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

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.

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.

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.

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.

Nucleated Cell Count Has Negligible Predictive Value for the Number of Colony-Forming Units for Connective Tissue Progenitor Cells (Stem Cells) in Bone Marrow Aspirate Harvested From the Proximal Humerus During Arthroscopic Rotator Cuff Repair

PURPOSE

To evaluate whether nucleated cell count (NCC) could serve as an approximation for the number of colony-forming units (CFUs) in concentrated bone marrow aspirate (cBMA) obtained from the proximal humerus.

METHODS

Bone marrow aspirate (BMA) was harvested from the proximal humerus in 96 patients (mean age 56.2 ± 7.0 years) during arthroscopic rotator cuff repair. Following concentration of the aspirate, nucleated cells of each sample were counted. The total number of CFUs was evaluated under the microscope at their first appearance, usually after 5 to 10 days in culture. Fluorescence-activated cell sorting analysis and assays for osteogenic, adipogenic, and chondrogenic differentiation were performed. Linear regression was assessed to predict the number of CFUs by using NCC. Age, sex, and body mass index (BMI) were evaluated as independent variables.

RESULTS

The average volume of the obtained BMA was 86.7 ± 35.2 mL. The cBMA contained a mean of 26.3 ± 6.8 × 10⁶ nucleated cells per mL, which yielded a mean of 1421.7 ± 802.7 CFUs in cell culture. There were no significant differences in NCC or number of CFUs when sex, volume of BMA, age, or BMI was examined independently (P >.05, respectively). Linear regression found that NCC was of limited predictive value for the total number of CFUs being yielded after cell culture (r² = 0.28 with a root mean square error of 679.4).

CONCLUSION

NCC was of negligible predictive value for the total number of CFUs for connective tissue progenitor cells in BMA harvested from the proximal humerus during arthroscopic rotator cuff repair.

CLINICAL RELEVANCE

NCC is often used to assess the quality of cBMA samples for biological augmentation during surgery. The limited predictive value of this measurement tool is of clinical importance, because effectiveness of BMA applications has been suggested to depend on the concentration of progenitor cells within the sample.

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.