Introduction Stair ascent and descent are physically demanding tasks requiring higher functional ability of the lower extremity muscles and joint range of motion than level walking, and are associated with patient satisfaction after total knee arthroplasty (TKA). This study aimed to investigate stair ascent and descent ability after cruciate-retaining (CR)-TKA using the patient-reported outcomes, and to examine the role of knee sagittal stability and handgrip strength in postoperative stair ascent and descent ability. Materials and methods This study included 84 female patients who underwent primary unilateral CR-TKA for knee osteoarthritis at our institute between April 2015 and February 2019. Patients were classified according to ascending and descending stair difficulty using the New Knee Society Score into those with (group D) and those without difficulty ascending and descending stairs (group A). The two groups were compared for age, height, weight, body mass index, postoperative grip strength, pre-operative and postoperative knee range of motion, anterior and posterior tibial drawer on stress radiography, and the New Knee Society Score (KSS). Result Group D and A consisted of 48 and 36 patients, respectively. The mean follow-up period was 2.9 years (range 1-5 years). Group D was significantly older (74.1 vs. 70.0 years old, p = 0.01) and shorter (148.6 vs. 153.3 cm, p = 0.017) than group A. The two groups demonstrated no significant differences in the range of motion preoperatively and postoperatively and in the amount of anterior tibial drawer at 20 degrees, anterior and posterior drawer at 90 degrees, and total anterior-posterior movement at 90 degrees. Postoperative handgrip strength (19.6 vs. 24.1, p < 0.01) and New KSS score (107 vs. 137, p < 0.01) were lower in group D than in group A. Conclusions Handgrip strength was associated with stair ascent and descent ability and postoperative activity in the patient-reported outcomes, rather than CR-TKA knee sagittal stability.
