Introduction It is still not clear what the relationship is between the vascular response of an Achilles tendon and the development of an overuse injury.

Methods This systematic review is reported following the PRISMA guideline. An electronic database search was conducted on PubMed and Web Of Science by using multiple keyword combinations regarding the PICO-question: The influence of neovascularization and blood flow (I) on the development of Achilles tendon injury (O) in the AT (P).

Results Sixteen articles were included in this review. For the 3 case-control studies the mean score was 3.6 on 6 [Alfredson, 2003; Malliaras, 2006; Ohberg, 2001]. Seven cross-sectional studies were scored on a total of 4 items [Boesen, 2006; Boesen 2012, Fahlstrom 2010; Malliaras P, 2008; Malliaras 2012; Reiter 2004; van Snellenberg 2007]. The mean score here is 2.4 on 4. Six cohort designed studies gained a mean of 6.16 on 8 [Boesen 2006; Hirschmuller 2012, Jhingan 2011, Knobloch 2006, Mahieu 2010, Ram 2013]. The cohort designed studies have the strongest mean methodological score. Only one study fails in the methodological scoring [van Snellenberg 2007]. Thirteen out of sixteen studies have a level of evidence B. Only one study has a level of evidence A2 [Hirschmuller 2012]. Two studies have a level of evidence C [Boesen 2012, Malliaras 2012].

Discussion The prognostic value of increased blood flow or neovascularisation inside the tendon is not clear. Furthermore it can be seen in symptomatic and in asymptomatic subjects, for example after physical activity. Five studies look at the neovessels after one single exercise moment, three other studies use an exercise protocol of a longer duration. Different loadings, different Doppler settings result in conflicting evidence. Most of the authors believe that neovascularisation could be a physiological adaptation, even in asymptomatic persons.

In the different studies, neovascularisation does not always correlate with pain. Otherwise neovascularisation is sometimes related with structural changes. Some studies assume that the development of an overuse injury is related to structural changes inside the tendon and to pain.

In conclusion,there is no conclusive answer found on the question “Does neovascularization and blood flow play a role in the development of Achilles tendon injuries?”. Further prospective research is needed to give a conclusive answer.

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