Bone adaptation compensates resorption when sciatic neurectomy is followed by low magnitude induced loading

Area of Science:

• Bone biology and mechanobiology
• Skeletal adaptation to mechanical loading
• Neural injury and bone loss

Background:

• Uniaxial tibial loading promotes bone formation via mechanoadaptation.
• Sciatic neurectomy induces bone loss by recruiting osteoclasts.
• High-magnitude loading combined with neurectomy increases bone formation.

Purpose of the Study:

• To determine if low-intensity loading maintains bone mass after sciatic neurectomy.
• To investigate if low-intensity loading promotes bone formation or prevents bone resorption.
• To understand the effects of low-magnitude, few-cycle loading on bone adaptation post-neurectomy.

Main Methods:

• Four groups of mice: sham surgery with 10 N loading, sham surgery with 5 N loading, sciatic neurectomy, and sciatic neurectomy with 5 N loading.
• Micro-computed tomography (micro-CT) to assess bone cross-sectional properties and marrow area.
• Histomorphometric analysis to evaluate bone formation and resorption at the mid-tibial diaphysis.

Main Results:

• 10 N loading significantly increased bone mass; 5 N loading effects were not detectable by micro-CT.
• Sciatic neurectomy alone caused significant bone loss.
• Combined sciatic neurectomy and 5 N loading prevented significant bone loss.
• 5 N loading increased periosteal bone formation and reduced endosteal osteoclasts.
• Combined neurectomy and 5 N loading accelerated periosteal mineral apposition and augmented endosteal resorption.

Conclusions:

• Low-intensity loading (5 N) is sufficient to maintain bone mass after sciatic neurectomy.
• This maintenance occurs by preventing osteoclast recruitment and compensating for disuse-induced resorption with periosteal formation.
• Findings have implications for mechanical loading strategies to preserve bone mass after injury or prolonged inactivity.