Sunday, April 4, 2010

Lateral Synovial Joint Loading Performed on Rats(pictures)

Here's lateral synovial joint loading performed on mice by Turner, Yokota, and Zhang et al.  There's a piezoactuator involved but a piezoelectric current is automatically generated as a result of bone deformation.

Knee loading stimulates cortical bone formation in murine femurs

Any type of mechanical load will generate a piezoelectric force so we have a check on that category for the pec deck/adductor/abductor/dumbell version of LSJL.  Notice how big the screw is relative to the size of the mouse(4mm).  Notice how the ends of the bones are highlighted on both the tibia and the femur which emphasizes that the importance in LSJL is loading the ends of the bones not say loading the patella or the cartilage.    Now, doing LSJL my way doesn't involve the loader but the purpose of the loader is to generate that piezoelectric current which is present under any mechanical load.

The study states that loading was most effective at 15 Hz than the 5, 10, and 20 Hz that they tested at.  However, this study only tested periosteal apposition rate rather than longitudinal growth rate and we as height seekers can't really control what Hz we apply our loads at.  Now when applying the load to the mice they had to remove a part of the surrounding tissue but we mice aren't apply to obey the instructions of scientists as well as us humans can and we can adjust our joint surfaces but rotating our feet and other such measures.  In the lengthening of mouse hindlimbs study, they used 5 Hz.  Lower Hz may be more effective for growing taller whereas higher Hz may be better for building bone as a lower frequency may allow for more hydrostatic pressure.  The loading used was 0.1% of the weight of the femur.

"Femoral cross-sections with knee loading. (A) Cross-section of the loaded femur with 0.5 N forces at 15 Hz. The section was obtained from the mid-diaphysis. Scale bar = 200 μm. (B) & (C) Double-labeled periosteal surface of the loaded femur. Bright lines represent fluorescent calcein strips. Scale bar = 20 μm. (D) Fluorescence intensity along the line indicated in C. The distance between two lines, 3.8 μm in the diagram, indicates the newly formed bone in 4 days after 3 min loading per day for 3 consecutive days."

Now again in this study they were not yet testing for longitudinal growth but the amount required for appopositional growth probably correlates well for longitudinal growth.  Their are really only four scientists dedicated to studying LSJL at this point and it'll take a bunch of studies to hammer out what the optimal load and duration is but 3 minute loading is a pretty good baseline for testing longitudinal growth.  In the longitudinal growth study they performed it for 5 minutes.  15 Hz generates the same amount of force as about 0.5N which is what they used on the longitudinal study.

Here's some pictures about how LSJL increases intramedullary pressure:

Now it's the lateral compression force that causes the increase in intramedullary pressure(remember LSJL causes both a lateral compression force and a stretching longitudinal force).  Note the muscular contraction in the rats thus stating if you feel some muscular contraction while performing this(and you will) then it's okay.

Too bad we have no idea about what the equivalent of 0.5N would be in terms of dumbell load for humans.  I'm using 60 lbs right now and using free hands to push down for additional force.  I have no idea why 20 Hz would be less effective than 15 Hz(maybe it's only less effective for appopositional growth and not longitidual growth?) but it's probably best to veer on the side of more weight rather than less.  Although, too much weight makes it much harder to perform and ensure that the dumbell or pad(if performing the pec-deck way) is in the right spot to cause optimal loading at the ends of the long bones.

3-5 minutes is quite a long time if you pick a weight that you can perform for that duration of time than you are probably picking a pretty "safe" weight and one that is close to the optimal weight for increasing longitudinal bone growth.

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