Is the Silfverskiöld Test a valid tool for evaluating calf muscles spastic overactivity in patients with stroke? A retrospective observational study

Background: Spastic equinus (plantar flexed) foot is a common postural pattern in patients who suffer from post-stroke spasticity. To date, some clinicians use the Silfverskiöld Test in their practice to differentiate between gastrocnemius and soleus muscle overactivity in patients with spastic equinus (plantar flexed) foot. This use of the Silfverskiöld Test goes beyond its original aim, which was to distinguish isolated gastrocnemius contracture in patients with equinus deformity. Aim: The aim of this study was to investigate the Silfverskiöld Test validity for evaluating spastic equinus (plantar flexed) foot (i.e., differentiation between gastrocnemius and soleus muscle overactivity) by checking its outcome against those of selective diagnostic nerve block of tibial motor nerve branches to the soleus, gastrocnemius and tibialis posterior muscles. Design: The design of the study was retrospective observational. Setting: The study was set in a university hospital. Population: Sixty-seven adult stroke patients with spastic equinus (plantar flexed) foot. Methods: Each patient underwent selective diagnostic nerve block of tibial motor nerve branches to the soleus, gastrocnemius and tibialis posterior muscles. All patients were evaluated before diagnostic nerve block by means of the Silfverskiöld Test which was considered positive when ankle joint passive dorsiflexion was greater with the knee flexed than extended. Furthermore, they were assessed before and after nerve block by means of the modified Ashworth Scale and the Tardieu Scale. Results: Our sample included 41 males and 26 females (mean age 57.6 years) suffering from spastic equinus (plantar flexed) foot due to chronic stroke (mean time from onset 2.4 years). Forty-eight patients out of 67 presented with positive Silfverskiöld Test. The χ2 test showed no association between the Silfverskiöld Test and spastic overactivity of the gastrocnemius (P=0.253), soleus (P=0.605) and tibialis posterior (P=0.462) muscles as evaluated by serial selective diagnostic block of the tibial nerve motor branches. Conclusions: Our findings do not support the Silfverskiöld Test as a valid tool for evaluating spastic equinus (plantar flexed) foot to differentiate between gastrocnemius, soleus and tibialis posterior spastic muscle overactivity in adult patients with stroke. Clinical rehabilitation impact: The choice for an appropriate management of spastic equinus (plantar flexed) foot in adults with stroke should not be mainly defined on the base of Silfverskiöld Test.