Is a PRP knee injection after physio likely to help me

For a knee that still hurts after a structured block of physiotherapy and activity change, a platelet-rich plasma (PRP) injection is sometimes considered as a “next step” when the working diagnosis is early-to-moderate osteoarthritis (cartilage wear) rather than a single mechanical problem that needs an operation. The best evidence in knee osteoarthritis suggests that PRP can improve both pain and day-to-day function over months rather than days—so it is typically used to support a return to walking, stairs and exercise tolerance over the next 6–12 weeks, not to provide instant numbing. [1]

PRP is made from a small sample of a patient’s own blood, processed to concentrate platelets, and then injected into the knee joint. [1] In some clinical protocols this is done as an ultrasound-guided outpatient injection, with ultrasound used to help place the PRP inside the joint space accurately. [2] Importantly, symptom improvement after PRP should not be interpreted as rapid “cartilage regrowth”: a 3D MRI study looking 6 months after PRP found that measurable cartilage thickening (>0.1 mm) occurred in only a minority of knees in key medial-compartment regions (reported as <20% in some of the most affected areas), suggesting early benefit is more likely linked to changes in inflammation and pain signalling than bulk cartilage rebuilding. [3]

In trials, the main check-in points are usually 1, 3, 6 and 12 months. A meta-analysis pooling 18 randomised controlled trials (1,995 patients) found PRP produced statistically better pain (VAS) and function (WOMAC) scores than placebo at each of those time points; functional improvements exceeded a minimal clinically important difference even at 1 month, while pain relief more consistently cleared that “clinically important” threshold around the 3-month mark. [1] An ultrasound-guided study using three monthly injections of leukocyte-poor PRP plus hyaluronic acid reported a gradual trajectory (for example, pain scores falling from about 7 to about 2.1 and WOMAC from ~62 to ~24 by 12 months), with clearer separation from hyaluronic acid alone emerging later, from around 6 months. [2]

Detailed, week-by-week milestones in the first 12 weeks are not well mapped in randomised trials, because most papers report outcomes at monthly (or longer) intervals. In practical terms, PRP is therefore judged as a medium-term strategy: compared with corticosteroid injections—where randomised evidence suggests faster early relief that often fades sooner—PRP tends to build more gradually and, on average, lasts longer, although individual responses vary and improvement is never guaranteed. [4]

Weeks 0 to 4 after PRP knee injection

Treatment day and the first 48 hours

PRP is typically delivered as an ultrasound-guided injection into the knee joint in an outpatient appointment, followed by a short period of observation in clinic on the same day. Many patients can walk out afterwards and manage basic tasks such as stairs or a short commute, but a temporary “ache” or stiffness around the knee over the first 24–48 hours can occur.

A short-lived flare—often described as soreness, a sense of fullness in the joint, or a step-up in baseline pain—can occur in the first 24–72 hours. In most cases this settles with simple measures used for many injection after-effects (relative rest for a couple of days, intermittent ice, and simple analgesia such as paracetamol if appropriate). A more intense or prolonged flare is less common; if the knee becomes increasingly hot and swollen over several days, if fever develops, or if weight-bearing becomes progressively harder rather than easier, clinicians generally treat that as a reason for urgent review.

Why some people flare more than others

Post-injection pain is not necessarily “just bad luck”. In a retrospective series of 225 people treated with PRP for knee osteoarthritis, higher anticoagulant doses used during PRP preparation and poorly controlled hyperuricaemia were associated with more post-injection knee pain and greater inflammatory markers, whereas lower-dose anticoagulant protocols had fewer pain flares and slightly better outcomes over time. [5] This supports a practical point: short-term worsening after PRP is possible, but it does not appear inevitable and may be influenced by preparation choices and metabolic factors (including high uric acid).

Walking, daily life and exercise: weeks 1 to 4

Because most PRP studies assess outcomes at 1 month (and later), there is no trial-tested “day-by-day” walking schedule. [1,2] In most specialist protocols, flat walking for day-to-day activities is usually continued within 1–2 days, while longer hikes, heavy lifting, deep squats and impact work (running, jumping, HIIT) are commonly avoided for roughly the first 1–2 weeks to limit unnecessary irritation.

Early physiotherapy in the first 2–4 weeks is usually kept deliberately low-load: gentle range-of-motion work, quadriceps and hip activation (for example, straight-leg raise patterns and controlled sit-to-stand), and gait practice so that limping does not become the new normal. By around week 4, many people start to notice that walking and stairs feel “less reactive” even if pain is not yet consistently better—matching the way knee PRP trials often first detect clearer functional change at the 1-month time point rather than in the first few days. [1]

Weeks 4 to 12 after PRP knee injection

Between week 4 and week 12, PRP tends to behave more like a slow “turning down” of joint irritability than a quick switch-off of pain. In the main knee osteoarthritis trials, function scores commonly show clinically meaningful change by the 1‑month check-in, while pain relief more often reaches a clearly noticeable threshold around the 3‑month mark—so in practical terms this middle phase is often about doing a bit more with a bit less payback, even if some discomfort is still present. [1]

Weeks 4–8: building capacity without provoking a flare

From around week 4, many rehabilitation programmes move from “settling” the knee to progressively strengthening it. Common priorities in weeks 4–8 include heavier resistance work (within good technique), closed-chain control (for example, sit-to-stand patterns and step work), and balance/proprioception drills that target confidence on stairs and uneven ground. Walking distance or cycling time is usually increased in small steps (for example, adding minutes or distance once or twice per week), with a bias towards consistency rather than occasional big jumps in load.

A lack of dramatic change at 4 weeks is not, on its own, treated as failure in published PRP work. In an ultrasound-guided series using three monthly injections of leukocyte-poor PRP plus hyaluronic acid, pain and function improved progressively over many months rather than peaking in the first few weeks, with clearer separation from hyaluronic acid alone emerging later in follow-up. That overall pattern fits with a “steady build” through the first 3–6 months, rather than immediate maximal benefit. [2]

Weeks 8–12: testing higher-level activity, in phases

By 8–12 weeks, some people who are trending in the right direction can start trialling more demanding but still controlled activities—such as brisk walking on hills, longer continuous walks, or more challenging gym sessions where volume and resistance increase gradually. Where running is a goal, published trials rarely provide a week-by-week “return to jog” plan; in practice, any return to impact (jogging, jumping, pivoting sport) is usually phased and governed by the knee’s 24‑hour response after each step-up, often alongside physiotherapy input.

Deciding what the 12‑week point means

At about 3 months, PRP studies commonly re-measure outcomes because this is the stage when pain relief often becomes more consistently meaningful at group level. If progress plateaus or reverses between week 8 and week 12—particularly if swelling, night pain, or walking tolerance worsens—many pathways move towards a clinical review to check diagnosis, mechanical drivers (such as meniscal/root problems or malalignment), and whether a different plan is needed.

It also helps to keep expectations grounded: a 6‑month 3D‑MRI study after PRP reported measurable cartilage thickening in only a minority of knees in key medial-compartment regions (with <20% in some of the most affected areas), so improvements seen by 12 weeks are usually best understood as better pain control and function rather than visible “rebuilding” of joint surface in that timeframe. [3] Finally, PRP outcomes are influenced by how the PRP is made—one systematic review found that study arms with better 6–12 month results tended to use higher total platelet doses (around 5.5×10^9 versus about 2.3×10^9)—so preparation differences may be one reason responses vary between clinics and studies. [6]

How ankle Lipogems and other fat injections actually work

For ankle cartilage pain—especially after an old sprain or fracture—online searches often lead to Lipogems-type “fat injections”. The idea is different from PRP: instead of concentrating platelets from blood, microfragmented adipose tissue (MFAT) uses a small amount of a person’s own fat as a source of biologically active tissue, delivered into a joint such as the ankle or the subtalar joint.

What the procedure involves (in practical terms)

In the published subtalar osteoarthritis case report, fat was taken from the abdomen, processed in the Lipogems kit for about 20 minutes, and then 10 mL of the final MFAT product was injected into the subtalar joint, with symptom scores tracked out to 6 months. That sequence—small-volume lipoaspiration, closed-system processing, then intra-articular injection—captures the essentials of what most clinics mean by a “Lipogems injection”, even though exact volumes and technique can vary between centres. [7]

What “Lipogems processing” actually does

A key feature of Lipogems-type MFAT is that the fat is mechanically fragmented and washed in a closed system, without enzymes. Technical descriptions emphasise that this washing step removes oil and blood residues and leaves small clusters of fat tissue that are relatively rich in perivascular and stromal cells (cells that sit around small blood vessels and in the supporting tissue framework). In plain terms, the processing is designed to make the fat injectable and “cleaner”, while preserving the cell niches that may help the joint environment. [7,8]

How MFAT is thought to help inside a joint

Laboratory work shows that MFAT contains a mixture of mesenchymal stromal cell subtypes that can be pushed towards cartilage-like or bone-like behaviour in vitro, which gives biological plausibility for “joint support” effects. That does not mean the injected tissue simply turns into new ankle cartilage; in living joints, MFAT is more often discussed as acting through signalling—releasing mediators (including extracellular vesicles) that may calm inflammation and influence matrix turnover in the joint lining and cartilage surface. [9] A 2025 study of MFAT-derived extracellular vesicles in thumb-base osteoarthritis reported improvements in pain and function over 12 months without radiographic progression, alongside mechanistic evidence of inflammation and matrix-pathway modulation—supporting the idea that paracrine signalling is likely central to symptom relief. [10]

What the clinical evidence says (and where it’s strongest)

The highest-quality outcomes data for MFAT come from knee osteoarthritis rather than the ankle. In a randomised-trial meta-analysis, both MFAT and PRP in the knee reached minimal clinically important differences in many pain and function outcomes up to 12 months, with MFAT showing a small statistical advantage over PRP at 6 months in some measures (the absolute differences were modest). [11] A separate meta-analysis comparing MFAT with PRP, bone marrow aspirate, hyaluronic acid, and corticosteroid reported no significant differences across pain (VAS) and KOOS subscales at 3–12 months and judged the certainty of evidence as low—so overall, MFAT looks broadly “in the mix”, not clearly superior. [12]

One knee randomised trial focused on an “inflammatory phenotype” (where swelling, stiffness and other inflammatory features are more prominent) and found MFAT produced greater improvement than hyaluronic acid for KOOS Symptoms at 6 months, alongside dGEMRIC MRI signals consistent with increased cartilage glycosaminoglycan in some responders. That combination—better symptom control in inflamed joints plus a compositional MRI signal—offers a plausible reason MFAT might help certain inflamed ankle or hindfoot joints, but it remains an extrapolation until ankle trials are done. [8]

What is known specifically for the ankle and hindfoot

Direct ankle/hindfoot evidence is currently limited to case-level reports. A 2025 Lipogems case report in advanced post-traumatic ankle osteoarthritis (a 43-year-old woman) described marked improvement in pain and function over the first 3 months after a single injection, with partial loss of benefit by 6 months—suggesting MFAT may provide a window of symptom relief in end-stage disease but may not be durable. [13] The subtalar osteoarthritis case similarly reported clinically important improvements maintained through 6 months without complications. Taken together, these reports support short- to mid-term safety signals and potential symptom benefit, while leaving major uncertainties around durability and whether MFAT can substitute for surgery when there is a large structural lesion, malalignment, or advanced degeneration. [7,13]

Who might suit ankle fat injections and who still needs surgery

MRI or CT findings usually help determine whether an ankle problem is something a biologic injection might calm down, or something that needs a structural repair.

An osteochondral lesion of the talus (OLT) is essentially a defect in the talar joint surface—cartilage and, in many cases, the bone just beneath it. [14] Pain intensity alone can be misleading: a small, contained surface defect can hurt a lot, while a larger unstable lesion may be “quiet” until loading increases.

A practical dividing line is whether the ankle has a mechanical problem that needs fixing. Examples seen on imaging include a clearly unstable fragment, a larger defect with a cyst under the cartilage, significant malalignment (varus/valgus), or evidence of bone loss/collapse in the talus. In those situations, an injection—whether microfragmented fat (MFAT) or PRP—may help symptoms in the short term, but it is unlikely to correct the underlying mechanics. [14]

By contrast, MFAT-type injections are most plausibly considered when the joint still looks mechanically “organised” on imaging: early-to-moderate post-traumatic change, small areas of cartilage wear, and an ankle that is reasonably well aligned, without major cystic bone change. In that narrower group, MFAT is best framed as biologic support aimed at reducing irritability and improving tolerance for rehabilitation, rather than as a definitive substitute for a lesion-stabilising procedure.

Direct ankle/hindfoot MFAT evidence remains limited to individual reports:

• In a 2025 case report of advanced post-traumatic ankle osteoarthritis (a 43-year-old woman), a single Lipogems MFAT injection was followed by marked improvement in pain and function over the first 3 months, with partial loss of benefit by 6 months—suggesting a potential “window” of relief in severe disease, but uncertain durability. [13]
• In a subtalar osteoarthritis case report (48-year-old man), symptom scores (VAS, MOXFQ, FAAM-ADL) improved and were maintained through 6 months without reported complications after a single Lipogems injection. [7]

Those 3–6 month signals can fit a “bridge” role—especially when the goal is to keep walking and rehab going—while keeping expectations cautious in advanced arthritis, where biologic injections have not been shown (in ankle trials) to substitute for structural procedures when mechanics are the limiting factor. [13,14]

Planning your next steps with knee and ankle cartilage pain

A workable plan usually starts with two timelines: the biologic response (measured in months) and the structural problem (shown on MRI or CT). To keep the emphasis on decision-making rather than where treatment is delivered, the key takeaway is that knee PRP is supported by randomised trial evidence with outcomes commonly judged at 1, 3, 6 and 12 months, whereas ankle MFAT/Lipogems remains supported by only case-level ankle data and stronger (but joint-specific) knee evidence. [1,11,13]

For a knee PRP pathway, “success” is usually a 3‑month question, not a 3‑week question: in an 18‑trial meta-analysis (1,995 patients), pain improvements became clearly clinically important mainly around 3–6 months, while function changes could be meaningful as early as 1 month. That makes ongoing rehabilitation and progressive loading the practical partner to the injection over the first 12 weeks. [1]

For the ankle, it helps to separate symptom control from lesion correction. A 2025 report of advanced post‑traumatic ankle osteoarthritis described marked improvement over 3 months after a single Lipogems MFAT injection, with partial loss of benefit by 6 months—consistent with a potential “bridge” role in some cases, but not a reliable substitute when imaging shows a mechanically significant osteochondral problem. [13,14]

Questions to bring to a review (MRI/CT report in hand) include:

• “Have I completed a structured physiotherapy block (e.g., 8–12 weeks) with objective strength and tolerance targets?”
• “Is the main limitation pain and swelling, or mechanical symptoms such as locking, catching, or giving way?”
• “What does imaging show about cartilage and the bone beneath it (cysts, collapse, malalignment)?”
• “What is the time horizon for a specific job or sport—3 months, 6 months, or 12 months?”

At London Cartilage Clinic on Harley Street, assessments are typically framed around imaging findings and functional goals, then mapped onto a spectrum that may include optimised physiotherapy, ultrasound‑guided injections (such as PRP for the knee or MFAT in selected ankle/hindfoot cases), and—when structure is the limiting factor—an opinion on joint‑preserving surgery within the wider MSK Doctors group. A consultation can be booked via londoncartilage.com.

1. [1] 3D-MRI analysis of cartilage thickness changes after PRP injection in medial knee osteoarthritis: A preliminary report. (2025). https://doi.org/10.1371/journal.pone.0321067 https://doi.org/10.1371/journal.pone.0321067