Older patient with knee osteoarthritis in a rehabilitation setting

All Completed Studies Peer-Reviewed · Published 2025

Journal of Clinical Orthopaedics & Trauma

Polyacrylamide Hydrogel
for Knee Osteoarthritis.

A PROMs-based prospective cohort study following 314 osteoarthritic knees for two years after polyacrylamide hydrogel (PAAG) injection — moving beyond “does it work?” to the question that matters in clinic: who benefits most.

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314

Knees Treated

Months Follow-Up

269

Patients Enrolled

Why This Study Was Needed

Not whether PAAG works — but who it works for.

Intra-articular polyacrylamide hydrogel is already known to be safe and effective in knee osteoarthritis. What the literature lacked was clear guidance on patient selection — which individuals stand to gain the most durable benefit from this minimally invasive, cartilage-sparing alternative to early surgery.

Which patient factors allow PAAG to deliver the greatest, most durable clinical benefit in knee osteoarthritis?

Measured with three validated PROMs

Visual Analogue Score

Pain intensity, tracked from baseline to 24 months.

Oxford Knee Score

Function and pain in daily activity, a core arthroplasty PROM.

Lysholm Score

Knee-specific function, stability and activity tolerance.

Four factors predict durable improvement.

Older age

Each additional year of age modestly raised the odds of reaching MCID across all three scores.

Lower OA grade

Knees with a lower Kellgren–Lawrence grade responded far more reliably than advanced disease.

No diabetes

Non-diabetic patients were more than twice as likely to achieve meaningful improvement.

Bilateral OA

Bilateral rather than unilateral knee OA nearly doubled the odds of reaching MCID.

Physical therapist working on a patient's knee

Reported In Full

Two years of real-world data.

Symptoms improved over 24 months, most consistently in older, non-diabetic patients with lower-grade disease.

Key Insight

Disease severity cut both ways — higher-grade osteoarthritis both predicted a poorer PAAG responseand strongly predicted eventual total knee replacement (b = 0·97, p < 0·001).

314

Knees Treated with PAAG

Across 269 patients recruited from clinics in Lincoln and London.

Progressed to TKR

Over two years — concentrated in patients with higher-grade osteoarthritis.

155 / 314

Knees Developed Complications

Transparently recorded across the cohort. The authors note the absence of a control group and a limited set of outcome measures, and call for further studies to validate efficacy, refine patient selection, and evaluate long-term impact.

Why It Matters Clinically

Better selection, better outcomes.

Gives clinicians an evidence-based profile of the knee OA patient most likely to benefit from PAAG.
Supports shared decision-making — setting realistic expectations for higher-grade disease.
Positions PAAG as a minimally invasive, joint-preserving option that can defer or avoid surgery in suitable patients.
Adds two-year, patient-reported real-world evidence to a treatment area where long-term data is scarce.

Published evidence — not assumption.

These findings sharpen patient selection for injection therapy and feed directly into how MSK Doctors sequences regenerative and joint-preserving care.