LIVRE JDG 2010

conventional instruments. For these reasons it

is useful to guide the surgeon during the

implant [9, 10]. Literature demonstrated that

CAS surgery could improve coronal plane ali-

gnment accuracy, rotational positioning in

axial plane of femoral component and balan-

ced-gap kinematics during TKA, as regards to

traditional techniques [11, 12].

A navigation system should assure not only

good alignment but also joint kinematics,

since it supplies a quantitative feedback, and

should increase reliability, repeatability and

accuracy of a surgical procedure. Many stu-

dies,

in vitro

and

in vivo

, used CAS to evalua-

te and improve the kinematic path of a specific

prosthesis design, comparing it with those of

intact knee [13].

Only few studies dealt with the effect that

pathologies like osteoarthritis could have on

knee kinematics and how kinematic changes

after TKA implant [14, 2].

In this paper we describe our experience with

the navigated TKA, in particular we focused our

attention on the analysis of in vivo knee kine-

matics with the purpose to obtain a customized

surgery, according not only to patients morpho-

logic features, but also to his kinematic patterns.

OUR EXPERIENCE

Our experience with surgical navigation star-

ted in 2001. The early researches was conduc-

ted

in vitro

to define and optimize the surgical

protocol [15] and subsequently we started in

vivo studies, on various surgical procedures as

TKA, UKA and ACL reconstruction [16, 17].

We used a navigation system equipped with a

software focused on knee kinematics acquisi-

tions; the set of data collected intraoperative-

ly are elaborated off-line with a specific tool-

box dedicated to diarthrodial joint kinematic

analysis [18].

As regards TKA, we focused our attention on

intraoperative passive kinematics analysis.

We evaluated knee stability before and after

TKA, computing knee laxities and 3D

motions, to study, with a customised acquisi-

tion protocol, the effect of prosthesis implant

on knee kinematics.

Besides controlling measurements like the

coronal plane alignment in the positioning of

total knee component, that is the original appli-

cation of a navigated TKA, our research activi-

ty was centred on some kinematic aspects like

the analysis of the passive range of motion

(PROM), the balanced-gap kinematics, the

evaluation of the knee laxities as varus/valgus,

at 0 deg and 30 deg of flexion, and ante-

rior/posterior, at 90 deg of flexion, laxities, and

the amount of internal/external tibial axial rota-

tion around the proximo-distal axis [1].

Recently the kinematic technique was also

used to study the functional flexion axis (FFA)

method to describe knee kinematics. The FFA

is a reference axis that doesn’t depend on sub-

jectively assessed anatomical landmarks but

that results directly from the biomechanical

behaviour of the single subject. In particular

starting from the hypothesis that in healthy

subjects there is a correspondence between the

transepicondylar axis (TEA) and FFA [19, 20,

21] we analysed whether there is the same cor-

respondence also for osteoarthritic knees and

we used this kinematic method to study the

effect of degenerative pathologies like osteoar-

thritis on the kinematic behaviour of the limb.

It is indeed common knowledge that this kind

of disease could affect knee motion and have a

deep influence on mobility and physical func-

tioning of the subject. They can cause joint

deformities, most commonly sagittal plane

deformities, and consequently alterations in

knee mobility and function. Therefore we

thought it would be important to understand

the role of the pathology on joint kinematics,

most of all to determine correctly the

limb alignment and the rotational positioning

of femoral component in TKA.

The main results of our studies demonstrated our

preliminary hypotheses that navigation system

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