NASA Human Research Program Investigators' Workshop (2012)
4265.pdf
Investigation of Countermeasures for Long Bone Fracture Healing in Hypogravity
C. Androjna1, S. Warden2, N.P. McCabe1, D. Burr3, H.Z. Ke4, and R.J. Midura1
1
2
Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195
Department of Physical Therapy, School of Health and Rehabilitation Sciences, Indiana University, Indianapolis, IN 46202
3
Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202
4
Amgen Inc., Thousand Oaks, CA 91320
STUDY OBJECTIVE:
Two systemically delivered bone-anabolic drugs (parathyroid hormone (PTH) peptide or sclerostin monoclonal
antibody (SAB)), and the anabolic biophysical modality low intensity pulsed ultrasound (LIPUS) are being
examined as potential treatments to augment femoral-healing responses in hind-limb unloaded (HLU) adult rats.
These particular countermeasure approaches are practical and might be used during a space mission to augment
fracture healing.
METHODS:
Simulated weightlessness was modeled using a conventional HLU protocol in female Sprague-Dawley rats (6-7
months old, 300 ± 50 g BW) [1]. All rats were subjected to 4-wks HLU prior to femoral fracture surgery. At 4-wks,
a state of osteopenia was confirmed via micro-CT assessment for losses in trabecular bone content within the
proximal tibia. All rats were then subjected to bilateral, closed femoral fractures [2]. HLU rats were randomized into
one of 4 treatment groups: PTH - PTH treatment at a dosage of 40 μg/kg body weight (BW) 1X per day, 5 days per
wk; SAB - SAB treatment at a dosage of 25 mg/kg BW 2X per wk; HLU - vehicle solution control; LIPUS - for
each rat, one limb was treated with LIPUS at intensity 30 mW/cm2 5 days per wk, 20 mins per day while the other
limb served as a control. All treatments began 1-day after fracture and continued throughout the 10-wk healing
period; note that HLU conditions were maintained as well. Femora were scanned during the 10-wk period using in
vivo micro-computed tomography (micro-CT) or planar x-ray imaging to determine the extent of fracture repair.
RESULTS:
Visual inspections of the 3-D femoral volumes indicate that callus size (volumes) do not appear to be significantly
different among the groups over the 10-wk healing period. However, full bridging across the fracture gap was
observed by week 5 in the PTH, SAB and LIPUS treatment groups (Figure 1 and 2). Full bridging was designated
only if both cortices were assessed as bridged in a planar view (2D). By week 10, all groups appeared to be
adequately bridged with fracture callus bone content appearing significantly enhanced in the PTH, SAB, and LIPUS
groups as compared to the non-treated HLU. Quantitative assessments are underway to determine hard callus
formation rate, maximum callus volume, extent of bridging across the fracture site, structural integrity, overall callus
strength and static histomorphometry.
CONCLUSIONS:
Both PTH and LIPUS therapies have been shown to enhance the endochondral healing response of femoral fractures
under normal gravity conditions [3, 4]. Our initial observations indicate that the femoral fracture healing response of
treated HLU rats parallels that of the ground based studies and appears to accelerate the fracture healing response
early on. SAB therapy has also been shown to demonstrate a potent bone-building capacity in rats exhibiting
estrogen-depletion osteoporosis and to enhance bone healing responses [5, 6]. Thus, this study’s observations,
together with previous results indicate that SAB, PTH or LIPUS treatment likely increases fracture healing
responses in hypogravity.
Figure 1: Representative cross-sectional micro-CT views (anterior to posterior),
of animals treated with PTH and SAB 1-day and 5-wks post surgery.
Figure 2: Representative planar x-rays of animals
treated with LIPUS 1-day and 5-wks post surgery.
REFERENCES
[1] Morey-Holton E, et al. (2005) Adv Space Biol Med 10, 7-40; [2] Bonnarens F, Einhorn TA. (1984) J Orthop Res 2(1), 97-101; [3] Kakar, S.,
et al (2007) J Bone Mineral Res 22, 1903-1912; [4] Warden, SJ, et al. (2006) Physical Therapy 86, 1118-1127; [5] Tian, XY, et al. (2011) Bone
48, 197-201; [6] Ominsky, MS, et al. (2011) J Bone Miner Res. 26(5), 1012-21.