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Patients undergoing total knee arthroplasty are
younger, more active, more informed and
more demanding than ever before. So, perfor-
ming a TKA, it is fundamental to restore
implanted knee anatomy as closely as possible
to those of the normal knee. Since all studies in
literature show a certain alteration of the kine-
matic of the knee after TKA, particularly due
to the sacrifice of the central pivot, bone resec-
tions play a very fundamental role in maintai-
ning the correct biomechanics.
The principles of knee prosthesis implantation
are restoration of femorotibial alignment,
balance of soft tissues, similar flexion and
extension space configurations, correct patel-
lofemoral biomechanics, and restoration of the
articular rim.
This last concept is fundamental for the suc-
cessful restoration of knee kinematics.
Restoration of articular space and height
influences functioning of the ligaments, the
soft tissues, and patellar alignment, which is
also influenced by whether the prosthesis com-
ponents have been correctly positioned.
Bone resection may be performed based sole-
ly on the instrumentarium, adjusting for anato-
mic landmarks, or on ligament tension in
flexion and extension, or on articular surfaces.
To do this, it is necessary to have an accurate
knowledge of knee anatomy in order to avoid
making excessive or insufficient resections
which will be occupied by the prosthesis com-
ponents, and to re-establish correct articular
rim height in both extension and flexion.
The anatomy and kinematics of the distal
femoral epiphysis are well known [1-4] and
various hypotheses have been proposed for
bone cuts and prosthesis component positio-
ning. One relies on the fact that the transepi-
condylar axis runs perpendicular to the mecha-
nical axis of the femur [5, 6], so that the distal
cut can be placed parallel to the transepicon-
dylar axis. Another is that the transepicondylar
axis only approximates the ideal axis around
which the knee joint is flexed [3]. Since this
axis runs through the femoral insertions of the
medial collateral and lateral ligament, it may
be conceived of as an optimal landmark for
performing femoral bone cuts, thus obtaining
good ligament balance and the same gap in
flexion and extension, all essential concepts
for ensuring a long prosthesis lifespan [7-9].
Actually, however, the literature describes two
different transepicondylar axes, one anatomic
and the other surgical, which is a frequent
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BONE CUTS FROM THE JOINT-LINE
P. ADRAVANTI, S. NICOLETTI, A. AMPOLLINI