Two different hip problems, two different treatments

The question most patients bring to a hip consultation is: which injection is better? For ChondroFiller™ and Arthrosamid®, that is the wrong question — because these two treatments are not competing alternatives for the same hip problem. They target structurally different disease states, and the hip anatomy itself determines which one is relevant.

The distinction rests on a single variable: whether the damage in the hip joint is focal or diffuse.

A focal cartilage defect is a discrete, bounded area of damage — a lesion with a floor, walls, and critically, intact surrounding cartilage. The rest of the joint surface is largely preserved. These defects typically arise from femoroacetabular impingement (FAI), a single traumatic event, or osteochondritis dissecans of the femoral head.

Diffuse osteoarthritis is the opposite picture. There is no single lesion to target because the cartilage has broken down broadly across the joint surface. The damage is generalised rather than localised, and no bounded defect exists to fill or scaffold.

Placing a regenerative scaffold into a diffusely worn joint, or a cushioning hydrogel into an otherwise intact joint with a focal lesion, is not a matter of preference — it is a mismatch of mechanism and indication. This distinction is visible on MRI and confirmed by clinical history; symptom severity alone does not determine it.

ChondroFiller for a focal hip cartilage defect

Focal cartilage defects of the kind described above call for a treatment that can address the lesion itself rather than the whole joint. ChondroFiller™ — an acellular Type I collagen scaffold manufactured by Meidrix Biomedicals GmbH — is designed precisely for that role.

The scaffold works through acellular matrix-induced chondrogenesis. Once placed, it acts as a structural template that recruits the patient's own progenitor cells from the surrounding synovium and subchondral bone into the defect space. Those cells migrate into the collagen matrix and support the body's own repair processes from within the lesion — a bottom-up biological rebuild rather than a top-down coating. ChondroFiller™ does not regrow cartilage directly; it provides the conditions that allow endogenous repair to take place.

The treatment is indicated for isolated, focal Grade III/IV chondral lesions where the surrounding cartilage borders are intact. Suitability depends on the geometry of the damage, not on radiographic severity alone. A hip that looks bone-on-bone on X-ray may still carry a discrete focal lesion with preserved margins — and provided those conditions hold, that patient is not automatically excluded from consideration.

At Lincolnshire Hip, ChondroFiller™ is delivered as an ultrasound-guided outpatient injection at clinics in Grantham and Sleaford under Professor Paul Lee, without the need for a theatre setting or arthroscopic access. The collagen gel is placed image-guided into the defect during a clinic appointment.

Published clinical data for hip applications suggest a modified Harris Hip Score improvement of approximately +33 points, with MOCART MRI cartilage regeneration scores in the range of 70–87. These figures come from a global dataset of more than 19,000 ChondroFiller® cases across multiple joints, with hip evidence covering focal chondral damage and associated structural pathology. As with any regenerative treatment, individual outcomes vary, and a consultant assessment is needed to confirm whether the specific lesion geometry makes a patient suitable.

Arthrosamid for diffuse hip osteoarthritis

Diffuse hip osteoarthritis presents a clinically different challenge: there is no bounded lesion to scaffold, because the cartilage has broken down across the whole joint surface. In that setting, Arthrosamid® — a non-biodegradable 2.5% polyacrylamide hydrogel (iPAAG, Contura International Ltd) — addresses a different therapeutic goal entirely.

Rather than filling or rebuilding a specific defect, Arthrosamid forms a permanent, viscoelastic sub-synovial cushion within the joint. After a single outpatient injection delivered under ultrasound or fluoroscopic guidance, the gel integrates through a host-tissue response: synovial cells proliferate and invade the hydrogel matrix within 10–14 days, and a stable sub-synovial layer — traversed by thin connective-tissue strands and covered by a synovial lining — has been characterised in animal models by day 30 (equine) and day 90 (rabbits). This process has been described in the literature as a low-level macrophage-driven foreign body response. The gel is permanent; it is not resorbed and is not a regenerative scaffold.

Its clinical target is Kellgren-Lawrence Grade III/IV osteoarthritis: advanced, diffuse joint wear where symptom management and functional life extension are the realistic aims rather than structural cartilage restoration.

An important regulatory caveat applies directly to hip use: Arthrosamid received European approval in 2021 for knee osteoarthritis. Application to the hip is currently off-label. This should be part of an explicit informed-consent discussion before treatment — off-label does not mean unsafe, but it does mean the formal evidence base is thinner for the hip than for the knee, and patients are entitled to know that distinction.

Published pain-relief data extend to three years from a single injection, and Professor Paul Lee's own research documents a reduction in bone marrow lesions following a single iPAAG injection in advanced osteoarthritis. Safety concerns sometimes raised in connection with polyacrylamide hydrogels originate mainly from large-volume soft-tissue cosmetic use (Aquamid), a context not directly analogous to small-volume intra-articular hip injection under image guidance; however, careful patient selection and clinical follow-up remain appropriate safeguards.

How the hip is assessed to confirm the right diagnosis

The distinction between a focal chondral lesion and diffuse osteoarthritis is not always obvious from symptoms alone — which is why imaging and clinical history form the diagnostic foundation before any injection is considered.

MRI is the most informative tool. A focal defect typically appears as a discrete, bordered area of full-thickness cartilage loss with structurally sound cartilage on either side — the geometry that makes a scaffold approach viable. Diffuse OA shows generalised cartilage thinning across the hip joint surface, often accompanied by subchondral changes and bone marrow lesions. X-ray Kellgren-Lawrence grading supplements MRI in diffuse disease, helping classify severity from early narrowing through to Grade III/IV bone-on-bone change.

Clinical history adds important context. A past diagnosis of femoroacetabular impingement (FAI), a specific traumatic hip event, or a history of osteochondritis dissecans increases the likelihood of focal pathology. A longer history of gradually worsening hip pain with early-morning stiffness fits more closely with diffuse osteoarthritis. Age and activity level inform the conversation but do not settle it — a 55-year-old can carry either condition.

Getting the diagnosis right has direct treatment consequences: Arthrosamid placed into a focal-defect hip does not scaffold the lesion; ChondroFiller used across a diffuse OA joint has no bounded target to work within. The assessment exists specifically to answer this question before either pathway is started.

Anyone attending a Lincolnshire Hip appointment benefits from arriving with prior imaging — MRI films or report, and any X-ray report that includes a Kellgren-Lawrence grade — as these give the clinical assessment its most useful starting point.

Evidence gaps and what current data cannot answer

Transparency about what the evidence can and cannot confirm is part of sound clinical practice — and both treatments have meaningful gaps worth naming.

Arthrosamid's strongest published data come from knee osteoarthritis trials. Hip-specific outcomes data are still emerging, and no large controlled hip study has yet been published to match the depth of the knee literature. Clinicians extrapolating from knee evidence are doing so reasonably, but not with the same certainty as they would apply to a knee-licensed indication.

For ChondroFiller injection — the ultrasound-guided outpatient route rather than arthroscopic delivery — hip-specific controlled trial data are also still accumulating. The global case series, covering more than 19,000 cases across joints, provides an encouraging safety and outcomes signal, but hip-specific data from large controlled trials are not yet available at that scale.

No head-to-head hip trial comparing the two products is likely to be designed: the treatments target different patient populations, so such a comparison would not be a clinically meaningful test.

On access, neither treatment is currently NHS-funded. The NHS pathway for hip osteoarthritis typically runs through physiotherapy, corticosteroid or hyaluronic acid injections, and, when conservative measures are exhausted, hip replacement. Both ChondroFiller and Arthrosamid are self-funded private treatments, priced from approximately £3,000, and that is a practical consideration for patients in Lincolnshire and the wider non-London catchment weighing their options.

Hip assessment at Lincolnshire Hip

Navigating a decision of this clinical complexity — focal defect or diffuse osteoarthritis, scaffold or cushion, injection or a longer pathway — is not something that resolves from a website alone. A structured hip assessment is the practical next step: it brings together imaging, clinical history, and consultant judgement to determine which treatment, if either, is genuinely indicated. Professor Paul Y. F. Lee, who has published peer-reviewed research on both hip cartilage repair and injectable hydrogel outcomes, leads that assessment at Lincolnshire Hip's outpatient clinics in Grantham and Sleaford. Patients do not need a GP referral to book. Lincolnshire Hip is part of the MSK Doctors group and accepts patients without referral for hip assessment.