Articular cartilage is the smooth, glistening surface covering the ends of the bones in a joint. It has no blood supply, so once it is damaged it has very little ability to heal. Cartilage damage is very common: in a review of more than 31,000 knee arthroscopies, more than 53,000 cartilage lesions were recorded,¹ and another series of 25,124 arthroscopies found cartilage lesions in 60% of patients, most often on the kneecap and the inner thighbone.² About 1 in 10 knee arthroscopies shows a full-thickness defect that may be suitable for repair.³

Untreated defects can enlarge over time. In a study of older adults with mild to moderate knee arthritis, cartilage defects on the inner side of the knee grew faster, especially in heavier patients and those with bow-legged (varus) alignment.⁴ This is one reason Dr. Dold evaluates alignment carefully.

Dr. Dold offers each of these procedures and will explain which fits your knee, the pros and cons of each, and whether surgery is needed at all. The right choice depends on the size and location of the defect, the condition of the bone underneath, your age and your goals.

Microfracture creates small holes in the bone beneath the defect so that bone marrow cells can form a repair tissue. It is a single, arthroscopic procedure. In a long-term study of patients 45 or younger, 80% rated themselves improved at 7 years.¹⁶ However, the repair tissue is fibrocartilage rather than true hyaline cartilage, and results tend to be best in smaller defects and younger patients, with some decline after 2 to 5 years.^6,7,8 In elite athletes, return to the same level is less predictable; a third of NBA players who had microfracture did not return to the league.¹⁷

OATS moves one or more plugs of your own healthy cartilage and bone from a low-demand area of the knee into the defect, replacing it with true hyaline cartilage in a single surgery. In a randomized trial of young athletes, 96% had good or excellent results after OATS vs 52% after microfracture, and 93% vs 52% returned to their previous sport level.²¹ At 10 years, failures were 14% after OATS vs 38% after microfracture,⁹ and another randomized trial found better results with OATS at 15 to 17 years.¹⁰ OATS is limited by how much donor tissue can be taken, so it is best for smaller defects.

An osteochondral allograft uses a fresh, carefully tested and size-matched donor graft of cartilage and bone to fill a larger defect or one with damaged bone underneath, such as osteochondritis dissecans. Dr. Dold co-authored a published surgical technique for osteochondral and meniscal allograft transplantation.²² See Dr. Dold’s research.

• A systematic review of 1,036 patients found 86.7% of grafts were still functioning at 5 years, 78.7% at 10 years and 72.8% at 15 years.¹¹
• In a 2025 study of 560 knees, graft survival was 89% at 5 years, 83% at 10 years and 75% at 15 years.²³
• For kneecap (patellofemoral) grafts, survival was 87.9% at 5 years and 77.2% at 10 years.²⁴
• 75.2% of athletes and active patients returned to sport or recreation, and 91% were satisfied.²⁵

Factors linked to a higher chance of failure include defects on both sides of the joint (bipolar), older age, higher body weight and very large grafts.^26,23

MACI is FDA-approved for the repair of symptomatic, single or multiple full-thickness cartilage defects of the knee, with or without bone involvement, in adults.²⁷ It is a two-stage procedure: first, a small sample of cartilage is taken arthroscopically; your cells are then grown in a laboratory on a collagen membrane and implanted into the defect at a second surgery.

• In the SUMMIT randomized trial of defects 3 cm² or larger, MACI gave significantly better pain and function than microfracture at 2 years, with fewer nonresponders (12.5% vs 31.9%).¹²
• The advantage over microfracture was maintained at 5 years.¹³
• In the first 1,000 U.S. patients, the average age was 34, the average defect was 4.7 cm², and the kneecap was the most commonly treated area.²⁸
• In a European study of matrix-associated chondrocyte implantation, about 74% of active patients returned to at least their previous sport level at 5 years.²⁹

The CartiHeal™ Agili-C™ implant (Smith+Nephew) is a porous scaffold made from aragonite, a natural form of calcium carbonate, placed into the defect in a single surgery to support regrowth of cartilage and the bone beneath. The FDA approved it in March 2022 for ICRS grade III or higher knee lesions with a total treatable area of 1 to 7 cm², in knees without severe arthritis (Kellgren-Lawrence grade 0 to 3).⁵

• In the randomized trial of 251 patients used for FDA approval, 77.8% of implant patients were responders vs 33.6% after microfracture or debridement, 88.5% had at least 75% defect fill on MRI at 2 years vs 30.9%, and failures were 7.2% vs 21.4%.¹⁴
• The benefit was maintained at 4 years in both men and women.³⁰
• At 5 years, responder rates were 74.7% vs 29.6% and failures 15.0% vs 35.7%, including in patients with mild to moderate arthritis.¹⁵

Learn more about CartiHeal Agili-C.

Dr. Dold has published peer-reviewed research on biologic treatments for damaged cartilage and on cartilage transplantation:

• Platelet-rich plasma in the management of articular cartilage pathology: a systematic review (Clinical Journal of Sport Medicine, 2014; first author). This review of 10 studies (662 joints, mostly knee or hip arthritis) found that 7 of 8 studies reported significant improvement in joint-specific scores after PRP for up to 6 months, and 3 of 4 comparative studies reported better clinical or pain scores than hyaluronic acid (gel) injections. It also concluded that the studies available at the time were of poor quality, that there was little data on PRP for focal cartilage injuries, and that higher-quality studies with longer follow-up were needed.³¹ Many of those larger trials have since been published; see PRP injections.
• Injectable biological treatments for osteoarthritis of the knee (JBJS Reviews, 2017; co-author). A review article on injectable biologic treatments for knee arthritis.³²
• Osteochondral proximal tibial and lateral meniscal allograft transplant (Arthroscopy Techniques, 2016; co-author). A published surgical technique for transplanting donor cartilage and bone together with a donor meniscus.²²

A cartilage repair is more likely to last when the reason for the damage is addressed. Depending on your knee, that may mean correcting leg alignment with an osteotomy, stabilizing the kneecap, reconstructing a torn ACL or treating a damaged meniscus, sometimes including meniscus transplant. Malalignment increases the load on the damaged area and is linked to faster progression of cartilage defects.⁴

Recovery depends on the procedure and the location of the defect. Most patients use crutches for several weeks to protect the repair, sometimes with a brace, and begin physical therapy early to restore motion. Strengthening continues for months, and return to impact or pivoting sports is gradual. In a meta-analysis of 2,549 patients, 76% returned to sport overall: 93% after OATS, 88% after osteochondral allograft, 82% after cell-based repair and 58% after microfracture. Average time to return ranged from about 5 months after OATS to about 12 months after cell-based repair.³³ Dr. Dold will give you a specific timeline before surgery.