Mechanics and differential healing outcomes of small and large defect injuries of the tendon-bone attachment in the rat rotator cuff

ABSTRACT

Introduction

Rotator cuff tear size affects clinical outcomes following rotator cuff repair and is correlated with the risk of recurrent tendon defects. This study aimed to understand if and how the initial defect size influences the structural and mechanical outcomes of the injured rotator cuff attachment in vivo.

Methods

Full-thickness punch injuries of the infraspinatus tendon-bone attachment in Long Evans rats were created to compare differences in healing outcomes between small and large defects. Biomechanical properties, gross morphology, bone remodeling, and cell and tissue morphology were assessed at both 3- and 8-weeks of healing.

Results

At the time of injury (no healing), large defects had decreased mechanical properties compared to small defects, and both defect sizes had decreased mechanical properties compared to intact attachments. However, the mechanical properties of the two defect groups were not significantly different from each other after 8-weeks of healing and significantly improved compared to no healing but failed to return to intact levels. Local bone volume at the defect site was higher in large compared to small defects on average and increased from 3- to 8-weeks. In contrast, bone quality decreased from 3- to 8-weeks of healing and these changes were not dependent on defect size. Qualitatively, large defects had increased collagen disorganization and neovascularization compared to small defects.

Discussion

In this study, we showed that both large and small defects did not regenerate the mechanical and structural integrity of the intact rat rotator cuff attachment following healing in vivo after 8 weeks of healing.

KEYWORDS:

• healing
• attachment
• biomechanics
• animal model
• rotator cuff

Supplemental Material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/03008207.2022.2152334

Acknowledgements

We would like to thank Francis Karani for animal handling and Dr. Gwen Talham for veterinary care and Dawn Elliott for sharing access to mechanical testing equipment.

Author contributions

ALS, RCL, RK, and MLK designed the experiments. ALS, RCL, RK, and MLK acquired the data. All authors analyzed and interpreted the data. ALS, JEC, and MLK drafted the manuscript. RCL, RK, CCL, and JEC edited the manuscript. All authors have read and approved the final submitted manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Delaware Space Grant Consortium [NNX15AI19H], the UD Dare to be FIRST Research Experience for Undergraduates, the National Science Foundation Grant [1460757], the University of Delaware Doctoral Fellowship, the Eunice Kennedy Shriver National Institute of Child Health & Human Development of the National Institutes of Health [K12HD073945], and the National Institute of General Medical Sciences of the National Institutes of Health [P30GM103333].