IN VIVO FLUOROSCOPIC STUDY OF THE KINEMATICS OF TOTAL KNEE ARTHROPLASTY WITH A MOBILE PLATEAU

Abstract

Purpose: In vivo analysis of the kinematics of total knee arthroplasty (TKA) is of particular interest because it i) enables measurements of mobile plateau displacements by degree of freedom (rotation, anteroposterior translation, mediolateral motion); ii) provides crucial information concerning polyethylene wear and loosening.

Material and methods: Twenty patients with a mobile plateau TKA with posterior stabilisation were selected on the basis of three inclusion criteria: follow-up greater than six months, unilateral prosthesis, satisfactory clinical result (HKS = 80). The lateral view on the image amplifier was recorded using a digital recorder while the patient produced flexion-extension movements of the loaded knee in the sitting position. We determined the position of the mobile plateau relative to the tibial base and to the femoral piece throughout the flexion cycle using two radio-opaque markers included in the mobile plateau.

Results: Rotation of the mobile plateau-tibial base interface was observed for all 20 TKA. There was an external rotation from flexion to extension of 3° to 16° in all cases. there was also an anteroposterior translation for 18/20 TKA. For ten TKA this was an anterior translation from flexion to extension. For eight TKA, it was a posterior translation of the mobile plateau. The movement was minimal (mean 2 mm) in all cases.

Discussion: We compared these findings with data in the literature obtained with the same fluoroscopic method. The behaviour observed was intermediary to that for two versions of a reference TKA with a mobile plateau (two mobile menisci, rotating platform).

Conclusion: We demonstrated rotation and anteroposterior translation movements of the mobile plateau total knee arthroplasty studied. The mobile plateau was in a “floating” situation in 18/20 cases. This is theoretically favourable to the transmission of stress forces. An in vitro study using stress gauges to measure stress at interfaces should provide complementary information to this fluoroscopic study.