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The development of metaphyseal cortex--implications for distal radius fractures during growth
Insights
Pediatric distal radius fractures are common because bone strength development lags behind mechanical challenges. During growth, the radius
Area of Science:
- Orthopedics
- Pediatric Bone Health
- Biomechanics
Background:
- Distal radius fractures are highly prevalent in children, yet the underlying developmental reasons remain unclear.
- Understanding bone development is crucial for addressing pediatric fracture incidence.
Purpose of the Study:
- To analyze distal radius development in children and adolescents.
- To investigate the relationship between bone strength and mechanical challenges during growth.
Main Methods:
- Peripheral quantitative computed tomography (pQCT) was used to assess bone density and dimensions in 337 children/adolescents and 107 adults.
- Cortical thickness, volumetric bone mineral density (vBMD), and Strength-Strain Index (SSI) were measured.
- Metaphyseal inwaisting was analyzed in a separate cohort of 44 children.
Main Results:
- Bone strength parameters (vBMD, cortical thickness, SSI) in children significantly lagged behind adult values.
- Mechanical challenge factors like forearm length and body weight increased substantially relative to bone strength.
- Endocortical apposition rates were high (10 microm/day) but insufficient to compensate for inadequate cortical thickening.
Conclusions:
- The increase in distal radius strength during childhood growth does not keep pace with escalating mechanical demands from falls.
- Insufficient metaphyseal cortical thickness development is a key factor contributing to this imbalance.
- The high endocortical apposition rate suggests limited potential for further adaptation to meet mechanical requirements.
Abstract:
Fractures of the distal radial metaphysis are very common in otherwise healthy children. The reasons for this high fracture incidence are not entirely clear. To address this problem, we undertook a detailed analysis of distal radius development using peripheral quantitative computed tomography (pQCT) at a site 4% proximal to the radial articular surface. The study population comprised 337 healthy children and adolescents (aged 6-18 years; 171 girls) and 107 adults (aged 29-40 years; 88 women). Total volumetric bone mineral density (vBMD) remained stable at about 70% of the adult value between the ages of 6-7 years and 14-15 years in both genders. Cortical thickness increased little between 6-7 years and 12-13 years in girls and 14-15 years in boys. Strength-Strain Index (SSI; a parameter combining geometry and density) was still at only 20% of the adult value in girls aged 10-11 years and at 21% of the adult level in boys aged 12-13 years. At these ages, factors that contribute to the mechanical challenge to the distal radius in case of a fall (forearm length and body weight) had already reached 49% and 36% of the adult value in girls and boys, respectively. The shaping of the distal radius cortex (metaphyseal inwaisting) was assessed by analyzing the decrease in cross-sectional bone size between adjacent bone slices in a separate population of 44 children (aged 8-19 years; 26 girls). The rates of periosteal resorption and endocortical apposition were estimated to average 8 microm/day and 10 microm/day, respectively, during the growth period. In conclusion, during growth the increase in distal radius strength lags behind the increase in mechanical challenges caused by a fall, because metaphyseal cortical thickness does not increase sufficiently. The endocortical apposition rate is already very high at that site and apparently cannot be further increased to levels that would be necessary to keep bone strength adapted to the mechanical requirements.