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Strains caused by daily loading might be responsible for delayed healing of an incomplete atypical femoral fracture

Gustafsson, Anna LU ; Schilcher, Jorg; Grassi, Lorenzo LU ; Aspenberg, Per and Isaksson, Hanna LU (2016) In Bone
Abstract
Atypical femoral fractures are insufficiency fractures in the lateral femoral diaphysis or subtrochanteric region that mainly affect older patients on bisphosphonate therapy. Delayed healing is often seen in patients with incomplete fractures (cracks), and histology of bone biopsies shows mainly necrotic material inside the crack. We hypothesized that the magnitude of the strains produced in the soft tissue inside the crack during normal walk exceeds the limit for new bone formation, and thereby inhibit healing.

A patient specific finite element model was developed, based on clinical CT images and high resolution μCT images of a biopsy from the crack site. Strain distributions in the femur and inside the crack were calculated for... (More)
Atypical femoral fractures are insufficiency fractures in the lateral femoral diaphysis or subtrochanteric region that mainly affect older patients on bisphosphonate therapy. Delayed healing is often seen in patients with incomplete fractures (cracks), and histology of bone biopsies shows mainly necrotic material inside the crack. We hypothesized that the magnitude of the strains produced in the soft tissue inside the crack during normal walk exceeds the limit for new bone formation, and thereby inhibit healing.

A patient specific finite element model was developed, based on clinical CT images and high resolution μCT images of a biopsy from the crack site. Strain distributions in the femur and inside the crack were calculated for load cases representing normal walk. The models predicted large strains inside the crack, with strain levels above 10% in more than three quarters of the crack volume. According to two different tissue differentiation theories, bone would only form in less than 1–5% of the crack volume. This can explain the impaired healing generally seen in incomplete atypical fractures. Furthermore, the microgeometry of the crack highly influenced the strain distributions. Hence, a realistic microgeometry needs to be considered when modeling the crack. Histology of the biopsy showed signs of remodeling in the bone tissue adjacent to the fracture line, while the crack itself contained mainly necrotic material and signs of healing only in portions that seemed to have been widened by resorption.

In conclusion, the poor healing capacity of incomplete atypical femoral fractures can be explained by biomechanical factors, and daily low impact activities are enough to cause strain magnitudes that prohibit bone formation.
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Contribution to journal
publication status
published
subject
in
Bone
publisher
Elsevier
external identifiers
  • scopus:84965115268
  • wos:000377925100015
ISSN
8756-3282
DOI
10.1016/j.bone.2016.04.020
language
English
LU publication?
yes
id
26a9c678-4f57-4756-9438-9c19ba3b062b
date added to LUP
2016-04-25 10:43:22
date last changed
2017-08-06 05:06:27
@article{26a9c678-4f57-4756-9438-9c19ba3b062b,
  abstract     = {Atypical femoral fractures are insufficiency fractures in the lateral femoral diaphysis or subtrochanteric region that mainly affect older patients on bisphosphonate therapy. Delayed healing is often seen in patients with incomplete fractures (cracks), and histology of bone biopsies shows mainly necrotic material inside the crack. We hypothesized that the magnitude of the strains produced in the soft tissue inside the crack during normal walk exceeds the limit for new bone formation, and thereby inhibit healing.<br/><br/>A patient specific finite element model was developed, based on clinical CT images and high resolution μCT images of a biopsy from the crack site. Strain distributions in the femur and inside the crack were calculated for load cases representing normal walk. The models predicted large strains inside the crack, with strain levels above 10% in more than three quarters of the crack volume. According to two different tissue differentiation theories, bone would only form in less than 1–5% of the crack volume. This can explain the impaired healing generally seen in incomplete atypical fractures. Furthermore, the microgeometry of the crack highly influenced the strain distributions. Hence, a realistic microgeometry needs to be considered when modeling the crack. Histology of the biopsy showed signs of remodeling in the bone tissue adjacent to the fracture line, while the crack itself contained mainly necrotic material and signs of healing only in portions that seemed to have been widened by resorption.<br/><br/>In conclusion, the poor healing capacity of incomplete atypical femoral fractures can be explained by biomechanical factors, and daily low impact activities are enough to cause strain magnitudes that prohibit bone formation.<br/>},
  author       = {Gustafsson, Anna and Schilcher, Jorg and Grassi, Lorenzo and Aspenberg, Per and Isaksson, Hanna},
  issn         = {8756-3282},
  language     = {eng},
  month        = {04},
  publisher    = {Elsevier},
  series       = {Bone},
  title        = {Strains caused by daily loading might be responsible for delayed healing of an incomplete atypical femoral fracture},
  url          = {http://dx.doi.org/10.1016/j.bone.2016.04.020},
  year         = {2016},
}