May 17, 2011
Tendinopathy is often multifactorial with contributing factors including genetic, biomechanical and regenerative faults. Excessive loading during repetitive exercise is thought to be the main pathological stimulus for intrasubstance degeneration and microtear formation. Continued loading may lead to further evolution of these tears with intrasubstance splits, macroscopic partial tears and even rupture. The latter may occur regardless of any intervention.
Recently, platelet-rich injections of blood have attracted a lot of interest in the media following treatment of high profile athletes, including Tiger Woods and Rafa Nadal. Growth factors are found on the surface of platelets contained in the alpha granules. The philosophy of platelet-rich plasma is that by concentrating the numbers of platelets, there will be more growth factor and cellular mediators to orchestrate a healing response. Platelets contain a number of proteins, cytokines and other factors that initate and regulate wound healing. PRP typically contains a 3 to 5 fold increase in platelet numbers when compared with standard blood injections, hence are felt more likely to be efficacious.
However, how these growth factors and cytokines precisely work remains unknown. Following injection of blood or platelet-rich plasma into a tendon, 70% of the stored growth factors are released within 10 minutes and almost all of the growth factors dissipate within an hour. Despite this, clinical improvement may take upwards of 12 weeks. Furthermore, the best proliferation in vitro has been induced by physiological platelet concentrations (i.e 2.5 times blood concentration) and higher platelet concentrations have been shown to induce negative effects. Tendon conditions typically treated with PRP include tennis and golfer’s elbow, patellar and Achilles tendinosis and hamstring origins. Patients typically require two injections 3-4 weeks apart. PRP has also been used for the treatment of muscle injuries, including hamstring tears and sidestrain injuries.
Ten mls of blood is drawn from the antecubital fossa of the patient and placed inside a sterile test-tube. The test-tube contains anticoagulant (i.e citrate) to bind ionised calcium and inhibit the clotting cascade. The blood is then centrifuged for 7 minutes to separate out the different blood components. The concentration of platelets is found in the buffy coating which forms at the interface of the sedimented red cells and plasma. This is then aspirated into a smaller syringe(see diagram). An activating agent is not used (or felt necessary).
The surface of the tendon is infiltrated with local anaesthetic. After waiting for the anaesthetic to take effect, the needle is placed under ultrasound guidance into the site of maximal tendon injury. The PRP is then injected into the sites of tendinopathy and fibril discontinuity.
At the time of injection a number of intra-substance tears and longitudinal splits often become prominent and readily visible where they were not seen readily seen prior to injection.
Rehabilitation and follow-up
Following injection the patient is advised to avoid exercise or strenuous activity for the next 48 hours.
The site of tendon injury may become painful after the anaesthetic wears off. Patients are advised to use ice or take paracetamol as necessary. Anti-inflammatories should be avoided as they can interfere with the growth factor activity.
Rehabilitation should be supervised by a physician or physiotherapist. After the second injection, an eccentric loading muscle programme is usuallycommenced. The patient is asked to perform the exercises daily for the next twelve weeks. These eccentric loading programmes are important in enabling the organisation and alignment of scar tissue formation, in addition to maintaining function of the tendon and calf musculature.