J
james3637
Iron
- Joined
- Sep 2, 2025
- Posts
- 242
- Reputation
- 185
I’ve been looking into the actual mechanics of Limb Lengthening (LL) surgery vs. all the non-surgical "methods" people talk about, and I want to get your thoughts on the physics behind LSJL (Lateral Synovial Joint Loading).
Most people here disregard it, but if you look at the Zhang et al. study, the mechanism isn't about "crushing" the bone; it’s about fluid dynamics.
The Theory:
We know Wolff's Law says vertical compression makes bone denser/wider. That's why sprinting usually just gives you high bone density, not length.
But the LSJL logic seems to rely on the fact that Bone Marrow is a liquid.
Liquids are incompressible.
If you apply heavy lateral compression to the Epiphysis (the spongy end of the bone, not the shaft), you are essentially reducing the volume of the trabecular meshwork. Since the marrow can't shrink, that internal hydrostatic pressure has to go somewhere. The theory implies that because you are clamping the sides, the fluid pressure forces the bone matrix to expand vertically (Longitudinally) to relieve the stress.
It’s basically the hydraulic press principle.
The Biological Trigger (Stem Cells):
This is the part I find interesting. The literature suggests that Mesenchymal Stem Cells (MSCs) inside the marrow differentiate based on mechanical signals:
Tension = Muscle/Tendon
Compression = Bone Density
Fluid Shear Stress / Hydrostatic Pressure = Chondrocytes (Cartilage)
So if you can generate enough lateral pressure to create that fluid shear, you technically trigger Endochondral Ossification (turning cartilage to bone) from the inside out. You're trying to induce a "pseudo-growth plate" response in fused bone.
The Issue / Discussion:
The mechanism makes sense on paper and worked in rats, but the scaling to humans seems to be the problem. A human femur is incredibly thick compared to a rat bone.
To get that specific "Fluid Shear" signal deep in the marrow, the clamping force required might be higher than what the skin/soft tissue can handle before necrosis sets in.
My question to the high IQ guys here:
Is the failure of LSJL in humans just an engineering issue? Most people just use a weak C-clamp and stop because of skin pain. But if we could engineer a rig that creates that specific internal pressure pulse without destroying the skin, does the biology theoretically hold up for adult height gain?
It seems like this is the only method that mimics the biochemical cascade of surgery (growth factors + pressure) without actually breaking the bone.
Thoughts?
Most people here disregard it, but if you look at the Zhang et al. study, the mechanism isn't about "crushing" the bone; it’s about fluid dynamics.
The Theory:
We know Wolff's Law says vertical compression makes bone denser/wider. That's why sprinting usually just gives you high bone density, not length.
But the LSJL logic seems to rely on the fact that Bone Marrow is a liquid.
Liquids are incompressible.
If you apply heavy lateral compression to the Epiphysis (the spongy end of the bone, not the shaft), you are essentially reducing the volume of the trabecular meshwork. Since the marrow can't shrink, that internal hydrostatic pressure has to go somewhere. The theory implies that because you are clamping the sides, the fluid pressure forces the bone matrix to expand vertically (Longitudinally) to relieve the stress.
It’s basically the hydraulic press principle.
The Biological Trigger (Stem Cells):
This is the part I find interesting. The literature suggests that Mesenchymal Stem Cells (MSCs) inside the marrow differentiate based on mechanical signals:
Tension = Muscle/Tendon
Compression = Bone Density
Fluid Shear Stress / Hydrostatic Pressure = Chondrocytes (Cartilage)
So if you can generate enough lateral pressure to create that fluid shear, you technically trigger Endochondral Ossification (turning cartilage to bone) from the inside out. You're trying to induce a "pseudo-growth plate" response in fused bone.
The Issue / Discussion:
The mechanism makes sense on paper and worked in rats, but the scaling to humans seems to be the problem. A human femur is incredibly thick compared to a rat bone.
To get that specific "Fluid Shear" signal deep in the marrow, the clamping force required might be higher than what the skin/soft tissue can handle before necrosis sets in.
My question to the high IQ guys here:
Is the failure of LSJL in humans just an engineering issue? Most people just use a weak C-clamp and stop because of skin pain. But if we could engineer a rig that creates that specific internal pressure pulse without destroying the skin, does the biology theoretically hold up for adult height gain?
It seems like this is the only method that mimics the biochemical cascade of surgery (growth factors + pressure) without actually breaking the bone.
Thoughts?
