Acute Ankle Sprain Alters Ankle Posture During Stair Landing

Key Takeaways

• In a laboratory stair-to-level-ground task, participants with acute ankle sprain contacted level ground more plantarflexed and internally rotated than healthy controls.
• Transverse-plane whole-body COM displacement was smaller after sprain, while ankle range of motion did not differ between groups in any of the three planes.
• Mean biceps femoris activation was lower after sprain, while mean medial gastrocnemius and tibialis anterior activation and peak tibialis anterior and soleus activation were higher.
• Within the sprain group, global efficiency, clustering coefficient, and network density were higher in the 0–25 Hz than the 25–50 Hz muscle-coherence band.

At the last stair tread, the landing limb must accept body weight while the body continues downward onto level ground. For people with a recent ankle sprain who can descend stairs, ankle contact posture, whole-body displacement, and muscle behavior capture different aspects of this transition.

In a cross-sectional laboratory study in the Journal of Foot and Ankle Research, investigators compared 30 participants with unilateral acute ankle sprain (AAS) within the preceding 7 days with 30 healthy controls. The sprain group had ankle-related symptoms but could descend stairs unaided with tolerable pain. Participants descended a custom staircase at a self-selected pace onto a level-ground force plate, using the affected ankle or an approximately side-matched control ankle. Motion capture measured contact angles and support-phase ankle range of motion; synchronized force plates marked initial contact and toe-off. A participant-scaled OpenSim model estimated whole-body center of mass (COM) displacement. Surface electromyography (sEMG) measured muscle activation relative to each participant’s maximum voluntary isometric contraction (MVIC) and separately informed intermuscular coherence networks. Investigators averaged valid landings per participant.

At initial contact, mean sagittal ankle angle was −25.436° with AAS versus −23.814° in controls, an AAS-minus-control difference of −1.622° (nominal, unadjusted p = 0.015). Negative sagittal angles denote plantarflexion, placing the sprained ankles in a more plantarflexed contact position.

Mean transverse ankle angle at initial contact was −4.002° with AAS versus −1.341° in controls, an AAS-minus-control difference of −2.661° (nominal, unadjusted p < 0.001). Negative transverse angles denote internal rotation. These contact-position differences did not correspond to a significant between-group difference in ankle range of motion during support in the sagittal, frontal, or transverse plane.

Transverse-plane COM displacement was 0.021 m with AAS versus 0.025 m in controls, an AAS-minus-control difference of −0.004 m (nominal, unadjusted p = 0.011). Mean biceps femoris activation was lower in the sprain group, whereas mean medial gastrocnemius and tibialis anterior activation and peak tibialis anterior and soleus activation were higher. Differences in normalized activation are expressed in percentage points of MVIC, not relative-percent changes. Within the AAS group, global efficiency, clustering coefficient, and network density were higher in the lower than the higher muscle-coherence frequency band. Muscle-pair edges were descriptive, and network indices were not compared inferentially between groups.

A one-time comparison cannot establish that sprain caused these patterns, that smaller displacement indicates better dynamic stability, or that the maneuver predicts clinical outcomes or rehabilitation benefit. Participants were physically active university students able to descend with tolerable symptoms; self-selected, unmonitored speed and unstandardized footwear and external ankle support further complicate comparison. Multiple outcomes were tested without multiplicity correction. The support-only window excluded anticipatory movement, and coherence cannot identify a specific neural source.

The authors described altered ankle contact orientation, smaller transverse COM displacement, and selected muscle activation differences during the stair-to-ground transition after AAS. They called for longitudinal examination of recovery and the clinical relevance of these task-specific observations.

Clinician Questions

Were AOFAS ankle-hindfoot and pain scores analyzed as outcomes after acute ankle sprain?

For participants with unilateral acute ankle sprain, an American Orthopaedic Foot and Ankle Society ankle-hindfoot score below 80 and a pain score no greater than 3 were eligibility requirements for a tolerable stair-descent task, not analyzed outcomes or validated sprain-severity cutoffs. Investigators could not relate those scores to biomechanical findings.

Does the 0–25 Hz muscle-coherence band after acute ankle sprain include signals below 5 Hz?

The surface-electromyography coherence signals were high-pass filtered at 5 Hz, attenuating lower frequencies; the nominal 0–25 Hz band was therefore effectively interpretable at approximately 5–25 Hz.

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