In vivo estimation and repeatability of force–length relationship and stiffness of the human achilles tendon using phase contrast MRI

Abstract

Purpose: To devise a method using velocity encoded phase contrast MRI and MR-compatible dynamometry, for in vivo estimation of elastic properties of the human Achilles tendon and to assess within-session and day-to-day repeatability of this technique. Materials and Methods:Achilles tendon force and calcaneus-movement-adjusted displacement were measured during a submaximal isometric plantarflexion in 4 healthy subjects, four repeated trials each. The measured forcelength (F-L) relationship was least-squares fitted to a cubic polynomial. Typical error was calculated for tendon displacement at multiple force levels, stiffness from the "linear region," and transition point from the displacement point separating the linear and nonlinear parts of the curve.Results: Displacements of the tendon were determined up to a maximum force of 500N, with mean stiffness of 234 Ϯ 53 N/mm, mean transition point of 2.70 Ϯ 0.23 mm and maximum tendon displacement of 3.38 mm. Variability of tendon displacement was not dependent on the force level. Overall typical errors were 0.09 mm and 0.16 mm for within-session and between days, respectively. Typical error of transition point was 0.05 mm and 0.14 mm. Stiffness had typical errors of 47.24 N/mm and 51.95 N/mm. The tendon cross-sectional area and calcaneus displacement were found to be very significant factors in minimizing the individual differences in F-L curves. Conclusion:The method yielded F-L relationships, stiffness, and transition point values that showed good within and day-to-day repeatability. The technique compared well with the more conventional one using ultrasonography. Its reliability indicates potential for measuring tendon structural changes after an injury, disease, and altered loading.

Computer‐controlled, MR‐compatible foot‐pedal device to study dynamics of the muscle tendon complex under isometric, concentric, and eccentric contractions

“…These 6 subjects were used for (i) testing the device at the two magnetic fields of 1.5T and 3T and using various coil configurations described below and (ii) for the acquisition of the physiological measurements of the fascicle length changes and aponeurosis separation reported in this paper only at 3T. Similar and additional types of physiological imaging including Diffusion Tensor and Spin Tag imaging have been reported in prior publications (12; 13). …”

A comparison of parallel- and series elastic elements in an actuator for mimicking human ankle joint in walking and running

“…Other options to reduce the requirements can be to use non-linear springs which represent better the non-linear tendon function of the plantar-flexors [13,14]. This can also be realized by adding unilateral springs to the system.…”

Achillodynia - Radiological Imaging of Acute and Chronic Overuse Injuries of the Achilles Tendon

“…However, the variation coefficient was significantly higher at approx. 17 % (intraday variability) for the stiffness measurement [62]. Since there is currently no data regarding pathologically altered tendons with respect to VE-PC-MRI, a final conclusion about clinical applicability cannot be made.…”

“…Velocity-encoded phase-contrast MRI (VE-PC-MRI) in combination with an MR-compatible interferometer is another option for the in vivo quantification of force-dependent length changes and stiffness properties of the Achilles tendon. In this way Shin et al were able to determine the forcelength curve of the Achilles tendon in the case of isometric contractions [62]. For the reproducibility of the transition point (change of the tendon length in mm at 40 N), there was good reproducibility with a variation coefficient of approx.…”