Introduction

Cartilage is essential for smooth, pain-free joint movement. When it wears or is damaged through injury, use, or ageing, joints can become painful and stiff. For people considering a non-surgical option, two practical questions tend to arise first: what exactly is the treatment made of, and how safe is it? This article focuses on both for the ChondroFiller injection — a non-surgical, ultrasound-guided collagen injection used to support cartilage repair in accessible joints.

What Is ChondroFiller and How Does It Work?

ChondroFiller is a Class III CE-marked medical device — a type I collagen hydrogel scaffold that is delivered as a non-surgical outpatient injection into the joint. The device is manufactured by Meidrix Biomedicals in Germany and is imported into the UK under prescription.

Once inside the joint, the collagen gel may settle over worn or damaged cartilage surfaces, providing a three-dimensional scaffold. The biological principle is acellular matrix-induced chondrogenesis: the implanted collagen attracts the patient's own progenitor cells from the surrounding synovium and subchondral bone marrow. These cells migrate into the scaffold, differentiate into cartilage-producing cells (chondrocytes), and gradually synthesise new cartilage-like tissue. The scaffold itself is resorbed over approximately one to two years as the body remodels the repair site.

It is important to be clear about what the injection is not: it does not cure or reverse arthritis, it does not involve surgery, and it does not guarantee cartilage regrowth. Benefits vary between individuals, and clinical evidence suggests improvements in pain and function for suitable candidates rather than universal outcomes.

What Is ChondroFiller Made Of?

ChondroFiller uses a dual-component delivery system in a sterile, single-use, double-chamber syringe. The two components are combined at the point of injection to initiate in-situ gelation.

• Component 1 is a solution of Type I collagen derived from the tail tendons of specific pathogen-free rats bred under stringent health-monitoring conditions. The collagen concentration in the final mixture is 8 mg/ml.
• Component 2 is a neutralisation solution — a HEPES buffer, sodium chloride, and acetic acid — that raises the pH of the acidic collagen solution, which triggers the gelation process.
• The final hydrogel is acellular (containing no living cells) and is biocompatible, meaning the risk of immune rejection is low.
• Gelation completes within approximately three to five minutes at body temperature, producing a self-adherent scaffold that bonds with the surrounding biological environment without requiring sutures or external fixative.

The collagen source — Type I collagen — is the same structural protein found naturally in skin, bone, and connective tissue, which contributes to the material's good compatibility with human tissue.

Is ChondroFiller Safe?

The safety record for ChondroFiller is well-documented. The manufacturer's clinical evaluation report, based on data from over 19,490 units sold since 2013, reports no serious incidents. The overall complaint rate is approximately 0.06%, and the most frequently noted device-related issue — non-gelation, where the scaffold fails to set correctly — occurs at a frequency of around 0.01%.

Clinical studies report a near-zero rate of serious complications, a meaningful contrast with more invasive surgical procedures. The device's acellular, biocompatible design means that systemic immune reactions are uncommon. As with any intra-articular injection, there is a small risk of local side effects related to the injection itself — including temporary discomfort, minor swelling, or a small risk of infection — but these apply broadly to injectable joint treatments rather than being specific to ChondroFiller's composition.

The CE Class III designation indicates the device has undergone rigorous regulatory review, including clinical evaluation against the European Union Medical Device Regulation (EU MDR 2017/745), confirming that its benefit-risk profile is considered favourable.

What the Clinical Evidence Shows

Published outcome data support cautious optimism for selected patients. In knee applications, clinical series report International Knee Documentation Committee (IKDC) score improvements of approximately 30 points over 12 to 36 months. In hip applications, modified Harris Hip Score (mHHS) improvements of over 30 points have been reported. MRI assessment using MOCART (Magnetic Resonance Observation of Cartilage Repair Tissue) scores in published studies indicate repair tissue quality around 80 and above, suggesting reasonable defect fill and tissue integration.

ChondroFiller has also been studied in smaller joints. A 2023 study by Corain and colleagues examined its use in trapeziometacarpal (thumb base) osteoarthritis, reporting significant pain reduction and functional improvement. These findings extend the evidence base beyond the knee and hip to joints where surgical intervention carries greater complexity.

It is important to note that these results come from the ChondroFiller scaffold — the CE-marked device — and reflect its performance as delivered through appropriate injection or surgical technique. They do not represent a guarantee of equivalent benefit for every patient.

ChondroFiller Injection vs Liquid Cartilage: Understanding the Difference

Patients researching ChondroFiller sometimes encounter the term Liquid Cartilage. These are not the same thing and should not be used interchangeably.

The ChondroFiller injection is a non-surgical, outpatient procedure. The scaffold is delivered via an ultrasound-guided injection without the need for theatre, general anaesthetic, or surgical incision. It is suited to accessible joints and smaller or moderate cartilage defects.

Liquid Cartilage — formally the Lee Liquid Cartilage Protocol — is a different pathway entirely. It is a keyhole (arthroscopic) surgical technique developed by Professor Paul Y. F. Lee that places the ChondroFiller scaffold under dry arthroscopic conditions, combined with biological adjuncts such as platelet-rich fibrin, platelet-rich plasma, tranexamic acid, and — where indicated — the patient's own mesenchymal stem cells from bone marrow or fat. This surgical approach is used for larger or load-bearing cartilage defects in joints such as the knee, hip, shoulder, and ankle. It involves theatre, anaesthesia, and a structured rehabilitation programme. The two pathways share the same scaffold material but are clinically distinct.

Conclusion

ChondroFiller is a CE-marked non-surgical collagen injection with a well-documented safety profile and evidence of clinically meaningful improvement in patient-reported outcomes in suitable candidates. Its Type I collagen composition is biocompatible and cell-free, and the manufacturing and regulatory standards it meets are stringent. It is not a cure for arthritis, and it does not replace the need for thorough individual assessment to determine suitability.

At the London Cartilage Clinic on Harley Street, specialist assessment is available for patients considering cartilage preservation options — including both the non-surgical ChondroFiller injection and the surgical Liquid Cartilage protocol — to ensure the right approach is matched to each individual's joint, defect, and goals.

References

Corain, M., Zanotti, F., Giardini, M., Gasperotti, L., Invernizzi, E., Biasi, V., & Lavagnolo, U. (2023). The use of an acellular collagen matrix ChondroFiller Liquid for trapeziometacarpal osteoarthritis. Cartilage.