Differences in the strain applied to Achilles tendon fibers when the subtalar joint is overpronated: a simulation study
The purpose of this study was to investigate the strain applied to each of the tendon fiber bundles of the medial head of the gastrocnemius (MG), the lateral head of the gastrocnemius (LG), and the soleus muscle (Sol) that compose the Achilles tendon (AT) when the subtalar joint is pronated and supinated.
Three AT twist types (least, moderate, extreme) were investigated. Using the MicroScribe system, the AT and the talocrural and subtalar joints were digitized to reconstruct three-dimensional models. Using this system, subtalar joint rotations in the pronation (20°) and supination (20°) directions were simulated, and the degrees of strain (%) on each tendon were calculated.
For all twist types, when the subtalar joint was pronated, MG, LG, and Sol stretched, and when supinated, MG, LG, and Sol shortened. In particular, the least and severe twist types had large degrees of strain of Sol when the subtalar joint was pronated, and furthermore, each tendon fiber composing Sol had different degrees of strain.
The study results suggest that the degree of strain applied within the AT with subtalar joint pronation is not constant, and that, especially in least and extreme twist types, the risk of developing AT disorders may increase.
KeywordsAchilles tendon Twisted structure Three-dimensional model Achilles tendon disorder
The authors would like to acknowledge and thank those anonymous individuals who generously donated their bodies so that this study could be performed. This study was supported by a Research Activity Young B Grant (17K13072) from the Japan Society for the Promotion of Science (JSPS) and a Grant-in-Aid program from Niigata University of Health and Welfare (H30B05).
ME and TT contributed to study design and data collection, and drafted the manuscript; TI and TK contributed to data analysis and made critical revisions to the manuscript; WI, EN, RH, MI, and FK made critical revisions to the manuscript; IK supervised the study, contributed to analysis and interpretation of data, and made critical revisions to the manuscript. All authors read and approved the final manuscript prior to submission.
This study was supported by a Research Activity Young B Grant (17K13072) from the Japan Society for the Promotion of Science (JSPS) and a Grant-in-Aid program from Niigata University of Health and Welfare (H30B05).
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
The methods were carried out in accordance with the 1964 Declaration of Helsinki, and the cadavers were legally donated for the research by the Nippon Dental University of Life Dentistry at Niigata in Japan.
Informed consent was obtained from the families of all subjects.
Availability of data and material
The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.
- 3.Edama M, Kageyama I, Kikumoto T, Nakamura M, Ito W, Nakamura E, Hirabayashi R, Takabayashi T, Inai T, Onishi H (2017) The effects on calcaneofibular ligament function of differences in the angle of the calcaneofibular ligament with respect to the long axis of the fibula: a simulation study. J Foot Ankle Res 10:60CrossRefPubMedCentralGoogle Scholar