[Mobility of a polyethylene tibial insert in a mobile total knee prosthesis].
OBJECTIVE
We have studied the mobility of a mobile tibial implant in total knee arthroplasty (TKA) by a radiographical evaluation.


METHODS
We analyzed mobility of the polyethylene tibial insert of 15 "G2S" TKA implanted for one year or more. We established a dynamic radiographical evaluation. We used 3 weight-bearing radiographs: AP in extension and two lateral (one in extension and one at 90 degrees of flexion), two AP with femoral internal and external rotation, 2 strict lateral X-rays in neutral rotation in antero-posterior replacement with a 25 kilograms strength Telos, and 2 AP in varus and valgus with Telos. Wilcoxon's test and Fisher's exact test were used for statistical evaluation.


RESULTS
Our study demonstrated preservation of the polyethylene mobility in tibial TKA implant in all movements: in rotation, in antero-posterior translation with Telos, and even in antero-posterior translation during physiological condition with flexion-extension weight-bearing radiographs. Statistical tests were very significant. We noticed that flexion induced anterior translation of tibial polyethylene when PCL was preserved.


CONCLUSIONS
This study answered to our question whether mobility of TKA tibial implant persists after implantation. This mobility should reduce loosening forces to the tibia and stress in the polyethylene component. Now we have to determine the amplitude of mobility required to reach this objective.
D019645:Arthroplasty, Replacement, Knee; D001672:Biocompatible Materials; D004867:Equipment Design; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging; D007720:Knee Prosthesis; D009068:Movement / Q000502:physiology*; D011095:Polyethylenes; D011474:Prosthesis Design; D011859:Radiography; D012399:Rotation; D013977:Tibia / Q000000981:diagnostic imaging / Q000601:surgery*