Eur J Anat, 1 (1): 23-30 (1997)

Geometry-to-pressure relationship in the human elbow joint - a qualitative analysis using MRI and finite elements

F. Eckstein¹, B. Merz^1,2, H. Sittek³, H. KOlem⁴, M. ReiserJ and R. Putz¹

1.-Anatomische Anstalt, Ludwig-Maximilians Umversitét München, Pettenkoferstr. 11, 0-80336 München, Germany 2.-Institut Straumann, eH 4437 Waldenburg, Switzerland 3.- Institut Für Radiologische Oiagnostik, Klinikum GroBhadern, Marchioninistr. 15, 0-81312 München, Germany 4.- Abteilung für MR-Applikationsentwicklung, Siemens Erlangen, Henkestr. 127, 0-91052 Erlangen, Germany

ABSTRACT In order to analyse the geometry-to-pressure re­ lationship in the human elbow joint, four speci­mens were investigated by magnetic resonance imaging. Sagittal sections of the humero-radial and humero-ulnar joints were obtained at a re­ solution of 1 x 0.2 x 0.2 mm3, using a fat-sup­ pressed FLASH sequence. From these images the relative form (congruity / incongruity) of the articular bodies was qualitatively evaluated. In a second step, three finite element models were designecl according to the MRI findings ancl loa­ ded with 100 to 6900 N. In the first moclel a he­ mispherical joint head was pressed into a he­ mispherical socket, in the second the socket was macle 2.5% wicler and in the third 2.5% deeper than the joint heacl. These variations in joint sha­ pe hacl profouncl effects on the clistribution of normal stresses. Whereas in models 1 ancl 2 the stress máxima were alwa ys in the centre of the socket, in rnodel 3 the location of the maxima depended on the magnitucle of the resultant for­ ce and showecl a more peripheral location at low ancl moderare joint loacls. Although the pressures calculated for model 2 were higher than those for model 1, those of moclel 3 (con­ cave incongruity) were considerably lower than those of models 1 and 2. These results tie in well with the biomechanical assessment of elbow joint contact areas ancl morphological findings on articular cartilage thickness and subchonclral bone density. A combination of MRI and finite element analysis may become a powerful tool in the stress / strain analysis of human joints ancl provide valuable information for the stucly of the functional adaptation of connective tissues as well as of the mechanical factors involved in the pathogenesis of osteoarthrosis.

Keywords: Elbow joint, magnetic resonance imaging, incongruity, joint loacling, finite-ele­ ment analysis.