Two injections, two different jobs in the hip

Choosing between ChondroFiller™ and Arthrosamid for hip pain is less a matter of preference and more a matter of timing — specifically, where a patient sits on the arc of hip joint disease.

ChondroFiller™ is a biodegradable injectable collagen scaffold. Manufactured by Meidrix Biomedicals GmbH and CE-marked as a Class III medical device, it is designed for focal, contained cartilage defects: areas where the joint surface has worn through but the surrounding cartilage remains healthy enough to support repair. Its mechanism is acellular matrix-induced chondrogenesis — the injected scaffold recruits the patient's own progenitor cells to promote endogenous repair tissue over several months, then gradually resorbs.

Arthrosamid is a different proposition entirely. It is a permanent polyacrylamide hydrogel (iPAAG) that integrates into the synovial lining and provides durable joint cushioning. It does not repair cartilage; it alleviates pain and reduces friction in joints where diffuse osteoarthritis has already taken hold.

The clinical dividing line is straightforward: focal defect with biological repair potential versus broad degenerative change requiring palliation. Both treatments sit between conservative management and hip replacement on the hip pain pathway, but at distinctly different stages of that journey. Neither is NHS-funded for hip indications, and both require specialist private assessment — including MRI — to determine suitability.

The sections that follow examine what that means in practice for patients seeking care at Lincolnshire Hip.

What ChondroFiller™ does inside the hip joint

The collagen scaffold works differently from any analgesic or lubricant injection. Placed inside the hip joint under ultrasound guidance as an outpatient appointment, the liquid sets within approximately three to five minutes at body temperature, conforming to the surface of the cartilage defect. It then creates the physical and biochemical environment — a process called acellular matrix-induced chondrogenesis — through which the patient's own progenitor cells, drawn from the surrounding synovium and subchondral bone, migrate into the matrix and begin generating repair tissue. No cells are supplied externally; the scaffold recruits what the body already carries.

That repair process unfolds over three to six months. The collagen matrix gradually resorbs as the repair tissue matures. Critically, there is no analgesic effect at the point of injection — benefit develops as repair tissue forms, which makes clear expectation-setting an important part of any pre-treatment consultation.

Suitability depends closely on defect characteristics. A 2021 peer-reviewed study by Perez-Carro et al., published via PMC, confirmed ChondroFiller™ as a viable approach for full-thickness acetabular cartilage defects, particularly in younger, more active patients affected by cam-type femoroacetabular impingement (FAI). The target profile is a discrete, contained focal lesion of approximately 200–450 mm², Tönnis grade below 2, with healthy cartilage at the defect margins. It is not indicated for diffuse osteoarthritis or widespread cartilage loss.

Published hip outcomes include a mean modified Harris Hip Score improvement of approximately 33 points and MOCART MRI cartilage regeneration scores in the range of 70–87.

What Arthrosamid does inside the hip joint

Unlike the temporary scaffold described in the previous section, Arthrosamid is designed to stay. Once injected into the hip joint — a single 6 mL dose placed under fluoroscopic or advanced ultrasound guidance — this polyacrylamide hydrogel (97.5% water, 2.5% polyacrylamide) begins integrating into the synovial lining within 10–14 days as host synovial cells proliferate into the gel. Animal studies have observed the resulting sub-synovial cushioning layer persisting for up to two years. The goal is sustained reduction in joint friction and inflammation, not cartilage repair; Arthrosamid does not regenerate tissue.

Its formal licence covers knee osteoarthritis. The major clinical trials — TACIT, IDA, and LUNA — are exclusively knee-focused and report sustained pain reduction in over 70% of patients for up to three to five years following a single injection. No large-scale peer-reviewed RCTs for hip use had been published as of mid-2026. Where UK private specialists use Arthrosamid for hip pain, they do so off-label — patients should raise this status directly with their treating consultant before proceeding.

The hip's deeper ball-and-socket anatomy makes accurate placement more technically demanding than in the knee, requiring fluoroscopic or advanced ultrasound guidance rather than the simpler approach the knee allows.

Two safety points warrant honest acknowledgement. First, Arthrosamid is permanent and non-reversible; once the gel has integrated into synovial tissue it cannot be removed. Second, some researchers have raised concern that residual acrylamide monomer — a known neurotoxin and suspected carcinogen — may leach slowly from the polymer matrix over time, a question that remains unresolved for long-term implanted use. The risk profile from the knee trials is broadly acceptable, but those data cannot be assumed to map directly onto hip populations without hip-specific study.

Which hip patient suits which treatment

The simplest way to navigate the choice is by disease stage and defect pattern — and only imaging can establish those reliably.

ChondroFiller™ suits a patient with a discrete, contained focal cartilage defect, most commonly a younger or more active person with early-stage damage (Tönnis grade below 2) and healthy cartilage at the defect margins. Biological repair potential is the key requirement: the scaffold works by recruiting the patient's own progenitor cells, so the surrounding tissue needs to be capable of that response. Chronological age is a guide rather than a strict criterion — defect pattern and tissue quality matter more than years alone. The treatment goal is structural: supporting endogenous repair tissue formation, not just palliation.

Arthrosamid, where used in the hip, targets a fundamentally different profile. The relevant patient has broader, more diffuse osteoarthritic change — Kellgren–Lawrence Grade III or IV equivalent — rather than a single localised lesion. They may be too young for hip replacement, not yet at the surgical threshold, or medically unsuited to a procedure. The aim is sustained cushioning and functional life extension, bridging the gap between conservative management and surgery rather than restoring tissue structure.

The two profiles rarely overlap, which is the point: these are complementary tools on a hip preservation pathway, not alternatives competing for the same patient. Someone with a contained focal defect and adequate repair potential is unlikely also to have the diffuse joint disease that makes Arthrosamid relevant — and vice versa.

Both routes require MRI review and specialist assessment of the imaging before any decision is made. Defect size, cartilage margin integrity, subchondral bone status, and disease stage cannot be determined from symptoms alone; neither treatment should be self-selected from a symptom description.

Cost, access, recovery, and practical expectations

Neither ChondroFiller™ nor Arthrosamid is NHS-funded for hip indications in the UK, and neither is routinely covered by major private medical insurers — including Bupa and AXA — for these applications. Both are self-funded, private pathways.

As a guide cost (confirm the current figure with the treating clinic before proceeding), ChondroFiller™ is typically priced between £3,000 and £8,000 privately in the UK, depending on the number of boxes needed for the defect size. Arthrosamid, where used off-label for hip pain, is generally in the £1,500–£3,000 range at private clinics.

Both are delivered as outpatient, image-guided injection appointments — no theatre admission, no incision, no general anaesthetic. The practical difference lies in what follows the injection.

After ChondroFiller™, a period of protected weight-bearing — typically one to six weeks — is usual while the collagen scaffold integrates and recruited cells begin forming repair tissue. This is not wound-healing recovery; it reflects the biology of scaffold maturation, which continues across three to six months as repair tissue gradually matures.

Arthrosamid carries no equivalent loading restriction. In the published knee trials, patients began reporting meaningful pain reduction around week four. Hip-specific onset data from RCT-level studies are not yet available, so that figure should be treated as indicative rather than reliable for the hip.

What the evidence actually shows — and where the gaps are

The ChondroFiller™ hip evidence rests on case series and single-centre investigations. The most cited is the 2021 Perez-Carro et al. study (PMC), which described the treatment as a viable approach for full-thickness acetabular cartilage defects — principally anterosuperior lesions arising from cam-type FAI in young, active patients. Published hip outcomes include a mean Harris Hip Score improvement of +33 points and MOCART regeneration scores of 70–87. These are meaningful clinical signals, but no large hip-specific RCT has been published for either treatment as of mid-2026, and no head-to-head comparative data between them exists.

The distinction between off-label and unproven is worth preserving. Off-label is a regulatory classification: Arthrosamid is licensed for the knee and used beyond that licence in the hip. The biological mechanism — hydrogel integrating permanently into the synovial lining — does not change by joint. What is genuinely absent is RCT-level confirmation of efficacy, optimal dosing, and long-term outcomes for hip anatomy specifically. That is a real gap; it is not the same as saying clinical experience is absent.

The absence of hip RCTs reflects the recency of hip preservation injection medicine as a field rather than an intrinsic deficiency of either product — and the evidence base is developing.

Three questions are worth raising at a specialist assessment: what does the MRI show about defect pattern and Tönnis grade; does the pathology favour biological repair or joint cushioning; and, if Arthrosamid is being considered, what does informed consent cover for off-label use. Answered with imaging in hand, those questions move the decision from the general to the individual — which is where it belongs.