Asynchronous muscle and tendon adaptation after surgical tensioning procedures

Area of Science:

• Biomedical Engineering
• Musculoskeletal Research
• Regenerative Medicine

Background:

• Tendon transfer surgery often involves significant muscle stretching beyond physiological limits.
• Limited understanding exists regarding muscle-tendon unit adaptation to extreme stretch, particularly in clinical scenarios.

Purpose of the Study:

• To investigate the adaptation of muscle and tendon following tendon transfer surgery in an animal model.
• To evaluate the timeline and nature of muscle-tendon unit response to supra-physiological stretch.

Main Methods:

• Utilized a rabbit model with extensor digitorum muscle transfer at a sarcomere length of 3.7 microm.
• Assessed muscle architecture (serial sarcomere number) and tendon properties (dimension, water content, cytokine levels) at multiple time points post-surgery.

Main Results:

• Observed a rapid, initial increase in serial sarcomere number within one week, followed by a paradoxical decrease towards baseline by eight weeks.
• Demonstrated significant tendon lengthening over eight weeks, indicating substantial adaptation to the imposed strain.
• Muscle adaptation (sarcomere number changes) preceded and occurred more rapidly than tendon adaptation.

Conclusions:

• This study is the first to report a biphasic adaptation pattern in serial sarcomere number post-tendon transfer.
• Muscle exhibits a faster adaptive response compared to tendon following surgical stretching.
• Highlights a complex, time-dependent interaction between muscle and tendon during recovery from tendon transfer.