What KL Grade III–IV means for your treatment options

"You've been told your knee is grade three, or bone on bone" — that phrase lands differently for every patient, but it usually marks the point at which a surgeon first mentions replacement. Kellgren-Lawrence (KL) grading describes joint deterioration on X-ray: Grade III shows partial cartilage loss, early joint-space narrowing, and subchondral sclerosis; Grade IV means near-complete or complete cartilage loss, significant narrowing, and visible bony change on both sides of the joint.

Being at KL III or IV does not automatically place you on a fixed surgical timeline. The grading describes the degree of damage visible on imaging — it does not specify when, or whether, a total knee replacement is inevitable for any individual patient. Age, activity level, pain profile, and the pattern of damage all shape that picture considerably.

That pattern is arguably the most decisive variable. A single-compartment KL Grade III knee — where cartilage loss is concentrated in one area and the surrounding joint remains reasonably intact — sits in a meaningfully different position from multi-compartmental KL IV disease, where bone meets bone across most of the joint surface. The first may be a candidate for joint-preservation strategies including injectable scaffold treatment; the second is a harder clinical case, and any honest appraisal of the evidence has to reflect that distinction clearly.

The sections that follow examine whether a ChondroFiller injection can shift the timeline — and which pattern of KL III–IV disease is most likely to benefit.

How the ChondroFiller injection works in a worn knee

Unlike hyaluronic acid, which acts immediately as a lubricant and begins clearing within weeks, ChondroFiller injection works through a fundamentally different process — and it takes considerably longer to mature.

The treatment is delivered in an outpatient clinic under ultrasound guidance: a liquid acellular Type I collagen solution is injected directly into the joint space. Once inside, it self-gels within minutes into a viscoelastic three-dimensional scaffold that adheres to the worn articular surfaces. No theatre, no general anaesthetic, no overnight stay.

At KL Grade III or IV, the scaffold's primary job is not to fill a neat, contained hole from the bottom up — the pattern of damage is too diffuse for that. Instead it acts as a top-down buffer: coating the exposed bone ends and absorbing mechanical load across a broader, worn surface. Alongside this cushioning role, the collagen matrix triggers matrix-induced chondrogenesis — it recruits the patient's own progenitor cells, which migrate into the scaffold and begin laying down new tissue from within. A 2025 ex vivo model using cartilage explants from patients undergoing total knee replacement confirmed a 2.4-fold increase in DNA content within 14 days of ChondroFiller placement, demonstrating that cell recruitment does occur even in significantly compromised tissue.

That biological process, however, takes time. Scaffold maturation occurs over 6–12 months, and a 2024 biomechanical study found that in its early phase, before the matrix has stabilised, ChondroFiller does not meaningfully reduce opposing cartilage damage under cyclic loading. This is why early weight-bearing is deferred: the scaffold needs time to integrate before it can perform its load-absorbing function reliably. Patients should expect a gradual trajectory of improvement, not the rapid symptomatic shift some associate with a steroid or lubricant injection.

What the clinical evidence shows

The most substantive knee-specific evidence comes from a 23-patient randomised multicentre study published in 2016. In the ChondroFiller arm, IKDC scores improved significantly from baseline at 3, 6, and 12 months (p<0.05), and MRI MOCART assessment at 52 weeks confirmed both good immediate defect filling and measurable cartilage maturation — a structural, not merely symptomatic, change. A later series from the University Hospital Pleven (17 patients, 2024) corroborated that trajectory: Lysholm and IKDC scores rose significantly across the same three timepoints and stabilised between months six and twelve, suggesting the scaffold matures within the first year.

Cross-joint data adds weight to the mechanism. A 2025 wrist study recorded a statistically significant shift in Outerbridge cartilage grade from 3 to 1.5 post-injection (p=0.006) — a measurable improvement in cartilage quality, not just reported pain, that supports the biological plausibility of the scaffold's regenerative role.

What the evidence does not include is an RCT with total knee replacement as its primary outcome. The conversion-to-surgery rate has not been measured against a control group. What exists — consistent functional score improvement and MRI-verified scaffold formation — are meaningful clinical signals, but they are surrogate endpoints. The published knee cohorts are small (23 and 17 patients respectively), and no knee series extends follow-up beyond 12 months. The delay claim therefore rests on biological inference rather than demonstrated arthroplasty avoidance. Establishing it formally would require a long-term trial — five to ten years, with arthroplasty conversion as the declared primary outcome — that has not yet been conducted.

The delay question: what ChondroFiller data realistically supports

Placing ChondroFiller in context means looking at what comparable injections have demonstrated in this disease-severity range — because the arthroplasty-endpoint gap, already established in the evidence review above, is not unique to this product.

Arthrosamid (iPAAG), a non-regenerative polyacrylamide hydrogel that integrates into the synovial membrane, carries the most specific published delay data: follow-up from Bliddal and colleagues (2021, 2024) documents two to three years of sustained symptom relief in selected patients. It does not regenerate cartilage; its role is mechanical cushioning. Stronger mid-term surrogate evidence comes from a 2024 study of BMAC injections into 37 KL Grade III–IV knees: over four years, IKDC scores rose from 56 to 73 (p<0.001), WOMAC fell from 40 to 18 (p<0.001), and not one of the 37 knees converted to prosthesis — a 95% success rate. That dataset, currently the most direct published evidence that an orthobiologic injection can hold severely arthritic knees back from replacement at mid-term, contextualises what ChondroFiller's own evolving follow-up may ultimately support.

ChondroFiller and Arthrosamid are sometimes combined in a single outpatient visit precisely because they address different structures: ChondroFiller (2.3 mL) is placed on the bone ends as a regenerative, cell-recruiting scaffold; Arthrosamid (6 mL) targets the synovial membrane as a mechanical cushion. They are not interchangeable, and combining them means using two distinct mechanisms rather than doubling the same effect.

For KL Grade III–IV patients, an honest summary runs as follows: 12-month improvement in function and pain is what ChondroFiller's published data demonstrates. A meaningful extension of the pre-surgery window — grounded in the scaffold's regenerative mechanism and supported by the BMAC comparator results — is a plausible working hypothesis, not a guaranteed timeline. Access and cost are part of that calculation: ChondroFiller is a CE-marked Class III medical device available only through specialist private clinics, is not NHS-funded, and is not FDA-approved, so patients weighing it against watchful waiting or eventual replacement should factor those realities in from the outset.

KL III vs KL IV: where the treatment boundary sits

The critical dividing line is not the KL grade itself but the pattern of disease behind it. Contained, single-compartment KL Grade III — enough surrounding cartilage to hold a scaffold in place, a preserved mechanical axis, and a joint space that still exists on weight-bearing imaging — sits within the ChondroFiller injection treatment envelope. The biological conditions for matrix-induced chondrogenesis remain viable: progenitor cells can be recruited, the scaffold can stabilise, and load absorption is meaningful.

Multi-compartmental bone-on-bone KL Grade IV is a different picture. When joint space has collapsed across two or three compartments, or when significant varus or valgus deformity is driving unequal load distribution, a collagen cushioning scaffold cannot meaningfully address what is structurally wrong with the joint. The hip arthroscopy cohort of 26 patients (12–60 months' follow-up) illustrates the mechanism: patients with Tönnis Grade 2–3 osteoarthritis had poor outcomes, and two of the 26 required total hip replacement. Severe background OA modifies results even in less-loaded joints — the same principle applies directly to the knee.

Age and activity level also enter the selection calculation. Younger, active patients with an isolated lesion and the capacity to commit to a rehabilitation period are the strongest candidates. Older patients with diffuse tri-compartmental loss are not — and saying so plainly is part of responsible assessment.

Where mechanical deformity contributes to focal overload, an osteotomy (HTO or DFO) may be considered as a complementary joint-preservation step: correcting alignment before or alongside a cartilage injection shifts load away from the damaged compartment and protects the scaffold's environment. These are parallel tools, not alternatives.

Determining which side of the boundary an individual patient sits on requires specialist review of weight-bearing X-rays and MRI — not self-assessment. Patient selection, more than any property of the product, is what determines whether ChondroFiller injection is appropriate at this disease stage.

Getting an assessment at the London Cartilage Clinic

For patients at KL Grade III–IV who are weighing whether an injection remains a realistic option before committing to replacement, the appropriate next step is specialist evaluation — not because the procedure itself is complex to receive, but because candidacy at this disease stage requires genuinely careful clinical judgement. Imaging review alone is insufficient; a specialist needs to assess compartmental pattern, mechanical axis, activity level, and what prior treatments have and have not achieved, in combination.

Liquid Cartilage™ / ChondroFiller injection is delivered in the UK at the London Cartilage Clinic on Harley Street — the UK certified delivery centre for the product. Professor Paul Y. F. Lee leads ChondroFiller injection delivery at the clinic; as with any technique-sensitive biological treatment, outcomes are shaped by how the product is applied and by whom, not by the product alone.

Patients who want an informed expert opinion before making a final decision about joint replacement can book an initial assessment at londoncartilage.com.

1. [1] Controlled, randomized multicenter study to compare compatibility and safety of ChondroFiller liquid with microfracturing of patients with focal cartilage defects of the knee joint. (2016). https://doi.org/10.5348/VNP05-2016-1-OA-1 https://doi.org/10.5348/VNP05-2016-1-OA-1
2. [2] Implantation of ChondroFiller Liquid as a scaffold material for the treatment of chondral lesions of the knee joint. (2024). https://doi.org/10.5272/jimab.2024304.5936 https://doi.org/10.5272/jimab.2024304.5936