Initiation and progression of rotator cuff tears due to fatigue loading: a cadaveric study

Figures

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  Figure 1. Representative setup for mechanical testing, with the red arrow delineating force direction

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  Figure 2. Example of the measured mechanical data throughout fatigue loading showing the stiffness (A) and strain (B) throughout the tendon's life cycle. Blue curves represent the average of all specimens fit to a quadratic polynomial (R2 = 0.83 and R2 = 0.87 for stiffness and strain, respectively). Filled grey area represents the standard deviation across all specimens. The life cycle is split into 2 regions, where 0-1 represents pretear mechanics and 1-2 represents post-tear mechanics.

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  Figure 3. Example of serial images tracking the initiation and progression of a tear due to fatigue loading, where (A) shows a left shoulder and the first image a tear is seen identified by the white dot showing the center of the tear. (B) Progression of the tear due to fatigue loading, where we see the tear has visibility increased in both the anterior – posterior (AP) and medial – lateral (ML) planes. (C) Results from all cadaveric experiments plotting the location of tear initiation relative to the anterior edge of the supraspinatus tendon. White outline shows the area of the critical zone within the supraspintus tendon, which is approximately 13 mm in the AP direction and 13 mm in the ML direction.26 Scale base was determined by taking the average width of the supraspinatus tendons tested and generating the mm/pix of the image to plot the precise locations for tear initiation.

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  Figure 4. Serial images tracking the tear progression in a cadaveric supraspinatus tendon (A), showing the increase in tear size throughout the tendons fatigue life. Images reveal the tendon fibers in the mid-substance, as the tear progresses and as the tendon pulls away from the humeral and resulting in a tear. A cartoon version (B) using the measured AP and ML tear dimensions is also shown to help show the progression of RC tears. AP, anterior-posterior; ML, medial-lateral; RC, rotator cuff.

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  Figure 5. Progression of supraspinatus tendon tear size during fatigue loading. (A) Changes in the AP and ML tear size during fatigue loading. (B) Changes in tear area during fatigue loading. (C) Relationship between AP and ML tear size. AP, anterior-posterior; ML, medial-lateral.

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  Figure 6. Relationship between the progression of supraspinatus tendon tear area and the damage accumulation. (A) Relationship between changes in tendon stiffness and tear area. (B) Relationship between changes in nominal strain and tear area. (C) Relationship between the effects of damage accumulation on stiffness and nominal strain.

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  Figure 7. Total damage based on various tear sizes for (A) stiffness damage coefficient and (B) strain damage coefficient.