Are the Mechanical or Material Properties of the Achilles and Patellar Tendons Altered in Tendinopathy? A Systematic Review with Meta-analysis.

Background: Changes in the mechanical behaviour of the Achilles and patellar tendons in tendinopathy could affect muscle performance, and have implications for injury prevention and rehabilitation strategies.

Objectives: To determine the effect of clinically diagnosed tendinopathy on the mechanical and material properties of the Achilles tendon (AT) and patellar tendon (PT).

Design: Systematic review with meta-analysis.

Methods: A search of electronic databases (SPORTDiscus, CINAHL, PubMed, ScienceDirect and Google Scholar) was conducted to identify research articles that reported local and global in vivo mechanical (e.g. strain, stiffness) and/or material properties (e.g. modulus) of the AT and/or PT in people with and without tendinopathy. Effect sizes and corresponding 95% confidence intervals for individual studies were calculated for tendon strain, stiffness, modulus and cross-sectional area.

Results: Eighteen articles met the inclusion criteria (AT only = 11, PT only = 5, AT and PT = 2). There was consistent evidence that the reported AT strain was higher in people with tendinopathy, compared to asymptomatic controls. People with Achilles tendinopathy had a lower AT global stiffness, lower global modulus and lower local modulus, compared to asymptomatic controls. In contrast, there was no clear and consistent evidence that the global or local mechanical or material properties of the PT are altered in tendinopathy.

Conclusions: The in vivo mechanical and material properties of the Achilles tendon-aponeurosis are altered in tendinopathy, compared to asymptomatic tendons. Despite a similar clinical presentation to Achilles tendinopathy, patellar tendinopathy does not appear to alter the tensile behaviour of the PT in vivo.