Mobile-bearing insert used with total knee arthroplasty does not rotate on the tibial tray during a squatting activity: a cross-sectional study

• Published in: Journal of orthopaedic surgery and research Vol. 15; no. 1; p. 114
• Main Authors: Hoshi, Kenji, Watanabe, Goro, Kurose, Yasuo, Tanaka, Ryuji, Fujii, Jiro, Gamada, Kazuyoshi
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 20.03.2020; BioMed Central; BMC
• Subjects: Aged; Analysis; Arthroplasty; Arthroplasty (knee); Arthroplasty, Replacement, Knee - instrumentation; Arthroplasty, Replacement, Knee - methods; Camcorders; Cameras; Clinical outcomes; Cohort Studies; Conformity; Cross-Sectional Studies; Female; Humans; Joint replacement surgery; Joint surgery; Kinematics; Knee; Knee joint; Knee Prosthesis; Knee replacement arthroplasty; Male; Medical research; Orthopedic surgery; Orthopedics; Osteoarthritis; Pain; Physical therapists; Physicians; Polyethylene; Prostheses; Prostheses and implants; Prosthesis Design - methods; Prosthetics; Range of Motion, Articular - physiology; Registration; Retrospective Studies; Rheumatoid arthritis; Rotation; Rotational behavior; Studies; Tibia - diagnostic imaging; Tibia - physiology; Total knee arthroplasty; Weight-Bearing - physiology; United States > US; Knee joint; Total knee arthroplasty; Rotation; Kinematics
• ISSN: 1749-799X; 1749-799X
• DOI: 10.1186/s13018-020-1570-6

Total knee arthroplasty (TKA) is commonly performed around the world. Implant designs include fixed-bearing and mobile-bearing. Mobile-bearing design was developed as a rotating platform that allows axial rotation of the insert around the longitudinal axis. This phenomenon may limit full exploitation of the characteristics of the mobile-bearing insert, which may cause wearing and reduce longevity. However, there is limited knowledge on rotational behavior of the polyethylene mobile-bearing insert under weight-bearing conditions. We aimed at determining the rotational motion of each component at full extension and flexed positions during a squatting activity after TKA. This study was a cross-sectional study (level 4) involving patients with severe knee osteoarthritis scheduled to receive TKA. We examined 13 knees of 11 patients after mobile-bearing TKA (NexGen LPS-Flex, Zimmer Inc.) at 10 weeks and 1 year postoperatively. Four identical metallic beads were embedded into the insert. Wide-base squatting was chosen for analyses. Three-dimensional in vivo poses of the prostheses were created using a 3D-to-2D registration technique. During flexion, rotation of the femoral component relative to the insert (FEM/INS) and tibial component (FEM/TIB) as well as insert rotation relative to the tibial component (INS/TIB) were computed. Repeated measure 2-way ANOVA and post hoc test was used. In the fully extended position, FEM/INS was significantly smaller than INS/TIB both at 10 weeks (- 0.3° vs. 6.3°, p = .013) and 1 year (- 0.8° vs. 4.9°, p = .011), respectively. During the squatting activity, rotation motions of FEM/TIB, FEM/INS, INS/TIB were 5.7°, 5.9°, and 1.8° at 10 weeks and 6.3°, 5.5°, and 1.6° at 1 year, respectively. Rotation motion of FEM/INS was significantly greater than that of INS/TIB at both 10 weeks (p < .001) and 1 year (p < .001). The mobile-bearing insert enhances the compatibility of FEM/INS in extension; the amount of INS/TIB rotation is significantly smaller than that of FEM/INS during a squatting activity. This information will inform surgeons to take caution to perform TKA with a fixed insert in which 6.3° of rotational offset would be added to the rotational alignment at FEM/INS at full extension. UMIN-CTR, UMIN000024196. Retrospectively registered on 9 September 2016.