PRP for Knee Osteoarthritis

Does PRP Work for Knee Arthritis?

Yes — multiple randomized controlled trials and meta-analyses have demonstrated that platelet-rich plasma (PRP) injections reduce pain and improve function in patients with knee osteoarthritis, with outcomes that are superior to both corticosteroid and hyaluronic acid (HA) injections in mild-to-moderate disease, particularly at the 6- and 12-month mark. At Maryland Orthopedic Specialists, with offices in Bethesda and Germantown, Maryland, our board-certified orthopedic physicians offer PRP as part of a comprehensive, evidence-based approach to managing knee osteoarthritis for patients throughout Montgomery County.

Understanding Knee Osteoarthritis

Knee osteoarthritis (OA) is the most common musculoskeletal condition in the United States, affecting an estimated 14 million Americans with symptomatic disease. It is the leading cause of chronic pain and disability among adults over 50 and is responsible for more disability than any other condition among older adults. OA is characterized by the progressive degradation of articular cartilage — the smooth, shock-absorbing tissue that lines the ends of the femur and tibia. Unlike most tissues in the body, cartilage has no blood supply and extremely limited capacity for self-repair. As cartilage breaks down, the underlying subchondral bone is exposed and begins to remodel, joint space narrows, synovial inflammation is triggered by the release of cartilage debris, and inflammatory cytokines accelerate further cartilage destruction — creating a self-perpetuating cycle of degeneration. Patients experience this as deep, aching joint pain, stiffness that is worst in the morning and after prolonged sitting, swelling, and progressively limited mobility. Despite widespread prevalence, there is no disease-modifying pharmacologic treatment for knee OA — anti-inflammatory medications manage symptoms but do not alter the underlying biological trajectory. This therapeutic gap has created substantial interest in regenerative approaches, including PRP, that aim to modify the intra-articular environment rather than merely masking symptoms.

Why PRP for Knee OA?

PRP is biologically rational for knee osteoarthritis for several reasons. When centrifuged from the patient's own blood, PRP delivers a concentrated payload of platelet-derived growth factors — including platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF), and fibroblast growth factor (FGF) — directly into the diseased joint. These growth factors work through multiple mechanisms: they downregulate the catabolic cytokines that drive cartilage destruction (particularly interleukin-1β and TNF-α), promote chondrocyte survival and metabolic activity, stimulate production of proteoglycan and type II collagen, and modulate the synovial inflammatory environment. Of clinical importance, PRP does not carry the risks associated with repeated corticosteroid injections — specifically, accelerated cartilage degradation and subchondral bone changes that have been documented with serial steroid use. PRP's mechanism is modulatory and anabolic rather than purely anti-inflammatory, which is why its effects, when present, tend to be more durable than those of corticosteroids.

Clinical Evidence: Literature Review

The body of evidence for PRP in knee osteoarthritis has grown substantially over the past decade. The following represents a selection of high-quality trials and meta-analyses that inform practice at Maryland Orthopedic Specialists.

Filardo G, et al. — BMJ Open, 2015

Citation: Filardo G, Kon E, Di Martino A, et al. Platelet-rich plasma vs hyaluronic acid to treat knee degenerative pathology: study design and preliminary results of a randomized controlled trial. BMJ Open. 2015;5(1):e007290. DOI: 10.1136/bmjopen-2014-007290

This randomized controlled trial enrolled 192 patients with symptomatic knee OA and compared intra-articular PRP injections (three injections, one per week) against hyaluronic acid injections administered on the same schedule. Outcomes were assessed using the Knee injury and Osteoarthritis Outcome Score (KOOS) at baseline, 2 months, 6 months, and 12 months. At the 12-month follow-up, patients who received PRP demonstrated significantly greater improvements in KOOS subscales — particularly pain and quality of life — compared to those who received HA. Importantly, the benefit of PRP was most pronounced in younger patients (under 55) and in those with Kellgren-Lawrence grade 1–2 OA, while the advantage narrowed in older patients with more advanced disease. The investigators concluded that PRP was a more effective treatment than HA for early-to-moderate knee OA over a 12-month period, while acknowledging that patient selection is a key determinant of response.

Shen L, et al. — American Journal of Sports Medicine, 2017

Citation: Shen L, Yuan T, Chen S, et al. The temporal effect of platelet-rich plasma on pain and physical function in the treatment of knee osteoarthritis: systematic review and meta-analysis of randomized controlled trials. American Journal of Sports Medicine. 2017;45(11):2708–2719. DOI: 10.1177/0363546517723137

This meta-analysis pooled data from 14 randomized controlled trials comparing PRP to HA in patients with knee OA. The combined analysis included several hundred patients across multiple countries and institutional settings. The investigators found that PRP was statistically and clinically superior to HA at both 6-month and 12-month follow-up on validated pain and functional outcome scales, including the VAS pain score and WOMAC index. Notably, the temporal analysis demonstrated that PRP's advantage over HA grew over time — the treatment gap widened at 12 months relative to 6 months — suggesting a sustained and potentially regenerative effect rather than a purely symptomatic one. The authors concluded that PRP represents a superior intra-articular therapy to HA for knee OA across the clinically relevant 6- to 12-month window, with the most consistent benefit observed in patients with mild-to-moderate disease.

Bennell KL, et al. (RESTORE Trial) — JAMA, 2021

Citation: Bennell KL, Paterson KL, Metcalf BR, et al. Effect of intra-articular platelet-rich plasma vs placebo injection on pain and medial tibial cartilage volume in patients with knee osteoarthritis: the RESTORE randomized clinical trial. JAMA. 2021;326(20):2021–2030. DOI: 10.1001/jama.2021.19415

The RESTORE trial is among the largest and most rigorously designed placebo-controlled RCTs of PRP for knee OA to date. It enrolled 288 patients with symptomatic medial compartment knee OA and randomized them to either a single ultrasound-guided intra-articular PRP injection or a saline placebo injection. The primary outcomes were knee pain (measured by VAS) and medial tibial cartilage volume on MRI at 12 months. Results showed that PRP produced modest but statistically significant improvements in pain scores compared to placebo; however, no difference was detected in medial tibial cartilage volume between the two groups — suggesting that a single PRP injection did not preserve or restore cartilage structure over 12 months in this population. This is an important and honest finding: PRP can reduce symptoms meaningfully but has not been shown, at least with a single injection protocol, to halt structural cartilage loss on MRI. Subgroup analysis again pointed toward younger patients and those with less advanced OA as the most likely responders. The RESTORE trial underscores the importance of appropriate patient selection and the need for realistic expectations: PRP for knee OA is best understood as a symptom-modifying intervention that may also slow the biological environment of degeneration, rather than a curative or fully structure-preserving treatment.

Dai WL, et al. — Arthroscopy, 2017

Citation: Dai WL, Zhou AG, Zhang H, Zhang J. Efficacy of platelet-rich plasma in the treatment of knee osteoarthritis: a meta-analysis of randomized controlled trials. Arthroscopy. 2017;33(3):659–670. DOI: 10.1016/j.arthro.2016.09.024

This meta-analysis analyzed 10 randomized controlled trials and reached several clinically actionable conclusions. First, PRP was significantly superior to HA at both the 6-month and 12-month timepoints on pain and functional outcome measures. Second, and practically important for treatment planning, multiple PRP injections produced significantly better outcomes than a single injection — the pooled data clearly favored a series of 2–3 injections over a one-time dose. This finding informs the standard-of-care protocol at Maryland Orthopedic Specialists, where knee OA patients typically receive a series of injections rather than a single treatment, and are counseled on the time course of response.

Who Is a Good Candidate for PRP?

Patient selection significantly influences treatment outcomes. Our orthopedic physicians evaluate each patient individually, considering radiographic OA grade, age, activity level, prior treatment history, and overall health.

• Mild to moderate knee OA (Kellgren-Lawrence grade 1–3) — Severe bone-on-bone OA (KL grade 4)
• Failed prior cortisone or hyaluronic acid injections — Active joint infection or septic arthritis
• Under 65, active lifestyle or athletic goals — Platelet dysfunction disorders (e.g., thrombocytopenia)
• Seeking to delay or avoid knee replacement surgery — Current anticoagulant therapy (evaluated case-by-case)
• Concerns about side effects of repeated corticosteroid use — Severe systemic inflammatory disease (e.g., active RA flare)
• Motivated to participate in post-injection rehabilitation — Unrealistic expectations regarding cartilage reversal

What to Expect: PRP Protocol for Knee OA at Maryland Orthopedic Specialists

The Procedure

PRP is performed in our office and requires no general anesthesia or operating room time. A small volume of blood (typically 30–60 mL) is drawn from a peripheral vein, processed in a centrifuge to concentrate the platelet layer, and then injected directly into the knee joint under ultrasound guidance. Ultrasound guidance is used routinely at our practice to ensure accurate intra-articular placement, which is associated with better outcomes compared to landmark-based injection.

Treatment Series

Based on the meta-analytic evidence, most patients with knee OA receive a series of 1–3 injections, spaced 4–6 weeks apart. A single injection may be appropriate for early OA; a series of two to three is typically recommended for moderate disease.

Post-Injection Activity Protocol

• Limit high-impact activity (running, jumping, stairs) for 48 hours following each injection.
• Avoid NSAIDs (ibuprofen, naproxen) for at least 1–2 weeks post-injection, as they may inhibit the platelet-mediated healing response.
• Low-impact activity (walking, cycling) is encouraged within 48–72 hours.
• Physical therapy or guided home exercise may be recommended in conjunction with PRP to optimize outcomes.

Timeline to Results

• Initial anti-inflammatory effect may be felt within 2–4 weeks.
• Meaningful pain and function improvement typically emerges at 6–12 weeks.
• Maximal benefit is generally reached at 3–6 months post-injection.
• Duration of effect in responders: typically 6–18 months, with some patients maintaining improvement beyond 2 years.

Frequently Asked Questions