title: Kinematics of three variations of the Freeman-Samuelson total knee prosthesis.
abstract: The effect of changes in the articulating surfaces on the kinematics of the Freeman-Samuelson total knee replacement was evaluated. Twenty-two patients (22 knees) (median age, 69 years) were randomized to a standard design with a fixed polyethylene bearing, a design with a mobile bearing, or a new design with a spherical medial femoral condyle with a fixed bearing. The patients were studied with radiostereometry and film-exchangers at 0 degrees nonweightbearing and during active weightbearing extension from 45 degrees to 15 degrees. The center of the tibial tray with a mobile-bearing prosthesis occupied a more anterior position than observed in the designs with a fixed bearing. The medial femoral condyle center had a more posterior position in the standard design than in the design with a spherical medial condyle. From a distally displaced position at 45 degrees, the medial condylar center displaced a mean of 1.8 mm proximally during extension in the standard design and had a constant position in the meniscal design. In the spherical design the medial condyle was displaced proximally at 45 degrees and displaced a mean of 1.6 mm distally during extension. The reduced anteroposterior and proximodistal translations in the meniscal design are compatible with improved congruency between the components. The design with a spherical medial condyle stabilized anteroposterior motions, but showed more pronounced proximodistal displacement medially than did the other two designs.
authors.affiliation: Department of Orthopaedics, Göteborg University, Sahlgrenska University Hospital, Göteborg, Sweden. tuuli.saari@swipnet.se
authors.forename: Tuuli
authors.initials: T
authors.lastname: Saari
authors.forename: Johan
authors.initials: J
authors.lastname: Uvehammer
authors.forename: Lars V
authors.initials: LV
authors.lastname: Carlsson
authors.forename: Peter
authors.initials: P
authors.lastname: Herberts
authors.forename: Lars
authors.initials: L
authors.lastname: Regnér
authors.forename: Johan
authors.initials: J
authors.lastname: Kärrholm
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D012399:Rotation