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Cost-Effectiveness of Closed Incision Negative Pressure Therapy for Surgical Site Management After Revision Total Knee Arthroplasty: Secondary Analysis of a Randomized Clinical Trial

Open AccessPublished:March 11, 2022DOI:https://doi.org/10.1016/j.arth.2022.03.022

      Highlights

      • The PROMISES clinical trial examined revision total knee arthroplasty outcomes.
      • Patients received closed incision negative pressure therapy or standard of care.
      • A health economic model was used to quantify the cost of surgical site complication.
      • Closed incision negative pressure therapy reduced mean per-patient cost by $989.
      • Among higher risk patients, cost savings increased to $2,536 per patient.

      Abstract

      Background

      The PROMISES (Post-market, Randomized, Open-Label, Multicenter, Study to Evaluate the Effectiveness of Closed Incision Negative Pressure Therapy Versus Standard of Care Dressings in Reducing Surgical Site Complications in Subjects With Revision of a Failed Total Knee Arthroplasty) randomized controlled trial compared closed incision negative pressure therapy (ciNPT) to standard of care (SOC) after revision total knee arthroplasty in high-risk patients. We assessed the costs associated with 90-day surgical site complications (SSCs) to determine the cost-benefit of ciNPT.

      Methods

      A health economic model was used to determine mean per-patient costs to manage the surgical site, including the costs of postoperative dressings, surgical and non-surgical interventions, and readmission. A subanalysis was performed to examine cost-benefit in “lower risk” (Charlson Comorbidity Index < 2) and “higher risk” (Charlson Comorbidity Index ≥ 2) patients.

      Results

      Patients with ciNPT experienced fewer SSCs (3.4% vs 14.3%; P = .0013) and required fewer surgical (0.7% vs 4.8%; P = .0666) and non-surgical (2.7% vs 12.9%; P = .0017) interventions compared to those with SOC. Readmission rates were significantly higher when patients experienced SSC (31% vs 4%; P = .0001). Using the economic model, respective per-patient costs for the ciNPT and SOC groups were $666 and $52 for postoperative dressings, $135 and $994 for surgical interventions, $231 and $970 for readmissions, and $15 and $70 for non-surgical interventions. Total per-patient costs for surgical site management were $1,047 for ciNPT and $2,036 for SOC. Among the lower risk population, mean per-patient cost was $1,066 for ciNPT and $1,474 for SOC. Among the higher risk population, mean per-patient cost was $676 for ciNPT and $3,212 for SOC.

      Conclusion

      Despite higher upfront costs for postoperative dressings, ciNPT was cost-effective in this health economic model, decreasing the costs of surgical site management after revision total knee arthroplasty by 49% in this study population and 79% in higher risk subgroup.

      Keywords

      In 2010, there were an estimated 4.7 million people in the United States with a total knee arthroplasty (TKA) [
      • Maradit Kremers H.
      • Larson D.R.
      • Crowson C.S.
      • Kremers W.K.
      • Washington R.E.
      • Steiner C.A.
      • et al.
      Prevalence of total hip and knee replacement in the United States.
      ]. Subsequent studies have estimated that annual counts of primary TKAs performed in 2030 and 2040 will increase to 1.9 million and 3.4 million, respectively [
      • Singh J.A.
      • Yu S.
      • Chen L.
      • Cleveland J.D.
      Rates of total joint replacement in the United States: future projections to 2020-2040 using the national inpatient sample.
      ]. Although all-cause complications are comparatively low in primary TKAs (2.5%) [
      • Nichols C.I.
      • Vose J.G.
      Clinical outcomes and costs within 90 days of primary or revision total joint arthroplasty.
      ], 2.2% of primary TKAs undergo revisions within 5 years [
      • Ong K.L.
      • Lau E.
      • Suggs J.
      • Kurtz S.M.
      • Manley M.T.
      Risk of subsequent revision after primary and revision total joint arthroplasty.
      ]. In contrast to the primary operation, the rates of all-cause complications and postoperative infections after revision TKA (rTKA) have been reported to be as high as 37.2% and 24.1%, respectively [
      • Nichols C.I.
      • Vose J.G.
      Clinical outcomes and costs within 90 days of primary or revision total joint arthroplasty.
      ]. Readmission within 90 days is also high among rTKAs, occurring in 23.1% of cases. Accordingly, rTKAs represent a significantly greater financial burden than primary TKAs [
      • Nichols C.I.
      • Vose J.G.
      Clinical outcomes and costs within 90 days of primary or revision total joint arthroplasty.
      ].
      Closed incision negative pressure therapy (ciNPT) is an option for managing the postoperative incision by maintaining a closed environment and removing exudate. In a prospective, randomized clinical trial of 160 patients undergoing rTKA or total hip arthroplasty, ciNPT was associated with a significantly lower rate of all-cause complication compared to silver-impregnated occlusive dressings [
      • Newman J.M.
      • Siqueira M.B.
      • Klika A.K.
      • Molloy R.M.
      • Barsoum W.K.
      • Higuera C.A.
      Use of closed incisional negative pressure wound therapy after revision total hip and knee arthroplasty in patients at high risk for infection: a prospective, randomized clinical trial.
      ]. This study was followed by the PROMISES (Post-market, Randomized, Open-Label, Multicenter, Study to Evaluate the Effectiveness of Closed Incision Negative Pressure Therapy Versus Standard of Care Dressings in Reducing Surgical Site Complications in Subjects With Revision of a Failed Total Knee Arthroplasty) multicenter randomized controlled trial (RCT), which examined the clinical outcomes of 294 patients at high risk for surgical site complications (SSCs) undergoing rTKA and prospectively managed with ciNPT or silver-impregnated antimicrobial dressings [
      • Higuera-Rueda C.
      • Emara A.K.
      • Nieves-Malloure Y.
      • Klika A.K.
      • Cooper H.J.
      • Cross M.B.
      • et al.
      The effectiveness of closed-incision negative-pressure therapy versus silver-impregnated dressings in mitigating surgical site complications in high-risk patients after revision knee arthroplasty: the PROMISES randomized controlled trial.
      ]. The study concluded with a significantly lower incidence of 90-day SSCs in the ciNPT versus the control group (3.4% vs 14.3%, respectively). Despite this apparent advantage, ciNPT dressings typically have a higher initial cost than standard of care (SOC) dressings, indicating a need for a cost-effectiveness analysis to support decision making when creating an incision management regimen. Evaluating the cost-benefit of an intervention is important for maintaining financial sustainability of medical providers without compromising patient outcomes. We therefore performed an economic evaluation of the PROMISES study data to evaluate the cost-benefit of ciNPT versus SOC dressings for 90 days after rTKA. Because cost data were not collected during the PROMISES RCT, a health economic model was employed to assess probable costs incurred by the development of SSC.

      Methods

      Study data from the PROMISES [
      • Higuera-Rueda C.
      • Emara A.K.
      • Nieves-Malloure Y.
      • Klika A.K.
      • Cooper H.J.
      • Cross M.B.
      • et al.
      The effectiveness of closed-incision negative-pressure therapy versus silver-impregnated dressings in mitigating surgical site complications in high-risk patients after revision knee arthroplasty: the PROMISES randomized controlled trial.
      ] RCT (registered NCT03274466 on clinicaltrials.gov) was used to develop a health economic model comparing ciNPT (3M Prevena Therapy; 3M, San Antonio, TX) to SOC silver-impregnated antimicrobial dressing (Aquacel Ag Dressing; ConvaTec, Deeside, UK) in patients at high risk for SSCs after rTKA. The trial was conducted at 18 sites in North America with a total of 294 patients recruited to the study between January 1, 2018 and August 31, 2019. The patients completing the study were 59.6% female and had a mean age of 64.9 years; detailed demographic data are described by Higuera-Rueda et al [
      • Higuera-Rueda C.
      • Emara A.K.
      • Nieves-Malloure Y.
      • Klika A.K.
      • Cooper H.J.
      • Cross M.B.
      • et al.
      The effectiveness of closed-incision negative-pressure therapy versus silver-impregnated dressings in mitigating surgical site complications in high-risk patients after revision knee arthroplasty: the PROMISES randomized controlled trial.
      ]. Deidentified patient study data were used to identify interventions per patient and type of SSC, which were recorded as open surgical drainage, percutaneous drainage, debridement, excision, reoperation, antibiotic therapy, ciNPT, or “other” with detailed descriptive text. Types of SSC included surgical site infection, full-thickness skin dehiscence, seroma or hematoma requiring drainage or surgery, skin necrosis, and continued drainage at the time of dressing removal. Interventions were grouped into surgical (reoperations, debridement performed in the operating room, or drainage procedure performed in the operating room) and non-surgical interventions (antibiotics, ciNPT, dressing changes, assessment visits, or bedside debridement).
      The Charlson Comorbidity Index (CCI) is a validated predictor of in-hospital mortality that has also been associated with higher risk of complications after orthopedic surgery [
      • Charlson M.E.
      • Charlson R.E.
      • Peterson J.C.
      • Marinopoulos S.S.
      • Briggs W.M.
      • Hollenberg J.P.
      The Charlson Comorbidity Index is adapted to predict costs of chronic disease in primary care patients.
      ,
      • Voskuijl T.
      • Hageman M.
      • Ring D.
      Higher Charlson Comorbidity Index Scores are associated with readmission after orthopaedic surgery.
      ]. To examine whether cost efficiency differed among patients with higher comorbidity, the cohorts were divided into higher risk (CCI ≥ 2) and lower risk (CCI < 2) subcategories. CCI scores were determined for all patients based on baseline patient characteristic details.
      A conservative health economic model was created to assess per-patient postoperative costs, which included the cost of postoperative dressings, SSC-related care (surgical and non-surgical interventions), and readmissions of patients with SSC. The mean per-patient cost of postoperative dressing was calculated for the dressing type (ciNPT or SOC) based on list prices for related products. The cost of rTKA-related surgical intervention (within a 90-day period) was derived from the Premier Healthcare Database (Premier Inc, Charlotte, NC), a large, all-payer database with real-world data reported by non-profit, non-governmental, and community and teaching hospitals and health systems in the United States [
      Premier Applied Sciences
      Premier healthcare database white paper: data that informs and performs.
      ]. rTKAs were identified by search for related Current Procedural Terminology (CPT) codes (27486, 27487) or Diagnostic Related Groups (DRG) (466, 467, 468) with International Classification of Diseases, 10th Revision, Procedure Coding System (ICD-10-PCS) codes (0SWC0JC, 0SWD0JC, 0SWT0JZ, 0SWU0JZ, 0SWV0JZ, 0SWW0JZ); from these cases, 996 same-knee, single-procedure surgical interventions within 90 days of the initial rTKA were isolated. The mean cost for each surgical intervention (ie, surgical drainage, reoperation) was calculated as the average of the total reported hospital costs on the day of surgery excluding the stay cost. The cost for non-surgical intervention included materials, antibiotics, and costs of procedures and assessment visits from the 2021 Physician Fee Schedule per the Centers for Medicare & Medicaid Services [
      Centers for Medicare & Medicaid Services
      Medicare Physician Fee Schedule.
      ]. Daily cost of inpatient stay was derived from the American Hospital Association Annual Survey [
      Kaiser Family Foundation State Health Facts
      Source: American Hospital Association. 1999 - 2019 AHA Annual Survey. Special Data Request, 2020.
      ]. For each component of the cost analysis, the total cost was calculated and divided across the patient population to determine the mean per-patient cost.
      Continuous variables were analyzed using the Mann-Whitney U-test and are presented as mean ± standard deviation. Categorical variables were analyzed using the Fisher’s exact test and are represented as the number of patients. Statistical significance was assessed at P < .05.

      Results

      Overall Cost Analysis

      Of the 147 patients receiving ciNPT dressings: 88 patients were managed with $495-per-application ciNPT dressings (3M Prevena Peel and Place Dressing), and 56 were managed with $830-per-application ciNPT dressings (3M Prevena Plus Customizable Dressings). The number of applications per patient were 1.06 and 1.07, respectively. SOC dressings cost $39 per application, and the 147 patients receiving SOC dressings underwent 1.34 applications per patient. Mean per-patient cost of postoperative dressings was $666 for ciNPT and $52 for SOC dressings.
      There were 8 patients with surgical interventions: 7 of these were reoperations and 1 was surgical drainage. For these 8 patients, there was 1 surgical intervention per patient (Table 1). The reasons for surgery were 4 surgical site infections, 2 surgical wound dehiscences, and 2 seroma/hematomas. Fewer patients managed with ciNPT required surgical (1/147 [0.7%] vs 7/147 [4.8%]; P = .0666) interventions to manage SSC, but this was not statistically significant (Table 2). The mean costs for 90-day surgical interventions were $22,152 for reoperation and $3,475 for surgical drainage, resulting in a $19,817 mean cost per surgical intervention. Based on the incidence of surgical intervention in each group, mean per-patient surgical costs across the entire ciNPT and SOC populations were $135 and $944, respectively (Table 3).
      Table 1Type of SSC and Related Interventions.
      Surgical Site ComplicationSurgical InterventionsNon-Surgical Interventions
      TypeTotal PatientsReoperationSurgical DrainagePatientsAntibioticsNPWTDressingNon-OR DebridementAspirationAssessment VisitsPatients
      Deep SSI and dehiscence111121
      Deep SSI321311112
      SSI and dehiscence11111
      Dehiscence42214123
      Seroma/hematoma5221274
      SSI3213
      Continued drainage96319
      Total26718514749223
      Individual patients could have undergone more than one intervention type.
      NPWT, negative pressure wound therapy; OR, operating room; SSC, surgical site complication; SSI, surgical site infection.
      Table 2Surgical and Non-Surgical Interventions for Treatment of SSCs.
      Type of InterventionciNPT (N = 147)SOC (N = 147)Total (N = 294)P-Value
      Surgical interventions
       Patients with surgical intervention, n (%)1 (0.7%)7 (4.8%)8 (2.7%).0666
      Reoperation/surgical interventions (n)167
      Surgical drainage (n)011
      Total surgical interventions (n)178
      Non-surgical interventions
       Patients with non-surgical intervention, n (%)4 (2.7%)19 (12.9%)23 (7.8%).0017
      Prescription antibiotics (n)055
      ciNPT applications (n)31114
      Additional dressings (n)257
      Non-surgical debridement visits (n)134
      Aspiration visits (n)189
      SSC-related assessment visits (n)022
      Total non-surgical interventions (n)73441
      Bold indicates statistically significant (P < .05).
      ciNPT, closed incision negative pressure therapy; SSC, surgical site complication; SOC, standard of care.
      Table 3Detailed Health Economic Model Results.
      Cost CategoryciNPT (N = 147)SOC (N = 147)
      Mean per-patient postoperative dressing cost (USD)$666.02$52.29
      Surgical intervention costs
       Patients with surgical intervention, n (%)1 (0.7%)7 (4.8%)
       Cost per surgical intervention (USD)$19,817.38
       Total cost of surgical interventions (USD)$19,817.38$138,721.63
      Mean per-patient surgical intervention cost (USD)$134.81$943.68
      Readmission cost for patients with SSC
       Patients with SSC, n (%)5 (3.4%)21 (14.3%)
       Readmission rate of patients with SSC (%)31%
       Mean length of stay upon admission (d)8.4
       Daily cost of an inpatient stay (USD)$2,607.00
       Cost of inpatient stay for readmitted patients (USD)$21,898.80
       Total cost of inpatient hospital stay (USD)$33,943.14$142,561.19
      Mean per-patient readmission cost (USD)$230.91$969.80
      Non-surgical intervention costs
       Patients with non-surgical intervention, n (%)4 (2.7%)19 (12.9%)
       Cost per patient with non-surgical care to manage SSC (USD)$542.72
       Total cost of non-surgical interventions (USD)$2,170.90$10,311.76
      Mean per-patient non-surgical intervention cost (USD)$14.77$70.15
      Mean per-patient total cost of care (USD)$1,046.51$2,035.92
      Total cost of care per study population (USD)$153,856.68$299,280.73
      ciNPT, closed incision negative pressure therapy; SSC, surgical site complication; SOC, standard of care; USD, United States dollar.
      Twenty-three patients required non-surgical interventions, with a mean 1.8 interventions per patient. For some patients, non-surgical interventions preceded surgical interventions (Table 1). Significantly fewer patients managed with ciNPT required non-surgical (4/147 [2.7%] vs 19/147 [12.9%]; P = .0017) interventions to manage SSC. Among the 23 patients, the mean per-patient cost for non-surgical intervention was $543. Due to the incidence of non-surgical intervention in each group, mean per-patient costs for non-surgical interventions across the entire ciNPT and SOC populations were $15 and $70, respectively.
      Among patients with SSCs, there were 8 readmissions: 1 in the ciNPT group and 7 in the SOC group. Readmission rates of patients with SSC were 20% in the ciNPT group versus 33% with SOC dressings. Readmission rates were significantly higher when patients experienced an SSC (8/26 [31%] vs 12/268 [4%]; P = .0001), for both SSCs that required non-surgical management (6/23 [26%] vs 12/268 [4%]; P = .0012) and those that required surgical management (5/8 [63%] vs 12/268 [4%]; P < .0001). Upon readmission, the mean length of stay for patients with SSC was 8.4 days. At $2,607 daily inpatient cost, the mean per-patient cost of inpatient stay was $21,899. Due to the incidence of SSC and readmission of patients with SSCs, the mean inpatient costs for patients with SSCs in the ciNPT and SOC groups was $230 and $970, respectively.
      In total, mean per-patient cost of care was $1,047 for ciNPT and $2,035 for SOC, indicating a cost savings of $989 per rTKA patient when treated with ciNPT. Total cost of care per study population was $153,857 for ciNPT and $299,280 for SOC.

      Cost Analysis per Patient Risk Profile

      CCI scores derived from patients’ diagnostic records revealed that 185 of 294 (63%) patients had a “lower risk profile” (CCI < 2). The number of patients with CCI < 2 was similar in both the ciNPT (62.6%) and the SOC (63.3%) groups (Table 4). The mean CCI score was 1.1 for the total study population, 1.2 for the ciNPT group, and 1.1 in the SOC group. Of the patients with CCI < 2, 16 (8.6%) patients developed SSCs, 3 (20%) of which were readmitted to the hospital for a mean 7-day length of stay. There were no significant differences in the rate of SSC, surgical interventions, non-surgical interventions, and readmissions between the ciNPT and SOC groups. Mean per-patient cost of care was $1,066 for ciNPT and $1,474 for SOC, indicating a cost savings of $409 per patient with CCI < 2.
      Table 4Outcomes in Patients With Charlson Comorbidity Index <2.
      Clinical Outcomes and Cost CategoryciNPT (N = 92)SOC (N = 93)Total (N = 185)P-Value
      Charlson Comorbidity Index (mean)0.210.150.18.4354
      Clinical outcomes, n (%)
       Surgical site complications4 (4.3%)12 (12.9%)16 (8.6%).0643
       Patients with surgical intervention for SSC1 (1.1%)4 (4.3%)5 (2.7%).3682
       Patients with non-surgical intervention for SSC4 (4.3%)12 (12.9%)16 (8.6%).0643
       Readmissions1 (1.1%)2 (2.2%)3 (1.6%)1
      Mean per-patient costs (USD)
       Postoperative dressings$666.02$52.29
       Surgical intervention$215.41$852.36
       Non-surgical intervention$35.37$128.28
       Readmission$148.77$441.51
      Mean per-patient total cost of care (USD)$1,065.56$1,474.44
      Total cost of care per study population (USD)$98,031.59$137,122.68
      ciNPT, closed incision negative pressure therapy; SSC, surgical site complication; SOC, standard of care; USD, United States dollar.
      Among 109 patients with a “higher risk profile” (CCI ≥ 2), 10 (9.2%) developed SSCs (Table 5). In this subpopulation, the ciNPT group had significantly fewer SSCs (1/55 [1.8%] vs 9/54 [16.7%]; P = .0081) and readmissions for patients with SSC (0/55 [0%] vs 5/54 [9.3%]; P = .0271) compared to the SOC group. Of the patients who developed SSCs, 5 (50%) were readmitted to the hospital with a mean 9.2-day length of stay. Mean per-patient cost of care was $676 for ciNPT and $3,212 for SOC, indicating a cost savings of $2,536 per patient with CCI ≥ 2.
      Table 5Outcomes in Patients With Charlson Comorbidity Index ≥2.
      Clinical Outcomes and Cost CategoryciNPT (N = 55)SOC (N = 54)Total (N = 109)P-Value
      Charlson Comorbidity Index (mean)2.732.932.8.6455
      Clinical outcomes, n (%)
       Surgical site complications1 (1.8%)9 (16.7%)10 (9.2%).0081
       Patients with surgical intervention for SSC0 (0%)3 (5.6%)3 (2.8%).1182
       Patients with non-surgical intervention for SSC1 (1.8%)6 (11.1%)7 (6.4%).0604
       Readmissions0 (0%)5 (9.3%)5 (4.6%).0271
      Mean per-patient costs (USD)
       Postoperative dressings$666.02$52.29
       Surgical intervention$0$1,100.97
       Non-surgical intervention$9.86$60.25
       Readmission$218.04$1,998.70
      Mean per-patient total cost of care (USD)$893.92$3,212.21
      Total cost of care per study population (USD)$49,165.60$173,459.22
      Bold indicates statistically significant (P < .05).
      ciNPT, closed incision negative pressure therapy; SSC, surgical site complication; SOC, standard of care; USD, United States dollar.

      Discussion

      TKA is a common and effective surgical procedure for the treatment of advanced osteoarthritis of the knee, and primary TKAs typically heal with low complication rates. However, in the case that a revision is needed, the rate of overall complication significantly increases, occurring in as many as 37.2% of patients [
      • Nichols C.I.
      • Vose J.G.
      Clinical outcomes and costs within 90 days of primary or revision total joint arthroplasty.
      ]. Compared to primary TKAs, revisions also have a higher rate of 90-day readmission, a significant driver of postoperative costs. The total cost associated with a single rTKA surgery is approximately $75,000 in the US healthcare system [
      • Delanois R.E.
      • Mistry J.B.
      • Gwam C.U.
      • Mohamed N.S.
      • Choksi U.S.
      • Mont M.A.
      Current epidemiology of revision total knee arthroplasty in the United States.
      ], contributing to an estimated $13 billion annual economic burden by 2030 [
      • Bhandari M.
      • Smith J.
      • Miller L.E.
      • Block J.E.
      Clinical and economic burden of revision knee arthroplasty.
      ]. Preventing complications after rTKA is an important goal for avoiding subsequent revisions, improving patient quality of life, and reducing healthcare costs.
      In the PROMISES RCT, the use of ciNPT was associated with a significant reduction in the rate of 90-day SSCs post-rTKA in a high-risk population [
      • Higuera-Rueda C.
      • Emara A.K.
      • Nieves-Malloure Y.
      • Klika A.K.
      • Cooper H.J.
      • Cross M.B.
      • et al.
      The effectiveness of closed-incision negative-pressure therapy versus silver-impregnated dressings in mitigating surgical site complications in high-risk patients after revision knee arthroplasty: the PROMISES randomized controlled trial.
      ]. Notably, the SSC rate in the patient group managed with SOC dressings (silver-impregnated antimicrobial dressings) was 14.3%, which is much lower than the historical rates for this procedure [
      • Nichols C.I.
      • Vose J.G.
      Clinical outcomes and costs within 90 days of primary or revision total joint arthroplasty.
      ]. However, the use of ciNPT lowered this rate to 3.4%, with SSCs occurring in just 5 of 147 patients. These outcomes suggested an opportunity for cost savings resulting from a reduction in SSC-related interventions, prompting this cost-benefit analysis.
      To create the health economic model, we calculated the mean per-patient cost for postoperative dressings, surgical interventions, non-surgical interventions, and readmissions for patients with SSCs. In the interest of avoiding an overestimate of cost savings, we first conservatively calculated means across the entire 294-patient population. For readmissions, this meant a 31% readmission rate among patients with SSCs and a mean length of stay of 8.4 days for both the ciNPT and SOC groups. These assumptions translated to 1.55 readmissions for the ciNPT group and 6.51 for the SOC group. This is in contrast to the observed outcome, in which only a single ciNPT patient was readmitted, for 1 day in hospital. This observation would not be considered to be representative of all readmissions in either group. Using this method results in a health economic model with higher costs in the ciNPT group and lower costs in the SOC group than observed for both readmissions and surgical interventions. However, the mean per-patient approach strengthens the general applicability of this cost analysis by minimizing the impact of rare events.
      Utilizing this health economic model concluded a mean cost savings of $989 per ciNPT patient, a 49% reduction from total per-patient costs with SOC dressings. These savings are attributed to the lower costs for readmissions, surgical interventions, and non-surgical interventions, despite the higher upfront cost of ciNPT dressings. For ciNPT, the cost of postoperative dressings was the greatest contributor, accounting for 64% of the mean per-patient total costs. Based on the type of ciNPT dressing, costs ranged from $495 to $830 per application, compared to $39 for SOC dressings.
      As expected, we observed that the likelihood of readmission was significantly higher in patients with SSCs, occurring in 31% of these patients versus 4% of patients without SSC. This suggests that lowering the rate of SSC is a practical target for reducing readmissions and associated costs, which is consistent with the published literature [
      • Lawson E.H.
      • Hall B.L.
      • Louie R.
      • Ettner S.L.
      • Zingmond D.S.
      • Han L.
      • et al.
      Association between occurrence of a postoperative complication and readmission: implications for quality improvement and cost savings.
      ]. Patients managed with ciNPT instead of SOC developed SSCs at significantly lower rates at 30, 45, and 90 days postoperatively [
      • Higuera-Rueda C.
      • Emara A.K.
      • Nieves-Malloure Y.
      • Klika A.K.
      • Cooper H.J.
      • Cross M.B.
      • et al.
      The effectiveness of closed-incision negative-pressure therapy versus silver-impregnated dressings in mitigating surgical site complications in high-risk patients after revision knee arthroplasty: the PROMISES randomized controlled trial.
      ]. Accordingly, mean per-patient readmission costs in the health economic model were 76% lower in the ciNPT versus SOC group.
      Although the rate of SSC-related surgical intervention was not significantly different between groups, the high cost per surgical procedure amplified the cost savings for each reoperation averted. Surgical interventions were required for 8 of 26 (31%) patients with SSC. This is in line with published literature, as infection alone is responsible for 20% of all rTKAs [
      • Delanois R.E.
      • Mistry J.B.
      • Gwam C.U.
      • Mohamed N.S.
      • Choksi U.S.
      • Mont M.A.
      Current epidemiology of revision total knee arthroplasty in the United States.
      ] and 44% of re-rTKAs [
      • Postler A.
      • Lutzner C.
      • Beyer F.
      • Tille E.
      • Lutzner J.
      Analysis of total knee arthroplasty revision causes.
      ]. The number of surgical interventions reported here differs slightly from that reported in the PROMISES publication [
      • Higuera-Rueda C.
      • Emara A.K.
      • Nieves-Malloure Y.
      • Klika A.K.
      • Cooper H.J.
      • Cross M.B.
      • et al.
      The effectiveness of closed-incision negative-pressure therapy versus silver-impregnated dressings in mitigating surgical site complications in high-risk patients after revision knee arthroplasty: the PROMISES randomized controlled trial.
      ] because 2 reoperations were classified as “Other/Adverse Event” in the original publication, and a third procedure (surgical incision and drainage) was omitted entirely. Detailed descriptions obtained from patient-level data made clear that these procedures were performed in the operating room. With these data, use of ciNPT represented an 86% reduction in mean per-patient costs for surgical intervention, compared to the use of SOC dressings.
      Non-surgical interventions for SSC included the costs of assessment visits, dressing changes, aspirations, antibiotics, and bedside debridements. Not included in the health economic model was the number of clinical visits and home health visits due to low incidence and lack of significant differences between treatment groups or patients with and without SSC. Visits for physical therapy were also not included because the occurrence of SSCs could delay the onset of rehabilitation, resulting in artificially limited duration and costs within the first 90 days.
      As with the PROMISES study, the advantage of ciNPT over alternative therapies is most apparent in patients with an elevated risk for SSCs [
      • Newman J.M.
      • Siqueira M.B.
      • Klika A.K.
      • Molloy R.M.
      • Barsoum W.K.
      • Higuera C.A.
      Use of closed incisional negative pressure wound therapy after revision total hip and knee arthroplasty in patients at high risk for infection: a prospective, randomized clinical trial.
      ,
      • Stannard J.P.
      • Volgas D.A.
      • McGwin 3rd, G.
      • Stewart R.L.
      • Obremskey W.
      • Moore T.
      • et al.
      Incisional negative pressure wound therapy after high-risk lower extremity fractures.
      ,
      • Atkins B.Z.
      • Wooten M.K.
      • Kistler J.
      • Hurley K.
      • Hughes G.C.
      • Wolfe W.G.
      Does negative pressure wound therapy have a role in preventing poststernotomy wound complications?.
      ,
      • Grauhan O.
      • Navasardyan A.
      • Hofmann M.
      • Muller P.
      • Stein J.
      • Hetzer R.
      Prevention of poststernotomy wound infections in obese patients by negative pressure wound therapy.
      ,
      • Scalise A.
      • Calamita R.
      • Tartaglione C.
      • Pierangeli M.
      • Bolletta E.
      • Gioacchini M.
      • et al.
      Improving wound healing and preventing surgical site complications of closed surgical incisions: a possible role of incisional negative pressure wound therapy. A systematic review of the literature.
      ]. Although all study participants exhibited at least one risk factor for postoperative SSC, there remained a variation in scores on the CCI. Voskuijl et al [
      • Voskuijl T.
      • Hageman M.
      • Ring D.
      Higher Charlson Comorbidity Index Scores are associated with readmission after orthopaedic surgery.
      ] reported that patients’ CCI scores accounted for 10% of the variation of orthopedic readmissions, adding an additional 0.45% risk for readmission with every point increase. Therefore, we examined whether subcategorizing the patients into higher and lower risk profiles based on CCI impacted the potential for cost savings. In both ciNPT and SOC groups, there were similar mean CCI scores and distribution of patients within each risk profile. However, among patients with the lower risk profile, any significant differences in the rate of SSC or readmissions dissipated, resulting in a reduced cost benefit between the mean per-patient total costs. In the higher risk patients, both the SSC and readmission rates were lower in the ciNPT group. This led to an increased cost benefit, in which the use of ciNPT represented a 78% reduction in mean per-patient surgical site management costs compared to the use of SOC dressings. These differences between the higher risk and lower risk profile patients, distinguishable even within a population that has at least one risk factor for SSC, suggest that the greatest cost utility of ciNPT may be observed in rTKA patients with multiple or severe comorbidities.
      In our health economic model, the total SSC-related incremental cost was $347,526 for 26 patients, resulting in a mean incremental cost of $13,366 per patient with SSC. This aligns with estimates derived from alternative sources of study data. In a retrospective cohort of consecutive primary total joint arthroplasties, 90-day postoperative costs for patients with SSC (excluding deep surgical site infection) were 63% ($5,349) higher than patients without SSC [
      • Luzzi A.J.
      • Anatone A.J.
      • Lauthen D.
      • Shah R.P.
      • Geller J.A.
      • Cooper H.J.
      How much does a surgical site complication cost after medicare total joint arthroplasty?.
      ]. In a second study retrospectively reviewing total joint arthroplasties between 2009 and 2013, 90-day postoperative costs of rTKA ($33,003) were approximately 50% higher than those of primary TKA [
      • Nichols C.I.
      • Vose J.G.
      Clinical outcomes and costs within 90 days of primary or revision total joint arthroplasty.
      ]. By using the $5,349 incremental cost for each primary TKA patient with SSC as a starting point and applying a 50% increase to account for the higher costs of rTKA, this would result in a conservative estimate of $8,024 cost difference per SSC patient. Alternatively, starting with the total 90-day postoperative costs for rTKA ($33,003) and proposing that the presence of SSC accounted for 63% of these costs, the total per-patient incremental cost for SSC after rTKA is $20,792. That our model’s cost estimate falls between these 2 scenarios provides validation that our analysis is compatible with the data of other arthroplasty studies.

      Limitations

      This study is limited first by the fundamental limitations of the RCT it is based on. The potential for bias is inherent due to the lack of ability to blind patients and investigators. However, the study methodology successfully minimized differences in baseline characteristics between treatment groups and loss to follow-up was low and proportionate. Health economic models are vulnerable to overestimation or underestimation of model parameters and can overlook important heterogeneous factors. The costs accumulated over the course of management for SSC are estimations based on external sources and were not collected during the PROMISES trial. We attempted to counteract the risk of bias by adopting a conservative estimation strategy to avoid generalizing rare outcomes, and by subdividing the study population into clinically meaningful subcategories for further analysis. However, it is important to note that the estimated cost savings produced by this model is not necessarily replicable across different patient populations.

      Conclusion

      The use of ciNPT for rTKA incision management provided a financial advantage over SOC dressings in this health economic model, in addition to the improved clinical outcomes reported in the PROMISES study. The lower total costs attributed to readmissions and surgical and non-surgical intervention cost for SSC overcome the initially higher costs of ciNPT dressings. Future investigations into the effectiveness of ciNPT in mitigating specific types of SSC or performing in certain patient subpopulations are needed to support informed decision making for better patient care.

      Acknowledgments

      The authors thank Mikaela Sifuentes, PhD (3M) for manuscript preparation assistance and Yuefeng Hou (3M) for support with data management and analysis.

      Appendix A. Supplementary Data

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