Is cartilage repair different from a knee replacement?

For many people, a diagnosis of cartilage damage triggers an immediate fear: knee replacement. In most cases, that step is further down the road than patients expect — and for a significant number, it may be avoidable altogether, at least for years or decades.

Cartilage repair sits at stage three of a four-stage pathway. Stage one is symptom management — physiotherapy, pain relief, activity modification. Stage two introduces biologic or injection support to reduce inflammation and buy time. Stage three is active cartilage restoration: surgical or minimally invasive procedures designed to rebuild the joint surface. Stage four — total knee replacement — becomes relevant only when the joint has deteriorated beyond what preservation can realistically address.

The reason repair is necessary at all comes down to biology. Articular cartilage has no blood supply and no nerve fibres, which means it cannot heal itself the way bone or muscle can. Left untreated, damage tends to produce inferior fibrocartilage rather than the original hyaline tissue, and the lesion often enlarges over time.

Critically, cartilage repair is a strategy for focal damage — a defined lesion or defect within an otherwise reasonable joint. It is not appropriate for advanced, diffuse osteoarthritis, where the joint surface has deteriorated throughout multiple compartments. That distinction — a focal cartilage lesion versus widespread degeneration — is what determines whether a preservation approach or a replacement conversation is clinically the right next step.

The overarching aim of every restoration technique is shared: relieve pain, restore function, and delay or prevent the need for arthroplasty.

What makes someone a good candidate for cartilage repair?

Three factors, more than any others, determine whether cartilage repair belongs in someone's treatment plan: the grade of the lesion, how it was caused, and the overall condition of the rest of the joint.

Lesion grade is assessed using the ICRS (International Cartilage Repair Society) scale. Grade 1 lesions involve superficial softening or fissuring of the surface; Grade 2 extend less than halfway through the cartilage thickness; Grade 3 penetrate more than halfway, sometimes reaching the bone beneath; Grade 4 break through into the subchondral bone entirely. Surgical repair is primarily targeted at Grade 3 and 4 lesions, where the defect is deep enough that conservative management alone is unlikely to prevent further deterioration.

How the damage occurred matters just as much as its severity. In athletes and active patients, traumatic cartilage lesions — caused by a single injury event such as a pivot or collision — carry a return-to-prior-sport rate of around 87% after repair. Degenerative lesions, which develop gradually through wear, carry a rate closer to 33%. That gap is large enough that lesion aetiology is now treated as a formal part of pre-operative assessment and patient counselling.

The condition of the wider joint sets the outer limit. Advanced osteoarthritis affecting multiple compartments is a hard contraindication for cartilage repair procedures. Where imaging shows bone-on-bone changes across a large portion of the knee, restoration techniques are unlikely to achieve meaningful improvement, and the clinical conversation appropriately moves toward joint replacement.

Age alone is not a cut-off. The strongest evidence base is for adults under 50 with a single, focal, traumatic defect in an otherwise healthy joint — but procedures such as osteochondral allograft transplantation remain viable for patients over 40, though outcomes vary by age and sex. A specialist assessment is needed to weigh these factors individually.

What treatment options exist for focal cartilage damage?

Techniques span a wide range of invasiveness — from an outpatient injection to a two-stage surgical procedure — and defect size is the primary factor that guides which approach is appropriate.

Outpatient injectable scaffold

ChondroFiller injection is an ultrasound-guided outpatient treatment using an injectable collagen scaffold. Once placed, the scaffold recruits the patient's own progenitor cells in a process called matrix-induced chondrogenesis. It is suitable for focal defects up to approximately 3 cm² (extendable to 6 cm² in some cases) and does not require theatre admission or general anaesthesia. For patients who are not yet ready for — or wish to avoid — a surgical pathway, this represents the least-invasive restorative option currently available.

Single-stage surgical options

AMIC (autologous matrix-induced chondrogenesis) combines standard marrow stimulation with a collagen matrix to improve the quality of the repair tissue. It bridges the gap between older microfracture techniques and cell-based repair, and is generally suited to small-to-mid-sized defects in a single-stage procedure.

OATS / mosaicplasty transfers one or more osteochondral plugs — cartilage and underlying bone — from a low-load area of the patient's own knee to the defect site. Typical lesion size is 1–2 cm², with mosaic configurations covering up to approximately 4 cm². Because healthy tissue is taken from elsewhere in the same joint, donor-site morbidity is a meaningful consideration that should be discussed during pre-operative planning.

Two-stage cell-based repair

ACI (autologous chondrocyte implantation) and its matrix-based variant MACI involve harvesting the patient's own cartilage cells, expanding them in culture over several weeks, then reimplanting them in a second procedure. This two-stage commitment is the main trade-off against stronger tissue quality. For defects of 3 cm² or more, the SUMMIT randomised controlled trial — currently the best available trial evidence at Level I — demonstrated that MACI produced superior KOOS pain and function scores compared with microfracture at both two- and five-year follow-up.

Large or complex defects

Osteochondral allograft (OCA) transplantation uses donor cartilage-bone tissue, making it the option of choice when defects are too large for autograft approaches or when a prior repair has failed. Long-term follow-up data support its use in appropriate patients.

A note on older techniques

Microfracture — once the default first-line procedure for small defects — is now used with caution. Evidence points to fibrocartilage breakdown at around two to three years and a risk of damage to the subchondral bone that can compromise future repair attempts. Chondroplasty (arthroscopic debridement) addresses pain temporarily but is not regenerative and does not restore the joint surface.

Why alignment and other knee injuries affect your treatment plan

Choosing the right repair technique is only part of the picture. How the knee is loaded — and whether other structures within it are damaged — can determine whether any cartilage procedure succeeds or fails.

The role of alignment

When the lower limb is bow-legged (varus malalignment), abnormal load concentrates on the medial compartment. For a medial cartilage repair to survive long-term, surgeons typically recommend combining it with a high tibial osteotomy (HTO) — a procedure that corrects the angle of the shin bone to redistribute force across the joint — when mechanical varus exceeds 3°. Where varus is greater than 5°, isolated cartilage repair is generally contraindicated, because the repaired surface would be continuously overloaded before it can mature. A distal femoral osteotomy (DFO) serves the equivalent purpose on the lateral side.

Osteotomy is not purely an adjunct. In younger patients with unicompartmental disease, HTO or DFO can relieve pain and restore function as a standalone procedure, buying meaningful time before any decision about joint replacement becomes necessary.

Concurrent injuries

Cartilage damage rarely presents alone. Meniscus tears, ligament ruptures, and patellar instability are common co-existing findings, and each can accelerate cartilage deterioration if left unaddressed. Where these are identified pre-operatively, the aim is to treat them during the same operative sitting rather than staging separate procedures.

A thorough assessment by a specialist — covering alignment, imaging, and the condition of surrounding structures — is what surfaces these co-existing factors before any repair is planned.

Recovery and realistic expectations after cartilage repair

Recovery after cartilage repair is measured in months and years, not weeks — and the primary determinant is the technique chosen.

The least demanding pathway is the ChondroFiller injection: ultrasound-guided, outpatient, no theatre admission. Because the procedure involves no surgical incision or general anaesthesia, initial downtime is substantially shorter than for operative approaches. Single-stage surgical options such as OATS sit in the middle: one procedure, but a period of protected weight-bearing while bone and cartilage integrate at the graft site. Two-stage cell-based procedures — ACI and MACI — carry the longest commitment; meaningful outcome evidence from trials such as SUMMIT is reported at two and five years post-surgery, which signals what the realistic evidence horizon looks like for that group. Specific weight-bearing protocols vary by technique, defect location, and individual circumstances; the treating specialist will set a personalised rehabilitation plan.

For active patients, lesion cause — already covered earlier in this article — shapes outcome expectations more than almost any other single factor. That difference in return-to-sport likelihood holds across technique categories, making it a central topic in any honest pre-operative conversation.

Looking further ahead, single-stage cell-based approaches — sometimes referred to as next-generation ACI — are in early development. Clinical trial data are accumulating, and their potential to shorten the two-stage pathway is a genuine area of research interest, though the established evidence benchmarks for now remain the 5–10 year follow-up series from MACI, ACI, and OATS.

Finding a specialist and the right next step

Cartilage repair sits within a subspecialty that not every knee surgeon covers. The techniques described earlier — from injectable scaffold to two-stage cell implantation — each require specific training and equipment, so the experience of the operating surgeon or interventional clinician matters as much as the technique itself.

When booking a first assessment, bring any MRI imaging you already have and a clear account of how symptoms began, how they have changed, and what activities you want to return to. That information allows the specialist to make a meaningful assessment rather than spending the consultation on background.

Questions worth raising at that first appointment

• What ICRS grade is my lesion, and how large is the defect area?
• Which technique suits that grade and size — and why?
• Does my alignment need correcting before or alongside repair?
• What does realistic recovery look like for the specific approach you are recommending?

Specialists with a dedicated interest in knee cartilage across the UK can be found via the Search MSK directory — filtering by region and specialty is the quickest way to identify someone suited to your situation.