Investigating the prevalence and influential factors of ankle pain following total knee arthroplasty in patients with varus and valgus knee deformities

Background: The postoperative time-dependent changes in knee alignment and the subsequent adaptive changes in the ankle and the mechanism of postoperative foot pain after total knee arthroplasty have not been well established. The aim of this study was to assess the imaging alterations in the ankle, subtalar, and knee joints following total knee arthroplasty (TKA)for correcting varus and valgus deformities, as well as to observe the incidence of post-TKA ankle pain and analyze its influencing factors. Method: This retrospective cohort study included 67 patients with varus and valgus knee osteoarthritis who underwent total knee arthroplasty . The patients were categorized into two groups based on the alignment of their knee joint, namely the varus group and the valgus group. Subsequently, they were further divided into a foot and ankle pain group or a foot and ankle non-pain group depending on the presence or absence of postoperative foot pain. Radiological assessments of the lower limbs, ankle joints, and hindfoot were conducted before surgery as well as at 3 months post-surgery, along with clinical evaluations of the ankle joint. Each data was compared between patients with and without foot pain. Result: When the lower limb was aligned to the neutral position by TKA, the distal tibia and talus exhibited a more horizontally oriented alignment relative to the ground compared to the preoperative alignment. Patients with knee varus demonstrated an evaginate transition towards varus, which was accompanied by an increase in ankle ectropion. In contrast, patients with genu valgus maintained their hind foot's varus position while experiencing an increased ankle varus. Due to the limited range of motion in the ankle and subtalar joints, acute correction of the knee following total knee arthroplasty cannot be compensated for by these joints. In comparison to the painless group, individuals experiencing foot discomfort maintained a preoperative force line in the ankle and subtalar joint while also undergoing a greater degree of correction in the contrapuntal line of the knee joint. Conclusion: About one fifth of total knee arthroplasty (TKA) patients experience postoperative foot pain. Despite obtaining an appropriate coronal alignment of the knee joint after surgery, these patients may still experience uneven foot force due to inadequate compensation of the ankle and subtalar joints. Surgeons should consider potential ankle and hindfoot compensation disorders and postoperative ankle pain when planning and performing TKA.