Factors associated with early swelling after total knee arthroplasty and poor venous return : the impact of quadriceps strength, activity and preoperative anticoagulation

To investigate the factors associated with early lower limb swelling after total knee arthroplasty (TKA), with a focus on factors potentially related to venous return impairment. A prospective observational study was conducted in 110 patients undergoing primary unilateral TKA. Baseline data, including demographic characteristics, medical history, Caprini score, and quadriceps strength, were collected. Circumferences were measured preoperatively and postoperatively (days 1–5) at five sites: 10 cm above the patella, 5 cm above the patella, the patella, the calf, and the ankle. Postoperative activities (e.g., ankle pump frequency, walking duration) were recorded daily. The degree of swelling was treated as a continuous variable (postoperative–preoperative difference). Influencing factors were analyzed using hierarchical multiple linear regression. The degree of swelling exhibited anatomical heterogeneity, with higher median swelling at proximal sites (10 cm above patella: 3.00 cm; 5 cm above patella: 3.60 cm) compared with distal sites (calf: 1.75 cm; ankle: 0.10 cm). In multivariable analysis, preoperative quadriceps strength grade 5 was associated with greater swelling at the 5 cm above patella site (B = 1.270, P = 0.039) and calf (B = 1.368, P = 0.047). Further analysis of strength change patterns revealed that patients with strong preoperative strength who developed severe postoperative weakness exhibited the highest swelling, suggesting that severe postoperative loss of muscle function, rather than preoperative strength itself, contributes to increased swelling. Preoperative anticoagulant use was associated with less swelling at the 10 cm above patella (B = − 2.522, P = 0.030), with similar trends at the patella (P = 0.097) and 5 cm above patella (P = 0.070). Age was associated with greater swelling at the 10 cm above patella (B = 0.124, P = 0.024). Walking time showed a trend toward greater calf swelling (B = 0.073, P = 0.050), while standing time showed a trend toward less calf swelling (B = − 0.074, P = 0.059). Early post-TKA swelling involves multiple mechanisms, and factors related to venous return exhibit distinct anatomical specificity. Targeted management strategies should prioritize postoperative activation of the quadriceps muscle pump, regulated activity (e.g., limiting walking duration, incorporating standing rests), and consideration of preoperative anticoagulation status to help alleviate site-specific swelling. Chinese Clinical Trial Registry, Registration Number: ChiCTR2500098167, Registration date: 04 March 2025.