Where do newer injections fit after standard NHS care

Persistent knee osteoarthritis pain often reaches a “next step” point after months of exercise work, weight management efforts, and regular use of basic pain medicines. In the NHS, that usually sits well before knee replacement is considered, so it is common to see people looking beyond the usual pathway and coming across “advanced injections” online.

The NHS England knee osteoarthritis decision aid published in 2023 sets out a straightforward core approach: building and maintaining leg strength, adjusting activity, and (where relevant) weight loss, alongside pain medicines. It also includes joint injections with steroid medicines as an option for some people, typically as a short-term measure to calm a painful flare and help people keep moving. When symptoms remain severe and persistent despite these steps, the decision aid moves the conversation on to surgical options such as knee replacement.

That same 2023 NHS decision aid is also clear about what is not part of routine care: it states that injections with hyaluronic acid “do not help” knee osteoarthritis, and it notes that not every possible treatment is available on the NHS. Versus Arthritis similarly explains that NICE does not recommend hyaluronan injections for osteoarthritis, even though some studies have reported short-term pain relief for some people. In practical terms, this is why many patients in the UK encounter hyaluronic acid, platelet-rich plasma (PRP), bone marrow aspirate concentrate (BMAC), or newer products such as Arthrosamid® outside standard NHS pathways rather than as a routinely commissioned option.

The newer injections discussed in this article sit in that “in-between” space: after core conservative care has been tried and before (or alongside) a decision about knee replacement. In plain language, they include:

• Arthrosamid® (polyacrylamide hydrogel): a single-injection, long-lasting hydrogel option intended to change the joint environment and reduce symptoms over time.
• PRP with or without hyaluronic acid: a blood-derived injection (platelet-rich plasma) sometimes combined with hyaluronic acid, aiming to improve pain and function in some cases.
• BMAC (“bone marrow stem cell” type injection): a marrow-derived orthobiologic, typically discussed in early-to-moderate osteoarthritis, but with more complex preparation than PRP.
• Ultrasound guidance: not a separate “medicine”, but a technique used to place injections more accurately in joints such as the knee and especially the hip.

These are not surgical procedures in the way a knee replacement is. They are usually delivered as outpatient, image-guided injections, but they are not all equally simple. A standard steroid injection is typically a single appointment, whereas BMAC, for example, generally involves an additional step of bone marrow collection and processing before the injection is placed.

The aim in the sections that follow is practical: to describe what each option is trying to do, how strong the evidence is (and where it is still limited), how access commonly works in the UK when treatments are not part of routine NHS care, and what realistic goals look like—most often symptom relief and, in some cases, delaying knee replacement rather than reversing arthritis.

Arthrosamid as a hydrogel device and UK access

In April 2021, Arthrosamid® was CE‑marked for the symptomatic treatment of knee osteoarthritis, and it has since been promoted in the UK as a single, outpatient injection option aimed at longer‑lasting symptom relief than short‑acting injectables. The evidence is summarised here in plain clinical prose, with supporting sources recorded separately rather than embedded as database-style tags.

What Arthrosamid is (and what it is not)

Arthrosamid is an injectable polyacrylamide hydrogel designed to be placed inside the knee joint. Rather than acting as a short‑lived anti‑inflammatory medicine, it is described as a hydrogel implant intended to remain in the joint environment and work by changing the conditions within the knee (for example, reducing friction and altering inflammatory signalling in the joint lining). It is used for symptomatic knee osteoarthritis—meaning the goal is typically reduced pain and stiffness and improved day‑to‑day function, not “repairing” arthritic joint surfaces.

A practical expectation-setting point is that Arthrosamid is not a cartilage‑regrowth treatment. Even when pain improves at 6–12 months, that should be understood as symptom change rather than a reversal of osteoarthritis.

What published studies suggest so far

Across clinical studies of injectable polyacrylamide hydrogel in knee osteoarthritis (including Arthrosamid‑branded cohorts and a randomised comparison against hyaluronic acid products such as Synvisc‑One), a consistent theme is that a single intra‑articular injection has been associated with clinically meaningful improvements in pain and function for many patients over at least the first 6–12 months. Short‑term safety findings in these reports are generally described as acceptable, with ongoing work using imaging and biomarkers (including ultrasound‑based assessments) to better understand how the treatment interacts with the synovium.

At the same time, multiple evidence summaries and evaluation documents highlight the same outstanding uncertainties: outcomes beyond 1–2 years are less well defined, the best “fit” patient profile is still being refined (for example, which patterns of symptomatic knee OA respond most reliably), and robust head‑to‑head comparisons versus other self‑funded injections are limited. Health‑technology proposals explicitly frame cost‑effectiveness as an open question, particularly in systems such as the NHS where commissioning decisions depend on value as well as clinical effect.

Why “medical device” status matters in the UK

Arthrosamid is regulated as a medical device rather than as a medicinal drug. UK device regulation classifies devices into risk‑based categories (Class I, IIa, IIb, III) under the medical-device framework, which is a different route from medicines regulation.

In practical terms, CE marking and device regulation can allow a treatment to be marketed and provided in private practice once the relevant conformity and safety requirements are met. However, routine uptake in the NHS is a separate step: NHS use at scale typically depends on health‑technology evaluation (clinical benefit, safety, and cost‑effectiveness) and then commissioning decisions, which may move more slowly than private availability.

NHS access versus private access (what this usually means on the ground)

Current UK-facing information about Arthrosamid commonly describes it as not yet widely available through routine NHS pathways, with access more often occurring via self‑funded private care, including private services that operate within the private wings of NHS hospitals. Alongside this, manufacturer communications describe NHS-based research intended to clarify how Arthrosamid performs in real‑world NHS settings.

This gap—private availability alongside limited routine NHS provision—largely reflects the same evidence needs that appear in evaluation proposals: longer follow‑up, clearer identification of who benefits most, and more complete cost‑effectiveness data in an NHS context.

A concrete “bottom line” for decision-making

• The best-supported timeframe in published work is symptom improvement out to around 6–12 months after a single injection; what happens beyond 1–2 years is less certain in the current literature.
• Arthrosamid is best thought of as a symptom-modifying option for symptomatic knee OA, not a procedure that removes arthritis or regrows cartilage.
• In the UK, it is generally encountered as a self-funded treatment or within research, because being CE‑marked as a device does not automatically translate into routine NHS commissioning.

Taken together, the current evidence base supports Arthrosamid as a genuine, single‑injection option with encouraging 6–12 month outcomes for pain and function in knee osteoarthritis, while leaving important open questions about longer-term durability, comparative effectiveness, and NHS cost-effectiveness that ongoing studies are designed to answer.

PRP alone or with hyaluronic acid

PRP (platelet‑rich plasma) is made from a small blood sample taken on the day of treatment and then processed (typically by centrifuge) to concentrate platelets before the final product is injected into the knee joint. The rationale is that platelets carry signalling molecules (often described as “growth factors”) that may help shift the joint towards a less inflammatory state and support symptom improvement, even though PRP is not a cartilage‑regrowth treatment. Preparation methods and platelet concentrations vary between providers, which is one reason results can look inconsistent across studies.

Hyaluronic acid (HA) injections sit in a different category: they are a gel‑like lubricant intended to mimic components of normal joint fluid and reduce friction, rather than alter inflammation via blood‑derived factors. In the UK context, NHS England’s 2023 knee osteoarthritis decision aid states that hyaluronic acid injections “do not help” knee OA, and Versus Arthritis notes that NICE does not recommend hyaluronan injections for osteoarthritis (despite some studies suggesting short‑term pain benefit for some people). This is a key reason HA is often encountered as a self‑funded treatment rather than a routine NHS option.

PRP versus HA — what reviews generally conclude

Across narrative reviews comparing common injection options for knee OA, PRP is frequently summarised as offering more durable symptom relief than HA or corticosteroid injections in many small‑to‑moderate trials, while also highlighting that PRP preparation methods and dosing protocols vary and may influence results.

PRP+HA — why the “add HA” question remains open

Those same reviews commonly note that there are fewer trials testing PRP+HA than PRP alone, and that PRP+HA protocols are heterogeneous—so the incremental value of adding HA to PRP remains uncertain rather than established.

Why PRP+HA is often treated as “still being tested” in the UK

The Health Research Authority describes an NHS‑based randomised trial designed to test whether adding hyaluronic acid to PRP improves outcomes compared with PRP alone for knee osteoarthritis. That kind of study design is usually pursued when routine care has not yet settled on a clear winner, and when decision‑makers still consider the comparative benefit (and therefore value) uncertain.

Thinking about “added benefit” versus “added cost”

In practical terms, combining PRP with HA usually means adding another product to the injection plan. Where HA is not recommended as a routine NHS treatment for knee OA, the decision to add it to PRP tends to sit firmly in the private, self‑funded space. The evidence to date, as summarised in reviews, suggests PRP is likely to outperform HA alone for many people with mild–moderate knee OA, while the advantage of PRP+HA over PRP alone has not yet been demonstrated strongly enough to be considered settled.

BMAC ‘stem cell’ injections compared with PRP

Bone marrow aspirate concentrate (BMAC) sits at the more involved end of “orthobiologic” injections for knee osteoarthritis, because it starts with a bone‑marrow harvest rather than a blood draw. In most outpatient pathways, a clinician uses a needle to draw marrow (commonly from the iliac crest of the pelvis) under local anaesthetic, processes the sample in a sterile system to concentrate the aspirate, and then injects the concentrate into the knee joint—often in the same appointment. Reviews consistently describe this as more invasive and resource‑intensive than PRP, even though the final step is still an injection rather than an open surgical procedure.

Why it is often called a “stem cell injection” (and why that label can mislead)

BMAC is frequently marketed as a “stem cell” treatment, but real‑world BMAC preparations are not a purified stem cell product. Expert and narrative reviews describe BMAC as a mixed concentrate that can include a range of cells (including progenitor/stromal cells) alongside platelets and other signalling molecules. Because preparation systems and protocols vary, the final injectate can differ meaningfully between centres—one reason the published evidence is harder to compare across studies.

A second practical implication of this terminology is expectation‑setting. Across these reviews, BMAC is generally discussed as a symptom‑modifying / biologic support approach (pain and function), and not as a reliably “regenerative” treatment that rebuilds worn joint surfaces in established osteoarthritis. The same articles highlight that study designs, follow‑up length and outcome measures are still too inconsistent to claim predictable structural restoration of the joint in typical knee OA.

What comparative studies suggest versus PRP (with important caveats)

A larger, more recent single‑centre clinical trial of 175 patients (registered as NCT03825133) compared BMAC, PRP and hyaluronic acid injections over 12 months, using WOMAC and SF‑36 quality‑of‑life measures. That study reported the greatest improvements in quality of life and physical functioning in the BMAC group overall, with PRP generally outperforming hyaluronic acid on some measures. Even so, being from one centre, the findings may not translate cleanly to other settings that use different preparation methods, dosing schedules, or patient selection thresholds.

Why BMAC is usually reserved for selected patients

Across narrative and expert reviews, the overall verdict is cautiously optimistic but not definitive. BMAC appears capable of short‑ to mid‑term symptom improvement in many published series, and some reports suggest it may delay knee replacement in certain cases; however, these same reviews emphasise that much of the evidence remains Level II–IV, with heterogeneous harvest techniques, processing systems, and rehabilitation protocols. As a result, superiority over PRP (or over other injectables) cannot currently be treated as established.

Practical trade‑offs also matter. Because BMAC involves a marrow harvest and processing step, reviews flag greater procedure complexity, potential for harvest‑site soreness/bruising, and higher resource use—factors that feed into ongoing uncertainty about economic feasibility and cost‑effectiveness compared with simpler injection pathways. In UK practice, this tends to place BMAC later in the decision‑set: often considered only after core non‑operative care has been tried and where the individual’s goals justify accepting a more invasive, less standardised treatment with a still‑maturing evidence base.

Why ultrasound guidance matters for hip and knee injections

Most advanced hip and knee injections are now done with ultrasound guidance, because it allows the clinician to see the joint space and the needle tip in real time on a screen. The set‑up is often compared to a pregnancy scan, but focused on guiding the injection: a small probe is moved over the skin with gel, and the needle is directed into the target while its path is watched live.

The practical reason for doing this is simple: an injection only has its intended effect if it actually lands inside the joint rather than in surrounding soft tissues. Evidence syntheses in musculoskeletal injection practice have reported that image guidance can improve intra‑articular placement accuracy compared with anatomical “landmark” techniques, which is one reason it is widely used.

For the hip joint, image guidance is often considered particularly important because the joint lies deep under muscle and soft tissue, and the target cannot be reliably judged by feel.

Most of the strongest “accuracy” data come from studies of steroid and hyaluronic acid injections, but the same placement logic applies to newer injectates used in osteoarthritis care. With treatments that are expensive, long‑acting, or intended to work specifically inside the joint—such as Arthrosamid (polyacrylamide hydrogel), PRP, or BMAC—a misplaced injection has a bigger downside: less chance of benefit, and more exposure of surrounding tissues to a product that was not meant to be deposited there. This is one reason image guidance is often treated as a safeguard for both value and safety, even when the knee joint feels “easy to find”.

In a typical ultrasound‑guided outpatient appointment, the patient remains awake on an examination couch; the skin is cleaned, and local anaesthetic may be used to improve comfort. The ultrasound probe (with gel) is then positioned to visualise the target, and the clinician advances the needle while watching its position on the screen before delivering the injectate into the joint. The key distinction is that this is an image‑guided clinic procedure, not an operation, and the “guidance” element is specifically about making intra‑articular placement more reliable.

When comparing providers, practical checks often used for hip and knee injections include:

• whether ultrasound guidance is used for every injection (not only “difficult” cases)
• who performs the injection (for example, a clinician who does large‑joint injections routinely)
• whether a clear intra‑articular view is documented on the scan before injecting, particularly for hip injections where landmark accuracy is known to be lower.

Putting Arthrosamid, PRP and BMAC into a personal plan

A workable personal plan usually comes down to one trade‑off: choosing between a single long‑acting option (such as Arthrosamid®, CE‑marked in April 2021) and a more ‘biologic’ approach that often involves multiple steps (PRP, or the more involved BMAC pathway). The decision points below focus on matching an injection to arthritis stage and priorities, rather than on where the injection is purchased.

At a high level, the options discussed earlier have distinct “shapes”. Arthrosamid is a one‑off hydrogel device injection aimed at longer‑lasting symptom control, with mid‑term results reported out to around 6–12 months in published studies, but with longer follow‑up and cost‑effectiveness still being clarified. PRP is an autologous blood product with a growing but variable evidence base that depends on preparation and protocol. PRP+HA remains a “nice idea, not yet settled”: reviews describe the combination as promising but supported by fewer heterogeneous studies, and UK research approvals (via the Health Research Authority) underline that the incremental benefit over PRP is still an active question. BMAC is the most resource‑intensive option here: it requires marrow harvest and processing, and comparative studies are promising but not definitive enough to claim clear superiority across settings.

Where these fit often depends on how far along knee OA is on imaging (X‑ray or MRI) as well as symptoms. In mild to moderate OA—where there is pain, swelling, and function loss but without major deformity—patients commonly aim to reduce pain and keep activity going while trying to delay bigger interventions. In advanced “bone‑on‑bone” change or marked deformity, injections may still offer symptom relief in some cases, but the ceiling on improvement is often lower, and planning tends to include an explicit discussion about surgical options if day‑to‑day function remains poor.

Access and affordability shape real‑world choices in the UK. The NHS England knee OA decision aid published in 2023 emphasises exercise, weight management, pain relief and (for some people) steroid injections, while stating that hyaluronic acid injections do not help knee OA and noting that not every treatment is routinely available. Against that backdrop, PRP, PRP+HA, Arthrosamid and BMAC are often encountered as self‑funded options or within research pathways, and the financial decision is inseparable from the remaining uncertainties (particularly long‑term outcomes and head‑to‑head comparisons).

Discussion points that can keep a GP, physiotherapist or specialist appointment grounded include:

• What does current imaging show (for example, mild vs moderate vs severe joint‑space loss), and does that match the pain pattern?
• Is the goal mainly pain control for a specific period (for example 6–12 months), or a longer attempt to delay knee replacement?
• For PRP protocols, what preparation method is used (given the variability highlighted in reviews), and is PRP+HA being considered because of a clear rationale rather than habit?
• For BMAC, what additional invasiveness is involved (harvest site, processing), and how does that align with the evidence level cited in narrative and expert reviews?
• For any intra‑articular injection, is ultrasound guidance used as standard—particularly relevant when the injectate is costly, technically demanding, or intended to remain intra‑articularly?
• How will “success” be measured at 3 months and 12 months (pain scales, WOMAC/KOOS‑type function measures, walking tolerance), and what is the back‑up plan if the response is limited?

Across all these routes, a consistent quality marker is not the product name but the basics: clear diagnosis, realistic goals, and reliable intra‑articular placement—especially when the plan involves an expensive or long‑acting injectate rather than a short‑acting flare‑management injection.

1. [1] Choice of intra-articular injection in treatment of knee osteoarthritis: platelet-rich plasma, hyaluronic acid or ozone options. (2017). https://doi.org/10.1007/s00167-016-4110-5 https://doi.org/10.1007/s00167-016-4110-5
2. [2] Quality of life changes in patients suffering from knee osteoarthritis treated with bone marrow aspirate concentrate, platelet-rich plasma and hyaluronic acid injections. (2025). https://doi.org/10.1080/17460751.2025.2472589 https://doi.org/10.1080/17460751.2025.2472589
3. [3] Intra-articular injections of platelet-rich plasma, hyaluronic acid or corticosteroids for knee osteoarthritis. (2019). https://doi.org/10.1007/s00132-018-03659-5 https://doi.org/10.1007/s00132-018-03659-5