Preoperative factors associated with quadriceps strength 1 year after total knee arthroplasty: a prospective longitudinal study

Background Quadriceps strength is highly related to physical function following total knee arthroplasty (TKA). Preoperative factors associated with long-term postoperative strength remain insufficiently understood. The aim of this exploratory study was to investigate preoperative factors associated with normalized quadriceps strength (NQS), changes in NQS and limb symmetry index (LSI) 1 year after TKA in patients with uncomplicated recovery. Methods A prospective longitudinal study was conducted. Measurements took place at three primary care rehabilitation facilities in Region Västra Götaland, Sweden. The final analysis included 39 participants aged 65 years or older who underwent elective fast-track primary TKA due to knee osteoarthritis and had an uncomplicated recovery. Preoperative factors associated with NQS in the operated limb after 1 year ( n = 39), changes in NQS from preoperative testing to 1 year after TKA ( n = 39), and LSI ( n = 35) were analyzed in three separate exploratory multiple linear regression models. Preoperative factors included age, sex, NQS, the 6-minute walk test (6MWT), and the LSI. Results Preoperative NQS ( B = 0.72, 95% CI: 0.40 to 1.0, p < 0.001) and LSI ( B = − 0.17, 95% CI: − 0.29 to − 0.037, p = 0.013) were significantly associated with NQS 1 year after TKA. LSI was the only preoperative factor significantly associated with changes in NQS ( B = − 0.19, 95% CI: − 0.32 to − 0.059, p = 0.006) and LSI 1 year after TKA ( B = 0.41, 95% CI: 0.15 to 0.68, p = 0.004). Conclusions In this selected and relatively small sample, greater normalized quadriceps strength in the operated limb and higher LSI 1 year after TKA appeared to be primarily associated with higher preoperative normalized quadriceps strength in the operated limb and higher preoperative LSI, respectively, whereas strength gains appeared to be associated with lower preoperative LSI. The findings should be considered exploratory and primarily applicable to older adults with uncomplicated recovery after TKA. Confirmation in larger studies is warranted. Trial registration Retrospectively registered February 9, 2022 ( http://clinicaltrials.gov , ID: NCT05248815).