Abstract
Background
Animal studies and clinical trials have suggested that early application of controlled
axial micromotion can accelerate healing of long bone fractures compared to rigid
fixation. However, experimental investigations of micromotion constructs have been
limited to external fixators, which have a higher incidence of complications than
intramedullary nails. The purpose of this study was to assess whether a novel intramedullary
nail design can generate stimulatory micromotion under minimal weight-bearing loads
typical of the early healing period.
Methods
Eight cadaver tibiae were reamed, osteotomised, and implanted with commercially-available
IM nails fitted with a custom insert that allowed 1 mm of axial micromotion after proximal/distal interlocking. Specimens were mounted
in a materials testing machine and subjected to cyclic axial loading while interfragmentary
motion was measured using an extensometer. Implants were also tested in standard statically-locked
mode.
Findings
The average force required to cause distraction of the fracture gap in micromotion
mode was 37.0 (SD 21.7) N. The mean construct stiffness was 1046.8 (SD 193.6) N/mm
in static locking mode and 512.4 (SD 99.6) N/mm in micromotion mode (significantly
different, P<0.001).
Interpretation
These results support the development of a micromotion-enabled IM nail because the
forces required to cause interfragmentary movements are very low, less than the weight
of the hanging shank and foot. In contrast to rigid-fixation nails, which require
significant weight-bearing to induce interfragmentary motion, the micromotion-enabled
nail may allow movement in non-weight-bearing patients during the early healing period
when the benefits of mechanical stimulation are most critical.
Keywords
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Article info
Publication history
Published online: September 22, 2011
Accepted:
August 16,
2011
Received:
March 24,
2011
Identification
Copyright
© 2011 Elsevier Ltd. Published by Elsevier Inc. All rights reserved.
