Which advanced knee injection could be worth considering?

People often start looking beyond standard knee injections after a steroid or hyaluronic acid (HA) course has helped only briefly, or when longer-lasting symptom control is being discussed as a way to stay active while delaying (or avoiding) knee replacement. In clinics across the UK, the “advanced” label usually means one of two things: a longer-acting material left in the joint (such as a hydrogel), or an autologous “orthobiologic” prepared from the person’s own blood, fat, or bone marrow.

Main injection types (a practical snapshot)

• Corticosteroid: aims for short-term anti-inflammatory relief, often used around a flare.
• Hyaluronic acid (HA): a lubricant-style viscosupplement; primarily for symptom control rather than cartilage repair.
• Arthrosamid (polyacrylamide hydrogel): a synthetic gel designed to remain in the joint and provide persistent cushioning/lubrication; published follow-up includes comparative cohort data to 12 months and extensions out to 5 years.
• PRP (platelet-rich plasma): a concentrated platelet fraction from a blood sample, used to support the body’s own repair processes.
• MFAT / Lipogems (microfragmented fat): processed adipose tissue obtained via lipoaspiration; a 2025 randomised trial compared MFAT with HA in an “inflammatory phenotype” knee OA group over 6 months.
• BMAC (bone marrow aspirate concentrate): concentrated marrow aspirate.

What the appointment involves

All options are delivered as image-guided (typically ultrasound-guided) outpatient injections. PRP, HA, steroid and Arthrosamid are usually “single-visit” injections. MFAT and BMAC add a same-day harvesting step (fat for MFAT; bone marrow aspiration for BMAC) before the processed material is injected.

What the evidence looks like (at a glance)

The evidence base is not even across treatments: comparative data exist for MFAT versus HA at 6 months, and for MFAT versus PRP across multiple randomised trials up to around 12 months in meta-analysis; Arthrosamid has smaller cohorts but longer follow-up out to 5 years.

Across the rest of this article, the key differentiators are: likely duration of benefit (weeks vs months vs years), how invasive the pathway is (simple injection vs harvest + injection), how robust the comparative evidence is, and the main risks/unknowns for each option.

Arthrosamid versus steroid and hyaluronic acid injections

Arthrosamid is positioned differently from standard “course-based” injections because it is a 2.5% non-biodegradable polyacrylamide hydrogel given as a single intra-articular dose (typically 6 mL). Rather than being absorbed over weeks, it is designed to integrate with the synovial lining and act as a long-lasting mechanical cushion/lubricant inside the knee. That “stays in place” design is the main attraction—and also the main trade-off—when comparing it with established options.

Mechanistically and practically, the comparison is usually framed around how often treatment needs repeating. In one 12‑month comparative cohort, the “anchor” doses were hyaluronic acid 60 mg/2 mL (a viscosupplement) and methylprednisolone 40 mg (a corticosteroid), each given as a single injection alongside Arthrosamid 6 mL. The implication for decision-making is straightforward: HA and steroid are generally chosen for symptom control over months, whereas Arthrosamid is chosen when a longer-acting, one-off approach is being considered.

Published short-term outcomes for Arthrosamid are encouraging but come largely from smaller cohorts and extension follow-up. In an open-label programme of 49 participants, improvements were reported and then assessed further in a 5-year extension among those who continued follow-up; these data can support Arthrosamid as a plausible longer-acting option for some people, but (as with any non-controlled cohort) they do not, on their own, demonstrate superiority over HA or steroid.

The most distinctive part of the Arthrosamid evidence is durability. Two separate 5‑year extension datasets report statistically significant improvements maintained to year 5, with mean WOMAC pain improvements around 14–16 points and no new device-related safety signals identified. One extension followed a randomised programme (reporting mean WOMAC pain change −16.2 at 5 years), and another extended the original open-label cohort (mean pain change −14.6 at 5 years, with 27 completers). The decision “pay-off” here is the possibility of multi‑year symptom relief from a single injection—counterbalanced by the reality that the long-term data still come from hundreds of treated knees rather than the very large experience base seen with HA and steroids.

Head-to-head comparative data against HA and steroid should be treated as suggestive rather than definitive. In a 150‑patient retrospective cohort (KL II–IV), median VAS pain fell from 7 to 3 at 3 months across Arthrosamid, HA and steroid. At 6 months, Arthrosamid outperformed steroid but did not clearly outperform HA; by 12 months, HA and steroid scores had returned to baseline on average while Arthrosamid remained slightly improved, yet between-group differences at 12 months were not statistically significant. Put simply: if the main goal is 3–6 month relief, the groups look similar; the differentiator being tested is whether Arthrosamid’s effect persists when single-injection HA and steroid benefits fade, but stronger comparative trials are still limited.

Questions that often shape a consultation about choosing between these three options include:

• Whether the aim is symptom control over weeks–months (steroid/HA) versus attempting a multi‑year effect from a single 6 mL hydrogel injection.
• What the clinician uses as success/failure criteria at 3 months and 12 months (for example, changes in VAS and WOMAC).
• What alternatives remain on the table if there is little response after 1 injection (including repeat HA courses, or moving to other injectables with different mechanisms).

Microfragmented fat injections (Lipogems) and how they compare

MFAT (microfragmented fat, often branded as Lipogems) is different from a standard knee injection because the “medicine” is prepared from the person’s own fat on the same day. In published protocols and studies, the fat is harvested by lipoaspiration under local anaesthetic, then processed in a closed system into small fat clusters that can be injected into the knee. The practical point is simple: it is still an outpatient treatment, but it has two procedure sites (harvest area + knee) rather than just the knee injection.

What typically happens on the day (and why it’s more involved)

• Local anaesthetic infiltration (often called “tumescent” anaesthetic) into the donor area.
• Lipoaspiration (a liposuction-style draw-off) to collect a small volume of fat.
• Mechanical processing and washing in a closed device to produce MFAT suitable for injection.
• Intra-articular knee injection of the processed MFAT.

MFAT is usually described as a biologic injection that may support the joint’s own repair and anti-inflammatory processes, rather than something that directly “regrows cartilage”. That framing matters because the best evidence to date is still mostly about symptom scores over months (pain, function, stiffness), not about guaranteed structural change on scans.

How MFAT compares with hyaluronic acid (HA)

The most direct head-to-head signal comes from a 2025 randomised controlled trial in an “inflammatory phenotype” knee OA group (n=53, randomised 2:1 to MFAT vs HA). At 6 months, both MFAT and HA groups showed statistically significant improvements in KOOS, WOMAC and VAS, and MFAT showed greater average gains across most measures; the clearest between-group difference was in KOOS Symptoms. The same trial also reported early MRI “cartilage matrix” signals (dGEMRIC) that increased in some MFAT participants—best interpreted as a possible early biomarker rather than proof of cartilage restoration.

A patient-level way to translate those findings: MFAT may be most appealing where the goal is “a biologic option for symptoms in early–moderate OA, especially where synovitis/inflammation is part of the picture”, but the evidence base is still small and 6-month follow-up cannot tell how durable the effect is compared with repeat HA courses.

How MFAT compares with PRP and other injectables

Across 6 randomised trials in a 2025 meta-analysis, MFAT and PRP both produced clinically meaningful improvements in pain and function up to 12 months, with similar short- to mid-term safety; MFAT showed only a small statistical advantage at 6 months on some outcomes and differences were not clearly maintained later. A separate 2025 systematic review/meta-analysis pooling comparisons against other orthobiologics, HA and corticosteroids reported no significant differences in pooled VAS pain or KOOS subscales at 3, 6 or 12 months, and rated certainty as low—a reminder that headline claims of superiority are not yet robust.

Risks, practical trade-offs, and what remains unknown

Reported adverse events in published studies are usually mild and short-lived: donor-site bruising/soreness and temporary knee swelling or discomfort are common themes, while serious complications are reported rarely in the available trials and reviews. There is also ongoing interest in whether MFAT can be processed and stored: a laboratory-focused study using storage at −80 °C found post-thaw viability around 56–60% with sterile cultures, which supports the feasibility of banking in principle, but it does not establish long-term clinical outcomes from stored injections. Overall, MFAT has a growing evidence base, but typical follow-up is still ≤24 months in much of the literature, so the long-term picture (including repeat-injection strategies) is less well characterised than for established options like HA and corticosteroid injections.

Bone marrow concentrate versus PRP for knee pain

Two of the most commonly discussed “orthobiologic” injections for knee osteoarthritis are PRP and bone marrow concentrate (often written BMC or BMAC). They are sometimes presented as alternatives because both use a person’s own tissue and are typically delivered as an intra‑articular knee injection—but the way they are obtained (and the strength of comparative evidence) differs.

PRP (platelet‑rich plasma) is prepared from a blood sample taken during an outpatient visit, then processed to concentrate platelets.

BMC/BMAC requires an additional step: bone marrow aspiration, followed by processing to concentrate the aspirate before injection into the knee. Compared with PRP, the practical trade-offs are usually clearer than the mechanistic ones:

• PRP: blood draw only; generally less invasive and often a shorter appointment.
• BMC/BMAC: marrow aspiration is more invasive and is often offered at a higher cost.

For outcomes, it is important to recognise how limited and heterogeneous the comparative evidence remains across orthobiologic injections for knee OA. In a 2025 systematic review/meta-analysis that included comparisons between MFAT and other orthobiologics (including PRP and bone marrow aspirate–based injections), pooled estimates did not show statistically significant differences between MFAT and comparators at 3, 6, and 12 months, and certainty of evidence was rated low—a useful reminder that “clear superiority” claims across orthobiologics are not well supported by robust, consistent data.

Questions that often shape PRP-versus-BMAC decision-making in a clinic appointment include:

• Whether the expected benefit justifies a marrow aspiration versus a blood draw.
• Whether outcomes are tracked consistently at set timepoints (such as 6 and 12 months) for both treatments.

How to weigh durability, risk and invasiveness across options

Trade-offs between injectables often come down to four practical axes: how long benefit might last, how involved the appointment is, how much is known from published follow-up, and whether the treatment is inherently “temporary” or designed to persist.

Durability signals (weeks, months, years)

In a 150‑patient retrospective comparison that tracked outcomes at 3, 6 and 12 months, single‑injection hyaluronic acid (60 mg/2 mL), methylprednisolone (40 mg) and polyacrylamide hydrogel (6 mL) all showed similar pain reduction at 3 months; by 12 months, HA and steroid scores had returned to baseline while the hydrogel group remained slightly improved (with no statistically significant between‑group differences at 12 months). Longer‑term follow-up for polyacrylamide hydrogel comes from extension cohorts reporting mean WOMAC pain improvements of roughly 14–16 points at 5 years after a single 6 mL injection.

Procedure burden and “invasiveness”

At the lower‑burden end, steroid and HA are typically just an intra‑articular knee injection. PRP adds a blood draw and lab processing but is otherwise similar on the day. MFAT (Lipogems‑type) and BMAC are more involved because they include a harvest step: MFAT uses a liposuction‑style fat harvest before the knee injection, while BMAC requires bone marrow aspiration before processing and injection. Polyacrylamide hydrogel feels like a single knee injection on the day, but it is non‑biodegradable and intended to integrate with the synovial lining rather than being cleared over time.

Safety, reversibility and the “known knowns”

For MFAT, published meta‑analyses and comparative reviews describe mostly mild, transient problems and low-certainty evidence without consistent superiority over other injectables at 3–12 months. Polyacrylamide hydrogel extension cohorts report improvements sustained to 5 years with no new device-related safety signals identified in those cohorts, but the overall experience base remains smaller than for longstanding options like HA and steroid injections.

Evidence strength (and what uncertainty looks like in practice)

Across these options, the most mature comparative picture is still for treatments that have been studied in larger volumes over time, while newer or more complex procedures (MFAT, BMAC, permanent hydrogels) often rely on smaller trials, single‑arm cohorts, and extension follow‑up. The key gap is the scarcity of high‑quality head‑to‑head trials that compare PRP, MFAT, BMAC and polyacrylamide hydrogel directly using consistent protocols and multi‑year outcomes. In real clinics, priorities often differ: some people accept a harvest procedure (MFAT or BMAC) for a chance at longer symptom control, while others prefer the least invasive route first (HA/PRP) or value the single‑injection durability signals reported for polyacrylamide hydrogel despite the smaller overall evidence base.

Questions to ask and how to find a suitable specialist

Four decision pivots tend to separate the “advanced” knee injections discussed here, and keeping these in view can prevent the conversation becoming a never-ending checklist. The pivots are: (1) persistence vs reversibility (temporary injectables versus options intended to remain in the joint), (2) procedure burden (simple injection versus a harvest step such as fat or bone marrow), (3) evidence maturity (how much published follow-up exists, and for which patient groups), and (4) how success will be tracked (for example, agreed scores at 3, 6 and 12 months and a clear “stop/next-step” plan).

General prompts that usually sharpen any consultation about knee OA injections:

• Rationale: why this option now, and why not a simpler comparator (HA, steroid, PRP) first or again.
• Fit: what published evidence best matches the person’s age, OA grade and activity level, and what would count as a “good-enough” response.
• Measurement: which outcome tools are used in follow-up (pain scale, WOMAC/KOOS), and at what dates (often 6–12 weeks, then 6–12 months).
• Alternatives: what the non-injection plan is (rehab progression, weight management, bracing, analgesia strategy), and what the surgical “plan B” would be if symptoms persist.

Treatment-specific prompts to keep the discussion grounded:

• Arthrosamid / PAAG: operator experience (rough number of cases), how long-term outcomes are reviewed, and how persistent problems would be handled given the gel is intended to be long-lasting.
• MFAT / Lipogems-type: who performs the fat harvest on the day, typical donor-site aftercare, and whether any tissue banking is offered; published evidence for repeat injections is still limited.
• PRP vs BMAC: why a marrow procedure is being proposed instead of PRP in this case, and what aspiration/processing protocol is used.

Practicalities worth pinning down before committing include ultrasound guidance, number of appointments, time off work, driving and sport/physio restart advice, and the total cost including follow-up reviews.

A balanced endpoint is often an agreed trial with clear review points rather than “the best injection”: these options differ most in persistence, procedure burden and evidence depth, and in some cases the most valuable next step is still optimising the non-injection foundations alongside (or before) any newer injectable.