Static Bilateral Plantar Load Sharing One Month After Total Knee Arthroplasty for Varus Osteoarthritis: A Prospective...

Background and Objectives: Total knee arthroplasty (TKA) reduces coronal malalignment, but whether this correction redistributes load at the foot early after surgery is unknown. We evaluated static plantar load distribution before and one month after TKA and tested whether the magnitude of axial correction predicted the magnitude of load change. Materials and Methods: Sixty-four consecutive patients undergoing unilateral TKA for advanced knee osteoarthritis were enrolled prospectively; 60 completed both assessments. Hip-knee-ankle (HKA) angle, Q angle, and passive extension deficit were recorded preoperatively and at a mean of 30.9 ± 3.3 days postoperatively, together with static pedobarography of both feet in a bilateral stance under an instruction to load both limbs symmetrically. The primary outcome was the relative bilateral load share of the operative foot. Change scores were analyzed with paired tests, two one-sided equivalence tests (TOSTs), correlation, multivariable regression, and a linear mixed model. Results: The HKA angle improved from 10.79 ± 4.24° to 3.31 ± 3.51° of varus (p < 0.001), although residual varus persisted in 47 of 60 patients. Load share of the operative foot did not change significantly (-1.74 percentage points, 95% CI -4.92 to +1.45; p = 0.247), and equivalence was demonstrated within the primary ±5-percentage point margin (TOST p = 0.022) but not within an exploratory ±3-point margin (p = 0.216). In a sensitivity analysis excluding seven patients with comorbidities or previous osteotomy (n = 53), equivalence within ±5 points was not demonstrated (p = 0.094). Regional load share and mean pressure were likewise unchanged. No statistically significant relationship was demonstrated between correction magnitude and the change in load share (r = 0.222, p = 0.088; adjusted β = 0.428 percentage points per degree, 95% CI -0.598 to 1.455; p = 0.407), although the confidence interval was wide. Conclusions: One month after TKA for advanced, predominantly varus osteoarthritis, static bilateral plantar load sharing measured under an instruction to load both limbs symmetrically was equivalent to its preoperative state within ±5 percentage points. This equivalence may in part reflect the standardized instructions rather than the absence of a biological effect. No relationship between the degree of coronal correction and load redistribution was demonstrated. These findings are confined to the first postoperative month and to an instructed symmetrical static stance. Dynamic loading, gait, and later adaptation were not assessed.