-Original-

In Vivo Postoperative Motion of Fixed and Mobile Medial Pivot Knees Under Weight-Bearing Conditions after Cruciate-Sacrificing Total Knee Arthroplasty

Toru Yoshioka¹, Nobukazu Okimoto^1,2, Mikiya Sawa¹, Kei Asano¹, Kenji Obayashi¹, Makoto Kawasaki³ and Tokifumi Majima⁴

¹Department of Orthopaedic Surgery, Shimura Hospital, Hiroshima, Japan
²Okimoto Clinic, Hiroshima, Japan
³Department of Orthopaedic Surgery, University of Occupational and Environmental Health, Fukuoka, Japan
⁴Department of Orthopaedic Surgery, Nippon Medical School, Tokyo, Japan

Background: In vivo three-dimensional (3D) motion under weight-bearing conditions was analyzed postoperatively in medial pivot cruciate-substituting (CS) knee systems with fixed and mobile inserts.
Methods: Tibiofemoral knee kinematics during squatting were captured with X-ray fluoroscopy for 4 patients in each cohort. The 3D motion of implants was analyzed with KneeMotion motion analysis software (LEXI Corporation; Tokyo, Japan). In addition, anterior-posterior (AP) movement of the distal-most points and the angle of axial rotation of the femoral component on the tibial component were assessed in both cohorts.
Results: Mean AP movement of the femoral component on the tibial component was 3.8±0.5 mm on the medial side and 9.5±0.5 mm on the lateral side in the cohort with fixed prostheses and 5.9±2.1 mm on the medial side and 10.0±2.5 mm on the lateral side in the cohort with mobile prostheses. The mean angle of axial rotation of the femoral component on the tibial component was 14.4±1.1 degrees and 8.2±2.7 degrees of external rotation for fixed knees and mobile knees, respectively.
Conclusions: Postoperative motion analysis confirmed that fixed and mobile CS implants, which have a similar design, guided medial pivot motion under weight-bearing conditions. However, motion differed between these implant types after mid-flexion: bicondylar rollback after medial pivot motion was noted in the mobile cohort.

J Nippon Med Sch 2023; 90: 103-110

Keywords
total knee arthroplasty, cruciate-substituting implant, medial pivot motion, motion analysis

Correspondence to
Toru Yoshioka, Department of Orthopaedic Surgery, Shimura Hospital, 3-13 Funairimachi, Naka-ku, Hiroshima, Hiroshima 731-0841, Japan
t-yossy@rc4.so-net.ne.jp

Received, April 28, 2022
Accepted, October 19, 2022