Due to the increasing incidence of osteoarthritis associated with the ageing global population, total knee arthroplasty (TKA) has become one of the most commonly performed orthopaedic procedures worldwide. The most common approach to determine causes and risk factors involves analysing readmission episodes among TKA patients within 30 days post-surgery.1 2 The 30-day readmission rate provides insight into the prevalence of postoperative complications, whereas the length of stay after readmission reflects the severity of those complications. A review of readmission causes is needed to assess the quality of hospital care and determine the adequacy of patient education (eg, wound management).3 An understanding of the 30-day readmission rate, causes, and risk factors can help hospitals improve clinical guidelines, reduce medical and surgical complications,4 and reduce the financial burden of treatment for these complications.5

Although multiple studies worldwide have adequately explored the 30-day readmission causes, rate, and length of stay among TKA patients,6 7 revealing important clinical insights, no such studies have been conducted in Hong Kong. The current study aimed to investigate the 30-day readmission rate, causes, and risk factors among TKA patients in the city.

This retrospective study included all patients who underwent TKA at our local university-affiliated hospital and were readmitted through an Accident and Emergency Department (AED) between 2001 and 2020. It evaluated the epidemiological characteristics, readmission causes, and preoperative co-morbidities of TKA patients.

We utilised data from the Clinical Data Analysis and Reporting System (CDARS), a well-established platform developed by the Hospital Authority (HA). The CDARS contains patient data, such as laboratory reports and radiological images; it covers all outpatients and inpatients at 43 public hospitals and institutions across seven service clusters in Hong Kong. Records in the CDARS include the details of patients with unplanned 30-day readmission to the AED of an HA hospital from either their homes or rehabilitation facilities, along with their discharge information. This platform is extensively used by research teams across Hong Kong.8 We obtained a list of TKA patients who underwent surgery at the study hospital and were readmitted to an HA hospital within 30 days. We matched these patient names with their corresponding electronic patient records to determine the reasons for readmission.

For patients who experienced 30-day readmission, both the records in the CDARS and electronic patient records were reviewed. For patients who did not require 30-day readmission, only CDARS records were reviewed. Medication records (ie, dispensing dates, dosages, and durations) were extracted from CDARS records to identify co-morbidities (online supplementary Appendix). All patient data were de-identified.

Based on factors described by Roger et al,6 we classified reasons for readmission into the following categories: orthopaedics-related, surgery-related, gastrointestinal-related, urological-related, neurological-related, cardiac-related, respiratory-related, renal-related, medication-related, and others. Orthopaedic specialists performed the classification to determine the cause of readmission.

The inclusion criteria were a recent history of TKA at our institution, readmission through the AED of an HA hospital, and inpatient admission. The exclusion criteria were a history of knee surgery, incomplete clinical assessment data, and/or orthopaedic tumours in the knee (for paediatric patients only).

Analyses of readmission cause, number, and rate, as well as organ dysfunction episodes, were episode-based. The analysis of risk factors for readmission was patient-based. Risk factors/co-morbidities were identified based on medications prescribed to the patients. If a patient received antihypertensive medication, that patient was assumed to have hypertension.

Data analysis was performed using R (R Foundation for Statistical Computing, Vienna, Austria) and R Studio software. All statistical tests were two-sided, and a 5% significance threshold was applied. The investigators and their research assistants were responsible for data collection and had access to the source data and study records. To evaluate categorical variables, Chi squared tests and/or Fisher’s exact tests were conducted, depending on the observed frequencies. To evaluate continuous variables, the Kruskal–Wallis test was used.

In total, 3878 records were initially reviewed; of these, 43 were excluded due to the presence of tumours (ie, osteosarcoma in the distal tibia), three were excluded due to incorrect data entry for revision surgery, and five were excluded because they constituted duplicate entries for the same readmission episode (online supplementary Fig 1).

Of the 3827 valid patient records, 2855 were included in the initial analysis after removal of duplicate records for 972 patients who underwent two unilateral TKAs during different admission episodes. Of the 3827 patients, 2815 (73.6%) were women and 1012 (26.4%) were men. The mean ages were 71.11 years for TKA patients who did not experience readmission and 73.10 years for TKA patients who experienced readmission (Table 16 9 10 11 12). The mean postoperative length of stay (±standard deviation) was 6.85±6.19 days (Table 2). Thus, the readmission rate at our institution was 3.4%, similar to rates reported worldwide (Table 1).6 7 13 There was an increase in the 30-day readmission rate between 2001 and 2020 (Table 2). The number of TKAs performed in our institution increased from 2001 to 2014 and remained consistently high (>200 TKAs annually except in 2020) [online supplementary Fig 2], in line with published literature.14

In total, 130 patients with valid readmission records were analysed to identify causes and risk factors (online supplementary Fig 1). Of these patients, 90 (69.2%) were women and 40 (30.8%) were men. The median length of stay after readmission was 2 days (interquartile range=1.25-5) and the mean time between surgery and readmission was 22 days (Table 3).

Unilateral knee pain (33.1%), unilateral knee swelling (26.2%), and gastrointestinal-related conditions (8.5%) were the most common causes of readmission (Table 4). Hypertension (67.7%) and diabetes mellitus (22.7% before March 2017 from which our institution modified the preoperative management pathway) were the most common co-morbidities among readmitted patients. Additionally, hypertension (odds ratio [OR]=2.08; P<0.001) and age ≥80 years (OR=1.63; P=0.01) were identified as significant risk factors for readmission (Table 5 and online supplementary Table 1). Patients who underwent bilateral TKA had a 58% lower risk of readmission (Table 6), possibly because they had better health condition before surgery and received more rigorous preoperative screening for high-risk co-morbidities.

Our results suggest that there is a substantial rate of readmission due to pain and swelling among TKA patients in Hong Kong, which is higher than the rates in previous studies (Table 1).6 9 12 Hospital resources should be reviewed to determine whether these patients require admission because most readmitted patients have non-severe conditions. To reduce the unnecessary allocation of clinical resources to non-severe cases, alternatives such as designated nurse clinics15 and patient consultation hotlines can provide medical advice for managing minor conditions (eg, pain and swelling) at home. These measures can reduce the workload of orthopaedic surgeons and improve postoperative follow-up care.

Hypertension and age ≥80 years were significant risk factors for readmission. The mean age of TKA patients in Hong Kong was higher than the mean ages of TKA patients in similar studies worldwide (Table 1)6 9 10 11 12; this difference aligns with the fact that Hong Kong has the longest life expectancy globally (mean age of 85.16 years in 2022).16

The increased risk of readmission with old age, consistent with findings in a previous study,17 may be related to the greater likelihood for older individuals to visit the AED for non-orthopaedic issues. In contrast, patients who underwent simultaneous bilateral TKA had a lower risk of readmission (OR=0.42; P=0.005) [Table 6].

At our institution, patients who underwent simultaneous bilateral TKA were aged <75 years and had no clinically significant cardiovascular co-morbidities (eg, stroke). Furthermore, in March 2017, our institution introduced routine glycated haemoglobin screening to identify diabetic and prediabetic patients, with the goal of minimising postoperative complications. Diabetes mellitus is known to increase the risk of periprosthetic joint infection after surgery.18 Patients with elevated glycated haemoglobin levels were referred to endocrinologists for better management of diabetes mellitus prior to TKA, thereby decreasing the OR for readmission from 1.24 to 0.74 (Table 5 and online supplementary Table 1). Considering that a substantial number of patients with the aforementioned co-morbidities exhibit a higher risk of readmission, the perioperative protocol could be improved. Suggested changes could include better coordination with each patient’s family medicine specialists or general practitioners, who usually have a better understanding of the patient’s underlying medical conditions, to develop effective preoperative and postoperative care plans.

Overall, 4.6% (n=6) of the patients were readmitted primarily due to falls (Table 4). This finding highlights the need for enhanced nursing support and education to prevent post-surgical falls among TKA patients. Furthermore, stronger occupational therapy and household aid programmes can help prevent falls at home and improve patient rehabilitation. Another 4.6% of patients were readmitted due to the adverse drug effects (Table 4 and online supplementary Table 2), particularly from tramadol/codeine/morphine and related medications; symptoms included vomiting and constipation. These results indicate a need for cautious painkiller prescribing to prevent future medication-related readmissions.

To the best of our knowledge, this is the first study on the readmission rate, causes, and risk factors among TKA patients within 30 days post-surgery. It also compared data collected in Hong Kong with results from other studies, yielding insights for local orthopaedic surgeons who seek to improve suboptimal surgical outcomes.

Notably, there were some limitations. Patient data in the CDARS may be incomplete because some doctors might have omitted the International Classification of Diseases, Ninth Revision codes for certain co-morbidities. To mitigate this issue, prescribed drugs were used to identify patients’ co-morbidities. However, this approach may have missed some patients with co-morbidities and no associated medication records.

This study showed that older TKA patients with hypertension were more likely to be readmitted through the AED within 30 days post-surgery. The most common reasons for readmission were pain, swelling, and gastrointestinal-related symptoms. To reduce readmissions, hospitals should place greater emphasis on pain and wound management for TKA patients. Furthermore, patient education efforts should be strengthened to increase awareness of pain and wound management.

Concept or design: OWK Tsui, PK Chan.
Acquisition of data: OWK Tsui, PK Chan, JHY Leung.
Analysis or interpretation of data: OWK Tsui, PK Chan, JHY Leung.
Drafting of the manuscript: OWK Tsui.
Critical revision of the manuscript for important intellectual content: All authors.

All authors had full access to the data, contributed to the study, approved the final version for publication, and take responsibility for its accuracy and integrity.

All authors have disclosed no conflicts of interest.

The research was presented at 42nd Annual Congress of the Hong Kong Orthopaedic Association, 5 November 2022, Hong Kong.

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

This research was approved by the Institutional Review Board of The University of Hong Kong/Hospital Authority Hong Kong West Cluster, Hong Kong (Ref No.: UW-22-313). The requirement for patient consent was waived by the Board due to the retrospective nature of the research.

The supplementary material was provided by the authors and some information may not have been peer reviewed. Accepted supplementary material will be published as submitted by the authors, without any editing or formatting. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by the Hong Kong Academy of Medicine and the Hong Kong Medical Association. The Hong Kong Academy of Medicine and the Hong Kong Medical Association disclaim all liability and responsibility arising from any reliance placed on the content.

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