IN-VIVO ANALYSIS OF KNEE KINEMATICS - A C OMPARISON OF 4 TYPES OF TOTAL KNEE PROSTHESIS

Purpose of the study The goal of the study was to assess in vivo kinem atics for four designs of knee prosthesis during level walking stair c limbing and non weight-bearing flexion-extension. Patient and methods 19 patients with unilateral total knee arthroplasty (TKA) were include d [5 bicruciate sparing prosthesis (BI), 5 posterior cruciate sparing prosthesis with fiat tibial polyethylene (PP) 5 posterior cruciate spa ring prosthesis with congruent tibial polyethylene (PC), 4 postero sta bilised (PS)]. Theses 19 patients had no prosthesis nor pathological s ituation in any other joint of the lower limbs. Each of these 19 prost hesis had an HSS score greater than 80 and no radiographic signs of lo osening. Magnitudes of the knee rotations (flexion-extension axial rot ation valgus-varus) were evaluated with a 6 degrees freedom of motion electromagnetic-goniometer during level walking, stair climbing acid n on weight-bearing flexion-extension. The magnitudes of the three rotat ions were recorded for the 19 prosthetic knees and for the 19 controla teral non prosthetic knees of the patients. Reproductibility of the me thod was also evaluated on 12 healthy subjects by comparison of magnit udes observed during two different recordings. Results Reproducibility was excellent for magnitudes of flexion (r = 0.95/p = 0.0001) and axi al rotation (r = 0.55/p = 0.002) but less satisfactory for valgus-varu s movements (r 0.46/p = 0.005). The magnitudes of the three rotations were inferior for TKA in comparison with healthy knees for and activit ies, By comparison of the 19 prosthetic and non prosthetic knees we re corded smaller magnitudes of axial rotation during swing phase for lev el and stair climbing and during non weight-bearing flexion extension movements. Between the four kind of prosthesis we observed-greater mag nitudes of flexion for BI and PC prosthesis during stair climbing (p < 0.05) and greater magnitudes of flexion for BI PC and PS prosthesis d uring stair descending (p < 0.05). PC prosthesis instead of a congruen t polyethylene tibial plateau had greater magnitudes of axial rotation than non constrained BI prosthesis during stair climbing (p = 0.009). In spite of a high femoro-tibial congruency we recorded axial rotatio n In PS prosthesis during each activities. Discussion and Conclusion O ur method evaluating in vivo knee kinematics was reproducible. These f our knee prosthetic designs in spite of a good functional results were unable to reproduce magnitudes of movements recorded in healthy subje cts. The small number of prosthesis included in the study prompt us to consider as no definitive the diferences observed between the 4 desig ns, Anyway the influence of design on kinematics should be considered as relative since we recorded axial rotation for all four cruciate sub stituting prostheses although they had high femoro-tibial congruency. Influence of femoro-tibial congruency and cruciate ligament sparing co uld be assessed in vivo by means of this reproducible method on a larg er population.