# Inflammatory-induced swelling after total knee arthroplasty: Obesity and preoperative joint pain as key predictors

## TL;DR

This study finds that obesity and preoperative joint pain are key factors in post-surgery swelling after knee replacement, with implications for identifying high-risk patients.

## Contribution

The study identifies obesity and preoperative joint pain as novel predictors of early postoperative swelling after total knee arthroplasty.

## Key findings

- BMI was a core predictor of lower limb swelling, with a 1-unit increase in BMI corresponding to a 0.18–0.24 cm increase in proximal leg circumference.
- Preoperative joint pain on touch was associated with swelling 10 cm above the patella, while postoperative joint pain at rest was linked to calf swelling.
- Obese patients and those with preoperative joint pain showed elevated inflammatory levels, exacerbating postoperative swelling.

## Abstract

Limited research exists on factors influencing early postoperative swelling after total knee arthroplasty (TKA). This prospective observational cohort study aims to analyze patterns and predictors of early postoperative inflammatory swelling following TKA, informing high-risk screening and interventions.

This study measured 110 TKA patients’ (76.4% female, mean age 69.51 ± 7.46 years) lower limb circumference (10 cm/5 cm above patella, patella, calf, ankle) preoperatively and postoperatively 1–5 days. Variables of interest included body mass index (BMI), preoperative joint pain, postoperative joint and thigh pain, cryotherapy duration, and inflammatory biomarkers.

Swelling peaked proximally at 5 cm above the patella on day 3 (4.16 ± 2.90 cm). Multivariable regression analysis identified BMI as a core predictor of lower limb swelling (P < 0.05), with a 1-unit increase in BMI corresponding to a 0.18–0.24 cm increase in proximal leg circumference. Pain timing was site-specific: swelling 10 cm above the patella was associated with preoperative joint pain on touch (β = 0.184, P = 0.052), calf swelling with postoperative joint pain at rest (β = 0.213, P = 0.022), and ankle swelling with postoperative thigh pain at rest (β = 0.228, P = 0.017). Other factors and inflammatory markers were not significantly associated with swelling (P > 0.05). However, preoperative joint pain during activity correlated with higher white blood cell (WBC) counts (P = 0.012), and postoperative thigh resting pain with elevated C-reactive protein (CRP) levels (P = 0.035).

Early postoperative proximal swelling following TKA warrants attention, as chronic pro-inflammatory states in obese patients and the progression of knee osteoarthritis lead to elevated inflammatory levels, exacerbating postoperative swelling. Focus should be placed on high-risk patients with obesity and preoperative joint pain on touch.

ChiCTR2500098167.

Video Abstract

Video Abstract

The online version contains supplementary material available at 10.1186/s42836-025-00344-9.