1. Introduction 2. The early response to tendon injury 3. Platelet-rich therapies 4. Tendinopathy 5. Expert opinion Review Tendon healing and platelet-rich plasma therapies Isabel Andia † , Mikel Sanchez & Nicola Maffulli † Osakidetza, Basque Health Service, Research, Zamudio, Spain Importance of the field: The therapeutic use of platelet-rich plasma (PRP) is an autologous biotechnology that relies on the local delivery of a wide range of growth factors and cytokines with the aim of enhancing tissue healing. Understanding both tendon healing and PRP therapies is an area of research that is critically important in developing optimal formulations and protocols to achieve the intended therapeutic effects. Areas covered in this review: We summarise recent information on the mecha- nisms inherent to the earliest response to tendon injury. We then describe the positive effect of PRP therapies on tendon healing. Research on tendinopathy has produced several biological hypotheses based on histopathological, bio- chemical and clinical findings showing that cell apoptosis, angiofibroblastic features or abnormal biochemical adaptations underlie the condition. What the reader will gain: The article provides insights into early heal- ing mechanisms and the influence of PRP therapies on inflammation, cell migration, angiogenesis and the proliferation and synthesis of extracellular matrix. The knowledge gained helps to better understand and optimize tendon therapies. Take home message: The use of endogenous therapies has a positive effect on experimental tendon healing. However, several obstacles need to be addressed to optimise medical practice in this field. Keywords: cell signalling, healing, platelet-rich plasma, tendinopathy, tendon Expert Opin. Biol. Ther. [Early Online] 1. Introduction Tendon problems are a major cause of musculoskeletal morbidity. Indeed, an estimated 30 -- 50% of all sports lesions are painful tendon injuries [1] that affect professional and recreational athletes in various anatomical locations. The location of these injuries is sport-specific. For example, Achilles tendinopathy is more prevalent in sports that have a large running component, while rotator cuff problems are frequent in sports requiring overhead motions and high-force throwing movements, and are prevalent in throwers and racquet sports players [2]. The Bone and Joint Decade (2001 -- 2010) has witnessed the development of platelet-rich plasma (PRP) technologies to improve tissue repair, especially in the musculoskeletal system [3]. The rise of such therapies in tendon problems dictates that the present knowledge of both healing mechanisms and PRP therapies needs to be better explored to translate such knowledge into biological plausible therapies. Thus, we first summarize recent information on the mechanisms inherent to the earliest response to injury. We then describe the status of the field of PR therapies and question whether this knowledge can be applied for clinical benefit. Finally, we summarize the different hypotheses regarding the biological mechanisms underlying tendinopathy. 10.1517/14712598.2010.514603 © 2010 Informa UK, Ltd. ISSN 1471-2598 1 All rights reserved: reproduction in whole or in part not permitted Expert Opin. Biol. Ther. Downloaded from informahealthcare.com by Salud Mental Ext Hospital Guipuzcoa Osakidetza on 08/18/10 For personal use only.