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

INTRODUCTION

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.

OBJECTIVE

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.