Two injectables, two different hip problems

Patients researching injectable options for hip pain often frame the choice as a straight competition — ChondroFiller™ versus Arthrosamid — but the two products are not interchangeable alternatives. They address different problems at different points on the spectrum of hip joint deterioration, and the clinical decision rests primarily on the nature of the damage rather than on pain severity alone.

ChondroFiller™ is an injectable collagen scaffold designed for focal, contained cartilage defects — a discrete zone of damage with healthy surrounding tissue. Arthrosamid is a polyacrylamide hydrogel aimed at diffuse, whole-joint degenerative osteoarthritis, where worn surfaces across the hip need cushioning rather than localised repair. A patient suited to one is rarely suited to the other.

Both are delivered as outpatient, image-guided injections under local anaesthesia — no theatre admission, no general anaesthetic, and no surgical incision. What separates them is candidacy, not convenience.

The sections that follow map each product's ideal patient profile in detail, covering disease stage, imaging findings, and the clinical thresholds that guide selection at Lincolnshire Hip.

ChondroFiller: the collagen scaffold for focal hip cartilage damage

Think of ChondroFiller™ as a temporary framework rather than a filler. The product — a CE-marked Class III acellular Type I collagen hydrogel manufactured by Meidrix Biomedicals in Germany — is injected as a liquid into a focal cartilage defect, where it self-sets within roughly three to five minutes. Once in place, the scaffold recruits the patient's own progenitor cells from the surrounding synovium and subchondral bone, supporting the body's own repair processes through a mechanism known as acellular matrix-induced chondrogenesis. It contains no living cells and no hyaluronic acid.

The ideal hip candidate is a younger, active patient who has an isolated, full-thickness (Grade III or IV) cartilage defect on the acetabulum or femoral head — typically identified on MRI — with healthy surrounding cartilage borders that can mechanically contain the graft. Femoroacetabular impingement (FAI) is the most common underlying driver of this type of focal lesion in this age group, making FAI-related cartilage damage one of the principal indications for ChondroFiller™ at the hip.

Published cohort data support cautious optimism for suitably selected patients. A prospective study of 26 patients with FAI-associated acetabular lesions greater than 2 cm², followed for 12 to 60 months, found good or excellent outcomes in 17 of 21 evaluable cases; the modified Harris Hip Score improved by approximately 30 points from baseline. Importantly, patients who had pre-existing osteoarthritis (Tönnis grade 2–3) showed poor results — confirming that the product is a joint-preservation tool for early-stage focal pathology, not a treatment for diffuse degeneration.

At Lincolnshire Hip, ChondroFiller™ is delivered as an image-guided outpatient injection under local anaesthesia. Long-term hip-specific outcome data continue to emerge, and individual suitability is assessed at consultation.

Arthrosamid: the hydrogel cushion for diffuse hip OA

Arthrosamid (iPAAG; Contura International) is officially licensed and CE-marked for knee osteoarthritis only — its use in the hip is off-label and must be led by a consultant on an individual patient basis. That regulatory context matters: the candidacy criteria and durability figures discussed here are extrapolated from knee evidence, not derived from a dedicated hip approval pathway.

The mechanism is fundamentally different from ChondroFiller™. Rather than scaffolding a discrete defect, Arthrosamid — a non-regenerative hydrogel composed of 2.5% cross-linked polyacrylamide and 97.5% water — integrates into the synovial membrane lining and provides sustained viscoelastic cushioning across the whole joint surface. It buffers mechanical load over degenerated cartilage; it does not restore tissue.

Candidacy principles extrapolated from the knee licence point to patients with mild-to-moderate diffuse hip osteoarthritis (Kellgren-Lawrence grade 2–3), aged under 70, who have not responded adequately to conservative measures such as physiotherapy and analgesia but still retain some joint space. Active infection, inflammatory arthritis, polyacrylamide allergy, or near-complete joint-space loss (bone-on-bone) each rule it out.

Knee trial data show a meaningful reduction in pain from approximately four weeks post-injection, maintained over 156 weeks. Hip-specific long-term outcome data are limited, which is where indirect evidence becomes worth considering. Because Arthrosamid and other iPAAG preparations share identical molecular composition, a 2025 veterinary study covering 150 joint injections in 100 dogs — including 28 hip injections — offers the closest available cross-joint signal for the same molecule: 82% of owners rated their animal as improved, and 44% of dogs receiving analgesia reduced or stopped their medication. Adverse events were mild and self-limiting in 10% of cases. Controlled prospective human studies in the hip remain an active evidence gap.

Candidacy side by side: who fits which pathway

The single most useful orienting question is not 'which product is better?' but 'what kind of hip damage does the patient actually have?'. That distinction — focal versus diffuse — is what separates the two candidacy profiles, and it is detectable on MRI before a consultation appointment.

If imaging shows an isolated, contained full-thickness defect with intact surrounding cartilage, ChondroFiller™ is the scaffold option to explore. If it shows diffuse cartilage thinning across a wider joint surface, with no discrete bordered lesion but preserved joint space, Arthrosamid (used off-label in the hip) becomes the more relevant cushioning option — provided conservative care has already been tried and ruled insufficient.

One genuinely new point the preceding sections do not address: the two candidacy profiles are not always mutually exclusive. Internal clinical documentation notes that when ChondroFiller™ is delivered as an injectable rather than a surgically placed implant, it may also function as a top-down mechanical cushion in patients with advanced Kellgren-Lawrence Grade III or IV diffuse OA — offering a non-surgical barrier over worn surfaces with high cell retention. This is an extension of the product's standard focal-defect indication, has less formal trial support than the focal-defect evidence base, and should be considered emerging use. It does not apply where joint space has been lost entirely.

Neither product is appropriate where the hip has reached bone-on-bone end-stage degeneration, where active infection is present, or where inflammatory arthritis is the primary diagnosis — these are exclusions common to both pathways.

No head-to-head comparison data exist for ChondroFiller™ versus Arthrosamid in the hip. Every candidacy distinction above is drawn from separate, independent evidence streams. Identifying which pathway — if either — is appropriate requires a consultant assessment; imaging findings alone are not sufficient for a treatment decision.

How both injections are placed in the hip

Placement accuracy is where hip anatomy demands particular attention. A 2016 systematic review by Hoeber et al. — drawing on over 120 citations — found that landmark-guided hip injections reached the intra-articular space in only 72% of attempts (95% CI 56–85%), compared with 100% accuracy under image guidance (95% CI 98–100%; p<0.0001). For either product to do its intended job, it first has to land precisely where the pathology is.

The reason accuracy carries greater weight at the hip than at a more superficial joint is anatomical. The femoral artery sits roughly 1.9 cm medial to the joint capsule; the femoral vein approximately 1.7 cm medial; the femoral nerve around 2.3 cm lateral. These structures leave a narrow corridor for needle placement — which is why ultrasound or fluoroscopic guidance at the hip shifts from a technical preference into a patient-safety standard.

Both ChondroFiller™ and Arthrosamid are delivered via this image-guided route — clinic appointments, with the patient awake under local anaesthesia and no surgical admission involved. Neither treatment is currently available on the NHS; both are self-funded private procedures, and guide costs should be confirmed directly with the treating team.

For patients in Lincolnshire and the surrounding region, Lincolnshire Hip provides image-guided hip injection access at Sleaford and Grantham, without the need for a GP referral.

When neither injectable is the right answer

Neither injectable suits every hip. Three situations place both ChondroFiller™ and Arthrosamid outside their indicated range.

The clearest is end-stage osteoarthritis with bone-on-bone contact and near-total joint-space loss. At that point, the structural problem exceeds what any injectable can meaningfully address, and total hip replacement — or, for suitable patients, a SPAIRE-technique hip replacement — becomes the appropriate next step. Surgery in these cases is not a fallback; it is the correct pathway for the right patient.

Active infection within the hip joint, or a primary diagnosis of inflammatory arthritis such as rheumatoid disease, contraindicates both products regardless of OA grade. Similarly, patients who have not yet worked through a structured course of conservative care — supervised physiotherapy, appropriate analgesia, and weight management where relevant — are not typically injectable candidates at this stage.

Before any consultation, one concrete preparation makes a material difference: bring recent hip imaging — ideally an MRI or weight-bearing X-ray — along with a clear account of which conservative measures have been tried and for how long. That information allows the clinician to assess OA grade, joint-space status, and functional goals and determine whether an injectable approach, joint preservation, or hip replacement is the most appropriate direction. Professor Paul Y. F. Lee maps this pathway across all three options at Lincolnshire Hip.

Lincolnshire Hip is part of the MSK Doctors group and accepts patients without referral for a hip pathway consultation.

1. [1] Owner-reported outcomes: intra-articular 2.5% polyacrylamide hydrogel injection in dogs with OA. (2025). https://doi.org/10.2460/javma.25.06.0398 https://doi.org/10.2460/javma.25.06.0398