Why the pattern of damage is the first question

The most common question at a first ChondroFiller® assessment is not 'am I bad enough for treatment?' — it is 'which approach is right for my knee?' The answer turns on the geometry of the damage rather than how much it hurts.

Two patterns present very differently on imaging, even when the patient's symptoms feel broadly similar. One is a single, well-defined lesion — a contained pocket of missing or thinned cartilage surrounded by structurally healthy tissue. The other is diffuse degenerative wear spread across multiple surfaces, with no intact cartilage borders remaining. These are not simply different points on the same spectrum; they are fundamentally different clinical situations that call for different treatment approaches.

MRI is the mandatory starting point, mapping defect size, location, and the quality of the cartilage immediately surrounding it. The scan also flags mechanical factors — malalignment, ligament instability, or a meniscal deficit — that may be driving or accelerating the wear. ChondroFiller® does not correct abnormal joint loading on its own, so any such factors need to be addressed before, or alongside, the collagen scaffold pathway.

Once that picture is clear, pathway selection follows naturally from what the imaging shows.

What ChondroFiller is and how it works

ChondroFiller® liquid (Meidrix Biomedicals GmbH, Germany) is a sterile, injectable Type I collagen scaffold — acellular, CE-marked as a Class III medical device, and used in over 19,000 cases across multiple joints globally. At room temperature it is a liquid; once placed at the cartilage surface, it polymerizes in situ, forming a structured three-dimensional matrix.

The biological process that follows is termed acellular matrix-induced chondrogenesis. The scaffold contains no donor cells of its own. Instead it functions as a chemotactic framework — recruiting the patient's own progenitor cells from the synovium and the subchondral bone beneath the defect into the repair site. Over the subsequent months, those migrating cells support the body's own endogenous repair. ChondroFiller® does not directly regrow cartilage; it establishes the structural environment in which the body can attempt to do so.

Both pathways discussed below deliver the same collagen liquid to the joint. Whether placed via an ultrasound-guided clinic injection or through the arthroscopic Liquid Cartilage™ procedure, the material reaching the cartilage surface is identical. Where the pathways diverge is in how that material is introduced — and, crucially, which anatomical situation allows each technique to work as intended.

The injection pathway for diffuse or widespread OA

For patients with diffuse or widespread degenerative change — including Kellgren-Lawrence Grade III/IV OA — the ultrasound-guided outpatient injection is the appropriate ChondroFiller® pathway. It is delivered entirely in a clinic setting: no general anaesthetic, no incisions, no theatre admission.

The reason this route suits diffuse wear follows from the mechanistic distinction noted earlier. The injection approach is additive: ChondroFiller® is placed under image guidance over worn articular surfaces in a fluid joint environment. Because the scaffold coats rather than fills a defined cavity, it does not require intact cartilage borders to contain it. In a joint with pan-articular degeneration — where no such healthy borders remain — the injection can still reach every worn surface. A single delivery session can coat the entire articular area with no upper ceiling on defect size, making it applicable across the full spectrum from focal wear to advanced OA.

Where assessment identifies a synovial pain component alongside cartilage wear, a dual-injection protocol can be delivered in the same clinic appointment. ChondroFiller® (2.3 mL) is directed at the load-bearing cartilage surfaces; Arthrosamid® (6 mL), a polyacrylamide hydrogel, is directed at the synovial lining. These are distinct products with different mechanisms acting on anatomically separate structures. ChondroFiller® is the regenerative scaffold component; Arthrosamid® provides mechanical cushioning within the synovium and is not a cartilage-regeneration therapy. Their combined use is a complementary strategy, not a single intervention, and Arthrosamid® is mentioned here only in that combination context.

For patients on an ongoing joint-preservation plan, a longitudinal programme incorporating bi-annual ChondroFiller® top-up injections and yearly MRI monitoring can be structured to support the joint over the longer term.

When a focal, contained defect changes the picture

A focal, contained cartilage defect presents a structurally different picture from the diffuse wear described in the previous section — and, for the right patient, opens a second, more targeted treatment option alongside the outpatient injection pathway.

The structural hallmarks of a true focal defect are a single Grade III or IV lesion with intact cartilage on all sides and a defect area of up to approximately 6 cm². The condition of the surrounding cartilage is not a minor detail: it functions as a physical boundary. When the adjacent tissue is structurally sound, it can hold a precisely placed scaffold within a defined repair zone. Where that healthy rim is absent — as is typical in pan-articular degeneration — a contained approach cannot work as intended regardless of the lesion's size.

MRI assessment is essential before any decision, both to confirm defect geometry and to verify the quality of the surrounding tissue. Imaging that shows widespread joint involvement rules out the contained-defect category. Uncorrected mechanical factors — significant malalignment, ligament instability, or a meniscal deficit driving the wear pattern — must also be resolved before any ChondroFiller® pathway proceeds.

For patients who meet all these criteria, the outpatient ultrasound-guided injection remains an option. Where a more targeted approach is preferred, the Liquid Cartilage™ keyhole procedure offers an alternative as a separate surgical pathway: performed under general anaesthesia in theatre, it allows the joint surface to be prepared, the defect debrided to a clean bone bed, and the same collagen scaffold placed under direct vision into a geometrically bounded, dry repair zone — conditions that a contained focal defect, with its healthy borders intact, uniquely provides. This is distinct from the outpatient injection service and is appropriate only in this specific structural scenario.

Clinical outcomes and what the evidence actually covers

Published evidence for ChondroFiller® provides a meaningful benchmark — though the source of that evidence matters as much as the headline figures.

In the knee, four studies included in the manufacturer's 2025 clinical evaluation report (CER v09) consistently show IKDC functional scores improving by approximately 30 points. The most rigorous of these, the Jerosch et al. post-market clinical follow-up study, recorded a mean improvement of 32.4 points sustained at three-year follow-up, with patients reaching a mean functional score of 80. That gain comfortably exceeds the minimum clinically important difference of 16.7 points. MRI MOCART scores in European cohorts range from 81.6 to 84.3, indicating more than 80% defect filling at follow-up. Complication rates are approximately 0%, and the reoperation rate of 3–8% compares favourably with microfracture (up to 41%) and ACI or MACI (up to 37%) in comparable populations. Beyond the knee, hip series report a mean Harris Hip Score gain of approximately 33 points; across joints, MOCART scores range from 70 to 87.

The evidence gap is worth stating plainly. The data above were generated primarily via the arthroscopic route in contained focal defect populations. Outcomes for the ultrasound-guided injection pathway — particularly in patients with diffuse or widespread OA — represent emerging rather than mature literature, and no head-to-head randomised trial has directly compared the two delivery routes. The available evidence supports cautious optimism for both pathways, but individual outcomes depend on defect pattern, joint health, and patient-specific factors that only a structured clinical assessment can weigh.

Getting the right assessment at London Cartilage Clinic

The assessment process begins with MRI. No pathway decision is reached without imaging that confirms the defect pattern, maps the quality of surrounding cartilage, and flags any mechanical factors — the malalignment, instability, or meniscal issues covered in earlier sections — that need resolution before either route is offered.

From that imaging, a structured clinical triage maps each patient to one of four working categories: Prevention (early wear with intact joint mechanics), Regeneration (focal or contained defects suitable for the ChondroFiller® injection pathway), Combination (cases pairing ChondroFiller® with a complementary treatment such as Arthrosamid® for coexisting synovial pain), or Support (advanced degeneration where preserving function ahead of possible replacement is the primary goal). This is a practical consultation tool, not a validated scoring instrument.

Professor Paul Y. F. Lee leads cartilage assessment and treatment planning at the clinic's Harley Street practice, with access to the full range of injection pathways and — where the focal-defect criteria described in the previous sections are met — surgical preservation options alongside them.

To arrange a cartilage assessment, visit londoncartilage.com.