Mechanical stability, muscle strength and proprioception in the functionally unstable ankle.
Functional instability of the ankle is common
following inversion sprain. Factors suggested
as causes of this disability include mechanical
instabilityofthetalocrural joint, peroneal muscle
weakness and motor incoordination due to
impaired proprioception. This study documented
physical examination characteristics of
functionally unstable ankles relevant to these
theories. Each ankle of 45 subjects with
unilateral functional instability was examined.
Mechanical stability was assessed by standard
clinical instability tests. Evertor and invertor
muscle strength was measured using the Cybex
II dynamometer. The Uni-axial Balance Evaluator
(UBE) was used to assess dynamic control ofthe
ankle and was considered capab:a of detecting
unilaterally impaired proprioception.
Mechanical instability was frequently absent in
the functionally unstable ankles tested. Evertor
muscle strength was similar in the normal and
functionally unstable ankles. UBE results were
consistent with the theory of impaired
proprioception contributing to functional
instability, but the need for further research is
emphasised.