Sunday, February 14, 2010

Microfractures and growing taller

I thought this article had some instructional purposes even though it dealt with bone remodeling. Bone modeling some say may be one possible way to increase height(such as surface osteoblasts depositing new bone on the subchondral plate) but bone modeling can occur in ways that do not increase height such as a decrease in porosity or an increase in width of the periosteum(an increase in periosteal width can increase height if it is an increase in width on the flat bone of the skull).  Bone remodeling is mostly rejuvenating old bone with new bone whereas bone modeling changes the structure and shape of the bone.

Even though the article deals with bone remodeling it does mention some facts about microfracture healing.

Mathematical modeling of spatio-temporal dynamics of a single bone multicellular unit.

"During bone remodeling, bone-resorbing osteoclasts and bone-forming osteoblasts are organized in bone multicellular units (BMUs), which travel at a rate of 20-40 mum/d for 6-12 mo, maintaining a cylindrical structure. However, the interplay of local BMU geometry with biochemical regulation is poorly understood."

A bone multicellular unit is also known  as an osteon.

"We developed a mathematical model of BMU describing changes in time and space of the concentrations of proresorptive cytokine RANKL and its inhibitor osteoprotegerin (OPG), in osteoclast and osteoblast numbers, and in bone mass. We assumed that osteocytes surrounding a microfracture produce RANKL, which attracted osteoclasts"

Osteoclasts are essential for proper bone remodeling and bone growth.

"OPG and RANKL were produced by osteoblasts and diffused through bone, RANKL was eliminated by binding to OPG and RANK. Osteoblasts were coupled to osteoclasts through paracrine factors. The evolution of the BMU arising from this model was studied using numerical simulations. Our model recapitulated the spatio-temporal dynamics observed in vivo in a cross-section of bone. In response to a RANKL field, osteoclasts moved as a well-confined cutting cone. The coupling of osteoclasts to osteoblasts allowed for sufficient recruitment of osteoblasts to the resorbed surfaces. The RANKL field was the highest at the microfracture in front of the BMU[more osteoclasts were attracted to the front of the osteon, by front what's likely meant is away from the center of the bone], whereas the OPG field peaked at the back of the BMU[so more osteoblasts tended to propagate torwards the center of the bone], resulting in the formation of a RANKL/OPG gradient, which strongly affected the rate of BMU progression and its size."

Manipulating RANKL and OPG fields may eventually be a way to grow taller.  You could for example put two OPG fields at the top and bottom of the bone to grow taller that way.

A comparison of the fatigue behavior of human trabecular and cortical bone tissue.

"The results showed that trabecular specimens had significantly lower moduli and lower fatigue strength than cortical specimens, despite their higher mineral density values. Fracture surface and microdamage analyses illustrated different fracture and damage patterns between trabecular and cortical bone tissue, depending upon their microstructural characteristics."

It's easier to cause microfractures in cortical bone than trabecular bone.

Causing microfractures in the cortical bone is not quite related to the mechanostat theory of bone adaptation(the theory provides a model of how bone adapts to strain).  But the mechanstat theory provides us with a model of how much strain is needed to cause a fracture which is about 15000 units of strain.  1000 Units of Strain is a 0.1% change in length of the bone.  So if you were in a medievial rack you would need your bones to be pulled apart by 1.5% to cause a fracture.

According to wikipedia,  "The fracture load for axial forces of the Tibia for example is about 50 to 60 times the body weight."

Axial means along the transverse plane.

"The fracture load for forces perpendicular to the axial direction is about 10 times lower"

That load is about 5 to 6 times bodyweight which is still a lot more than people can lift(except in the leg press).

The load needed to cause cortical microfractures is unclear.

A possible experiment would be loaded hangs.  Measure the original length of the radius(a forearm bone).  And continue to hang with more attached weight until the length of the raidus increases by 1%.  Then perform an X-ray for microfracture.

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