Estimated Time to Maximum Medical Improvement of Intra-articular Injections in the Treatment of Knee Osteoarthritis-A Systematic Review

Arthroscopy. 2022 Mar;38(3):980-988.e4. doi: 10.1016/j.arthro.2021.08.026. Epub 2021 Aug 27.


Purpose: The purpose of the current study is to perform a systematic review of the literature and evaluate maximum medical improvement and minimal clinically important difference (MCID) of different injectables in the treatment of symptomatic knee osteoarthritis.

Methods: A systematic review was performed to evaluate maximum medical improvement and MCID in patients undergoing injections of different modalities for knee osteoarthritis. Demographic factors of the patients being reviewed were analyzed, with patient-reported outcomes as reported by visual analog scale (VAS) and Western Ontario and McMaster Universities Arthritis Index (WOMAC) being used to evaluate the clinical trajectory of patients receiving intra-articular injections.

Results: Overall, 79 (level of evidence I: 79) studies met inclusion criteria, with 8761 patients. Corticosteroid (CS) injections, middle molecular weight hyaluronic acid (MMW-HA), and leukocyte-rich platelet rich plasma (LR-PRP) injections reached their maximum pain control at 4 to 6 weeks after injection, as measured by VAS. The lowest VAS scores were reached for low molecular weight hyaluronic acid (LMW-HA), high molecular weight hyaluronic acid (HMW-HA), and leukocyte-poor platelet rich plasma (LP-PRP) by 3 months after injection. Similarly, the WOMAC scores were lowest at 4 to 6 weeks after CS and MMW-HA injections, and at 3 months after HMW-HA and LP-PRP injections. LR-PRP demonstrated the most prolonged pain relief relative to the other injection types, with the lowest VAS score of all groups measured at final follow-up. LP-PRP showed the lowest WOMAC scores at final follow-up, one year post-injection.

Conclusion: PRP injections provide continued pain relief at up to 1 year after injection. Corticosteroids and hyaluronic acid have good efficacy and are suitable for many patients but lack this longevity.

Level of evidence: Level I, a systematic review of Level I studies.

Publication types

  • Review
  • Systematic Review

MeSH terms

  • Humans
  • Hyaluronic Acid
  • Injections, Intra-Articular
  • Osteoarthritis, Knee* / drug therapy
  • Platelet-Rich Plasma*
  • Treatment Outcome


  • Hyaluronic Acid