Knee Cartilage Injury and Restoration

Patient information — Dr Christopher Spelman, Orthopaedic Surgeon

Overview

Articular cartilage is the smooth, gliding surface that covers the ends of the bones in the knee. A focal cartilage (chondral) injury is a localised area of damage to this surface, from a sports injury, a previous dislocation, or wear. Unlike widespread arthritis, a focal defect affects a defined area and, in the right patient, can be treated to relieve symptoms and help protect the joint. Cartilage has almost no blood supply and very limited capacity to heal itself, which is why these injuries are important and why a range of “restoration” techniques exist. Where the damage extends into the bone beneath the cartilage, it is called an osteochondral injury and is treated slightly differently.

Symptoms and assessment

Cartilage injuries can cause pain, swelling, and catching or a sense of something loose in the knee. MRI is used to assess the size, depth and location of the defect (often graded using the ICRS system) and to check for associated injuries. Arthroscopy allows direct assessment and treatment. Identifying and addressing any associated problem – malalignment, meniscal loss or ligament instability – is essential, because these overload the cartilage and determine whether a repair will succeed.

Treatment options — matched to the defect

Treatment is tailored mainly to the size and depth of the defect, the patient’s age and demands, and the state of the rest of the knee:

●      Microfracture (a marrow-stimulation / reparative technique) – tiny holes are made in the bone beneath a small defect to recruit a healing clot. Simple and low-cost, and reasonable for small lesions (generally under about 2 cm²), but the repair tissue is less durable and results deteriorate over time for larger lesions.

●      Osteochondral autograft transfer (OAT/OATS) – one or more plugs of the patient’s own cartilage and bone are moved from a low-load area to fill the defect; well suited to small and mid-sized defects (roughly 1–3 cm²) and to osteochondral lesions where bone is involved.

●      Autologous chondrocyte implantation (ACI/MACI) – the patient’s own cartilage cells are harvested, grown in a laboratory and re-implanted into the defect (a two-stage procedure); suited to larger defects (often above 3–4 cm²).

●      Osteochondral allograft – donor cartilage and bone, used for large or deep osteochondral defects, or as a salvage option.

Correcting alignment (osteotomy), replacing a lost meniscus, or stabilising the ligaments is frequently done at the same time to protect the repair – doing the cartilage work in isolation while leaving the cause untreated is a common reason for failure.

What the evidence shows

Systematic reviews show that all of these techniques improve knee pain and function, and that most athletes return to sport – an overall return-to-sport rate of around 80%. Osteochondral autograft (OAT) has the fastest return (about 5 months, with return rates around 93%), while osteochondral allograft and ACI take longer (roughly 9–12 months) but also achieve high return rates (around 88% and 82%). By contrast, microfracture for medium-to-large defects has limited long-term durability, with a high rate of arthritis progression and lower return-to-sport rates (around 17–20%) at ten years. Overall, the restorative techniques (OAT, ACI/MACI, allograft) give better long-term results and lower failure rates than microfracture for anything but small lesions.

Complications

Cartilage procedures are generally safe, but considerations include:

●      Failure of the repair, or incomplete relief of symptoms – more likely with larger or older lesions, and if the underlying cause is not corrected.

●      Stiffness, which is why structured rehabilitation, and for some procedures a period of protected weight-bearing and restricted range, are important.

●      Donor-site issues (with OAT), and the need for two operations with cell-based (ACI/MACI) techniques.

●      Progression to more widespread arthritis over time, and the general low risks of knee surgery (infection, blood clots).

Summary

A focal cartilage injury is different from generalised arthritis and can often be treated to relieve symptoms and protect the knee, especially in younger patients. Matching the technique to the size and depth of the defect – and correcting any alignment, meniscal or ligament problem – gives the best result. Dr Spelman will assess the whole knee and advise the most suitable approach.