Microfracture surgery of the knee is a minimally invasive arthroscopic procedure that treats damaged joint cartilage. This technique stimulates the body’s natural healing response by creating tiny punctures in the bone beneath the cartilage defect. A clot forms at the injury site, developing into a replacement surface for the joint. It is typically considered for patients with isolated, full-thickness cartilage damage who meet specific criteria regarding the size and location of the lesion.
Understanding Cartilage Damage in the Knee
The ends of the bones within the knee are covered by articular cartilage, a smooth, rubbery tissue that allows for frictionless movement and acts as a shock absorber. This specialized tissue is composed primarily of Type II collagen and water. A significant limitation of articular cartilage is its lack of a direct blood supply.
Because it has no blood vessels, damaged cartilage cannot heal itself naturally the way other tissues, like skin or muscle, can. A full-thickness defect extends all the way down to the underlying subchondral bone. If left untreated, these lesions can progress, potentially leading to chronic pain and the development of osteoarthritis over time. Microfracture surgery is typically reserved for small- to medium-sized defects, generally less than two to three square centimeters, where the edges of the surrounding healthy cartilage are well-defined.
How the Microfracture Procedure is Performed
The microfracture technique is performed arthroscopically. The first step involves preparing the damaged area by removing any damaged cartilage down to a stable border. This debridement ensures the defect is a clean, full-thickness lesion exposing the subchondral bone plate.
Using specialized surgical instruments called awls, the surgeon creates multiple tiny holes, or microfractures, in the exposed bone surface. These perforations are made approximately three to four millimeters apart and are deep enough to penetrate the hard subchondral bone layer. The intentional puncturing of the bone allows blood and bone marrow from the deeper bone tissue to seep out into the cartilage defect.
This released fluid is rich in growth factors and mesenchymal stem cells, which are the body’s natural repair cells. The fluid mixes with the defect site to form a clot that fills the entire defect area. This clot serves as the initial foundation, or scaffold, for the new tissue that will eventually form over the damaged site.
Post-Operative Recovery
The success of a microfracture procedure depends heavily on the post-operative rehabilitation protocol. The newly formed blood clot must be protected from excessive mechanical stress, particularly compressive weight-bearing forces. Patients are typically required to remain non-weight-bearing on the operated leg for an extended period.
During the initial phase, a Continuous Passive Motion (CPM) machine is frequently used for several hours a day for the first six to eight weeks. This machine gently moves the knee through a controlled range of motion without putting weight on the joint. The slow and controlled progression through physical therapy is necessary to allow the tissue to mature and gain resilience.
Returning to daily activities is gradual, beginning with light weight-bearing after the initial non-weight-bearing period. More strenuous activities, such as jogging, jumping, or sports that involve cutting movements, are typically prohibited for four to six months or even longer. Rushing the weight-bearing progression can compromise the quality of the repaired tissue and lead to failure of the procedure.
Expected Outcomes and Long-Term Considerations
The repair tissue that forms from the “super-clot” is not the same as the original hyaline cartilage. Instead, the body regenerates a tissue called fibrocartilage, which is primarily composed of less resilient Type I collagen.
Fibrocartilage is biomechanically inferior to native hyaline cartilage. While microfracture often provides good short-term pain relief and functional improvement, its durability is a concern. Clinical benefits often begin to diminish after two to five years, though some patients maintain satisfactory results for ten years or more.
The long-term success of the procedure is influenced by factors like the patient’s age, weight, and the size of the initial defect. Microfracture is generally considered less effective for defects larger than two to three square centimeters or in older patients. The formation of fibrocartilage remains a limitation of the procedure, as it is more prone to breakdown over time compared to the joint’s original surface.