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

Table I - Micromotion results at the tip of the stem categorized by loading side (dorsal,
lateral, volar and medial) and load applied in each side (mean ± SD).
Micromotion at tip [µm]
DORSAL LATERAL VOLAR MEDIAL
20N 50.2 ± 1.31 4.4 ± 0.12 25.2 ± 1.18 5.2 ± 0.25
40N 79.5 ± 1.06 9.2 ± 2.76 45.2 ± 0.66 7.5 ± 0.24
80N 130.3 ± 1.64 37.4 ± 0.20 58.1 ± 0.40 12.5 ± 0.19
5. DISCUSSION
In this study, micromotion of the Re-Motion radial component due to three levels of
applied edge loading (20, 40 and 80N) for four orientations (dorsal, lateral, volar and
medial) were calculated. The results demonstrated micromotion that was significantly
higher when loads were applied in the sagittal plane. Also demonstrated was that
micromotion was significantly related to the load applied.
Previous studies have indicated micromotion less than 40 µm could result in
osseointegration while micromotion of 150 µm had resulted in a interposition of a
fibrous tissue layer at the stem–bone interface 12,13 . In general, studies reported that
physiological loads giving rise to implant-bone relative micro-movements of the order
of 100 or 200 µm may inhibit bone in-growth eventually promoting loosening of the
implant 14-17 .
Measured values of the radial component of the Re-Motion for this individual trial were
below this threshold. Further biomechanical testing including multiple samples would
be necessary to document the initial fixation this implant. This preliminary data is
being utilized to validate an analytical model for the purpose to study variations in
loading, bone geometry and bone quality.
This study has three main limitations. As mentioned one limitation is that this represents
only one sample. Second, these results were obtained from a radius from an elderly
donor. Bone quality can affect stability for press fit cementless implants. Third, further
refinement of the experimental method based on this pilot could improve the accuracy
and .reliability of the measurements.
ACKNOWLEDGEMENT
Biomechanics and Motion Analysis Laboratory at Mayo Clinic for welcoming and
supporting the researcher Susana Meireles.
Fundacão para a Ciência e a Tecnologia for funding Susana Meireles through Grant
SFRH/BD/45320/2008.
6. REFERENCES
1. Cobb T.K. and Beckenbaugh R.D., Biaxial long-stemmed multipronged distal
components for revision/bone deficit total-wrist arthroplasty, J. Hand Surg., 1996,
21A(5), 764–70.