Microfracture

Microfracture is a surgical procedure used to treat small to medium-sized defects in articular cartilage, typically found in the knee joint. This procedure aims to promote the formation of reparative tissue (fibrocartilage) in areas where the cartilage has been damaged or worn away. However, fibrocartilage does not have the same durability as the original hyaline cartilage.

Microfracture is a marrow stimulation technique achieved by perforating the bone to recruit stem cells to the cartilage defect which can turn into fibrocartilage to fill and remodel the injured area. In some instances, the marrow stimulation procedure is augmented with a collagen membrane to perform an AMIC (Autologous Matrix Induced Chondrogenesis) procedure. Studies have demonstrated that AMIC can result in improved outcomes compared to basic microfracture and also promotes the formation of hyaline-like cartilage (vs fibrocartilage). Another generic term that can be used to describe the AMIC procedure is ‘microfracture-plus’.

Microfracture is typically considered when a patient presents with a symptomatic (pain, swelling) cartilage defect in the knee, often caused by trauma and repetitive use. It is most suitable for small to medium-sized defects that affect the articular cartilage, which covers the ends of the bones within the joint. It is not suitable for large defects or degenerative conditions such as osteoarthritis. For defects larger than 2 cm or for a patellofemoral procedure, an AMIC procedure is preferred over basic microfracture.

Microfracture uses the body’s own healing abilities to enrich the damaged cartilage to regenerate new cartilage.

The procedure is performed arthroscopically, a minimally invasive approach that minimizes tissue damage and promotes faster recovery. Under regional or general anesthesia, several small incisions are made around the knee, and an arthroscope is inserted to visualize the joint. An arthroscope is a long, thin tube with a camera on its end. The camera is attached to a video monitor in the operating room and allows the surgeon to see inside the knee joint.

The key feature of the microfracture procedure is the creation of multiple tiny holes or “microfractures” in the subchondral bone, which is the layer of bone just beneath the damaged cartilage. These holes are made using specialized tools like awls, picks or small drills.

The microfracture technique works in two ways:

1. The microfractures allow blood and bone marrow cells to flow into the damaged area to form a superclotclot that creates the foundation for the creation of new tissue. This blood contains cells, growth factors, and nutrients that facilitate the growth of new tissue and the healing process.
2. Over time, the influx of these biological components prompts the formation of fibrocartilage within the cartilage defect. Fibrocartilage is different from the hyaline cartilage that normally covers the joint surfaces, but it can provide some functional improvement.

During AMIC®, damaged cartilage is removed. Following marrow stimulation, cells from the underlying bone are released into the defect, where they promote new tissue growth. The area is covered with a small piece of collagen membrane, which protects the new forming tissue from substances and forces in the joint.

To summarize, both microfracture and AMIC generate a super clot via marrow stimulation.  This super clot contains undifferentiated chondrocyte precursor cells, known as mesenchymal stem cells (MSCs), which can help regenerate cartilage. In AMIC, this clot is covered with a membrane to protect the MSCs and keep them in place. This protection helps create a suitable environment for the differentiation and growth of MSCs and the regeneration of the cartilage in an even and functional manner, during which time the membrane is resorbed. This new tissue can eventually form hyaline-like cartilage as opposed to fibrocartilage.

Following the surgery, patients typically use a continuous passive motion machine that will gently exercise the leg for 6-8 hours a day for six weeks. For the first six to eight weeks no weight bearing is allowed. The patient will use crutches and participate in a structured rehabilitation program for three to six months to gradually regain strength and range of motion in the affected knee. Return to sport is between 6-12 months depending on the resolution of symptoms and swelling, as well as the individual demands of the patient.  Recovery timelines and protocols can also be affected by concomitant procedures such as ligament repair, meniscus transplantation or osteotomy.