Objective: To investigate the role of weakness of the bilateral triceps surae muscles-the gastrocnemius and soleus muscles-in astasia without abasia and whether compensating for muscle weakness with ankle-foot orthoses improves this disability.
Design: Case-control study of clinical findings and before and after trial of ankle-foot orthoses.
Setting: Clinics of the departments of rehabilitation medicine of two university hospitals.
Patients: A stilts group consisting of 23 patients with astasia without abasia, and a non-stilts group without this phenomenon consisting of 12 patients with hereditary motor sensory neuropathy, 15 patients with lumbosacral spondylotic radiculopathy or spondylolisthesis, and 20 healthy volunteers.
Main outcome measure: Clinical findings of the stilts and non-stilts groups were compared and the sensitivity and specificity of each clinical finding was calculated. The length of the centre of foot pressure (COP) while standing was measured in a bilateral below knee amputee and 16 consecutive patients in the stilts group with and without ankle-foot orthoses.
Results: Weakness of the triceps surae muscles was the only finding that differed significantly between the two groups and was both sensitive and specific. The amputee was unable to stand in place without dorsiflexion bumpers, which functioned similarly to the triceps surae muscle. Bilateral ankle-foot orthoses improved the COPs of 14 out of 16 patients.
Conclusion: The main cause of astasia without abasia is weakness of the triceps surae muscles, and this disability is improved by bilateral ankle-foot orthoses.