الفهرس 
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Abstract
6.1.1. Introduction
Total knee arthroplasty (TKA) involves replacing a damaged knee joint with an artificial prosthesis, primarily addressing pain and functional limitations. However, 12.8% may experience surgical site complications (SSC), with Periprosthetic joint infection (PJI) being the most common. PJI treatment options include Debridement, antibiotics, and implant retention (DAIR), two-stages revision, and single-stage revision. Antibiotics play a crucial role, with optimal duration still debated. Negative Pressure Wound Therapy (NPWT) has proven effective in reducing PJI risks. Single-use NPWT devices (sNPWT) offer portability and cost-effectiveness, but their use is suggested for high-risk patients due to higher costs. Economic decisions regarding sNPWT in TKA require consideration.
6.1.2. Aim of the study
Conducting a cost-effectiveness analysis of sNPWT in comparison to standard care (SC) among Egyptians having TKA. This aim will be achieved through the following objectives:
1.Calculating the ICER of sNPWT in comparison to SC among Egyptians undergoing primary TKA, using a hybrid model.
2.Quantification of the effect of uncertainty in the model
3.Assessment of the value of perfect information among model parameters.
4.Identifying special populations that could benefit from sNPWT as a cost-effective strategy in relevant research areas.
6.1.3. Material and Methods
Study design: cost-effectiveness, using hybrid model.
Setting: El-Hadarah Alexandria University Hospital.
Inclusion criteria: patients aged ≥65 years old underwent primary TKA and suffered from PJIs in the period between September 2021 to September 2022.
Exclusion criteria: patients underwent PJIs after revision.
Study perspective: the Egyptian state-funded medical treatment program
Study time horizon: fifteen years (one year in decision tree and 14 in Markov model).
Study model: A hybrid hypothetical model, combination of decision tree and Markov model, was used to evaluate the cost-effectiveness of sNPWT in primary TKA using the actual PJI probability in the El-Hadarah Alexandria University Hospital. The hybrid decision model was adapted from the model published by Antonios et al, 2021 and validated by expert orthopaedics consultation, in the orthopaedics unit of El-Hadarah Alexandria University hospital, the main hospital in Alexandria that undertakes TKA procedures under the coverage of the Egyptian state-funded medical treatment program. Our hybrid model was built to predict the cost-effectiveness of sNPWT in primary TKA versus the SC strategy, using the conventional dressing, from the Egyptian state-funded medical treatment program perspective.
The conventional dressing and sNPWT were used for 7 days after primary TKA. The conventional dressing was used after each surgery in both cohorts, while sNPWT was used once after primary TKA in one cohort. The model compared two hypothetical cohorts of patients underwent primary TKA and aged 65 years old. One cohort received the SC strategy, and the other cohort received the sNPWT strategy.
To assess the uncertainty of the cost-effectiveness analysis, both probabilistic (PSA) and deterministic (DSA) sensitivity analyses were performed. PSA was carried out by 10,000 Monte Carlo simulation. The probability of sNPWT being a cost-effective strategy was estimated by cost-Effectiveness Acceptability analysis (CEAC).
Multiple linear regression analysis using (relaimpo) library, R version 4.2.1, was used to identify the relative importance of each parameter of the model. The dependent variable was the ICER estimated by PSA. Independent variables were the probability of deep infection, success of first DAIR, failure after second DAIR, mortality after failure second DAIR, retained infection, SMR of revision, revision failure, RR of infection with sNPWT, RR of reoperation with sNPWT, revision cost, sNPWT cost, conventional dressing cost, revision utility, first DAIR utility, second DAIR utility, failure utility, and success utility.
One-way sensitivity analysis was used to test the effect of parameters variation by ±15% on the resulting ICER, DSA through tornado chart included the most important parameters, the deep infection probability, sNPWT cost, RR of infection with sNPWT, and RR of reoperation with sNPWT. Two-way sensitivity analysis included the probability of deep infection and the cost of sNPWT, which illustrated the effect of the change of the two parameters on ICER.
High-risk populations with significant PJIs relative risks were identified and verified by the orthopaedics consultant. The relative risks for diabetes mellitus, men, lung diseases, and the ASA score ≥ 3 were derived from a meta-analysis of Zhong et al., 2020. While the relative risk for RA was identified from a meta-analysis of Xiaolei Ren 2021. Regarding the relative risk for obesity (BMI>35 kg/m2), blood transfusion, smoking, anemia, and heart diseases , they were calculated from significant odds ratio by ClinCalc.
6.1.4. Results
Our hybrid model revealed that using sNPWT resulted in an additional cost of $24,289 for each additional QALY obtained with a 2.5% probability of infection following primary TKA, the infection rate in Elhadara university hospital. In terms of the lower and upper boundaries of the Egyptian WTP criterion, this base case scenario is deemed non-cost effective. Even though the PSA findings fall between the dominant and trade-off quarters of cost-effectiveness curve, the likelihood that sNPWT would be cost-effective at the upper and lower boundaries of Egyptian WTP criteria, was 24% and 16% respectively. The deep infection probability and sNPWT cost were the two most relevant parameters that affected the uncertainty. The two-way DSA indicated that when the risk of deep infection exceeded 2.5%, the cost-effectiveness probabilities of sNPWT increased while decreased when the cost of sNPWT exceeded $238 (current cost). The higher cost of sNPWT up to USD 280 is considered a cost-effective strategy
with 5% PJIs probability. The current sNPWT cost at $238 is considered to be cost-effective with a 4.5% PJIs probability.
Considering the upper Egyptian WTP threshold sNPWT was a cost-effective strategy for patients with ASA≥3 (ICER $1,351), diabetes (ICER $7,577.08) , and smoking (ICER $7,878.77). The PSA demonstrated sNPWT probabilities to be a cost-effective strategy for ASA≥3, diabetes, and smoking with probabilities 44%, 25%, and 22% respectively.
Although sNPWT with rheumatoid arthritis patients was not cost-effective (ICER $13,281.8230) exceeding the upper Egyptian WTP threshold, the probability of being cost-effective by CEAC was 68%. Likewise, using sNPWT for male gender was not a cost-effective strategy in base-case results (ICER $8,247.94) exceeding the upper Egyptian WTP threshold, while the probability of being cost-effective by CEAC was 26%. sNPWT was not a cost-effective strategy with blood transfusion, lung disease, heart disease, obesity, and anemia.
6.2. Conclusion
sNPWT is not regarded as a cost-effective strategy from the Egyptian state-funded medical treatment program perspective. Although there is 24% probability for sNPWT to be cost effective below the upper Egyptian WTP threshold and 16% probability to be cost-effective under the lower Egyptian WTP threshold.
The deep infection probability and the sNPWT cost are the most important and sensitive parameters affecting ICER, as a slight change in them affects the ICER. Thus, they can be the keys for the decision makers when sNPWT could be a cost-effective option. sNPWT is considered a cost-effective PJIs preventive measure in institutions with PJIs rates higher than 4.5%.
Also, sNPWT is a cost-effective PJIs preventive option in PJIs’ high-risk populations such as those with ASA≥3, diabetes, smoking, and may be considered for RA patients for high probability of being cost-effective in this population 68%.