The tibialis anterior reflex in healthy subjects and in L5 radicular compression.

Phasic stretch reflexes were evoked in the tibialis anterior (TA) muscle, by tapping the dorsal side of the foot with a hand-held reflex hammer. The responses were recorded by means of surface electrodes. The TA reflex was examined in 70 healthy subjects and in 18 patients with L5 radicular compression. In 58 (83%) of the healthy subjects the reflex could be recorded bilaterally, in eight (11%) subjects no reflex was found on either side, and in four (6%) it was absent in one leg. Simultaneous recordings from the gastrocnemius-soleus showed that TA responses were not caused by volume conduction from that muscle. In the 18 patients with L5 radicular compression the TA reflex was absent on the affected side 13 times (72%) and present bilaterally in the other five cases. If asymmetry of the reflex (unilateral absence) is considered as a test for the presence of L5 radicular compression, the likelihood ratio for a positive test is 12.0, and for a negative test 0.3. The examination of the TA reflex is easily performed and can be useful in the diagnosis of L5 radicular compression.