The biomechanics of the human patella during passive knee flexion

Abstract

Abstract-The fundamental objectives of patello-femoral joint biomechanics include the determination of its kinematics and of its dynamics, as a function of given control parameters like knee flexion or applied muscle forces. On the one hand, patellar tracking provides quantitative information about the joint's stability under given loading conditions, whereas patellar force analyses can typically indicate pathological stress distributions asso ciated for instance with abnormal tracking, The determination of this information becomes especially relevant when facing the problem of evaluating surgical procedures in terms of standard (i.e. non-pathological) knee functionality. Classical examples of such procedures include total knee replacement (TKR) and elevation of the tibial tubercle (Maquet's procedure).Following this perspecti ve, the current study was oriented to ward an accurate and reliable determination of the human patella biomechanics during passive knee flexion. To this end, a comprehensive three-dimensional computer model, based on the finite element method, was developed for analyzing articular biomechanics. Unlike previously published studies on patello-femoral biomechanics, this model simultaneously computed the joint's kinematics, associated tendinous and ligamentous forces, articular contact pressures and stresses occurring in the joint during its motion. The components constituting the joint (i.e. bone, cartilage, tendons) were modeled using objective forms of non-linear elastic materials laws. A unilateral contact law allowing for large slip between the patella and the femur was implemented using an augmented Lagrangian formulation, Patellar kinematics computed for two knee specimens were close to equivalent experimental ones (average deviations below 0.5° for the rotations and below 0.5 mm for the translations) and provided validation of the model on a specimen by specimen basis. The ratio between the quadriceps pulling force and the patellar tendon force was less than unity throughout the considered knee flexion range (30-150°), with a minimum near 90° of flexion for both specimens. The contact patterns evolved from the distal part of the retropatellar articular surface to the proximal pole during progressive flexion. The lateral facet bore more pressure than the medial one, with corresponding higher stresses (hydrostatic) in the lateral compartment of the patella. The forces acting on the patella were part of the problem unknowns, thus leading to more realistic loadings for the stress analysis, which was especially important when considering the wide range of variations of the contact pressure acting on the patella during knee flexion.

Human patellar articular proportions: recent and Pleistocene patterns

“…The degree of medial versus lateral contact force, whether studied in vitro (Burnotte et al 1976 ;Ahmed et al 1983 ;Huberti & Hayes, 1984 ;Hayes et al 1990 ;Singerman et al 1995), inferred from cartilage thickness (Eckstein et al 1992) or estimated through finite element modelling (Heegaard et al 1995), appears to be variable within and between analyses. In general, lateral facet forces are greater than medial facet ones.…”

Three‐dimensional patellar motion at the natural knee during passive flexion/extension. An in vitro study

“…1,2 Motion of the patella relative to the femur is generally called patellar tracking or patellofemoral joint (PFJ) kinematics. Patellar maltracking results in many PFJ joint disorders, and can be associated to abnormalities at the PFJ interface and/or to lower limb malrotations.…”

Motion Analysis of the Patella in Asymptomatic Patellofemoral Joints by Transparent 3D Imaging

“…The test subjects had no history of knee pain or trauma 3DMR imaging was performed using a 3-Tesla MR system (Intera Achieva 3.0 T Quasar Dual gradient R2.6; Philips, Best, The Netherlands) with a flex coil (Flex S_2 channel Phased Alley Coil; Philips, Best, The Netherlands) to obtain images at knee flexion angles of 120°, 90° and 60°. The limbs were examined in the lateral decubitus position, with care taken to ensure that the rotation of the tibia was not affected by the motion of the patella [20][21][22]. The MR scans were obtained by 3D WATS with a 15° flip angle, TR=20 ms, slice thickness=1.5 mm, and FOV=150 mm × 150 mm.…”

“…Therefore, studies using cadavers are being performed in order to accurately analyze the movement of the patella [19][20][21][22]. However, these studies are also limited because cadavers do not move in the same way as living subjects.…”