Articular cartilage is a unique and complex tissue. The interactions among chondrocytes, water, and matrix macromolecules provide articular cartilage with its special properties, including the absorption and distribution of compressive loads and low-friction articulation of synovial joints. However, this complex, unique, and sophisticated tissue does not repair itself well and cartilage repair recently has become the target of numerous investigations. Indeed, the natural history of articular cartilage defects is not well defined and thus the development of treatment strategies has been limited. One technique that has gained some success is microfracture.
Microfracture is a commonly employed operative technique that is considered to be safe, relatively inexpensive, and minimally invasive as a first-line treatment for small, contained articular cartilage defects. The scientific basis of microfracture is that disruption of blood vessels in the subchondral bone will cause bleeding in the cartilage defect, leading to the formation of a fibrin clot. It has been suggested that if the clot is protected from loading, undifferentiated mesenchymal stem cells from the bone marrow will migrate into the defect, proliferate, and differentiate into fibrochondrocytes. These chondrocytes then synthesize a fibrocartilaginous matrix that fills the defects. Evidence has shown that microfracture has acceptable short-term clinical results, but those results can be expected to decline over time. What is most important for the surgeon is to determine which patients are the best candidates for this procedure and which patients should not be so treated.
Determining which patients and which cartilage defects are best treated with microfracture can be difficult. Moreover, as the results have been reported over the years, the indications for this technique have narrowed. Clinical experience has shown that lesions measuring >4 cm2 have been associated with worse outcomes. On the other hand, the minimum defect size for which microfracture should be used has not been clearly defined. Another factor is age, with younger patients having better clinical outcomes. Defect location also affects outcomes, with better results having been reported following the treatment of defects involving the femoral condyles. Finally, body mass index (BMI) is a potential risk factor for the failure of this procedure as patients with a BMI of >30 kg/m2 have had significantly lower outcomes scores and subjective ratings compared with those with a BMI below that threshold.
In the June 2016 issue of JBJS Reviews, Sommerfeldt et al. provide a critical overview of microfracture. The authors conclude that microfracture is likely to produce acceptable clinical results in the short term but that the results cannot be guaranteed over the long term. This is an important article for orthopaedic surgeons who perform this technique and for surgeons who seek to understand the basic mechanisms that support this treatment modality.
Thomas A. Einhorn, MD
Editor, JBJS Reviews