Comparisons of kinematics during stair motion in total knee arthroplasty: Single-radius versus J-curved designs

Abstract

Background: Patients who undergo TKA continue to report difficulty in ascending and descending stairs. However, it is unknown how kinematic pattern TKA knees demonstrate during stair ascending and descending. The purpose of the present study was (1) to determine how kinematics TKA knees demonstrate during stair ascending and descending; (2) to investigate whether TKA kinematics during stair ambulation are different among designs of implants as well as during squatting.Methods: We analyzed twenty two knees (19 patients, all female) that implanted with single-radius PS TKA which was the Triathlon posterior stabilized knee prosthesis or the J-curved PS TKA which was the Legacy flex posterior stabilized knee prosthesis. Each patient performed stair ascending and descending at patient’s comfortable pace. We evaluated the kinematics of stair ascending and descending using 2-dimensional to 3-dimensional registration technique.Results: Anteroposterior translation was significantly less in single-radius PS TKA compared to J-curved PS TKA during stair ascending and descending. At foot strike, post-cam engagement was observed in all 11 knees implanted with single-radius PS TKA and in three of 11 knees with J-curved PS TKA during stair ascending.Conclusions: Single-radius design of the femoral component, constrained articulation and less posterior slope might lead to less anteroposterior translation of the femur during stair ascending and descending. Additionally, it is also associated with the stability that the post cam contact prevented the femur from moving anteroposterior before and after foot strike during stair ascending and escending. It should be necessary that the post cam mechanism is designed not only for inducing rollback motion, but also for controlling anteroposterior translation in mid-flexion range