Abstract
Condylar liftoff can undoubtedly occur with total knee replacements (TKR); it occurs in the surgeon’s hands and has been shown to occur in vivo. However, the reported incidence of condylar liftoff and the implications for articular surface damage require further scrutiny. A three-part argument is made that the incidence of condylar liftoff has been overstated, and there is little direct evidence that condylar liftoff is a significant factor in the wear performance of coronally flat-on-flat TKR’s. First, an analysis of fluoroscopic measurement errors based on the uncertainty in measuring varus/valgus angles (the parameter used to determine liftoff) reveals that the standard error for liftoff measurements is 1.2mm, nearly identical to the mean liftoff value in recent published reports. Second, because most TKR’s have some anterior/posterior curvature of the tibial insert, any axial rotation of the knee induces a varus/valgus angulation that can be interpreted as liftoff, even though the condyles remain in contact. Third, condylar liftouff has been used to justify the need for coronally round-on-round geometries, yet an analysis of 100 unselected retrieved tibial inserts from three coronally flat designs reveals no difference in wear type, magnitude, severity, depth, or symmetry between the medial and lateral aspects of the tibial inserts. Although condylar liftoff certainly can occur in vivo, an argument can be made that the incidence of liftoff in experimental studies has been overstated, and that there is little evidence from retrievals that contemporary coronally flat-on-flat TKR’s are uniquely susceptible to articular damage from condylar liftoff.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
