A novel method for bone fatigue monitoring and prediction

Abstract

Bone fatigue, often manifest as stress fractures, is a common injury that plagues many individuals, adversely affect quality of life, and is an obstacle to extended human spaceflight. This manuscript details a pilot study that was conducted to determine if the Phase Space Warping (PSW) methodology could be used to monitor/predict fatigue failure in bone tissue. A Moon's beam experimental apparatus was used to perform variable amplitude fatigue tests on bovine bone specimens. Scanning electron microscopy was used to evaluate the fracture surface and identify the fracture type. The PSW method allowed for successful identification of the various damage modes and may lead to the development of a viable tool for predicting the health and fatigue life of bone.

Keywords: 00-01; 99-00; Bone fatigue; Bone health monitoring; Dynamical systems; Stress fractures.

Fig. 1

Shaker system testing apparatus: (a) VTS-100 shaker (b) Nexus breadboard (c) 8 in aluminum connector piece (d) aluminum C-frame (e) specimen pendulum (f) LJ-V7300 Keyence laser vibrometer (g) aluminum laser stand (h) Neodymium rare earth magnets or electromagnets (i) aluminum linear guide conversion piece (j) AC-NMS-4 linear guide (Cler, 2016).

Fig. 2

Diagram depicting the location and alignment of the specimens within the bone, where the lateral side of the bone is to the left and the medial side is to the right.

Fig. 3

(a) The direction of brittle fracture propagation was through the thickness of the specimen and delamination was apparent. (b) The direction of ductile fracture propagation was across the width of the specimen and beach marking was apparent. (c) Combination fracture surfaces displayed regions that failed by ductile fracture and regions that failed by brittle fracture. Ductile fracture occurred first until the specimen failed by fast brittle fracture.

Fig. 4

SEM images of different fracture mechanisms. Upper left: A indicates brittle delamination. Upper right: A indicates ductile beach markings and B indicates osteon pullout. Lower left: A indicates beach markings and B indicates delaminations. Lower right: A indicates delamination, B indicates beach markings and C indicates osteon pullout.

Fig. 5

PSW calculated SOVs (eigenvalues) for each specimen.

Fig. 6

PSW calculated SOCs for each specimen. Lines are colored and textured such that the leading SOV is plotted with a black line, second SOV with a red line, third black dotted, fourth red dotted, fifth black diamond, and sixth red diamond. Only those SOCs with structure distinguishable from noise are plotted. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)