A microfracture is a minimally invasive surgical procedure used to repair damaged cartilage in a joint, most commonly the knee. The surgeon creates tiny holes in the bone beneath the damaged cartilage, triggering the body to form new repair tissue over the defect. It’s one of the most widely used cartilage restoration techniques, typically recommended for isolated areas of damage smaller than 2 square centimeters.
How the Procedure Works
Microfracture is performed arthroscopically, meaning the surgeon works through small incisions using a camera and specialized instruments. The first step is removing all the damaged cartilage from the defect down to the underlying bone. The surgeon then scrapes away a thin layer of calcified cartilage at the base of the lesion, exposing fresh bone underneath.
Next, the surgeon uses a pointed instrument called an awl to punch small holes into the bone, spaced about 4 to 5 millimeters apart, to a depth of 3 to 4 millimeters (sometimes up to 6 millimeters). These perforations penetrate into the bone marrow space, releasing blood and stem cells that flow up into the prepared defect. The blood pools and forms a clot over the damaged area, and the stem cells within that clot gradually transform into cells that produce new cartilage-like tissue.
The Repair Tissue Isn’t Identical to Original Cartilage
This is the key limitation of microfracture. The tissue that fills the defect is called fibrocartilage, which is structurally different from the smooth, glassy hyaline cartilage that originally lined the joint. Native hyaline cartilage is made up of more than 90% type II collagen, which gives it a resilient, slippery quality ideal for absorbing shock and allowing smooth joint movement. Fibrocartilage, by contrast, is dense with type I collagen fibers and relatively deficient in type II collagen. This makes it stiffer, rougher, and mechanically weaker than the original surface.
In practical terms, fibrocartilage can relieve pain and improve function, but it doesn’t hold up as well under long-term stress. Think of it as a patch rather than a full restoration.
Who Is a Good Candidate
Microfracture works best for younger, active patients, generally between 18 and 50, with a single, well-defined area of cartilage damage on the thighbone (femoral condyle) or the groove where the kneecap sits (trochlea). The defect should be smaller than about 2 square centimeters. Beyond that size, the repair tissue tends to be less reliable, and surgeons typically recommend more advanced procedures.
It’s also important that the rest of the knee is relatively healthy. Patients with widespread arthritis, significant malalignment, or ligament instability are less likely to get good results, because the underlying problem will continue damaging any new tissue that forms.
Recovery and Rehabilitation
Recovery from microfracture is slower than many patients expect. Protecting the fragile blood clot and developing repair tissue is critical, so weight-bearing restrictions are a central part of rehabilitation. For defects on the main weight-bearing surfaces of the knee, the standard protocol involves staying off the leg entirely (or only touching the toe down for balance) for the first 2 to 4 weeks. Gradual progression to partial and then full weight bearing follows over the next several weeks.
For defects behind the kneecap, the approach is slightly different. The knee is locked straight in an immobilizer for 2 to 4 weeks to prevent the kneecap from gliding against the healing surface, while partial weight bearing is allowed earlier since walking in a straight leg doesn’t stress that area as much.
Continuous passive motion, where a machine gently bends and straightens the knee, is often used in the early weeks to nourish the developing tissue. Most patients can expect a recovery period of several months before returning to demanding activities. Athletes average about 8 months before returning to sport, with a range of 2 to 16 months depending on the size and location of the defect.
Long-Term Success Rates
In the short term, microfracture reliably reduces pain and improves function for most patients. A study following patients for over a decade found survival rates of about 89% at 5 years, 68% at 10 years, and 46% at 12 years. “Survival” here means the patient hadn’t needed additional surgery on the same area. So while most people do well in the first several years, the repair tissue does tend to deteriorate over time, particularly in patients who are older, heavier, or more active.
For athletes specifically, about 66% to 67% successfully return to sports participation, and roughly the same proportion return to their preinjury level of competition. That means about a third of athletes don’t fully get back to where they were before the injury.
Potential Complications
Beyond the general risks of any arthroscopic surgery (infection, blood clots, stiffness), microfracture carries some unique concerns related to what happens beneath the repair tissue. Studies have found that 30% to 50% of patients develop changes in the bone underneath the treated area, including thickening and hardening of the bone surface, cyst formation, and the growth of bony bumps called intralesional osteophytes.
These bony changes matter because they alter the mechanical environment. When the bone beneath the cartilage becomes stiffer than normal, it concentrates stress in the deep layers of the overlying repair tissue, making it more vulnerable to breakdown. If bony overgrowth pushes upward into the defect, the already-thin layer of fibrocartilage becomes even thinner and less capable of absorbing load. This is one reason microfracture results can deteriorate over time, and it can also complicate any future procedures done on the same area.
How It Compares to Other Cartilage Procedures
Microfracture is often the first-line treatment because it’s a single, relatively simple surgery with no need for tissue grafts or lab-grown cells. But for larger defects (3 square centimeters or more), more advanced options tend to outperform it. A major randomized trial comparing microfracture to a technique that implants a patient’s own lab-cultured cartilage cells on a scaffold (known as MACI) found that MACI produced significantly better pain relief and function scores at 5 years for defects of that size. MRI scans showed both treatments filled the defect similarly, but patients in the MACI group reported meaningfully better outcomes in daily activities.
Other alternatives include transferring small plugs of healthy cartilage and bone from a non-weight-bearing area of the knee into the defect, or using donor tissue from a cadaver for very large lesions. These procedures are more invasive and expensive, which is why microfracture remains the go-to option for smaller defects in younger patients where the biology is favorable.