Tuesday, January 13, 2009

Fracture Risk during puberty and why?

Kirmani S, Christen D, van Lenthe GH, et al. Bone Structure at the Distal Radius During Adolescent Growth. J Bone Miner Res. 2008. Available at: http://www.ncbi.nlm.nih.gov/pubmed/19113916 [Accessed January 13, 2009].

In conference today Dr. Kirmani presented his data on the topic of increased fractures in puberty. He noted that in reviewing data gathered over the last 4-5 decades by the Mayo Clinic, there is an increase in fractures during puberty in both boys and girls. Overall, the frequency of fractures is also increasing over this time period.

In order to study this, the group looked at the distal radius (the most common site of fractures in this age group). They used a novel technique of high-res QCT to obtain images that were very close in detail to bone biopsy. By enrolling subjects in different age groups, they were able to gather data regarding the changes that take place in terms of bone.

As seen in the figure, the cortical portion of the bone becomes the weakest during puberty as bone growth occurs. This may be due a delay in the formation of cortical bone as opposed to trabecular bone as overall lengthening occurs. The reasons behind this are unknown but many in the audience suggested a local action of PTH in serving up cortical bone as a source of calcium (similar to that seen in breast feeding).

Regardless of the etiology, due to the lenghtening process without adequate thickening, the bone strength is approximately 1/8 that of the original bone thus leading to increase fractures.


  1. Did they comment on whether the environment was affecting this change? Are there demographic data with these changes? What about the hormone levels?

  2. Absolutely great points. They do feel the the environment may be contributing. One the kids are more obese now and just putting more strain on the bone with a fall. Due to the general prevalence of inactivity, the kids are less coordinated and maybe more prone to falling as well when they do participate in physical activity. There are epidemilogic studies for Omstead County (where the Mayo Clinic is located) published by Dr. Khosla showing an increase in fractures but I think the population is not as diverse here as you may find in Los Angeles. The hormone issue will be addressed in their next project, but they did emphasize that this may all be a local effect and not really detectable in serum.

  3. Along those lines, but from a different perspective, could an increase in activity level (specifically kids in competitive sports for whom the training in some cases has become extremely rigorous) also be contributing to the increased fracture rate.


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