A microfracture is a minimally invasive surgical procedure used to repair damaged cartilage in the knee. During the surgery, a surgeon creates tiny holes in the exposed bone beneath a cartilage defect, prompting the body to form a blood clot that eventually develops into new repair tissue. It’s one of the most common first-line treatments for cartilage injuries smaller than about 2 square centimeters, roughly the size of a postage stamp.
How the Procedure Works
Microfracture is performed arthroscopically, meaning the surgeon works through small incisions using a camera and specialized instruments. First, any loose or damaged cartilage is cleared away to create a clean, stable border around the defect. Then a small pointed tool called an awl is used to punch tiny holes into the bone just beneath the cartilage surface. These holes penetrate into the bone marrow, releasing blood and stem cells that pool into the defect and form a clot. Over the following weeks, that clot gradually transforms into repair tissue that fills the gap.
The procedure is relatively quick, typically performed as outpatient surgery, and avoids the need for larger incisions or tissue transplants. Its simplicity is a major reason it remains a go-to option for smaller cartilage lesions.
The Repair Tissue Isn’t Identical to Original Cartilage
This is the most important thing to understand about microfracture: the tissue it produces is not the same as the cartilage you were born with. Healthy knee cartilage is hyaline cartilage, a smooth, glassy material with specific structural properties that allow it to absorb shock and glide without friction. What microfracture generates is fibrocartilage, a tougher, less organized tissue with different biomechanical properties.
Fibrocartilage does fill in the defect and provides meaningful pain relief, especially in the short and medium term. But it lacks the durability of native hyaline cartilage. Lab analysis of repair tissue after microfracture consistently shows it has reduced cartilage-specific structural components compared with surrounding healthy cartilage. This difference in tissue quality is the central limitation of the procedure and the main reason outcomes can deteriorate over time.
Who Is a Good Candidate
Microfracture works best for relatively small, contained cartilage defects. In a survey of international cartilage surgeons, 56% reported limiting the procedure to lesions of 2 square centimeters or less, while about 35% were willing to extend it to lesions up to 4 square centimeters. For anything larger, surgeons typically turn to more involved techniques that restore true hyaline cartilage.
Age is less of a hard cutoff than you might expect. Half of surveyed surgeons reported no upper age limit, and a quarter said they would perform microfracture on patients over 60. That said, younger, active patients with isolated cartilage injuries and otherwise healthy knees tend to see the best results. Patients with widespread arthritis, significant misalignment, or ligament instability may not be ideal candidates because these factors put additional stress on the repair tissue.
Recovery Timeline
Recovery from microfracture is slower than the surgery itself might suggest. The repair tissue needs time to form and strengthen, and rushing the process can compromise the result.
For lesions on the main weight-bearing surfaces of the knee (the femoral condyles and tibial plateau), the traditional protocol calls for non-weight-bearing or very limited weight bearing for the first 2 to 4 weeks. You’ll use crutches and may wear a brace. For lesions on the kneecap or the groove it sits in, the approach is slightly different: the knee is locked straight for 2 to 4 weeks, with gradual return to weight bearing over the following 2 weeks.
Biologically, the repair goes through distinct phases. During the first 4 weeks, new cells are rapidly filling in the defect (the proliferation phase). From roughly 4 to 12 weeks, the repair tissue strengthens and matures (the transition phase). By around 12 weeks, the defect is typically filled in. That doesn’t mean full recovery, though. For athletes, return to sport varies considerably. One study of soccer players using a similar bone marrow stimulation technique found they returned to play at an average of about 11 weeks, though this involved an accelerated rehabilitation protocol with early weight bearing. For most people, a gradual return to high-impact activity over 4 to 6 months is more typical.
Continuous passive motion, where a machine gently bends and straightens your knee while you rest, is often part of the early rehabilitation to nourish the developing tissue and encourage smooth healing.
Long-Term Success Rates
Microfracture provides good short-term relief for most patients, but the results do decline over the years. A study tracking patients for over a decade found survival rates of 88.8% at 5 years, 67.9% at 10 years, and 45.6% at 12 years. “Survival” here means the repair was still functioning well enough that no further surgery was needed.
Those numbers tell a clear story: the fibrocartilage repair tissue holds up reasonably well in the first several years, but roughly a third of patients will need additional intervention within a decade. This gradual decline is directly related to the inferior durability of fibrocartilage compared with native hyaline cartilage. For younger patients expecting decades of knee use, this timeline is an important factor in decision-making.
How It Compares to Other Cartilage Procedures
Microfracture sits at one end of a spectrum of cartilage repair options, organized largely by lesion size and complexity.
- Microfracture: Best for lesions under 2 square centimeters. Minimally invasive, single surgery, but produces fibrocartilage rather than true hyaline cartilage.
- Osteochondral autograft transfer (OAT): Suitable for lesions between 2 and 4 square centimeters. Involves transplanting a small plug of cartilage and bone from a non-weight-bearing area of your own knee into the defect. Restores true hyaline cartilage but creates a secondary injury at the donor site.
- Autologous chondrocyte implantation (ACI): Works for lesions from 2 to over 4 square centimeters. Cartilage cells are harvested from your knee, grown in a lab, then reimplanted in a second surgery weeks later. Produces tissue closer to native cartilage but requires two separate procedures.
- Osteochondral allograft transplantation: Uses donor cartilage and bone from a tissue bank. Suitable for larger lesions and cases where the bone beneath the cartilage is also damaged. Avoids donor site injury but depends on tissue availability.
The general principle is straightforward: microfracture is the simplest and least invasive option, making it a logical first step for small defects. If it fails, or if the lesion is too large, the more involved techniques are available as next steps.
Augmented Microfracture Techniques
One of the main weaknesses of standard microfracture is that the blood clot forming in the defect can dislodge before it matures into stable repair tissue. This can lead to incomplete filling of the defect and poorer outcomes. A technique called Autologous Matrix-Induced Chondrogenesis (AMIC) addresses this by placing a scaffold over the microfracture site to anchor the clot in place.
The scaffold stabilizes the clot within the defect, reducing the risk of it breaking loose. Certain scaffold materials have also been shown to promote differentiation of stem cells toward cartilage-producing cells, potentially leading to repair tissue that more closely resembles native hyaline cartilage. AMIC is increasingly used as a way to get the benefits of microfracture’s simplicity while improving the quality and reliability of the repair.