Platelet-rich Plasma Injection for Achilles Tendinopathy: A Technology Assessment

Jeffrey A. Tice, MD

Disclosures

CTAF 

In This Article

Background

Achilles Tendon Injuries

The Achilles tendon connects the muscles of the calf (gastrocnemius and soleus) to the heel bone (calcaneus). During exercise it may be subject to forces up to twelve times the person's body weight.[2] Achilles tendinopathy, previously called Achilles tendonitis, is a common injury in runners and other athletes. The diagnosis is based on symptoms of pain and swelling in the tendon that limits activities. [3,4] The diagnosis is usually separated into two distinct entities: insertional Achilles tendinopathy, which occurs within two cm. of the insertion of the tendon into the calcaneus and mid-portion Achilles tendinopathy, which occurs between two and six cm. proximal to the insertion of the tendon. The common sports injury is mid-portion tendinopathy and it will be the focus of this review.

Achilles tendinopathy is usually thought of as an overuse injury. Activities leading to Achilles tendinopathy include a rapid increase in running distance or speed, an increase in hill climbing, new running shoes, overpronation, and wearing high-heeled shoes.[5,6] Pain is typically felt in the middle of the tendon. After the initial injury, there is often morning stiffness and pain that may occur only when warming up or after exercise. These symptoms may progress over time to constant pain.

Achilles tendinopathy is common in runners accounting for approximately 11% of injuries. Tendons have a limited blood supply, which may contribute to poor healing following injury. Some estimate that as many as half of patients with Achilles tendinopathy are still symptomatic one year after the initial injury.

Non-surgical Treatment

Rest, combined with icing and NSAIDS, is the usual initial treatment though there is limited evidence for efficacy of any of these interventions. Resting the injured tendon is thought to be an essential component of successful therapy, so encouraging the individual to switch to another activity, such as swimming or cycling, can help promote a sufficiently long rest period to allow healing to occur. A recent systematic review evaluated the clinical trial evidence supporting eccentric exercises, extra-corporeal shock wave therapy, concentric exercises, night splints, sclerosing injections, topical glycerol nitrate, and corticosteroid injections for the treatment of Achilles tendinopathy.[7] The strongest evidence for efficacy was for eccentric exercises with conflicting evidence for the other treatment modalities. Eccentric exercises combine stretching with contraction of the muscles. For Achilles tendinopathy, this usually involves standing on a step and slowly lowering the heel. The number of repetitions and the load applied to the Achilles tendon is increased gradually over weeks.

Platelet-rich Plasma (PRP)

The use of PRP grows out of long-standing research into how to harness growth factors to promote healing. Platelets contain packets of growth factors called alpha granules. The growth factors in alpha granules include platelet-derived growth factor, transforming growth factor-beta, vascular endothelial growth factor, epidermal growth factor, insulin-like growth factors I and II, and fibroblast growth factor.[8–10] These factors promote the formation of extracellular matrix, granulation tissue, epithelial tissue as well as stimulating cell growth and proliferation, angiogenesis, and cell migration. The hope is that coordinated use of these growth factors will accelerate the removal of necrotic tissue and speed tissue regeneration and healing.

The normal concentration of platelets is approximately 200,000 per microliter. The goal of devices used to produce PRP is to raise the concentration to at least 1 million platelets per microliter – the threshold that is felt to be clinically active. To produce PRP, anticoagulated blood is centrifuged to separate red and white blood cells from the platelet and plasma and to separate the plasma into platelet-rich and platelet-poor fractions.

There are several approaches to trigger the release of the growth factors from the PRP. Some systems add bovine thrombin to activate clotting, though concerns have been raised about immune reactions to the bovine thrombin. This approach leads to rapid release of the growth factors. Another uses calcium chloride, which creates a fibrin gel that traps platelets and releases growth factors over approximately seven days. A third system uses type I collagen to activate the platelets and to create a collagen gel. Finally, the PRP can be directly injected and allow the patient's own collagen to activate the platelets. In all cases, the patient's own blood is the source for the PRP.

PRP has been promoted for use in non-healing tendon injuries, acute tendon injuries, muscle and ligament strains, osteoarthritis, articular cartilage injury, diabetic wound healing, bone fracture healing, and spinal fusion. The editor of the American Journal of Sports Medicine coined the phrase "platelet-rich panacea" to describe the current enthusiasm for PRP.[11] Most articles have minimized the harms of PRP, but concerns have been raised about the potential for excessive growth, delays in tissue remodeling, and excessive scarring.[12]

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