Histological and biochemical changes in a rat rotator cuff tear model with or without the subacromial bursa

Abstract

Abstract Background The subacromial bursa (SAB) plays an important role in the tendon healing process. Based on previous reports, co-culture of the rotator cuff (RC) and SAB have been shown to increase the expression of tendon-related genes and inflammatory cytokines, as well as to improve tensile strength in biomechanical evaluations. However, no studies have reported the nature of the biochemical changes occurring in vivo during tendon repair in the presence or absence of the SAB. In this study, we used a rat model of a full-thickness RC tear to determine how the presence or absence of the SAB alters the histological characteristics and gene expression in vivo in the injured RC. Methods The bilateral supraspinatus (SSP) tendons of rats were transected to create a full-thickness RC tear model. The right shoulder SAB was removed, and the left shoulder SAB was preserved. After 3 and 6 weeks, tissues were collected for histological (hematoxylin and eosin staining, Masson’s trichrome staining, immunohistochemistry) and real-time quantitative polymerase chain reaction (RT-qPCR) evaluations. Results Histological results revealed greater cell density (3 weeks), neovascularization within the repaired tendon (6 weeks), and tendon thickening (6 weeks) with SAB preservation. Immunostaining results revealed significant increases in type 3 collagen (COL3) expression at 6 weeks with SAB preservation. The RT-qPCR results showed that SAB preservation induced statistically significant increases in the expression of scleraxis, matrix metalloproteinase-13 (MMP-13), interleukin-1β (IL-1β), and inducible nitric oxide synthase (iNOS) at 3 weeks and significant increases in COL3, IL-10, and arginase-1 (Arg-1) at 6 weeks. Conclusion An RC tear undergoes more appropriate inflammatory and repair phases during the tendon repair process when the SAB is retained.