THE ROLE OF MUSCLE FORCES IN JOINT LOADING AND INTRA-ARTICULAR LOAD DISTRIBUTION: EXPERIMENTAL RESULTS AND IMPACT ON MODELLING

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In human movement studies it is common to calculate the net joint moments of the proximal joint of a body
segment using an inverse dynamic approach. More detailed models distribute the net moments and net forces
acting on a given joint to muscle forces, bone-to-bone forces and ligament forces. Such models use a number of
assumptions e.g. the muscle moment arm, muscles’ line of action, take additional information into account (e.g.
muscle activation) and quite often use static optimization with a more or less randomly chosen cost function to
solve the mathematically underdetermined problem. Finite element models can probably estimate the intra-articular
stress and stress distribution but such models are strongly depend on information on the material properties of the
elements and the force applied to the joint through muscle forces, inertial forces, axial and shear forces.
Direct pressure distribution measurements have been applied in ex-vivo studies to joints of the human leg and
especially to the talocrural joint, the patello-femoral joint and the tibio-femoral joint. Potthast et al. (2008) showed in
a systematic approach using a pneumatic loading simulator on fresh frozen cadaveric legs the strong effect of the
application of muscle forces to the talocrural joint. The muscle forces and their distribution have been shown to
build the dominant determinants of intra-articular joint and biological tissue loading. The data demonstrated
extreme individual results. Recent data demonstrated the role the muscles play in the tibio-femoral joint. The study
used a pneumatically driven knee simulator in an ex-vivo experiment and allowed an inside view into changes in
intra-articular loading patterns related to joint alignment (varus, valgus) and muscle forces of thigh and shank.
Depending on the muscle forces applied the centre of intra-articular pressure moved up to 12 mm in medio-lateral
and 5 mm in anterior-posterior directions.
The effect of different quadriceps loading patterns on the patello-femoral contact pressure during simulated weight
bearing knee flexion was recently reported by Wünschel et al. (2011). The impact of more medial or lateral applied
quadriceps loading to the pressure distribution between patella and trochlea and especially the centre of contact
pressure was clearly demonstrated.
The ex-vivo data explore the dominant role the muscle forces play for intra-articular joint loading and therefore joint
tissue loading. A more detailed inspection of the results allows a significant inside view into the variability of
intra-articular loading patterns in different subjects and the high individuality of results. These finding should have a
major impact on modelling especially if individualized estimates of intra-articular or tissue loading are the purpose
of research.
Original languageEnglish
Title of host publication16th annual Congress of the European College of Sport Science, 6.-9. July 2011, Liverpool, ECSS
Publication date2011
Publication statusPublished - 2011
EventAnnual Congress of the ECSS - Liverpool, United Kingdom
Duration: 06.07.201109.07.2011
Conference number: 16

ID: 259209

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