Comparison of Preparation Techniques for Isolating Subacromial Bursa-Derived Cells as a Potential Augment for Rotator Cuff Repair

Bone Marrow Stimulation Does Not Lead to Lower Retear Rates, Better Functional Outcomes, or Higher Complication Rates at Short-Term Follow-Up for Arthroscopic Rotator Cuff Repair: A Meta-analysis of Randomized Controlled Trials

PURPOSE

To determine the effect of bone marrow stimulation (BMS) on retear rates, functional outcomes, and complication rates in patients who underwent arthroscopic rotator cuff repair (RCR) through a meta-analysis of randomized controlled trials.

METHODS

PubMed, EMBASE, Web of Science, and The Cochrane Library were searched on March 25, 2023. Two evaluators independently screened the literature, extracted data, and assessed the methodologic quality of the enrolled studies. Meta-analysis was conducted using RevMan software, version 5.4.

RESULTS

A total of 7 randomized controlled trials with 638 patients were included. The evaluation of rotator cuff tendon integrity was conducted using distinct imaging modalities. Specifically, 259 patients underwent magnetic resonance imaging whereas 208 patients underwent ultrasound. Additionally, a subset of 95 patients underwent either of these modalities; however, the precise distribution between these 2 modalities was not explicitly delineated. Compared with RCR alone, RCR combined with BMS provided similar retear rates (P = .51, I2 = 46%), Constant-Murley scores (P = .14, I2 = 0%), American Shoulder and Elbow Surgeons (standardized shoulder assessment form) scores (P = .56, I2 = 0%), Western Ontario Rotator Cuff Index scores (P = .20, I2 = 0%), visual analog scale scores (P = .19, I2 = 0%), forward flexion (P = .18, I2 = 0%), external rotation (P = .62, I2 = 0%), severe complication rates (P = .56, I2 = 0%), and mild complication rates (P = .10, I2 = 0%).

CONCLUSIONS

Compared with the outcomes observed after isolated arthroscopic RCR, arthroscopic RCR with BMS showed comparable results in terms of retear rate, functional outcomes, and incidence of complications.

LEVEL OF EVIDENCE

Level II, meta-analysis of Level I and II studies.

Human Rotator Cuff Tears Reveal an Age-Dependent Increase in Markers of Cellular Senescence and Selective Removal of Senescent Cells With Dasatinib + Quercetin Increases Genetic Expression of COL1A1 In Vitro

PURPOSE

To quantify cellular senescence in supraspinatus tendon and subacromial bursa of humans with rotator cuff tears and to investigate the in vitro efficacy of the senolytic dasatinib + quercetin (D+Q) to eliminate senescent cells and alter tenogenic differentiation.

METHODS

Tissue was harvested from 41 patients (mean age, 62 years) undergoing arthroscopic rotator cuff repairs. In part 1 (n = 35), senescence was quantified using immunohistochemistry and gene expression for senescent cell markers (p16 and p21) and the senescence-associated secretory phenotype (SASP) (interleukin [IL] 6, IL-8, matrix metalloproteinase [MMP] 3, monocyte chemoattractant protein [MCP] 1). Senescence was compared between patients <60 and ≥60 years old. In part 2 (n = 6) , an in vitro model of rotator cuff tears was treated with D+Q or control. D+Q, a chemotherapeutic and plant flavanol, respectively, kill senescent cells. Gene expression analysis assessed the ability of D+Q to kill senescent cells and alter markers of tenogenic differentiation.

RESULTS

Part 1 revealed an age-dependent significant increase in the relative expression of p21, IL-6, and IL-8 in tendon and p21, p16, IL-6, IL-8, and MMP-3 in bursa (P < .05). A significant increase was seen in immunohistochemical staining of bursa p21 (P = .028). In part 2, D+Q significantly decreased expression of p21, IL-6, and IL-8 in tendon and p21 and IL-8 in bursa (P < .05). Enzyme-linked immunosorbent assay analysis showed decreased release of the SASP (IL-6, MMP-3, MCP-1; P = .002, P = .024, P < .001, respectively). Tendon (P = .022) and bursa (P = .027) treated with D+Q increased the expression of COL1A1.

CONCLUSIONS

While there was an age-dependent increase in markers of cellular senescence, this relationship was not consistently seen across all markers and tissues. Dasatinib + quercetin had moderate efficacy in decreasing senescence in these tissues and increasing COL1A1 expression.

CLINICAL RELEVANCE

This study reveals that cellular senescence may be a therapeutic target to alter the biological aging of rotator cuffs and identifies D+Q as a potential therapy.

The effect of augmenting suture material with magnesium and platelet-rich plasma on the in vitro adhesion and proliferation potential of subacromial bursa-derived progenitor cells

Background

Connective tissue subacromial bursa-derived progenitor cells (SBDCs) have been suggested as a potent biologic augment to promote healing of the repaired rotator cuff tendon. Maximizing the amount of retained progenitor cells at the tendon repair site is essential for ensuring an optimal healing environment, warranting a search for proadhesive and proliferative adjuvants. The purpose was to evaluate the effect of magnesium (Mg), platelet-rich plasma (PRP), and a combination of both adjuvants on the in vitro cellular adhesion and proliferation potential of SBDCs on suture material commonly used in rotator cuff surgery.

Methods

SBDCs were isolated from subacromial bursa samples harvested during rotator cuff repair and cultured in growth media. Commercially available collagen-coated nonabsorbable flat-braided suture was cut into 1-inch pieces, placed into 48-well culture dishes, and sterilized under ultraviolet light. Either a one-time dose of 5 mM sterile Mg, 0.2 mL of PRP, or a combination of both adjuvants was added, while a group without treatment served as a negative control. Cellular proliferation and adhesion assays on suture material were performed for each treatment condition.

Results

Augmenting the suture with Mg resulted in a significantly increased cellular adhesion (total number of attached cells) of SBDCs compared to PRP alone (31,527 ± 19,884 vs. 13,619 ± 8808; P < .001), no treatment (31,527 ± 19,884 vs. 21,643 ± 8194; P = .016), and combination of both adjuvants (31,527 ± 19,884 vs. 17,121 ± 11,935; P < .001). Further, augmentation with Mg achieved a significant increase in cellular proliferation (absorbance) of SBDCs on suture material when compared to the PRP (0.516 ± 0.207 vs. 0.424 ± 0.131; P = .001) and no treatment (0.516 ± 0.207 vs. 0.383 ± 0.094; P < .001) group. The combination of Mg and PRP showed a significantly higher proliferation potential compared to PRP alone (0.512 ± 0.194 vs. 0.424 ± 0.131; P = .001) and no treatment (0.512 ± 0.194 vs. 0.383 ± 0.094; P < .001). There were no significant differences in the remaining intergroup comparisons (P > .05, respectively).

Conclusion

Augmenting suture material with Mg resulted in a significantly increased cellular adhesion of SBDCs compared to untreated suture material, as well as augmentation with PRP alone or a combination of both adjuvants. Further, Mg with or without PRP augmentation achieved a significant increase in the cellular proliferation of SBDCs on suture material compared to untreated sutures and augmentation with PRP alone. Application of Mg may be a clinically feasible approach to optimizing the use of SBDCs as a biological augment in rotator cuff repair, while combined augmentation with PRP may harness the full potential for optimized tissue recovery due to the high concentration of PRP-derived growth factors.

Clinical outcomes of rotator cuff repair with subacromial bursa reimplantation: a retrospective cohort study

Background

The subacromial bursa has been found to be a rich, local, source of mesenchymal stem cells but is removed for visualization during rotator cuff repair. Reimplantation of this tissue may improve rotator cuff healing. The purpose of this study is to evaluate clinical outcomes of rotator cuff repair with and without subacromial bursa reimplantation.

Methods

Patients aged 37-77 with a full-thickness or near full-thickness supraspinatus tears underwent arthroscopic transosseous-equivalent double row rotator cuff repair. In patients prior to July 2019, the subacromial bursa was resected for visualization, and discarded. In patients after July 2019, the subacromial bursa was collected using a filtration device connected to an arthroscopic shaver and reapplied to the bursal surface of the tendon at the completion of the rotator cuff repair. Rotator cuff integrity was evaluated via magnetic resonance imaging on bursa patients at 6 months postoperatively. Minimum 18-month clinical outcomes (Single Assessment Numeric Evaluation, American Shoulder and Elbow Surgeons, patient satisfaction) were compared between bursa and nonbursa cohorts.

Results

A total of 136 patients were included in the study (control n = 110, bursa n = 26). Preoperative demographics and tear characteristics were not different between groups. Average follow-up was significantly longer in the control group (control: 3.2 ± 0.7 years; bursa: 1.8 ± 0.3 years; P < .001). The control group showed a significantly higher Single Assessment Numeric Evaluation score (control: 87.9 ± 15.8, bursa: 83.6 ± 15.1, P = .037) that did not meet minimum clinically important difference. The American Shoulder and Elbow Surgeons and patient satisfaction scores were similar between the groups. Symptomatic retears were not significantly different between groups (control: 9.1%, bursa 7.7%, P = .86). Seven patients in the control group underwent reoperation (6.4%), compared to 0 patients in the bursa group (0%, P = .2). Six-month postoperative magnetic resonance images obtained on bursa patients demonstrated 85% rotator cuff continuity (n = 17/20) as defined via Sugaya classification.

Conclusion

Augmentation of rotator cuff repair with bursal tissue does not appear to have negative effects, and given the accessibility and ease of harvest of this tissue, further research should be performed to evaluate its potential for improved tendon healing or clinical outcomes.

Orthobiologics: Current Status in 2023 and Future Outlook

Orthobiologic agents, including platelet-rich plasma, connective tissue progenitor cells derived from bone marrow, adipose, and other tissues, and purified cytokines and small peptides, have tremendous potential to target deficiencies in soft-tissue healing. The principal limitation currently is the variability in the composition and biologic activity of orthobiologic formulations, making it difficult to choose the optimal treatment for a specific tissue or pathology. Current data suggest that orthobiologics are "symptom-modifying," but there is little evidence that they can lead to true tissue regeneration ("structure-modifying"). A critically important need at this time is to identify sentinel markers of potency and biologic activity for different orthobiologic formulations so that we can match the treatment to the desired biologic effect for a specific tissue or pathology. Improved understanding of the underlying cellular and molecular mechanisms of tissue degeneration and repair will allow a precision medicine approach where we can choose the optimal orthobiologic treatment of specific orthopaedic problems. It is important for the clinician to be aware of the evolving regulatory status of orthobiologic treatments. Emerging therapies such as the use of exosomes and gene therapy approaches hold great promise as improved methods to both treat symptoms and affect tissue regeneration.

Subacromial bursa increases the failure force in a mouse model of supraspinatus detachment and repair

BACKGROUND

It has been shown that subacromial bursa (SAB) harbors connective tissue progenitor cells. The purpose of this study was to evaluate the effects of implantation of SAB-derived cells (SBCs) suspended in a fibrin sealant bead and implantation of SAB tissue at rotator cuff repair site on biomechanical properties of the repair in a mouse (C57Bl/6) model of supraspinatus tendon (ST) detachment and repair.

METHODS

Part 1: Murine SAB tissue was harvested and cultured. Viability of SBCs suspended in 10 μL of fibrin sealant beads was confirmed in vitro and in vivo. Eighty mice underwent right ST detachment and repair augmented with either fibrin sealant bead (control group) or fibrin sealant bead with 100,000 SBCs (study group) applied at the repair site. Part 2: 120 mice underwent right ST detachment and repair and were randomized equally into 4 groups: (1) a tissue group, which received a piece of freshly harvested SAB tissue; (2) a cell group, which received SBCs suspended in fibrin sealant bead; (3) a fibrin sealant group, which received plain fibrin sealant bead without cells; and (4) a control group, which received nothing at the ST repair site. An equal number of mice in each group were killed at 2 and 4 weeks. Specimens underwent biomechanical testing to evaluate failure force (part 1 and 2) and histologic analysis of the repair site (part 1 only).

RESULTS

Part 1: The mean failure force in the study group was significantly higher than controls at 2 and 4 weeks (3.25 ± 1.03 N vs. 2.43 ± 0.56 N, P = .01, and 4.08 ± 0.99 N vs. 3.02 ± 0.8 N, P = .004, respectively). Mean cell density of the ST at the repair site was significantly lower in the study group at 2 weeks than in controls (18,292.13 ± 1706.41 vs. 29,501.90 ± 3627.49, P = .001). Study group specimens had lower proteoglycan contents than controls, but this difference was not statistically significant. Part 2: There was no difference in failure force between cell and tissue groups at the 2- and 4-week time points (P = .994 and P = .603, respectively). There was no difference in failure force between fibrin sealant bead and control groups at the 2- and 4-week time points (P = .978 and P = .752, respectively).

CONCLUSION

This study shows that the application of SBCs and SAB tissue at the rotator cuff repair site increases the strength of repair in a murine model of rotator cuff detachment and repair.

Clinical perspectives for repairing rotator cuff injuries with multi-tissue regenerative approaches

Background

In the musculoskeletal system, bone, tendon, and muscle form highly integrated multi-tissue units such as the rotator cuff complex, which facilitates functional and dynamic movement of the shoulder joint. Understanding the intricate interplay among these tissues within clinical, biological, and engineering contexts is vital for addressing challenging issues in treatment of musculoskeletal disorders and injuries.

Methods

A wide-ranging literature search was performed, and findings related to the socioeconomic impact of rotator cuff tears, the structure-function relationship of rotator cuff bone-tendon-muscle units, pathophysiology of injury, current clinical treatments, recent state-of-the-art advances (stem cells, growth factors, and exosomes) as well as their regulatory approval, and future strategies aimed at engineering bone-tendon-muscle musculoskeletal units are outlined.

Results

Rotator cuff injuries are a significant socioeconomic burden on numerous healthcare systems that may be addressed by treating the rotator cuff as a single complex, given its highly integrated structure-function relationship as well as degenerative pathophysiology and limited healing in bone-tendon-muscle musculoskeletal tissues. Current clinical practices for treating rotator cuff injuries, including the use of commercially available devices and evolving trends in surgical management have benefited patients while advances in application of stem/progenitor cells, growth factors, and exosomes hold clinical potential. However, such efforts do not emphasize targeted regeneration of bone-tendon-muscle units. Strategies aimed at regenerating bone-tendon-muscle units are thus expected to address challenging issues in rotator cuff repair.

Conclusions

The rotator cuff is a highly integrated complex of bone-tendon-muscle units that when injured, has severe consequences for patients and healthcare systems. State-of-the-art clinical treatment as well as recent advances have resulted in improved patient outcome and may be further enhanced by engineering bone-tendon-muscle multi-tissue grafts as a potential strategy for rotator cuff injuries.

Translational Potential of this Article

This review aims to bridge clinical, tissue engineering, and biological aspects of rotator cuff repair and propose a novel therapeutic strategy by targeted regeneration of multi-tissue units. The presentation of these wide-ranging and multi-disciplinary concepts are broadly applicable to regenerative medicine applications for musculoskeletal and non-musculoskeletal tissues.

Characterization of murine subacromial bursal-derived cells

PURPOSE/AIM

The purpose of this study is to identify a cell population within the murine subcromial bursal-derived cells with characteristics compatible to an accepted mesenchymal stem cell description given by the International Society for Cellular Therapy (ISCT).

MATERIALS AND METHODS

Murine subacromial bursa was harvested using microsurgical technique. Subacromial bursal-derived cells were classified through colony-forming units, microscopic morphology, fluorescent-activated cell sorting, and differentiation into chondrogenic, adipogenic, and osteogenic lineages.

RESULTS

Subacromial bursal samples exhibited cell growth out of the tissue for an average of 115 ± 29 colony-forming units per 1 mL of complete media. Subacromial bursal-derived cells exhibited a long, spindle-shaped, fibroblast-like morphology. Subacromial bursal-derived cells positively expressed mesenchymal stem cell markers CD73, CD90, and CD105, and negatively expressed mesenchymal stem cell markers CD31 and CD45. Subacromial bursal-derived cells, examined by Image J analysis and quantitative gene expression, were found to differentiate into chondrogenic, adipogenic, and osteogenic lineages.

CONCLUSIONS

This study demonstrated the feasibility of harvesting murine subacromial bursal tissue and identified a cell population within the subacromial bursa with characteristics compatible to an accepted mesenchymal stem cell description. The results of this study suggest that the mouse subacromial bursal-derived cell population harbors mesenchymal stem cells. Murine subacromial bursal tissue is a potential source for obtaining cells with mesenchymal stem cell characteristics for future utilization in orthopedic research to look into treatment of rotator cuff pathology.

Subacromial Bursal Tissue and Surrounding Matrix of Patients Undergoing Rotator Cuff Repair Contains Progenitor Cells

PURPOSE

To build upon previous literature to identify a complete analysis of cellular contents of subacromial bursal tissue as well as the matrix surrounding the rotator cuff.

METHODS

Samples of subacromial bursal tissue and surrounding matrix milieu from above the rotator cuff tendon and above the rotator cuff muscle bellies were obtained from 10 patients undergoing arthroscopic rotator cuff repair. Samples were analyzed using fluorescent-activated cell sorting and histologic analysis with staining protocols (Oil Red O, Alcian Blue, and Picro-Sirius Red), for identification of matrix components, including fat, proteoglycans, and collagen.

RESULTS

Progenitor cells and fibroblast-type cells were present in significant amounts in subacromial bursal tissue in both tissues obtained from over the tendinous and muscle belly portions. Markers for neural tissue, myeloid cells, and megakaryocytes also were present to a lesser extent. There were prominent amounts of fat and proteoglycans present in the matrix, based on ImageJ analysis of stained histologic slides.

CONCLUSIONS

The subacromial bursal tissue and surrounding matrix of patients undergoing rotator cuff repair contains progenitor cells in significant concentrations both over the tendon and muscle belly of the rotator cuff.

CLINICAL RELEVANCE

This presence of progenitor cells, in particular, in the subacromial bursal tissue provides a potential basis for future applications of augmentation purposes in rotator cuff healing, and calls into question the practice of routine bursectomy. As the potential role of bursal tissue contents in growth and regeneration in the setting of rotator cuff healing is more well understood, maintaining this tissue may become more relevant. Concentration of these cellular components for use in autologous re-implantation is also an avenue of interest.

Differentiation Ability of Tendon-Derived Stem Cells and Histological Characteristics of Rotator Cuff Remnant on the Greater Tuberosity Degenerated With Age and Chronicity

PURPOSE

To explore and measure the presence and activity of tendon-derived stem cells (TDSCs), as well as histological changes of rotator cuff remnant by age and chronicity of the rotator cuff tear (RCT).

METHODS

154 patients with a full-thickness tear of supraspinatus and/or infraspinatus tendon were included. 52 qualified remnants of the greater tuberosity were captured through arthroscopy. TDSCs in the remnants were isolated for proliferation ability, basal gene expression, and trilineage differentiation detection. Histological characteristics were evaluated by observation of staining under a light microscope and transmission electron microscopy (TEM). To observe the effect of age, samples were divided into two groups: young (＜60 years old) and old (≥60 years old). For chronicity comparison, samples were divided into three groups: acute group (＜3 months), intermediate group (3-12 months), and chronic group (≥12 months).

RESULTS

Between age groups, the remnants in older patients were found to have lower TDSC proliferation ability (cell counting kit-8 results, old: .5325 ± .050, young: .6623 ± .196; P = .008) and basal expression of aggrecan (.630 ± .239; P = .002) and TGF-β1 (transforming growth factor-β1, .589 ± .326, P = .008), weaker ability of chondrogenic differentiation. Furthermore, the remnant tendons in chronic group was found to have weaker adipogenic and chondrogenic differentiation ability of TDSCs, lower tendon degenerative score (acute: 3.57 ± 1.902, intermediate: 5.94 ± 2.313, chronic: 6.86 ± 2.193; P = .023), increased type III collagen region ratio in insertion area (acute: 86.10% ± 8.29%, intermediate: 94.06% ± 5.36%, chronic: 98.90% ± .49%; P = .023), and larger fibril diameters.

CONCLUSION

Differentiation ability of TDSCs derived from the rotator cuff remnant was reduced with age and chronicity. Histological degeneration of remnant tendon deteriorated with chronicity. Remnant in the greater tuberosity was still alive, but those in young or acute injury patients were more active after full-thickness RCT.

CLINICAL RELEVANCE

TDSCs exist in rotator cuff remnant on the greater tuberosity and have multilineage differentiation ability. But the remnant degenerated with age and chronicity.

Stem cell sheet interpositioned between the tendon and bone would be better for healing than stem cell sheet overlaid above the tendon-to-bone junction in rotator cuff repair of rats

Background

Although stem cells might enhance natural enthesis healing in surgical rotator cuff repair, not much attention has been given to the delivery and location of delivering stem cells. The purpose of this study to know where to locate those stem cells during repair.

Methods

Animal model of chronic rotator cuff tear was created in 24 rats. Adipose-derived stem cells were engineered as a sheet and transplanted 1) between a torn tendon and humerus (interposition group) or 2) over a repaired tendon-to-bone junction (overlay group) at the time of surgical repair. Tracking of stem cells with overexpression of green fluorescent protein (GFP) were carried out at the time of sacrifice in additional 4 shoulders in each group. Histological and Biomechanical evaluation was performed to compare the differences in tendon-to-bone healing.

Results

Histology showed increased fibrocartilage, a clear boundary at the mineralized fibrocartilage, abundant collagen type III, and higher total scores, especially in the interposition group. GFP-overexpression was observed at the transplanted site at 2 weeks after repair. Although two groups where stem cell sheets applied showed higher load to failure than the repair-only group, the load to failure was not different between the interposition and overlay group.

Conclusion

In the chronic rotator cuff repair model, stem cell sheets enhanced regeneration of the tendon-to-bone junction. This regeneration was effective when the stem cell sheet was interpositioned at the tendon-to-bone interface.

Level of evidence

Basic Science Study; In Vivo Animal Model; Histology and Biomechanics.

Efficacy of Arthroscopic Shavers for the Retrieval and Processing of Connective Tissue Progenitor Cells from Subacromial Bursal Tissue

The purpose of this study is to determine if arthroscopic shavers can effectively collect and process connective tissue progenitor (CTP) cells from subacromial bursal tissue for utilization in rotator cuff repair augmentation. Subacromial bursal tissue was collected and processed using two arthroscopic shavers, Shaver A and Shaver B, in 10 patients undergoing arthroscopic rotator cuff repair. Each shaver was used in a random order for the same patient. Tissue samples underwent testing for cellular proliferation, cellular concentration, number of colony-forming units (CFU), live/dead assay, fluorescence-activated cells sorting (FACS) analysis, cytokine analysis, and growth factor analysis. Shaver A produced more CFUs compared to Shaver B (210.3 vs. 125.9; p < 0.001). At 3 weeks, cells collected via Shaver A had greater cellular proliferation (0.35 vs. 0.51; p < 0.001) as well as more viable cells (214,773 vs. 132,356 cells/gram; p < 0.001). Tissue collected with Shaver B had greater amounts of the cytokines MMP-1 (3741 vs. 5500 pg/mL; p < 0.001), MMP-3 (1131 vs. 1871 pg/mL; p < 0.001), and MMP-13 (179 vs. 401 pg/mL; p < 0.001), while those collected with Shaver A had greater vascular endothelial growth factor (VEGF) (47.8 vs. 9.0 pg/mL; p < 0.05). Arthroscopic shavers are capable of harvesting and processing CTP cells from subacromial bursal tissue. Different shavers may produce different yields of viable CTP cells.

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.

Autograft Long Head Biceps Tendon Can Be Used as a Scaffold for Biologically Augmenting Rotator Cuff Repairs

PURPOSE

We create a viable, mechanically expanded autograft long head biceps tendon (LHBT) scaffold for biologically augmenting the repair of torn rotator cuffs.

METHODS

The proximal aspect of the tenotomized LHBTs was harvested from patients during rotator cuff repair surgery and was mechanically formed into porous scaffolds using a surgical graft expander. LHBT scaffolds were evaluated for change in area, tensile properties, and tenocyte viability before and after expansion. The ability of endogenous tenocytes derived from the LHBT scaffold to promote tenogenic differentiation of human adipose-derived mesenchymal stromal cells (ADMSCs) was also determined.

RESULTS

Autograft LHBTs were successfully expanded using a modified surgical graft expander to create a porous scaffold containing viable resident tenoctyes from patients undergoing rotator cuff repair. LHBT scaffolds had significantly increased area (length: 24.91 mm [13.91, 35.90] × width: 22.69 mm [1.87, 34.50]; P = .011) compared with the native LHBT tendon (length: 27.16 mm [2.70, 33.62] × width: 6.68 mm [5.62, 7.74]). The structural properties of the autograft were altered, including the ultimate tensile strength (LHBT scaffold: .56 MPa [.06, 1.06] vs. native LHBT: 2.35 MPa [1.36, 3.33]; P = .002) and tensile modulus (LHBT scaffold: 4.72 MPa [-.80, 1.24] versus native LHBT: 37.17 MPa [24.56, 49.78]; P = .001). There was also a reduction in resident tenocyte percent viability (LHBT scaffold: 38.52% [17.94, 59.09] vs. native LHBT: 68.87% [63.67, 74.37]; P =.004). Tenocytes derived from the LHBT scaffold produced soluble signals that initiated ADMSC differentiation into an immature tenocyte-like phenotype, as indicated by an 8.7× increase in scleraxis (P = .040) and a 3.6× increase in collagen type III mRNA expression (P = .050) compared with undifferentiated ADMSC controls.

CONCLUSIONS

The ability to produce a viable autologous scaffold from the proximal biceps tendon having dimensions, porosity, mechanical characteristics, native ECM components, and viable tenocytes that produce bioactive signals conducive to supporting the biologic augmentation of rotator cuff repair surgery has been demonstrated.

CLINICAL RELEVANCE

This biologically active construct may help to improve the quality of healing and regeneration at the repair site of rotator cuff tears, especially those at high risk for retear.

Significant Improvement in Shoulder Function and Pain in Patients Following Biologic Augmentation of Revision Arthroscopic Rotator Cuff Repair Using an Autologous Fibrin Scaffold and Bone Marrow Aspirate Derived From the Proximal Humerus

Purpose

To clinically evaluate patients who underwent a biologic augmentation technique in revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and concentrated stem cells isolated from bone marrow aspirate (BMA) obtained from the proximal humerus.

Methods

This is a retrospective review of prospectively collected data from patients who underwent biologic augmentation of revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and BMA obtained from the proximal humerus between 2014 and 2015. Minimum follow-up was 12 months. Outcome measures were collected preoperatively and postoperatively including range of motion as well as American Shoulder and Elbow Surgeons Shoulder Form, Simple Shoulder Test, single assessment numeric evaluation, and visual analog score. In addition, BMA samples of each patient were assessed for the number of nucleated cells and colony-forming units. Regression analysis was performed to investigate whether the number of nucleated cells and colony-forming units had an influence on outcome and failure.

Results

Ten patients who underwent biologic augmentation of revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and concentrated BMA obtained from the proximal humerus between 2014 and 2015 were included. The mean follow-up time was 30.7 (range: 12-49) months. Four patients were revised at final follow-up. Postoperative clinical scores improved significantly: American Shoulder and Elbow Surgeons (28.1 ± 5.4 to 60.9 ± 9.0; P < .01), single assessment numeric evaluation (6.6 ± 2.3 to 65.1 ± 10.9; P < .01), visual analog scale (7.2 ± 0.9 to 3.1 ± 0.9; P < .01), and Simple Shoulder Test (1.6 ± 0.5 to 10.3 ± 5.7; P < .01). Postoperative range of motion increased significantly with regard to flexion (97.0 ± 13.6 to 151.0 ± 12.2; P < .01) and abduction (88.0 ± 14.0 to 134.0 ± 15.1; P = .038) but not with external rotation (38.0 ± 5.7 to 50.5 ± 6.5; P = .16). Less pain was correlated to an increased number of nucleated cells (P = .026); however, there was no correlation between failure rate and number of nucleated cells (P = .430).

Conclusions

Patients who underwent biologic augmentation of revision arthroscopic rotator cuff repair using an autologous fibrin scaffold and concentrated BMA demonstrated a significant improvement in shoulder function along with reduction of pain. However, the overall revision rate for this procedure was 40%.

Level of Evidence

Level IV, therapeutic case series.

Trochanteric Bursa Is a Source of Connective Tissue Progenitor Cells

Purpose

To investigate the presence of connective tissue progenitor cells (CTPs) in the trochanteric bursa harvested over the gluteus medius muscle belly and tendon during open hip procedures.

Methods

Trochanteric bursa samples from nine patients (63.1 ± 8.6 years) undergoing total hip arthroplasty for primary osteoarthritis were obtained from 2 sites: over the gluteus medius tendon at the greater trochanter and over the muscle belly. Bursal tissue was digested with collagenase and grown in culture. The nucleated cell count, cellular concentration, cellular proliferation, fluorescence-activated cell sorting (FACS) analysis, and differentiation using immunostaining and quantitative polymerase chain reaction (PCR) were used to determine and quantify the presence of CTPs.

Results

Bursa-derived CTPs were identified in all harvested samples. At t = 0, there was no difference in nucleated cell count over muscle and tendon (1.69 ± 1.26 × 10⁸ and 1.41 ± 1.12 × 10⁸ cells/g, respectively; P = .162). Similarly, the cellular concentration at 3 weeks was not significantly different between bursa harvested over muscle and tendon (6.61 ± 5.14 × 10⁶ and 5.58 ± 4.70 × 10⁶ cells/g, respectively; P = .532). High cellular proliferation was identified for both bursal tissue overlying muscle and tendon (2.28 ± .95 and 1.66 ± 1.05, respectively; P = .194). FACS analysis revealed high positivity rates (>95%) of CTP-specific surface epitopes (CD105, CD90, and CD73) and low positivity rates (<1.3%) of negative markers (CD45, CD31). Osteogenic, adipogenic, and chondrogenic differentiation potential was demonstrated with immunostaining and quantitative PCR for gene expression.

Conclusions

Connective tissue progenitor cells are found in the trochanteric bursa overlying the muscle and tendon of the hip abductors.

Clinical Relevance

During open hip procedures, the trochanteric bursa is often partially excised to identify muscular boundaries and tissue planes for surgical exposure. The function of the trochanteric bursa remains largely unknown. However, this tissue is a source of connective tissue progenitor cells, which may be important in the healing response of surgically repaired abductor tendons.

Analysis of Patient Factors Affecting In Vitro Characteristics of Subacromial Bursal Connective Tissue Progenitor Cells during Rotator Cuff Repair

Unsatisfactory failure rates following rotator cuff (RC) repair have led orthopaedic surgeons to explore biological augmentation of the healing enthesis. The subacromial bursa (SB) contains abundant connective tissue progenitor cells (CTPs) that may aid in this process. The purpose of the study was to investigate the influence of patient demographics and tear characteristics on the number of colony-forming units (CFUs) and nucleated cell count (NCC) of SB-derived CTPs. In this study, we harvested SB tissue over the supraspinatus tendon and muscle in 19 patients during arthroscopic RC repair. NCC of each sample was analyzed on the day of the procedure. After 14 days, CFUs were evaluated under a microscope. Spearman’s rank correlation coefficient was then used to determine the relationship between CFUs or NCC and patient demographics or tear characteristics. The study found no significant correlation between patient demographics and the number of CFUs or NCC of CTPs derived from the SB (p > 0.05). The study did significantly observe that increased tear size was negatively correlated with the number of CFUs (p < 0.05). These results indicated that increased tear size, but not patient demographics, may influence the viability of CTPs and should be considered when augmenting RCrepairs with SB.

Editorial Commentary: Point-of-Care Harvest and Application of Resident Stem Are Practical and Cost-Effective

Point-of-care harvest and application of residence stem cells are practical and cost-effective. Tissue formerly considered waste contains these biologically potent cells, and use of such tissue may represent a big part of biologics going forward. The practical application of orthobiologics has slowed because of 3 hurdles: the regulatory requirements of stem cell technologies; the energy, time, and money required to develop a clinical evidence base; and the expense that they present to patients and institutions. Orthobiologic technologies that are simple and cheap and that leverage tissues that are already readily available at the point of care (i.e., the surgical procedure) solve many of these challenges. Cell sources could include knee synovium, shoulder subacromial bursa, bone marrow aspirate, and anterior cruciate ligament injury effusion fluid and stump tissue. A current concern is that collagenase processing and culture expansion are steps resulting in regulatory hurdles in the United States.

Decreased Colony-Forming Ability of Subacromial Bursa-Derived Cells During Revision Arthroscopic Rotator Cuff Repair

Purpose

To compare the cellular viability and differentiation potential of subacromial bursa-derived cells (SBDCs) located over the rotator cuff muscle and tendon of patients undergoing primary versus revision arthroscopic rotator cuff repair (ARCR).

Methods

Subacromial bursa was harvested from 18 primary (57.1 ± 4.6 years) and 12 revision ARCRs (57.3 ± 6.7 years). Bursa was collected from 2 sites (over rotator cuff tendon and muscle), digested with collagenase, and grown in culture. The number of nucleated cells, colony-forming units (CFUs), differentiation potential, and mesenchymal stem cell surface markers were compared in primary and revision cases.

Results

There was no difference in the number of nucleated cells between primary and revision ARCR harvested from the subacromial bursa overlying the tendon (3019.3 ± 1420.6 cells/mg and 3541.7 ± 2244.2 cells/mg, respectively; P = .912) or muscle (2753.5 ± 1547.1 cells/mg and 2989.0 ± 2231.4 cells/mg, respectively; P = .777). There was no difference in the number of CFUs between primary and revision ARCR over the rotator cuff tendon (81.5 ± 49.5 CFUs and 53.0 ± 36.9 CFUs, respectively; P = .138), but there were significantly fewer CFUs over the muscle in revision cases (28.1 ± 22.7 CFUs) compared with primary cases (55.7 ± 34.5 CFUs) (P = .031). SBDCs from revision ARCR expressed characteristic mesenchymal stem cell surface epitopes and had multidifferentiation potentials for chondrogenesis, osteogenesis, and adipogenesis.

Conclusions

SBDCs harvested over the rotator cuff muscle demonstrated significantly decreased colony-forming abilities in revision arthroscopic rotator cuff repairs compared with primary repairs. However, the subacromial bursa retains its pluripotent differentiation potential for chondrogenic, osteogenic, and adipogenic lineages in the revision setting.

Clinical Relevance

The subacromial bursa may play a role in the healing response of the repaired rotator cuff. This capacity is not necessarily diminished in the revision setting and may be harnessed as an orthobiologic.

Arthroscopic Rotator Cuff Repair Augmented with Autologous Subacromial Bursa Tissue, Concentrated Bone Marrow Aspirate, Platelet-Rich Plasma, Platelet-Poor Plasma, and Bovine Thrombin

As recurrent rotator cuff tears following repair remain a significant problem, improving healing potential using biologic adjuvants, including concentrated bone marrow aspirate (cBMA), platelet-rich plasma (PRP), or subacromial bursa tissue (SBT), has become increasingly popular in recent years. In an attempt to combine the benefits of these various biologic adjuvants and maximize the healing potential of the repaired tendon, an arthroscopic rotator cuff repair technique biologically augmented with autologous SBT, cBMA, PRP, platelet-poor plasma (PPP), and bovine thrombin has been developed. The created clot is used as a biologic scaffold for sufficient delivery, and it is stabilized using bovine thrombin in order to ensure maximum stability and retainment of the applied biologic augments at the repair site.

CLASSIFICATIONS

I: shoulder; II: rotator cuff.

The interaction between human rotator cuff tendon and subacromial bursal tissue in co-culture

BACKGROUND

The role of subacromial bursa in rotator cuff pathology is unclear. Along with recognized inflammatory potential, current data demonstrate the presence of mesenchymal stem cells and potential regenerative properties of the bursa. The purpose of this study was to (1) approximate an in vitro co-culture model that represents interaction between torn rotator cuff tendon and subacromial bursa, (2) quantify the cellular activity of tendon and bursa and their interactions, (3) use this model to induce a state of inflammation present with rotator cuff pathology.

METHODS

In part 1, tendon and bursa samples were obtained from 6 patients undergoing rotator cuff repair. Tendon and bursa were cultured alone and together in co-culture wells for 21 days. Markers specific for tenocyte gene expression (tenascin C, decorin, etc) were measured in both tendon and bursa alone and compared to co-culture models. In part 2 of the study, an inflammatory state was induced with interleukin-1β treatment, and markers of inflammation were measured via protein assay at 0 and 21 days in samples from 7 additional patients.

RESULTS

There was an increase in tendon and bursa markers in nearly all groups as evidenced by increased gene expression of known tendon and bursa markers. There was a significant increase in gene expression when torn tendon was co-cultured with bursa compared with culturing alone. Additionally, a state of inflammation was induced as evidenced by increased markers of inflammation, inflammatory protein concentration, and inflammatory cells and disruption of histologic morphology.

CONCLUSION

There is a clear interaction between rotator cuff tendon and the milieu produced by the subacromial bursa in this in vitro co-culture system that is significantly different when compared to an isolated culture of tendon and bursa. This system was successfully used to induce a state of inflammation that may represent in vivo inflammation. This in vitro model of rotator cuff pathology can aid investigators in testing effects of agents proposed to improve rotator cuff healing. This can lead to further knowledge regarding effective treatment options.

Arthroscopic Bursa-Augmented Rotator Cuff Repair: A Vasculature-preserving Technique for Subacromial Bursal Harvest and Tendon Augmentation

Rotator cuff repairs are associated with suboptimal outcomes and possibly greater incidence of retears if the biological healing environment is compromised. Strategies to optimize tendon-bone healing include the use of bioinductive scaffolds and regenerative stem cell therapy. The subacromial bursa has been shown to have significant pluripotent stem cell potency for tendon healing and has the advantage of easy accessibility and no added cost. However, a reproducible surgical technique for bursal mobilization, harvest, and vascularity preservation has not been described. We describe our technique for vasculature-preserving bursal mobilization and harvest of the entire posterosuperior and lateral subacromial bursa, and its use in rotator cuff repair augmentation is presented. The technique involves mobilization of the bursa as a continuous layer by maintain its medial and lateral vascularity. The bursa is advanced laterally, and the "vascular bursal duvet" and cuff tendons are repaired together as a tendon-bursa unit.

The Effect of Insulin and Insulin-like Growth Factor 1 (IGF-1) on Cellular Proliferation and Migration of Human Subacromial Bursa Tissue

Purpose

To evaluate the effect of a one-time dose of insulin or insulin-like growth factor 1 (IGF-1) on cellular proliferation and migration of subacromial bursa tissue (SBT) over time.

Methods

SBT was harvested from over the rotator cuff tendon in 4 consecutive patients undergoing primary arthroscopic rotator cuff repair. SBT was cultured for 3 weeks in complete media until reaching confluence. The culture dishes were stored in a humidified, low oxygen tension (5% CO₂) incubator at 37°C. SBT of each patient underwent treatment with a one-time dose of insulin or IGF-1, whereas nontreated SBT served as a negative control. Cellular proliferation and migration were evaluated after 24, 48, 72, and 96 hours of incubation. SBT-derived cells migrated in the detection field were visualized using fluorescent microscopy.

Results

Cellular proliferation at 24, 48, 72, and 96 hours was 1.40 ± 0.27, 1.00 ± 0.20, 1.47 ± 0.31, and 1.68 ± 0.28 for IGF-1; 1.44 ± 0.24, 1.15 ± 0.27, 1.60 ± 0.36, and 1.61 ± 0.32 for insulin; and 1.51 ± 0.35, 1.29 ± 0.33, 1.53 ± 0.35, and 1.57 ± 0.38 for nontreated SBT. Untreated SBT demonstrated a significantly greater proliferation when compared with IGF-1 and insulin within the first 48 hours, although this effect was found to subside by 96 hours. Cellular migration at 24, 48, 72, and 96 hours was 575.7 ± 45.0, 641.6 ± 77.7, 728.3 ± 122.9, and 752.3 ± 114.5 for IGF-1; 528.4 ± 31.3, 592.5 ± 69.8, 664.2 ± 115.2, and 695.6 ± 148.2 for insulin; and 524.4 ± 41.9, 564.4 ± 49.8, 653.2 ± 81.5, and 685.7 ± 115.5 for nontreated SBT. Insulin showed no difference in migration at each timepoint compared to nontreated SBT (P > .05, respectively).

Conclusions

Insulin and IGF-1 initially inhibit cellular proliferation of human SBT, although this effect was found to subside by 96 hours. Further, neither insulin nor IGF-1 changed the slope of cellular migration over time. However, each treatment group demonstrated a significant increase in cellular proliferation and migration.

Clinical Relevance

In the setting of biologic augmentation of rotator cuff repair, the compatibility and synergistic effect of insulin on human SBT is highly limited.

Subacromial Bursa-Derived Cells Demonstrate High Proliferation Potential Regardless of Patient Demographics and Rotator Cuff Tear Characteristics

PURPOSE

To investigate the influence of patient demographics and rotator cuff tear characteristics on the cellular proliferation potential of subacromial bursa-derived cells (SBDCs).

METHODS

Patients undergoing arthroscopic rotator cuff repair between December 2017 and February 2019 were considered for enrollment in the study. Basic demographic information as well as medical and surgical history were obtained for each patient. Subacromial bursa was harvested from over the rotator cuff tendon. Cellular proliferation was evaluated after 3 weeks of incubation by counting nucleated SBDCs. Fluorescence-activated cell sorting (FACS) analysis was performed to confirm the presence of mesenchymal stem cell (MSC) specific surface markers. Using preoperative radiographs and magnetic resonance imaging (MRI), acromiohumeral distance (AHD), severity of cuff tear arthropathy, and rotator cuff tear characteristics were evaluated.

RESULTS

Seventy-three patients (mean age: 57.2 ± 8.5 years) were included in the study. There was no significant difference in cellular proliferation of SBDCs when evaluating the influence of age, sex, body mass index (BMI), smoking status, and presence of systemic comorbidities (p > .05, respectively). Similarly, there was no significant difference in cellular proliferation of SBDCs when looking at rotator cuff tear characteristics (size, tendon retraction, fatty infiltration, muscle atrophy), AHD, or severity of cuff tear arthropathy (p > .05). FACS analysis confirmed nucleated SBDCs to have a high positive rate of MSC specific surface markers.

CONCLUSION

Subacromial bursa consistently demonstrated a high cellular proliferation potential regardless of patient demographics, rotator cuff tear characteristics, and severity of glenohumeral joint degeneration.

CLINICAL RELEVANCE

These findings may alleviate concerns that subacromial bursa might lose cellular proliferation potential when being used for biologic augmentation in massive and degenerated rotator cuff tears, thus assisting in predicting tendon healing and facilitating surgical decision-making.

Editorial Commentary: Mesenchymal Stem Cell Preparation Methods Affect the Properties of Shoulder Subacromial Bursa-Derived Cells

Augmentation of mesenchymal stem cells (MSCs) from the subacromial bursa in the setting of irreparable rotator cuff tears is a powerful candidate for future regenerative medicine. However, little is known about whether the preparation technique affects the individual differences and potentials of subacromial bursa-derived MSCs. The yields obtained by chopping or cell-expansion techniques with a high-density of initial nucleated cells seem to be lower than those obtained with low-density cell-expansion techniques. Differences in cell-preparation methods may affect whether individual differences in their properties exist. Further studies are required using a low-density cell-expansion technique to establish a new regenerative treatment using subacromial bursa-derived MSCs for irreparable rotator cuff tears.

Biologic Augmentation of Arthroscopic Rotator Cuff Repair Using Minced Autologous Subacromial Bursa

Failure of rotator cuff repair surgery can be attributed to a variety of factors, including insufficient biologic environment to support healing. The subacromial bursal tissue has been shown to have a reservoir of mesenchymal stem cells and is a potential source for biologic augmentation during rotator cuff repair. We have developed a technique to capture the subacromial bursal tissue during subacromial bursectomy and then reimplant the tissue on the bursal surface of the rotator cuff tendon after rotator cuff repair. Our goal is to describe our technique of subacromial tissue collection and reimplantation that obviates the need of suturing a whole sleeve of bursal tissue while improving cell yield for rotator cuff healing.

Local Autologous Stem Cells Application in Rotator Cuff Repairs: "LASCA" Technique

Rotator cuff tears are among the most common orthopaedic conditions, with a very high social impact. A major concern is failure rates. To reduce these rates, recent years have seen increased attention to the biological augmentation of rotator cuff tears repairs, with a special focus on the application of mesenchymal stem cells (MSCs). Among the many tissues recognized as a source of MSCs, subacromial bursa recently has emerged. Another promising cell source was found to be the long head of the biceps tendon. Both those local MSC sources, unfortunately, are commonly considered discharge material. The purpose of this paper is to describe a simple yet fast arthroscopic technique of biological augmentation for rotator cuff repairs by mechanical harvesting and deployment of local MSCs sources, called LASCA (local autologous stem cells application), a feasible technique accessible to every shoulder surgeon and adaptable to many different techniques.

Preliminary Clinical Outcomes Following Biologic Augmentation of Arthroscopic Rotator Cuff Repair Using Subacromial Bursa, Concentrated Bone Marrow Aspirate, and Platelet-Rich Plasma

Purpose

To evaluate the clinical outcomes of patients who underwent arthroscopic rotator cuff repair augmented using subacromial bursa, concentrated bone marrow aspirate (cBMA), and platelet-rich plasma.

Methods

Sixteen patients were included in the study who underwent arthroscopic rotator cuff repair augmented using subacromial bursa, cBMA, and platelet-rich plasma from January 2018 to July 2018 and had a minimum 1-year follow-up. American Shoulder and Elbow Surgeons (ASES), Simple Shoulder Test, Constant-Murley, and Single Assessment Numerical Evaluation (SANE) scores were collected preoperatively and at terminal follow-up. To determine the clinical relevance of ASES scores, the minimal clinically important difference, substantial clinical benefit, and the patient acceptable symptomatic state thresholds were used. In vitro cellular proliferation of subacromial bursa (nucleated cells/gram) and cBMA (nucleated cells and colony-forming units/cc) samples was evaluated and correlated to clinical outcomes scores.

Results

Mean follow-up was 12.6 ± 1.8 months (range 12-19 months). Patients achieved significant improvement in ASES (45.8±22.5_pre vs 88.5 ± 14.6_post, Δ44.7 ± 20.7; P = .001), Simple Shoulder Test (4.3 ± 3.2_pre vs 10.4 ± 1.6_post, Δ5.7 ± 3.9, P = .002), Constant-Murley (44.3 ± 18.2_pre vs 83.6 ± 17.5_post, Δ37.2 ± 21.8; P = .001), SANE (13.3 ± 10.7_pre vs 86.3 ± 17.5_post, Δ71.9 ± 22.9; P = .001), and pain scores (5.0±2.8_pre vs 1.1 ± 1.6_post, Δ3.5±2.5, P = .001) at final follow-up. With regards to ASES score, 93.8% of patients achieved the minimal clinically important difference, 93.8% the substantial clinical benefit, and 62.5% reached or exceeded the patient acceptable symptomatic state criteria. There was a significant positive correlation of nucleated cell count of cBMA with postoperative SANE score (r = 0.707; P = .015) and delta in ASES score (r = 0.727; P = .011). All other correlations were found to be nonsignificant (P > .05, respectively).

Conclusions

Patients undergoing arthroscopic rotator cuff repair augmented using the Mega-Clot with bursa technique achieved significant improvement in functional outcomes at a minimum 1-year follow-up, with 93.8% of patients reaching substantial clinical benefit.

Level of Evidence

Level IV, therapeutic case series.

Analysis of Time to Form Colony Units for Connective Tissue Progenitor Cells (Stem Cells) Harvested From Concentrated Bone Marrow Aspirate and Subacromial Bursa Tissue in Patients Undergoing Rotator Cuff Repair

Purpose

To evaluate the time required for colonies to develop from concentrated bone marrow aspirate (cBMA) and subacromial bursal tissue samples.

Methods

Samples of cBMA and subacromial bursa tissue were harvested from patients undergoing rotator cuff repair surgery between November 2014 and December 2019. Samples were analyzed for time to form colonies and number of colonies formed. The impact of age, sex, and cellularity (cBMA only) was analyzed. Samples were cultured and evaluated daily for colony formation in accordance with the guidelines of the International Society for Cellular Therapy. Demographic factors were analyzed for impact on time to form colonies and number of colonies formed.

Results

Samples of cBMA were obtained from 92 patients. Subacromial bursa tissue was obtained from 54 patients. For cBMA, older age was associated with more days to form colonies (P = .003), but sex (P = .955) and cellularity (P = .623) were not. For bursa, increased age was associated with longer time to form colonies (P = .002) but not sex (P = .804). Conclusions: Increased age (in cBMA and subacromial bursa tissue) and lower initial cellularity (in cBMA) are associated with longer time to form colonies in culture.

Clinical Relevance

Although connective tissue progenitor cells are widely used in orthopaedic practice, there are few metrics to determine their efficacy. Time to form colonies may serve as an important measurement for determining connective tissue progenitor cell viability for augmentation of rotator cuff repair. Subacromial bursa tissue may represent a viable alternative to cBMA for augmentation of rotator cuff repair, capable of forming colonies expediently in vivo.

Editorial Commentary: Mesenchymal Stem Cells in the Shoulder Subacromial Bursa: Do Cells Understand Statistical Significance?

Local, arthroscopic harvest of mesenchymal stem cells is of interest due to their potential to augment healing. The high rates of retear after rotator cuff repair are a significant concern, and solutions, such as augmentation with mesenchymal stem cells, are being sought. The subacromial bursa of the shoulder is a potential source of cells to augment healing.

Intraoperative and In Vitro Classification of Subacromial Bursal Tissue

PURPOSE

To classify subacromial bursal tissue using intraoperative and in vitro characteristics from specimens harvested during arthroscopic shoulder surgery.

METHODS

Subacromial bursa was harvested over the rotator cuff from 48 patients (57 ± 10 years) undergoing arthroscopic shoulder surgery. Specimens were characterized intraoperatively by location (over rotator cuff tendon or muscle), tissue quality (percent of either fatty or fibrous infiltration), and vascularity before complete debridement. Nucleated cell counts were determined after 3 weeks incubation and histological sections were reviewed for degree of fatty infiltration and vascularity. Mesenchymal stem cell surface markers were counted via flow cytometry (n = 3) and cellular migration was observed using a fluoroscopic assay (n = 3).

RESULTS

Intraoperatively, muscle bursa was found most often to have >50% fatty infiltration (n = 39), whereas tendon bursa showed majority fibrous tissue (n = 32). Cellular proliferation did not significantly differ according to intraoperative tissue quality. Intraoperative vascularity was associated with greater proliferation for highly vascular samples (P = 0.023). Tendon bursa demonstrated significantly greater proliferation potential than muscle bursa (P = 0.00015). Histologic assessment of fatty infiltration was moderately correlated with gross tissue fattiness (ρ = -0.626, P = 7.14 × 10^-11). Flow cytometry showed that 90% to 100% of bursal cells were positive for MSC surface markers. Peak cellular migration rates occurred between 18 and 30 hours' incubation.

CONCLUSIONS

Intraoperative and in vitro subacromial bursa characteristics were not found to reliably correlate with the degree of cellular proliferation. However, the anatomic location of subacromial bursa was consistently predictive of increased proliferation potential. Bursa-derived nucleated cells were confirmed to include mesenchymal stem cells with migratory potential.

CLINICAL RELEVANCE

The anatomic distinction between muscle and tendon bursa provides a simple classification for predicting cellular activity.

Editorial Commentary: Are We Ready to Apply Stem Cell Therapy in Rotator Cuff Tear Surgery?

For rotator cuff tear surgery, application of mesenchymal stem cells (MSCs) is a promising new option. Among various MSC sources, synovial tissue contains a high number of MSCs with high chondrogenic potential. Because chondrogenic formation is an important factor in enthesis healing in rotator cuff repair, synovial MSCs derived from the subacromial bursa are superior candidates for the augmentation of rotator cuff tear surgery.