Introduction
A common question about ChondroFiller is how the gel stays in place inside a joint without the stitches or anchors associated with open surgery. The answer lies in the material's chemistry and physical form rather than in any surgical fixation. Understanding this helps patients form realistic expectations — and distinguishes two different delivery pathways that use the same scaffold.
What ChondroFiller Is
ChondroFiller is a Class III CE-marked type I collagen hydrogel scaffold, manufactured as a dual-component sterile syringe. It is acellular — cell-free by design — and is intended to provide a three-dimensional matrix that the body's own progenitor cells can migrate into and populate. The device is used either as a non-surgical outpatient injection (the ChondroFiller injection) or as part of Liquid Cartilage, Professor Paul Y. F. Lee's keyhole surgical protocol, where it is placed arthroscopically alongside biological adjuncts. In both settings the self-gelling property is central.
How the Gel Sets in Place
ChondroFiller is formulated as two components held in separate chambers of a single syringe. One chamber contains a solution of type I collagen; the other contains a neutralising buffer. When the two are co-extruded through a mixing adapter, the rise in pH triggers collagen fibrillogenesis — the collagen molecules self-assemble into a fibrous network. At body temperature the process is complete within approximately three to five minutes, producing a soft, cohesive hydrogel that has taken on the three-dimensional shape of the defect site.
The gelation is temperature-dependent: optimal processing occurs around 33°C. The device must not be warmed above 35°C, as this can cause irreversible collagen denaturation and prevent gelation. Strict handling of the device before application is therefore important for clinical success.
Natural Adhesion — No Stitches Needed
Once formed, the hydrogel is self-adherent. It bonds with endogenous fibrin present in the surrounding cartilage margins and subchondral bone. This intrinsic adhesiveness means the implant remains securely fixed within the defect without requiring sutures or external fibrin glue, regardless of whether it has been placed by injection or by arthroscopic technique.
For the non-surgical ChondroFiller injection, there is no incision and no theatre. The scaffold is delivered under ultrasound guidance as an outpatient procedure. Because sutures are never part of the non-surgical pathway, the adhesion chemistry is the sole means of retention — making the material's self-gelling behaviour the key practical feature.
When ChondroFiller is placed during Liquid Cartilage keyhole surgery, the arthroscopic approach also benefits from this adhesion: the surgeon does not need to suture the scaffold in place, which simplifies the procedure and reduces tissue handling.
Positioning and Preparation Matter
The self-gelling mechanism works best when the defect is dry and the affected limb is positioned so that the defect surface is horizontal at the time of delivery. This prevents the liquid collagen from draining away before it gels. Irrigation fluid is drained before application, and some arthroscopic procedures use gas insufflation rather than saline to keep the environment dry. These technical details apply principally in the surgical setting, but they illustrate why the preparation around delivery is as important as the material's intrinsic properties.
Stability During Movement
Patients often ask whether the gel remains secure during normal joint movement — bending the knee, rotating the hip, or walking. Clinical experience and published series suggest that the adhesion and gel cohesion are sufficient for physiological joint movement once the material has set. Activity is typically restricted in the days immediately after treatment to allow initial integration, with a structured return to movement guided by the treating clinician.
ChondroFiller is collagen-based, and the therapeutic goal is matrix-induced chondrogenesis: progenitor cells recruited from the synovium and subchondral bone migrate into the scaffold, differentiate into chondrocyte-like cells, and begin producing cartilage matrix over the following months. The scaffold itself is gradually resorbed and replaced over an expected period of one to two years. Benefits vary between individuals, and ChondroFiller does not cure or reverse arthritis.
Conclusion
ChondroFiller stays in place through its chemistry: a pH-triggered self-gelling collagen solution that bonds with endogenous fibrin in the surrounding tissue. This eliminates the need for stitches or external anchors in both the non-surgical injection setting and the arthroscopic surgical setting. The approach minimises tissue disturbance while providing a stable scaffold for the body's own repair process.
Whether the ChondroFiller injection or Liquid Cartilage keyhole surgery is the appropriate pathway depends on the size and location of the defect, joint accessibility, and individual circumstances. At the London Cartilage Clinic, patients receive an individual assessment to determine which approach, if any, is likely to be suitable.
References
Corain M, Zanotti F, Giardini M, Gasperotti L, Invernizzi E, Biasi V, Lavagnolo U. The use of an acellular collagen matrix ChondroFiller Liquid for trapeziometacarpal osteoarthritis. Cartilage. 2023.
Frequently Asked Questions
- When the two components of the syringe are mixed, a pH change triggers the collagen to self-assemble into a gel within approximately three to five minutes. The resulting hydrogel bonds naturally with fibrin in the surrounding cartilage and bone, so no sutures or external anchors are needed.
- Clinical experience suggests that, once set, the gel remains stable during physiological movement. Activity is usually restricted for the initial recovery period to allow integration, after which movement is reintroduced gradually according to clinical guidance. Benefits vary between individuals.
- No. ChondroFiller is the scaffold material. It can be delivered as a non-surgical, ultrasound-guided outpatient injection for accessible lesions. It can also be placed arthroscopically during Liquid Cartilage — Professor Paul Y. F. Lee's keyhole surgical protocol — where it is combined with biological adjuncts for larger or more complex defects. The two pathways are distinct.
- Liquid Cartilage is a keyhole (arthroscopic) surgical protocol developed by Professor Paul Y. F. Lee at the London Cartilage Clinic. It delivers the ChondroFiller scaffold alongside biological adjuncts such as platelet-rich fibrin or plasma, and where indicated the patient's own mesenchymal stem cells, under a general or regional anaesthetic in theatre. It is genuine surgery with a structured recovery programme. The ChondroFiller injection, by contrast, is non-surgical, outpatient, and requires no theatre or anaesthetic.
- No. Suitability depends on the grade, size, and location of the cartilage defect, the joint involved, and individual factors such as body weight, alignment, and overall joint health. An experienced specialist should assess each patient individually. ChondroFiller is not appropriate for all presentations of joint wear or osteoarthritis, and benefits cannot be guaranteed.
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