The most common procedure currently in use for cartilage repair is microfracture, which really means making a series of tiny holes (with a special awl) in order to stimulate the stem cells of the bone marrow. We all have stem cells in the bone marrow throughout life, but the prevalence of these cells is about 1 in 10,000, and decreases with age. The idea is to release these cells into the hole created by the loss of cartilage. If the cells form a clot, there is a good chance that some may start to grow into a new tissue that in some sense resembles cartilage, even if not perfectly; it is certainly better than no fill of the hole at all.
Microfracture requires the same rehabilitation protocol as ACI, but it has the advantage of being performed arthroscopically. It is therefore considerably less expensive, and on that score alone has been promoted by many as being a “first line” approach. By this it is meant that if microfracture fails, the option for ACI or other techniques is still open. Insurance companies sometimes react positively when confronted with the information that microfracture has already been tried to heal a cartilage lesion.
Microfracture works especially well for small cartilage holes, and is considerably more successful in young people. Nevertheless, the success rates are variously quoted as between 60-75% even in the best hands and with the most motivated patients. This large a failure rate is not typical for other orthopaedic procedures (ACI will succeed apprx. 90% of the time), so of course the patient should know just what the odds are before embarking on the microfracture protocol, which really means an investment of about one year. Patient compliance and willingness to take directions is totally essential for microfracture! It may be for this reason, amongst others, that the well motivated young athlete has a higher success rate than the typical patient.
Patients are instructed that the rehab must go according to protocol, and especially as regards return to impact sports, that decision cannot be made by the patient alone or on the basis of how the patient feels. In other words, stay with the recipe, no embellishments. This problem has been reported in the popular press when professional athletes sometimes are allowed to return too early—this may result in repeat surgery.
My approach is to match the best procedure to a particular patient. The size of the cartilage lesion, the location, the age of the patient, the work situation—which sometimes means: is the patient willing to undergo the rehab twice (if the microfracture fails); all of these factors contribute to the decision to proceed with microfracture, to perform ACI or—in some cases—to not perform cartilage repair. This latter decision is particularly difficult to make, but it does appear to be logical as patients age and the possibility of a total knee replacement appears less daunting.
Stay tuned for procedures in the works that increase the efficacy of microfracture without requiring the growth of cells.
Reference: “The Microfracture Technique for the Treatment of Articular Cartilage Lesions in the Knee” in The Journal of Bone & Joint Surgery