Cutoff values of knee extensor strength for stair ascent and descent after bicruciate-stabilized total knee arthroplasty.

Abstract

Patient satisfaction after total knee arthroplasty (TKA) is strongly influenced by the ability to ascend and descend stairs. Although knee extensor strength is considered essential for stair negotiation, the specific functional threshold values required for stair ascent and descent after bicruciate-stabilized (BCS) TKA remain unclear. This study aimed to identify functional factors associated with stair ascent and descent after BCS TKA and to determine cutoff values for knee extensor strength. This prospective cohort study included 94 patients (117 knees) who underwent unilateral BCS TKA between October 2017 and January 2023. Stair ascent and descent abilities were evaluated at 1 year postoperatively using a three-step staircase. Patients were classified into a normal ability group or a reduced ability group based on their stair negotiation pattern. Knee extensor strength, knee range of motion, and demographic variables were assessed. Multiple logistic regression analyses were performed separately for stair ascent and stair descent. Cutoff values were determined using receiver-operating characteristic (ROC) curve analysis. For stair ascent, knee extensor strength, age, and sex were independently associated with stair ascent ability. The cutoff value of knee extensor strength required for normal stair ascent was 1.04 Nm/kg (area under the curve [AUC] = 0.76). For stair descent, knee extensor strength was the only independent factor associated with performance. The cutoff value required for normal stair descent was 1.10 Nm/kg (AUC = 0.86). Successful stair ascent and descent after BCS TKA require sufficient knee extensor strength. The identified cutoff values may serve as clinically useful reference targets for postoperative rehabilitation aimed at improving stair negotiation ability.