Abstract
Intraoperative patellar position (eversion, lateralization, or in situ) influences
the ligamentous balancing in knee flexion and thereby the correct positioning of the
femoral component during total knee arthroplasty. The correct ligament balancing is
crucial when, as in our experience, prostheses with medial pivot design are used.
It was shown that the flexion gap in the normal knee is not rectangular and that the
lateral compartment is significantly slacker than the medial. Therefore, to obtain
a correct kinematics of a medial pivot anatomical prosthesis, it is essential to recreate
an anatomical flexion gap slacker in the lateral compartment. We conducted a prospective
study on a consecutive series of 87 total knee prostheses. The objective of this study
is to evaluate the femoral external rotation angle in each patient with everted patella
as well as with pure subluxated patella. The purpose of this study is to offer guidance
about the optimal femoral rotation angle to achieve best outcomes of a knee replacement.
The evaluation was done using an instrument developed by Medacta International (Switzerland)
with our direct collaboration (Tensor, Medacta, Switzerland) and standardizing the
basic conditions of each patient (knee 90 degrees flexed, medial transquadricipital
surgical access, lateral displacement of the patella, tourniquet inflated at 250 mm
Hg, spinal anesthesia). Each group was subdivided into subgroups according to gender,
preoperative varus or valgus deformity, and patellar height. Our study advises against
evaluating the flexion gap with everted patella due to high risk of underestimation
of the lateral compartment laxity (differences up to + 3 degrees with pure subluxated
patella compared with everted patella).
Keywords
patellar eversion - patellar lateralization - total knee arthroplasty - medial knee
stability - lateral knee laxity - knee gap balancing
