Which pathway suits your knee

'My consultant has mentioned both ChondroFiller and BMAC — how do I know which one is right for me?' That question comes up regularly, and it is a good one, because the two treatments look superficially similar but work in entirely different ways.

Both are outpatient, ultrasound-guided injection pathways. Neither requires surgery, a general anaesthetic, or a hospital stay. That is where the similarities end.

ChondroFiller® is an acellular collagen scaffold — a cell-free gel injected directly into the cartilage defect. It creates the structural environment for your own progenitor cells to migrate in and begin repair. The body does the biological work; the scaffold provides the architecture.

BMAC (Bone Marrow Aspirate Concentrate) takes a different approach. A small amount of bone marrow is drawn from your hip, concentrated in a centrifuge, and injected into the damaged area. The aim is to deliver the regenerative cells — mesenchymal stem cells and growth factors — directly to where they are needed.

One pathway supplies the structure; the other supplies the cellular machinery. Neither is universally superior. The right choice depends on the character of the defect, the condition of the bone beneath it, and your own biology — factors a consultant assessment will determine.

The sections below explain how each pathway works, what the evidence shows, and when combining them may be considered.

How ChondroFiller works as an injectable scaffold

ChondroFiller® is a CE-marked Class III medical device manufactured by Meidrix Biomedicals in Germany. The product is supplied in a ready-to-use two-chamber syringe — one chamber holds murine-derived Type I collagen, the other a neutralising solution. Mixed at the point of injection and placed under ultrasound guidance directly into the focal cartilage defect, it transitions from a liquid to a dimensionally stable hydrogel within approximately 3–5 minutes, conforming to the defect geometry without bone drilling, donor-site biopsy, or any arthroscopic procedure.

The scientific term for what follows is acellular matrix-induced chondrogenesis. In plain terms: the scaffold itself contains no cells. What it provides is a chemotactic signal — a structured collagen matrix that draws the patient's own progenitor cells, from the surrounding synovium and the subchondral bone immediately beneath the defect, into the implanted scaffold. Once there, those cells begin producing the extracellular matrix components that mature progressively into hyaline-like repair tissue.

That maturation is not instantaneous. Structural repair quality can be tracked using MOCART scores — an MRI-based measure of defect fill and tissue integration. Published data show MOCART scores rising from approximately 65 at four weeks to between 81 and 84 at twelve months, confirming that the repair process continues to develop rather than simply reducing symptoms in the short term. Patients should expect the full maturation cycle to span 12–24 months.

ChondroFiller is indicated for grade III and IV focal cartilage defects — the clinically significant lesions where surface damage is substantial but the joint remains a preservation candidate. The repair tissue it supports holds up under sustained loading in a way that microfracture-generated fibrocartilage does not: published evidence places fibrocartilage failure at 62% by four years, while ChondroFiller's hyaline-like tissue retains its structural integrity at the same stage.

How BMAC delivers its regenerative effect

Unlike a conventional injection drawn from a pre-prepared vial, BMAC requires biological material to be obtained from the patient during the same appointment. Under local anaesthetic, a small volume of bone marrow is aspirated from the posterior iliac crest — the back of the hip — using a fine-bore needle. The sample is centrifuged in clinic, concentrating mesenchymal stem cells (MSCs), growth factors, and anti-inflammatory cytokines into a 5–7 mL injectate. That concentrate is then placed under ultrasound guidance into the cartilage defect. The procedure is carried out as an outpatient; no general anaesthetic, no surgical incision, and no overnight admission are involved, though patients should understand that the harvest step makes this more involved than a simple single-syringe injection.

The regenerative effect operates through three distinct biological pathways. First, MSCs within the concentrate can differentiate toward chondrocytes — the specialised cells responsible for producing and maintaining cartilage. Second, once active, those cells synthesise extracellular matrix (ECM) components, progressively rebuilding the structural substrate of the damaged tissue. Third, the anti-inflammatory cytokines modulate the joint environment, dampening the chronic low-grade inflammation that impedes natural repair. Cotter et al. (2017) characterised BMAC as a clinically viable strategy both as an adjunct and as a standalone approach for chondral defect repair, while Centeno et al. (2018) reported significant improvements in knee function scores sustained at two-year follow-up in KL grade 2–3 osteoarthritis patients treated with a BMAC-based injectate, with no serious adverse events recorded.

One clinically important variable is MSC yield. The concentration of stem cells within the aspirate is not fixed — it declines with age and is influenced by overall health and bone marrow quality. For older patients or those with systemic conditions affecting marrow cellularity, a consultant assessment should include a realistic appraisal of what the aspirate is likely to deliver before BMAC is selected as the primary pathway.

What the clinical evidence shows

The published datasets for the two pathways are substantive but structurally different, and placing them side by side requires some care.

ChondroFiller outcome data

Across four multi-centre knee studies, IKDC scores — a patient-reported measure of knee symptoms, function, and sport activity — improve by approximately 30 points on average, consistently exceeding the minimum clinically important difference (MCID) of 16.7 points. Jerosch et al.'s three-year post-market clinical follow-up (PMCF) study is the most informative long-term data point: mean improvement reached 32.4 IKDC points, with patients sustaining a functional score of approximately 80 at the three-year mark. Over 19,000 procedures have been carried out globally, with a reported complaint rate of around 0.06%. It is worth noting that the 12–24 month maturation window means outcomes measured at 12 months do not yet represent the ceiling of structural repair.

BMAC outcome data

Cotter et al. (2017, 143 citations) confirmed BMAC's clinical viability for chondral defect repair both as a standalone strategy and as an adjunct procedure. Centeno et al. (2018) reported significant improvements across KSS-knee and KSS-function scores — which measure pain and capacity for daily activities — alongside SF-12 physical component and range of motion in KL grade 2–3 patients, sustained at two-year follow-up with no serious adverse events. An aggregate figure of 95% patient improvement is sometimes cited in BMAC literature; it reflects pooled clinical experience rather than a controlled trial outcome and should not be read as directly equivalent to the IKDC figures above — the measurement tools are different, the populations are heterogeneous, and the baseline conditions vary.

The evidence gap

No published randomised controlled trial has directly compared ChondroFiller against BMAC in matched patient populations. Both pathways carry peer-reviewed evidence in their own right, but no study has yet established one as superior to the other under controlled head-to-head conditions. Clinical selection therefore rests on defect characteristics, patient biology, and consultant judgement rather than on trial-level comparative data — a limitation worth acknowledging plainly before proceeding.

How consultants decide between them

The starting point in any consultant assessment is the character of the defect itself, because the two pathways address different rate-limiting steps in repair.

For a focal, contained grade III–IV lesion with healthy surrounding cartilage and structurally sound subchondral bone beneath it, ChondroFiller's acellular scaffold is typically the primary consideration. The structural environment is already capable of supporting repair; what the defect lacks is a physical matrix into which the patient's own progenitor cells can migrate and differentiate. Placing an injectable collagen scaffold fills that gap directly, without the need to introduce exogenous cells.

Where the subchondral bone is compromised — thinning, sclerotic, or showing early oedema on imaging — the calculation shifts. A structural scaffold alone may not address a damaged biological substrate, and BMAC's concentrated mesenchymal stem cells and growth factors become more relevant precisely because they act on that underlying environment as well as the surface lesion. The same reasoning applies when active cellular repair capacity is in question — for instance, following prior procedures that have already drawn on the local progenitor cell pool.

When both structural scaffolding and active cellular signalling are judged to be necessary, the two can be used together. The rationale is mechanistic rather than merely additive: ChondroFiller provides the matrix architecture; BMAC supplies the regenerative cellular environment that drives it. The London Cartilage Clinic's Liquid Cartilage™ pathway combines both in a single outpatient setting for patients where dual-layer treatment is clinically appropriate. It is worth stating clearly, though, that combination use is a targeted clinical decision, not a routine upgrade — the evidence does not establish it as universally superior.

Diffuse osteoarthritis, rather than a discrete focal defect, changes the indication profile substantially for both pathways. Neither is designed to address full-thickness, widespread cartilage loss, and an MSK Doctors consultant assessment would consider a broader range of management options in that setting.

Getting assessed and what to expect

Practically, neither ChondroFiller nor BMAC is NHS-funded, and most UK private medical insurers do not cover either pathway. Both are accessed on a self-funded private basis — a reality patients researching these options usually already anticipate.

MSK Doctors accepts patients without a GP referral. Consultant-led cartilage assessments are available at the Sleaford clinic in Lincolnshire (NG34) — which houses an Open MRI scanner — and at the Grantham centre (NG31), with no NHS-style waiting period.

At an initial appointment, the consultant reviews existing imaging, examines the joint clinically, and takes a detailed history of symptoms and prior treatment. Where MRI detail is needed to characterise defect size, depth, and boundary more precisely, that can be arranged and reviewed as part of the same pathway. From that picture — defect grade, subchondral integrity, symptom timeline — the consultant advises whether ChondroFiller, BMAC, a combined approach, or a different management route is most appropriate for that presentation.

If treatment proceeds, both pathways are delivered as outpatient injections. A ChondroFiller appointment is brief. A BMAC session takes longer because the marrow harvest and concentration step are completed during the same visit. In both cases, patients are typically mobile and able to travel home independently. Structural repair develops progressively over months: gains in comfort and reduced inflammation tend to come first, with tissue maturation confirmed on follow-up imaging later.

Patients can book an initial consultant assessment without a GP referral at mskdoctors.com.