Comorbidities in Patients Undergoing Total Knee Arthroplasty: Do They Influence Hospital Costs and Length of Stay?

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.

Questions/purposes: 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.

Conclusion: 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.

Level of Evidence: Level IV, economic and decision analysis. See the Instructions for Authors for a complete description of levels of evidence.