title: Comorbidities in patients undergoing total knee arthroplasty: do they influence hospital costs and length of stay?
abstract: BACKGROUND
  Increasing national expenditures and use associated with TKA have resulted in pressure to reduce costs through various reimbursement cuts. However, within the arthroplasty literature, few studies have examined the association of medical comorbidities on resource use and length of stay after joint arthroplasty.
  
  
  OBJECTIVE
  The purpose of this study was to examine the association between individual patient characteristics (including demographic factors and medical comorbidities) on resource allocation and length of stay (LOS) after TKA.
  
  
  METHODS
  We queried the 2009 Nationwide Inpatient Sample dataset for International Classification of Diseases, 9(th) Revision code, 81.54, for TKAs. An initial 621,029-patient cohort was narrowed to 516,745 after inclusion of elective TKAs on patients aged between 40 and 95 years. Using generalized linear models, we estimated the effect of comorbidities on resource use (using cost-to-charge conversions to estimate hospital costs) and the LOS controlling for patient and hospital characteristics. Across the 2009 national cohort with TKAs, 12.7% had no comorbidities, whereas 32.6% had three or more. The most common conditions included hypertension (67.8%), diabetes (20.0%), and obesity (19.8%). Mean hospital costs were USD 14,491 (95% confidence interval [CI], 14,455-14,525) and mean hospital LOS was 3.3 days (95% CI, 3.29-3.31) in this data set.
  
  
  RESULTS
  Patients with multiple comorbidities were associated with increased resource use and LOS. Higher marginal costs and LOS were associated with patients who had an inpatient death (USD +8017 [95% CI, 8006-8028], +2.3 [CI, 2.15-2.44] days over baseline), patients with recent weight loss (USD +4587 [95% CI, 4581-4593], +1.5 [CI, 1.45-1.61) days], minority race (USD +1037 [95% CI, 1035-1038], +0.3 [CI, 0.28-0.33] days), pulmonary-circulatory disorders (USD +3218 [95% CI, 3214-3221], +1.3 [CI, 1.25-1.34] days), and electrolyte disturbances (USD +1313 [95% CI, 1312-1314], +0.6 [CI, 0.57-0.60] days). All p values were < 0.001.
  
  
  CONCLUSIONS
  Multiple patient comorbidities were associated with additive resource use and LOS after TKA. Current reimbursement may not adequately account for these patient characteristics. To avoid potential loss of access to care for sicker patients, payment needs to be adjusted to reflect actual resource use.
  
  
  METHODS
  Level IV, economic and decision analysis. See the Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, University of Iowa Hospitals and Clinics, 200 Hawkins Drive, 01008 JPP, Iowa City, IA, 52242, USA, andrew-pugely@uiowa.edu.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pugely
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Martin
authors.forename: Yubo
authors.initials: Y
authors.lastname: Gao
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Belatti
authors.forename: John J
authors.initials: JJ
authors.lastname: Callaghan
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000191:economics*; D015897:Comorbidity; D005260:Female; D006295:Health Resources / Q000191:economics / Q000706:statistics & numerical data; D017721:Hospital Costs; D006801:Humans; D007349:Insurance, Health, Reimbursement; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D007902:Length of Stay / Q000191:economics*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D018803:Models, Economic; D010043:Outcome and Process Assessment, Health Care / Q000191:economics*; D012307:Risk Factors; D013997:Time Factors; D016896:Treatment Outcome