Notas / Notes - Active Congress.......

MIÉRCOLES / WEDNESDAY
58
placement, and employing the combined anteversion method,
the occurrence of impingement should significantly be reduced
and this will improve the immediate and long-term results
for total hip replacement.
Fewer studies have explored femoral component malposition
than acetabular component malposition. Femoral malposition
is thought to be more easily avoidable intraoperatively, and
is more difficult to assess postoperatively by standard radiographs.
McCollum& Gray thought the orientation of the femoral
component as less critical and less complex than the
orientation of the acetabular component. It was believed that
the femoral anteversion can always be controlled to the desired
position of 10-15 degrees. Surgeons therefore implant
the acetabular cup targeting a fixed angle of anteversion based
on the assumed femoral anteversion.
The surgeon can control the amount of anteversion of a cemented
stem but not of a noncemented stem. Anteversion
of cemented stems can be controlled by the surgeon because
a stem with a diameter smaller than that of the medullary
canal of the femur can be used and can be inserted into 15
+/- 5 degrees of anteversion while being fixed with cement.
The surgeon has much less ability to control anteversion of
a cementless femoral stem because the rigid metal stem
must be fit into a specific geometric shape of the femur. The
anterior bow of the femoral diaphysis, which can be as much
as 10 degrees, influences the anteversion of the pros-thetic
stem. Anteversion has been found to show an inverse relationship
with the degree of femoral bowing.
D’Lima et al., in their finite-element study found the femur
has variable anteversion of the neck and variable anterior
diaphyseal bowing, both of which influence the anteversion
of the prosthetic neck in relation to the femoral axis. With
use of postoperative computed tomography scans, Wines
and McNicol, with both cemented and cementless stems,
found a range of 15 degrees of retroversion to 45 degrees
of anteversion (mean of 16.8 degrees) and Pierchon et al.,
with cemented stems, reported a similar observation with
range of 30 degrees of retroversion to 37 degrees of anteversion
(mean of 16.5 degrees).
In our institute, using imageless computer navigation, we
found a mean of 9 degrees of anteversion of the femoral
stem in men and a mean of 19 degrees in women. Our finding
is similar to that of Maruyama et al. who measured intact
cadaver femora to have a mean anteversion if 9.8
degrees. In our patients, cementless stem position is between
10-20 degrees anteversion in only 43% of hips; 10% are in
absolute retroversion; 42% between 0-9 degrees anteversion;
and 5% have more than 20 degrees anteversion. The mean
anteversion for cementless stems was 8-10 degrees. This
data means that there is the potential for cementless stem
anteversion to be 15 degrees different than the anticipated
position of 15 degrees anteversion. Therefore, the risk exists
that the stem may have an outlier of 10 degrees, and if the
cup does too, the combined anteversion could be 20 degrees
than anticipated.
Ranawat taught a ‘manual combined anteversion test for total
hip replacement since the early 1990s. According to him,
with the cup and stem in place, the lower limb is positioned
in neutral (or slight hip flexion) and is internally rotated until
the femoral head is symmetrically seated (coplanar) in the
cup. The combined anteversion is the amount of internal rotation
in degrees needed to produce a coplanar head and cup.
Ranawat and Maynard recommended a combined anteversion
of approximately 45 degrees in female patients, and 20 degrees
to 30 degrees in male patients. McKibbin defined the
stability index for anatomic hips to be 30 degrees to 40
degrees, with a range of 20 degrees to 35 degrees for men
and 30 degrees to 45 degrees for women. A combined anteversion
of