ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

ensure good short-term and long-term results 10 . Thus, any new design should be
subjected to preclinical tests specifically designed to assess stability under physiological
loads. Implant-bone micromotion is a reliable indicator of implant primary stability and
a potential predictor of failure 11 . The purpose of this study was to measure stem-bone
micromotion in the proximal component of the Re-Motion prosthesis after implanting in
a cadaveric model.
3. MATERIALS AND METHODS
One fresh frozen human cadaveric radius of a woman was utilized. The age of the donor
at the time of death was 72 years. The study was approved by the Mayo Clinic
Institutional Review Board. The specimen did not present any sign of bony pathology
by visual inspection and radiography. Extensometers were fixed to the medial and
lateral distal surfaces of the radius (Figure 1), and in a similar fashion in the dorsal and
volar orientation in order to measure the relative micromotion of the implant to the
adjacent bony surface. Forces were applied to magnitudes of 20, 40 and 80 N to the
medial (M), lateral (L), dorsal (D) and volar (V) edges of the implant while
simultaneously recording micromotion. Micromotion of the tip of the stem relative to
the bone was calculated utilizing the extensometer data and the geometry of the implant
and radius for each loading condition.
Figure 1: Mounted specimen after implantation of the Re-Motion radial component.
M
A geometric model was used to convert the vertical motion (measured from
extensometers) to stem micromotion (Figure 2). In a right triangle, the tilting angle (α)
was calculated from the extensometer displacement (D) (sin α = D/L). In an isosceles
triangle, the stem micromotion at the level of tip (dt) was calculated from a (sin α/2 =
[dt/2]/lt).
V
D
L