Muscle changes can account for bone loss after botulinum toxin injection

Area of Science:

• Orthopedics and Regenerative Medicine
• Skeletal Biology and Musculoskeletal Research

Background:

• Botulinum toxin type A (BTX) is widely believed to affect bone indirectly via muscle interactions.
• Previous research has not fully elucidated the direct impact of BTX on bone morphometry independent of muscle effects.

Purpose of the Study:

• To investigate if BTX has an independent effect on bone morphometry beyond its impact on muscle.
• To compare the effects of BTX combined with tenotomy versus tenotomy alone on bone and muscle.

Main Methods:

• Female BALB/c mice (n=73) were divided into four groups: BTX injection with Achilles tenotomy (BTX-TEN), BTX injection with sham surgery (BTX-sham), Achilles tenotomy (TEN), and sham surgery.
• Muscle cross-sectional area (MCSA) and tibial bone morphometry were assessed using micro-CT at 4 weeks post-procedure.
• Statistical analyses were performed to compare outcomes between groups and after adjusting for MCSA.

Main Results:

• All treatments except sham surgery led to significant muscle and bone loss (P < 0.05).
• The BTX-TEN group exhibited the most substantial muscle and bone loss compared to other groups.
• While BTX-sham showed reduced MCSA and bone volume fraction compared to TEN and sham groups, these differences became insignificant after accounting for MCSA.

Conclusions:

• BTX injection exacerbated muscle and bone loss, with combined effects amplified when paired with tenotomy.
• The observed bone morphometry changes are primarily attributable to muscle loss (MCSA), suggesting a minimal independent effect of BTX on bone.
• The direct impact of botulinum toxin type A on bone morphometry appears negligible compared to its effects on muscle function.