Proximal Humerus and Ilium Are Reliable Sources of Bone Marrow Aspirates for Biologic Augmentation During Arthroscopic Surgery

Patient Demographic Factors Are Not Associated With Mesenchymal Stromal Cell Concentration in Bone Marrow Aspirate Concentrate

Purpose

To describe the capacity for concentration of a single processing machine for bone marrow aspirate concentrate (BMAC) production and investigate the effects of demographic factors on the number of mesenchymal stromal cells (MSCs) in BMAC.

Methods

Patients enrolled in our institution's randomized control trials involving BMAC who had complete BMAC flow cytometry data were included. Multipotent MSC phenotype, defined as cell-surface coexpression of specific-identifying antigens (≥95% positive) and the absence of hematopoietic lineage markers (≤2% positive), was determined for both patient bone marrow aspirate (BMA) and BMAC samples. The ratio of cells in BMA:BMAC samples was calculated and Spearman correlations (i.e., body mass index [BMI]) and Kruskall-Wallis (i.e., age: <40, 40-60, >60 years) or Mann-Whitney (i.e., sex) tests were used to determine the relationship of cell concentration to demographic factors.

Results

Eighty patients were included in analysis (49% male, mean age: 49.9 ± 12.2 years). Mean concentration of BMA and BMAC was 2,048.13 ± 2,004.14 MSCs/mL and 5,618.87 ± 7,568.54 MSC/mL, respectively, with a mean BMAC:BMA ratio of 4.35 ± 2.09. A significantly greater MSC concentration was observed in the BMAC samples when compared with BMA (P = .005). No patient demographic factors (age, sex, height, weight, BMI) were found to predict MSC concentration in the BMAC samples (P ≥ .01).

Conclusions

Demographic factors, including age, sex, and BMI do not impact the final concentration of MSCs in BMAC when using a single harvest technique (anterior iliac crest) and a single processing system.

Clinical Relevance

As the role of BMAC therapy expands in clinical application, it becomes increasingly important to understand the determinants of BMAC composition and how it is affected by different harvesting techniques, concentrating processes, and patient demographics.

Arthroscopy and Musculoskeletal Biologics

Orthopaedic biologics holds great promise. Absent peer-reviewed clinical musculoskeletal research, orthobiologics indications and treatment recommendations will remain opaque. In a Call for Papers, Arthroscopy; Arthroscopy Techniques; and Arthroscopy, Sports Medicine, and Rehabilitation editors invite authors to submit clinical musculoskeletal biologics original scientific research, and technical notes with video. Each year, the top articles will be awarded inclusion in an annual Biologics Special Issue. Future investigators and current readers could follow the science while being mindful of the regulatory environment.

Orthopaedic Musculoskeletal Biologics Research Impacts Patient Care: The First Annual Arthroscopy Orthobiologics Virtual Special Issue

Orthobiologics can modify symptoms and improve healing in a variety of musculoskeletal conditions as a part of office-based care or as an adjunct to surgery. Orthobiologics harness the benefits of naturally derived blood components, autologous tissue, and growth factors to reduce inflammation and optimize the host-healing environment. The Arthroscopy family of journals seeks to positively influence evidence-based clinical decision-making by publishing peer-reviewed biologics research. This special issue contains recent influential articles strategically chosen to positively impact patient care.

Harvest and Application of Bone Marrow Aspirate Concentrate to Address Acetabular Chondral Damage During Hip Arthroscopy

Background

During hip arthroscopy, managing concomitant cartilage damage and chondrolabral junction breakdown remains an ongoing challenge for orthopaedic surgeons, as previous studies have associated such lesions with inferior postoperative outcomes1-7. Although higher-level studies are needed to fully elucidate the benefits, recent literature has provided supporting preliminary evidence for the utilization of bone marrow aspirate concentrate (BMAC) in patients with moderate cartilage damage and full-thickness chondral flaps undergoing acetabular labral repair7,8. Thus, as the incorporation of orthobiologics continues to advance, there is a clinical demand for an efficient and reliable BMAC-harvesting technique that utilizes an anatomical location with a substantial concentration of connective tissue progenitor (CTP) cells, while avoiding donor-site morbidity and minimizing additional operative time. Thus, we present a safe and technically feasible approach for harvesting bone marrow aspirate from the body of the ilium, followed by centrifugation and application during hip arthroscopy.

Description

After induction of anesthesia and appropriate patient positioning, a quadrilateral arrangement of arthroscopic portals is established to perform puncture capsulotomy9. Upon arthroscopic visualization of cartilage/chondrolabral junction injury, 52 mL of whole venous blood is promptly obtained from an intravenous access site and combined with 8 mL of anticoagulant citrate dextrose solution A (ACD-A). The mixture is centrifuged to yield approximately 2 to 3 mL of platelet-rich plasma (PRP) and 17 to 18 mL of platelet-poor plasma (PPP). Then, approaching along the coronal plane and aiming toward the anterior-superior iliac spine under fluoroscopic guidance, a heparin-rinsed Jamshidi bone marrow biopsy needle is driven through the lateral cortex of the ilium just proximal to the sourcil. Under a relative negative-pressure vacuum, bone marrow is aspirated into 3 separate heparin-rinsed 50 mL syringes, each containing 5 mL of ACD-A. Slow and steady negative pressure should be used to pull back on the syringe plunger to aspirate a total volume of 40 mL into each syringe. To avoid pelvic cavity compromise and minimize the risk of mobilizing marrow-space contents, care should be taken to ensure that no forward force or positive pressure is applied during the aspiration process. A total combined bone marrow aspirate/ACD-A mixture of approximately 120 mL is consistently harvested and subsequently centrifuged to yield roughly 4 to 6 mL of BMAC. The final mixture containing BMAC, PRP, and PPP is combined with thrombin to generate a megaclot, which is then applied to the central compartment of the hip.

Alternatives

Currently, strategies to address acetabular cartilage lesions may include microfracture, autologous chondrocyte implantation, matrix-induced autologous chondrocyte implantation, autologous matrix-induced chondrogenesis, osteochondral allografts, and orthobiologics10. Orthobiologics have shown mixed yet promising results for addressing musculoskeletal injuries and may include bone-marrow-derived mesenchymal stromal cells, adipose tissue derivatives, and PRP7,8,11,12. Specifically, bone marrow aspirate can be harvested from numerous locations, such as the iliac crest, the proximal aspect of the humerus, the vertebral body, and the distal aspect of the femur. Moreover, alternative approaches have utilized multiple-site and/or needle-redirection techniques to optimize cellular yield16,17, while also appreciating the potentially variable cellular characteristics of aspirated and/or processed samples18. However, previous literature has demonstrated that the body of the ilium contains a CTP cell concentration that is similar to or greater than other harvest locations when utilizing this outlined single-site and unidirectional aspirating technique13,14.

Rationale

This versatile and updated technique is a safe and reproducible method for BMAC harvesting, processing, and application that avoids donor-site morbidity, obtains a substantial concentration of CTP cells, minimizes additional operative time, and limits the hip arthroscopy and aspiration to a single procedure15. Specifically, this technique details an evidence-supported approach to addressing chondral injury in patients undergoing acetabular labral repairs7,8.

Expected Outcomes

Patients with moderate cartilage damage treated with BMAC at the time of labral repair experienced significantly greater improvements in functional outcomes at 12 and 24 months postoperatively compared with similar patients without BMAC augmentation7. Furthermore, patients with full-thickness chondral flaps treated with BMAC at the time of arthroscopic labral repair demonstrated significantly greater improvements in functional outcomes at 12 months compared with microfracture. Moreover, 77.6% of the BMAC cohort reached the minimal clinically important difference threshold for the International Hip Outcome Tool-33 (iHOT-33) compared with 50.0% in the microfracture group8.

Important Tips

Utilize the previously established Dienst arthroscopic portal for the bone marrow aspiration in order to avoid secondary donor site morbidity.Under fluoroscopic guidance, approach the ilium along the coronal plane, aiming toward the anterior superior iliac spine.With a heparin-rinsed Jamshidi bone marrow biopsy needle, penetrate the lateral cortex of the ilium just proximal to the sourcil in order to consistently harvest a total combined bone marrow aspirate/ACD-A volume of approximately 120 mL.Simultaneously perform the bone marrow aspirate and whole venous blood centrifugation during the hip arthroscopy procedure in order to minimize additional operative time.Bone marrow aspiration should be performed without applied traction in order to minimize the risk of neurovascular complications associated with extended traction time.

Acronyms and Abbreviations

ACD-A = anticoagulant citrate dextrose solution AADSCs = adipose-derived stem cellsASIS = anterior superior iliac spineBMAC = bone marrow aspirate concentrateCI = confidence intervalCTP = connective tissue progenitorDVT = deep vein thrombosisHOS-ADL = Hip Outcome Score, Activities of Daily LivingiHOT-33 = International Hip Outcome Tool-33MCID = minimal clinically important differenceMRA = magnetic resonance arthrogramMSCs = mesenchymal stromal cellsPPP = platelet-poor plasmaPRP = platelet-rich plasmaRBCs = red blood cellsSD = standard deviationT1 = longitudinal relaxation timeT2 = transverse relaxation timeWBCs = white blood cells.

Interpositional scaffold anchor rotator cuff footprint tear repair: excellent survival, healing, and early outcomes

PURPOSE

Shoulder function limitation duration after a full-thickness rotator cuff tendon (RCT) tear may influence post-repair healing and outcomes. A suture anchor was developed to improve footprint repair fixation and healing through biological fluid delivery and scaffold augmentation. The primary multicenter study objective was to evaluate RCT repair failure rate based on 6-month MRI examination, and device survival at 1-year follow-up. The secondary objective was to compare the clinical outcomes of subjects with shorter- and longer-term shoulder function limitation duration.

METHODS

Seventy-one subjects (46 men) with moderate-to-large RCT tears (1.5-4 cm), at a median 61 years of age (range = 40-76), participated in this study. Pre-repair RCT tear location/size and 6-month healing status were confirmed by an independent radiologist. Subjects with shorter- (Group 1: 17.8 ± 21 days, n = 37) and longer-term (Group 2: 185.4 ± 89 days, n = 34) shoulder function limitation durations were also compared over 1 year for active mobility, strength, American Shoulder and Elbow Surgeon's Shoulder Score (ASES score), Veterans RAND 12 Item Health Survey (VR-12), and visual analog scale (VAS) pain and instability scores.

RESULTS

Three of the 52 subjects [5.8%] who underwent 6-month MRI experienced a re-tear at the original RCT footprint repair site. By the 1-year follow-up, overall anchor survival was 97%. Although Group 2 displayed lower ASES and VR-12 scores pre-repair (ASES = 40.1 ± 17 vs. 47.9 ± 17; VR-12 physical health (PH) = 37.2 ± 9 vs. 41.4 ± 8) (p ≤ 0.048), at 3-month post-RCT repair (ASES = 61.3 ± 19 vs. 71.3 ± 20; VR-12 PH = 40.8 ± 8 vs. 46.8 ± 9) (p ≤ 0.038), and at 6-month post-RCT repair (ASES = 77.4 ± 18 vs. 87.8 ± 13; VR-12 PH = 48.9 ± 11 vs. 54.0 ± 9) (p ≤ 0.045), by 1-year post-RCT repair, groups did not differ (n.s.). Between-groups VR-12 mental health score differences were not evident at any time period (n.s.). Shoulder pain and instability VAS scores also did not differ (n.s.), displaying comparable improvement between groups from pre-RCT repair to 1-year post-RCT repair. Groups had comparable active shoulder mobility and strength recovery at each follow-up (n.s.).

CONCLUSION

At 6-month post-RCT repair, only 3/52 of patients [5.8%] had a footprint re-tear, and at 1-year follow-up, overall anchor survival was 97%. Use of this scaffold anchor was associated with excellent early clinical outcomes regardless of shoulder function impairment duration.

LEVEL OF EVIDENCE

II.

Concentrated Bone Marrow Aspirate Is More Cellular and Proliferative When Harvested From the Posterior Superior Iliac Spine Than the Proximal Humerus

PURPOSE

The purpose of this study is to determine whether concentrated bone marrow aspirate (cBMA) from the posterior superior iliac spine (PSIS) or proximal humerus (PH) produces a more productive cellular harvest in patients undergoing arthroscopic rotator cuff repair.

METHODS

Patients under 80 years old undergoing surgery for arthroscopic rotator cuff repair were enrolled. Two 60 mL aliquots of BMA were harvested from each subject, one from the PSIS and one from the PH. Each aliquot was processed independently to create cBMA. Cellular composition was determined using an automated hemocytometer and proliferative potential was studied with colony forming unit (CFU) assays.

RESULTS

Twelve patients were recruited (7 male, 5 female). The average age was 64.3 years (range 46.1-77.25 years) with body mass index of 26.8 (range 20.0-34.3). The average total nucleated cells (TNC) from PH was 18.7 × 10⁶ cells/mL (95% confidence interval [CI], 4.4-33.0; standard deviation [SD], 24.8) with 3.9 CFU/mL (95% CI, 0.3-7.5, SD, 5.7). The average TNC count from the PSIS was 55.9 × 10⁶ cells/mL (95% CI, 25.3-86.4; SD, 52.9) with 32.5 CFU/mL (95% CI, 11.5-53.5; SD, 33.1). The PSIS had a 3.0 times greater total nucleated cell yield (P = .014) and 8.3 times greater number of CFU/mL (P = .024) when compared to the PH. The average harvest time from the PSIS was 5.6 minutes and from the PH was 11.0 minutes (P = .043); harvest time did not account for additional time to prep and drape the PSIS.

CONCLUSIONS

The cBMA harvested from the PSIS resulted in a 3.0 times greater cellular yield and an 8.3 times greater proliferative product than cBMA from the PH.

CLINICAL RELEVANCE

When a more cellular cBMA product is sought to augment rotator cuff tear repair surgery, the PSIS is the preferred site for harvest.

Impact of the Process Variables on the Yield of Mesenchymal Stromal Cells from Bone Marrow Aspirate Concentrate

Human bone marrow (BM) has been highlighted as a promising source of mesenchymal stromal cells (MSCs) containing various growth factors and cytokines that can be potentially utilized in regenerative procedures involving cartilage and bone. However, the proportion of MSCs in the nucleated cell population of BM is only around 0.001% to 0.01% thereby making the harvesting and processing technique crucial for obtaining optimal results upon its use in various regenerative processes. Although several studies in the literature have given encouraging results on the utility of BM aspiration concentrate (BMAC) in various regenerative procedures, there is a lack of consensus concerning the harvesting variables such as choice of anesthetic agent to be used, site of harvest, size of the syringe to be used, anticoagulant of choice, and processing variables such as centrifugation time, and speed. In this review article, we aim to discuss the variables in the harvesting and processing technique of BMAC and their impact on the yield of MSCs in the final concentrate obtained from them.

High Variability of Mesenchymal Stem Cells Obtained via Bone Marrow Aspirate Concentrate Compared With Traditional Bone Marrow Aspiration Technique

Background:

Bone marrow aspirate (BMA) is a common source for harvesting mesenchymal stem cells (MSCs), other progenitor cells, and associated cytokines and growth factors to be used in the biologic treatment of various orthopaedic pathologies. The aspirate is commonly centrifuged into a concentrated volume that can be immediately administered to a patient using commercially available kits. However, the handling and efficacy of BMA concentrate (BMAC) are still controversial.

Purpose:

To characterize BMA versus BMAC for MSC quantity, potency, and cytokine profile.

Study Design:

Controlled laboratory study.

Methods:

From 8 participants (age, 17-68 years), 30 mL of bone marrow was aspirated by a single surgeon from either the proximal humerus or distal femur and was separated into 2 equal samples. One sample was kept as BMA, and the other half was centrifuged into BMAC. The 2 samples then underwent flow cytometry for detection of MSCs, cell analysis for colony-forming units (CFUs), and cytokine profiling. A 2-tailed t test was used to detect differences between MSCs, CFUs, and cytokine density concentrations between BMA and BMAC.

Results:

The average concentration of MSCs in both BMA and BMAC was 0.001%. Average MSC events detected by flow cytometry were significantly higher in BMA versus BMAC (15.1 and 8.1, respectively; P < .045). Expanded MSCs demonstrated similar phenotypes, but CFUs were significantly increased in BMA compared with BMAC (104 vs 68 CFUs, respectively; P < .001). Total protein concentration and cytokine profiling demonstrated great variability between BMA and BMAC and between patients. Most importantly, BMAC failed to concentrate MSCs in 6 of 8 samples.

Conclusion:

There is great variability in MSC concentration, total protein concentration, and cytokine profile between BMA and BMAC.

Clinical Relevance:

When studying the clinical efficacy of BMAC, one must also evaluate the sample itself to determine the presence, concentration, and potency of MSCs if this is to be considered a cell-based therapy. Further standard operating procedures need to be investigated to ensure reproducible results and appropriate treatments.

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.

Injection of Bone Marrow Aspirate for Glenohumeral Joint Osteoarthritis: A Pilot Randomized Control Trial

Purpose

To compare the efficacy of a single, intra-articular, nonconcentrated bone marrow aspirate (BMA) injection in comparison to cortisone for the treatment of glenohumeral joint osteoarthritis (GHJ OA).

Methods

Inclusion criteria were patients between the ages of 18 and 75 with a diagnosis of GHJ OA on radiograph. Patients were randomized to receive an ultrasound-guided, intra-articular cortisone injection or BMA injection (without concentration). The primary outcome measure was the Western Ontario Osteoarthritis of the Shoulder (WOOS) index at 12 months. Secondary outcome measures were the QuickDASH, EuroQOL 5-dimensions 5-level questionnaire (EQ-5D-5L) and visual analogue scale.

Results

The study included 25 shoulders of 22 patients who completed baseline and 12 months’ patient-reported outcome measures (12 shoulders received cortisone, 13 shoulders received BMA) after the study was terminated early by changes in Health Canada regulations. Baseline characteristics demonstrated a significant difference in the ages of the 2 groups, with the BMA group being older (61.6 vs 53.8 mean years, P = 0.021). For the BMA group, a significant improvement was seen in the WOOS index (P = 0.002), the QuickDASH (P < 0.001), and the EQ-5D-5L pain dimension (P = 0.004) between baseline and 12 months. No significant difference was seen for any outcome in the cortisone group between baseline and 12 months. No significant difference was demonstrated between changes in the WOOS scores from baseline to 12 months when compared between groups (P = 0.07). However, a significant difference in changes in scores was seen in the QuickDASH (P = 0.006) and the EQ-5D-5L pain scores (P = 0.003) and the EQ-5D-5L health scores (P = 0.032) in favor of BMA.

Conclusions

The results of this study demonstrate that patients with GHJ OA treated with BMA have superior changes in the QuickDASH and EQ-5D-5L pain and health scores but not in the WOOS outcomes measures at 12 months post injection when compared to patients treated with cortisone. However, because of the limited number of patients as a result of the early termination of the study, larger randomized studies are required to confirm these findings.

Level of Evidence

Level II, randomized controlled trial.

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.

Editorial Commentary: Shoulder Rotator Cuff Tendon Repair Using Bone Marrow Aspirate: Stem Cell Quantity Does Not Equal Quality

The use of biological agents in orthopaedic surgery is rapidly evolving. The potential to augment the healing environment at a surgical repair site is an especially exciting possibility. There are a few popular biological agents, including platelet-rich plasma, concentrated bone marrow aspirate (BMA), and adipose-derived connective tissue progenitor cells. BMA is an especially appealing biological agent because it can be harvested from a variety of sources, including the iliac crest, distal femur, and proximal humerus. As a result, BMA is readily accessible with minimal added surgical time and morbidity during surgical procedures on the hip, knee, and shoulder. In particular, the surgically repaired rotator cuff tendon is a prime candidate for biological augmentation, and the proximal humerus is an appealing source of concentrated BMA given its ease of access and low harvesting morbidity at the time of arthroscopic repair. The nucleated cell count may be considered a surrogate for the quality of BMA and can be readily calculated at the time of harvest. However, the quantity of nucleated cells does not necessarily equate to the quality of nucleated cells as colony-forming units after cell culture, nor do we know how ex vivo cell culture correlates with in vivo stem cell proliferation and healing. Most of all, future research must determine what factors (if any) do positively correlate with the number of colony-forming units.

Editorial Commentary: Bone Marrow Aspirate Concentrate: Time to Harvest Locally?

Cell therapies hold great promise as primary and adjuvant treatments for a range of musculoskeletal conditions. Bone marrow harvested from the iliac crest represents the gold-standard source of progenitor cells with a recognized ability to release trophic factors, modulate local immune environments, and differentiate into multiple musculoskeletal cell types in vitro. Identifying accessible locations that limit donor-site morbidity while increasing efficiency during aspiration of bone marrow is essential. There is increasing evidence to suggest that the number of progenitor cells present in bone marrow aspirated from multiple sites, including the proximal humerus and ilium, is at least equivalent to that from the iliac crest. Because many of these sources lie within the surgical field, the requirement for iliac crest harvest and the risks associated with secondary harvest sites can be mitigated. Although there is a clear need for further studies evaluating the biological attributes and clinical benefit of bone marrow aspirate concentrate in a range of clinical settings, the use of local harvesting sites is likely to reduce morbidity and improve the experience for patients.