Medial-pivot total knee arthroplasty is associated with reduced perceived difficulty during stair descent than conventional designs: A propensity-matched cohort study.

BACKGROUND

Implant design in total knee arthroplasty (TKA) may influence knee stability and muscle demand during stair descent. However, comparative clinical data remain limited. This study compared postoperative stair-descent ability between medial-pivot (MP) TKA and conventional cruciate-retaining (CR) and posterior-stabilized (PS) TKA.

METHODS

Female patients who underwent unilateral MP (EVOLUTION, MicroPort Orthopedics) or conventional CR/PS TKA (ATTUNE, DePuy Synthes) were retrospectively reviewed and propensity score-matched (1:1) for age, body mass index, and preoperative handgrip strength. At 1 year postoperatively, bilateral knee range of motion (ROM) and isometric quadriceps strength (normalized to body weight) were measured. Stair descent over three 20-cm steps was evaluated for gait pattern (step-over-step or step-to-step) and perceived difficulty.

RESULTS

A total of 164 patients were included (82 MP and 82 conventional TKA). Postoperative ROM in both knees was comparable between groups. Significantly fewer patients in the MP group reported difficulty during stair descent than in the conventional group (27% vs. 45%, p = 0.015). The proportion of patients who used a step-over-step pattern was similar between groups (82% vs. 71%, p = 0.12). In the conventional group, patients who descended using a step-over-step pattern demonstrated significantly greater preoperative handgrip strength and higher postoperative quadriceps strength than those who descended using a step-to-step pattern; however, no such differences were observed in the MP group. Among patients using the step-over-step pattern, the quadriceps strength of the operated limb was significantly lower in the MP group than in the conventional group (0.345 vs. 0.385 kgf/kg; p = 0.04).

CONCLUSION

MP TKA was associated with less difficulty during stair descent than conventional CR/PS TKA. Although the frequencies of step-over-step descent were similar, MP TKA enabled effective stair descent despite lower quadriceps strength, suggesting reduced muscular demand during weight-bearing flexion.