July 2011

Anterior stiffness differentiates chronic ankle instability from ‘potential copers’

In the moment: Sports medicine

Anterior stiffness may be a key differentiator between people who develop chronic instability following an ankle sprain and those who recover fully, according to research presented in June at the annual meeting of the National Athletic Trainers Association.

Investigators from the University of Delaware found that anterior ankle stiffness was significantly greater in 19 ankles of “potential copers” than in 22 functionally unstable ankles or 39 healthy ankles. Potential copers were defined as individuals with a history of ankle sprain but no current instability or episodes of giving way as assessed using the Cumberland Ankle Instability Tool (CAIT).

“Stiffness properties seem to be important in people who are coping with ankle sprain,” said Charles “Buz” Swanik, PhD, ATC, an assistant professor of health, nutrition, and exercise science at the university, who presented his group’s findings at the NATA meeting.

The increased stiffness may help enable copers to sense and respond to an impending inversion event more effectively than patients with instability, Swanik said.

A Delaware study presented at the NATA meeting a year earlier found that detection of afferent signals was impaired in patients with unstable ankles (see “Altered ability to detect joint loading plagues chronically unstable ankles”), and a third study from the same group presented this year found that muscle spindle afferent activity was related to ankle stiffness.

The extent to which a sprained ankle is allowed to heal in the acute phase may ultimately determine ankle stiffness—and, potentially, afferent detection—in the long term, Swanik theorized.

“It may be that covalent bonding that forms in early rest and immobilization [in copers] may be what is preventing the giving-way episodes,” he said.

Plyometrics and other conditioning exercises may be useful for modifying muscle spindle activity in the unstable subjects, Swanik said.

Elsewhere at the NATA meeting, researchers from Virginia Commonwealth University found that 21 copers and 23 patients with functional ankle instability all stood with significantly less static hindfoot dorsiflexion than 23 healthy participants, and that active range of motion in the sagittal plane was significantly reduced in only the FAI group.

The active ROM findings were consistent with those of a 2008 study from the University of Georgia published in Clinical Biomechanics that found significantly less sagittal plane displacement during five tasks in mechanically unstable ankles than in copers or healthy ankles.

Previous reports, including an October 2006 study in the British Journal of Sports Medicine, have found that decreased ankle dorsiflexion is predictive of lateral ankle sprain risk.

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