Partial-width injuries of the rat rotator cuff heal with fibrosis

ABSTRACT

Purpose: Identify the healing outcomes following a partial-width, full-thickness injury to the rotator cuff tendon-bone attachment and establish if the adult attachment can regenerate the morphology of the healthy attachment.

Hypothesis: We hypothesized that a partial-width injury to the attachment would heal via fibrosis and bone remodeling, resulting in increased cellularity and extra-cellular matrix deposition, reduced bone volume (BV), osteoclast presence, and decreased collagen organization compared to shams.

Materials and Methods: A partial-width injury was made using a biopsy punch at the center one-third of the rat infraspinatus attachment. Contralateral limbs underwent a sham operation. Rats were sacrificed at 3 and 8 weeks after injury for analyses. Analyses performed at each time point included cellularity (Hematoxylin & Eosin), ECM deposition (Masson’s Trichrome), BV (micro-computed tomography; microCT), osteoclast activity (Tartrate Resistant Acid Phosphatase; TRAP), and collagen fibril organization (Picrosirius Red). Injured and sham shoulders were compared at both 3 and 8 weeks using paired, two-way ANOVAs with repeated measures (Sidak’s correction for multiple comparisons).

Results: Cellularity and ECM deposition increased at both 3 and 8 weeks compared to sham contralateral attachments. BV decreased and osteoclast presence increased at both 3 and 8 weeks compared to sham contralateral limbs. Collagen fibril organization was reduced at 3 weeks after injury compared to 3-week sham attachments.

Conclusions: These findings suggest that a partial-width injury to the rotator cuff attachment does not fully regenerate the native structure of the healthy attachment. The injury model healed via scar-like fibrosis and did not propagate into a full-width tear after 8 weeks of healing.

KEYWORDS:

• Collagen organization
• osteoclast
• rotator cuff healing
• tendon-bone attachment
• tendon injury

Acknowledgements

Special thanks to Terry Kokas, Histology Specialist III (Nemours-A.I. duPont Hospital for Children Histochemistry and Tissue Processing Core; supported by NIH-NIGMS: P20 GM103446 and the state of Delaware) and Crystal Idleburg, HT (ASCP) (Washington University Musculoskeletal Research Center, NIH NIAMS: P30 AR057235) for assistance with histology. The injury illustration (Figure 1A) was created by Katelyn McDonald, MA, CMI (Certified Medical Illustrator).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

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Additional information

Funding

This work was supported by the Delaware Space Grant Consortium [DESGC NNX15AI19H];National Center for Medical Rehabilitation Research [K12HD073945]; National Institute of General Medical Sciences [8 P20 GM103446-16]; University of Delaware Research Foundation [UDRF 16A01396]; Washington University Musculoskeletal Research Center (NIH P30 AR057235); Delaware Rehabilitation Institute (P30GM103333).