Chronic Ankle Instability - Mechanical vs. Functional

Chronic ankle instability arises from three interacting contributing factors: mechanical ankle instability, functional ankle instability, and perceived ankle instability. To decide on the most appropriate individual recommendation for therapeutic options, it is necessary to assess which of the two main aetiologies - functional vs. mechanical - is dominant in causing the perceived impairment. It is essential to perform a thorough analysis and diagnosis, even though quantifying mechanical ankle instability is still a challenge in the clinical approach to this common pathology. When diagnosing mechanical instability, the most established procedure is physical examination, although this unfortunately does not allow the deficit to be quantified. Additional options include stress-ultrasound, 3 D stress-MRI (3SAM), ankle arthrometry, marker-based 3 D motion analysis, and diagnostic ankle arthroscopy. Of these the latter is considered the gold standard, even though it is an invasive procedure, it may not be performed for diagnostic reasons only, and it also does not allow the mechanical instability to be quantified. For diagnosing functional instability there are non-instrumented tests such as the Star Excursion Balance Test or Y-Balance Test, posturography/stabilometry, and gait and running analysis, possibly combined with EMG acquisition and isokinetic strength testing. To date, the standard of care is conservative management of ankle instability, and the therapy should include sensorimotor training, strength training of the periarticular muscles, balance training, and gait and running exercises on different surfaces. However, it is increasingly clear that a certain degree of mechanical instability cannot be compensated for by functional training. Thus, it is the goal of differential diagnostics to identify those patients and guide them to mechanical therapy, including ankle bracing, taping, and surgical ligament reconstruction.