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Published on: June 12, 2020
Compressive behaviour of child and adult cortical bone
Caroline Öhman1, Massimiliano Baleani, Carla Pani
1Laboratorio di Tecnologia Medica, Istituto Ortopedico Rizzoli, Bologna, Italy.
Insights
Pediatric cortical bone exhibits lower strength and stiffness than adult bone, primarily due to reduced ash density. However, yield strain remains consistent across age groups, indicating its invariant nature in bone tissue.
Area of Science:
- Orthopedics
- Biomechanical Engineering
- Materials Science
Background:
- Investigating pediatric cortical bone mechanical properties is challenging due to tissue scarcity.
- Understanding age-related bone differences is crucial for clinical applications and injury prevention.
Purpose of the Study:
- To compare the compressive mechanical behavior of pediatric and adult cortical bone.
- To determine the correlation between mechanical properties and ash density in both age groups.
- To test if yield strain is an invariant property regardless of age and density.
Main Methods:
- Cortical bone specimens were obtained from pediatric (4-15 years) and adult (22-61 years) donors.
- Compressive mechanical testing was performed at a strain rate of 0.1 s(-1).
- Specimens were analyzed for ash density, and mechanical properties (Young's modulus, yield stress, ultimate stress, ultimate strain) were calculated.
Main Results:
- Pediatric bone showed significantly lower Young's modulus (-34%), yield stress (-38%), ultimate stress (-33%), and ash density (-17%) compared to adults.
- Pediatric bone exhibited higher compressive ultimate strain (+24%).
- Ash density strongly correlated with tissue strength and stiffness (R(2) = 0.86-0.91) in both groups, and yield strain appeared invariant.
Conclusions:
- Pediatric cortical bone has distinct mechanical properties compared to adult bone, largely attributable to differences in ash density.
- Ash density is a reliable predictor of bone strength and stiffness across age groups.
- Compressive yield strain is a consistent biomechanical property, invariant to age and bone density.
Abstract:
In this study, cortical bone tissue from children was investigated. It is extremely difficult to obtain human child tissue. Therefore, the only possibility was to use bone tissue, free from any lesion, collected from young bone cancer patients. The compressive mechanical behaviour of child bone tissue was compared to the behaviour of adult tissue. Moreover, two hypotheses were tested: 1) that the mechanical behaviour of both groups is correlated to ash density; 2) that yield strain is an invariant. Small parts of the diaphysis of femora or tibiae from 12 children (4-15 years) and 12 adults (22-61 years) were collected. Cylindrical specimens were extracted from the cortical wall along the longitudinal axis of the diaphysis. A total of 107 specimens underwent compressive testing (strain rate: 0.1 s(-1)). Only the specimens showing a regular load-displacement curve (94) were considered valid and thereafter reduced to ash. It was found that the child bone tissue had significant lower compressive Young's modulus (-34%), yield stress (-38%), ultimate stress (-33%) and ash density (-17%) than the adult tissue. Conversely, higher compressive ultimate strain was found in the child group (+24%). Despite specimens extracted from both children and adults, ash density largely described the variation in tissue strength and stiffness (R(2)=in the range of 0.86-0.91). Furthermore, yield strain seemed to be roughly an invariant to subject age and tissue density. These results confirm that the mechanical properties of child cortical bone tissue are different from that of adult tissue. However, such differences are correlated to differences in tissue ash density. In fact, ash density was found to be a good predictor of strength and stiffness, also for cortical bone collected from children. Finally, the present findings support the hypothesis that compressive yield strain is an invariant.
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