Augmentation with BMAC has emerged as a prominent biological augmentation strategy in the field of orthobiologics. The BMAC is harvested from the intramedullary canal of three well-known sites: the iliac crest, proximal tibia, or proximal humerus [25]. The efficacy of BMAC is believed to stem from its ability to manipulate and concentrate specific cellular, cytokine, and growth factor populations [26]. In addition, regenerative capacity is achieved, as MSCs are within the harvested population, thus facilitating the ability to differentiate into bone, cartilage, or tendons [9]. Furthermore, the anti-inflammatory properties are provided by the associated increasing concentration of interleukin 1 receptor antagonist (IL-1Ra) in the final concentrate [26]. Consequently, the pro-inflammatory and tissue-degrading effects of excessive inflammation are regulated and suppressed, promoting enhanced biological healing [26].

In recent years, BMAC has been theorized to enhance biological healing due to the ability of the MSC population to differentiate into mesenchymal-origin cells, including bone, tendon, muscle, and cartilage [9]. This differentiation increases the density of type I collagen fibers, resulting in a more mechanically stable repair construct and enhanced local biological healing that resembles the native enthesis morphology [9]. This has been demonstrated in preclinical models where BMAC-augmented rotator cuff animal models demonstrated improved outcomes in comparison with standard cuff repairs [14, 27].

Gulotta et al. [14] observed enhanced mechanical and histological properties—specifically load to failure, stiffness, and fibrocartilage density—in rat rotator cuff models injected with scleraxis-transduced bone marrow MSCs compared with those receiving only MSCs. Their results reflect the importance of additional cellular, cytokine, and growth factor manipulation, a key principle behind BMAC utilization. Similarly, in rabbit rotator cuff models, Liu et al. [27] demonstrated that BMAC-augmented repairs biomechanically and histologically outperformed those treated with normal saline (NS), PRP, and bone marrow aspirate (BMA) at 6 weeks post-surgery. They attributed the ability of BMAC to enhance biological healing to its higher concentrations of MSCs, regulation of the inflammatory cascade (via increased IL-1Ra), and the vast presence of associated growth factors such as VEGF, PDGF, TGF, and IGF, compared with NS, PRP, and BMA. However, translating these promising preclinical results into clinical practice requires further evaluation.

While harvesting from the iliac crest is generally possible, the senior authors of this review prefer harvesting BMAC from the proximal humerus for RCR augmentation due to its proximity to the surgical site. This technique has been described in detail by Allahabadi et al. [25].

Before starting the concomitant surgical procedure, the osseous landmarks proximal humerus and glenohumeral joint are identified. The harvesting needle is positioned 3 cm distal to the midpoint between the anterior and posterior acromial borders and directed into the intramedullary cavity while aiming medially, anteriorly, and inferiorly (Fig. 3a). A sharp trocar located within the needle’s inner circle aids in penetration of the humeral cortex to a depth of ~3 cm. A mallet is used to adequately position the needle within the cancellous bone, past the nearby bony cortex (Fig. 3b). Once the needle is properly placed, the inner trocar stylet is removed, leaving the needle in situ. Two anticoagulant 30-mL syringes are used sequentially to aspirate a total of 60 mL of bone marrow (Fig. 3c). Aspiration is facilitated by rotating the syringe 90° every 5–10 mL (Fig. 3d), thus enhancing trabecular breakdown and further content aspiration. After aspiration, the needle is withdrawn, and the specimen is taken for processing while the concomitant surgical procedure continues.

Bone marrow aspirate harvesting: bone marrow aspiration performed from the proximal humerus. The harvesting needle (Arthrex, Naples, FL, USA) is inserted 3 cm distal to the midpoint between the acromial borders (a) and directed medially, anteriorly, and inferiorly. A mallet is used to impact the needle (b) and approximately 60 mL of bone marrow is aspirated (c) using slight twists (d) for further processing

Processing of the specimen begins with filtering of the aspirate, i.e., by using the Angel system (Arthrex). This is followed by centrifugation at the 7% setting to isolate and concentrate the desired cellular, growth factor, and cytokine populations, yielding approximately 5 mL of BMAC. The supernatant is then placed in a sterile syringe and returned to the surgical field for application. First, watertight closure of all arthroscopic portals and removal of excess intra-articular fluid are performed before BMAC injection to prevent extravasation and dilution of the concentrate, respectively. The BMAC can then be applied to the RCR, with half of the BMAC volume injected into the tendon at the bone junction and the remaining half injected at the footprint site.

By harvesting the sample at the beginning of the procedure, this technique allows the specimen to be processed concurrently with the RCR, thereby expediting the overall process. Additionally, the proximity of the proximal humerus eliminates the need for patient repositioning, further streamlining the harvesting process. However, this technique has its limitations. It requires specialized equipment and expertise to ensure a smooth BMAC harvest and processing. Furthermore, the quality of the BMAC harvest from the proximal humerus may be compromised in older individuals.