OTA 2006 Posters
Scientific Poster #86 Basic Science
The Effects of Intermittent Axial Compression on Bone Healing
Michael J. Gardner, MD (a-OREF);
Marjolein C. H. van der Meulen, PhD (a-NIH);
Demetris Demetrakopoulos, BS (*); Timothy M. Wright, PhD (a-NIH);
Elizabeth R. Myers, PhD (a-NIH);
Mathias P. Bostrom, MD (a-Oxnard Foundation);
Hospital for Special Surgery, New York, New York, USA
Background: Abundant evidence exists that fracture healing can be
influenced by mechanical loading. However, the specific loading parameters
that are osteogenic remain unknown. The purpose of this study was to apply
noninvasive external compression to mouse tibial osteotomies to determine
the effects that particular variations in timing and load magnitude have
on bone healing. In addition, the utility of microcomputed tomography (microCT)
in predicting the mechanical properties of callus was assessed.
Methods: Eighty 12-week-old C57BL/J6 mice underwent surgical osteotomy
of the left tibia followed by intramedullary nailing with a 27-gauge needle.
Mice were divided into 6 groups based on days delayed until application
of load (0 days or 4 days) and amplitude of cyclic load (0.5 N, 1 N, or
2 N). Loading regimens were applied at 1 Hz for 100 cycles per day, 5 days
per week for 2 weeks, using an external device that applied axial compression
to the tibia. Bone healing was assessed by both microCT and 4-point bend
testing. Differences between groups were compared using one-way ANOVA and
Bonferroni multiple comparison tests.
Results: In the group with a 4-day delay and 0.5 N amplitude, the
maximum bending moment was significantly higher (19.8 vs. 14.2 N-mm) than
the control group. However, callus mineralized volume, mineral content,
and density were not significantly different between these groups. Callus
strength decreased significantly as load amplitude increased from 0.5 N
to 2 N in the 4-day delay groups. Groups in which loading began immediately
following surgery (0-day delay) were significantly weaker than the control
specimens. The overall volume and mineral content of calluses in these groups
were, however, larger than controls. Bone mineral density at the osteotomy
site did not show any significant differences between any of the groups,
and neither bone mineral density nor content correlated with mechanical
strength of the healing bones.
Conclusions: A short delay followed by cyclic application of a relatively
low load led to improved fracture healing, as determined by increased callus
strength, but this enhancement disappeared as load amplitudes increased.
Load initiation immediately following fracture inhibited healing, regardless
of the magnitude of load applied. MicroCT measurements of calluses in the
early healing stage did not predict the mechanical strength of the fractures.
Clinical Relevance: These findings establish that controlled, noninvasive
cyclic loading can improve the strength of healing callus and suggest that
mechanical intervention could be effective in the clinical setting. For
example, lower extremity fractures treated with flexible fixation, such
as locked plates or intramedullary nails, may be stimulated to heal with
a limited touchdown weight-bearing protocol. As the loading parameters necessary
to enhance fracture healing become refined, external compression may be
used as a potent stimulus for treating fractures with decreased biological
capacity. Additionally, radiographic parameters such as callus density may
be inaccurate in predicting mechanical qualities during the early healing
phase.
If noted, the author indicates something of value received.
The codes are identified as a-research or institutional support; b-miscellaneous
funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts
disclosed, and *disclosure not available at time of printing.
·
The FDA has not cleared this drug and/or medical device for the use
described in this presentation (i.e., the drug or medical device is being
discussed for an "off label" use). · · FDA
information not available at time of printing.