Platelet-Rich Plasma (PRP) Injection

Platelet-rich plasma (PRP) is a newer modality of treatment available for a few years for the management of a number of orthopaedic conditions including sport injuries. 

Although blood is mainly a liquid (called plasma), it also contains small solid components.  The major solid components of blood are red blood cells (RBC), white blood cells (WBC), and platelets. Whilst platelets, which are small discoid blood cells with granules, are best known for their importance in blood clotting, they also contain hundreds of proteins called growth factors which are released during the healing process. On activation, the platelets accelerate the inflammatory cascade as well as healing by the release of the granules containing growth factors. Platelets have an average lifespan of 7–10 days. A normal blood specimen contains only 6% platelets whereas platelet rich plasma (PRP) contains a much higher concentration of platelets.  

Mechanism of Action of PRP

Although it is not exactly clear how PRP works, laboratory studies have shown that the increased concentration of growth factors in PRP can potentially speed up the healing process.

Indications for PRP Injection

A PRP injection is generally recommended in the treatment of tendon or muscle injuries with a success rate of quoted in the region of 70-80%, though four to six weeks may be required for complete healing, and often a second injection at 4 weeks is recommended.

Certain factors can influence the effectiveness of PRP treatment including:

• The area of the body being treated
• The overall health of the patient
• Whether the injury is acute (such as from a fall) or chronic (an injury developing over time)
• Use of anti-inflammatory medications (these should usually be ceased at least 7 days prior to the initial treatment, and not recommenced until at least 4 weeks after treatment.

Chronic Tendon Injuries

According to the research studies currently reported, PRP is most effective in the treatment of chronic tendon injuries, especially tennis elbow, a very common injury of the tendons on the outside of the elbow.  It has also been used for partial abductor (gluteal) tendon tears of the hip, proximal hamstring partial tears from the ischium (pelvis), chronic Achilles tendonitis, and patellar tendon inflammation (“jumper’s knee”).

Acute Ligament and Muscle Injuries

Much of the publicity PRP therapy has received has been about the treatment of acute sports injuries, such as ligament and muscle injuries. PRP has been used to treat professional athletes with common sports injuries like pulled hamstring muscles in the thigh and knee sprains. There is no definitive scientific evidence, however, that PRP therapy actually improves the healing process in these types of injuries, but there are anecdotal reports of responses.

Surgery

More recently, PRP has been used during certain types of surgery to help tissues heal. It was first thought to be beneficial in shoulder surgery to repair torn rotator cuff tendons. However, the results so far have shown little or no benefit when PRP is used in these types of surgical procedures. Surgery to repair torn knee ligaments, especially the anterior cruciate ligament (ACL) is another area where PRP has been applied. At this time, there appears to be little or no benefit from using PRP in this location.

Knee Arthritis

Some initial research has been done to evaluate the effectiveness of PRP in the treatment of the arthritic knee. Currently there is NO indication for PRP, and in fact the Australian Orthopaedic Association and the Royal Australasian College of Surgeons recommend that PRP currently has no role for knee osteoarthritis.

PRP Preparation and Procedure

To develop a PRP preparation, blood must first be drawn from a patient  (approximately 10 mls is taken from a large vein at the elbow). The platelets are separated from other blood cells and their concentration is increased during a process called centrifugation, which takes about 10 minutes. Then the increased concentration of platelets and plasma are extracted ready for subsequent injection. The relevant injured part of the body is injected with local anaesthetic, and then the PRP concentrate is injected into the affected area utilising ultrasound guidance.

Post PRP Procedure

Following the PRP injection procedure, normal daily routine activities may be resumed as comfort dictates but strenuous activities such as heavy exercise or lifting should be limited. Some pain is often felt during the injection, which may last for a couple of days. Cold compresses and pain medication (such as Panadol) may be prescribed for pain relief.  Anti-inflammatory medications should be avoided for up to one month after the injection, as they can affect the platelet function and may also lower the inflammatory response that is being induced by the PRP injection to improve healing.

Risks and Complications

Risks and complications post PRP injection are uncommon, but can include infection, nerve or blood vessel injury, scar tissue formation, and calcification at the injection site. 

Special precautions are also required in individuals with low platelet count, bleeding disorders, those on blood thinning medications or anti-inflammatory medications, individuals allergic to local anaesthetic agents, those with active infections, and women who are pregnant or breast feeding.