Effect of knee laxity on in vivo kinematics of meniscal-bearing knee prostheses.
BACKGROUND
This study determined the relationship between the in vivo kinematics and joint laxity of mobile-bearing knees.


METHODS
Ten subjects who were judged clinically successful after a posterior-cruciate-ligament-retaining mobile-bearing total knee arthroplasty were analyzed under dynamic conditions using fluoroscopy, following a quantitative evaluation of coronal and sagittal laxity using Telos and KT-2000 arthrometers under static conditions.


RESULTS
Under static conditions, the anteroposterior laxity averaged 10.3 mm at 30 degrees of flexion, and 8.3 mm at 75 degrees . Abduction and adduction at full extension averaged 3.7 and 4.4 mm, respectively. Under dynamic conditions, 7/10 subjects demonstrated posterior femoral rollback of their lateral condyle moving from full extension to maximum knee flexion, and 8/10 experienced normal axial rotation patterns during deep knee bend activity. Furthermore, 7/10 subjects exhibited screw-home motion. 4/10 subjects experienced greater than 1.0 mm of condylar liftoff.


CONCLUSIONS
We could not predict a consistent relationship between the laxity and kinematics. The activity of the muscles and ligamentous tension under dynamic conditions might have a much greater effect on the kinematics with currently used prosthetic designs than the laxity of ligamentous structures under static conditions.
Ishii
Yoshinori
Y
Ishii Orthopaedic and Rehabilitation Clinic, 1089 Shimo-Oshi, Gyoda, Saitama 361-0037, Japan. ishii@sakitama.or.jp
Noguchi
Hideo
H
Matsuda
Yoshikazu
Y
Takeda
Mitsuhiro
M
Walker
Scott A
SA
Komistek
Richard D
RD
D000368:Aged; D053587:Arthrometry, Articular; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005471:Fluoroscopy; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging / Q000503:physiopathology*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000601:surgery; D007720:Knee Prosthesis; D016059:Range of Motion, Articular / Q000502:physiology; D012399:Rotation