Published 10/1/2017
Maureen Leahy

Resource Utilization is High in Patients Undergoing TKA Revision for Infection

Study results highlight need for risk adjustment
A study that examined whether risk adjustment is necessary in value-based reimbursement models for infected total joint replacement found that patients who undergo revision total knee arthroplasty (TKA) for infection utilize more resources in a 30-day episode of care than patients who undergo aseptic revision TKA.

The study, “Risk Adjustment is Necessary in Value-Based Outcomes Models for Infected Total Knee Arthroplasty,” was named one of the Best Papers of the Musculoskeletal Infection Society’s 27th Annual Open Scientific Meeting. The data were presented by coauthor P. Maxwell Courtney, MD, of The Rothman Institute in Philadelphia.

Passage of the Medicare Access and CHIP Reauthorization Act (MACRA) in 2015 repealed the sustainable growth formula and accelerated a shift from volume- (fee-for-service) to value-based payments. Under MACRA, eligible providers are reimbursed through one of two payment tracks: the Merit-based Incentive Payment System (MIPS) or Advanced Alternative Payment Models (Advanced APMs), such as bundled payments.

“The problem with these value-based metric models is that there is little or no risk adjustment for patients with complex conditions who utilize more resources,” Dr. Courtney explained. “Bundled payments have become very popular for primary joint replacement and some centers are now participating in bundled payment arrangements for revision arthroplasties. However, revision TKA performed for infection is a substantial economic and clinical burden. The results of several studies reveal that revision TKAs cost three to four times more than a primary joint replacement and that revisions for infected total knees cost twice as much as aseptic revisions.”

Retrospective cohort analysis
The researchers conducted their study to determine resource utilization in patients undergoing revision TKA for infection compared to patients undergoing revision for aseptic reasons. They also sought to identify differences in specific complications between the two groups as well as independent risk factors for poor 30-day outcomes following surgery.

Using CPT and ICD-9 diagnosis and procedure codes and the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database, the researchers identified 10,844 consecutive patients (mean age = 65 years) who had undergone revision TKA from 2012 to 2015. Patients whose primary diagnosis for the procedure was malignancy were excluded.

The patients were divided into two groups: those who had undergone revision for infection (n = 1,999) and those who had undergone aseptic revision (n = 8,845). Among the infected patients, 41 percent (n = 820) had undergone knee explantation with placement of an antibiotic spacer. Postoperative infections were defined as superficial surgical site infections, deep surgical site infections, or wound dehiscence.

Demographics, medical comorbidities, and 30-day episodes-of-care outcomes—hospital length of stay, discharge disposition, readmissions, mortality, complications, and reoperations—were compared between the groups. Complications included the following:

  • surgical site infection
  • pneumonia
  • respiratory complication requiring reintubation
  • pulmonary embolism
  • deep vein thrombosis
  • renal insufficiency or failure
  • urinary tract infection
  • stroke
  • cardiac arrest
  • bleeding requiring transfusion
  • myocardial infarction
  • sepsis or septic shock

The chi-square test was used to determine significant differences in outcomes between the groups; continuous variables were analyzed with an unpaired, two-tailed Student’s t test; and multivariate logistic regression analysis was performed to control for confounding variables.

Infected patients utilize more resources
Analysis of demographics and medical comorbidities revealed that patients in the infected revision cohort were slightly older, more likely to be male, had a worse comorbidity profile, and had a higher American Society of Anesthesiologists classification than patients in the aseptic revision group. Patients undergoing revision TKA for infection also had a longer length of stay, were more likely to be discharged to a rehabilitation facility, and had higher 30-day readmission, mortality, and complication rates than patients undergoing revision for aseptic reasons (Table 1).

Specifically, with respect to complications, the infected group had a higher incidence of transfusion (25 percent vs. 12 percent), renal failure (1.1 percent vs. < 0.1 percent), pneumonia (1.5 percent vs. 0.5 percent), and postoperative surgical site infection (10 percent vs. 3 percent) (P < 0.001 for all comparisons). The researchers found no differences in the rates of pulmonary embolism, stroke, myocardial infarction, or cardiac arrest between the two groups.

Dr. Courtney added that infected patients who had undergone knee explantation with placement of an antibiotic spacer had slightly worse outcomes than the other infected patients. “Patients in the explant and spacer group were more likely to experience a complication, and their mortality rate was 1 percent—1 in 100 died within 30 days,” he said.

When controlling for demographic factors and medical comorbidities, revision TKA for infection was found to be an independent risk factor for 30-day postoperative complication, reoperation, hospital readmission, and mortality.

Dr. Courtney noted that the results of the study—that patients undergoing revision TKA for infection are more likely to be readmitted to the hospital and are more likely to have complications—are not surprising. The take-away is that value-based reimbursement models need to risk adjust for patients who utilize more resources.

“Without risk adjustment, patients with prosthetic joint infection of the knee will likely experience access to care problems,” Dr. Courtney said. “We need to advocate for our patients and make policy makers aware of this.”       

Dr. Courtney’s coauthors are Anthony Boniello, MD; Craig J. Della Valle, MD; and Gwo-Chin Lee, MD.

The authors’ disclosure information can be accessed at www.aaos.org/disclosure.

Maureen Leahy is assistant managing editor of AAOS Now. She can be reached at leahy@aaos.org.

Bottom Line

  • Newer payment and quality reporting models lack risk adjustment for physicians and hospitals that care for patients with complex conditions.
  • In this study, researchers compared resource utilization in patients undergoing TKA revision for infection with patients undergoing revision for aseptic reasons.
  • TKA revision for infection was an independent risk factor for complications, readmission, reoperation, and 30-day mortality, which can increase episode-of-care costs.
  • The study’s results highlight the need for value-based reimbursement models to risk adjust for complex patients who utilize more resources.


  1. Hebert CK, Williams RE, Levy RS, Barrack RL: Cost of treating an infected total knee replacement. Clin Orthop Relat Res [Internet]. 1996 Oct [cited 2017 Aug 22];(331):140–5. Available from: http://www.ncbi.nlm.nih.gov/pubmed/8895630