Revised approach may be needed
Patients with chronic ankle instability demonstrate impaired plantar sensation but, surprisingly, do not exhibit increased ligament laxity, according to two studies presented in June at the annual meeting of the American College of Sports Medicine.
By Jordana Bieze Foster
The findings suggest the most effective interventions for CAI might be those with somatosensory or neuromuscular effects rather than those that provide mechanical stabilization, which has long been the standard of care based on anecdotal evidence of an association between ligament laxity and a history of multiple ankle sprains.
“You would think that the more you sprain your ankle, the looser the ligaments would become, but ligament laxity does not seem to be a chronic problem,” said Kathy Liu, MS, a graduate student in the Biomechanics and Movement Science Program at the University of Delaware, who presented her group’s findings at the ACSM meeting. “We’re not seeing the trend we thought to be true.”
Liu and colleagues studied 106 National Collegiate Athletic Association athletes and looked for correlations between the number of sprains sustained by each of the 212 ankles and arthrometric measurements of ligament laxity. They found no relationship between number of sprains and anterior displacement or inversion or eversion rotation of the ankle.
Despite these findings in a chronic patient population, previous research suggests that mechanical stabilization does have a role for managing ligament laxity following acute ankle sprain. In a study published in the July 2009 issue of the Archives of Physical Medicine & Rehabilitation, researchers from the University of North Carolina at Charlotte found that 16 patients with acute ankle sprains demonstrated significantly greater anterior displacement and inversion rotation than 16 healthy participants. These differences were significant not only when measured three days after injury, but eight weeks later as well.
The findings of a second study presented at the ACSM meeting suggest that stabilizing interventions such as ankle braces may provide somatosensory benefits for patients with chronic ankle instability even if laxity is no longer an issue.
Researchers from the University of Kentucky in Lexington assessed vibration detection thresholds (VDT) in eight adults with CAI and eight healthy volunteers. Mechanical stimuli were delivered to the sole of the foot at the first metatarsal head, the base of the fifth metatarsal, and the center of the heel. The VDT for each location was defined as the amplitude at which the participant positively detected the stimulus 50% of the time.
When the stimulus sites were pooled, the individuals with CAI had significantly higher VDT values (indicating decreased sensitivity) than the control group regardless of the frequency of the stimulus, according to Matthew C. Hoch, PhD, ATC, who presented his group’s findings at the ACSM meeting.
“These results provide evidence that cutaneous receptors could be involved in sensorimotor alterations associated with chronic ankle instability,” said Hoch, who recently completed his doctoral studies in rehabilitation sciences at Kentucky. “These alterations weren’t associated with any one specific site, which suggests that people with CAI may have difficulty detecting boundary-relevant information for making postural corrections.”
Although the retrospective nature of the injury history aspect of the study makes it difficult to draw conclusions about the chronology of sensorimotor alterations relative to ankle instability, Hoch hypothesized that the changes are the result of injury rather than its cause and that they occur centrally rather than being localized to the ankle.
To improve cutaneous sensitivity in this patient population, Hoch suggested that sports medicine practitioners could learn from other researchers who have used textured insoles and electrical stimulation to address postural instability in elderly patients and those with neurodegenerative conditions (for example, see “Vibration stimulus at the feet lowers gait variability, could prevent falls”).