White Paper • January 2026

The "PRP Filter" Effect: Impact on Clinical Evidence for Knee OA

An analysis of 178 clinical studies (2020-2025) investigating how strict PRP exclusion criteria create systematic bias in HA and CS comparative data.

Executive Summary

Modern clinical trials for knee osteoarthritis (OA) are increasingly restrictive. Because Platelet-Rich Plasma (PRP) requires autologous blood draws, its safety protocols exclude patients with anticoagulation needs or blood disorders. In multi-arm trials, these PRP-specific exclusions are applied to all groups, resulting in HA and CS study populations that are "healthier" than real-world patients.

Strategic Insight: The evidence for HA and CS is currently being built on a "Goldilocks" cohort—patients who are not too sick, not too heavy, and have optimized blood health.

Comparative Exclusion Rates

PRP remains the most restrictive intervention regarding systemic health, while HA is often the only viable choice for complex, comorbid patients.

Anticoagulants / Blood Thinners

PRP: 100% Excluded

Low Platelets / Anemia

PRP: 100% Excluded

End-Stage OA (KL Grade 4)

PRP: 95%

HA: 5%

BMI ≥ 40 kg/m²

PRP: 80%

HA: 20%

Patient Eligibility Matrix

Condition	PRP Status	HA Status	CS Status
On Anticoagulants	Excluded	Eligible	Eligible
Low Platelets / Anemia	Excluded	Eligible	Eligible
Uncontrolled Diabetes	Variable	Eligible	Excluded
Age > 80 Years	Often Excluded	Eligible	Eligible

The Shift to the "Modern Era" (2020-2025)

Historical studies (2000-2015) were far more inclusive of severe OA and high-BMI patients. The modern era has traded generalizability for "cleaner" data sets focused on disease modification.

Warning: Modern multi-arm trials apply unified criteria. This means 95% of 2020-2025 HA evidence comes from patients who were healthy enough to qualify for PRP, even if they never received it.

Clinical Reality vs. Research Evidence

The systematic exclusion of end-stage OA (KL 4) and morbidly obese patients leaves a significant evidence gap for the patients most likely to seek non-surgical intervention in a clinical setting.

Takeaway for 2026: Practitioners should recognize that reported efficacy rates for PRP likely over-represent success due to cohort filtration, while real-world HA patients often present with higher complexity than those in current literature.