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ABSTRACT
The purpose of this study was to analyze the
positioning of unicompartmental knee arthro-
plasty (UKA) and to compare between the
medial and lateral compartments. All patients
were examined postoperatively using computed
tomography with three-dimensional analysis of
the lower limb from the hip to the ankle. There
were 18 lateral and 19 medial UKAs. All knees
were analyzed using an image processing soft-
ware that enabled 3D bone reconstructions and
digitization. We measured the varus-valgus
inclination and internal-external rotation of the
femoral and tibial components. The rotation of
the femoral component was external (mean
3.2°, SD 7.3°) for the medial compartment, and
internal (mean 5.8°, SD 7.2°) for the lateral
compartment, and the difference was statistical-
ly significant (p < 0.001). The rotation of the
tibial component was external for the medial
compartment (mean 6.5°, SD 5.1°) as well as
for the lateral compartment (mean 7.3°, SD
10.3°), and the difference was statistically insi-
gnificant (p = 0.717). The inclination of the
tibial component was in varus (5.5°, SD 2.8) for
medial compartment, and in valgus (mean 1.3°,
SD 4.0) for the lateral compartment. Our study
presents the first 3D
in vivo
analysis of UKA
positioning for both compartments, which
remains a difficult surgical procedure.
INTRODUCTION
A number of studies demonstrate good results
with unicompartmental knee arthroplasty
(UKA). The design and positioning of UKA
implants is yet not well understood. Most stu-
dies of UKA present two-dimensional radiolo-
graphic analyses of the implant positioning in
the sagittal and frontal plans [25]. The kinema-
tics of UKA were more recentlystuied using
fluoroscopy [8, 12, 15, 17, 19], though none of
the studies focused on implant rotation.
Argenson [2] studied the rotation of the tibial
component relative to the femoral component
during flexion, without attention to the anato-
mic position of the implant. Assor [3] conduc-
ted a two-dimensional radiographic study of
implant rotation but focused soley on the femo-
ral component. Campbell [4] analyzed UKA
positioning using Computed Tomographic
(CT) scans but focused only on implant rota-
tion in the medial compartment.
There are very few tools available for three-
dimensional (3D) analysis of UKA. The pur-
pose of the study was to describe ideal positio-
ning of the UKA in three dimensions. We
chose computed tomography (CT) to allow 3D
analysis with great accuracy. After performing
a CT-scan with reconstruction on the operated
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THREE-DIMENSIONALANALYSIS
OF UNICOMPARTIMENTAL KNEE
IMPLANT POSITIONING
E. SERVIEN, M. SAFFARINI, S. LUSTIG, S. CHOMEL, PH. NEYRET