Knee cartilage can now be repaired surgically when the damage is a focal defect in an otherwise healthy knee – with the strongest evidence for cultured cartilage cell implantation (ACI/MACI) in larger defects – but no injection has yet been shown to regrow cartilage in an arthritic knee. Matching the treatment to the type of damage is the key to a good result.
Cartilage injuries are common in footballers, badminton and kabaddi players, runners and people who have twisted or injured their knee. This guide from the knee team at Sports Orthopedics Institute explains the types of cartilage damage, the treatments available, what the research shows for each, and what recovery involves.
Key takeaways
- Focal defects and arthritis are different problems. Surgical cartilage repair is for well-defined defects; widespread arthritis needs a different approach.
- Small defects (under about 2 cm²) can be treated with microfracture or osteochondral plugs.
- Larger defects in younger, active patients have the best evidence for ACI/MACI, which outperformed microfracture at five years in a randomised trial.
- PRP and stem cell injections do not regrow cartilage; their benefit for knee arthritis is limited or unproven.
- Alignment, stability and rehabilitation decide whether any cartilage repair lasts.
How to read the evidence ratings
|
Rating |
What it means |
|---|---|
|
Strong |
Consistent randomised controlled trials or high-quality meta-analyses |
|
Moderate |
Multiple comparative studies or smaller RCTs with consistent findings |
|
Limited / mixed |
Small or conflicting studies; benefit possible but uncertain |
|
Experimental |
Laboratory, animal or early human studies only |
Understanding Knee Cartilage Damage
Articular cartilage is the smooth tissue covering the ends of the bones in the knee; it has no blood supply, so once damaged it does not heal well on its own.
Focal defect or arthritis?
This distinction drives every treatment decision:
|
|
Focal cartilage defect |
Osteoarthritis |
|---|---|---|
|
What it is |
A well-defined hole or flap in otherwise healthy cartilage |
Widespread thinning and loss of cartilage across the joint |
|
Typical patient |
Younger, active, often after an injury |
Usually older; gradual onset |
|
Main treatments |
Surgical cartilage repair or restoration |
Exercise, weight loss, injections, osteotomy, partial or total knee replacement |
Common causes
- Sports injuries: twisting, landing or direct impact, often with an ACL or meniscus tear
- Kneecap dislocation: can shear cartilage off the kneecap or femur
- Osteochondritis dissecans: a fragment of bone and cartilage separates, usually in adolescents and young adults
- Overload: malalignment (bow legs or knock knees), meniscus loss or excess body weight
- Osteoarthritis: gradual wear over time
Symptoms
- Pain with activity, particularly stairs, squatting or impact
- Swelling after activity
- Catching, locking or a grinding sensation
- Stiffness and reduced movement
These symptoms overlap with meniscus and ligament injuries, so a specialist examination and MRI are needed to make the diagnosis.
Diagnosis and Choosing a Treatment
The right treatment depends on the size and location of the defect, the health of the rest of the knee, and your age and goals.
Assessment includes: a history and examination, standing X-rays (including long-leg views to check alignment), and MRI to measure the defect and look for meniscus or ligament damage. Sometimes the defect is best sized at arthroscopy.
|
Factor |
What we look at |
|---|---|
|
Defect size |
Under about 2 cm² (small) vs larger defects |
|
Depth |
Cartilage only, or cartilage plus underlying bone |
|
Location |
Femoral condyle, kneecap or trochlea, tibia |
|
Rest of the knee |
Healthy cartilage elsewhere, or early arthritis |
|
Alignment and stability |
Bow legs or knock knees, ACL deficiency, kneecap instability |
|
Meniscus |
Present and functioning, or previously removed |
|
Patient |
Age, activity level, body weight, smoking, goals |
Important: any malalignment, instability or meniscus deficiency usually needs to be corrected at the same time, or the cartilage repair is likely to fail.
Surgical Cartilage Repair Techniques
Surgical options either stimulate repair tissue, transfer healthy cartilage, or implant your own lab-grown cartilage cells.
|
Procedure |
How it works |
Best for |
Stages |
Evidence |
|---|---|---|---|---|
|
Microfracture (bone marrow stimulation) |
Small holes in the bone under the defect release marrow cells that form fibrocartilage |
Small defects (under about 2 cm²), lower-demand patients |
One, arthroscopic |
Moderate; results often decline after 3–5 years |
|
Osteochondral autograft (OATS / mosaicplasty) |
Plugs of healthy cartilage and bone moved from a low-load area of your knee |
Small to medium defects, including those with bone loss |
One |
Moderate |
|
Osteochondral allograft |
A matched donor cartilage-and-bone graft fills a large defect |
Large or deep defects, failed earlier repairs |
One |
Moderate; availability of donor grafts can be limited |
|
ACI / MACI (autologous chondrocyte implantation) |
Your cartilage cells are harvested, grown in a laboratory for about 3–6 weeks, then implanted on a membrane or in a gel |
Larger defects (around 2–3 cm² or more) in younger, active patients |
Two: arthroscopic biopsy, then implantation |
Strong for larger defects |
About microfracture
Microfracture is quick and inexpensive, and many patients improve in the first one to two years. However, it produces fibrocartilage, which is mechanically weaker than normal (hyaline) cartilage, and results tend to decline after several years, especially in larger defects and older patients.
About ACI and MACI
ACI produces repair tissue that is more similar to normal cartilage (“hyaline-like”) than microfracture. MACI is a refinement in which the cells are grown on a collagen membrane, making the implantation simpler, without the need to harvest a periosteal patch. Both still require two procedures: a small arthroscopic biopsy, then implantation several weeks later.
What the Evidence Shows for Surgical Repair
The best-quality comparison favours cultured cell implantation over microfracture for larger defects.
MACI vs microfracture: the SUMMIT trial
In the SUMMIT randomised trial of 144 patients with knee cartilage defects of 3 cm² or larger, MACI gave clinically and statistically better pain and function than microfracture, and that advantage was maintained at five years (American Journal of Sports Medicine, 2018). MRI showed improved defect filling with both treatments.
Autologous chondrocyte implantation in India
ACI is available in India through cultured cartilage cell products approved by the Indian drug regulator (CDSCO). A multicentre Indian study of a gel-based ACI product (CARTIGROW) in patients aged 19–38 reported significant improvement in pain and function sustained to four years, though it included only 14 patients and had no comparison group (International Orthopaedics, 2022).
Microfracture durability
Microfracture often gives good short-term relief, but the fibrocartilage it creates tends to deteriorate over time. For this reason, it is now generally reserved for small defects, while larger defects in active patients are better treated with ACI/MACI or osteochondral grafts.
Injections: What They Can and Cannot Do
Injections can ease symptoms for some people, but none has been shown to regrow cartilage. They are mainly used for early arthritis rather than focal defects.
|
Injection |
What the evidence shows |
Rating |
|---|---|---|
|
Corticosteroid |
Short-term relief of pain and inflammation; repeated frequent use is not advised |
Moderate for short-term relief |
|
Hyaluronic acid |
Modest benefit in some patients |
Limited / mixed |
|
PRP |
Better pain relief than hyaluronic acid in many meta-analyses, but no better than saline placebo in the large RESTORE trial |
Limited / mixed |
|
Stem cell / bone marrow / fat-derived cells |
No better than a steroid injection at one year in a 480-patient trial; no change in MRI arthritis scores |
Limited |
PRP
A meta-analysis of 20 randomised trials found PRP reduced pain more than hyaluronic acid at 6 and 12 months (Journal of Orthopaedic Surgery and Research). However, the placebo-controlled RESTORE trial in 288 adults with knee osteoarthritis found no significant difference from saline in symptoms or cartilage volume at 12 months (JAMA, 2021).
Stem cell injections
In a 2023 multicentre trial, bone marrow concentrate, fat-derived and umbilical cord-derived cell injections were no better than a corticosteroid injection, or each other, at one year (Nature Medicine). Injected cells have not been shown to turn into new cartilage.
In India, the ICMR–DBT National Guidelines for Stem Cell Research treat stem cell use outside approved blood disorders as investigational, to be carried out only within approved clinical trials (Nature India). Be cautious of any clinic offering stem cell injections for knee cartilage as routine paid treatment.
Non-Surgical Management
For early arthritis and some small, stable defects, a structured non-surgical programme is the right first step.
- Exercise therapy: strengthening the quadriceps, hamstrings and hip muscles reduces load on the joint and is a core treatment for knee arthritis.
- Weight management: every kilogram lost reduces load through the knee with each step.
- Activity modification: swap high-impact activities for cycling, swimming or the elliptical trainer while symptoms settle.
- Bracing: an unloader brace can shift load away from a damaged compartment.
- Medicines: short courses of anti-inflammatory painkillers if safe for you. Evidence for glucosamine and chondroitin supplements is weak.
When to consider surgery: persistent pain, swelling, catching or locking despite three months or more of good conservative care, particularly in a younger person with a focal defect.
Recovery After Cartilage Surgery
Cartilage repair needs patience: the new tissue keeps maturing for 12–24 months, and returning to impact too early is a common cause of failure. Exact protocols depend on the procedure and the defect's location.
|
Phase |
Typical timing |
Focus |
|---|---|---|
|
Protection |
Weeks 0–6 |
Crutches with limited weight-bearing (often 6 weeks for femoral condyle defects; kneecap defects may allow earlier loading in a brace); early pain-free range of motion; quadriceps activation |
|
Early strengthening |
Weeks 6–12 |
Gradual return to full weight-bearing; normal walking; cycling; closed-chain strengthening |
|
Intermediate |
Months 3–6 |
Progressive strength, balance and functional training; return to desk work earlier and to most daily activities |
|
Return to sport |
Months 6–18 |
Running, then sport-specific drills, guided by strength and hop testing |
Typical return to sport
- Microfracture: about 6–9 months
- Osteochondral autograft: about 6–9 months
- ACI / MACI: about 9–18 months for pivoting and contact sports
Tips for the best result
- Follow weight-bearing and motion restrictions closely, even if you feel well.
- Keep up your home exercises between physiotherapy sessions.
- Maintain a healthy weight, eat a balanced diet with adequate protein, and avoid smoking.
- Contact your surgeon promptly for a sudden increase in pain or swelling, fever, wound problems, or the knee giving way.
Outcomes and What Affects Success
Most well-selected patients improve significantly after cartilage repair, but success depends as much on the knee and the patient as on the technique.
|
Favours a good result |
Raises the risk of failure |
|---|---|
|
Younger age (under about 40) |
Older age |
|
Single, well-contained defect |
Multiple defects or early arthritis |
|
Normal alignment, or alignment corrected |
Uncorrected bow legs or knock knees |
|
Stable ligaments and a functioning meniscus |
ACL deficiency or previous meniscus removal |
|
Healthy body weight, non-smoker |
Obesity, smoking |
|
Shorter duration of symptoms |
Long-standing symptoms or previous failed surgery |
|
Committed rehabilitation |
Early return to impact |
We do not quote single “success rates” because they vary widely between studies, techniques and patient groups. Your surgeon should give you an estimate based on your own knee.
Future Directions
Several promising technologies are in development, but none is yet routine treatment.
- Single-stage cell techniques and improved scaffolds that avoid the need for two operations
- 3D-bioprinted and tunable hydrogel implants matched to the defect's shape and stiffness – currently in laboratory and animal studies
- Gene therapy and growth factor combinations to boost cartilage-producing cells
- Laboratory-grown cartilage tissue for transplantation
Rating: Experimental. We will update our guidance as evidence emerges.
How Sports Orthopedics Institute Can Help
We match the treatment to your cartilage problem, your knee and your goals – and explain the evidence behind every option.
- Accurate assessment: examination, standing and long-leg X-rays, and MRI to define the defect, alignment and any associated injuries.
- The full range of cartilage care: microfracture, osteochondral grafting, autologous chondrocyte implantation, and combined procedures such as osteotomy, ACL reconstruction or meniscus repair.
- Honest advice on injections: including when they are unlikely to help.
- Integrated rehabilitation: protocols designed around cartilage healing and safe return to sport.
Knee pain, swelling or catching after an injury? Book a consultation with our knee cartilage specialists in Bengaluru.
Frequently Asked Questions
Can knee cartilage regenerate on its own?
Very little. Cartilage has no blood supply, so significant defects rarely heal by themselves. Surgical techniques can create repair tissue or transplant healthy cartilage into a defect.
Can knee cartilage regenerate without surgery?
No injection or supplement has been shown to regrow cartilage. Non-surgical care – exercise, weight management and sometimes injections – can reduce symptoms and protect the joint, especially in early arthritis.
What is the best treatment for a knee cartilage defect?
It depends on the defect and the patient. Small defects may suit microfracture or osteochondral plugs; larger defects in younger, active people have the strongest evidence for ACI/MACI. Alignment and stability problems must be addressed too.
Is MACI a single operation?
No. MACI still needs two steps: a small arthroscopic procedure to take a cartilage sample, then implantation of the lab-grown cells several weeks later. The implantation itself is simpler than older ACI techniques.
Do stem cell injections regrow knee cartilage?
There is no good evidence that they do. In a large 2023 trial, cell injections were no better than a steroid injection at one year. In India, stem cell use for this purpose should only take place within an approved clinical trial.
Does PRP help knee cartilage?
PRP may ease pain in some people with early arthritis, but it does not regrow cartilage, and a large placebo-controlled trial found no benefit over saline.
How long is recovery after cartilage surgery?
Most people use crutches for about six weeks. Return to sport takes around 6–9 months after microfracture or osteochondral grafting, and 9–18 months after ACI/MACI.
Can I walk after cartilage surgery?
Usually with crutches and limited weight on the leg for the first few weeks, depending on the procedure and defect location. Your surgeon will give you specific instructions.
What happens if cartilage damage is left untreated?
Some small defects cause few symptoms for years. Larger symptomatic defects can enlarge and contribute to arthritis over time. An early specialist assessment helps decide whether treatment is needed.
Is there an age limit for cartilage repair?
There is no strict cut-off, but outcomes are best in people under about 40–50 with a focal defect and no established arthritis. Older patients with widespread arthritis are usually better served by other treatments.
References
- MACI versus microfracture: five-year follow-up of the SUMMIT randomized trial. American Journal of Sports Medicine, 2018.
- Pathak S, et al. Efficacy and safety of CARTIGROW in articular cartilage defects of the knee: a four-year prospective study. International Orthopaedics, 2022.
- Bennell KL, et al. Effect of intra-articular PRP vs placebo in knee osteoarthritis: the RESTORE trial. JAMA, 2021.
- PRP versus hyaluronic acid in knee osteoarthritis: a meta-analysis. Journal of Orthopaedic Surgery and Research, 2020.
- Mautner K, et al. Cell-based versus corticosteroid injections for knee pain in osteoarthritis: a randomized phase 3 trial. Nature Medicine, 2023.
- ICMR–DBT National Guidelines for Stem Cell Research, 2017 (Nature India summary).
Disclaimer: This article is for educational purposes only and does not replace a consultation with a qualified orthopedic surgeon.