R. Nagamine et al., PATELLAR TRACKING AFTER TOTAL KNEE ARTHROPLASTY - THE EFFECT OF TIBIAL TRAY MALROTATION AND ARTICULAR SURFACE CONFIGURATION, Clinical orthopaedics and related research, (304), 1994, pp. 263-271
The effect of total knee arthroplasty (TKA) with neutrally aligned and
malrotated tibial trays was studied in five fresh anatomic specimen k
nees. Patellar shift, tilt, and rotation, and the rotational position
of the tibia were measured in normal knees and after TKA with the Orth
oloc Modular knee system. Both semiconstrained and unconstrained artic
ular surfaces were assessed in the neutral position and at anatomic, 1
5 degrees internal, and 15 degrees external rotation of the tibial tra
y. After TKA, the patellae shifted slightly medially in the early phas
e of knee flexion because the anterior lateral flange of the femoral c
omponent was longer than the lateral trochlea of the femur and because
the tibia rotated internally. The raised lateral flange on the femora
l component tilted the patella medially at full extension after TKA. T
he semiconstrained tray allowed minimal tibial rotation because of its
articular configuration. As much as 15 degrees malrotation of the unc
onstrained tibial tray did not affect patellar tracking. The semiconst
rained tibial tray in the neutral position had almost the same patella
r tracking as the unconstrained tray, but at 15 degrees external rotat
ion, the semiconstrained tray internally rotated the tibia, leading to
medial shift of the patella. Although 15 degrees internal rotation ca
used external rotation of the tibia, the patella did not shift as much
laterally, despite the increase in the Q angle.