Knee pain has a way of shrinking a person’s world. A mile-long walk becomes four laps around the kitchen. You catch yourself scanning every curb like it’s a cliff. Over the last decade I have watched platelet rich plasma therapy move from experimental to mainstream in orthopedic clinics for people in this exact spot, the ones not ready for surgery yet not satisfied with pills and ice. PRP is not magic, and it is not for everyone, but used well it can change the trajectory of a painful knee.
This guide explains what happens in a PRP injection appointment, how to judge whether you are a good candidate, what the benefits look like in real life, and where expectations need to be honest. Along the way I will touch on the variations in technique that matter, because the details, from centrifuge settings to injection guidance, can make or break outcomes.
What PRP is, and what it isn’t
PRP, or platelet rich plasma, is your own blood processed so the platelet concentration is higher than baseline. Platelets carry growth factors and signaling proteins that call in the body’s repair crew. When a clinician performs a platelet rich plasma injection into the knee, the goal is not to numb or lubricate, it is to nudge biology toward healing, reduce inflammation, and improve pain and function over weeks to months.
It is not stem cell therapy. Some patients lump PRP with “stem cells,” but platelets are not cells that become tissue. PRP is an autologous therapy, meaning it comes from you, which lowers the risk of immune reaction. It is considered a biologic therapy in the broader field of regenerative medicine, alongside treatments like bone marrow aspirate concentrate and adipose grafts, but it is distinct. Think of PRP as a biologic signal booster rather than a structural replacement.
Outside of orthopedics, clinics use PRP for skin and hair. You will see terms like PRP facial, PRP microneedling, PRP with microneedling, and “vampire facial,” aimed at collagen production, fine lines, acne scars, and under eye rejuvenation. PRP hair restoration and PRP hair treatment target hair loss and hair growth. Those applications rely on the same platelet biology, but the evidence base and dosing are different. For knee pain, keep your focus on PRP joint therapy, PRP orthopedic injection protocols, and studies in osteoarthritis, tendinopathy, and sports injury recovery.
Who benefits most from PRP in the knee
PRP tends to shine in a middle zone. Too little damage, and symptoms may resolve with rest, physical therapy, or a short course of anti-inflammatories. Too much damage, and the joint may have lost enough cartilage or alignment that no injection will restore mechanics. Most of the people who benefit cluster in three groups.
First, mild to moderate knee osteoarthritis, typically Kellgren-Lawrence grade II or III on X-ray. In this group, PRP injections often outperform hyaluronic acid in head-to-head trials over 6 to 12 months for pain and function scores. Patients describe easier stair descent, less night pain, and a longer leash for activities like cycling and hiking. The effect size is meaningful but not universal, and responders usually notice improvements building from the 4 to 12 week window.
Second, chronic patellar or quadriceps tendinopathy, or a pes anserine tendinopathy that has resisted rest and eccentric loading. The response relies on technique, including whether the clinician performs peppering or fenestration of the tendon and whether they use a leukocyte-poor or leukocyte-rich PRP local prp injections preparation. I have seen jumpers’ knee athletes purchase six extra months of sport with the right protocol.
Third, acute on chronic flares after sports injury, such as a partial MCL sprain layered onto an arthritic knee. Here, platelet therapy injection acts as a bridge, reducing inflammatory pain while the ligament heals, and sometimes preventing the spiral into prolonged deconditioning.
There are patients who do not do well. Severe malalignment, bone-on-bone arthritis, or large meniscal root tears with extrusion often limit PRP’s ability to help because the mechanical load remains punitive. A joint locked by loose bodies or a knee with recurrent effusions due to inflammatory arthritis needs a different playbook. People on certain medications, like high-dose anticoagulants, may not be candidates for needling procedures without a coordinated plan.
What to expect on the day of the PRP procedure
The day looks more medical than surgical, more like a lab visit than an operating room. You should set aside 60 to 90 minutes, though the injection itself takes only a few minutes.
You will sign consent after an unhurried discussion of risks and benefits. Most clinics use a local anesthetic to make the skin comfortable, but they avoid anesthetic inside the joint because lidocaine can dampen platelet function. If anxiety is an issue, mild oral anxiolytics can be used, though you will need a ride home.
Blood draw comes next, typically 15 to 60 milliliters depending on the kit and whether a clinician plans one knee or both, or tendon plus joint. The vial goes into a centrifuge. The settings matter. Broadly, there are two families of PRP preparation. Leukocyte-rich PRP contains more white blood cells along with platelets, and leukocyte-poor PRP filters most white blood cells out, favoring a cleaner platelet concentrate. For knee osteoarthritis, many clinicians favor leukocyte-poor PRP to reduce the risk of post-injection inflammation. For tendon work, leukocyte-rich can be appropriate because a brief inflammatory response is part of the therapeutic aim. The final product will be two to eight milliliters of amber plasma, with a platelet concentration two to five times baseline in most commercially available systems.
Before injection, the knee is cleaned with chlorhexidine or povidone iodine. I recommend ultrasound guidance for most PRP orthopedic therapy injections. You do not get extra credit for landmark-only injections if accuracy suffers. Ultrasound allows a clinician to confirm intra-articular placement, avoid synovial plicae, and deliver precisely to a tendon tear or a pes bursa. Some surgeons use fluoroscopy for intra-articular placement, especially for posteromedial approaches in post-surgical knees, but ultrasound covers 90 percent of scenarios without radiation.
The injection is slow and steady. You may feel pressure deep in the joint as the platelet rich plasma spreads through the synovial space. In tendon cases, the needling sensation is sharper, like a pencil eraser pressing and releasing. Most patients tolerate it without heavy sedation. The needle comes out, a small bandage goes on, and you sit for 10 to 15 minutes to ensure there is no vasovagal reaction. Then you go home.
What the first few days feel like
If you walk out of a PRP appointment and feel perfect a few hours later, that is luck, not the norm. Expect a flare. Heat, soreness, a heavy feeling in the joint are common for 24 to 72 hours. Some patients describe it as a deep bruise. You can use ice in cycles, elevate the leg, and take acetaminophen for pain. Avoid nonsteroidal anti-inflammatory drugs for at least a week, ideally two, because they can blunt platelet signaling. If you regularly take NSAIDs for other conditions, bring this up before the visit so you and your clinician can plan.
Activity should be limited the first few days. Short indoor walks are fine. Avoid heavy leg day, long hikes, and pick-up basketball. Most people resume desk work the next day. If your job is physical, plan a long weekend buffer.
By day three to five, the knee typically settles. This is the window when some patients feel a small change and others still feel baseline stiffness. Do not use this early snapshot to judge whether PRP “worked.” The biologic effect curves in over weeks. I ask people to wait to rate their response until week four, week eight, and week twelve.
The arc of improvement
Improvement usually declares itself in phases. First, morning stiffness shortens. That 12-minute limbering walk shrinks to six, then to three. Next, stairs stop barging to the front of your mind. You still hold the rail, but you forget to fear the pivot at the landing. Then, the unplanned tests arrive. You lunge for the subway door and realize afterward the knee did not punish you. You pick up a sleeping toddler for a longer carry without a flare that night.
Objective data in trials mirrors this. WOMAC pain and function scores tend to show meaningful differences from baseline at 4 to 6 weeks, with peaks at 12 weeks, and durability at 6 to 12 months. Some patients hold gains at 18 months, but the median expectation should be about a year. Repeat injections can extend benefit, and many rehab-focused clinics use a series of two or three PRP injections for knee osteoarthritis spaced two to six weeks apart. There is no single correct schedule, but I have seen diminishing returns if sessions are packed too tightly without giving the joint time to respond.
For tendinopathy, the slope is steeper early if the clinician also performed fenestration to stimulate a local bleeding response. Those cases often feel sore for a week, then settle with function gains in the next two to six weeks, provided the loading program is structured and graded.
How PRP compares with other knee injections
Patients often ask to stack or sequence PRP with corticosteroids or hyaluronic acid. Corticosteroid injections deliver fast relief in days but are short lived and can weaken cartilage and tendon tissue if repeated. I use them cautiously for severe flares when sleep is broken and rehab is on pause. Hyaluronic acid acts as a lubricant and viscoelastic supplement. It helps some patients, especially at mild OA grades, but response is variable. In meta-analyses, PRP for knees tends to outperform hyaluronic acid by small to moderate margins at 6 to 12 months. The trade-off is cost and early flare discomfort. Platelet therapy treatment is rarely covered by insurance in many regions. Patients pay out of pocket, with prices spanning a wide range depending on kit costs, clinic overhead, and whether image guidance is included.
There are combination protocols. Some clinicians mix PRP with hyaluronic acid in the same session, or sequence a hyaluronic acid series followed by a PRP booster treatment. Evidence is evolving. My bias is to avoid diluting PRP unless there is a specific rationale, and to reassess after a single PRP injection before adding layers.
Technique details that actually matter
Not every PRP injection is equal, and this explains why you hear wildly different reports from friends. Quality depends on several controllable factors.
Platelet dose and concentration. Too low and you do not cross the biologic threshold. Too high and you can provoke excessive inflammation. Most clinical successes have used two to five times baseline platelet concentration, delivering a total dose in the range of 2 to 10 billion platelets intra-articularly. Clinicians do not shout these numbers at you in the room, but they should be able to describe their preparation and typical yields.
Leukocyte content. For knee osteoarthritis, I favor leukocyte-poor PRP to limit cytokine-driven synovitis after injection. For tendon indications, leukocyte-rich PRP is defensible, but I still tailor it to the irritability of the tissue.
Activation. Some systems add calcium chloride or thrombin to “activate” PRP and form a clot before injection. For joints, I usually prefer non-activated PRP so it disperses within the synovial fluid. For focal tendon tears, adding a small platelet gel can make sense.
Guidance. Ultrasound guidance is a quality marker. Hitting the joint reliably is not difficult, but accuracy rises to near 100 percent with ultrasound and allows attention to avoid structures that can spark pain flares.
Number of sessions. For knee OA, I usually recommend one injection, reassess at six to eight weeks, and decide on a second based on response and goals. Tendon cases may benefit from a planned two-session protocol. A three-injection package should not be sold as mandatory to everyone.
Building a smart plan around the injection
PRP is not a stand-alone fix. The best results come when you pair the biologic nudge with mechanical reality: strength, mobility, and load management. After the first week, begin a light range-of-motion routine and gradually layer in closed-chain exercises. I aim for two to three sessions per week of targeted work for the first month, not daily marathons. The quad, posterior chain, and calf complex all share the knee’s job. Do not neglect the hip abductors and external rotators, which govern knee valgus in single-leg tasks.
Footwear matters. Patients who switch from worn-out shoes to a supportive pair, or who use a mild medial wedge for valgus collapse, often feel the PRP benefits more clearly because the knee is not fighting poor mechanics.
Weight management deserves a frank mention. Every pound off the scale reduces knee joint reaction forces by several pounds during gait. No injection can fully counteract the physics of load. Many patients use the pain relief window after PRP to regain capacity for brisk walking or cycling, which supports gradual weight loss. That is the synergy to target.
Safety, side effects, and real risks
PRP is generally safe because it is autologous. The most common side effect is a transient pain flare for one to three days. Bruising at the draw site or injection site happens, usually minor. Infection is rare but not zero. Any expanding redness, fever, or severe swelling should prompt a call to the clinic. Allergic reactions are uncommon because the injectate is your own plasma, though sensitivities can occur to antiseptics or bandage adhesives.
There are edge cases. Patients with platelet disorders, uncontrolled diabetes, active cancer, or severe anemia may not be good candidates. Anticoagulation increases bleeding risk. Immunosuppressed patients may heal unpredictably. Discuss your full medication list and health history with the clinician. A good clinic will decline or delay the procedure if safety is questionable.
Costs, insurance, and the value equation
In many countries PRP injection therapy is not covered by standard insurance for knee osteoarthritis. Out-of-pocket prices range widely. I have seen quotes from a few hundred dollars to over two thousand per session depending on the city, the kit, and the practice’s approach. Beware of prices that are suspiciously low or high, and ask what is included: consultation, ultrasound, post-injection follow-up, and whether a series discount locks you into a schedule before you know your individual response.
Value depends on relief, duration, and what you reclaim. If a $900 PRP procedure gives a year of easier walking, fewer missed workouts, and less need for pain medication, many patients see that as a good trade. Others prefer to try hyaluronic acid first, often covered, and reserve PRP as a second line. There is no one correct financial choice. An honest clinic will lay out options without hard selling.
How PRP interacts with other therapies
Some patients come in on the heels of a steroid injection that helped for two months. Most clinicians ask for a gap of 6 to 12 weeks after a cortisone injection before performing PRP. Nonsteroidals should be paused around the injection window as noted earlier. Supplements like turmeric, fish oil, or collagen do not seem to alter outcomes meaningfully, but if you are on high doses of any anti-inflammatory supplement, discuss timing.
Braces and offloading can complement PRP, especially in unicompartmental osteoarthritis. An unloader brace for medial compartment OA can amplify relief by shifting forces. Taping techniques serve as a lighter touch for activity days. Physical therapy is not optional. Coupling PRP’s biologic window with skilled rehab often determines whether relief translates into lasting function.
Sorting marketing claims from evidence
You will encounter glossy promises: PRP regenerative injection restores cartilage, PRP joint restoration reverses arthritis, PRP total rejuvenation. The sober truth is that MRI or ultrasound sometimes shows small improvements in cartilage quality or synovial environment, but wholesale regeneration is not the typical result. The proven benefits are reduction in pain, improved function, and reduced inflammatory flares in appropriate candidates. That is still valuable.
Ask for specifics. How many PRP knee cases does the clinician perform each month? Do they use platelet rich plasma therapy with ultrasound guidance? Which preparation, leukocyte-poor or rich, and why for your case? What percentage of their last 50 similar patients saw a meaningful improvement at 3 months? Good clinicians track outcomes and speak in numbers, not slogans.
A brief word on PRP beyond the knee
PRP’s popularity in aesthetics has some patients curious about double-duty sessions. It is common to see PRP for face and PRP skin rejuvenation marketed alongside orthopedic services. Techniques such as PRP facial, PRP skin treatment for acne scars, PRP for under eyes and dark circles, and PRP for wrinkles pursue collagen remodeling. PRP for hair loss and PRP hair restoration apply small volumes to the scalp to stimulate follicles. None of that should distract from the orthopedic indication. If a clinic offers both medical therapy and cosmetic therapy, ensure the orthopedic program stands on its own with appropriate protocols, not as a side offering. Combining same-day facial PRP with a knee injection is usually unnecessary and sometimes unwise, as it draws on the same blood sample and complicates dosing.
A grounded way to decide
The decision to pursue a PRP procedure for knee pain should balance medical fit, life timing, and tolerance for uncertainty. If you are in the sweet spot of mild to moderate osteoarthritis or persistent tendinopathy, if you have already worked on strength and load without enough relief, and if you prefer a non surgical treatment while you keep options open down the road, PRP is reasonable to trial. Plan for a flare, clear your schedule for a few light days, and commit to the rehab plan. If you expect an instant fix or a cure for bone-on-bone wear, it will disappoint you.
Over the years I have watched retirees get back to nine holes and parents get back to sideline soccer without a folding chair. I have also watched knees that refused to budge after a well-done PRP injection. The difference often came down to selection and execution. When the pieces line up, the gains feel like getting a key back to a door you thought was jammed for good.
A concise checklist to bring to your consultation
- Ask which PRP system is used, its typical platelet concentration, and whether it is leukocyte-poor or leukocyte-rich for your indication. Confirm ultrasound guidance for the injection and who performs it. Clarify the number of sessions planned, spacing, and the criteria for repeating. Review medication holds, especially NSAIDs and anticoagulants, plus aftercare activity rules. Discuss costs in detail, including follow-up and what success or failure will look like at 4, 8, and 12 weeks.
What success looks like over the year
At one month, you should notice less morning stiffness and a little more confidence on stairs. By three months, you should be able to name activities that feel easier and track fewer pain spikes. If you keep a log, expect a 20 to 50 percent drop in worst pain scores for responders, and an uptick in daily step counts or cycling minutes. By six months, benefits stabilize. If you had a partial response, a second platelet therapy injection can extend gains. If you had no response, it is time to pivot: consider hyaluronic acid, bracing, gait retraining, or a surgical consult for alignment or cartilage issues.
The aim is not perfection, it is capacity. PRP is a biologic rehearse button for a joint that still has something to give. When aligned with smart rehab and realistic expectations, it can turn a knee from a daily adversary into a manageable teammate. That shift, for many people, is the difference between guarding every step and getting back to a life that moves.