Changes in the ankle reflex related to posture.

Depression of the ankle reflex is the most common neurological change in patients with impairment of conduction of the 51 nerve root. Unilateral absence of the ankle jerk is easily recognised, but it may be difficult to detect a slight reduction of response. This may be important, not only for diagnosis, but also for prognostic and therapeutic purposes, since the decrease in the reflex is very often directly related to the degree of nerve root dysfunction. The ankle jerk may be examined with the patient in various positions : supine with hip and knee flexed; sitting ; kneeling on a chair; or lying prone with the knee flexed. It is our experience that the activity of the ankle reflex may be conditioned by posture, but we could find no mention of this in the literature. Methods. We tested the ankle reflex in each of the four postures listed above in 118 men and 92 women, aged 21 to 74 years. All had a unilateral 51 root syndrome, either isolated or associated with an L5 root syndrome. Patients with bilateral absence of the ankle jerk were excluded from the study. Results. The ankle reflex on the symptomatic side in all four postures was normal in 58 patients and absent in 77. In the remaining 65 patients, reflex activity differed according to the posture in which the test was carried out (Table I). In 35 patients the reflex was normal, slightly depressed or markedly depressed when tested in the supine, sitting or kneeling positions and, respectively, slightly depressed, markedly depressed or absent in the prone position. In 13 patients it was uncertain whether the reflex was normal or depressed in the first three positions, while it was clearly decreased in the prone position. In eight cases the reflex was normal in both supine and kneeling positions and decreased in both the sitting and prone postures. Nine patients had a normal or uncertain reflex in the supine, kneeling and prone positions, but definite depression in the sitting position. Of the 65 patients showing modifications in reflex with change of posture, 48 had one or more CT scans,