PhD Fekete - SZIE version - 2.2 - Szent István Egyetem

Summary
6. SUMMARY
In this doctoral thesis, two novel mechanical models were presented: an analytical-kinetical
model with regard to the kinetics of the human knee joint under non-standard squatting, and a
numerical-kinematical model with regard to the local kinematics of the knee joint under
standard squatting.
The new analytical-kinetical model is capable to calculate the patellofemoral, tibiofemoral,
patellar tendon and quadriceps forces in the knee joint under different squatting motions. The
results of this model showed that a moderate trunk motion, the horizontal movement of the
center of gravity, decreases the forces approximately 25% in the knee joint. The published
results are in good agreement with the compared inverse dynamics results taken from the
literature.
The main advantage and value of the presented model, that while the inverse dynamics method
requires expensive measuring system and programs to determine the forces, our new model
gives accurate results by simple algebraic equations. Through the approach of the modelling
and the creation of the equations, similar modelling issues become more understandable and
solvable.
The second aim of the thesis was to unfold the sliding-rolling phenomenon related to the
currently applied knee prostheses under standard squatting movement. The phenomenon, which
has been so far not studied in such depth regarding knee prostheses, was addressed by means of
multibody models, which considered real three-dimensional geometries, the effect of friction
between the condyles, and collateral ligaments as well. The sliding-rolling ratio functions,
derived from the multibody models, showed a convincing trend.
As a conclusion of the numerical results, an averaged third-order function has been created with
its standard deviation along the active functional arc of the knee joint. In addition, the slidingrolling
curves of the individual knee replacements were also determined in the interest of
showing the differences between the examined prostheses regarding the local kinematics.
The obtained results can be beneficial for the practice in the field of total knee replacements as
well: as it was concluded by McGloughlin and Kavanagh [McGloughlin and Kavanagh, 1998],
higher sliding-rolling ratio generates higher wear rate, thus depending on the testing angle, a
proper ratio has to be applied during tribological tests.
The currently determined pattern based on the five different prosthesis geometries, can provide
a future limit for experimental tests related to applicable sliding-rolling ratio with the actual
load. These applicable loads are represented in this thesis as tibiofemoral forces.
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