Tibiales Malalignment bei Mobile-bearing-Prothesen

Abstract

Total knee replacement requires exact implantation in order to avoid long-term failure. Longitudinal in vivo studies of malaligned prostheses are problematic for ethical reasons. To assess the critical angle of tibial (varus/valgus) malalignment of knee prostheses in vitro, a simulator investigation was performed. Mobile-bearing prostheses were implanted in a simulator with 1-3 degrees valgus and varus malalignment as well as in a neutral position. More extreme malalignment caused unacceptable forces in the simulator. After each 500,000 cycles (ca. 0.5 years of walking) the replicas of the polyethylene inlay were examined and the extent of the tribocontact areas was measured until 1,500,000 total cycles. Finally the original polyethylene was examined with a scanning electron microscope. The polyethylene showed only abrasive wear without any fatigue effect. Tribocontact areas of 900-1500 mm(2) were observed under malalignment of mobile-bearing prostheses according to the manufacturer's specifications. With 1-3 degrees of malalignment, tribocontact areas were located at atypical polyethylene zones, but still showed abrasive wear only. Increasing malalignment due to a lift off of the femoral part of the prostheses with a strong torsional strength of the polyethylene made more extreme simulation impossible. Malalignment of 3 degrees could be suggested as maximum in vivo tolerability; perfect alignment with ideal implantation should be the goal. Soft tissue was given less consideration in this simulator study.

Encouraging treatment algorithm for computer-assisted navigated total knee arthroplasty (TKA)

“…Computer-assisted navigated total knee arthroplasty (TKA) was shown to result in higher implantation accuracy compared to the conventional TKA technique.1,3,4,6-10 This was in contrast to the findings of several other studies.11-13 However, there is still no consensus, whether an exact reconstructed mechanical lower limb axis is essential to end up in a higher long-term survival rate with an improved clinical outcome. [14][15][16][17][18] To the best of our knowledge, there are only few recent published articles available reporting on clinical outcome data and survival rate after a postoperative follow-up rate of 5-10 years or more.5,19-22 Kim 25) we introduced a treatment algorithm for navigated computerassisted TKA in our institution. To the best of our knowledge, this is one of the first studies published so far reporting on radiological outcome data where navigated TKA was preserved for special indications as described above.…”

CT-basierte und CT-freie Navigation in der Knieendoprothetik - eine prospektive Vergleichsstudie unter klinischem und radiologischem Aspekt

“…In einer Simulatorstudie wurde gezeigt, dass Fehlimplantationen der Tibiakomponente der NexGen ® MBK-Prothese bis zu maximal 38 Varusoder Valgusabweichung vom Implantat kompensiert werden können. Eine höhergradige Fehlimplantation führt zu einer Extremfehlbelastung mit den Folgen des vermehrten Abriebs [2]. Jeffery et al [5] berichten von einer aseptischen Lockerungsrate von 24 % bei Abweichung der mechanischen Beinachse von mehr als 38.…”

A rare case of bilateral large osteolysis following cemented and cementless total knee arthroplasties

“…One possible mechanism contributing to the generation of PE debris is malalignment, leading to excessive eccentric wear (Insall and Dethmers 1982, Rorabeck 1995). In an in vitro simulator study, malalignment of more than 3° (varus or valgus) led to higher PE wear in TKA, which is a major reason for loosening (Loer and Plitz 2003). In our case, the alignment of both TKAs was only 1°, suggesting that axial malalignment was not a major contributory factor to the wear.…”