The Challenge and the Promise of Bone Marrow Cells for Human Cartilage Repair

The cartilage repair potential of bone marrow-derived stem cells has been well described. Harnessing this potential for human articular cartilage repair remains challenging. Accessing bone marrow repair cells through marrow stimulation techniques such as microfracture is readily achieved with generally good but inconsistent results. Animal and human studies show feasibility for ex vivo processing of bone marrow to isolate, concentrate, and culture mesenchymal stem cells. Nevertheless, it has been difficult to show consistent and clinically meaningful improvement using bone marrow cell preparations above what has been achieved with microfracture. Consequently, microfracture continues to be the simplest and most commonly used method to enhance repair of focal articular cartilage defects. Emerging preclinical work in the equine model suggests a role for enhancing marrow-stimulation techniques through the use of natural scaffolds such as autologous platelet enriched fibrin as well as optimization of joint biology through localized gene therapy to support cartilage repair. In contrast to joint replacement where inert materials of known mechanical properties are used, host biology determines the relative success, failure, and durability of cartilage repair. As such, development of personalized strategies to improve the quality and durability of bone marrow cell-based articular cartilage repair represent exciting new areas of inquiry. Continued advances in stem cell biology, scaffold technologies, and methods to delineate and enhance host biology, both systemically and within the joint, hold promise for harnessing the full power of bone marrow cells to facilitate cartilage repair and regeneration.