The influence of sex and pre-operative obesity on biomechanics two years after total knee arthroplasty: A longitudinal cohort study

Background: Sex and obesity may influence knee biomechanics associated with poor outcomes following primary total knee arthroplasty (TKA) however their long-term impact has not been investigated. Research question: Does sex and/or pre-operative obesity influence change in gait biomechanics from pre-TKA to two-years after TKA, and do knee biomechanics return to normal two-years after TKA? Methods: In this longitudinal study, gait analysis was performed on 78 patients undergoing TKA for knee osteoarthritis prior to surgery (baseline), and on 66 (85 %) of these who returned at the two year follow-up. Gait biomechanics were also collected on a reference sample of 40 asymptomatic participants. Knee variables were analyzed according to time (pre- and post-TKA), sex (men and women), pre-operative obesity (obese vs non-obese), and group (TKA vs reference). Mixed linear regression models were used to examine the effects of TKA, obesity status, gender and all interactions. Results: There were two-year reductions in peak knee frontal plane angle (mean difference −7.21°; 95% confidence intervals −9.37 to −5.05), peak knee adduction moment (KAM) (-17.64Nm; −23.04 to −12.24) and KAM impulse (-9.40Nm.s; −12.04 to −6.77) in males. These and other variables were unchanged in women. At two years, men exhibited a greater varus-valgus thrust excursion (4.9°; 2.7–7.2), and a lower peak knee frontal plane angle (−4.4°; −7.1 to −1.7) and peak KAM (−13.1Nm; −20.9 to −5.4), compared to the reference sample. Biomechanics at two years did not differ between pre-operative obesity subgroups, or between female TKA patients and the reference sample. Significance: Changes in gait biomechanics two years after TKA are influenced by sex but not obesity. Men but not women showed altered knee biomechanics two years following TKR and compared to a reference sample. It is unknown whether these altered biomechanics in men impact longer term clinical outcomes and satisfaction following surgery.