplemented with 0.03% (v/v) sodium azide solution in deionised water, as an antibacterial agent, and was changed approximately every 0.33Mc. Wear was assessed gravimetrically and moisture uptake accounted for using unloaded soak controls. Results. The wear rates for the moderately cross-linked inserts (XLK) were significantly lower than the conventional polyethylene (GVF) for all geometries (ANOVA, p<0.05). There was a significant reduction in wear rate as the insert geometry became less conforming for both materials (ANOVA, p<0.05). The wear scars areas were comparable in size and shape between materials, within a geometry group. The size of the wear scar changed with conformity, with the curved inserts showing the largest scars in both anterior-posterior and medial-lateral dimensions, and the flat inserts showing the smallest wear scars. Discussion/Conclusion. The introduction of a moderately cross-linked polyethylene insert was shown to significantly reduce the wear of a fixed bearing total knee replacement compared with a conventional material. There was a trend for reducing wear rate with reducing conformity for both materials, suggesting that reduced conformity results in higher contact pressures and reduced contact area, leading to a reduced surface for wear to occur. Both material and conformity were shown to have a significant impact on the wear of a fixed bearing TKR, and therefore provide opportunity for enhancing wear performance through material and design selection

Periprosthetic joint infections (PJIs) are uncommon but are devastating complications of total knee replacement (TKR). We analysed the risk factors of revision for PJI following primary TKR and their association with PJI at different post-operative periods. Primary TKRs and subsequent revision surgeries performed for PJI from 2003–2014 were identified from the National Joint Registry (NJR). Multilevel piece-wise exponential non-proportional hazards models were used to estimate the effect of the investigated factors at different post-operative periods. Patient, perioperative and healthcare system characteristics were investigated and data from the Hospital Episode Statistics for England were linked to obtain information on specific comorbidities. The index TKRs consisted of 679,010 primaries with 3,659 subsequently revised for PJI, 7% within 3 months, 6% between 3–6months, 17% between 6–12months, 27% between 1–2years and 43% ≥2 years from the index procedure. Risk factors for revision for PJI included male sex, high BMI, high ASA grade and young age. Patients with chronic pulmonary disease, diabetes and liver disease had higher risk of revision for PJI, as had patients who had a primary TKR for an indication of trauma or inflammatory arthropathy. Surgical procedure, fixation method, constraint and bearing type influenced the risk of revision for PJI. Their effects were period-specific. No or small associations were found with the operating surgeon grade, surgical volume and hospital surgical volume. These findings from the world's largest joint replacement registry show a more complex picture than the meta-analyses published to date with specific time-dependent effects for the identified risk factors

Osteoarthritis (OA) is traditionally believed to affect the osteochondral unit by wear-and-tear from the superficial zone to the deep zone of cartilage and extended to subchondral plate. Obesity is commonly considered as a risk of OA development and hence total knee replacement (TKR), but the mechanism remains unclear. We hypothesized that obesity accelerated OA development by deteriorating tidemarks and increasing bone remodelling. 616,495 cases of TKR for OA from Australia and British joint replacement registries were collected, and data indicated that patients with higher BMI had TKR at earlier age. Specifically, patients with BMI ≤25kg/m. 2. showed 8 years younger than patients with BMI ≥40kg/m. 2. (P<0.0001) when they received TKR. We next examined tibia plateaus of 88 knee OA patients by micro-CT and histomorphometry. Linear regression showed that less cartilage degradation was associated with increased BMI in the load-bear compartment (p<0.05), while 58.3% of patients with BMI≥40kg/m. 2. demonstrated a clear anatomical separation close to tidemarks filled with fibrosis, erythrocytes and bone fragments (compared to BMI ≤25kg/m. 2. group: 7.7%, p<0.01). In subchondral bone, elevated bone formation was associated with increased BMI, as higher thickness of osteoid (p<0.01), percent osteoid volume (p<0.01), percent osteoid surface (p<0.01) were found in obese patients. However, no alteration of bone resorption and microstructural parameters was found to be associated with BMI. We suspected that the abnormal loading in knee joint due to high BMI led to the direct deterioration of binding site of osteochondral unit, which might be the mechanism of the rapid progression in obesity-related OA

Tibial bone density may affect implant stability and functional outcomes following total knee replacement (TKR). Our aim was to characterise the bone density profile at the implant-tibia interface following TKR in mechanical versus kinematic alignment. Pre-operative computed tomography scans for 10 patients were obtained. Using surgical planning software, tibial cuts were made for TKR either neutral (mechanical) or 3 degrees varus (kinematic) alignment. Signal intensity, in Hounsfield Units (HU), was measured at 25,600 points throughout an axial slice at the implant-tibia interface and density profiles compared along defined radial axes from the centre of the tibia towards the cortices. From the tibial centre towards the lateral cortex, trabecular bone density for kinematic and mechanical TKR are similar in the inner 50% but differ significantly beyond this (p= 0.012). There were two distinct density peaks, with peak trabecular bone density being higher in kinematic TKR (p<0.001) and peak cortical bone density being higher in mechanical TKR (p<0.01). The difference in peak cortical to peak trabecular signal was 43 HU and 185 HU respectively (p<0.001). On the medial side there was no significant difference in density profile and a linear increase from centre to cortex. In the lateral proximal tibia, peak cortical and peak trabecular bone densities differ between kinematic TKR and mechanical TKR. Laterally, mechanical TKR may be more dependent upon cortical bone for support compared to kinematic TKR, where trabecular bone density is higher. This may have implications for surgical planning and implant design

One of the main surgical goals when performing a total knee replacement (TKR) is to ensure the implants are properly aligned and correctly sized; however, understanding the effect of alignment and rotation on the biomechanics of the knee during functional activities is limited. Cardiff University has unique access to a group of local patients who have relatively high frequency of poor alignment, and early failure. This provides a rare insight into how malalignment of TKR's can affect patients from a clinical and biomechanical point of view to determine how to best align a TKR. This study aims to explore relationship clinical surgical measurements of Implant alignment with in-vivo joint kinematics. 28 patient volunteers (with 32 Kinemax (Stryker) TKR's were recruited. Patients undertook single plane video fluoroscopy of the knee during a step-up and step-down task to determine TKR in-vivo kinematics and centre of rotation (COR). Joint Track image registration software (University of Florida, USA) was used to match CAD models of the implant to the x-ray images. Hip-Knee-Ankle (HKA) was measured using long-leg radiographs to determine frontal plane alignment. Posterior tibial slope angle was calculated using radiographs. An independent sample t-test was used to explore differences between neutral (HKA:-2° to 2°), varus (≥2°) and valgus alignment (≤-2°) groups. Other measures were explored across the whole cohort using Pearson's correlations (SPSS V23). There was found to be no statistical difference between groups or correlations for HKA. The exploratory analysis found that tibial slope correlated with Superior/Inferior translation ROM during step up (r=−0.601, p<0.001) and step down (r=−.512, p=0.03) the position of the COR heading towards the lateral (r=−.479, p=0.006) during step down. Initial results suggest no relationship between frontal plane alignment and in-vivo. Exploratory analyses have found other relationships that are worthy of further research and may be important in optimizing function