Which injection are you really choosing between

A common decision point in the UK is persistent knee (or hip) osteoarthritis pain despite months of physiotherapy, strengthening work, weight management and regular tablets—when stairs, walking distance or sleep are still being limited, but joint replacement does not feel like the next step. At that stage, injections are usually being considered as a way to reduce pain and improve day-to-day function for a period of time, rather than to “fix” arthritis permanently.

In practice, the choice is often between four broad categories of intra‑articular injection (sometimes combined with an approach to improve accuracy, such as ultrasound guidance):

• Corticosteroid (“cortisone”): typically used to calm an inflammatory flare and provide shorter‑term symptom relief; it is one of the most commonly injected agents in knee OA studies of image‑guided versus landmark‑guided technique.[6]
• Hyaluronic acid (HA): a lubricating/viscoelastic injection intended to temporarily improve joint fluid “slip” and shock absorption; umbrella‑review evidence suggests moderate improvements in pain and function overall, with a generally favourable safety profile but mixed guideline recommendations.[2]
• Arthrosamid (2.5% polyacrylamide hydrogel): a non‑biodegradable hydrogel designed to integrate with the synovial lining and form a cushioning, “shock‑absorbing” layer, aiming for longer‑lasting mechanical symptom relief from a single treatment.[1]
• Platelet‑rich plasma (PRP): a blood‑derived biologic injection; recent meta‑analyses of randomised trials generally report better symptom outcomes with PRP than HA, and placebo‑controlled RCT meta‑analysis suggests clinically meaningful benefit in many protocols (though results vary between studies).[4,5]

These are usually delivered as outpatient injections rather than surgery. Image guidance matters because a Level I review of 12 randomised trials (1,431 patients) found ultrasound‑guided knee injections were more accurate than “blind” injections across every portal studied, and a 2016 hip meta‑analysis reported significantly higher accuracy with ultrasound than landmark guidance (p<0.0001).[6,7]

Across Arthrosamid, HA, PRP and steroid injections, the most consistent evidence is for symptom modification over months to years (depending on the product and patient)—not cartilage regrowth, and not a guaranteed way to avoid joint replacement.

The rest of this article addresses five practical questions that tend to drive real decisions: how safe a permanent hydrogel implant is, how costs compare in the UK, how often HA tends to be repeated, whether PRP is genuinely better than “filler” injections, and why ultrasound guidance matters for knees and hips.

Arthrosamid side effects and long term safety

Short‑term after‑effects

Arthrosamid is given as a single intra‑articular injection of 2.5% polyacrylamide hydrogel (often described as 6 mL for the knee) and is designed to integrate with the synovial lining rather than biodegrade quickly.[1,8] UK clinical information pages describe the immediate trade‑off clearly: the treatment aims to create a cushioning layer in the joint, but it can cause a short period of “reactive” symptoms around the injection itself. Commonly described early after‑effects include mild to moderate pain, swelling, bruising, stiffness, warmth, or a feeling of fullness in the knee, typically settling over a few days.[1,8] More serious issues such as infection, allergic reaction, or persistent inflammation are consistently described as rare.[1,8]

What 1‑year and 5‑year studies reported

The best described medium‑term safety data come from a multicentre open‑label study of 49 people with knee osteoarthritis who received a single 6 mL intra‑articular polyacrylamide hydrogel injection and were followed to 52 weeks.[9] In that report, between weeks 26 and 52 there were 8 adverse events in 5 participants, including one serious cerebrovascular accident (stroke); importantly, none of these events were judged device‑related by the investigators.[9]

A 5‑year extension followed a subset from the same cohort: 35 entered the extension and 27 completed 5 years. Over years 2–5, the authors reported 47 adverse events, with no serious events attributed to the device and no new device‑related adverse effects observed during the extension period.[10] These longer follow‑ups are reassuring in the sense that they did not identify a late “new” pattern of device‑linked harm, but they are still based on a relatively small, non‑randomised group.[10]

10‑year signals and real‑world “complications”

Beyond 5 years, the most frequently cited longer‑term signal is a manufacturer press release summarising a 10‑year follow‑up abstract. It describes very few patients recalling ongoing pain or problems after injection and reports no unusual reactions in surgical records for people who later went on to knee replacement—but the level of published detail in that format is limited, and it is explicitly company‑linked.[11]

A larger “real‑world” picture comes from a 24‑month cohort of 269 patients (314 knees). While outcomes improved on patient‑reported measures, the paper also reports 49 patients proceeding to total knee replacement within 2 years, and notes 155/314 knees with recorded “complications”. The authors highlight the lack of a control group and the need to better define and characterise what counts as a complication—so those numbers are important context, but not a definitive comparison with HA, PRP or doing nothing.[12]

Overall, published evidence to 1–5 years suggests a manageable short‑term side‑effect profile and no clear signal of serious device‑related harm in the studied cohorts,[9,10] while the non‑biodegradable nature of the hydrogel makes long‑term data quality—independent, comparative, and clearly reported—particularly important when weighing this as a symptom‑modifying (not cartilage‑restoring) option.

What Arthrosamid costs and how it compares

In UK private practice, Arthrosamid is usually priced as a high‑upfront, “one‑off” knee injection rather than a lower‑cost treatment that is routinely repeated every few months.[13,14] Online UK pricing examples commonly cluster around £2,000–£3,000 per knee, and one London private hospital advertises package pricing starting at about £3,025 for one knee (and £5,895 for two).[13,14] These figures vary widely depending on what is bundled (for example, a specialist consultation, ultrasound assessment, the injection appointment itself, and follow‑up care) and are best treated as illustrative rather than a fixed national tariff.

By comparison, UK clinic price lists typically place corticosteroid (“cortisone”) injections at the lower end: one UK injection clinic gives an example total of £170 for a new consultation plus one injection, and £220 for a follow‑up plus two injections.[15] Hyaluronic acid (HA) is often mid‑range per episode in private clinics, commonly quoted at roughly £300–£850 per knee injection, with some settings higher depending on the product, clinician, and whether imaging and review are included.[16]

The practical difference is that Arthrosamid is generally marketed and delivered as a single injection per knee, while HA is frequently framed as something that may need repeat treatment series if symptoms return.[13,16] A UK clinic cost breakdown notes that many people have one to two HA series per year,[16] and a 2018 systematic review of 17 studies reported that repeated HA courses in knee osteoarthritis were effective and did not identify new safety concerns, with patient‑facing summaries emphasising mostly transient local reactions.[17,3]

Thinking about “value” therefore tends to involve more than the price on the day. For someone comparing a single £2,000–£3,000 treatment with HA priced per course, the trade‑offs often include:

• Cost per year of symptom control, rather than cost per appointment, especially when HA is repeated every 6–12 months in some pathways.[16]
• Number of clinic visits (one appointment versus a course plus possible repeats), and the knock‑on costs of travel, time off work, and scheduling.
• What is included (imaging, consultation, and follow‑up), since “all‑in” packages and “injection‑only” pricing can look very different on paper.

NHS access adds another layer, because commissioning and availability of HA or newer injectables vary by region and guideline position; many of the published prices above reflect a private, self‑pay pathway rather than routine NHS provision.

Single vs repeat hyaluronic acid courses

Hyaluronic acid (HA) injections are a form of viscosupplementation: the injected HA is intended to temporarily improve the joint’s lubrication and shock absorption, reflecting HA’s normal role in synovial fluid.[3] Patient information sources describe HA injections as used mainly for knee osteoarthritis, and sometimes for hips and shoulders, with benefits framed as symptom relief rather than structural repair of the joint.[3]

Evidence on repeating HA is strongest in the knee. A 2018 systematic review (17 studies) of repeated intra‑articular HA courses in knee OA reported that, when people had further series after an initial course, pain relief was typically maintained or improved compared with the first series, and the review did not identify new safety concerns emerging with repeat treatment.[17] In the same body of evidence, adverse effects were largely described as transient local reactions (for example, short‑lived swelling or discomfort around the injection).[17,3]

The broader picture remains mixed because HA trials vary a lot by product, dosing schedules, and study design. A 2025 umbrella review concluded that intra‑articular HA provides moderate improvements in pain and function—especially in early‑to‑moderate knee OA—and generally has a favourable safety profile, but it emphasised substantial heterogeneity and noted that major guidelines differ on routine use.[2] Across these reviews, HA is not presented as a disease‑modifying treatment: consistent evidence that it slows joint damage or prevents progression has not been established.

For the hip, repeated‑course evidence is thinner in the retrieved sources: HA is described as used “occasionally” in hips,[3] but large, hip‑specific repeat‑course trials are limited compared with the knee literature, so clinical practice is often informed by extrapolation.

Conceptually, this sets up a clear trade‑off with a single, longer‑residence “filler” approach such as Arthrosamid: HA tends to be positioned as a temporary symptom‑modifying option that may be topped up when effects wear off, whereas a permanent hydrogel implant is designed as a one‑off intervention with durability as the main advantage, balanced against the implications of placing a non‑biodegradable material in the joint.[1]

PRP vs filler injections in osteoarthritis

Unlike gel-type injections that arrive pre-made in a syringe, platelet-rich plasma (PRP) begins with a small blood sample taken on the day and processed to concentrate platelets before the PRP is injected back into the osteoarthritic knee. PRP is generally presented as a biologic approach: platelets carry signalling molecules (often described as “growth factors”) that may influence inflammation and tissue-healing pathways, rather than working mainly by physically cushioning the joint space. Evidence still does not show PRP reliably regrows cartilage, so reported benefits are best understood as symptom and function changes rather than joint “repair”.

This mechanistic difference helps explain why PRP is often discussed separately from “filler” options. Arthrosamid is described as a non-biodegradable polyacrylamide hydrogel that integrates with the synovial lining to provide longer-term cushioning,[1] while hyaluronic acid (HA) is a naturally occurring joint lubricant used for viscosupplementation with time-limited effect in many pathways.[3] In practice, PRP is often chosen when the aim is to try a biologically active injection, whereas Arthrosamid or HA are typically framed around altering lubrication/cushioning within the joint environment rather than changing cellular signalling as the primary mechanism.

When PRP is compared directly with HA in knee osteoarthritis trials, pooled results usually favour PRP, but not uniformly. A 2021 meta-analysis of randomised trials (Belk et al.) concluded that outcomes with PRP were better than with HA,[4] and a 2025 meta-analysis (Li et al.) similarly reported PRP to be more effective overall.[18] However, a 2024 systematic review (Ivander et al.) judged that—while both PRP and HA appeared effective for symptom relief—the evidence was still too heterogeneous to declare PRP definitively superior across settings, reflecting variation in study quality and in how PRP is prepared and delivered.[19]

Two further signals support PRP having real biological activity (beyond expectation effects) while also highlighting why results can vary. A 2025 meta-analysis of 18 RCTs (1,995 patients) reported clinically and statistically significant improvements for PRP versus placebo (saline) at follow-ups from 1 to 12 months.[5] Separately, a 2024 systematic review linked better outcomes to higher platelet doses (around 5.5×10^9 platelets in “positive” trial arms versus ~2.3×10^9 where results were not significant), suggesting that PRP protocols may matter at least as much as the label “PRP”.[20]

Direct head-to-head evidence comparing PRP with Arthrosamid is limited in the retrieved sources, so any contrast between them is largely indirect and mechanism-based. A pragmatic way clinicians often think about roles is:

• PRP: potentially better than HA on average in meta-analyses, and better than placebo in RCTs, but outcomes depend on preparation and dosing.[4,5,20]
• HA: viscosupplementation with moderate, time-limited benefit in many studies, and a track record of repeat-course use in knee OA.[2,17]
• Arthrosamid: a single-injection, longer-residence cushioning approach, with decision-making influenced by the implications of placing a non-biodegradable material in the joint and the current lack of PRP-vs-Arthrosamid comparative trials.[1]

Why ultrasound guidance changes the injection experience

In an ultrasound‑guided joint injection, a clinician places an ultrasound probe on the skin and uses live imaging to track the needle as it advances, aiming to confirm that the tip is in the joint space before the injection is delivered. This differs from landmark‑guided (“blind”) injections, where placement relies on surface anatomy and feel alone.

For the knee, the clearest advantage shown in research is accuracy. A Level I systematic review of 12 randomised trials covering 1,431 patients found ultrasound guidance was more accurate than blind techniques across every needle portal studied, with blind accuracy varying widely depending on the approach.[6] The trials included commonly used injectates such as corticosteroid, hyaluronic acid and platelet‑rich plasma (PRP), so the finding is directly relevant to these treatments.[6]

The same theme appears in deeper joints. A 2016 systematic review and meta‑analysis reported that ultrasound‑guided hip injections had significantly higher intra‑articular accuracy than landmark‑guided injections (p<0.0001).[7] In practical terms, the hip’s depth and surrounding anatomy mean that confirming needle position with imaging may matter more than it does in some superficial joints.

Higher accuracy does not automatically guarantee better long‑term outcomes, because many studies measure whether the injection reaches the joint rather than months‑to‑years symptom change. Even so, accurate placement has straightforward potential advantages: a better chance the injectate is actually delivered where intended, and potentially fewer problems linked to injecting into soft tissues or near blood vessels. This principle may be particularly relevant for longer‑residence intra‑articular materials (such as polyacrylamide hydrogel), while still being beneficial for HA and PRP.

Modern musculoskeletal services often describe ultrasound guidance as routine for joint injections; for example, one UK injection clinic states that it delivers cortisone injections under ultrasound and that blind injections are still used elsewhere but are “not recommended”.[15] An AMSK enquiry or online suitability assessment can help confirm whether image‑guided placement is part of the proposed injection pathway for Arthrosamid, HA or PRP.

1. [1] PRP Injections for the Treatment of Knee Osteoarthritis: The Improvement Is Clinically Significant and Influenced by Platelet Concentration: A Meta-analysis of Randomized Controlled Trials. (2025). https://doi.org/10.1177/03635465241246524 https://doi.org/10.1177/03635465241246524
2. [2] A Higher Platelet Dose May Yield Better Clinical Outcomes for PRP in the Treatment of Knee Osteoarthritis: A Systematic Review. (2024). https://doi.org/10.1016/j.arthro.2024.03.018 https://doi.org/10.1016/j.arthro.2024.03.018
3. [3] Polyacrylamide hydrogel injections in knee osteoarthritis: A PROMs-based 24 month cohort study. (2025). https://doi.org/10.1016/j.jcot.2025.103136 https://doi.org/10.1016/j.jcot.2025.103136