Recent publications from The Hospital for Special Surgery (HSS) in New York (1) and the University of Sassari in Italy (2) compared NanoFx® to microfracture and k-wires for marrow stimulation and its effect on the subchondral bone architecture. The HSS study demonstrated that larger instruments caused more disruption to the bone and the Italian results showed that the deeper NanoFx® (Nanofracture) perforations led to a better restoration of the subchondral bone architecture at 6 months. An additional concern highlighted in the Zedde et al. publication was that 75% of the microfracture subjects had subchondral cysts, whereas no cysts were found in the Nanofracture group.
Within the past 10 years, the Sports Medicine community has shifted its focus away from the tissue that eventually fills the defect area and towards the osteochondral unit. As the HSS article commented, “any technique that can change the structure of the subchondral bone has the potential to affect the biomechanics of the osteochondral unit, the repair process, and the overall cartilage resurfacing outcome.” Similar to the construction of a house, the foundation has become just as important, if not more, than the roof.
Marrow stimulation remains one of the most common first-line treatment options for cartilage defects. However, the decline in clinical outcomes seen with microfracture at 18-36 months after the procedure22-28 continues to drive surgeons to search for a new alternative to the standard of care. The research highlights three key elements that affect outcomes when performing marrow stimulation techniques:
Channel diameter and
Subchondral bone disruption
Chen et al demonstrated that to access the marrow-rich subarticular spongiosa, a depth greater than 6mm was best. Hoemann and colleagues assessed the bone disruption of awls and found that the larger and deeper the awls went, the more compaction damage there was to the lesion surface. In 2014, Eldracher et al. compared marrow stimulation using 1.0 or 1.8mm drills at a standardized depth of 10 mm in an ovine model.20 The smaller 1.0mm subchondral drill holes that reflected the physiological trabecular distance significantly improved osteochondral repair in a translational model more effectively than larger drill holes.
The goal of marrow stimulation is to perforate the bone to allow access to the marrow compartment which contains the stem cells, growth factors and healing proteins necessary to form a superclot that includes the essential biological elements needed to initiate a repair of the defect site. Increasing type II collagen and reducing type I is also seen as vital to the development of a more robust cartilage-like tissue. When the data from these various sources is combined with the Nanofracture® comparative data from HSS and the University of Sassari, a clear picture for a more successful marrow stimulation repair emerges. The ideal instrument must be able to perforate deeply into the bone, have a diameter of 1mm to match the trabecular distance, do so without disrupting the subchondral bone unit, self-seal to avoid cyst formation all while stimulating type II collagen synthesis in the defect area to improve biological healing.
Smaller, Deeper, Better is not simply a marketing slogan but rather the criteria for a new standard of care in marrow stimulation.
Gianakos AL, Yasui Y, Fraser EJ, Ross KA, Prado MP, Fortier LA, Kennedy JG. The Effect of Different Bone Marrow Stimulation Techniques on Human Talar Subchondral Bone: A Micro-Computed Tomography Evaluation. Arthroscopy. 2016 Oct;32(10):2110-2117. doi: 10.1016/j.arthro.2016.03.028. PubMed PMID: 27234650.
Zedde P, Cudoni S, Giachetti G, Manunta ML, Masala G, Brunetti A, Manunta AF. Subchondral bone remodeling: comparing nanofracture with microfracture. An ovine in vivo study. Joints. 2016 Aug 18;4(2):87-93.