Micro and macroarchitectural changes at the tibia after botulinum toxin injection in the growing rat

Area of Science:

• Orthopedics
• Translational Research
• Animal Models

Background:

• Disuse atrophy significantly impacts bone development and structure.
• Understanding the effects of muscle paralysis on growing bone is crucial for pediatric orthopedic conditions.

Purpose of the Study:

• To investigate the impact of unilateral muscle paralysis on tibia microarchitecture and macroarchitecture in growing rats.
• To establish a reliable murine model for studying disuse-induced bone changes.

Main Methods:

• Eight-week-old rats received Botulinum toxin (BTX) injection in the right quadriceps muscle, with saline injection in the left hind limb as control.
• Muscle surface area and tibia microarchitecture/macroarchitecture (length, width, curvature) were analyzed using microtomography at various time points (Day 1, 14, 21, 28, 35).

Main Results:

• BTX injection induced rapid paralysis and significant muscle atrophy in the right hind limb.
• The right tibia showed decreased trabecular bone volume and cortical thickness, with increased cortical porosity starting at Day 14.
• While tibia length growth was unaffected, the diaphyseal cross-section became more rounded, indicating reduced width growth.

Conclusions:

• Unilateral muscle paralysis in growing rats leads to rapid muscle loss and detrimental effects on bone width and structure.
• Tibia length and curvature are resilient to disuse-induced changes in this model.
• This study provides valuable insights into bone adaptation during growth under conditions of muscle disuse.