Microfracture surgery is performed to try to restore a full-thickness cartilage defect of the knee. Introduced over 20 years ago, this arthroscopic procedure uses the body’s own healing abilities to enrich tissue regeneration to the chondral surface.
What Are The Symptoms Of An Articular Cartilage Injury That Can Be Treated With Microfracture Surgery?
- Loose fragments floating in the knee can cause intermittent swelling.
- Pain with prolonged walking or climbing up stairs.
- The knee occasionally buckling or giving way when weight is placed on it.
- Loose, floating pieces of cartilage may catch as the knee joint bends, causing the knee to lock or have limited range of motion.
- The knee may make noise, called crepitus, during motion, especially if the cartilage on the back of the kneecap is damaged. This noise is typically described as a, “snap, crackle, or pop”.
After Articular Cartilage Damaged Has Been Diagnosed, What Factors Indicate Microfracture?
- The patient has a full-thickness defect in either a weightbearing area between the femur and tibia or in an area of contact between the back of the patella.
- The patient has unstable cartilage covering the underlying bone.
- The patient has degenerative changes in the knee that is normally aligned.
What factors Should be Considered Before Microfracture Surgery?
- The patient’s age
- The patient’s activity level
- The patient’s knee alignment. Patients with “knock-kneed” or “bowlegged” are not good candidates for this procedure.
In general, microfractures are best performed in cartilage defects that have good surrounding cartilage. This is called good “containment”. In addition, microfractures do best in smaller cartilage defects, usually less than 2 cm2 in size. Larger cartilage defects may require a fresh osteoarticular allograft to provide the best chance for the patient to have a good outcome.
What is the Pathology of Articular Cartilage Damage?
In effect, a cartilage defect in the knee is like a “pothole” in the road. The opposing surface of cartilage can bump against it and either roll over it or become gouged out over time. The purpose of the microfracture surgery is to fill in the “pothole.” Just like a pothole being filled in in the street, if a microfracture is subjected to lower loads, like on a side street with light traffic, there is a better chance that it will be more durable over time than one that is subjected to higher-impact loads, like those potholes on the highway which frequently have to be resurfaced every year because of big trucks causing the potholes to reform. Thus, a patient will be more likely to have a better outcome after a microfracture if they participate in low impact activities instead of returning to higher impact activities like running.
How is Microfracture Surgery Performed?
Microfracture surgery is performed arthroscopically. Most of the time, microfractures are performed on the end of the femur (thigh bone), where the outcomes are more predictable. In addition, the size of the defect that is being treated can make a big difference because smaller defects have more durable fibrocartilage scar tissue heal in the area of the microfracture.
When a microfracture surgery is performed, holes are made in the exposed bone, about 3 to 4mm apart, to try to release some of the stem cells which will ultimately form a clot in the area of the microfracture. This marrow rich clot is the base for new tissue formation. The microfracture technique produces a rough bone surface that the clot adheres to more easily. This clot eventually matures into firm repair tissue that become smooth and durable.
During the initial timeframe, the clot is at risk for being dislodged if the patient bears too much weight or performs too many activities. That is the reason that patients are kept nonweightbearing for 6 weeks after a microfracture. In addition, constant motion over the area of the microfracture can help it to form better to the contour on the end of the bone. This is why we use a continuous passive motion machine (CPM) postoperatively to try to ensure that the microfracture will have the best contour and healing surface.
What is Microfracture Recovery Like?
For microfracture recovery, the rehabilitation program is crucial to optimize the success of the surgical technique. Weightbearing is usually initiated at 6 weeks after the microfracture. During this time, it is important that a slow progression of weightbearing is followed to allow the microfracture tissue to harden more over time. If activities are initiated too quickly after microfracture recovery, the microfracture may not heal or may heal with soft fibrocartilage. If the microfracture heals with a more softened state, even though it does cover the end of the bone, it often may not be functional and patients may have a recurrence of pain. Depending upon the location of the microfracture and the size of the defect, it can take anywhere from 4 to 7 months to be able to heal to the point where patients can increase their activities and potentially initiate occasional impact activities.
What Type of Complications May Occur with Microfracture?
Most patients progress through the post-op period with little or no difficulty. After microfracture has been performed in the patella (kneecap) and the trochlear groove (the groove on the femur in which the patella glides during motion), some patients may develop mild transient pain. Small changes in the articular surface of the patellofemoral joint may produce a grating or “gritty” sensation. This sensation will typically occur when a patient discontinues use of the knee brace and begin normal weightbearing through full range of motion. Patients rarely have pain at this time, and this grating sensation typically resolves on its own in a few days or weeks.
If a steep perpendicular rim was made in the trochlear groove, patients may notice “catching” or “locking” as the ridge of the patella rides over this area during joint motion. Some patients may notice these symptoms while using continuous passive motion machine (CPM). If this locking sensation is painful, the patient is advised to limit weightbearing and avoid the bothersome joint angle for an additional period. These symptoms usually dissipate within 3 months.
In most cases, any swelling and joint effusion (fluid in the joint) disappears within 8 weeks after microfracture. Occasionally, a recurrent effusion develops between 6 to 8 weeks after surgery for a defect on the femur; usually when a patient begins to put weight on the injured leg. This effusion may mimic the preoperative or immediate preoperative effusion, although it is usually painless. It typically resolves within several weeks. Rarely is a second arthroscopy required for recurring effusions.