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In vivo kinematics of total knee arthroplasty: Flat compared with concave tibial joint surface
Author(s) -
Uvehammer J.,
Kärrholm J.,
Brandsson S.,
Herberts P.,
Carlsson L.,
Karlsson J.,
Regnér L.
Publication year - 2000
Publication title -
journal of orthopaedic research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.041
H-Index - 155
eISSN - 1554-527X
pISSN - 0736-0266
DOI - 10.1002/jor.1100180603
Subject(s) - medicine , knee joint , orthodontics , kinematics , anatomy , anterior cruciate ligament , surgery , physics , classical mechanics
Abstract This study evaluated the influence of the geometric configuration of the tibial joint area on the kinematics of the knee. Twenty‐two patients with noninflammatory arthritis and minor preoperative deformity were studied. They each received an AMK total knee replacement with retention of the posterior cruciate ligament. Eleven patients without any knee abnormalities were used as controls. The patients were stratified to either the flat (terminology of the manufacturer: standard) or concave (terminology of the manufacturer: constrained) polyethylene insert (n = 11 in each group). Knee kinematics were assessed 1 year after the operation by having the patient ascend a platform corresponding to an extension of the knee from 50 to 70° of flexion. During this motion, two film‐exchangers simultaneously exposed six to 13 pairs of serial stereoradiographs. The concave geometric configuration of the tibial insert resulted paradoxically in increased anterior‐posterior translations compared with the flat insect but no significant change of rotations and translations in the other directions. Compared with normal knees, the most obvious abnormality was increased anterior‐posterior translations (p < 0.004). At 50° of flexion, the implants with the flat tibial polyethylene insert had displaced 2 times and the concave ones had displaced 2.5 times more posteriorly than the normal knees (p ⩽ 0.001). Less internal tibial rotation was also recorded in the flexed positions for both types of inserts compared with the normal knees (p < 0.02). Four knees in four patients, who reported symptoms of instability and abnormal knee function, showed significantly increased proximal displacement of the center of the tibial plateau in the flexed position. The findings suggest that current prosthetic designs and surgical technique do not restore normal knee kinematics and indicate that design improvements should rely on in vivo kinematic studies.