Histological and molecular features of the subacromial bursa of rotator cuff tears compared to non-tendon defects: a pilot study

Abstract

Background The role of the subacromial bursa in the development or healing of shoulder pathologies is unclear. Due to this limited knowledge, we aimed to understand specific reactions of the subacromial bursa according to rotator cuff (RC) pathologies compared to non-tendon defects of the shoulder. We hypothesized that the tissue composition and inflammatory status of the bursa are likely to vary between shoulder pathologies depending on the presence and the extent of RC lesion. Method Bursa samples from patients with either 1) shoulder instability with intact RC (healthy bursa, control), 2) osteochondral pathology with intact RC, 3) partial supraspinatus (SSP) tendon tear, or 4) full-thickness SSP tear were investigated histologically and on gene expression level. Result Bursae from SSP tears differed from non-tendon pathologies by exhibiting increased chondral metaplasia and TGFβ1 expression. MMP1 was not expressed in healthy bursa controls, but strongly increased with full-thickness SSP tears. Additionally, the expression of the inflammatory mediators IL1β, IL6, and COX2 increased with the extent of SSP tear as shown by correlation analysis. In contrast, increased angiogenesis and nerve fibers as well as significantly upregulated IL6 and COX2 expression were features of bursae from patients with osteochondral pathology. Using immunohistochemistry, CD45+ leukocytes were observed in all examined groups, which were identified in particular as CD68+ monocytes/macrophages. Conclusion In summary, besides the strong increase in MMP1 expression with SSP tear, molecular changes were minor between the investigated groups. However, expression of pro-inflammatory cytokines correlated with the severity of the SSP tear. Most pronounced tissue alterations occurred for the osteochondral pathology and full-thickness SSP tear group, which demonstrates that the bursal reaction is not exclusively dependent on the occurrence of an SSP tear rather than longstanding degenerative changes. The present bursa characterization contributes to the understanding of specific tissue alterations related to RC tears or non-tendon shoulder pathologies. This pilot study provides the basis for future studies elucidating the role of the subacromial bursa in the development or healing of shoulder pathologies.

Contribution of pathogenic T helper 1 and 17 cells to bursitis and tenosynovitis in polymyalgia rheumatica

“…Control bursa tissue was not included in the current study. However, prior reports indicate that normal SASD bursa tissue only contains sporadic leukocytes located around small vessels, with most of these cells being macrophages rather than T cells ( 52 , 53 ). T cells were only rarely detected in the SASD bursa tissue of patients with rotator cuff disease ( 54 ).…”

Subacromial Bursa: A Neglected Tissue Is Gaining More and More Attention in Clinical and Experimental Research

“…However, inflammatory leukocyte cell infiltrates were not identified as a common phenomenon [ 51 ]; whereas later on, others reported on the presence of T-lymphocytes and monocytes/macrophages in patients with impingement syndrome and pain at rest but not in patients experiencing pain only during movement [ 52 ]. Currently, it is not debatable that immune cells are a relevant cell type in subacromial bursa tissue, which is not only the case in pathological conditions but also in healthy bursae to a lesser extent [ 53 ]. This seems to indicate that the bursa can serve as a reservoir for relevant immune cell populations.…”

“…Therefore, the authors postulated the early removal of the subacromial bursa for better healing outcomes [ 71 ]. However, recently, no differences in BMP-2 expression were found in bursa tissue of healthy donors compared to different shoulder pathologies including partial and full-thickness SSP tear [ 53 ]. The presence of pro-inflammatory cytokines and cells in the bursa tissue often lays the basis for a negative association of the subacromial bursa in rotator cuff repair.…”

“…The presence of pro-inflammatory cytokines and cells in the bursa tissue often lays the basis for a negative association of the subacromial bursa in rotator cuff repair. It has been described that inflammatory cytokines, such as SDF-1, IL-1β, TNF-α, TGF-β, and IL-6 as well as pain-associated mediators (cyclooxygenase 1 (COX-1) and 2) and proteolytic enzymes (matrix metalloproteases (MMPs)) are increased in subacromial bursae from patients with rotator cuff tear or frozen shoulder compared to healthy controls [ 14 , 53 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ]. Most authors postulated from this result that a partial bursectomy is necessary during rotator cuff surgery to reduce pain and inflammation and, thus, improve rotator cuff repair.…”

The Role of the Subacromial Bursa in Rotator Cuff Healing

“…It is reasonable to speculate that this vasculature is essential in cellular infiltration and debris clearance during the inflammatory response to rotator cuff injury. The bursa even undergoes observable phenotypic changes toward fibrous, fatty, and/or vascular matrix that progress as rotator cuff pathology advances to a full-thickness tear 56 . Taken together, these observations of bothersome pain, inflammation, reparative healing, cellularity, regeneration, vascularity, and phenotypic changes during pathogenesis suggest that this tissue may have a more expansive role in rotator cuff pathology than we previously understood (Fig.…”