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was a useful and accurate tool for kinematic ana-
lysis. The correct limb alignment was always
restored after navigated TKA. The PROM test
was highly repeatable (intraclass correlation
coefficients between repeated motions were
0.97 when performed by the same surgeon, and
0.87 when performed by different surgeons).
The varus/valgus laxity at 0 deg was significant-
ly reduced by 2 deg ± 2 deg whereas varus val-
gus laxity at 30 deg remained similar to that of
OA knee. During PROM the anterior/posterior
displacement before reconstruction showed a
posterior displacement of 23 ± 8 mm, while after
reconstruction showed an abnormal anterior
translation of the femur up to 60 deg of flexion
followed by a rollback of 12 ± 5 mm (fig. 1).
Analysing the tibial axial rotation during
PROM we found that TKA influenced the pat-
tern of tibia rotation during flexion but not the
total amount of internal/external rotation
during the whole range of flexion which did
not change before 8deg ± 4deg; or after TKA
6deg ± 5deg (fig. 2).
As regards FFA we could affirm that on axial
plane the osteoarthritis does not influence the
evaluation of functional flexion axis, compared
to healthy subjects, that on axial plane FFA cor-
responded to the transepicondylar axis (mean
difference is 1 deg) also for pathologic patients
and that, still on axial plane, FFA was a reliable
reference also for OA subjects. On the contrary
some difference as been found on frontal plane
(mean difference is 4 deg). Therefore the FFA is
a reliable reference for the determination of
femoral implant positioning on axial plane, even
in surgical setup on osteoarthritic patients, repla-
cing traditional reference axes, that depend on
surgeon ability to assess anatomical landmarks
correctly. Moreover we could affirm that the
correspondence between FFA and TEA changed
in pathologic knees and, most of all, was corre-
lated to the preoperative level of limb deformity.
TOTAL KNEE REPLACEMENT KINEMATICS ASSESSMENT BY CAS
141
Fig. 1: Anterior (+)/pos-
terior (-) translation in
function of flexion
during the PROM test.
Values are expressed
as mean ± SD in OA
knees before TKA and
in TKA knees
Fig. 2: Internal (+)/exter-
nal (-) rotation in func-
tion of flexion during
the PROM test. Values
are expressed as mean
± SD in OA knees before
TKA and in TKA knees