Osteoarthritis of the knee is the result of progressive deterioration of the articular cartilage and menisci of the joint. Articular cartilage deteriorates because of trauma and wear and tear. This leads to exposure of the bone surface. Symptoms include pain, stiffness, swelling and difficulty walking.
Considering the evidence, PRP therapy is a minimally invasive injection procedure that appears to be safe and effective. Since PRP injections biologically change the articular cartilage, they may be a worthwhile treatment option even in moderate knee osteoarthritis. Further studies are required with larger sample sizes with longer follow-ups and objective outcome measures.
Treatment depends on the severity of the osteoarthritis. Conservative treatments include analgesics and corticosteroid injections to relieve pain and inflammation, and physiotherapy and prescribed exercise to improve function and mobility. When symptoms are severe, surgery may be indicated: options include upper tibial osteotomy and unicompartmental or total knee replacement.
Platelet-rich plasma injections aim to promote cartilage repair and relieve osteoarthritic symptoms, potentially delaying the need for joint replacement surgery. Platelets produce growth factors that are thought to stimulate chondrocyte proliferation, leading to cartilage repair.
Platelet-rich plasma (PRP) is an autologous concentration of a high number of platelets in a small volume of plasma. Platelets contain significant amounts of cytokines and growth factors which are capable of stimulating cellular growth, vascularization, proliferation, tissue regeneration, and collagen synthesis. Delivery of high concentrations of cytokines and GFs to damaged tissues by PRP is considered to have a beneficial effect on tendon and cartilage tissue regeneration.
Blood is taken from the patient and centrifuged to obtain a concentrated suspension of platelets. Platelet-rich plasma can be prepared by carrying out 2 spin cycles using a standard bench-top centrifuge, or by using commercially available single-step preparation systems. Different preparation methods may affect the concentration of platelets. Agents such as calcium chloride may be added to activate the platelets. The final platelet-rich plasma product is injected into the joint space in the knee, usually under ultrasound guidance.
A meta-analysis in a systematic review of 16 studies, including 1543 patients, pooled International Knee Documentation Committee (IKDC), WOMAC and Knee Injury and Osteoarthritis Outcome Score (KOOS) scales to compare knee function scores before platelet-rich plasma treatment against scores after treatment. The study reported an overall standardized mean difference, at 12 months, of 2.9 in favour of post-treatment scores.
In a randomised controlled trial of 120 patients treated by platelet-rich plasma (n=60) or hyaluronic acid injections (n=60), mean total WOMAC scores (ranging from 0 to 96 with lower scores indicating better outcomes) improved from 79.6 to 36.5 in the platelet-rich plasma group (p<0.01) and from 75.4 to 65.1 in the hyaluronic acid group (p<0.01) at 6‑month follow-up. Improvements were greater in the platelet-rich plasma group (p<0.001).
A randomized prospective study conducted in Turkey included a total of 102 patients with grade 3 knee OA, randomly divided into three groups: Group 1 received a single injection of PRP, Group 2 received two injections of PRP two weeks apart, Group 3 received three injections of PRP at 2-weeks intervals. One of the major results of this study was the effectiveness of PRP treatment for pain and physical function in grade 3 knee OA. However, the effectiveness of a single injection was found to be significantly lower than that of two or three injections. In this study, during the follow-up period, significant improvements were observed in the VAS, WOMAC and TUG values of all of the three groups compared to their pre-injection values, and they showed a tendency of gradual decrease over time.
Despite poorer results, patients with advanced OA still benefit from PRP. In a comparative study of PRP and hyaluronic acid (HA) in grade 1–3 knee OA, the PRP group showed significantly better results after 6 months and the worst results were observed in HA-treated subjects with grade 3 knee OA). Kon et al. speculate that additional biological mechanisms, not currently known, are responsible for the improvement of OA symptoms after PRP treatment). In the advanced stages of OA, PRP might not have a direct effect on the chondrocyte anabolic process, but an anti-inflammatory effect through the regulation of joint homeostasis and the cytokine level.
Outcome measures include improvements in pain relief, knee function scores, delaying the need for knee replacements (arthroplasty), and radiographic, MRI or arthroscopic evidence of improvement in osteoarthritis of the knee.
PRP therapy is generally a safe procedure and complications are rare. Pain and stiffness in the knee, which lasted for up to 2 days, have been reported following PRP therapy for knee osteoarthritis. Mild swelling of the knee can also occur but this usually settles within a couple of weeks. Infection, bleeding and nerve injury are rare complications.
The National Institute of Clinical Excellence noted in 2014 that there were many published trials and also systematic reviews that assessed platelet-rich plasma injections for osteoarthritis of the knee. However, the Committee considered that the heterogeneous patient populations, variations in treatment techniques and inconsistencies in the findings of these studies meant that the evidence was inadequate to be confident about the procedure’s efficacy. In making this judgement the Committee was mindful that osteoarthritis of the knee is very common and robust evidence is therefore necessary.