Postoperative Functional Assessment for Total Knee Arthroplasty using Medial Pivot Concept
+1Yamamoto, K; 1Suguro, T; 1Nakamura, T; 1Miyazaki, Y; 1Kogame, K; 1Kubota, A; 2Banks, S A;
1
Department of Orthopaedic Surgery, School of Medicine, Toho University, Tokyo, JAPAN
2
Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL
Senior author [email protected]
PUEPOSE:
Recently, total knee arthroplasty (TKA) has been generalized as an
operation that achieves excellent clinical results. However, younger and
more demanding patients require even greater implant longevity and
functional performance, and there are many variations in the prosthesis
design.
Banks et al have been reported that the kinematic outcome from TKA
varies with the prosthesis design: the CR and mobile types of TKA
provide lateral pivot motion, whereas the PS type provides medial pivot
motion1). Schmidt et al have been reported that the Medial Pivot type
TKA has reproduced medial pivot motion2).
We assessed the postoperative function of two types of medial pivot
type TKA in vivo in order to determine if medial pivot motion is
reproduced.
METHODS:
The subjects were 16 osteoarthritis patients undergoing TKA in 16
joints. TKA was performed with the ADVANCE Medial Pivot Knee
System (ADVANCE TKA) made by WRIGHT MEDICAL Technology
in 8 joints (Fig.1), and with the FINE Total Knee System CR type (FINE
TKA) made by NAKASHIMA MEDICAL in JAPAN in 8 joints (Fig.2).
The posterior cruciate ligament was preserved in all cases.
The ADVANCE TKA femoral component has a constant sagittal
radius of curvature extending from full extension to 90 degrees of
flexion. The spherical medial femoral condyle pivots about the matching
spherical depression on the tibial insert, while 15 degrees of rotation
around the medial pivot is allowed with an arcuate path on the lateral
plateau. This “ball in socket” medial pivot mechanism maximizes
medial congruency while providing controlled A-P translation on the
lateral plateau.
The FINE TKA is designed with a 3-degree step of the joint line in
order to reconstruct the anatomic geometry. This system has an
asymmetrical design between the medial and lateral femoral condyle, the
medial femoral condyle designed to be 3 degrees larger than the lateral
femoral condyle. In comparison, the tibial insert is designed in such a
manner that the medial plateau is lower than the lateral plateau by 3
degrees. By incorporating the 3 degrees joint line step into the TKA
prosthesis design, the anatomical geometry and posterior condyle offset
is rebuilt. The tibial insert is designed to conform to the medial plateau.
The lateral plateau is designed with a posterior slope, so that it adopts
the tibial internal rotation through medial pivot motion.
The kinematic postoperative functional assessment was performed in
the 16 patients using a 3D-to-2D model registration technique1). Singleplane fluoroscopic imaging was used to record and quantify the motions
of knees during a stair-step activity. The contact points between the
tibiofemoral motions and the tibial rotational angle were evaluated.
Fig.1. ADVANCE TKA
generally recognized. Therefore, the ADVANCE TKA demonstrated the
medial pivot pattern; tibial external rotation was shown in early stages of
flexion, and tibial internal rotation was shown with flexion up to 90
degrees.
In the FINE TKA, the average contact point on the medial plateau
showed a 0.9 mm femoral roll back from 0 to 30 degrees of flexion, 0.9
mm femoral roll forward from 30 to 70 degrees of flexion, and femoral
roll back from 80 to 90 degrees of flexion. The average contact point on
the lateral plateau, however, showed femoral roll back at a constant rate
from 0 to 90 degrees of flexion, with 9 mm of femoral rollback at 90
degrees of flexion. The average tibial rotational angle was 0.5 degrees at
0 degree of flexion, and after reaching 1.7 degrees of internal rotation at
20 degrees of flexion, an approximately constant rate of tibial internal
rotation was shown, with 16.9 degrees of internal rotation was shown at
90 degrees of flexion. In every case, tibial internal rotation was generally
accepted. From these results, the FINE TKA showed the medial pivot
pattern; tibial internal rotation was shown with flexion up to 90 degrees
(Fig.3).
Fig.3. Contact points and tibial rotation
DISCUSSION:
From the analysis, both the ADVANCE TKA and FINE TKA
showed tibial internal rotation due to medial pivot motion. The
reproducibility of the design concept was recognized during stair-step
activity. A kinematic difference between the two types TKA models was,
however, recognized.
Following ADVANCE TKA, although tibial external rotation was
shown in the early stages of flexion, it shifted to tibial internal rotation
with flexion approaching 90 degrees. In the FINE TKA, only internal
rotation was shown with flexion up to 90 degrees. These differences are
considered to be a result of the different kinematic TKA prosthesis
designs.
It has been reported that the femoral posterior condyle offset and
femoral roll back influence the maximum flexion of the knee joint1).
From this analysis, the anatomical femoral posterior condyle offset was
reconstruct within the TKA design and 9.0 mm femoral roll back on the
lateral plateau was shown at 90 degrees of flexion in the FINE TKA. As
shown in our analyses of TKA performed with the FINE TKA, it is
possible for the maximum flexion angle of the knee joint to be increased
due to femoral roll back.
Fig.2. FINE TKA
RESULTS:
In the ADVANCE TKA, the average contact point on the medial
plateau of the tibiofemoral motion was constant from extension to
flexion. In the lateral plateau, the average contact point showed a 1.1
mm femoral roll forward with flexion to 20 degrees and a 3.9 mm
femoral roll back with flexion to 90 degrees. The average tibial
rotational angle was 2.7 degrees of tibial internal rotation at 0 degrees of
flexion, 0.3 degrees of tibial external rotation from 0 to 20 degrees of
flexion, and 8.2 degrees of tibial internal rotation with flexion up to 90
degrees. In every case, although a distributed trend could be seen in the
internal rotational position set at 0 degrees, tibial internal rotation was
CONCLUSIONS:
The kinematic postoperative functional assessment of these two
prosthesis designs was performed in vivo. In both designs, internal
rotation by medial pivot motion was observed. The difference in the
results is due to the different design of the two types of TKA prosthesis.
REFARENCES:
1) Banks SA, Hodge WA: Implant Design Affects Knee Arthroplasty
Kinematics during Stair-stepping. Clin Orthop 426: 187-193, 2004.
2) Schmidt R, Komistek RD, Blaha JD et al: Fluoroscopic analysis of
cruciate-retaining and medial pivot knee implants. Clin Orthop 410:
139-147, 2003.
Poster No. 2045 • 56th Annual Meeting of the Orthopaedic Research Society