PRP injections for knee OA – do they work?

29th November 2021, Dr Chee L Khoo

Knee osteoarthritis

If you are over 50 years old, there is no Medicare rebate for an MRI of the knee. They won’t do a “clean out” arthroscopy for symptom relief even if you have significant pain requiring opioids because the symptom relief is only temporary and you will end up needing a total knee replacement anyway. Oh, by the way, they frown on you if you leave them on opioids for more than 12 months. In the old days, your patients have to earn the right for a joint replacement which means you have to suffer enough. Really? Remember, they took our rebate away for corticosteroid injections some years ago but they will pay the radiologist a lot more if we refer. The relief from these injections may or may not last long. Will a platelet rich plasma injection work better?

Experts continue to debate the usefulness of intra-articular corticosteroid (ICS) injections and each come to a different conclusion. Nonetheless, ICS injections have been widely used for decades to treat knee OA. In theory, steroids act as local anti-inflammatory medications and are thought to counteract the inflammatory processes by altering T- and B-cell immune function [1,2]. Synthetic corticosteroids exhibit more anti-inflammatory effect than their native counterparts, and methylprednisolone acetate and triamcinolone are the most commonly used ICS for knee OA.

A recent Cochrane review regarding ICS for knee OA assessed 27 low-quality and heterogeneous RCT’s that included 1767 patients [1]. One month post-injection, pain scores in the ICS group compared to placebo improved by only 1.0 cm on the 10‐cm visual analogue scale (VAS score), corresponding to a number needed to treat of 8 (95% CI 6–13). Furthermore, at 13 weeks, steroid injections provided an even smaller benefit in pain control, and the effect was absent by 26 weeks. The Cochrane review also used the Western Ontario and McMaster Universities Arthritis Index (WOMAC) to assess function after ICS injection. Overall, a moderate improvement at 1-2 weeks was detected, but the effect declined by 4–6 weeks and was all gone by 13 weeks.

What about the fancy PRP injections? The clinical safety or efficacy on pain decrease and function promotion of platelet rich plasma (PRP) is still controversial, especially compared with other traditional conservative therapy, including oral NSAIDs, intra-articular ICS or hyaluronic acid, and even placebo. PRP concentrates a high number of platelets in a small volume of plasma, and it is prepared by centrifugation of autologous blood [3]. Generally, PRP is prepared with two centrifugations, including separating erythrocytes in the first spin and concentrating platelets from the second spin [4,5]. Intra-articular injection of PRP has occurred as a disease modification therapy in recent years since it had been proved as a simple, low-cost, and minimally invasive therapy that provides a natural concentrate of autologous blood growth factors that can be used to enhance tissue regeneration [4].

Some systematic reviews reported favourable pain and function outcomes associated with PRP compared with saline or hyaluronic acid (6) and suggested that benefit was greatest in patients with mild to moderate radiographic disease. However, clinical trials of efficacy to date have been limited by a high risk of bias in PRP trials, particularly lack of blinding.

A recent randomised, 2-group, placebo-controlled, participant-, injector-, and assessor-blinded clinical trial enrolled community-based participants (n = 288) aged 50 years or older with symptomatic medial knee OA in Sydney and Melbourne from August 2017 to July 2019 (6). The 12-month follow-up was completed on July 22, 2020. Interventions involved 3 intra-articular injections at weekly intervals of either leukocyte-poor PRP using a commercially available product (n = 144 participants) or saline placebo (n = 144 participants)

Among 288 patients with symptomatic mild to moderate radiographic knee OA, intra-articular injection of PRP, compared with injection of saline placebo, did not result in a significant difference in symptoms or joint structure at 12 months. These findings do not support use of PRP for the management of knee OA.

Analyses showed that the PRP preparation used in this study contained elevated concentrations of growth factors and cytokines that promote tissue healing and inhibit inflammatory processes, proposed mechanisms by which PRP achieves its effects. Yet, despite elevated concentrations of these “active ingredients,” symptom and structural benefits were not evident.

In randomised trial to compare physical therapy with glucocorticoid injection in the primary care setting in the U.S. Military Health System, patients with osteoarthritis of the knee who underwent physical therapy had less pain and functional disability at 1 year than patients who received an intraarticular glucocorticoid injection (5).

Well, back to physiotherapy then.


  1. P. Juni, R. Hari, A. W. Rutjes et al., “Intra-articular corticosteroid for knee osteoarthritis,” Cochrane Database Systematic Reviews, vol. 10, 2015.
  2. A. Jones and M. Doherty, “Intra-articular corticosteroids are effective in osteoarthritis but there are no clinical predictors of response,” Annals of the Rheumatic Diseases, vol. 55, no. 11, pp. 829–832, 1996.
  3. G. Kavadar, D. T. Demircioglu, M. Y. Celik, and T. Y. Emre, “Effectiveness of platelet-rich plasma in the treatment of moderate knee osteoarthritis: a randomized prospective study,” Journal of Physical Therapy Science, vol. 27, no. 12, pp. 3863–3867, 2015.
  4. G. Filardo, E. Kon, R. Buda et al., “Platelet-rich plasma intra-articular knee injections for the treatment of degenerative cartilage lesions and osteoarthritis,” Knee Surgery, Sports Traumatology, Arthroscopy, vol. 19, no. 4, pp. 528–535, 2011.
  5. Deyle GD, Allen CS, Allison SC, Gill NW, Hando BR, Petersen EJ, Dusenberry DI, Rhon DI. Physical Therapy versus Glucocorticoid Injection for Osteoarthritis of the Knee. N Engl J Med. 2020 Apr 9;382(15):1420-1429. doi: 10.1056/NEJMoa1905877. PMID: 32268027.
  6. 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