Detailed time course of postoperative swelling after knee arthroplasties

Postoperative swelling is a common clinical issue after knee arthroplasty and may delay functional recovery. Although swelling after total knee arthroplasty (TKA) has been reported, detailed comparisons with unicompartmental knee arthroplasty (UKA) remain scarce. In this prospective study, a total of 39 patients (29 TKA, 10 UKA; mean age 75 ± 8 years) were evaluated. Swelling was assessed using a validated optoelectronic device (Perometer) preoperatively and during six postoperative Phases (Phase2: POD2–4, Phase3: POD5–7, Phase4: POD8–10, Phase5: POD11–13, Phase6: ≥POD14). Non-parametric tests were applied due to the small sample size. Swelling was significantly greater in the operated side after TKA than after UKA at Phase5 ( p = 0.017, Hedges’ g = 0.85) and Phase6 ( p = 0.016, g = 0.61). Compared with baseline, TKA demonstrated significant swelling at Phase2–5 (all p ≤ 0.0007, Cohen’s d = 0.68–1.02), whereas UKA showed no increase at Phase2–5 and even decreased at Phase6 ( p = 0.0117, d = − 1.17). No significant differences were observed between procedures in the non-operated side. TKA therefore induces greater and more prolonged swelling than UKA, particularly within the first two postoperative weeks, and these findings highlight the importance of procedure-specific rehabilitation strategies.