Who cartilage repair is actually for

The most practical question a patient can ask is direct: am I actually a candidate for cartilage repair, or is my joint past that point?

Four clinical variables determine the answer: age, activity level, lesion grade (scored using the ICRS classification), and defect size. Each carries weight independently.

Younger, active patients produce a stronger biological response to cartilage repair and can sustain the intensive rehabilitation that follows — which is why age and activity level are assessed first. The typical candidate is under 50, physically active, and motivated to commit to a recovery period measured in months rather than weeks. Activity level is evaluated separately from age: a sedentary 35-year-old may not be an ideal candidate, while a fit and active 48-year-old may well be.

Lesion grade and size define the biological challenge ahead. The ICRS system grades cartilage damage by depth:

• Grade 2 — partial-thickness loss involving less than half the cartilage depth
• Grade 3 — damage extending beyond halfway through the cartilage
• Grade 4 — full-thickness loss reaching the subchondral bone beneath

Defect size then determines which specific repair technique is appropriate for that grade of damage.

The structural condition of the joint as a whole is assessed alongside these four variables. Concomitant problems — meniscal tears, ligament instability, or malalignment — must be corrected at the same time as any cartilage procedure; leaving them untreated undermines the repair and increases the risk of recurrence.

One boundary is firm. Patients with diffuse or advanced osteoarthritis — widespread cartilage loss rather than a single focal defect — are generally outside the scope of cartilage repair. For them, joint preservation strategies or joint replacement become the relevant clinical conversation.

Why cartilage cannot repair itself

Articular cartilage contains no blood vessels. That single anatomical fact explains almost everything about why cartilage injuries are so clinically serious: without a blood supply, the healing cascade that repairs most other tissues simply cannot begin. The body has no reliable mechanism for restoring damaged cartilage on its own.

Size matters too. Defects smaller than 1 cm² may remain stable in some patients, but lesions beyond that threshold tend to enlarge and deepen over time, gradually progressing towards osteoarthritis if left unaddressed. This trajectory is why the timing of assessment — and intervention — carries real clinical weight. Acting at the focal-defect stage consistently produces better outcomes than waiting for damage to spread.

Accurate staging requires MRI, which is the diagnostic gold standard for cartilage injury. Advanced sequences — T2 mapping, dGEMRIC, and T1ρ imaging — can characterise defect depth and tissue composition in ways that plain imaging cannot. X-ray and CT have a role in surgical planning or where significant bony changes are present, but they do not reliably show the extent of cartilage damage.

This is why a specialist assessment — with weight-bearing imaging and MRI reviewed together — is the appropriate starting point, rather than a GP X-ray alone.

The four stages of joint preservation

Treatment options for cartilage damage follow a logical progression — and knowing where any one procedure sits within that hierarchy makes it easier to evaluate what is genuinely being offered.

Stage 1 — Symptom management. Physiotherapy, activity modification, and appropriate pain relief reduce load on the damaged area, maintain the surrounding musculature, and slow further deterioration. For some patients these measures are sufficient; for others, they stabilise the joint ahead of further treatment.

Stage 2 — Biologic and injection support. PRP (platelet-rich plasma), hyaluronic acid, and BMAC can reduce joint inflammation and serve as bridging options. Stage 2 supports the joint environment; it does not restore the cartilage itself. These are adjuncts or holding measures — not cartilage-regeneration procedures — and understanding that distinction prevents misaligned expectations before any treatment is agreed.

Stage 3 — Cartilage restoration. Repair procedures range from minimally invasive options — including the ChondroFiller injection (an ultrasound-guided outpatient injectable collagen scaffold), AMIC, and OATS — through to cell-based reconstruction with ACI or MACI, and fresh osteochondral allograft for larger or posttraumatic defects. Lesion grade and size, covered in the preceding sections, determine which of these is clinically appropriate.

Stage 4 — Joint replacement. When cartilage loss is diffuse and joint preservation is no longer achievable, replacement becomes the relevant clinical pathway.

Most patients presenting with a focal, symptomatic defect are, by definition, at Stage 3 territory — which is where specialist assessment of repair options carries the most weight.

Matching the procedure to the defect

No two cartilage defects are identical, and the procedure a specialist recommends follows directly from defect size, depth, and location — not from a fixed protocol. The tiers below reflect how clinical practice currently groups the available options.

Marrow-stimulation tier

Microfracture was historically the first-line choice for small, contained defects under 2 cm². Drilling into the subchondral bone triggers a healing response, but the tissue produced is fibrocartilage — mechanically weaker than native hyaline cartilage. Published evidence shows results typically deteriorate after two to three years, and the procedure damages the bone plate in ways that can limit future repair options. Its use is declining in specialist practice.

AMIC (autologous matrix-induced chondrogenesis) places a collagen matrix over a microfracture site to retain marrow-derived cells and provide a more structured repair environment. It remains single-stage but represents a biological step up from standard microfracture.

Injectable scaffold tier

ChondroFiller injection is an ultrasound-guided outpatient procedure using an injectable collagen scaffold. The scaffold self-gels within the defect, is resorbable rather than permanent, and recruits the patient's own progenitor cells. Published data report a complaint rate of approximately 0.06%. It is suited to focal defects up to 3 cm², with evidence supporting selected use up to 6 cm². Placement accuracy is critical, and it is not appropriate for advanced arthritis.

Autograft tier

OATS / Mosaicplasty transfers cylindrical plugs of healthy bone and cartilage from a low-load area of the same joint into the defect. Typical applications cover 1–2 cm²; mosaic configurations can address up to 4 cm². Donor-site morbidity — the risk of pain or functional change at the harvest site — is a meaningful consideration in patient selection.

Cell-based tier

ACI and MACI are two-stage procedures for larger defects, typically 2–10 cm². A first-stage harvest collects cartilage cells; a second procedure reimplants them under a periosteal patch (ACI) or seeded onto a collagen membrane (MACI). MACI reduces some of the technical complexity of the first generation, and both approaches have 10-year outcome data in published series.

Allograft tier

OCA (osteochondral allograft) uses donor tissue for large or posttraumatic defects where the autograft supply from the patient's own joint would be insufficient. Long-term follow-up data are available in the published literature.

Specialist assessment — weighing defect grade, size, location, and the patient's previous treatments — determines which tier applies. No single technique is the right answer across all presentations.

What recovery looks like

Nine to eighteen months — that is how long articular cartilage repair tissue takes to mature fully, and it is the number most patients do not hear until after they have committed to surgery. Understanding it early shapes more realistic expectations across the whole recovery arc.

The early milestones are consistent across most theatre-based procedures. Non-weight-bearing on crutches typically runs for four to six weeks; the repaired tissue must be protected from load while it begins to integrate. Physiotherapy generally starts at approximately two weeks post-operation, focusing initially on range of motion and reducing swelling before progressing to muscle activation and functional movement. High-impact sport — running, jumping, cutting movements — is avoided for at least three months, and graduated return to activity continues well beyond that point, guided by the pace of tissue maturation rather than a fixed date.

The published recovery timelines above describe surgical and theatre-based procedures such as microfracture, OATS, ACI, and MACI. The ChondroFiller injection pathway, as an ultrasound-guided outpatient treatment, does not follow the same post-operative restrictions — specific recovery parameters will differ, and no equivalent published range currently exists for direct comparison. Ask your specialist for a procedure-specific timeline before planning anything around it.

Pre-surgical preparation is one area where the patient has direct influence over the result. Maintaining peri-articular muscle strength through low-impact exercise, eating a diet rich in collagen and Vitamin C, and staying well hydrated (a minimum of two litres of water daily) all support tissue quality ahead of any procedure. Practical considerations — ground-floor sleeping arrangements, mobility aids, ice packs and compression garments for post-operative swelling — are consistently underestimated until they are needed.

How to find the right cartilage specialist

Cartilage repair outcomes depend substantially on how frequently a surgeon performs the specific procedure being offered — not surgery in general, but that technique on defects of comparable grade and size. This is a subspecialty within a subspecialty, and surgical experience is a clinically meaningful variable, particularly for technique-sensitive procedures.

No universal benchmarks exist for evaluating a cartilage surgeon, but useful starting signals include ICRS affiliation or accreditation and published outcome data — not just case volume, but evidence that results are being tracked and reported. At a consultation, practical questions worth asking directly: how many times per year do you perform this specific procedure? What outcome measures do you use? Will you assess me for concomitant issues — alignment, ligament stability, meniscal pathology — that need addressing at the same time as the cartilage repair?

A specialist who welcomes those questions is demonstrating the transparency that subspecialty practice warrants.

If you have been told that joint replacement is your only option, a second opinion from a cartilage subspecialist is clinically reasonable. That assessment may confirm the original recommendation — or it may identify a repair or restoration pathway that has not yet been fully considered.

Search MSK lists cartilage and joint-preservation specialists across the UK, with filters by region, specialty, and treatment offered, which can help identify who to approach for a first or second opinion. The questions above are worth taking into whichever consultation follows.