# Hypothyroidism is associated with higher healthcare utilisation and higher need for blood transfusion after primary total knee arthroplasty (TKA) in patients with osteoarthritis: A National Inpatient Sample analysis

## TL;DR

This study found that patients with hypothyroidism who undergo knee replacement surgery have longer hospital stays, higher costs, and more blood transfusions compared to those without hypothyroidism.

## Contribution

The study is the first to show a link between hypothyroidism and increased healthcare use and blood transfusion needs after knee replacement surgery in osteoarthritis patients.

## Key findings

- Hypothyroidism was associated with longer hospital stays after knee replacement surgery.
- Patients with hypothyroidism had higher hospital charges and more blood transfusions.
- Non-routine discharge was more common in patients with hypothyroidism.

## Abstract

To examine the association of hypothyroidism with primary total knee arthroplasty (TKA) outcomes in adults with primary underlying diagnosis of osteoarthritis (OA).

We identified a prospective cohort of patients in the 2016–2020 national inpatient sample (NIS) that received primary TKA with an underlying diagnosis of OA, identified using International Classification of Diseases, Tenth Revision, Common Modification (ICD‐10‐CM) and Procedure Coding System (ICD‐10‐PCS) codes in the primary procedure and diagnosis positions, respectively. We performed multivariable‐adjusted regression analyses for healthcare utilisation (length of hospital stay, hospital charges and discharge destination) and clinical outcomes (blood transfusion; prosthetic fracture, dislocation or infection; inpatient mortality), adjusted for age, sex, race, income, comorbidity, insurance payer, elective surgery, hospital bed size, census region and teaching status.

Between 2016 and 2020, we identified 2,922,075 adults who underwent primary TKA with an underlying diagnosis of OA, of whom 447,875 (16%) had hypothyroidism. For the primary TKA OA cohort, the average age was 66.8 years, 61.4% were female, and 81.3% were White. In the primary TKA OA cohort, hypothyroidism was associated with significantly higher multivariable adjusted odds ratio (aOR) for length of hospital stay above the median, 1.06 (95% confidence interval [CI]: 1.05–1.08, p < 0.001); total hospital charges above the median, aOR 1.07 (95% CI: 1.04–1.09, p < 0.001); non‐routine discharge, aOR 1.07 (95% CI: 1.05–1.09, p < 0.001); and the need for blood transfusion, aOR 1.15 (95% CI: 1.08–1.23, p < 0.001).

Hypothyroidism was associated with increased healthcare utilisation and need for blood transfusion after primary TKA for OA. Future studies should investigate whether preoperative optimisation of hypothyroidism can positively improve primary TKA outcomes.

Level II, prospective cohort study.