Microfracture surgery of the knee is indicated to resurface well-defined, small to medium size areas of full-thickness articular cartilage defects of the knee. The work-up for determining if one is a patient for a microfracture surgery is very important. In addition to the history, a well-performed physical exam, and radiographic assessment is required. The best candidates for microfracture surgery are young (physiologic age < 50) have well-localized articular cartilage defects with good articular cartilage edges of the remaining cartilage present (well-shouldered) and who have good ligament stability of their knee (or who are undergoing concurrent ligament reconstruction), have normal lower extremity alignment, and who have good remaining meniscal tissue (the protective cushioning material for the articular cartilage).
The technique of microfracture was initially developed by Dr. Richard Steadman. Dr. Steadman performed a series of studies with researchers at Colorado State University to determine the best techniques to ensure a successful result. Through these studies, it was found that nonweightbearing with the use of a continuous passive motion machine for 6-8 weeks, having well-defined edges of the remaining cartilage, and removing the calcified cartilage layer was necessary to have optimal outcomes after a microfracture surgery.
The principles of microfracture surgery are to make small holes in the bone to allow for stem cells to migrate from the bone into the area of the defect and to form a well-defined clot over the defect. In patients who do not have good edges of cartilage (well-shouldered) or with larger defects, there is a lesser chance that this clot will form in the correct position due to abrasion from the opposing cartilage surface or from the clot not having a proper edge to form along. Over time, the clot matures with the majority of patients having a combination of fibrocartilage and hyaline cartilage forming to repair the defect. Microfracture surgery has been reported to restore about 75% of athletes back to their sporting activities.
It has been well determined that the principles of microfracture surgery must be very carefully followed. In addition to making sure that one has the best prepared area for the clot to form, which involves removing the scar tissue and calcified cartilage layer, a well-shouldered rim of remaining cartilage and good joint stability is required. We keep our patients nonweightbearing for 6-8 weeks after microfracture surgery and use a continuous passive motion machine for 8 hours a day to try to help the repair tissue to form the best quality-healing cartilage. After the initial 6-8 weeks, patients may slowly wean off their crutches based on their symptoms, start the use of a stationary bike, and other initiate other low impact activities as tolerated. One should avoid impact activities for several months, with most of our athletes recommended to avoid them for 6-9 months, to maximize healing of the microfracture.
Microfracture surgery has withstood the test of time in terms of the treatment of articular cartilage defects. While it was the first technique developed, most level 1 randomized studies do not show any significant improvement of a patient’s function compared to some of the newer, and much more expensive and invasive, articular cartilage resurfacing techniques. Thus, for the majority of patients, an initial surgical treatment with a microfracture would be recommended because it is a one-stage surgery, commonly involves the use of only two arthroscopic incisions, and causes minimal patient discomfort.
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