cadera / hip - Active Congress.......

JUEVES / THURSDAY
240
to the mechanical axis of the lower extremity,
and roughly parallel to the epicondylar axis.
In the fl exed position, anatomic landmarks
are equally important for varus-valgus alignment.
Incorrect varus-valgus alignment in
fl exion not only malaligns the long axes of
the femur and tibia, but also incorrectly positions
the patellar groove both in fl exion and
extension.
Finding suitable landmarks for varus-valgus
alignment has led to efforts to use the posterior
femoral condyles, epicondylar axis, and
anteroposterior (AP) axis of the femur. The
posterior femoral condyles provide excellent
rotational alignment landmarks if the femoral
joint surface has not been worn or otherwise
distorted by developmental abnormalities or
the arthritic process. However, as with the
distal surfaces, the posterior femoral condylar
surfaces sometimes are damaged or
hypoplastic (more commonly in the valgus
than in the varus knee) and cannot serve as
reliable anatomic guides for alignment. The
epicondylar axis is anatomically inconsistent
and in all cases other than revision total
knee arthroplasty with severe bone loss,
is unreliable for varus-valgus alignment in
fl exion just as it is in extension. The AP axis,
defi ned by the lateral border of the posterior
cruciate ligament posteriorly and the deepest
part of the patellar groove anteriorly, is
highly consistent, and always lies within the
median sagittal plane that bisects the lower
extremity, passing through the hip, knee,
and ankle. When the articular surfaces are
resected perpendicular to the AP axis, they
are perpendicular to the AP plane, and the
extremity can function normally in this plane
throughout the arc of fl exion.
In the valgus knee with signifi cant posterior
deformity or erosion, the posterior femoral
condyles are unreliable as rotational alignment
landmarks, and the anteroposterior axis
provides a reliable landmark for rotational
alignment of the femoral surface cuts.
Technique for Femoral Bone Resection
Intramedullary alignment instruments usually
are used for the femoral resection. The
distal femoral surfaces are resected at a
valgus angle of 5-7°. A medialized entry
point generally is advised because the distal
femur curves toward valgus in the valgus
knee. The current technique is to reference
the resection from the distal medial femoral
surface. The distal femoral cutting guide is
seated on the distal surface of the medial
femoral condyle, which is resected equal to
the thickness of the distal condylar surface
of the implant. If the distal lateral femoral
condylar surface is defi cient, considerably
less is resected from the lateral surface than
from the medial surface, and in many cases
of a severe valgus angle, no bone is present
to resect from the distal lateral surface.
Seating on bone is necessary on the lateral
distal side, but this can be accomplished with
the anterior lateral bevel surface. In cases
of severely defi cient lateral femoral condylar
bone stock, the anterior bevel surface is the
only bony contact for the distal lateral surface
of the femoral component. This leaves a gap
that is fi lled with bone graft between the distal
bone surface and the inner surface of the implant
on the lateral side. When the posterior
fl ange and the anterior bevel surfaces are
seated on viable bone, the distal defect can
be treated as a contained defect and needs
no structural grafting. Rotational alignment of
the distal femoral cutting guide is adjusted to
resect the anterior and posterior surfaces perpendicular
to the anteroposterior axis of the
femur. The AP axis is drawn and the femoral
cutting guides are aligned to make the cuts
perpendicular to this line. In the valgus knee
this almost always results in much greater
posteromedial than posterolateral femoral
condylar resection.
Technique for Tibial Bone Resection
Intramedullary alignment instruments are
used to real tibial surface is based on the
height of the intact medial bone surface. A
maximum thickness of 10 mm is removed