Acute Lateral Ankle Sprain Impairs Function and Strength Without Altering Muscle or Tendon Stiffness: A Controlled Observational Study

TL;DR

An acute lateral ankle sprain causes pain and reduced function but does not change muscle or tendon stiffness over six weeks.

Contribution

This study is the first to use shear wave elastography to show no stiffness changes in calf muscles and Achilles tendon after acute lateral ankle sprain.

Findings

Acute lateral ankle sprain leads to reduced ankle function, increased pain, and edema.

No significant changes in stiffness of calf muscles or Achilles tendon were observed in sprained ankles.

Plantar flexion strength was lower in the sprained group but improved over time.

Abstract

Acute lateral ankle sprain (LAS) frequently results in persistent functional limitations. Understanding changes in calf muscle and Achilles tendon (AT) stiffness after LAS may shed light on mechanisms underlying impaired function.

To investigate the effects of acute LAS on the mechanical properties of the calf muscles and the Achilles tendon, ankle function, pain, edema, and strength.

This controlled observational study was conducted from August 2023 to January 2025. Fourteen participants with acute LAS and 14 healthy controls were evaluated twice, 6 weeks apart. Shear wave elastography (SWE) assessed the stiffness of the triceps surae and AT. Ankle function, pain, and edema were evaluated using the Foot and Ankle Outcome Score, Visual Analog Scale, and figure‐of‐eight method. Plantar flexion strength was measured via isometric dynamometry.

No significant differences in stiffness were found between or within groups (soleus: p = 0.932; MG: p = 0.760; LG: p = 0.800; AT: p = 0.070), although a time effect (p = 0.005, η2 = 0.269) indicated a general increase in AT stiffness over time (MD = −0.72, p = 0.05, d = 2.86). At baseline, the LAS group exhibited reduced ankle function (MD = 3.43, p < 0.001, d = 2.20), increased pain (MD = 1.88, p < 0.001, d = 1.86), and greater edema (MD = −51.27, p < 0.001, d = −3.58). Over time, improvements were noted in function (MD = −37.04, p < 0.001, d = 2.27), pain (MD = 2.66, p < 0.001, d = −1.31), and edema (MD = 1.07, p = 0.014, d = −0.95), but ankle function remained lower in the LAS group at follow‐up (MD = −14.17, p < 0.001, d = −1.79). For plantar flexion strength, no group × time interaction was found (p = 0.745), but a group effect indicated lower peak torque in the LAS group (MD = −32.05, p = 0.012, d = −3.82). A time effect (p < 0.001, η2 = 0.622) showed increased torque across both groups (MD = −18.74, p < 0.001, d = 3.07).

LAS reduces ankle function and leads to pain and edema but does not induce notable changes in calf muscle or AT stiffness within 6 weeks.

This study used shear‐wave elastography to assess Achilles tendon and calf muscle stiffness following acute lateral ankle sprain (LAS). Despite the expected alterations due to injury and unloading, no significant stiffness changes were observed over 6 weeks. Findings suggest potential compensatory mechanisms preserving tissue mechanical properties post‐LAS.

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