Cartilage Repair Surgery

Cartilage damage in the knee

Articular cartilage is the smooth, low-friction surface covering the ends of the femur, tibia and the back of the kneecap. It has no blood supply, so once damaged it has very limited capacity to heal on its own. A full-thickness defect can cause pain, swelling, catching and giving way, and over time may progress to osteoarthritis.

Cartilage damage is commonly caused by a twisting injury, a patellar dislocation, osteochondritis dissecans (OCD), or alongside an ACL or meniscal injury. Not every defect needs surgery. Small or minimally symptomatic lesions often settle with physiotherapy, weight management and activity modification.

Cartilage repair is aimed at a focal defect in an otherwise healthy joint, not at generalised osteoarthritis. Success depends on treating the whole knee: malalignment is corrected with an osteotomy, an unstable knee with ACL reconstruction, and a missing meniscus may need a meniscal allograft transplant (MAT). Repairing cartilage without addressing these usually fails.

The right procedure depends on the size, depth and location of the defect, whether the underlying bone is involved, your age, activity level and any previous surgery. The options I use are described below.

Autologous chondrocyte implantation (ACI)

ACI uses your own cartilage cells, grown in a laboratory, to repair the defect. It is a two-stage procedure. At the first operation, a keyhole arthroscopy, a small biopsy of healthy cartilage is taken from a non-weight-bearing part of the knee. The cells are multiplied in the laboratory over several weeks. At the second operation they are implanted into the prepared defect.

The current UK version is Spherox, in which the cells are grown into small spheres that stick to the base of the defect. Spherox is recommended by NICE for symptomatic full-thickness cartilage defects in the knee, and can be implanted arthroscopically or through a small incision.

ACI is suited to medium to large defects of the cartilage surface (typically 2 to 10 cm²) where the underlying bone is healthy. It produces hyaline-like repair tissue with good long-term results in the published trials. The trade-offs are two operations, a long rehabilitation, and full recovery taking 12 to 18 months as the repair tissue matures.

Autologous matrix-induced chondrogenesis (AMIC)

AMIC is a single-stage procedure. The defect is cleaned back to stable edges, the bone beneath is perforated to release marrow cells, and a collagen membrane is fixed over the top with fibrin glue or sutures. The membrane holds the marrow clot in the defect and protects it while it matures.

AMIC is an improvement on microfracture alone, with better medium-term results in comparative studies, and avoids the two operations and laboratory costs of ACI. It is generally used for small to medium defects of the cartilage surface. The repair tissue is still largely fibrocartilage, and long-term data are more limited than for ACI or osteochondral grafting.

Osteochondral autograft transfer (OATS)

OATS, also called mosaicplasty when several plugs are used, moves cylindrical plugs of your own bone and cartilage from a less important, non-weight-bearing area at the edge of the knee into the defect. The plug brings mature hyaline cartilage on its own bone base, which heals to the surrounding bone.

It is a single-stage operation that gives an immediate cartilage surface. It suits small defects, usually under 2 cm², including those involving the underlying bone such as small OCD lesions. It is less suitable for larger defects because of the limited amount of spare cartilage, and there is a risk of pain at the site the plugs are taken from.

Osteochondral allograft (OCA)

An osteochondral allograft is a block of bone and living cartilage from a carefully screened deceased donor, shaped to match the defect and press-fitted into place. Fresh grafts are used so that the cartilage cells are still alive at the time of transplant.

OCA is the main option for large defects (over 2 to 4 cm²) and for defects where the underlying bone is damaged or lost, such as osteochondritis dissecans (OCD), osteonecrosis, or failure of a previous cartilage repair. Because the graft is not taken from your knee, there is no donor-site problem and large areas can be treated in one operation. It restores a mature hyaline cartilage surface immediately. Pooled long-term series report graft survival of 94% at 5 years, 84% at 10 years, 71% at 15 years and 45% at 20 years [1]. Since October 2022 fresh OCA has been routinely commissioned by NHS England for osteochondral defects of the knee [3].

Our research on OCA

I co-authored a systematic review and economic evaluation of OCA with Professor Norman Waugh’s health economics group at Warwick Medical School [1]. It found good evidence that OCA is clinically effective, with high graft survival over 20 years, and that it is highly cost-effective at around £4,700 per quality-adjusted life year, well under the £20,000 threshold used by NICE. A second OCA after a failed first graft also appeared cost-effective.

UHCW set up a tertiary fresh OCA service in 2017. We presented our early results at BASK in 2023 [2]. In 37 patients, mean age 32, outcome scores improved significantly by 12 months, and graft survival was 97% at a mean follow-up of 3.1 years. Many had a combined procedure at the same time: 16 had MAT, 6 an osteotomy and 4 a ligament reconstruction. The rate of further operations was high, as in other OCA series, so this is something I discuss with every patient.

Fresh grafts are currently imported from the USA, size-matched to your knee and must be implanted within 28 days of donation, so surgery is planned around graft availability. The bone part of the graft takes several months to heal into your own bone, so weight-bearing is protected early on. As with any donor tissue, there is a very small risk of disease transmission, which donor screening reduces to extremely low levels.

ProChondrix

ProChondrix CR is a thin disc of living donor cartilage, about 1 mm thick, on a very thin layer of bone. It is made by AlloSource in the USA and distributed by Stryker. The deep surface is laser-etched with tiny channels to help cells migrate out of the graft and bond it to the base of the defect.

The graft is cryopreserved using a process that keeps the cartilage cells alive. Laboratory testing shows around 95% cell viability after 2 years of storage, compared with 99% in fresh cartilage. Unlike a fresh allograft, it is available off the shelf rather than waiting for a matched donor.

It is a single-stage procedure for defects of the cartilage surface, where the underlying bone is healthy. The defect is prepared, the graft is trimmed to fit and fixed in place. It aims to combine the convenience of a single operation with the delivery of mature hyaline cartilage and living cells, avoiding the two operations of ACI.

ProChondrix is a newer treatment. Early prospective results are encouraging, with 5-year interim data presented in 2025 [4], but longer-term and comparative evidence is still limited. With colleagues at the University of Warwick I am leading research on ProChondrix, including an independent UK comparison with fresh OCA and laboratory work on the graft.

Choosing the right option

The table summarises where each procedure fits. Your MRI scan, examination and often an arthroscopy determine which is right for you.

All cartilage repair needs a committed rehabilitation programme. Most patients use crutches for the first few weeks to protect the repair, with a gradual return to normal activity over 6 to 12 months. Return to running and pivoting sport usually takes 9 to 18 months, depending on the procedure and the size and location of the defect. Your rehabilitation plan is tailored to your repair.

If you have a cartilage injury and would like to discuss your options, please get in touch to arrange a consultation.

Procedures I don’t routinely do

Microfracture

Microfracture involves making small holes in the bone beneath a cartilage defect so that bleeding and marrow cells fill it with a clot, which matures into scar-like fibrocartilage.

Isolated microfracture is now largely abandoned, due to poor long-term results. Fibrocartilage is mechanically inferior to the original hyaline cartilage and tends to deteriorate after 2 to 5 years. Microfracture can also thicken and weaken the bone beneath the defect, which makes later cartilage repair procedures less successful. For these reasons I do not offer microfracture as a stand-alone treatment. Marrow stimulation is now used, if at all, combined with a scaffold (see AMIC above).

References

1. Mistry H, Metcalfe A, Smith N, Loveman E, Colquitt J, Royle P, Waugh N. The cost-effectiveness of osteochondral allograft transplantation in the knee. Knee Surg Sports Traumatol Arthrosc 2019;27:1739–53.
2. Osteochondral allograft transplantation in the knee: early experience in the United Kingdom. Orthopaedic Proceedings (BASK May 2023).
3. NHS England. Fresh osteochondral allograft transplantation for osteochondral defects of the knee in adults and post-pubescent children. Clinical Commissioning Policy (URN 2007), October 2022.
4. Esterl E, Rorick C, Wilkins R. 5-year outcomes after cryopreserved osteochondral allograft: interim analysis of IKDC and KOOS scores in knee cartilage repair. ICRS World Congress 2025.