A Careful, Honest Comparison
ChondroFiller® vs
ACI
ACI is the original two-stage autologous chondrocyte implantation, largely superseded in modern practice by MACI but still encountered in older literature and some centres. ChondroFiller® is a single-stage scaffold injection. Here is the honest comparison.
Reviewed byProf Paul Lee MBBch, FRCS (Tr & Orth), PhDLast reviewed 1 May 2026Quick Answer
ChondroFiller® is a single-stage scaffold injection; ACI is the original two-stage cell-based surgical implant under a periosteal patch. ACI (autologous chondrocyte implantation) was the first commercial cell-based cartilage repair technique, originally published in 1994. It involves a cartilage biopsy, several weeks of laboratory cell culture and a second surgery to inject the cells under a periosteal flap sewn over the defect. Most centres have moved to MACI, which uses a collagen membrane instead of periosteum and has fewer complications. ChondroFiller® offers a different alternative: no cell harvest, no second surgery, single-stage scaffold injection.
The Headline Difference
ChondroFiller® vs ACI — the key difference
ACI is a two-stage cell-based surgical technique: cartilage cells are harvested at an arthroscopy, cultured in a laboratory for four to six weeks and then injected as a suspension under a periosteal patch sewn over the defect at a second open operation. ChondroFiller® takes a different approach: a sterile collagen scaffold is placed in a single ultrasound-guided injection, and the body’s own cells migrate in over six to twelve months. No periosteal patch. No two-stage surgery. No laboratory phase.
Mechanism of Action
How each treatment works
ChondroFiller® is a sterile type I/III collagen scaffold injected as a liquid directly into a mapped cartilage defect under ultrasound guidance. It sets into a gel that occupies the defect within minutes.
The patient’s own cells then migrate into the scaffold and lay down new cartilage matrix over six to twelve months. Single-stage. No cell harvest. No lab phase. No periosteal harvest.
ACI requires two surgeries. First, an arthroscopy harvests a small piece of cartilage from a non-weight-bearing area. The chondrocytes are sent to a specialist laboratory and expanded in culture for four to six weeks.
A second open or mini-open surgery follows: a piece of periosteum is harvested (usually from the tibia) and sewn over the prepared defect, and the cultured chondrocytes are injected as a suspension under the patch to mature into new cartilage.
How Long Results May Last
Duration and number of injections
Tissue formation over 6–12 months
Long-term published cohorts to 10–15 years
Direct duration comparison is partly historical. Most centres that offer cell-based implantation today use MACI rather than first-generation ACI, because the membrane-based approach has fewer complications.
Treatment Course
Number of injections
Typically one injection course, with the box quantity (one, two or three) decided from MRI. ChondroFiller® can be repeated for a separate new defect if needed.
ACI is a one-off two-stage course. A repeat would require a fresh cartilage biopsy and full cell expansion again. Revision surgery for periosteal hypertrophy is sometimes needed in the months and years after the original procedure.
Safety and Infection
Safety considerations
Very different risk profiles. ChondroFiller® at London Cartilage Clinic is an ultrasound-guided outpatient injection with routine IV antibiotic cover. The most serious risk is joint infection, which is rare.
ACI involves two surgeries with the standard surgical risks (infection, deep-vein thrombosis, anaesthetic complications) at each operation, plus procedure-specific issues: periosteal hypertrophy (overgrowth of the patch requiring reoperation), graft delamination, donor-site morbidity at the periosteum and a prescriptive rehabilitation programme. These were the main drivers behind the field moving from ACI to MACI.
Patient Selection
Who each treatment may suit
ACI is appropriate for symptomatic knee cartilage defects in adults with otherwise reasonably preserved joints, in centres still offering the procedure. In modern practice, MACI is usually offered in preference to ACI for the same indications. If you have been recommended ACI specifically, it is worth asking whether MACI is an option at the same centre.
ChondroFiller® is appropriate for focal cartilage defects up to roughly 6 cm² with reasonably preserved surrounding cartilage. It is delivered as an injection, which suits patients who want to avoid open surgery, a periosteal patch and a two-stage pathway. See who is suitable for ChondroFiller?
Cost and Value
What each treatment costs
At London Cartilage Clinic, ChondroFiller® costs from £3,000 for one box, £5,500 for two and £8,000 for three, all-in. See the ChondroFiller® cost guide.
Where ACI is still offered privately it typically costs £25,000 to £35,000 in the UK because the cell processing and two surgeries are inherently expensive. NHS availability of ACI specifically is now very limited; most NHS centres have moved to MACI for cell-based cartilage repair.
The headline cost gap is meaningful, but the more important question is whether a cell-based two-stage operation or a single-stage scaffold injection is the right answer for the defect on imaging.
Our Honest Take
When we may recommend each
A focal cartilage defect on MRI where a single-stage scaffold injection is reasonable.
You want to avoid a two-stage operation, periosteal harvest and the historical complications of ACI.
You are looking at a private-pay cell-based pathway and want to understand the alternatives.
ACI is increasingly recommended only in specific centres where the surgeon has long experience with the technique and a particular reason to prefer it over MACI.
For most patients considering a cell-based cartilage implant, MACI is the more current option — see ChondroFiller® vs MACI for that comparison.
When Each Is The Wrong Answer
When we would not recommend each
Very large or multi-zone defects where a surgical cell-based or co-delivery procedure is more appropriate.
Unstable subchondral bone, significant bone marrow oedema or a joint that has progressed to diffuse bone-on-bone arthritis.
Small focal defects where a two-stage cell-based pathway is over-treatment.
Most modern indications, where MACI is the preferred cell-based option over original ACI.
Patients unwilling to accept the periosteal-patch-specific risks or unable to complete the rehabilitation programme.
The Bottom Line
In summary
ACI was the original cell-based cartilage-repair technique and still has a place in specialist centres, but modern practice has largely moved on to MACI for the same indications. ChondroFiller® offers a different alternative again: a single-stage scaffold injection without cell harvest, periosteal patch or two-stage surgery. The right answer is decided from imaging and a clear conversation about trade-offs, not from a default label.
ChondroFiller® vs ACI
Frequently asked questions
What is the difference between ACI and MACI?
ACI is the original technique: cultured cartilage cells injected as a suspension under a periosteal patch sewn over the defect. MACI is the modern variant: the same cultured cells are pre-loaded onto a porcine collagen membrane and the membrane is implanted into the defect. MACI was developed to reduce the periosteal-patch-specific complications of ACI.
Should I have ACI today, or is it outdated?
ACI is still offered in specific specialist centres, but in modern UK practice MACI is usually preferred for the same indications. If ACI specifically has been recommended to you, it is worth asking whether MACI is available at the same centre, and what the rationale is for ACI over MACI in your case.
Is the donor-site morbidity from the periosteum a real concern?
It is a recognised issue in published ACI series — pain at the periosteal harvest site and occasional functional impact. It is one of the reasons MACI, which uses a collagen membrane instead of harvested periosteum, became the more common cell-based technique. ChondroFiller® avoids the question entirely because there is no harvest.
Can ChondroFiller® be used after ACI has failed?
Sometimes yes — where the failed ACI has left a contained defect with reasonably stable surrounding tissue and no significant overgrowth or bony irregularity, ChondroFiller® can occasionally be considered. We review the post-ACI imaging before deciding.
How does the long-term evidence compare?
ACI has the longest cell-based cartilage-repair publication history because it was the first commercially available technique, with cohorts out to ten and fifteen years. ChondroFiller® has a younger publication record, with maintained outcomes (IKDC, Harris Hip Score, MOCART MRI) at five years and over 19,000 cases of clinical use across joints. See the ChondroFiller® clinical evidence page.
Why would I choose ChondroFiller® over the cell-based options?
For some patients, the single-stage scaffold injection avoids the two-stage surgical pathway, the cell-harvest step, the periosteal patch (in ACI) and the cost of cell processing. For other patients, particularly with larger or more demanding defects, a cell-based pathway is the better answer. The decision is made at consultation with imaging review.
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Learn More about ChondroFiller
Deep dive into our clinical resources and patient guides.
Cost in the UK
ChondroFiller® cost in the UK from £3,000, what is included and why prices vary.
Suitability
Who is suitable for ChondroFiller® as an injection, and who may need caution.
Clinical Evidence
IKDC, Harris Hip Score and MOCART MRI outcomes for ChondroFiller® cartilage regeneration.
Self-Assessment
Five-question ChondroFiller® pathway self-assessment for Prevention, Regeneration, Combination, or Support.
In London
Private ChondroFiller® cartilage repair at our Harley Street clinic.
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ChondroFiller® is a registered trademark of Meidrix Biomedicals GmbH. London Cartilage Clinic is not affiliated with or endorsed by Meidrix Biomedicals.