Seasonal Variation in Subscapularis Tendon Strain in Baseball Pitchers Assessed by Ultrasonography-based Analysis

Area of Science:

• Orthopedics
• Sports Medicine
• Biomechanics

Background:

• Rotator cuff tendon injuries are prevalent in baseball pitchers due to repetitive overhead motions.
• Current methods for monitoring tendon loading in vivo face technical challenges, particularly in the rotator cuff.
• Ultrasonography-based strain analysis offers a promising, non-invasive approach for assessing cumulative tendon stress.

Purpose of the Study:

• To develop and validate a novel ultrasonography-based strain analysis procedure for the subscapularis tendon.
• To test the hypothesis that regular-season pitching increases peak subscapularis tendon strain.
• To establish a practical tool for monitoring in-season tendon loading in pitchers.

Main Methods:

• Ultrasound image sequences of the subscapularis tendon were captured from nine pitchers during the preseason and regular season.
• Tendon displacement during the eccentric phase was quantified using optical flow tracking.
• The optical flow method was validated against NCORR software for accurate material deformation measurement.

Main Results:

• Peak subscapularis tendon strain was significantly higher during the regular season (18.7 ± 3.1%) compared to the preseason (8.8 ± 2.7%).
• This increase in strain suggests a heightened risk of microdamage and injury during the pitching season.
• The developed ultrasonography procedure demonstrated robustness and reliability.

Conclusions:

• Intense pitching activity during the season leads to elevated subscapularis tendon strain.
• Ultrasonography strain analysis is a valuable tool for tracking in-season tendon loading and identifying potential injury risks.
• The proposed method is practical, reliable, and easy to implement for clinical and research applications in baseball pitchers.