Download Common Areas of Articulation of the Native Patella

Common Areas of Articulation of the Native Patella and Tibia on the Femur
2
Dimachkieh, O; 1Stal, D; 1Jones, H; +1,2Noble, P C
+1Institute of Orthopedic Research and Education, Houston, TX; 2Baylor College of Medicine, Houston, TX
Senior author [email protected]
Introduction:
A common source of failure among today’s implants used in total
knee arthroplasties is the patellofemoral joint.1 Problems with this joint
present clinically as anterior knee pain, retro-patella pain, patella
dislocation and subluxation, and patella clunk syndrome due to
maltracking.2 Surgeons commonly resurface the patella during TKA in
order to lessen the incidence of these problems.3 When designing
femoral components the natural topography of the trochlear groove,
sulcus, and medial and lateral ridges of the anterior and distal femur
must be taken into account. In addition, certain regions of the femur are
articulate with the tibia in early flexion and then again with the patella in
deeper flexion. The purpose of this study was to determine the surfaces
of the native femur that share articulation with both the tibia and patella
at varying degrees of knee flexion.
Materials and Methods:
Fresh-frozen lower limb specimens were stripped of skin,
subcutaneous tissue, and muscle, sparing the quadriceps muscles. The
quadriceps muscles and hamstring tendons were prepared in such a way
as to allow independent loading of each muscle group. Plastic spherical
fidicual markers were rigidly attached to the tibia to provide spatial
reference for registration of scanned data sets with solid models of each
specimen, after which helical CT scans were obtained of each specimen.
Three-dimensional reconstructions of the tibia, femur, and patella were
prepared using image processing software (Materialise, Belgium)
resulting in solid models of each bone. Each specimen was loaded onto a
mechanical loading frame that applied weight to the muscles in
proportion to their physiologic cross-sectional area and carried the
specimen through a maneuver replicating the standard lunge. The threedimensional positions of the femur, tibia, and patella at each flexion
angle were tracked with a 2-camera motion analysis system (NDI
Polaris, Canada) in conjunction with a six degree of freedom high
definition laser scanner (Immersion Corp., USA) and a system of
photoreflective flags. Using the CT reconstruction of each specimen, the
three-dimensional position of the knee was reconstructed with respect to
the femur at 0º, 15º, 30º, 60º, 90º and 120º. Contact points for each
flexion angle were determined by calculating the points on the bony
surfaces at which the distance between the femoral condyles and the
articular surfaces of the tibia and patella were minimal. In order to
account for the presence of cartilage in intact specimens, the presumed
cartilage thickness was estimated using data obtained from Li, et al.4 The
area of the contact envelope between the opposing bony surfaces was
determined by calculating the two-dimensional area of the resulting
surface. Areas of the femur that were in contact with both the tibia in
early flexion and the patella in deeper flexion were determined by
constructing interference curves at the regions of overlap between the
respective shells. The total surface area of femur that articulates with
both tibia and patella was then determined. All three-dimensional
imaging was analyzed using Rapidform 2006 (INUS Technology, USA).
Results:
The total surface area of articulation of the patella on the femur
was 39.53cm2 through 120⁰ of flexion while tibiofemoral articulation
covered 48.07cm2. The total surface area of the femur that shared
common articulation with both the tibia and patella at varying degrees of
flexion was 9.12cm2.
Degree of
Flexion
Surface Area of
Patella on Femur
(cm2)
Surface Area of Tibia
on Femur (cm2)
0°
15°
30°
60°
90°
120°
Total
5.95
6.46
3.35
3.91
10.6
9.26
39.53
8.25
8.22
5.78
6.42
8.7
10.7
48.07
Figure 2 – Grid system with contact of tibia (green) and patella (red) on
the distal femur through varying degrees of flexion
Using the grid system pictured in Figure 2, the areas of the femur
in contact with both the tibia and patella through varying degrees of
flexion include areas 9, 14, 15, 17, 20, 21, and 23, located primarily
along the inner region of the medial condyle. The lateral condyle had
regions of shared articulation as well, although these contributed less
overall.
Discussion:
Recent new femoral component designs have begun to focus on
patellar articulation. Although patellar maltracking has been recognized
as a design problem, one should remain mindful of the tibiofemoral
joint. This study shows regions of shared articulation of both the patella
and tibia with the femur throughout flexion. As can be seen in figure 2,
manipulations of the inner lateral condyle to accommodate patellar
articulation may not affect the tibiofemoral joint. The medial inner
condyle, however, may be more sensitive to geometric changes
especially in extension when the tibia tends to pivot on the medial side.
References:
1. Waters, T.S. et al. J Bone Joint Surg Am, 2003;85:212-217.
2. Fukunaga, K. et al. J Bone Joint Surg Br, 2009;91-B:463-468.
3. Meneghini, R.M. et al. The Journal of Arthrplasty, 2008;23:11-14.
4. Li, G. et al. Clinical Biomechanics, 2005;20:736-744.
Figure 1 – 3D position of the femur, tibia, and patella
Poster No. 2059 • 56th Annual Meeting of the Orthopaedic Research Society