PRP for knee osteoarthritis: what do placebo-controlled trials show?

Polish version: PRP w chorobie zwyrodnieniowej kolana — co pokazuje metaanaliza badań z placebo?

A meta-analysis and meta-regression published on 17 August 2026 in Knee Surgery, Sports Traumatology, Arthroscopy examined not only whether platelet-rich plasma (PRP) benefits knee osteoarthritis, but which patient and preparation characteristics might influence outcomes. Only placebo-controlled randomized trials were included.

Why this study matters

PRP is not a single standardised product. Preparations differ in platelet concentration, leukocyte content, activation, volume and number of injections. These differences limit extrapolation from one preparation system to another. The authors investigated whether age and PRP characteristics could explain some of the heterogeneity.

Review methods

Three databases were searched through 25 May 2025 for placebo-controlled RCTs of intra-articular PRP in knee osteoarthritis. Pain and function were assessed at 6 and 12 months. Twenty studies included 26 PRP groups with 1,774 patients and 20 placebo groups with 1,518 patients. Random-effects meta-analysis was followed by meta-regression using patient-related and preparation-related variables.

Main results

PRP was associated with significantly better pain and function than placebo at both 6 and 12 months. The authors described the effect as large, while rating the certainty of evidence as very low.

At 6 months, younger age, a higher platelet enrichment factor and calcium chloride activation were associated with better outcomes. Leukocyte-rich PRP was associated with better knee function. At 12 months, none of the assessed moderators explained the PRP advantage.

Preparation characteristics were not independent: PRP type and platelet concentration were correlated, limiting attribution of effects to any single parameter.

Clinical interpretation for an orthopaedic surgeon

The label “PRP” is insufficiently precise when products differ biologically. Variation in composition may contribute to variation in clinical outcomes. The age association is plausible but does not define an eligibility threshold: younger patients may also have less advanced disease, different activity levels or a different biological profile. Study-level meta-regression cannot separate these relationships as reliably as direct randomized comparisons of tightly standardised products.

Limitations

• Certainty in the benefit over placebo was very low.
• Meta-regression identifies associations between study characteristics and outcomes, not causation.
• Correlated preparation parameters prevent identification of a single optimal ingredient.
• PRP characteristics were inconsistently and incompletely reported.
• Moderators explained some differences at 6 months but not at 12 months.

Implications for practice

The findings support more detailed reporting of PRP composition in research and clinical records, with interpretation in the context of age and patient phenotype. They do not yet justify routinely preferring leukocyte-rich PRP or calcium chloride activation.

The study does not establish LR-PRP as superior to LP-PRP for an individual patient, identify an optimal platelet concentration or support automatic eligibility based on younger age. These are hypotheses requiring direct, well-standardised comparisons.

References

Delgado D, Andrade R, Gomes E, Lopes T, Azofra J, Espregueira-Mendes J, Sánchez M. Younger age and platelet-rich plasma characteristics influence short-term outcomes in knee osteoarthritis, but independent effects remain uncertain: A systematic review with meta-analysis and meta-regression of placebo-controlled randomised trials. Knee Surg Sports Traumatol Arthrosc. 2026 Aug 17. DOI: 10.1002/ksa.70567. PubMed.

This summary is based on the publicly available abstract and publication metadata.

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Content prepared by: Tomasz Poboży - orthopaedic surgeon.