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

The subacromial bursa modulates tendon healing after rotator cuff injury in rats

Rotator cuff injuries result in more than 500,000 surgeries annually in the United States, many of which fail. These surgeries typically involve repair of the injured tendon and removal of the subacromial bursa, a synovial-like tissue that sits between the rotator cuff and the acromion. The subacromial bursa has been implicated in rotator cuff pathogenesis and healing. Using proteomic profiling of bursa samples from nine patients with rotator cuff injury, we show that the bursa responds to injury in the underlying tendon. In a rat model of supraspinatus tenotomy, we evaluated the bursa's effect on the injured supraspinatus tendon, the uninjured infraspinatus tendon, and the underlying humeral head. The bursa protected the intact infraspinatus tendon adjacent to the injured supraspinatus tendon by maintaining its mechanical properties and protected the underlying humeral head by maintaining bone morphometry. The bursa promoted an inflammatory response in injured rat tendon, initiating expression of genes associated with wound healing, including Cox2 and Il6. These results were confirmed in rat bursa organ cultures. To evaluate the potential of the bursa as a therapeutic target, polymer microspheres loaded with dexamethasone were delivered to the intact bursae of rats after tenotomy. Dexamethasone released from the bursa reduced Il1b expression in injured rat supraspinatus tendon, suggesting that the bursa could be used for drug delivery to reduce inflammation in the healing tendon. Our findings indicate that the subacromial bursa contributes to healing in underlying tissues of the shoulder joint, suggesting that its removal during rotator cuff surgery should be reconsidered.

Rotator cuff tears

Rotator cuff tears are the most common upper extremity condition seen by primary care and orthopaedic surgeons, with a spectrum ranging from tendinopathy to full-thickness tears with arthritic change. Some tears are traumatic, but most rotator cuff problems are degenerative. Not all tears are symptomatic and not all progress, and many patients in whom tears become more extensive do not experience symptom worsening. Hence, a standard algorithm for managing patients is challenging. The pathophysiology of rotator cuff tears is complex and encompasses an interplay between the tendon, bone and muscle. Rotator cuff tears begin as degenerative changes within the tendon, with matrix disorganization and inflammatory changes. Subsequently, tears progress to partial-thickness and then full-thickness tears. Muscle quality, as evidenced by the overall size of the muscle and intramuscular fatty infiltration, also influences symptoms, tear progression and the outcomes of surgery. Treatment depends primarily on symptoms, with non-operative management sufficient for most patients with rotator cuff problems. Modern arthroscopic repair techniques have improved recovery, but outcomes are still limited by a lack of understanding of how to improve tendon to bone healing in many patients.

State transition and intercellular communication of synovial fibroblasts in response to chronic and acute shoulder injuries unveiled by single-cell transcriptomic analyses

PURPOSE

We aimed to investigate the heterogeneity of synovial fibroblasts and their potential to undergo cell state transitions at the resolution of single cells.

MATERIALS AND METHODS

We employed the single-cell RNA sequencing (scRNA-seq) approach to comprehensively map the cellular landscape of the shoulder synovium in individuals with chronic rotator cuff tears (RCTs) and acute proximal humerus fractures (PHFs). Utilizing unbiased clustering analysis, we successfully identified distinct subpopulations of fibroblasts within the synovial environment. We utilized Monocle 3 to delineate the trajectory of synovial fibroblast state transition. And we used CellPhone DB v2.1.0 to predict cell-cell communication patterns within the synovial microenvironment.

RESULTS

We identified eight main cell clusters in the shoulder synovium. Unbiased clustering analysis identified four synovial fibroblast subpopulations, with diverse biological functions associated with protein secretion, ECM remodeling, inflammation regulation and cell division. Lining, mesenchymal, pro-inflammatory and proliferative fibroblasts subsets were identified. Combining the results from StemID and characteristic gene features, mesenchymal fibroblasts exhibited characteristics of fibroblast progenitor cells. The trajectory of synovial fibroblast state transition showed a transition from mesenchymal to pro-inflammatory and lining phenotypes. In addition, the cross talk between fibroblast subclusters increased in degenerative shoulder diseases compared to acute trauma.

CONCLUSION

We successfully generated the scRNA-seq transcriptomic atlas of the shoulder synovium, which provides a comprehensive understanding of the heterogeneity of synovial fibroblasts, their potential to undergo state transitions, and their intercellular communication in the context of chronic degenerative and acute traumatic shoulder diseases.

Pro-Resolving Mediators in Rotator Cuff Disease: How Is the Bursa Involved?

So far, tendon regeneration has mainly been analyzed independent from its adjacent tissues. However, the subacromial bursa in particular appears to influence the local inflammatory milieu in the shoulder. The resolution of local inflammation in the shoulder tissues is essential for tendon regeneration, and specialized pro-resolving mediators (SPMs) play a key role in regulating the resolution of inflammation. Here, we aimed to understand the influence of the bursa on disease-associated processes in neighboring tendon healing. Bursa tissue and bursa-derived cells from patients with intact, moderate and severe rotator cuff disease were investigated for the presence of pro-resolving and inflammatory mediators, as well as their effect on tenocytes and sensitivity to mechanical loading by altering SPM signaling mediators in bursa cells. SPM signal mediators were present in the bursae and altered depending on the severity of rotator cuff disease. SPMs were particularly released from the bursal tissue of patients with rotator cuff disease, and the addition of bursa-released factors to IL-1β-challenged tenocytes improved tenocyte characteristics. In addition, mechanical loading modulated pro-resolving processes in bursa cells. In particular, pathological high loading (8% strain) increased the expression and secretion of SPM signaling mediators. Overall, this study confirms the importance of bursae in regulating inflammatory processes in adjacent rotator cuff tendons.

Preclinical assessment of IL-1β primed human umbilical cord mesenchymal stem cells for tendon functional repair through TGF-β/IL-10 signaling

Background

Inadequate repair capacity and disturbed immune compartments are the main pathological causes of tendinopathy. Transplantation of mesenchymal stem cells (MSCs) become an effective clinic option to alleviate tendinopathy. Interleukin-1β (IL-1β) could confer on MSCs enhanced immunoregulatory capability to remodel the repair microenvironment favoring tissue repair. Therefore, IL-1β activated UC-MSCs (1βUC-MSCs) may exert favorable efficacy in promoting tendon repair in a preclinical tendinopathy rat model.

Methods

Tendon-derived stem cells (TDSCs) were isolated and characterized. In vitro, the levels of immunoregulatory-related cytokines such as IL-1β, IL-6, IL-10, and TGF-β secreted by 1βUC-MSCs and unprimed UC-MSCs was measured. And tendon-specific markers expressed by TDSCs cultured with primed cultured medium (CM) or unprimed CM were detected. In vivo, Achilles tendinopathy was induced by 30 μL collagenase I injection in Sprague Dawley rats. One week later, the rats were randomly injected with UC-MSCs primed with IL-1β (106 cells per tendon), UC-MSCs, or PBS. After rats were sacrificed, histological evaluation, electron microscopy, biomechanical tests, gait performance were conducted to evaluate the structural and functional recovery of Achilles tendons. The inflammation and metabolic state of the extracellular matrix, and the potential mechanism were assessed by immunohistochemical staining and Western blot.

Results

UC-MSCs were activated by IL-1β to secrete higher levels of IL-10 and TGF-β while the secretion levels of IL-6 and IL-1β were not changed significantly, promoting a higher expression level of COL I and TNMD in TDSCs under proinflammatory environment. In vivo, the transplanted 1βUC-MSCs could survive up to 5 weeks after injection with tenogenic differentiation and improved tendon healing histologically semi-quantified by modified Bonar scores. This structural regeneration was further confirmed by observation of ultrastructural morphology, and led to good functional recovery including improved biomechanical properties and gait performance. During this process, the inflammatory response and metabolism of the extracellular matrix was improved through TGF-β/IL-10 pathway.

Conclusion

This study demonstrated that the transplantation of UC-MSCs activated by IL-1β exhibited satisfactory ability for promoting tendon functional repair in a tendinopathy rat model. During this process, the balance of inflammatory response and extracellular matrix metabolism was remodeled, and the TGF-β/Smad2/3 and IL-10 signaling pathways were activated simultaneously. We cautiously conclude that the IL-1β primed UC-MSCs could be a promising strategy for enhancing the ability of MSCs to treat tendinopathy.

The subacromial bursa is a key regulator of the rotator cuff and a new therapeutic target for improving repair

Rotator cuff injuries result in over 500,000 surgeries performed annually, an alarmingly high number of which fail. These procedures typically involve repair of the injured tendon and removal of the subacromial bursa. However, recent identification of a resident population of mesenchymal stem cells and inflammatory responsiveness of the bursa to tendinopathy indicate an unexplored biological role of the bursa in the context of rotator cuff disease. Therefore, we aimed to understand the clinical relevance of bursa-tendon crosstalk, characterize the biologic role of the bursa within the shoulder, and test the therapeutic potential for targeting the bursa. Proteomic profiling of patient bursa and tendon samples demonstrated that the bursa is activated by tendon injury. Using a rat to model rotator cuff injury and repair, tenotomy-activated bursa protected the intact tendon adjacent to the injured tendon and maintained the morphology of the underlying bone. The bursa also promoted an early inflammatory response in the injured tendon, initiating key players in wound healing. In vivo results were supported by targeted organ culture studies of the bursa. To examine the potential to therapeutically target the bursa, dexamethasone was delivered to the bursa, prompting a shift in cellular signaling towards resolution of inflammation in the healing tendon. In conclusion, contrary to current clinical practice, the bursa should be retained to the greatest extent possible and provides a new therapeutically target for improving tendon healing outcomes.

One Sentence Summary

The subacromial bursa is activated by rotator cuff injury and regulates the paracrine environment of the shoulder to maintain the properties of the underlying tendon and bone.

ULTRASOUND DIAGNOSIS OF SUBACROMIAL FIBROSIS IN PATIENTS WITH ROTATOR CUFF IMPINGEMENT SYNDROME

Rotator cuff impingement syndrome (SURM) of the shoulder is considered one of the most common causes of pain in the shoulder joint in people of working age, mostly males. Due to the absence of characteristic signs of this pathology of the shoulder joint at the initial stage of the disease, fibrotic changes in the subacromial space (FI SAP) are detected late. The aim of the study was to evaluate the effectiveness of ultrasound navigation in the diagnosis and verification of fibrous changes in the subacromial space in patients with rotator cuff entrapment syndrome. Materials and methods. An analysis was made of 86 patients with cuff impingement syndrome, in whom fibrotic changes in the subacromial space are was initially detected according to ultrasound data. In group N1 (n1 = 42), the study data were analyzed without a minimally invasive intra-articular treatment procedure at the stage of conservative treatment, and in group N2 (n2 = 44) – with ultrasonic navigation of the subacromial space during a minimally invasive intra-articular treatment procedure. The comparison group (N3; n3 = 25) represented individuals without shoulder joint pathology. All patients underwent an ultrasound examination of the shoulder joint (Philips Sparq ultrasound scanner, linear high-density multifrequency transducer 5–13 MHz). Verification of the results of ultrasound of the shoulder joint is confirmed by the data of other methods of radiation imaging. Results. Ultrasound examination of the shoulder joint using dynamic functional tests before the start of therapeutic manipulations in patients with fibrotic changes in the subacromial space (in groups N1 and N2) visualization of the thickening of the supraspinatus tendon in combination with a decrease in the thickness of the subacromial space correlated with limitation of movement of the upper limb in the shoulder joint (p < 0,001). Comparative results in the study groups showed that the use of ultrasound diagnostics and navigation technologies during a minimally invasive intra-articular treatment procedure for fibrotic changes in the subacromial space provides an improvement in clinical manifestations. Conclusions. The possibility of ultrasonic visualization of the supacromial space in normal conditions without pathological changes in the shoulder joint and with fibrous changes in the subacromial space allows us to recommend the proposed method of ultrasound examination of the shoulder joint to be included in the treatment and diagnostic algorithm for the syndrome of incarceration of the rotator cuff of the shoulder. Ultrasound navigation as an effective method for diagnosing and verifying subacromial fibrosis in patients with rotator cuff entrapment syndrome.

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

Background

Although polymyalgia rheumatica (PMR) is a very common rheumatic inflammatory disease, current insight into the pathobiology of PMR is limited and largely based on studies in blood. We investigated T helper 1 (T_H1) and T helper 17 (T_H17) cell responses in blood, synovial fluid and bursa tissue of patients with PMR.

Materials and methods

Blood samples were collected from 18 patients with new-onset PMR and 32 healthy controls. Synovial fluid was aspirated from the inflamed shoulder bursae or biceps tendon sheath of 13 patients. Ultrasound-guided biopsies of the subacromial-subdeltoid (SASD) bursa were obtained from 11 patients. T cells were examined by flow cytometry, immunohistochemistry and immunofluorescence staining.

Results

Besides an increase of T_H17 (CD4⁺IL-17⁺IFN-γ^-) cells and T cytotoxic 17 (T_C17; CD8⁺IL-17⁺IFN-γ^-) cells, no other major changes were noted in the circulating T cell compartment of patients with PMR. Absolute numbers of CD4⁺ and CD8⁺ T cells were similar in blood and synovial fluid of patients with PMR. Synovial fluid T cells showed an effector-memory (CD45RO⁺CCR7^-) phenotype. Percentages of T_H1 (CD4⁺IFN-γ⁺IL-17^-) cells and T_H1/T_H17 (CD4⁺IFN-γ⁺IL-17⁺) cells, but not T_H17 or T_C17 cells, were increased in the synovial fluid. Bursa tissue biopsies contained a small number of T cells, which were mostly CD8 negative. The majority of bursa tissue T cells produced IFN-γ but not IL-17. For comparison, B cells were scarcely detected in the bursa tissue.

Conclusion

Although the circulating T_H17 cell pool is expanded in patients with PMR, our findings indicate that T_H1 cells are involved in the inflammation of bursae and tendon sheaths in this condition. Our study points towards the T_H1 cell pathway as a potential target for therapy in PMR.

Comparison of single platelet-rich plasma injection with hyaluronic acid injection for partial-thickness rotator cuff tears

BACKGROUND

Partial-thickness rotator cuff tears (PTRCTs) is not uncommon, and various nonsurgical injection therapy for PTRCTs emerged. Platelet-rich plasma (PRP) and hyaluronic acid (HA) injection were proposed for treating PTRCTs; however, the relation of dose among injectates was still lacking.

METHODS

This was a prospective, nonrandomized, comparative study. The aim of the study was to compare the effects of ultrasound-guided single PRP injection with three doses of HA injection, combination of postinjection rehabilitation, for treating PTRCTs. Subjects received either ultrasound-guided PRP injection and rehabilitation exercise, or ultrasound-guided subacromial HA injection and rehabilitation exercise. Shoulder Pain and Disability Index (SPADI), range of motion (ROM), pain visual analog scale (VAS), and Constant-Murley Shoulder Score (CMSS) were recorded before injection, and at 1 and 3 months after injection.

RESULTS

Forty-eight patients were enrolled. They received either ultrasound-guided single PRP (n = 24) intralesional and peritendinous injection or three doses of HA (n = 24) subacromial injection plus rehabilitation exercise. In the PRP group, SPADI scores, VAS scores, CMSS significantly improved at 1-month and 3-month follow up; flexion and abduction ROM significantly increased at 3-month follow up. In the HA group, SPADI scores, VAS during overhead activities, VAS night pain, and CMSS significantly improved in the first and third months; flexion and active abduction ROM significantly increased in the third month. The PRP group revealed significantly better passive abduction ROM and CMSS at third month than HA group.

CONCLUSION

Ultrasound-guided single PRP injection exhibited comparable benefit to three doses of HA injection in patients with PTRCTs short-termly, with an extended effect regarding passive shoulder abduction ROM and CMSS.

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

The subacromial bursa has long been demolded as friction-reducing tissue, which is often linked to shoulder pain and, therefore, partially removed during shoulder surgery. Currently, the discovery of the stem cell potential of resident bursa-derived cells shed a new light on the subacromial bursa. In the meanwhile, this neglected tissue is gaining more attention as to how it can augment the regenerative properties of adjacent tissues such as rotator cuff tendons. Specifically, the tight fibrovascular network, a high growth factor content, and the large progenitor potential of bursa-derived cells could complement the deficits that a nearby rotator cuff injury might experience due to the fact of its low endogenous regeneration potential. This review deals with the question of whether bursal inflammation is only a pain generator or could also be an initiator of healing. Furthermore, several experimental models highlight potential therapeutic targets to overcome bursal inflammation and, thus, pain. More evidence is needed to fully elucidate a direct interplay between subacromial bursa and rotator cuff tendons. Increasing attention to tendon repair will help to guide future research and answer open questions such that novel treatment strategies could harvest the subacromial bursa's potential to support healing of nearby rotator cuff injuries.