Two injections, two completely different hip problems

Patients who ask about ChondroFiller and Arthrosamid in the same breath are often surprised to learn the two injections are not competing for the same patient. They address different stages of hip joint disease — and which one is appropriate depends almost entirely on what the imaging and clinical assessment show, not on personal preference.

ChondroFiller is an injectable collagen scaffold designed for a specific structural problem: an isolated, full-thickness cartilage defect with an intact surrounding rim. It suits the younger or more active patient whose hip joint is otherwise in reasonable condition but carries a contained focal lesion — often following a labral repair or femoroacetabular impingement (FAI) correction.

Arthrosamid is a polyacrylamide hydrogel aimed at the opposite end of the spectrum: diffuse, advanced osteoarthritis where cartilage has degraded broadly across the joint surface rather than at a single site. For patients with Kellgren-Lawrence Grade III or IV hip OA who want pain relief and more time before considering joint replacement, Arthrosamid addresses a problem that a focal scaffold cannot.

In the current UK private pathway, both are delivered as outpatient, ultrasound-guided hip injections — neither requires theatre admission in this context. Neither is funded by the NHS, and neither is covered by major UK private medical insurers, so both represent a self-funded decision. The starting point, however, is always diagnosis: the pathology determines the candidate.

What ChondroFiller does inside the hip joint

The gel itself works by giving the body a structure to build on. ChondroFiller — manufactured by Meidrix Biomedicals as a CE-marked Class III medical device — is a purified Type I collagen scaffold placed under ultrasound guidance directly into the floor of a focal cartilage defect. Within three to five minutes of placement, the liquid collagen sets in situ, forming a porous matrix that fills the lesion cavity.

From that point, the process is biological rather than mechanical. The scaffold recruits the patient's own progenitor cells — drawn from surrounding tissue and subchondral bone — which migrate into the matrix and begin differentiating into cartilage-producing cells. The clinical term for this is acellular matrix-induced chondrogenesis: the device contains no donor cells of its own; it supports the body's own repair processes from the base of the lesion upward. This bottom-up repair depends on an intact cartilage rim encircling the defect to contain the gel and define the boundary of the repair zone — without that rim, the scaffold has no wall to build against.

That structural requirement shapes the patient profile precisely. The hip presentations suited to ChondroFiller are isolated ICRS Grade III or IV defects, typically between 200 and 450 mm² in area, in patients who are younger or particularly active and whose overall joint health remains early-stage (Tönnis grade below 2). Candidates must also be free of inflammatory arthritis, metabolic arthropathy, or collagen allergy.

The hip's considerable depth and spherical geometry demand accurate placement, which is why image-guided delivery is central to the Lincolnshire Hip pathway. Perez-Carro et al. (2021) confirmed that injectable ChondroFiller is a viable approach for full-thickness acetabular cartilage defects with promising short-to-medium-term results, while noting that longer-term outcome studies are still needed. Mazek et al. (2021), writing in the Journal of Hip Preservation Surgery, characterised the collagen matrix as a protective scaffold that permits chondrocyte migration — consistent with the bottom-up regenerative rationale described above.

What Arthrosamid does inside the hip joint

Unlike ChondroFiller's bottom-up rebuild, Arthrosamid works from the surface inward — and its clinical target is a fundamentally different hip problem.

Manufactured by Contura A/S, Arthrosamid is a 2.5% non-biodegradable injectable polyacrylamide hydrogel (iPAAG). When placed intra-articularly under ultrasound or fluoroscopic guidance, the hydrogel integrates into the synovial membrane and forms a permanent viscoelastic cushion across the articular surface. It does not rebuild cartilage tissue or recruit cells to repair a lesion; its role is mechanical — absorbing friction and redistributing load over degenerated joint surfaces that can no longer do this adequately themselves. A 2 ml saline flush follows injection to ensure complete product delivery, and a seven-day course of NSAIDs is standard post-procedure.

Patients should know, plainly, that Arthrosamid received European CE approval in 2021 specifically for knee osteoarthritis. Its use in the hip is currently off-label and emerging, with clinicians reporting successful application in carefully selected patients — but the hip's greater depth and more complex access geometry mean that dedicated hip-specific trial data remain limited. That off-label status is worth discussing openly at consultation rather than treating as a reason to dismiss the option.

For the right hip patient, the rationale is coherent: in diffuse, advanced OA (Kellgren-Lawrence Grade III or IV), where cartilage has degraded broadly rather than at a single focal point, there is no intact surrounding rim for a regenerative scaffold to build against. Arthrosamid addresses that reality by cushioning what remains rather than attempting structural reconstruction. One study (Maulana, Cole and Lee, Journal of Arthritis, 2022) observed a reduction in patellofemoral bone marrow lesions following a single iPAAG injection — a potentially relevant secondary finding, though it was conducted in a knee population and should not be extrapolated as a confirmed hip benefit.

Key differences at a glance: pathology, mechanism and patient profile

Taken together, these two treatments sit at opposite ends of the hip joint pathology spectrum. The table below sets out the five main clinical axes side by side.

| | ChondroFiller | Arthrosamid | |---|---|---| | Target pathology | Isolated focal cartilage defect with an intact surrounding rim | Diffuse, joint-wide cartilage degeneration | | Mechanism | Bottom-up scaffold: collagen matrix recruits the patient's own cells to rebuild from the lesion floor | Top-down cushioning: permanent hydrogel integrates into the synovial membrane and absorbs friction across the joint surface | | Disease stage | Early-stage joint health (Tönnis grade below 2 — minimal or no joint-space narrowing) | Advanced osteoarthritis (Kellgren-Lawrence Grade III or IV — significant joint-space loss) | | Typical patient | Younger or more active; preservation candidate with a contained lesion, often following FAI correction or labral repair | Older patient, or those with widespread OA, seeking sustained pain relief and functional extension before considering joint replacement | | Primary goal | Promoting endogenous repair toward structural improvement of a localised lesion | Symptom relief, friction reduction, and joint-life extension — not tissue rebuilding |

The rehabilitation difference is worth a brief note. ChondroFiller requires the repair scaffold to mature undisturbed, so a structured, graduated return to activity follows the injection. Arthrosamid's post-injection period centres on settling the hydrogel and managing any initial inflammatory response with a short NSAID course; functional recovery is typically quicker, though individual guidance should come from the treating clinician.

The practical implication is that selecting between these two options is primarily a diagnostic sorting exercise rather than a preference question. A patient with a discrete focal lesion and good surrounding cartilage is not a candidate for a hydrogel cushion; a patient whose hip shows diffuse, advanced wear has no intact rim for a regenerative scaffold to work against. For many people with hip pain, the consultation itself answers the question — the imaging and clinical findings will point clearly to one pathway or, in some cases, to neither.

What the evidence currently shows for hip use

Both treatments carry early but biologically coherent evidence for hip use — not yet the large multicentre randomised controlled trials that would underpin a routine NHS pathway, but sufficient to inform a clinical decision in carefully selected patients.

For ChondroFiller, the two peer-reviewed hip studies — Perez-Carro et al. (2021) and Mazek et al. (2021, Journal of Hip Preservation Surgery) — are open-label, single-centre series rather than blinded multicentre RCTs. What they contribute beyond mechanism description is a measure of clinical outcome quality: MOCART cartilage imaging scores in the range of 70–87 following collagen scaffold placement suggest tissue-level repair activity, while hip-specific functional scores (mHHS) show approximately 30-point gains — a clinically meaningful threshold. The biological plausibility for hip application rests on the same scaffold mechanism that produces comparable improvements in knee cohorts: the collagen matrix behaves identically whether placed against a femoral condyle or an acetabular defect, provided the lesion is suitably contained and surrounded by healthy cartilage.

For Arthrosamid, controlled trial evidence originates almost entirely in the knee, where symptom relief data now extend to three years post-injection. The hip application — inherently more demanding to access — has not yet been the subject of a dedicated randomised trial. Clinicians using it off-label in the hip draw on the same mechanical rationale: a non-biodegradable viscoelastic hydrogel integrating into the synovial membrane is not joint-specific in its cushioning effect, even if image-guided delivery requires additional precision at the hip's greater depth. The bone marrow lesion reduction observed in Professor Paul Y. F. Lee's iPAAG research (Maulana, Cole and Lee, Journal of Arthritis, 2022) has not yet been replicated in a dedicated hip cohort and should not be read as a confirmed hip benefit.

For both options, mechanism-level confidence is stronger than long-term hip-specific outcome data — a distinction worth holding onto when weighing a self-funded treatment decision.

Seeking assessment at Lincolnshire Hip

Deciding between these two pathways — or concluding that neither fits — begins with a clear picture of where a patient sits on the focal-to-diffuse spectrum. Clinical examination combined with appropriate imaging, including MRI where lesion characterisation is needed, is what moves the conversation from a treatment name to an actual indication.

Both ChondroFiller and Arthrosamid are available as outpatient ultrasound-guided hip injections through the private pathway at Lincolnshire Hip. Consultations are held in Sleaford and Grantham, making the service accessible to patients across Lincolnshire and the wider East Midlands. The service also accepts patients from the broader non-London UK catchment who prefer a specialist hip-focused setting.

Lincolnshire Hip is part of the MSK Doctors group and accepts patients without GP referral for hip assessment.

The treatment question most patients arrive with — "which injection is right for me?" — is ultimately answered by the diagnostic findings. The consultation is where that answer begins.