Pitfalls in the study of neovascularisation in achilles and patellar tendinopathy: a review of important factors for clinicians to consider and the need for greater standardisation

Background: The search for new vessels in pathological tendons is a relatively new field. In spite of a rapid growth in research and clinical experience, there is still poor agreement in the musculoskeletal community regarding the significance and measurement of so called "neovascularisation". Any relationship between vascularity, tendon healing, degeneration and pain is not yet clear, as it has been considered as a normal physiological adaptation to loading yet also seen in chronic painful Achilles tendons. An expression of the degree of "neovascularisation" could potentially have significance if the amount of neovascularisation could be related to the degree of symptoms or dysfunction caused by the pathology in the tendon. Objectives: This review examines the potential variables that can affect the quantification of the Doppler signal in Achilles and patellar tendinopathy under three perspectives. Firstly, the variables that arise from the actual technology that allows the capturing of the Doppler signal from intra-tendinous microvasculature flow, secondly by an awareness of known and highly likely physiological factors that may alter the rate of flow and thirdly by an exploration describing the actual methods and qualities of acquiring quantitative data of the microvascular flow with Doppler. Methods: A literature search was conducted across AMED, CINAHL, Google Scholar, SPORTDiscus, MEDLINE and NCBI (PubMed) for studies related to the qualitative or quantitative measure of the Doppler signal in relation to a clinical outcome of Achilles or patellar tendinopathy. Parameters regarding machine settings and examination conditions were extracted to identify the utilisation of important factors and consistency with a narrative analysis. Discussion: Many of these influential factors have never been controlled for in previous studies and the methods have been unreliable and poorly reported. There is a need for international agreement on a standardised protocol in the assessment of the microvascularity of tendons, which could then help determine if the quantification of "neovascularisation" is a reliable and clinically relevant finding.