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.