Does the Microfracture Technique for Articular Cartilage Repair Hold Up Over Time?
Before a surgical technique can be conclusively declared a success, many studies must be done to look at treatment effects, long-term results, patient satisfaction, and function. One study (no matter how large) is never enough to satisfy the need for evidence to prove the benefits of the procedure. In this article, a systematic review is conducted of the long-term results for microfracture cartilage repair of the knee. Systematic review means a number of studies were examined. The results of any study looking at the ability of this procedure to repair cartilage and improve knee function were included.
The success of this repair technique was evaluated by looking at scores on tests of knee function, quality of the repair, and other findings on MRI studies. The microfracture technique is used for patients with defects in the articular cartilage of the knee joint. The articular cartilage is the smooth surface of the joint just above the first layer of bone. Fractures in the cartilage can lead to fragments of the cartilage breaking off leaving holes in the joint surface.
The microfracture method of repair involves several steps. First, the surgeon removes any ragged edges along the tear. This is called debridement. Then the layer of calcified (hard) cartilage is removed to expose the subchondral bone. Subchondral just means the bone is right below the articular cartilage -- like subflooring in a house. Next, the surgeon takes a special tool and forms tiny holes (microfracture) in the subchondral surface.
Microfracture works by stimulating a bleeding and healing response. Blood from inside the bone marrow seeps up through the holes and fills the hole or defect in the cartilage with a clot. The articular cartilage doesn't have much of its own blood supply or an ability to heal itself. That's why the surgeon tries to help it along with techniques like microfracture. There are other methods used to stimulate healing but microfracture has become popular with good short-term results and that is the only focus of this systematic review.
The question is: do the benefits of this treatment last? For how long? Six months? A year? Five years? The authors found 28 studies assessing the microfracture technique. Over 3,000 patients were involved in the combined analysis. Some studies followed patients for one year. Others extended beyond that to two years. Only five studies followed patients for five or more years but those studies accounted for over half of all the patients who had this procedure.
Not everyone used the same measuring tools to assess outcomes. Pain, swelling, level of athletic activity, and ability to perform strenuous work were used as the primary measures of results in five studies. Some researchers used the well-known Western Ontario and McMaster Universities (WOMAC) index while others used the equally well-known Cincinnati knee score. Other tools used to measure before and after knee function included the Tegner activity scale, Baumgaertner score, Japanese Orthopaedic Association knee score, and the Knee injury and osteoarthritis outcome score (KOOS). In fact, there were a total of 15 different scales used to measure knee function. So you can see there wasn't a uniform method of studying results, which could make it more difficult to get a handle on how well this procedure does work.
They also found that the type of lesions studied wasn't always the same from study to study. Many studies included patients with both acute (new) and chronic (old injuries) of varying sizes and depths. Very few studies recorded whether the patient had previous knee surgeries or repair for other injuries at the time of the microfracture procedure. Most of the studies did not record the patients' body mass index (BMI), an indicator of overweight or obese status. Any of these features could really affect long-term results.
The final analysis suggests that microfracture helps improve knee function in the early months to year following surgery. But many patients experience deterioration over time. In other words, the benefit of the procedure doesn't seem to last so the durability of microfracture is questionable. When the defect filled in nicely, patients had the best results.
But not everyone got a nice even and full healing response. A closer look at that showed some possible (predictive) risk factors. For example, younger patients (less than 40 years old) with smaller cartilage defects and lower BMIs had the best results. Not surprising, the more active, athletic patients who went back to full levels of activity had poorer results. Patients who had the microfracture technique first before any other treatment approach did better than those for whom the microfracture was a salvage procedure when other treatment failed.
The authors conclude that with no systematic evaluation of the benefits of microfracture, this systematic review was timely and helpful. It showed that short-term improvement following microfracture for articular cartilage defects is a certain benefit for most patients. The technique is safe, minimally invasive, and effective even when it doesn't produce normal cartilage. Decline in function is to be expected with time but even so, the final results in terms of activity and function are still better than before surgery.
Further studies are needed to find out why microfracture fails, the optimum time to perform the surgery, and which patients can benefit the most from this technique as a first-line approach. The authors also suggest taking a look at why some patients have poor fill volume of the defect after microfracture and which factors are the most significant in those patients who end up with deterioration over time. Using arthroscopic examination is one way to take a look inside the joint and possibly identify what's going on and why. The authors suggest that second-look arthroscopic studies are needed at various points along the way (e.g., after six months, 12 months later, and beyond the two-year mark) -- possibly even 10 (or more) years later.
Kari Mithoefer, MD, et al. Clinical Efficacy of the Microfracture Technique for Articular Cartilage Repair in the Knee. In The American Journal of Sports Medicine. October 2009. Vol. 37. No. 10. Pp. 2053-2063.